JSCE Guidelines for Concrete
No.17

STANDARD SPECIFICATIONS FOR CONCRETESTRUCTURES  2007
"Maintenance"

Japan Society of Civil Engineers

JSCE Guidelines for Concrete
No.17

STANDARD SPECIFICATIONS FOR CONCRETESTRUCTURES  2007
"Maintenance"

Published bySubcommittee on
English Version of Standard Specifications for Concrete Structures - 2007
Japan Society of Civil Engineers (JSCE)
Yotsuya 1-chome, Shinjuku-ku, Tokyo 160-0004, JAPANFAX +81-3-5379-2769 E-mail pub@jsce.or.jp
December 2010

Copyright  JSCE 2010 Concrete Committee
Printed in Japan
英文版 2007 年制定コンクリート標準示方書［維持管理編］ 1.1

ISBN 978-4-8106-0754-3

Preface
Concrete structures have supported our society as infrastructures. The society can only preserve itself inwholesome with tough, beautiful and durable concrete structures. Concrete Committee of Japan Society of Civil
Engineers (JSCE), leading organization for investigation, research, technological promotion and education of
concrete in Japan, considers the issuance and revision of Standard Specifications for Concrete Structures as its
most important activity. Standard Specifications for Concrete Structures (JSCE-SSCS), which show the model
for plan, design, execution, maintenance and repair of concrete structures, have been highly recognized in practiceand contributed to the development of concrete technology in Japan since its first publication as “Standard
Specifications for Reinforced Concrete – 1931.”
In order to cope with the development of concrete technology in Japan and the worldwide trend, Concrete
Committee converted all Specifications in JSCE-SSCS namely ‘Structural Performance Verification,’ ‘Seismic
Performance Verification,’ ‘Materials and Construction,’ ‘Maintenance,’ ‘Dam Concrete’ and ‘Pavement,’ from the“Prescriptive Code” to “Performance-based Code” and completed the work in 2002.
This revised edition adopts the technological development after 2002 and intends to enhance theperformance-based nature in Standard Specifications. For practical efficiency, the three Specifications ‘Design,’ ‘Materials and Construction’ and ‘Dam Concrete’ present not only general provisions for verification of
specified performance requirements but also standard methods as simplified methods to achieve the performancerequirements under certain conditions. JSCE-SSCS is ready for practical use as it describes the role of eachSpecification during the plan, design, execution, maintenance and repair phases as well as the relationship among
them. And for the first time, it also describes roles of engineers for construction works. This JSCE-SSCS is yet
an ultimate one. There are still remaining tasks, such as inclusion of provisions for scenario of concrete
structures during service life. What readers can find in this revised edition is rationality with “theperformance-based concept” and the applicability for practice, showing the high level of technology in Japan.
This revised JSCE-SSCS consists of five Specifications; ‘Design,’ which combines the previous ‘Structural
Performance Verification’ and ‘Seismic Performance Verification’ together, ‘Materials and Construction,’‘Maintenance,’ ‘Dam Concrete’ and ‘Test Methods and Specifications.’ Specification of ‘Test Methods andSpecifications’ was issued separately in May 2007. Specification of ‘Pavement’ was published as “Standard
Specifications for Pavements – 2007” by the Committee on Pavement Engineering of JSCE, which has taken overthe issuance and revision works from JSCE-SSCS.
Finally I would like to show my most sincere gratitude to Prof Taketo UOMOTO and Dr Tadayoshi ISHIBASHI,
Chairman and Secretary General of Sub-committee on Revision of Standard Specifications for Concrete
Structures as well as its Secretaries, Conveners and Members who devoted themselves continuously despite thetight drafting schedule. My gratitude also goes to Advisors, Secretaries, Executive Members and Members ofConcrete Committee, who reviewed the draft.
December 2007

Toyoaki MIYAGAWA, Chairman
Concrete Committee of Japan Society of Civil Engineers

Preface to the English Version
The Japan Society of Civil Engineers’ (JSCE) Concrete Committee has been publishing the Standard
Specifications for Concrete Structures in Japanese since 1931.

The English versions were published twice in1987 and 2005 when the limit state design and the performance-based concept were introduced in the 1986 and2002 editions of Standard Specifications for Concrete Structures (JSCE-SSCS) for the first time, respectively.

Since 2004 the Concrete Committee has put efforts to enhance information dissemination overseas by presenting
various English publications including the series of “JSCE Guidelines for Concrete.”also decided to prepare the English version of every edition of JSCE-SSCS.

Concrete Committee hasThis Sub-committee on English

Version of Standard Specifications for Concrete Structures was established in 2008.

Our task is to prepare the English version of four Specifications: ‘Design,’ ‘Materials and Construction,’‘Maintenance’ and ‘Dam Concrete’ of the 2007 edition of JSCE-SSCS.

Specification of ‘Test Methods andSpecifications’ of JSCE-SSCS is not included in this English version.

However, some of these standard test

methods and specifications have been translated for publication in a series of “JSCE Guidelines for Concrete.”
Please visit the website of Concrete Committee at http://www.jsce.or.jp/committee/concrete/e/index.html for the
information on the English publications.

This English version includes most of the contents in the original Japanese version.

Utmost efforts have been

made to ensure that the translation accurately convey the description in the original Japanese version. If there
were any discrepancy between the Japanese and English versions, however, reference should be made to theoriginal Japanese version.

Translation of technical work does not only require expertise but a lot of time and dedication.
the members for their tiring efforts.

I am grateful to all

My heartfelt appreciations go to Prof YOKOTA Hiroshi (Secretary General),

Dr SHIMOMURA Takumi (Head, WG for Design), Prof SUGIYAMA Takafumi (Head, WG for Materials andConstruction), Dr MAEDA Toshiya (Head, WG for Maintenance), Prof AYANO Toshiki (Head, WG for Dam
Concrete) and Dr ISHIZUKA Takayuki who proof-read all the translated Specifications. Without them thisEnglish version would not have been published.

December 2010

UEDA Tamon, Chairman
Sub-committee on English Version of Standard Specifications for Concrete Structures

JSCE Committee on
Revision of Standard Specifications for Concrete Structures
Taketo UOMOTO, Chairman
Tadayoshi ISHIBASHI, Secretary
Members
Hiroyuki IKEDA

Tomoya IWASHITA

Tamon UEDA

Kimitaka UJI

Hidetaka UMEHARA

Nobuaki OTSUKI

Hiroshi ONUMA

Satoshi OKAZAWA

Tsutomu KANAZU

Yuichi KANEKO

Toru KAWAI

Hirotaka KAWANO

Etsuo SAKAI

Koji SAKAI

Tsutomu SATO

Ryoichi SATO

Motoyuki SUZUKI

Shigeyuki SOGO

Koji TAKEWAKA

Takao CHIKADA

Yukikazu TSUJI

Tomoaki TSUTSUMI

Rokuro TOMITA

Kazuyuki TORII

Junichiro NIWA

Yoshinobu NOBUTA

Chikanori HASHIMOTO

Makoto HISADA

Tsutomu FUKUTE

Koichi MAEKAWA

Yasunori MATSUOKA

Kyuichi MARUYAMA

Tetsuya MISHIMA

Toyoaki MIYAGAWA

Hiroshi MUTSUYOSHI

Hiroshi YOKOTA

Keitetsu ROKUGOFormer Members
Takashi SASAKI

Yasuo INOKUMA

Working Group for 'Maintenance'
Koji TAKEWAKA, Chairman
Yuichi KANEKO, Secretary
Members
Isao UJIKE

Kazuo EGUCHI

Toshiro KAMADA

Yasushi KAMIHIGASHI

Takahiro KANNO

Yukio KITAGO

Kazuhiro KUZUME

Hirohisa KOGA

Koichi KOBAYASHI

Yasuhiko SATO

Masashi SOEDA

Yoshinori TAKEDA

Yasuhiro DAN

Tomoaki TSUTSUMI

Masamichi TEZUKA

Seiichi TOTTORI

Kazuyuki TORII

Atsushi HATTORI

Hidenori HAMADA

Makoto HISADA

Toshiya MAEDA

Hideki MATSUMURA

Tsuyoshi MARUYA

Hidenori MORIKAWA

Atsuro MORIWAKE

Hidetoshi YAMASHITA

Kosuke YOKOZEKI

Hiroshi YOKOTA
Former Members
Etsutaka MAEDA

Subcommittee on English Version of Standard Specifications for Concrete Structures
Tamon UEDA, Chairman
Hiroshi YOKOTA, Secretary General

Secretaries
Toshiki AYANO

Takayuki ISHIZUKATakafumi SUGIYAMA

Toshiya MAEDA

Takumi SHIMOMURA

Members
Tetsuya ISHIDA

Hajime ITO

Mitsuyasu IWANAMI

Takao UEDA

Atsushi UENO

Masahiro OUCHI

Yoshinobu OSHIMA

Yoshitaka KATO

Minoru KUNIEDA

Yoshimori KUBO

Hirohisa KOGA

Koichi KOBAYASHI

Shigehiko SAITO

Goro SAKAI

Yasutaka SAGAWA

Toshiya TADOKORO

Hiroaki TSURUTA

Hideki NAITO

Kohei NAGAI

Kenichiro NAKARAI

Akira HOSODA

Tomohiro MIKI

Maki MIZUTA

Hiroshi MINAGAWA

Shinichi MIYAZATO

Toshinobu YAMAGUCHI

Ken WATANABE

Working Group for 'Maintenance'
Toshiya MAEDA, Chairman

Members
Yoshinobu OSHIMA

Hirohisa KOGA

Hiroshi MINAGAWA

Toshinobu YAMAGUCHI

Koichi KOBAYASHIJSCE Guideline for Concrete No. 17

Standard Specifications for Concrete Structures -2007“Maintenance”
CONTENTS
Application of Standard Specifications for Concrete Structures ................................................... i

PART 1 MAINTENANCE
CHAPTER 1 GENERAL ................................................................................................................ 1
1.1 Scope ........................................................................................................................................ 1
1.2 Principles of Maintenance ........................................................................................................ 3
1.3 Definitions ................................................................................................................................ 5
CHAPTER 2 PERFORMANCE REQUIREMENTS ................................................................ 11
2.1 Principle ................................................................................................................................. 11
2.2 General ................................................................................................................................... 11
CHAPTER 3 METHODS FOR MAINTENANCE .................................................................... 15
3.1 Principle ................................................................................................................................. 15
3.2 Maintenance Plans ................................................................................................................. 16
3.2.1 General ............................................................................................................................ 16
3.2.2 Categories and details of maintenance ............................................................................ 18
3.3 Assessments ........................................................................................................................... 19
3.3.1 General ............................................................................................................................ 19
3.3.2 Initial assessments ........................................................................................................... 20
3.3.3 Periodic assessments ....................................................................................................... 23
3.3.4 Extraordinary assessments .............................................................................................. 24
3.4 Remedial Measures ................................................................................................................ 26
3.5 Recording ............................................................................................................................... 27
CHAPTER 4 INVESTIGATIONS IN ASSESSMENT .............................................................. 28
4.1 Principle ................................................................................................................................. 28
4.2 Investigations in Initial Assessment ....................................................................................... 31
4.3 Investigations in Routine Assessment .................................................................................... 35
4.4 Investigations in Regular Assessment .................................................................................... 36
4.5 Investigations in Extraordinary Assessment .......................................................................... 39
4.6 Investigations in Emergency Assessment .............................................................................. 40
4.7 Investigation ........................................................................................................................... 41
4.7.1 General ............................................................................................................................ 41
4.7.2 Investigation items .......................................................................................................... 42
4.7.3 Investigation methods ..................................................................................................... 44
4.7.3.1 General ..................................................................................................................... 44(1)

4.7.3.2
4.7.3.3
4.7.3.4
4.7.3.5
4.7.3.6
4.7.3.7
4.7.3.8
4.7.3.9

Document search ...................................................................................................... 47
Visual observations and hammer tapping ................................................................ 48
Methods using nondestructive testing equipment .................................................... 49
Investigations involving local destruction ............................................................... 52
Loading and vibratory loading tests of existing structures ...................................... 53
Investigations for evaluating loads and environmental actions ............................... 53
Tests of materials for repair and strengthening ........................................................ 54
Monitoring investigations ........................................................................................ 55

CHAPTER 5 IDENTIFICATION OF DETERIORATION MECHANISM AND
PREDICTION OF DETERIORATION PROGRESS ........................................ 56
5.1 Principles ................................................................................................................................ 56
5.2 Methods for Identification of Deterioration Mechanisms ...................................................... 58
5.3 Prediction of Deterioration Progress ...................................................................................... 64
CHAPTER 6 EVALUATION AND JUDGMENT ...................................................................... 66
6.1 Principles ................................................................................................................................ 66
6.2 Evaluation and Judgment in Initial Assessment ..................................................................... 67
6.2.1 General ............................................................................................................................ 67
6.2.2 Evaluation based on investigations in initial assessment ................................................ 67
6.2.3 Judgment based on investigations in initial assessment .................................................. 68
6.2.4 Review of maintenance plan based on results of initial assessment ............................... 69
6.3 Evaluation and Judgment in Periodic Assessments ............................................................... 69
6.3.1 General ............................................................................................................................ 70
6.3.2 Evaluation and judgment based on investigations in routine assessments ..................... 70
6.3.3 Evaluation of performance based on investigations in regular assessments ................... 72
6.3.4 Judgment based on investigations in regular assessments .............................................. 72
6.4 Evaluation and Judgment in Extraordinary Assessments....................................................... 73
6.4.1 General ............................................................................................................................ 73
6.4.2 Evaluation based on investigations in extraordinary assessments .................................. 73
6.4.3 Judgment based on investigations in extraordinary assessments .................................... 74
6.4.4 Evaluation and judgment based on investigations in emergency assessments ............... 74
6.5 Evaluation and Judgment based on Detailed Investigations .................................................. 75
CHAPTER 7 REMEDIAL MEASURES..................................................................................... 78
7.1 Principles ................................................................................................................................ 78
7.2 Types and Selection of Remedial Measures ........................................................................... 80
7.2.1 General ............................................................................................................................ 80
7.2.2 Intensified investigation .................................................................................................. 82
7.2.3 Repair .............................................................................................................................. 82
7.2.4 Strengthening .................................................................................................................. 83
7.2.5 Functional improvement ................................................................................................. 83
7.2.6 Restriction in service ....................................................................................................... 84
7.2.7 Dismantling/removal of structure ................................................................................... 84
7.3 Repair and Strengthening ....................................................................................................... 84
7.3.1 Principles ......................................................................................................................... 84
7.3.2 Design of repair or strengthening.................................................................................... 85
7.3.3 Execution of repair or strengthening ............................................................................... 90
7.3.4 Maintenance after repair or strengthening ...................................................................... 91(2)

CHAPTER 8 RECORDING ......................................................................................................... 93
8.1 Principle ................................................................................................................................. 93
8.2 Method of Recording ............................................................................................................. 93
8.3 Items to be Recorded .............................................................................................................. 94
8.4 Storage of Records ................................................................................................................. 95

MAINTENANCE FOR SPECIFIC DETERIORATIONMECHANISMS
CHAPTER 9 MAINTENANCE OF STRUCTURES SUBJECT TO CARBONATION ........ 97
9.1 General ................................................................................................................................... 97
9.2 Maintenance Planning ............................................................................................................ 99
9.2.1 Basis of planning ............................................................................................................. 99
9.2.2 Determination of maintenance category ....................................................................... 100
9.2.3 Preparation of maintenance manuals ............................................................................ 101
9.3 Assessment ........................................................................................................................... 101
9.3.1 General .......................................................................................................................... 101
9.3.2 Investigation in assessment ........................................................................................... 102
9.3.2.1 General ................................................................................................................... 102
9.3.2.2 Investigation in initial assessment.......................................................................... 103
9.3.2.3 Investigation in routine assessment........................................................................ 105
9.3.2.4 Investigation in regular assessment........................................................................ 105
9.3.2.5 Detailed investigation ............................................................................................ 106
9.3.3 Methods for predicting performance degradation of structures .................................... 109
9.3.3.1 General ................................................................................................................... 109
9.3.3.2 Prediction of carbonation ....................................................................................... 110
9.3.3.3 Prediction of steel corrosion .................................................................................. 112
9.3.3.4 Modification of prediction ..................................................................................... 115
9.3.4 Evaluation and judgment............................................................................................... 115
9.4 Remedial Measures .............................................................................................................. 118
9.4.1 Selection of remedial measures..................................................................................... 118
9.4.2 Repair and strengthening .............................................................................................. 119
9.5 Recording ............................................................................................................................. 121
CHAPTER 10 MAINTENANCE OF STRUCTURES SUBJECT TO
CHLORIDE ATTACK......................................................................................... 122
10.1 General ............................................................................................................................... 122
10.2 Maintenance Planning........................................................................................................ 124
10.2.1 Basis of planning ........................................................................................................ 124
10.2.2 Determination of maintenance category ..................................................................... 124
10.2.3 Preparation of maintenance manuals .......................................................................... 125
10.3 Assessment......................................................................................................................... 126
10.3.1 General ........................................................................................................................ 126
10.3.2 Investigation in assessment......................................................................................... 126
10.3.2.1 General................................................................................................................. 126
10.3.2.2 Investigation in initial assessment ....................................................................... 127
10.3.2.3 Investigation in routine assessment ..................................................................... 128
10.3.2.4 Investigation in regular assessment ..................................................................... 129
10.3.2.5 Detailed investigation .......................................................................................... 130(3)

10.3.3 Methods for predicting performance degradation of structures.................................. 132
10.3.3.1 General................................................................................................................. 132
10.3.3.2 Prediction of chloride ion diffusion ..................................................................... 133
10.3.3.3 Prediction of steel corrosion ................................................................................ 136
10.3.3.4 Modification of prediction ................................................................................... 138
10.3.4 Evaluation and judgment ............................................................................................ 138
10.4 Remedial Measures ............................................................................................................ 141
10.4.1 Selection of remedial measures .................................................................................. 141
10.4.2 Repair and strengthening ............................................................................................ 142
10.5 Recording ........................................................................................................................... 144
CHAPTER 11 MAINTENANCE OF STRUCTURES SUBJECT TO FROST ATTACK...... 145
11.1 General ............................................................................................................................... 145
11.2 Maintenance Planning........................................................................................................ 148
11.2.1 Basis of planning ........................................................................................................ 148
11.2.2 Determination of maintenance category ..................................................................... 148
11.2.3 Preparation of maintenance manuals .......................................................................... 149
11.3 Assessment......................................................................................................................... 149
11.3.1 General ........................................................................................................................ 149
11.3.2 Investigation in assessment......................................................................................... 150
11.3.2.1 General................................................................................................................. 150
11.3.2.2 Investigation in initial assessment ....................................................................... 151
11.3.2.3 Investigation in routine assessment ..................................................................... 152
11.3.2.4 Investigation in regular assessment ..................................................................... 153
11.3.2.5 Detailed investigation .......................................................................................... 154
11.3.3 Methods for predicting performance degradation of structures.................................. 156
11.3.3.1 General................................................................................................................. 156
11.3.3.2 Prediction of occurrence of frost attack ............................................................... 157
11.3.3.3 Prediction of depth of deterioration by frost attack ............................................. 158
11.3.3.4 Modification of prediction ................................................................................... 158
11.3.4 Evaluation and judgment ............................................................................................ 159
11.4 Remedial Measures ............................................................................................................ 161
11.4.1 Selection of remedial measures .................................................................................. 161
11.4.2 Repair and strengthening ............................................................................................ 161
11.5 Recording ........................................................................................................................... 163
CHAPTER 12 MAINTENANCE OF STRUCTURES SUBJECT TO
CHEMICAL ATTACK ........................................................................................ 164
12.1 General ............................................................................................................................... 164
12.2 Maintenance Planning........................................................................................................ 167
12.2.1 Basis of planning ........................................................................................................ 167
12.2.2 Determination of maintenance category ..................................................................... 167
12.2.3 Preparation of maintenance manuals .......................................................................... 168
12.3 Assessment......................................................................................................................... 169
12.3.1 General ........................................................................................................................ 169
12.3.2 Investigation in assessment......................................................................................... 169
12.3.2.1 General................................................................................................................. 169
12.3.2.2 Investigation in initial assessment ....................................................................... 170
12.3.2.3 Investigation in routine assessment ..................................................................... 172
12.3.2.4 Investigation in regular assessment ..................................................................... 173(4)

12.3.2.5 Detailed investigation .......................................................................................... 173
12.3.3 Methods for predicting performance degradation of structures.................................. 177
12.3.3.1 General................................................................................................................. 177
12.3.3.2 Prediction of chemical erosion ............................................................................ 178
12.3.3.3 Prediction of steel corrosion ................................................................................ 181
12.3.3.4 Modification of prediction ................................................................................... 182
12.3.4 Evaluation and judgment ............................................................................................ 183
12.4 Remedial Measures ............................................................................................................ 186
12.4.1 Selection of remedial measures .................................................................................. 186
12.4.2 Repair and strengthening ............................................................................................ 186
12.5 Recording ........................................................................................................................... 188
CHAPTER 13 MAINTENANCE OF STRUCTURES SUBJECT TO
ALKALI-SILICA REACTION .......................................................................... 189
13.1 General ............................................................................................................................... 189
13.2 Maintenance Planning........................................................................................................ 192
13.2.1 Basis of planning ........................................................................................................ 192
13.2.2 Determination of maintenance category ..................................................................... 193
13.2.3 Preparation of maintenance manuals .......................................................................... 194
13.3 Assessment......................................................................................................................... 194
13.3.1 General ........................................................................................................................ 194
13.3.2 Investigation in assessment......................................................................................... 194
13.3.2.1 General................................................................................................................. 194
13.3.2.2 Investigation in initial assessment ....................................................................... 196
13.3.2.3 Investigation in routine assessment ..................................................................... 197
13.3.2.4 Investigation in regular assessment ..................................................................... 198
13.3.2.5 Detailed investigation .......................................................................................... 199
13.3.3 Methods for predicting performance degradation of structures.................................. 202
13.3.3.1 General................................................................................................................. 202
13.3.3.2 Prediction of ASR induced expansion of concrete .............................................. 204
13.3.3.3 Prediction of steel corrosion ................................................................................ 205
13.3.3.4 Prediction of steel damage ................................................................................... 205
13.3.3.5 Modification of prediction ................................................................................... 206
13.3.4 Evaluation and judgment ............................................................................................ 206
13.4 Remedial Measures ............................................................................................................ 209
13.4.1 Selection of remedial measures .................................................................................. 209
13.4.2 Repair and strengthening ............................................................................................ 210
13.5 Recording ........................................................................................................................... 214
CHAPTER 14 MAINTENANCE OF REINFORCED CONCRETE SLABSSUBJECT TO FATIGUE .................................................................................... 215
14.1 General ............................................................................................................................... 215
14.2 Maintenance Planning........................................................................................................ 218
14.2.1 Basis of planning ........................................................................................................ 218
14.2.2 Determination of maintenance category ..................................................................... 218
14.2.3 Preparation of maintenance manuals .......................................................................... 219
14.3 Assessment......................................................................................................................... 219
14.3.1 General ........................................................................................................................ 219
14.3.2 Investigation in assessment......................................................................................... 220
14.3.2.1 General................................................................................................................. 220(5)

14.3.2.2 Investigation in initial assessment ....................................................................... 221
14.3.2.3 Investigation in routine assessment ..................................................................... 222
14.3.2.4 Investigation in regular assessment ..................................................................... 223
14.3.2.5 Detailed investigation .......................................................................................... 224
14.3.3 Methods for predicting performance degradation of structures.................................. 225
14.3.3.1 General................................................................................................................. 225
14.3.3.2 Modification of prediction ................................................................................... 226
14.3.4 Evaluation and judgment ............................................................................................ 227
14.4 Remedial Measures ............................................................................................................ 229
14.4.1 Selection of remedial measures .................................................................................. 229
14.4.2 Prevention measures ................................................................................................... 230
14.4.3 Repair and strengthening ............................................................................................ 230
14.5 Recording ........................................................................................................................... 232
CHAPTER 15 MAINTENANCE OF REINFORCED CONCRETE BEAMSSUBJECT TO FATIGUE .................................................................................... 233
15.1 General ............................................................................................................................... 233
15.2 Maintenance Planning........................................................................................................ 236
15.2.1 Basis of planning ........................................................................................................ 236
15.2.2 Determination of maintenance category ..................................................................... 237
15.2.3 Preparation of maintenance manuals .......................................................................... 238
15.3 Assessment......................................................................................................................... 238
15.3.1 General ........................................................................................................................ 238
15.3.2 Investigation in assessment......................................................................................... 238
15.3.2.1 General................................................................................................................. 238
15.3.2.2 Investigation in initial assessment ....................................................................... 240
15.3.2.3 Investigation in routine assessment ..................................................................... 241
15.3.2.4 Investigation in regular assessment ..................................................................... 242
15.3.2.5 Detailed investigation .......................................................................................... 243
15.3.3 Methods for predicting performance degradation of structures.................................. 244
15.3.3.1 General................................................................................................................. 244
15.3.3.2 Prediction of fatigue ............................................................................................ 246
15.3.3.3 Modification of prediction ................................................................................... 248
15.3.4 Evaluation and judgment ............................................................................................ 248
15.4 Remedial Measures ............................................................................................................ 250
15.4.1 Selection of remedial measures .................................................................................. 250
15.4.2 Repair and strengthening ............................................................................................ 251
15.5 Recording ........................................................................................................................... 252
CHAPTER 16 MAINTENANCE OF STRUCTURES SUBJECT TO ABRASION ............... 253
16.1 General ............................................................................................................................... 253
16.2 Maintenance Planning........................................................................................................ 255
16.2.1 Basis of planning ........................................................................................................ 255
16.2.2 Determination of maintenance category ..................................................................... 256
16.2.3 Preparation of maintenance manuals .......................................................................... 257
16.3 Assessment......................................................................................................................... 257
16.3.1 General ........................................................................................................................ 257
16.3.2 Investigation in assessment......................................................................................... 258
16.3.2.1 General................................................................................................................. 258
16.3.2.2 Investigation in initial assessment ....................................................................... 259
16.3.2.3 Investigation in routine assessment ..................................................................... 260(6)

16.3.2.4 Investigation in regular assessment ..................................................................... 261
16.3.2.5 Detailed investigation .......................................................................................... 261
16.3.3 Methods for predicting performance degradation of structures.................................. 263
16.3.3.1 General................................................................................................................. 263
16.3.3.2 Prediction of abrasion .......................................................................................... 264
16.3.3.3 Modification of prediction ................................................................................... 265
16.3.4 Evaluation and judgment ............................................................................................ 265
16.4 Remedial Measures ............................................................................................................ 267
16.4.1 Selection of remedial measures .................................................................................. 267
16.4.2 Repair and strengthening ............................................................................................ 268
16.5 Recording ........................................................................................................................... 269
CHAPTER 17 SEISMIC RETROFIT ......................................................................................... 271
17.1 General ............................................................................................................................... 271
17.2 Seismic Retrofit Planning .................................................................................................. 271
17.3 Seismic Assessment ........................................................................................................... 272
17.3.1 General ........................................................................................................................ 272
17.3.2 Investigation for seismic assessment .......................................................................... 272
17.3.3 Evaluation of seismic performance and judgment of necessity
for seismic retrofit....................................................................................................... 273
17.4 Selection of Seismic Retrofit Method ................................................................................ 274
17.5 Design of Seismic Retrofit ................................................................................................. 276
17.6 Execution of Seismic Retrofit ............................................................................................ 276
17.7 Maintenance after Seismic Retrofit ................................................................................... 277
17.8 Recording ........................................................................................................................... 278(7)

Application of Standard Specifications for Concrete Structures

Application of Standard Specifications for Concrete Structures
Editorial notes for the English Version:(1) The Standard Specifications for Concrete Structures are a model code which is supposed to be
applied in Japan and have no legal bindings.
(2) Therefore, some contents, such as Chapters 2 and 3 of “Application of Standard
Specifications for Concrete Structures,” may not fit to practical scheme in construction industry inthe other countries.
(3) However, it is hoped that the Standard Specifications for Concrete Structures could be amodel code for the other countries after necessary modifications of the contents considering the
local conditions.

1. Basic concept concerning the organization of the Standard Specifications for Concrete
Structures
The Standard Specifications for Concrete Structures are regularly revised reflecting thestate-of-the-art concrete technologies developed in Japan and other countries, and provide standards
concerning the technical aspects of concrete structures in a series of phases from planning to design,
construction and maintenance.
In this revised edition, the “Standard Specifications for Concrete Structures, Design” iscomposed of the “Standard Specifications for Concrete Structures, Structural Performance
Verification” and “Standard Specifications for Concrete Structures, Seismic Performance
Verification” to enhance the convenience of design practice. Durability check and initial cracking
check, which should be discussed in the “Standard Specifications for Concrete Structures, Design”
have been transferred from the “Standard Specifications for Concrete Structures, Materials andConstruction” to “Standard Specifications for Concrete Structures, Design”. The preparation andrevision of the “Standard Specifications for Concrete Structures, Pavement” has been handed overto the Committee on Pavement Engineering, JSCE (Japan Society of Civil Engineers). The results
are now published separately under the title of the Standard Specifications for Pavement. Thus, theStandard Specifications for Concrete Structures include five components: Design, Materials andConstruction, Maintenance, Dam Concrete, and Test Methods and Specifications.
The General Requirements for “Design”, “Materials and Construction” and “Dam Concrete” aredescribed based on the concept of performance-based code. Performance requirements are specified
for structures and the methods for checking the compliance with requirements are shown in the
General Requirements. In the Standard Methods, standard methods for satisfying the General
Requirements under certain conditions are given for more efficient and simpler design andconstruction. In cases where no conditions specified in the Standard Methods are met, performanceverification should be conducted in accordance with the General Requirements. For establishing
new standards fitting for structures or regions to which no Standard Methods are applicable, theStandard Methods may be referred to.
Concrete structures are generally constructed for providing services in the phases of planning,
design, construction and maintenance in accordance with the respective components of the Standard
Specifications. Each type of work is not independent of the others. Data are handed over from an(i)Standard Specifications for Concrete Structures-2007, Maintenance

upstream to a downstream phase that are required for carrying out the work downstream to meet theconditions specified upstream. Handing over the data is therefore important to proper
implementation of work in respective phases. In the Standard Specifications for Concrete Structures,“Design”, “Materials and Construction” and “Maintenance” are closely interrelated to one another.
Then, the required data shown in each Specifications should be accurately handed over to the next
phase without fail.
Performance requirements for durability, safety, serviceability and restorability that are specified
in the “Standard Specifications for Concrete Structures, Design” are determined in the design phase.
Construction and maintenance methods are roughly determined in the phase. The data that affectconstruction and maintenance should therefore be handed over to the next phase without fail in theform of design drawings.
Construction records that are specified in the “Standard Specifications for Concrete Structures,
Materials and Construction” provide important data for assessment, deterioration prediction andimplementation of remedial measures in the maintenance phase. Accurate construction records
should therefore be handed over to maintenance engineers. Construction plans and various
inspection reports should also be provided to engineers as required.

Planning

Data
Feedback

DesignData

Construction

Data

MaintenanceFeedback
Fig. 1

Flow of work

Figure 1 shows a flow of work from the planning of a concrete structure to service
commencement. Data collected in the maintenance phase are not transferred to engineering works
in the planning, design or construction phase. It should, however, be taken into consideration thatreflecting the data in the maintenance phase in the planning, design and construction of anotherstructure for improvement is important to extend the service life of the structure. Theinterrelationship is basically the same for design, construction and maintenance described in the“Standard Specifications for Concrete Structures, Dam Concrete.”
Each component of the Standard Specifications for Concrete Structures is described below.
The “Standard Specifications for Concrete Structures, Design” shows standard methods for
performance verification of concrete structures such as reinforced concrete, prestressed concreteand steel-concrete composite structures, and stipulates the preconditions for checking and structuraldetails. The revised Standard Specifications for Concrete Structures are not applicable tounreinforced concrete structures. Material design values or other applicable items may, however, beapplied to unreinforced concrete structures.
The “Standard Specifications for Concrete Structures, Materials and Construction” provides
basic general rules concerning the construction of concrete structures. In the construction phase, theconstruction method and the performance during the construction work are determined based on thedesign drawings and restrictions on construction. Then, materials are selected and concrete mix(ii)Application of Standard Specifications for Concrete Structures

proportions are determined, where a concreting plan is developed so as to meet the requirements forwater content, cement amount, cement type and other parameters. Whether the concreting plan
meets the construction requirements or performance requirements of the structure or not is verified
by an appropriate method. If the requirements are not satisfied, the concreting method is
re-specified or the mix proportions are modified as long as the conditions handed over from thedesign phase are met.
The “Standard Specifications for Concrete Structures, Maintenance” provides general basic
principles concerning the maintenance of concrete structures. In the maintenance phase, documents
such as the design drawings and maintenance plans handed over from the design phase, and theconstruction plans, as-built drawings, construction records and inspection reports handed over fromthe construction phase should be fully used for efficient and effective maintenance work. In cases
where the use or functions of the structure change due to social changes, performance verification
should be made to verify whether the structure meets the resultant performance requirements or not.
If designated performance requirements are not ensured, repair, strengthening or other remedial
measures should be considered.
The “Standard Specifications for Concrete Structures, Dam Concrete” stipulates performanceand quality requirements for dam concrete, and describes the methods for verifying the compliancewith the requirements and the basic design and construction principles. The descriptions concerning
design, construction and maintenance in the “Standard Specifications for Concrete Structures, Dam
Concrete” are different from the contents of the Standard Specifications “Design”, “Materials andConstruction” and “Maintenance” with many respects because of the factors unique to dam concretesuch as the unreinforced nature and low or zero slump of dam concrete. The “Standard
Specifications for Concrete Structures, Dam Concrete” therefore describes the matters concerning
the design, construction and maintenance of dam concrete.
The “Standard Specifications for Concrete Structures, Test Methods and Specifications” lists theJapan Industrial Standards, provisions of JSCE and other standards for the methods mentioned in
the other four components of the Standard Specifications. Figures 2 through 4 show work steps inrespective phases described in the Standard Specifications for Concrete Structures “Design,”“Materials and Construction” and “Maintenance.”

2. Roles and deployment of responsible engineers
To produce and maintain a reliable structure that meets the performance requirements, theengineers involved should have a capacity to carry out the work and a high level of ethics.
In the planning, design, construction and maintenance of a concrete structure, the engineers
should make appropriate decisions under varying work conditions. Therefore, the engineers withrequired technical skills should be deployed according to the level of difficulty of work. In theplanning, design, construction and maintenance, therefore, responsible engineers not only withrequired technical expertise but also with responsibility and authority should be deployed inorganizations of the owner, the consultant and the contractor.

(iii)

Standard Specifications for Concrete Structures-2007, Maintenance

Use and functions of structure

Plan for the structure
Specifications for Design
Specification of performancerequirements
Structural planning

Design plans(Structural format, materials used, dimensions ofmajor elements, construction method, etc.)

Design of the structure
Specifications for Design
Specification of structural details
Structural details (Cross section,materials, bar arrangement, etc.)
NG

Performance verification
for the structure
OK

Design drawings and other materials(Structure, materials, construction method,maintenance plan, etc.)

Construction of the structure

Fig.2

Work steps described in “Specifications for Design”(iv)Application of Standard Specifications for Concrete Structures

Planning of the structure

Design of the structure

Construction of the structure
Specifications for Materials andConstruction
Construction planning

NG

Verification and approval
OK

Construction

Quality control

NG

Inspection
OKAs-built drawings and construction records

Maintenance of the structure

Fig. 3Work steps described in “Specifications for Materials and Construction”(v)Standard Specifications for Concrete Structures-2007, Maintenance

Planning of the structure

Design plans

Design of the structure

Design drawings and other materials

Construction of the structure

As-built drawings and construction
records

Maintenance of the structure
Specifications for Maintenance
Maintenance plan

Investigation, deterioration
prediction and evaluation
Recording

Not required

Assessment
Remedial measuresrequired or not?
Required

Recording

Implementation ofremedial measures

Storage of maintenancerecords

Fig. 4Work steps described in “Specifications for Maintenance”(vi)Application of Standard Specifications for Concrete Structures

The technical skills required for responsible engineers should be defined according to a scale of
the work, importance and difficulty of planning, design, construction or maintenance.
As capacity classifications of engineers, engineer qualifications authorized by JSCE are listed inTable 1. The qualifications for the special senior engineers and senior engineers are generally
required for responsible engineers.
The JSCE technical qualifications cover several fields. Responsible engineers to be deployed inprojects need to have qualifications only for major fields related to the specific project.

Table 1Engineer qualifications authorized by JSCE

Qualification

Required skills

Executive
Professional
Civil Engineer

Japan’s leading civil engineer with high-level knowledge andexperience in his or her field of specialty, or with comprehensive
civil engineering expertise

SeniorProfessional
Civil Engineer

Engineer with high-level knowledge and experience in multiple
fields or with comprehensive knowledge on civil engineering who
can solve key problems as a leader

Professional
Civil Engineer

Engineer with knowledge and experience at least in one special field
who can carry out task at his or her discretion

Associate
Professional
Civil Engineer

Civil engineer with required basic knowledge who can carry out
assigned task

3. System for ensuring reliability
Many groups are involved in the planning, design, construction and maintenance of a structure.
In order to ensure the high reliability of the structure in each work phase, the organizations involved
should play their role providing their know-how and assuming due responsibility.
To ensure reliability in the design (and planning) phase, two independent groups should
basically check the design. After the design and check by the design company, engineers of thecontractor should re-check the design, or request a third party to check the design. Then, fully
skilled engineers should be selected for checking so that safety or other reliability parameters may
be satisfied. The design drawings serving as a basis for contracting should carry the signatures of
responsible engineers of the two groups that assume responsibility.
In the construction phase, reliability is ensured through the quality management by thecontractor and the quality verification by the inspector independent of the contractor. Inspections
have generally been conducted directly by the Owner and/or Consultant. Completed structures
should be inspected wherever possible. If inspecting completed structures is impossible, inspections
should be conducted while the structure is being constructed. If the Owner cannot directly inspect(vii)

Standard Specifications for Concrete Structures-2007, Maintenancethe structure under construction, the Owner may request an agent independent of the contractor.
Adopting as many highly reliable methods as possible can reduce the labor required for quality
management and inspection. In cases where adopting not so reliable methods is inevitable, the levelof quality management should be raised or inspections should be conducted more frequently to
improve reliability. Inspection items and decision criteria should be specifically presented at thetime of contracting because they greatly affect the quality of the structure and the construction cost.
Ensuring safety requires regular investigations. When defects are detected, decision should bemade as to remedial measures. For decision making concerning remedial measures for extremely
difficult deformation, listening to the opinions of engineers with high skills who have experienced
numerous cases is important.
In order for a system for ensuring reliability to work properly, the people or organization withtechnical skills fit for the specific work should be granted explicit responsibility and authority andassigned to the work. The compensation for the work and time required for the work should also be
provided.

(viii)

Part 1 MaintenanceChapter 1

GeneralCHAPTER 1 GENERAL

1.1 Scope(1) This Specification for "Maintenance” (hereafter, this Specification) describes themaintenance of concrete structures.
(2) Part1: “Maintenance” describes the principles of maintenance of concrete structures.
(3) Part2: “Maintenance for Specific Deterioration Mechanisms” describes the principles
and standard methods of maintenance of concrete structures subject to a specificdeterioration mechanism.

[Commentary] (1) Maintenance is the act of maintaining the performance of a concrete structure(hereafter referred to as “structure”) within the allowable range during its service period.
Maintenance is as important as and is closely related to design and construction. Maintaining a
structure within the allowable range generally means to retain it above the required levels.
This Specification is not intended for maintaining structures of a specific structuralformalization or those that are built using a specific design or specific construction method. This
Specification presents basic ideas concerning the maintenance of all concrete structures, including
plain concrete, reinforced concrete, prestressed concrete and steel-concrete composite structures.
This Specification can be applied to the structures designed and constructed not in accordance withthe “Design” and the “Construction” volumes of the Standard Specifications. The structures that aredesigned and constructed in accordance with these specifications are based on explicit design andconstruction ideas and are in accordance with this Specification, which facilitates the maintenanceof the structures.
This Specification covers the maintenance of both newly constructed and existing structures.
New structures constructed in accordance with specified design and construction standards areunlikely to be subject to outstanding severe deterioration within the design service period. The"Design" and the "Construction" volumes of the Standard Specifications explain that concrete or
reinforcing materials of structures built in accordance with the “Design” and the “Construction”
volumes of the Standard Specifications are highly unlikely to be subject to outstanding deterioration
within the design service period of the structure because the durability of the structure is checked byconfirming that the quality of concrete and reinforcing materials and the performance requirements
for materials are not reduced within the design service period; and because appropriate remedial
measures are taken even in cases where initial defects are detected inacceptance verification of
concrete, verification of execution, or verification of the structure. In cases where they are built inaccordance with the “Design” and the “Construction” volumes of the Standard Specifications,ordinary structures can be maintained adequately by investigations in routine or regular assessments
based mainly on visual observations and require no detailed investigations except for certain key
structures. Thus, maintenance can be facilitated.
The durability check specified in the "Design" volumes of Standard Specifications, however,falls short of quantitatively checking all the external forces expected to act on structures. Under theconditions more severe than expected, the reliability of the check is not necessarily high. Climatechange or other factors may create conditions more severe than the design conditions. Structuresthat are constructed carefully using the materials considered appropriate at the time of design may
require repair or other remedial measures because of the outstanding deterioration with time. For
1

Standard Specifications for Concrete Structures-2007, Maintenancesome structures, the planned service period is set longer than the design service period. Then,
maintenance plans should be developed properly considering the possibility of outstanding
deterioration after expiring the design service period of the structure.
For existing structures, unsuitable materials may have been adopted or no due consideration
may have been given to design or construction because of a lack of understanding of structural
durability. Initial defects may sometimes have been overlooked in investigations at the completionof construction or structures may have been used without adequate repair. The performance ofstructures may have been explicitly reduced below the level at the time of just after construction
even under not so severe conditions and repair or other remedial measures may be required. In thecase, the defective event should be identified to the maximum extent possible by investigation todetermine whether the defective event is ascribable to the initial defects, damage or deterioration
and what the main cause is, and necessary remedial measures should be taken. In the case of initialdefects or damage, quick and appropriate measures including emergency measures are required. In
cases where deterioration is outstanding that affects time-based deterioration of the structure, thedeterioration mechanism should be identified to the maximum extent possible and the structure
should be maintained adequately based on the prediction of deterioration progress and theevaluation and determination of performance degradation.
Some of the civil engineering structures with a service period of 50 to 100 years may require
remedial measures under the conditions where performance requirements vary in changing social
situations, e.g. wheel load increases on bridges due to the traffic of larger vehicles and where
seismic motions stronger than the design level act on the structure. When design criteria are revisedor new criteria are established, the structures and members that have been designed and constructedin accordance with the criteria before the revision or establishment become nonconforming as
existing structures and members. The revised or newly established criteria are applicable
exclusively to the structures to be designed and constructed after the revision or establishment but
do not require the compliance of all structures including those designed and constructed before
criteria revision or establishment. Revising criteria or establishing new criteria basically aims at
improving the considerations in design and construction of structures to meet the current situations.
Civil engineering structures are generally of high public nature. Appropriate measures should
therefore be taken for structures in service at the time of revision or establishment of criteria inorder to prevent structures from being subject to performance degradation and serious damage,failure and collapse due to nonconformity of existing structures.
This Specification, based on the above discussions, describes all the management actions tomaintain the designated performance of existing and newly constructed structures during theirservice period, and the principles and major methods for appropriate maintenance. Structures are inservice for a long time and performance requirements vary greatly. The number of structures inservice will be exorbitant if relatively small ones are counted. Carefully maintaining all of thestructures is not easy. Under the circumstances, it is important for the engineers involved tomaintain structures in ways suitable to actual conditions duly respecting the major points of thisSpecification and considering not only the defect but also the importance, remaining service life orcost performance of the structure.
(2) and (3) This Specification is composed of two sections. Part 1 “Maintenance” presents
the principles, methods and procedures for effectively maintaining structures comprehensively
considering the initial defects, damage and performance degradation. For the deterioration
mechanisms affecting the performance degradation of the structure, namely, carbonation, chloride
attack, frost attack, chemical erosion, alkali-silica reaction, fatigue (slabs and beams) and abrasion,
the basic and specific maintenance methods for each are described in Part 2 “Maintenance for2

Chapter 1

Generalspecific deterioration mechanisms” in detail based on the description in Part 1. Also presented are
the basic ideas of seismic retrofitting and required diagnostic methods, which are key maintenancefactors.
This specification should be used basically to maintain structures in accordance with Part 1,
while referring to Part 2 in necessary in cases where the main deterioration mechanism is clearly
identified. In cases where the deterioration mechanism is clearly identified, structures may be
maintained in accordance with the descriptions of deterioration mechanisms in Part 2. Then, thepossibility of composite actions with other types of deterioration should be examined. Maintenancemethods should basically be confirmed in accordance with Part1.
When adopting special materials, methods and construction not adequately described in thisSpecification, the major points of this Specification should be duly respected to meet actual
situations. For special materials, methods and construction, the Society of Civil Engineers of Japanhas prepared recommendations and manuals as listed below.

Recommended Practice for High Strength Concrete, 1980
Recommendations for Design and Construction of Steel Fiber Reinforced Concrete, 1983
Manual of Design and Construction for Lightweight Aggregate Concrete Structures, 1985
Recommendations for Design and Construction of Structures by Prestressed Concrete Panel Composite Slab
Method (draft), 1988
Recommendations for Design and Construction of Prestressed Concrete Method, 1991
Recommendations for Design and Construction of Anti-washout Underwater Concrete, 1991Design Code for
Steel-Concrete Sandwich Structures (draft), 1992
Recommended Practice for Concrete Containing Air-entraining High range Water-reducing Agents, 1993
Recommended Practice for Expansive Concrete, 1993
Recommendations for Design and Construction of Concrete Structures Using Continuous Fiber Reinforcing
Material, 1996
Recommendations for Design and Construction of Composite Structures, 1997
Recommendations for Construction of High-Flowable Concrete, 1998
Guidelines for Retrofit of Concrete Structures, 1999
Recommendations for Design of Reinforced Concrete Columns with Steel Fiber (draft), 1999
Recommendations for Upgrading of Concrete Structures with Use of Continuous Fiber Sheets, 2000
Recommendations for Design and Construction of Structure using Self-compacting, High-strength and Durable
Concrete (draft), 2001
Recommendations for Design and Construction of Electrochemical Corrosion Control Methods, 2001
Recommendations for Design and Construction of Concrete Structures Using Epoxy Coated Reinforcing SteelBars (revised edition), 2003
Recommendations for Design and Construction of Ultra High Strength Fiber Reinforced Concrete Structures,
2004
Recommendations for Concrete Repair and Surface Protection of Concrete Structures, 2005
Recommendations for Shotcreting, 2005
Recommendations for Environmental Performance Verification for Concrete Structures, 2005
Recommendations for Design, Fabrication and Evaluation of Anchorages and Joints in Reinforcing Bars [2007] ,2007

1.2 Principles of Maintenance
The maintenance manager for structures shall develop plans for maintaining theperformance of structures within the allowable range during their planned service period,build a system for maintenance and properly maintain structures.

3

Standard Specifications for Concrete Structures-2007, Maintenance［Commentary］It is necessary to maintain the performance of the structure within the allowable
range during its planned service period. To that end, the maintenance manager shall develop
maintenance plans in advance; build a system for properly performing a series of maintenance workfrom assessment that is composed of such specific jobs as investigations, prediction of deterioration
progress, evaluation and judgment of necessity for remedial measures and recording; and maintainstructures.
The performance of structures deteriorates with time. The degree of deterioration varies
according to the quality of concrete and steel that constitute the structure, structural regions or
members, and the environmental condition. The maintenance manager should first consider the stateof the structure, accurately predict time-based changes of performance requirements in such terms
as safety, serviceability, hazards for third party and aesthetic appearance and landscape, prepare a
scenario indicating how the structure needs to be, and develop maintenance plans based on the
scenario to maintain the designated performance of the structure during its planned service period.
Then, the maintenance manager should evaluate the performance of structures in service based on
the maintenance plans and maintain the performance of structures at the level designated in the
scenario while taking remedial measures as required. More effective maintenance may be possible
by enhancing the cost effectiveness through the introduction of life cycle cost evaluation methods
and by increasing the reliability of performance evaluation of structures through the adoption of
new technologies.
Structures need to be maintained continuously over a long period of time. In the process,social conditions and environment are expected to be subject to greater change than predicted andthe use and importance of the structure may vary from those specified in the original scenario.
Reviewing the original maintenance plans may become necessary to secure the budget and humanresources required for maintenance. The maintenance manager should therefore build a system foradequately and flexibly respond to the above situations.
Fig. C1.2.1 shows an example of maintenance of a civil engineering structure. Adequately
maintaining either a newly constructed or existing structure basically requires the development of asystem for implementation, definition of responsibilities and assignment of engineers withdesignated skills. It is, however, generally difficult to cover all the maintenance work including
simple daily maintenance works by highly skilled engineers. The level of engineer inevitably varies
according to the level of investigation, evaluation or judgment. For example, in investigations inroutine assessment can be conducted not only by responsible engineers who can make a high-levelcomprehensive decision based on the investigation results, or professional engineers who have a
specialized knowledge and skills, but also by investigators with no highly specialized knowledge
but with basic knowledge in accordance with the manuals that specifically describe the methods ofinvestigations and of evaluation of results. In the maintenance of structures, therefore, it isimportant to properly assign a responsible engineer who is held responsible for the maintenance andis authorized to perform maintenance work and to have professional engineers and investigators
fulfill their respective roles under the control of the responsible engineer.

4

Chapter 1

General

Owner of structure (e.g. the public owns a public structure)
Contractor conducting assessment
ReportOutsource

Maintenance manager

Outsource

Chief manager ------------ Chief of the organization or a person withequivalent responsibility
Intention of
the owner

Responsible engineer ---- Make final confirmation ofcontracted work

Professional engineer ---- Propose maintenance plans,

Reportimplement investigations inregular assessment and detailed
investigation, and evaluate thecondition of structure

ReportResponsible engineer ---- Develop maintenance plans and make final
decisions concerning maintenance work
Instruct

Report andconsult

discussion

Professional engineer ---- Propose maintenance plans, implement andInstruct

Report andconsult

Contractor taking remedial measures

evaluate the results of investigations inregular assessment and detailed
investigation, propose the determination,and evaluate the results of diagnose
outsourced work and remedial measures

Outsource

Responsible engineer ----Make technical proposals andassume responsibility forconstruction management

ReportInvestigator --------------- Mainly conduct investigations in routine
assessment

Professional engineer ----Design, implement and supervise
construction work

: Covered by "Maintenance“

RequestComment: Implemented: Implemented as required

Third party organizations, Academic expert, etc.

Fig. C1.2.1 Examples of a system for structure maintenance and roles of engineers

The deterioration and damage of structures are never homogeneous. The equipments used ininvestigations for assessments, and the methods and materials adopted for repair, strengthening andother measures therefore vary greatly. Making highly specialized investigations or implementing
special construction methods are sometimes required. Conducting maintenance work exclusively byin-house engineers may be difficult on certain occasions. Then, part of the maintenance work needs
to be outsourced to contractors with specialized skills. The maintenance manager should confirm
that a responsible engineer capable of and responsible for performing the contracted work is
assigned in the contractor and that a system is built under which the maintenance manager can
finally evaluate the result of work and make decisions.
The responsible engineer means an Executive professional civil engineer or Seniorprofessional civil engineer authorized by Japan Society of Civil Engineers, a Professional engineer
in the field of design, construction or maintenance of concrete structures authorized by The
institution of Professional Engineers Japan, or a person with equivalent capacity. The professional
engineer means a professional civil engineer authorized by Japan Society of Civil Engineers,
concrete diagnosis & maintenance engineer authorized by Japan Concrete Institute, a first-classcivil engineering construction management engineer or an engineer with similar capacity.

1.3 Definitions
Terms used in this Specification are defined as follows:
Maintenance: All technical actions for maintaining the performance of the structure above
the required level during its service period.
Required performance: The performance required of the structure according to its
5Standard Specifications for Concrete Structures-2007, Maintenancepurpose and function.
Preventive maintenance: The maintenance for preventing performance degradation of thestructure proactively.
Corrective maintenance: The maintenance conducted reactively according to the degreeof performance degradation of the structure.
Observational maintenance: The maintenance mainly composed of investigations byvisual observation. No direct measures are applied to the structure such as repair andstrengthening. The maintenance by indirect observation is included e.g. indirect
observation of deformations in the soil and structures in the vicinity in cases where no
direct observation is possible for underground members of foundations.
Planned service period: A period during which the structure is scheduled to be in service.
It may be modified with a review of maintenance plans.
Design service period: A period during which the structure or member should fully
achieve its objective functions as specified in the design phase.
Remaining planned service period: A period between the time of investigation or review
and the end of planned service period.
Remaining design service period: A period between the time of investigation or review
and the end of design service period.
Function of structure (member): The role that the structure (or its member) depending on
the purpose and requirements.
Performance of structure (member): The capacity shown the structure (or its member)depending on the purpose and requirements.
Durability: The resistance of the structure to time-based deterioration of performance dueto the degradation of members of the structure under an assumed action.
Safety: The performance of the structure for keeping the life or property of the user or of aperson in the vicinity free from any threat.
Serviceability: The performance of the structure for enabling the user of the structure to
comfortably use the structure or prevent a person in the vicinity from feeling
uncomfortable owing to the structure, and the performance for properly providing otherfunctions required of the structure.
Hazards for third party: Effects of damage to people or property caused by concrete
pieces falling off the structure.
Investigation in assessment: Any action in diagnosis for checking for problems with thestructure or member.
Investigation in initial assessment: An investigation made at the start of maintenancemainly to identify the initial conditions of the structure.

6

Chapter 1

GeneralInvestigation in routine assessment: An investigation that is made periodically once inseveral days through once a week and is composed mainly of simple inspections
including visual observation.
Investigation in regular assessment: An investigation made periodically once in several
years to identify the conditions of the structure or member that cannot be confirmed byinvestigations in routine assessment.
Investigation in extraordinary assessment: An investigation made temporarily to identify
the conditions of the damage to the structure caused by accidental loads during a greatearthquake or typhoon or, by artificial accidental loads at the time of a crash of vehicles or
ships or fire.
Investigation in emergency assessment: An investigation made urgently in the event of an
accident or damage greatly affecting a structure to verify whether or not similar structures
or structures under similar conditions are subject to a similar accident or damage.
Standard investigation: A specified package of investigation items in the maintenanceplan.
Detailed investigation: Any investigation to collect detailed data not obtained in standard
investigation.
Monitoring: Identifying the conditions of the structure or member using the sensors
installed in the structure or member.
Repair: A measure to remove the hazards for third party or restore or improve esthetic
appearance and landscape or durability. Included are the measures to restore mechanicalperformance in terms of safety and serviceability to the level available to the structure at
the time of construction.
Strengthening: A measure to raise the mechanical performance in terms of safety andserviceability above the level available to the structure at the time of construction.
Seismic retrofitting: A kind of retrofitting conducted to achieve the seismic performancein accordance with the latest criteria in cases where the seismic performance of an
existing structure becomes no longer conforming to new criteria because of the revisionof design standards.

[Commentary] Preventive maintenance: The performance of structures generally starts
deteriorating as the degradation of members becomes outstanding. Preventive maintenance is amethod of maintaining structures by taking appropriate measures to prevent outstanding
deterioration from occurring. Preventive maintenance is the most desirable maintenance method
because it minimizes the deterioration of the structure or member. Detailed investigations andmonitoring are required even before the deterioration becomes outstanding. Predicting deterioration
with relatively high precision is also required. Preventive maintenance is effective especially for
maintaining important structures and structures with a long planned service period.
Remedial maintenance: This maintenance method is composed of relatively simple
investigations mainly based on visual observations before the occurrence of outstanding
deterioration, and implementation of appropriate measures to control deterioration after the7

Standard Specifications for Concrete Structures-2007, Maintenancedeterioration is determined outstanding. At present, this category of maintenance is carried out innumerous cases.
Observational maintenance: In cases where a structure has been in service with no special
repair or strengthening or where a member that is relatively easy to replace is replaced at thediscretion of the persons who perform maintenance work, neither detailed investigations are madenor remedial measures are implemented and the structure or member is maintained through simple
visual observations. Observational maintenance is applied to structures or members for which direct
investigations are not or cannot be implemented but which are checked for an anomaly indirectly byinspecting the deformations of soils or the structures in the vicinity. Examples include undergroundstructures and foundation structures for which direct investigations are difficult.
Planned service period and design service period: The planned service period is determined aswell as the design service period at the time of design. In design, the design service period is
generally assumed to be longer than the planned service period (Fig. C1.3.1). Maintenance may beplanned on the assumption of the design service period shorter than the planned service period andof repair and strengthening while the structure is in service. The maintenance manager sometimes
revises the planned service period based on the social or economic factors such as future changes intype and level of performance requirements for the structure. The planned service period may also
be prolonged owing to the revision of maintenance plans with social changes while the structure isin service. Then, the structure will be maintained by repair or strengthening to achieve theperformance requirements throughout the revised planned service period.

Planned service period
As of design or
maintenance planning

Design service period

Service period
elapsedRemaining planned service life

Remaining design service life

commencementof service

investigation

Fig. C1.3.1 Image of useful life and service period(in the case of design service period longer than planned service period)

Durability, Safety, Serviceability and Hazards for third party: Refer to Chapter 2 Performance
Requirements.
Investigation in assessment: The objective of investigation is to identify the performance of thestructure and collect data required for maintenance. In this Specification, investigation is defined toinclude document search, inspection and testing. Assessment refers to any action not only forinvestigation, or checking for an anomaly in the structure, but also for prediction of deterioration
progress based on investigation results, performance evaluation of the structure and judgment of8

Chapter 1

Generalnecessity for remedial measures.
Standard investigation and Detailed investigation: The methods should be specified inmaintenance plans for making investigation to obtain specific data on the conditions of the structure
or member during the investigations in such as routine, regular and extraordinary assessments. In
this Specification, the investigation specified in the maintenance plans is defined as the standard
investigation and the investigation for obtaining more detailed data not collected in standard
investigation is defined as the detailed investigation.
Monitoring: The methods for continuously identifying the progress of deterioration of concrete
structures or members include identifying the progress of deterioration by detailed investigations
conducted at relatively short intervals before outstanding deterioration occurs, identifying the
progress of deterioration by collecting at designated times detailed data including the data obtainedin fracture tests using specimens exposed around the structure and grasping the conditions of thestructure or member real-time using sensors installed in the structure or member. In thisSpecification, the method of grasping the conditions of the structure or member using sensors isdefined as monitoring.
Repair and Strengthening: Restoring the mechanical performance of the structure or member
reduced by deterioration or damage to or above the level available at the time of construction isdefined as repair or strengthening respectively. Remedial measures taken when the performancerequirements for durability or the hazards for third party are not met are all defined as repair either
for restoring performance to or above the level available at the time of construction (Fig. C1.3.2).
Repair work is thus carried out generally in cases where mechanical performance higher than at thetime of design or construction is required. Repair includes seismic retrofitting for structures
determined non-conforming to new criteria because of revision of design standards.

Mechanical performancein terms of safety andserviceability[Strengthening]
Initial performance[Repair][Repair]

Required performancecommencementof service

investigation remedial measure

Fig. C1.3.2 Definitions of repair and strengthening

9tStandard Specifications for Concrete Structures-2007, Maintenance
Performance in terms ofdurability and hazards
for third party[Strengthening]
Initial performance[Repair][Repair]

Required performancecommencementof service

investigation remedial measuret

Fig. C1.3.2 Definitions of repair and strengthening

Seismic retrofitting: Seismic retrofitting is a type of repair to help the seismic performance of astructure meet new design standards in cases where the present seismic performance of the structure
becomes no longer conforming to new criteria. Seismic retrofitting has been defined separatelyfrom other types of repair because it is higher required in Japan, one of the earthquake-prone
countries in the world.

10Chapter 2

Performance requirements

CHAPTER 2 PERFORMANCE REQUIREMENTS

2.1 Principle
In the maintenance of a structure, the performance requirements for the structure shallbe identified.

[Commentary] In cases where the performance requirements for the structure are not defined
explicitly, only inconsistent corrective maintenance is conducted. Then, no structures can be
maintained effectively. Identifying the performance requirements of the structure is essential tomaintenance. In maintenance, the performance requirements for the structure are checked
throughout its planned service period to confirm that the requirements are maintained within theallowable range. When the performance requirements are evaluated and determined to be below thedesignated level, necessary remedial measures are taken.
The performance requirements are all types of performance required to achieve the purpose
for which the structure is used. The performance requirements are generally designated in design. In
performance based design, performance requirements are explicitly defined such as safety,
serviceability, restorability and other parameters as designated in the "Design" volume of theStandard Specifications. For existing structure, however, performance requirements for the structure
in design may be unknown. For maintaining structures, therefore, not only the performancerequirements considered in design but also the performance requirements that are not considered indesign but are important from the maintenance viewpoint should be identified.

2.2 General(1) The performance requirements in maintenance for an ordinary structure covers aresafety, serviceability, hazards for third party, esthetic appearance and landscape, anddurability .
(2) Safety is related to safety against sectional fracture and seismic load, safety against
fatigue fracture and safety with respect to the stability of structures.
(3) Serviceability is related to the performance that enables the user of the structure to use
the structure comfortably and the functions required of the structure.
(4) Hazards for third party are related to public damage to third parties caused bystructures such as the falling of cover concrete lumps and the noise that is caused while
the structure is in service.
(5) Esthetic appearance and landscape are related to the harmonization with thesurrounding environment including the effects of stain of rust and cracks due todeterioration.
(6) Durability is related to the durability in terms of safety, serviceability, the hazards forthird party, and esthetic appearance and landscape.

11

Standard Specifications for Concrete Structures-2007, “Maintenance”［Commentary］(1) There are wide varieties of structures. The functions required of respective
structures also vary greatly. The maintenance of structures is a process in a series from construction,
service (maintenance), demolishing and removal or reuse. Maintenance is the act to secure theperformance required while the structure is in service based on a comprehensive concept. In thisSpecification, the basic performance requirements for ordinary structures have been classified into
safety, serviceability, hazards for third party, esthetic appearance and landscape or durability (Fig.
C2.2.1). The "Design" volume of the Standard Specifications lists safety, serviceability, restorability
and other performance requirements as the performance requirements for structures. This
Specification basically covers the same performance requirements but additionally describes thehazards for third party, esthetic appearance and landscape, and durability because structures ormembers are given different performance priorities in design and in maintenance. Details areprovided below.
Restorability is defined in the "Design" volume of the Standard Specifications as theperformance for restoring the functions of the structure in the designated period of time to make thecontinuous use of the structure possible. The restorability of the structure after it is put into service
can, however, be evaluated by checking safety or serviceability. This Specification therefore
provides no description about restorability as a performance requirement.
In relation to other performance requirements, resources should be used effectively andcarbon dioxide emissions, energy consumption and environmental impact should be reduced in theprocess from the demolishing to reuse of structures. This should be fully considered during
maintenance. An increasing number of researches have recently been conducted and discussions
made concerning the basic concepts and methods related to this issue. This Specification should
specifically present evaluation technologies once they have been established. Article concerning
this issue can be referred to the Recommendations for Environmental Performance Verification forConcrete Structures.

Safety against sectional fracture
SafetySafety against fatigue fracture andsafety with respect to stability

Required
performances

Amenity (e.g. driver comfort)
Serviceability
Performance determined by
the function of the structure(e.g. water-tightness)

Hazards for third party
Aesthetic appearance
and landscape
Durability*Durability is assessed based on the above-required
performances at the end of planned service period thatare evaluated from the results of prediction ofdeterioration progress.

Fig. C2.2.1 Classifications of performance requirements(2) The performance requirements for safety have been designated like thedesign-performance requirements in the "Design" volume of the Standard Specifications. The safety
12Chapter 2

Performance requirements

against sectional fracture should be evaluated for all the loads and environmental actions that arelikely to be applied while the structure is in service, which include accidental loads such as
earthquakes and impact loads due to the collision with vehicles or ships.
Also included in the performance requirements for safety are the safety against fatigue
fracture and the safety with respect to the stability of the structure (performance to maintain thestability of the structure against slides or collapses mechanism), and the functional safety to ensure
the travel of vehicles and trains.
(3) The performance requirements for serviceability have also been designated like thedesign-performance requirements in the "Design" volume of the Standard Specifications. Included
are the performances for amenity while using the structure and the performance for the functions
required of the structure.
The "Design" volume of the Standard Specifications lists the comfort of vehicle occupants
and pedestrians, facades, and noise and vibration levels as amenity factors. In maintenance, facades
are related to aesthetic appearance and landscape, and noise and vibration levels are related to thehazards for third party. The comfort of vehicle occupants and pedestrians should therefore be
evaluated as the performance for serviceability.
As the performance for the functions required of the structure, capacities to intercept or
permeate materials such as the water-tightness, permeability, sound proofing, moisture proofing,and protection from cold or heat should be evaluated in maintenance. Many of the performancefactors are subject to time-based changes from the initial level. The performance for the functions
required of the structure generally varies with the changes of social conditions. For example,
highway bridges need to have sufficient lanes to carry actual traffic volumes.
(4) The hazards for third party are specified as one of the safety performances in the "Design"
volume of the Standard Specifications such as public damage of the structure to third parties due tothe falling of cover concrete lumps. The hazards for third party however are not related to the load
bearing capacity of the main body of the structure and require a different performance verification
process from that for safety. Addition to that, those are one of the important performancerequirements in maintenance. The hazards for third party are therefore treated separate from safety
in this Specification. Noise affecting the surrounding area while the structure is in service isincluded in the hazards for third party.
(5) The "Design" volume of the Standard Specifications stipulates that structures should bedesigned so as to be provided with aesthetic appearance and landscape that are in good harmony
with the surrounding environment. The effects of rust and cracks due to the smudging or
deterioration of the structure on aesthetic appearance and landscape may sometimes be important indetermining maintenance measures. Aesthetic appearance and landscape have therefore been
specified as a performance requirement.
(6) This Specification has designated durability as a performance indicator tocomprehensively determine whether safety, serviceability, hazards for third party, and aesthetic
appearance and landscape can be maintained within the allowable range over the planned service
period as the "Design" volume of the Standard Specifications. While the structure is in service, theperformance requirements for safety, serviceability, hazards for third party, and aesthetic appearance
and landscape should be achieved from a maintenance viewpoint. If time-based change in these
performance factors can be verified with sufficient accuracy, there is no need to consider durability
as a performance indicator. The techniques to predict deterioration or evaluate performance haverecently been advancing remarkably. However, those techniques are not practically mature atpresent. In this Specification, therefore, durability, which has been generally used in and out of13

Standard Specifications for Concrete Structures-2007, “Maintenance”

Japan, has been designated as a parameter that comprehensively indicates these performance factors
during the planned service period. Verifying durability is considered to serve as an alternative toverifying whether performance requirements are met or not in terms of safety, serviceability,
hazards for third party, and aesthetic appearance and landscape during the planned service period of
the structure.
Considering durability as performance requirements is related to how the planned service
period should be specified and what level of performance requirements should be achieved in termsof safety, serviceability, hazards for third party, and aesthetic appearance and landscape during theplanned service period of the structure. In this Specification, therefore, the durability of thestructure is assumed to be guaranteed during the planned service period of the structure if it can be
confirmed that the performance requirements for the structure are achieved in terms of safety,
serviceability, hazards for third party, and aesthetic appearance and landscape both at the time ofinvestigation and at the end of the planned service period of the structure. Durability should be
examined properly not only by quantitative methods but also semi-quantitative methods (e.g.
grading).

14

Chapter3

Methods for Maintenance

CHAPTER 3 METHODS FOR MAINTENANCE

3.1 Principle
The maintenance manager for structures shall develop plans for maintaining theperformance of structures within the allowable range during their planned service period.
The manager also shall appropriately assess structures, take remedial measures based on
the results of assessments and record the results of assessments and remedial measures.

[Commentary] Collectively referred to as the maintenance of structures is the action formaintaining the performance of a structure within the allowable range during its planned service
period. The maintenance of structures is composed of assessments consisting of investigations,estimations of deterioration mechanisms, predictions of deterioration, performance evaluation of
structures and judgment of necessity for remedial measures; remedial measures taken as required
based on the results of assessments; and recording of the results of assessments and remedial
measures, as shown in Fig. C3.1.1. In order to carry out all the work properly, the maintenanceauthority for structures should first develop maintenance plans and maintain structures inaccordance with 1.2 “Principles of Maintenance. ”
Group ofstructures

Structure
Maintenance plan
for a group of
structures

Maintenance planfor structure

Records
Records
Records
Records

Investigation
Identification of deterioration
mechanism and predictionof deterioration progress
Performance
evaluation
No remedial
measures are
required

Determination of maintenance plan

Assessment

Recording

Are remedial
measures required?
Remedial measures
are required

Remedial measures

Review of maintenance plan

Fig. C3.1.1 Procedure for maintaining a structure
For the maintenance of structures, methods have been studied for developing structure
maintenance plans more efficiently while optimizing the budget by regarding multiple social
infrastructure systems (a group of structures) including the particular structure as an asset and15

Standard Specifications for Concrete Structures-2007, Maintenancebuilding an asset management system for the group of structures. In these methods, maintenanceplans are first developed for the group of structures, and then for individual structures constituting
the group, and the plans are implemented. No satisfying maintenance methods have, however, been
established for groups of structures. No maintenance for groups of structures is therefore describedin this Specification.
3.2 Maintenance Plans
3.2.1 General(1) Maintenance plans should select the maintenance categories; and describe thedeterioration mechanisms expected during the planned service period; methods ofassessments composed of investigation of structures, regions and members, predictionsof deterioration, performance evaluation for structures and judgment of necessity for
remedial measures; and remedial measures fit for the expected deterioration and methods
for selecting remedial measures.
(2) Maintenance plans shall be developed before the performance of maintenancework, modified as required based on the results of initial assessments that are madefollowing the development of the plan, and then finalized. Maintenance plans should be
reviewed as required during the maintenance.
(3) Once maintenance plans have been developed, manuals should be prepared that
present maintenance procedures based on the maintenance plans.

[Commentary] (1) Maintenance plans comprehensively describe the timing, frequency, methods
and systems (organizations, human resources, budgets, etc.) of assessments, remedial measures andrecording regarding the condition of the structure.
Fig. C3.2.1 outlines a procedure for developing maintenance plans. For developing
maintenance plans for a structure, the period should first be determined for maintaining thestructure based on the planned service period of the structure assumed in the design phase. In cases
where no planned service period has been specified in the design phase, the design service period
may be regarded as the planned service period for developing maintenance plans. The design
service period is sometimes determined for a certain structure, region or member based on theassumption of renovating the structure, region or member during its planned service period. Then,the renovation plan should be incorporated into the maintenance plan. When developing amaintenance plan for a structure in service, the remaining planned service period, which is obtainedby subtracting the service period elapsed from the planned service period, should be specified as theperiod of maintenance.
Importance, planned service period and environmental conditions vary from structure to
structure. Maintaining structures placed under different conditions in one and the same manner is
not rational. It is therefore important to classify maintenance optimally according to the conditionsof structures. For specific descriptions of maintenance types, refer to 3.2.2 “Categories and Detailsof Maintenance.”
The phenomena that deteriorate structures such as carbonation, chloride attack, frost attack andalkali-silica reaction are referred to as deterioration mechanisms. Structures are deteriorated byeither external or internal factors. External factors include environmental, meteorological andexternal force conditions at the location of the structure. Internal factors are related to design
parameters such as the dimensions of regions and members, concrete cover, arrangement of steel,16

Chapter3

Methods for Maintenancedesign strength, mix proportions and material quality, or to construction parameters such as thecondition of fresh concrete, method of placement and method of curing. Deterioration mechanisms
vary for structures under the same environmental conditions if the structures are affected bydifferent internal factors. The above points should be taken into consideration when developing
maintenance plans to properly estimate deterioration mechanisms that are expected to be found in
structures.

ImportanceConditions of structure
Hazards for third party Planned service period
Environmental conditions

OthersDeveloping
maintenance plans
Identifying the categoryof maintenance

Estimating deterioration
mechanism

Maintenance plans-Initial assesment plan
-System for performing maintenance work
-Category of maintenance-Period of maintenance-Assesment plans following the initial assessment(inspection methods, etc.)-Structure renovation plan

Review is required

Initial assessment
Iincludeing
investigation)(including investigation)
No review is required

Finalizing maintenance plans
Periodic (routine/regular) assessments(including investigations)Fig. C3.2.1 Procedure for developing maintenance plans
As described above, maintenance plans are developed after the period and category of
maintenance are specified and deterioration mechanism is estimated. Maintenance plans define
specific components of assessment such as the details (e.g. method and frequency) of inspections
conducted in inspection methods for estimating deterioration, methods for evaluating theperformance of the structure, and criteria for determining the need of remedial measures according
to the objective of assessment; and present the planned method, scale, time and sequence of
implementation of remedial measures fit for the expected deterioration. When developing
maintenance plans in the planning and design phases of a new structure, cooperating the design andthe development of maintenance plans for the structure may be effective. For example, inspection
passages or ladders may be installed to facilitate maintenance work. Studying the cost effectivenessof investigations or remedial measures enables the selection of a more efficient maintenancescenario at optimal life cycle cost. It is also important to develop maintenance plans while
anticipating natural disasters such as earthquakes and typhoons and accidents like fire and crashesof ships.
(2) For a new structure, maintenance plan development should be started in the planning and17

Standard Specifications for Concrete Structures-2007, Maintenancedesign phase of the structure. Data should be collected at the initial assessment upon the completionof the construction to verify the need for reviewing the original maintenance plan. Modifications
should be made to the maintenance plan as required, and then the maintenance plan should be
finalized. When maintaining an existing structure in service in accordance with this Specification,
initial assessment should be specified in the maintenance plan, and the adequacy of the maintenanceplan should be examined based on the information on the structure obtained in investigations in theinitial assessment before finalizing the maintenance plan. After large-scale remedial measures aretaken or if the results of prediction of deterioration progress based on the investigation results aredifferent from the initial prediction of deterioration progress, the maintenance plan that is being
implemented should be reviewed as required. Structures are in service over a long period of time.
The required performances for structures are highly likely to vary during the period because ofchanges of public life-style or needs, changes in physical distribution or social changes. Reviewing
maintenance plans may become necessary to reflect such changes.
(3) Structures in service are not always maintained by the responsible engineer who developed
the maintenance plan. Investigation in the routine assessment is not always conducted by aprofessional engineer. Once the maintenance plan has been developed, therefore, manuals should be
prepared and training programs should be implemented for those who are engaged in maintenancework as required so as to carry out maintenance as scheduled.
3.2.2 Categories and details of maintenance(1) The category of maintenance shall be selected based on the importance, hazards
for third party, planned service period and environmental conditions of the structure or
member.
(2) The category of maintenance shall be selected from among the following three.
A: Preventive maintenance
B: Corrective maintenance
C: Observational maintenance[Commentary] Structures should be maintained properly after the category of maintenance isselected considering their importance, hazards for third party, planned service period andenvironmental conditions. The importance of maintenance varies greatly according to the social andeconomic importance, hazards for third party and planned service period of the structure or member.
The ease of the components of maintenance such as the prediction of deterioration progress, repair
and strengthening also varies from structure to structure. Applying any uniform concept ofmaintenance is therefore not effective. The category of maintenance should be defined that isproperly fit for the conditions of the structure or member.
This Specification adopts three types of maintenance: A Preventive maintenance, B Corrective
maintenance and C Observational maintenance. A Preventive maintenance and B Corrective
maintenance should be treated as standard types of maintenance.
The characteristics of structures that require the respective types of maintenance are described
below.
A: Preventive maintenance(i) No deterioration should occur because outstanding deterioration makes maintenancedifficult.
(ii) Deterioration of concrete surface causes failure.
18Chapter3

Methods for Maintenance(iii) Safety for third parties is extremely important.
(iv) The design service period is long.
The structures in this category are generally very important, so monitoring is effective innumerous cases. Monitoring means continuous measurement of stress, deformation, corrosion andtemperature of members using sensors installed on the surface of or inside the structure.
B: Corrective maintenance(i) Remedial measures can be taken easily even after the occurrence of outstanding
deterioration.
(ii) Outstanding deterioration causes no trouble.
C: Observational maintenance(i) The structure is used as long as possible with no design service period being specified.
(ii) Evaluation and judgment are conducted by investigating structures indirectly (surveying,soil settlement, leakage, etc.) due to the extreme difficulties in investigating structures directly.
3.3 Assessments
3.3.1 General(1) In the assessment of structures, investigations shall be carried out following themaintenance plan. Based on the results of the investigation, confirmation of deterioration
based on the results of investigations, identification of deterioration mechanisms,
prediction of deterioration progress, evaluation of performance of the structure andjudgment of necessity for remedial measures shall be done appropriately.
(2) Assessments include initial, periodic and extraordinary assessments. Professional
engineers or engineers at a higher position with knowledge and experience shall conduct
assessments based on the investigation plan defined during the development of themaintenance plan.

[Commentary] (1) Assessment collectively means a series of actions during maintenance forfinding defects in the structure or member. The series is composed of investigation, evaluation of
performance of the structure and the judgment of necessity for remedial measures. For properly
maintaining structures based on plans, the conditions of the structure should first be identified byinvestigations, the deterioration mechanisms that occur or are likely to occur in the structure shouldbe estimated, and deterioration should be predicted. Based on the results of investigations anddeterioration predictions, whether the required performances for the structure are expected to beachieved or not during its planned service period in terms of safety, serviceability, hazards for third
party, and aesthetic appearance and landscape should be determined; and whether the remedial
measures are required or not should be determined. The prediction of deterioration progress means
predicting the future deterioration of the structure, region or member caused by the deterioration
mechanism estimated based on the results of investigations. Examples are predictions of the
progress of corrosion of steel in concrete due to carbonation or chloride attack, or concrete surface
deterioration due to frost attack.
This Specification defines deterioration as the defect that progresses with time and distinguishdeterioration from the initial defects such as crack, honeycombing, formation of cold joints andsand streaking that is generated during construction or the damage that occurs in a short period oftime but remains unchanged subsequently such as the crack and peeling due to earthquakes or19

Standard Specifications for Concrete Structures-2007, Maintenancecrashes. This Specification describes the methods of maintenance mainly in the case of performancedegradation of structures due to deterioration. In cases where part of the initial defects are left
unattended in the structure or where damage is caused by earthquakes or crashes, the effects of thedefect should be evaluated by assessment.
In cases where the design loads are changed or the required performances of the structure arechanged to comply with new seismic performance criteria during its service period, it becomes
necessary to make assessments to evaluate the load bearing capacity or seismic performance of thestructure, to review the maintenance plan to maintain the structure in accordance with the newcriteria and to take remedial measures including strengthening as required.
(2) The details of investigations required and the levels of prediction of deterioration progress,
evaluation of performance of the structure and judgment of necessity for remedial measures vary
greatly according to the objective of assessment. Positioning assessments similarly and making
assessments at one and the same technical level are not effective. This Specification therefore
classifies assessments as the initial assessments conducted initially in maintenance, periodic
assessments conducted routinely or periodically during the period of maintenance, or extraordinary
assessments conducted in cases where accidental loads act on the structure.
Fig. C3.3.1 shows flowcharts for maintenance and the positioning of assessments. For detailsof the respective actions in a series of assessment from investigation to the judgment of necessity
for remedial measures, refer to the chapters indicated in the figure.
Assessments are very important actions that determine the future of the structure that is being
maintained. Professional engineers or engineers at higher positions with adequate knowledge andexperience should conduct assessments based on the assessment plan that the maintenance authority
defined during the development of the maintenance plan.
Responsible engineers should make the assessments that involve higher level decision-making
concerning the future and cost performance of the whole group of structures. Other engineers thanprofessional engineers may be assigned to daily assessments that involve simple decision-making
based on the available manuals such as the determination of whether the structure has defect or notthat the considerations in inspections are made available to the engineers.
3.3.2 Initial assessments(1) The initial assessment shall be conducted when identifying the initial conditions of
the structure or when reviewing the maintenance plan is required after a large-scale repair
or strengthening.
(2) In the initial assessment, it is necessary to estimate the deterioration mechanism,
evaluate the performance of the structure, judge the need of remedial measures, and verify
the validity of the maintenance plan based on the results of investigation.
(3) In cases where emergency or other measures are found necessary in the initialassessment, appropriate actions shall be taken.

[Commentary] (1) The initial here means the initial stage of maintenance conducted in accordancewith this Specification. The initial assessment means the assessment conducted for a new structure
for the first time since the commencement of service. The initial assessment also means the first20Chapter3

Methods for Maintenance

Maintenance plan (3.2)

Initial assessment (3.3.2)
Investigations in initial assessesmet (4.2)
Standard investigation

Emergency
measuresIs detailed invesDetailed
tigation required? Required investigation
Not required
Identification of deterioration mechanism andprediction of deterioration progress (Chapter 5)

Review of maintenance plan (as required) (3.2) (7.3.4)

Evaluation of performance (6.2.2)(6.2.3)Are remedial measures required?
Required

Remedial
measures

Review and finalization of maintenance plan (6.2.4)

Assessments (Chapters 3, 4, 5 and 6)

If the deterioration mechanism is known, referto the respective chapters below.
Chapter 9 Maintenance of Structures Subject
to Carbonation
Chapter 10 Maintenance of Structures
Subject to Chloride Attack
Chapter 11 Maintenance of Structures
Subject to Frost attack
Chapter 12 Maintenance of Structures
Subject to Chemical Attack
Chapter 13 Maintenance of Structures
Subject to Alkali-silica Reaction
Chapter 14 Maintenance of Reinforced
Concrete Decks Subject to Fatigue
Chapter 15 Maintenance of Reinforced
Concrete Beams Subject to Fatigue
Chapter 16 Maintenance of Structures
Subject to Abration

Not required
Recording (Chapter 8)
Periodic assessment (3.3.3)

Extraordinary assessment (3.3.4)<<Conducted routinely>>

Investigation in extraordinary
assessment (4.5)

Investigation in routine assessment (4.3)
Standard investigation(6.3.2)Is detailed investigation required?
Not requiredStandard investigation

Emergency
measures(4.5)
Is detailed invesDetailed
tigation required?
Required investigation
Not required

Required

Evaluation of performance (6.4.2)

Recording (Chapter 8)<<Conducted at intervals of one to several years>>Investigation in regular assessment (4.4)
Standard investigation

Emergency
measures

Emergency
measures

(4.3)
(4.4)
Is detailed invesDetailed
tigation required?
Required investigation
Not required
Identification of deterioration mechanism andprediction of deterioration progress (Chapter 5)

Remedial
measures

Not required
Recording (Chapter 8)

Investigation in emergency
assessment (4.6)
Emergency
Investigation
measures(6.4.4)
Are remedial measures required?
Required
Not required
Recording (Chapter 8)

Remedial measures (Chapter 7)
Selection of remedial measures (7.2)
Intensified investigation

RepairRemedial
measures

Evaluation of performance (6.4.4)

Evaluation of performance (6.3.3)(6.3.4)
Are remedial measures required?
Required(6.4.3)Are remedial measures required?
Required
Not required
Recording (Chapter 8)Strengthening

Dismantling/removal
Functional improvement

Design and construction (7.3)
Recording (Chapter 8)

21

Restriction in service

Remedial
measuresStandard Specifications for Concrete Structures-2007, MaintenanceFig. C3.3.1 Flowcharts for maintenance and positioning of assessments
assessment of an existing structure that has not been maintained and for which a new maintenanceplan has been developed. The initial assessment also means the assessment conducted for the firsttime since a review of the maintenance plan was considered necessary because of a large-scale
repair or strengthening of an existing structure or for other reasons.
(2) and (3) The initial assessment is conducted to grasp the initial conditions of the structure interms of various performance parameters to enable the maintenance of the structure in accordancewith a designated plan. The initial assessment has three major objectives.
(i) To verify the validity of the maintenance plan developed before the initial assessment and tocollect data for finalizing the maintenance plan(ii) To collect basic data (initial values) for starting the maintenance of the structure(iii) To discover potential problem areas in future maintenance such as the initial defects,
damage or deterioration to take remedial measures in the initial stages
The major objectives of the investigation in the initial assessment are to determine whether a
new structure has been constructed properly or not, or whether a large-scale repair or strengthening
was carried out properly or not for an existing structure, and to collect data required for starting themaintenance of the structure. The investigation is important to the confirmation of initial defects(e.g. cracks, cold joints and honeycombs) and damage, and to the identification of the initial data forpredicting deterioration. Determining the need of emergency measures is also desirable in theinvestigation. For details of investigations in the initial assessment, refer to 4.2 “Investigations in
Initial Assessment.”
In order to properly maintain a structure based on a predetermined plan, predicting how thestructure, region or member will change in the planned service period is important. In the initialassessment, therefore, the deterioration mechanism expected to occur in the structure should be
estimated based on the results of the investigation, and future deterioration should be predicted forthe deterioration mechanism using an appropriate model. For the specific methods for estimating
deterioration mechanisms and predicting deterioration, refer to Chapter 5 “Identification ofdeterioration mechanisms and Prediction of Deterioration Progress.”
If no initial defects, such as deterioration, damage and initial defect, are found in the structure,region or member in the investigation, it is assumed that the required performances at initial stageof meintanance are achieved. If any defects or damage is outstanding, appropriate measures should
be taken. The performance of the structure during or at the end of its planned service period shouldbe evaluated based on the results of deterioration prediction described earlier. The results ofperformance evaluation should be considered when examining the validity of the maintenance plandeveloped. The maintenance plan may be reviewed if a review is found necessary as a result of theexamination of the validity of the plan. In cases where serious deterioration is found outstanding in
the initial assessment and the degradation of performance of the structure is highly likely,
appropriate remedial measures should be taken and the investigation should be conducted again. For
details of the evaluation of the performance of the structure and judgment of necessity for remedial
measures based on the results of the investigation, refer to 6.2 “Evaluation and Judgment in theInitial Assessment.”
Professional engineers with adequate knowledge about the design, construction and22

Chapter3

Methods for Maintenancemaintenance of the concrete structure or engineers with deeper knowledge should conduct the initialassessment.
3.3.3 Periodic assessments(1) The periodic assessment shall be conducted to evaluate the performance of astructure in service and to judge the need of remedial measures.
(2) The periodic assessment shall consist of routine assessment, in which structures
are investigated by routine patrols, and of regular assessment, in which small regions ofstructures that can hardly been identified by routine patrol are investigated in detail.
(3) In the periodic assessment, whether the initial defects, damage or deterioration isfound or not should be determined through investigations. Based on the results of theinvestigations, the deterioration mechanism should be estimated, deterioration progressshould be predicted, the performance of the structure shall be evaluated and the need of
remedial measures shall be judged.

[Commentary] (1) Periodically assessing a structure in service to identify the changes of itscondition may enable the early detection of defect of the structure and the control of performancedegradation. Making preparations for repair or other actions in accordance with a designated planalso becomes possible and an efficient and effective maintenance plan can be implemented. Thus,
periodic assessments are the most basic and important action in maintenance.
(2) The performance of the structure is evaluated either directly or indirectly and the need of
remedial measures is judged as required, based on the results of investigations in routine assessment
conducted at intervals of approximately several days to one month and of investigations in regularassessment conducted at a relatively long intervals, e.g. in several years.
The roles of investigations in the periodic and regular assessment differ to each other. In theinvestigation in the routine assessment, qualitative identification of the defect of the structure isimportant. Accurate identification of defect is required. In the investigation in the regularassessment, quantitative identification of the defect of the structure is important. For structures towhich maintenance category C is applied, it is sometimes difficult to investigate them directly, as inunderground structures. Such structures may be investigated indirectly considering the conditions of
the structures in the vicinity as required.
For details of these investigations, refer to 4.3 “Investigations in Routine Assessment” and 4.4“Investigations in Regular Assessment,” respectively.
(3) Periodic assessments are conducted periodically in maintenance, so the maintenancemanager should prepare appropriate assessment manuals when developing the maintenance plan. If
no deterioration, damage or initial defects are found in the structure, region or member in the
periodic assessment, the structure is assumed to meet the designated required performances at the
point of assessment. If the structure is found to maintain its required performances at the end of theplanned service period by predicting deterioration progress based on the results of investigations,
there is no need to revise the maintenance plan and the structure may be maintained easily. In reality,
however, predicting the future of a structure based on the limited investigation results is not easy.
Evaluating the performance of the structure or predicting deterioration based only on theinvestigation results is therefore difficult. In cases without any defect, the structure is assumed to besound at the time of investigation. In cases where deterioration, damage or initial defects are23

Standard Specifications for Concrete Structures-2007, Maintenancedetected including the delamination of surface concrete leading to the spalling of concrete covering
affecting third parties, emergency measures should be taken immediately.
In cases where defect is found in the structure in standard investigation in routine or regularassessment, detailed examination should be made to identify the defect as deterioration, damage or
initial defects. In the case of deterioration, the deterioration mechanism should be identified anddeterioration progress should be predicted based on the investigation results. For details of theidentification of deterioration mechanisms and the prediction of deterioration progress, refer to
Chapter 5 “Identification of deterioration mechanism and Prediction of Deterioration Progress.”
After the prediction of deterioration progress, the performance of the structure should be evaluatedand the need of remedial measures should be determined based on the results of prediction. The
need should be determined in principle in accordance with the criteria pre-designated in themaintenance plan. The criteria should be defined by the maintenance manager for the structure or a
responsible engineer who can serve as a representative of their view by comprehensively
considering the results of evaluation of the performance of the structure at the time of investigationor during the planned service period, the importance of the structure, and the category of
maintenance. For details of performance evaluation and the judgment of necessity for remedial
measures, refer to 6.3 “Evaluation of Performance and Judgment of the Need of Remedial Measures
in Periodic Assessments.”
Periodic assessments should be conducted by professional engineers with adequate knowledge
about the design, construction and maintenance of concrete structures. Standard investigations inroutine assessment may, however, be conducted by engineers other than professional engineers aslong as adequate manuals and the guidance of professional engineers are available.
3.3.4 Extraordinary assessments(1) The extraordinary assessment shall be conducted in cases where an assessment
is urgently required such as in the case where accidental loads act on the structure.
(2) The extraordinary assessment shall be conducted aiming at identifying the degreeof defect of the structure due to damage or deterioration, evaluate the performance of thestructure and determine the need of remedial measures through investigations.
(3) In cases where any damage to people due to the collapse of the structure orserious social and economic effects are predicted in the extraordinary assessment,
appropriate measures should be taken as soon as possible.

[Commentary] (1) Extraordinary assessments are conducted under the following conditions incases where the structure is subjected to great seismic forces, or to external forces of other natural
disaster such as typhoons, fire or accidents.
1. The structure or the member has been damaged and its performance has explicitly been
deteriorated.
2. Verifications are made for local problems in performance in terms of safety, serviceability,
hazards for third party, and aesthetic appearance and landscape of the structure although the disasteris not so serious.
3. Structures similar to the one that suffered damage are checked for a possibility of similar
24

Chapter3

Methods for Maintenancedeterioration or damage, and preventive measures are planned or the maintenance plan is reviewed.
The cases that require extraordinary assessments are described below.
Extraordinary assessments in the case of a natural disaster: The Specification for "Design"
stipulates that the seismic performance of a structure should be checked in the design phase in cases
where the structure is expected to be subjected to external forces due to an earthquake. Even the
structures designed in that way are likely to be damaged when subjected to large seismic forces. In
cases where the structure is subjected to an extremely large seismic forces, it may collapse. In theevent of an earthquake sufficiently large to affect the structure, extraordinary assessments should be
conducted to verify whether the structure, region or member has been damaged or not.
In the event of a typhoon, large wind loads or wave forces may cause damage to the structure.
In the event of the flushing of river water, collision of driftwood is likely to damage the structure or
scouring is likely to depress bridge piers. The rising of groundwater levels due to heavy rains maylead to the collapse of earth retaining walls. In the wake of a typhoon of a magnitude that is likely toaffect the structure, extraordinary assessments should be conducted to verify whether the structure,region or member has been damaged or not.
In the event of other natural disaster than earthquakes or typhoons, extraordinary assessments
are required based on the same idea as described above if the scale is large enough to affect thestructure.
Extraordinary assessments in the case of a fire: In cases where a structure, region or member is
exposed to considerable heat during a fire, concrete or reinforcement is likely to be changed its
properties. In the event of a fire near the structure, the regions and members subjected to the fire
and the surrounding areas should be given extraordinary assessment.
Extraordinary assessments in the case of crashes of vehicles or ships: In cases where a vehicle
or ship crashed into the structure, the position subjected to the crash or the region or member near
the position may be damaged. Extraordinary assessments are therefore required.
Extraordinary assessments with the revision of criteria: In cases where the design loads andseismic performance criteria are changed with the revision of relevant criteria during the service
period of a structure, whether the structure constructed in accordance with the older criteria meetsthe new performance criteria or not should be verified. Then, extraordinary assessments are
conducted.
Extraordinary assessments required urgently: In the event of an accident due to the defect of astructure such as the initial defects, damage or deterioration, accidents are likely to occur also inother structures that are similar to the structure subjected to the accident or in a similar condition. In
order to prevent similar accidents, therefore, all of these structures should also be given
extraordinary assessment. The structures that are constructed at the same time or in the same format
as those in which considerable defect has been detected in periodic assessments should also begiven extraordinary assessment to verify whether they are likely to be subjected to similar
deterioration or damage.
(2) Extraordinary assessments are conducted as the assessment of a structure, region ormember after a disaster or accident to provide data for identifying the condition or degree ofdamage and for evaluating the performance of the structure.
25

Standard Specifications for Concrete Structures-2007, Maintenance

Extraordinary assessments are urgently required in numerous cases. In cases where thestructure is subjected to a natural disaster or an accident, it is highly likely to collapse or fail, or see
its safety greatly deteriorated. Extraordinary assessments should be conducted as soon as possible
after such occurrences. In cases where the structure has collapsed or failed, the area around thestructure should be closed to unauthorized people or the use of the area should be restricted even if
the structure appears to be intact.
In cases where an accident occurs due to the defect of a structure, all the structures similar tothe one affected by the accident may be given extraordinary assessment. Then, assessment is madeurgently mainly to prevent similar accidents from occurring. In this Specification, such assessment
is referred to as emergency assessment separate from extraordinary assessment. For details ofinvestigations in extraordinary and emergency assessments, refer to 4.5 “Investigations in
Extraordinary Assessment” and 4.6 “Investigations in Emergency Assessment,” respectively. For
details of the evaluation of the performance of the structure and the judgment of necessity for
remedial measures based on the investigation results, refer to 6.4 “Evaluation of Performance andJudgment of the Need of Remedial Measure in Extraordinary Assessments.”
Extraordinary assessments should in principle be conducted by professional engineers withadequate knowledge about the design, construction and maintenance of concrete structures orengineers with deeper knowledge.
(3) A natural disaster or an accident is likely to cause the structure to collapse in the worst case.
Preventing secondary disasters is important such as the damage to people and serious social andeconomic effects causing the malfunction of lifeline systems. In cases where any potential damage
to people or property has been confirmed in extraordinary assessment such as the spalling of
concrete due to the delamination of surface concrete, measures should be taken immediately.
3.4 Remedial Measures
In cases where it was determined that remedial measures should be taken to control
the progress of deterioration or the degradation of performance of a structure, appropriate
remedial measures shall be taken so as to maintain the performance of the structure for adesignated period considering the importance of the structure, category of maintenance,
remaining planned service period, ease of maintenance, hazards for third party and cost
performance.

[Commentary] Remedial measures are classified into intensified investigation, repair,strengthening, functional improvement, restriction in service or dismantling/removal. Whether
taking remedial measures is beneficial or not should be determined comprehensively based on the
category of maintenance, remaining service life, ease of maintenance, hazards for third party andlife-cycle cost. Then, appropriate remedial measures should be selected.
For implementing remedial measures, examinations should be made to select a specific method,
and an optimal plan should be developed that specifies the budget, organization and humanresources in order to take effective measures. An appropriate method should be selected consideringvarious methods, timing of implementation, effects of construction work and life cycle cost. The
remedial measures should be properly recorded because the records will serve as the basis for areview of the maintenance plan and future maintenance of the structure.
For details of remedial measures, refer to Chapter 7 “Remedial measures.”26

Chapter3

Methods for Maintenance

3.5 Recording
In order to maintain structures properly, the results of investigation, prediction ofdeterioration progress, evaluation of performance of the structure and judgment ofnecessity for remedial measures in the process of assessment, and the details andmethods of remedial measures shall be recorded and stored.

[Commentary] Recording is an action essential to effective maintenance of structures. Records
serve not only as the data for the maintenance of the structure but also for reference when
maintaining similar structures. The results of investigation, identification of deterioration
mechanisms, prediction of deterioration progress, evaluation of performance of the structure andjudgment of necessity for remedial measures conducted in a series in assessment; and the details ofremedial measures should be recorded in such a format as facilitates reference and stored in while
the structure is in service. When a maintenance authority organises maintenance work
simultaneously maintains several structures, recording and storage should be done uniformly.
For details of recording, refer to Chapter 8 “Recording.”

27

Standard Specifications for Concrete Structures-2007, Maintenance

CHAPTER 4 INVESTIGATIONS IN ASSESSMENT

4.1

Principle(1) The investigations in assessment of a structure shall be conducted by a method fit
for the objective of the assessment.
(2) In the initial assessment at the start of maintenance, the investigation for identifying
the initial conditions of the structure from a viewpoint of maintenance shall be conducted.
(3) In the periodic assessment, the investigation in routine assessment and theinvestigation in regular assessment shall be conducted to identify changes in condition of
the structure.
(4) In cases where an extraordinary assessment is required, the investigation in
extraordinary assessment or the investigation in emergency assessment shall be
conducted according to the objective of the assessment.
(5) In the investigations in assessment, standard investigation should be conductedwith the frequency, for the contents and by the method specified in the maintenance plan.
In cases where identifying the detailed conditions of the structure is determined
necessary based on the results of standard investigations, detailed investigations shall be
conducted.
(6) In cases where emergency measures are determined necessary as a result ofinvestigations in assessment, emergency measures shall be taken immediately.

[Commentary] (1) Adequately maintaining concrete structures, either new or existing ones,
requires adequate assessments. Adequate assessments are based on the acquisition of data on thesafety, serviceability, hazards for third party, aesthetic appearance and landscape, and durability ofthe structure by investigations fit for the objective of the assessment.
Investigations in assessment are classified according to the objective and frequency ofassessment and the details of the investigations to be conducted. In this specification, investigationsin assessment are classified according to the objective of assessment into the investigations to be
conducted at the initial, periodic and extraordinary assessments (Fig. C4.1.1).
The investigations carried out in periodic assessment have been classified according to thefrequency into the investigation in routine assessment and the investigation in regular assessment.
The investigations carried out in extraordinary assessment have been classified according to theobjective of assessment into the investigation in extraordinary assessment and the investigation in
emergency assessment (Fig. C4.1.1). Comparing information obtained in these investigations
provides information required for reasonable maintenance of structures (Fig. C4.1.2). Reasonable
maintenance here means the changes in condition of the structure from service beginning or theprediction of changes in condition of the structures after investigations in assessment.
For conducting investigations in assessment, the investigation items, structural regions to beinvestigated, frequency of investigation and investigation method should be specified properly inaccordance with purposes.

28

Chapter 4

Investigations in Assessment

Assessments
Initial assessments

Investigations in initial assessment

Conducted to identify theconditions of the structure

Periodic assessments

Investigation in routine assessment

Conducted daily to identify changes in
condition of the structure

Investigation in regular assessment

Conducted annually or once in several
years to identify the conditions of thestructure extensively.

Investigation in extraordinary assessment

Conducted for structures damaged byexternal forces

Investigation in emergency assessment

Conducted for structures similar todamaged ones

Extraordinary assessments

initialFig. C4.1.1 Types of investigations in assessment

Completion verification

Identify the initial conditions of the structure

CompareAssessment
Investigation in assessment
Investigations in initial assessment
Investigations in
extraordinary assessment
Investigation in
emergency assessment

Investigations
in routine assessment
Investigations
in regular assessment

Estimation of deterioration mechanism
andPrediction of deterioration progress

Identify changes in condition of thestructure up to the start of maintenance (inthe case of an existing structure)

Identify changes in condition of the structure
at the time of beginning of maintenance
CompareIdentify changes in condition of thestructure during service

Identify the conditions of the structure at the timeof investigation
CompareIdentify changes in condition of thestructure expected while in service

Identify the future condition of the structure

Evaluation and judgment

Flow of ordinary assessment steps
Flow of steps of assessments conducted depending on the condition

Fig. C4.1.2 Types of investigations in assessment and changes in condition of the structure tobe identified(2) When the initial assessment is carried out, the investigation in initial assessment isconducted to obtain information on the initial conditions of the structure. This information obtainedin the investigation in initial assessment is used as the initial value for identifying the condition of
the structure. In cases where the results of investigation in initial assessment are different from the29

Standard Specifications for Concrete Structures-2007, Maintenanceconditions assumed while developing the maintenance plan, the maintenance plan may need to bereviewed. The information obtained in the investigation in initial assessment is very important tosubsequent maintenance of the structure. The investigation in initial assessment should therefore be
conducted for such investigation items and by such an investigation method that pertinent
information may be obtained, and the results obtained should be stored properly.
For newly constructed structures, verifications are generally conducted during or at the end of
construction. If these verifications are conducted in consideration of investigation items for which
the investigation in initial assessment is to be conducted, the verification results may be used as theresult of investigation in initial assessment. For existing structures, no design and construction
drawings may be available according to the service period. Even if these drawings are available, thecondition of the structure may be different from the condition at the commencement of service. In
the investigation in initial assessment, therefore, the structure should be investigated firsthand. In
cases where regarding the results of the investigation in initial assessment as the initial condition of
the structure is determined inappropriate because of a large-scale repair or strengthening,
investigation in initial assessment should be conducted anew. Then, the results should be regarded
as the initial conditions of the structure during maintenance.
(3) Changes in condition of the structure can be identified adequately by conducting
investigations periodically. A rational approach to periodic assessment is to combine simple
investigations such as visual observation while patrolling the structure on a routine basis withintensified investigations of the structure at the closest range possible by visual observations orusing instrumentations. In this Specification, the former is referred to as investigation in routine
assessment and the latter as investigation in regular assessment.
(4) In cases where a structure is subjected to the actions of external forces due to earthquakes,
typhoons or crashes of trains or ships, extraordinary assessments should be conducted quickly. For
extraordinary assessments, investigations in extraordinary assessment should be conducted. In cases
where design criteria are revised while the structure is in service, assessments should be conducted
to verify whether the performance of the structure meets the revised criteria. The investigations forthese assessments are also categorized as investigations in extraordinary assessment.
In cases of confirming an accident in the structure due to defects, assessments are conductedurgently and simultaneously for structures similar to the one that suffers the accident or for
structures in a similar environment. Such assessments are included in extraordinary assessments.
The main objective of such assessments is to prevent similar accidents from occurring. In thisSpecification, the investigations in such assessment are referred to as investigations in emergency
assessment, separate from investigations in extraordinary assessment. For structures that are built inthe same period or format as those for which great defects have been confirmed in periodic
assessments, investigations are conducted in assessments for verifying whether similar deterioration
or damage is likely to occur or not. Such investigations are regarded as investigations in emergency
assessment.
(5) In the investigation in assessment of a structure, it is important to identify the condition of
the structure in service as adequately as possible according to the designated maintenance plan. The
objective is achieved by the most effective method fit for the condition of the structure. Tests andother actions performed to obtain specific information on the conditions of the structure andmembers are referred to as investigations here.
Defined in this Specification are standard investigations that are normally conducted for thedesignated items, at the designated time, with the designated frequency based on the maintenanceplan; and detailed investigations that are conducted in cases where detailed information is found30

Chapter 4

Investigations in Assessment

necessary as a result of standard investigations. The investigations conducted in initial, periodic andextraordinary assessments should be conducted based on the full understanding of the objective andby properly designating the items, method and scope so as to obtain information required for
identifying the condition of the structure.
The standard investigations conducted in the investigations in routine or regular assessments
aim mainly at determining as soon as possible whether or not the structure, region or member to beinvestigated is subject to defects, or whether existing defects have progressed or not bycontinuously conducting the same contents of investigations with an appropriate frequency. For
standard investigations therefore, methods should be selected considering efficiency, promptness
and cost performance. Investigation methods vary according to the type of investigations. Standard
investigations are generally conducted mainly by methods based on visual observations and byhammer tapping or using simple nondestructive testing equipment as required. Making
investigations at the same location over a certain period of time enables the identification of thecondition of the structure.
In cases where it has been determined as a result of standard investigations that inadequate
information is available for evaluating the performance of the structure and for determining theneed of remedial measures, more detailed investigations are required. At this point, detailed
investigations are conducted. In detailed investigations, acquiring required information without failis essential rather than efficiency or promptness. The contents of detailed investigations conducted
are highly likely to depend on the results of standard investigations. In cases where the deterioration
mechanism of the structure can be identified to some extent in the phase of development of themaintenance plan, the specifics and methods of detailed investigations to be applied when thedetailed investigations are required should be presented in the maintenance plan based on existingcase studies.
(6) In cases where emergency measures are determined necessary for a structure in the course ofstandard or detailed investigations, such measures should be taken immediately.

4.2

Investigations in Initial Assessment(1) Investigations in Initial assessment should be conducted for the entire structure.

(2) The method and contents of standard investigations conducted in investigations ininitial assessment should involve the investigations of the entire structure by visualobservations or hammer tapping and the design and construction document search.
(3) Detailed investigations shall be conducted as required based on the results ofstandard investigations.
(4) In cases where concrete defects are confirmed that could affect third parties due tothe falling of concrete pieces in the investigation in initial assessment, remedial measures
shall be taken immediately.

[Commentary] (1) The main objective of investigations in initial assessment is to identify the
initial conditions of the structure at the start of maintenance with respect to the performance of thestructure. The regions or members where outstanding deterioration or damage occurs are not always
uniformly distributed in the structure in service. In investigations in initial assessment, therefore,
identifying the initial conditions properly in all the regions and members of the structure isimportant wherever possible. For the regions for which investigations are difficult after the31

Standard Specifications for Concrete Structures-2007, Maintenancecommencement of service such as the back of a foundation or an underground structure, however,
the initial conditions are estimated based on the results of design and construction records search.
(2) The standard investigations in investigation in initial assessment may basically involve theinvestigations by visual observations and hammer tapping and the document search concerning
design and construction records. Nondestructive testing equipment should also be used as required
because nondestructive testing can be conducted easily. For the items and methods of standard
investigations and the information obtained by respective methods and the precision of the methods,
refer to Section 4.7“Investigation.” Investigations in initial assessment should be conducted basedon the characteristics decided according to newly constructed structures, existing structures andstructures that have undergone large-scale repair or strengthening. These characteristics aredescribed below.
In newly constructed structures and structures that have undergone large-scale repair orstrengthening, aging deterioration has rarely occurred. In standard investigations for such structures,
document search and confirmations of initial defects and damage by visual observations are
generally conducted. For the new structures designed and constructed properly in accordance withthe “Design” and “Construction” volumes of the Standard Specifications in particular, design
documents or records of verifications conducted during or at the end of construction can be usedeffectively as information on the initial conditions of the structure. The general information requiredfor identifying the initial conditions of and maintaining newly constructed structures is shown
below. The information should be used as a basis for selecting investigation items as required. In
cases where deformations have been confirmed by the records of verifications conducted at the endof construction or no deformations have been recognized, the investigations by visual observationsor hammer tapping described in 3) below can be eliminated.
1) Information obtained from design documents-

Criteria applied (including the year in which the specifications were established orrevised, etc)-

Design service life-

Design values for performances of concrete (e.g. strength)-

Design values for cover depth, reinforcement arrangement (e.g. anchorage positions andjoint positions)-

Design values for environmental actions-

Shape and dimensions, etc

2) Information obtained from the records of verifications during and at the end of construction-

Items related to construction outline (e.g. contractor, completion date, construction
period and structural type)-

Quality of concrete at major regions (e.g. type of material used, record of verificationsof mix proportions, results of verifications of water content per unit volume of concrete,mean and minimum administrative strengths and chloride ion content in fresh concrete)-

Record of verifications of cover depth and reinforcement arrangement, anchorage
positions and joint positions at major regions, etc.

32

Chapter 4-

Investigations in Assessment

Results of verifications of initial defects or damage including cracks (e.g. locations,lengths, and maximum and mean crack widths) and records of remedial measures taken

3) Information obtained by visual observations, hammer tapping or nondestructive testing
method-Existence of initial defects (e.g. cracks, honeycomb, cold joints and sand streaking)-Items related to the appearance of the structure at the commencement of maintenance(e.g. outer shape, size, color and defects)-

Existence and degrees of peeling and spalling-

Meteorological and other environmental conditions (e.g. air-borne salt and frost attackin winter)-

Loading conditions for the structure (e.g. live loads)-

Conditions for using the structure (e.g. cyclic wetting and drying, use of deicing agents)

For structures that have just undergone large-scale repair or strengthening, records of the designand construction of the remedial measures taken are also required in addition to the investigations
listed above.
Existing structures see their performance changed while they are in service until the point of theinvestigation of initial assessment from the point of completion owing to the progress ofdeterioration, occurrence of damage or initial defects left unattended. The information listed below
should therefore be obtained by nondestructive testing method in addition to review of design
records, record of verifications during construction, and conducting visual observations, hammer
tapping tests. In cases where neither design records nor the verification records during construction
have been stored, conducting additional investigations should be considered for collecting required
data.
- Defect of the appearance of concrete with time (e.g. deformation, scaling, exposure of
aggregate and lack of section)- Measurements of concrete performance (e.g. strength and chloride diffusion coefficient)- Measurements of cover depth- Existence of cracks, stain rust, free lime, gel, etc. (in case of existence, condition and periodof occurrence, etc.)- Occurrence of steel corrosion (in case of occurrence, form, degree and range of corrosion,etc.)- Existence of damage to supplementary equipment (in case of existence, location, degree, etc.)- Existing assessment records- Existing records of repair and strengthening(3) Detailed investigations are conducted in the following cases as required according to theresults of standard investigations.
(i) Defect has been confirmed and determined undoubtedly to be deterioration.
33

Standard Specifications for Concrete Structures-2007, Maintenance(ii) Defect has been confirmed but whether it is deterioration, damage or initial defect is
unknown.
(iii) No defect has been confirmed but failures have been found in materials through document
search, and conducting more sophisticated investigations and monitoring the progress of defects
have become necessary.
In case (i), the deterioration mechanism causing the defect should be identified, and Part 2
Maintenance for Specific Deterioration Mechanisms should be consulted and investigation items
and methods should be selected so as to collect data for identifying the progress of deterioration andfor predicting deterioration. Then, detailed investigations should be conducted.
In case (ii), after the occasion of the defect is clarified, investigation methods should be selected
for determining whether the defect is ascribable to deterioration, damage or initial defects. Then,detailed investigations should be conducted. In cases where the defect has been determinedascribable to deterioration, further detailed investigations based on the results of the detailed
investigations in case (i) are required. In case where the defect of the structure is determinedascribable to damage or initial defects based on the results of detailed investigations, appropriate
remedial measures should be taken.
In case (iii), detailed investigations should be conducted in cases where it has been foundevident that considerable deformation is highly likely to occur while the structure is in service. The
degree and period of expected defect should be verified in advance by conducting detailed
investigations properly and the plan for subsequent maintenance should be revised accordingly.
Detailed investigations should be conducted as required in cases where it is assumed from thedesign or construction records that the design cover depth is insufficient or the actual cover depth isconsiderably smaller than the design level despite the existence of no initial defects, damage ordeterioration, or in cases where the quality of concrete or reinforcement is assumed to be poor basedon the construction records.
Insufficient grouting in a post-tensioned prestressed concrete structure is one of the construction
defects. Confirming this construction defects from construction records is, however, difficult.
Insufficient grouting may cause prestressing steel to corrode, leading to the reduction of tensioning
force or fracture in the worst case. In the areas with insufficient grouting, cracks along the sheath,free lime or water leakage is found relatively early after construction. In cases where such a defecthas been found, detailed investigations should be conducted to verify grouting conditions by partial
boring or using nondestructive testing equipment such as X-ray method and ultrasonic methods.
Whether cracks exist or not near the anchorage, delamination of backfill concrete and strain of rustshould also be investigated.
For items and methods of detailed investigations, refer to Section 4.7 “Investigation.”(4) In cases where defects are discovered that are likely to cause concrete pieces to fall such as
the delamination of cover concrete or cold joints, third parties including people and property arelikely to be damaged. Then, emergency measures should be taken immediately. As emergency
measures, the area of delaminated concrete is generally chipped and patched. Concrete pieces may
fall before emergency measures are taken. In cases where defects are discovered that are likely tocause concrete pieces to fall, the area under the point of defect should be cleared of people orproperties, and nets should be put up in the area. Trains and vehicles should be ordered to slow
down and the restricted traffic for heavy vehicles should be taken.

34

Chapter 4

4.3

Investigations in Assessment

Investigations in Routine Assessment(1) Investigations in routine assessment should be conducted to determine whether
deterioration, damage or initial defects have occurred or not and how serious they are in
the coverage where investigations are possible during daily patrol of the structure.
(2) When conducting investigations in routine assessment, the items, methods andfrequency of the investigation shall be determined properly considering the objective of
the investigation, maintenance category, and importance of the structure and results ofdeterioration prediction.
(3) Standard investigations in investigations in routine assessment shall be mainlycomposed of visual observations using the naked eye, photographs and binoculars aswell as driving feeling. Hammer tapping and other investigations shall be conducted
depending on the situation.
(4) Detailed investigations shall be conducted as required based on the results ofstandard investigations.
(5) In cases where concrete defects are confirmed in the investigation in routine
assessment that could affect third parties due to the falling of concrete pieces, remedial
measures shall be taken immediately.

[Commentary] (1) and (2) Investigation items: In investigations in routine assessment,
investigations are basically conducted by visual observations and hammer tapping for the damage,defect and deformation of the appearance, the state of service of the structure, the conditions ofconcrete and steel, the conditions of structure authorship and supplementary equipment, theenvironmental actions and the existing remedial measures.
Investigation points: Investigations in routine assessment, which are conducted in the coverage
where investigations are possible during daily patrol of the structure, should be conducted in the
coverage as wide as possible. In locations where investigations are difficult during daily patrol ofthe structure, investigations in routine assessment can be conducted by installing a permanent
scaffold. In case of important structures, members and regions as well as deterioration anddamage-sensitive, installation of supplementary equipment such a permanent scaffold should beconsidered at the stage of design and construction from viewpoints of the importance of structure
and the economic efficiency. Then this equipment should be installed if possible.
Investigation frequency: The frequency of investigation should be properly determinedconsidering the staff actually conducting investigations and the budget, the importance of thestructure, the hazards for third party and the results of deterioration prediction.
(3) Standard investigations in investigations in routine assessment are classified into some majorgroups: visual observations using the naked eye, photographs and binoculars, hammer tapping aswell as driving feeling. For respective investigation methods, refer to Section 4.7 “Investigation.”
The investigations by visual observations are conducted for all the regions. The investigation byhammer tapping is conducted only for the regions where hammer tapping is possible. The
investigation by driving feeling intends to find malfunctions of expansion joints or to determine
whether excessive deflection or vibration exists or not, and is therefore related direct toserviceability.
For investigations in routine assessment, investigation manuals should be prepared based on the35

Standard Specifications for Concrete Structures-2007, Maintenancecharacteristics of the structure, and investigations should be conducted in accordance with themanuals. Investigation procedures, methods of recording defects of concrete surface or abnormalsounds and considerations for ensuring safety during investigations should be specified to enable
the people with no specialized knowledge about maintenance to conduct investigations.
(4) In cases where defect has been confirmed in standard investigations and (i) the defect isoutstanding, (ii) the cause for the defect is unknown, or (iii) the deterioration is much different fromthe prediction results, a professional engineer should verify the condition and conduct detailed
investigations in investigations in routine assessment as required. Detailed investigations ininvestigations in routine assessment should be conducted like detailed investigations ininvestigations in regular assessment.
(5) For actions in cases where the delamination of concrete or other problems that are expected
to affect third parties have been confirmed in investigations in routine assessment, refer toCommentary (4) in Section 4.2 “Investigations in Initial Assessment.”

4.4

Investigations in Regular Assessment(1) Investigations in regular assessment should be conducted by the method and withthe frequency specified in the maintenance plan to determine whether deterioration,
damage or initial defects have occurred or not and how serious they are throughout thestructure.
(2) The contents, regions, frequency and investigation methods for investigations inregular assessment shall be selected properly considering the objective of theinvestigation in regular assessment, maintenance category, importance of the structure,region or member, existing maintenance records and deterioration prediction.
(3) In standard investigations in regular assessment, visual observations and hammer
tapping shall be conducted. Investigations using non-destructive test machines or coresamples shall be also conducted as required.
(4) Detailed investigations shall be conducted as required based on the results ofstandard investigations.
(5) In cases where concrete defects are confirmed in an investigation in regularassessment that could affect third parties due to the falling of concrete pieces, remedial
measures shall be taken immediately.

[Commentary] (1) Investigations in regular assessment intend to determine by simple methods
such as visual observations and hammer tapping whether deterioration, damage or initial defects
have occurred or not and how serious they are throughout the structure including the regions andmembers where determination is difficult in investigations in regular assessment. To determine
whether deterioration, damage or initial defects have occurred or not and how serious they are in theregions and members where adequate determination is impossible; installing scaffolds may become
necessary.
Investigations in regular assessment should be conducted under the guidance of a professionalor responsible engineer, or an engineer whose technical level equal to them with knowledge about
the design, construction and maintenance of concrete structures, in accordance with manuals
36Chapter 4

Investigations in Assessment

prepared based on the professional knowledge about the design, construction and maintenance ofconcrete structures.
(2) and (3) Investigation contents: Investigations in regular assessment are basically conductedby visual observations and hammer tapping for the items related to damage, defect and deformationof the appearance of the structure, and to the state of service of the structure. In cases where ascaffold is installed, investigations can be conducted in proximity to concrete. Then, investigations
using non-destructive test machines or core samples can also be employed. The width and length ofcracks and the area of delaminated concrete should be measured using scales to quantitatively
determine the defect on concrete surface. The results of estimation of the deterioration mechanism
and the deterioration conditions at an early stage can be verified by properly combining the methods
using nondestructive testing equipment concerning the estimated deterioration mechanism. Items
for standard investigations in investigations in regular assessment are listed below.
- Cracks (e.g. time of occurrence, width, length and pattern of occurrence)- Stain of rust, free lime, discoloration, scaling, lack of section and production of gel- Concrete performance (e.g. strength and chloride diffusion coefficient)- Measured value of cover depth- Penetration of deleterious materials (in case of occurrence, types of materials and the degreeof penetration, etc.)- Occurrence of steel corrosion (in case of occurrence, form, degree and range of corrosion,etc.)- Existence of damage to supplementary equipment (in case of existence, location, degree, etc.)- Existing records of assessment and remedial measures taken- Meteorological or other environmental conditions working as deterioration-related
environmental action (e.g. air-borne salt, frost attack in winter)- Service conditions of the structure (e.g. cyclic wetting and drying, use of deicing agents)
Standard investigations should be conducted for selected appropriate items by a relatively
simple and economical method. Comparing the results of standard investigations with the previous
investigation results obtained in investigations in initial assessment and investigations in regularassessment enables the identification of changes in condition of the structure since the start ofmaintenance (Fig. C4.1.2). Investigation items may be changed on a timely basis in view of thebudgetary restraints or for conducting effective maintenance. For example, relatively simple
investigations may be conducted for a limited number of investigation items in limited investigation
areas in biennial investigations in regular assessment while more intensified investigations are
conducted for more items approximately once in ten years. For the items of standard investigations
and corresponding methods, refer to Section 4.7 “Investigation.”
Investigation points: Investigations should be conducted throughout the structure in principle.
Conducting careful investigations is important at locations where confirmation is difficult ininvestigation in routine assessment or regions and members that are likely to be subjected todeterioration or damage. In large structures such as viaducts or tunnels, it is difficult to conduct
full-coverage investigation for the structure at a time. Then, the area to be investigated may be
divided into some sections and consecutive investigations may be conducted at proper intervals. To
that end, the area and sequence of investigation should be determined considering the existing37

Standard Specifications for Concrete Structures-2007, Maintenancemaintenance records, importance of regions and members and cost performance.
Frequency of investigation: The frequency of investigations in regular assessment should beproperly determined considering the results of deterioration prediction, importance of the structure,region or member, type of structure, design service life, remaining service life, environmental
condition, maintenance category, existing maintenance records and cost performance. Investigations
in regular assessment are generally conducted once in several years. The interval of investigations
in regular assessment has generally been set at one to five years for marine structures, five to ten
years for plant structures, five years for road bridges and two years for railroad institutions. Flexibly
adjusting the interval is important to effective maintenance. For example, long intervals are set in
the initial stages of service with a small likelihood of emergence of deterioration, and shorter
intervals are adopted in the stages where deterioration is likely to become outstanding in view of theprediction of deterioration progress.
(4) Detailed investigations in investigations in regular assessment should be conducted when thefollowing conditions are found as a result of standard investigations.
(i)

Deterioration has been confirmed and the deterioration mechanism is unknown ordifferent from estimation.

(ii)

Deterioration has been confirmed and its progress is far different from the prediction ofdeterioration progress.

(iii) Defect has been confirmed but its cause is unknown.
(iv) No defect has been confirmed but the service condition of the structure, loading
conditions and environmental actions have changed considerably.
Detailed investigations should be conducted at an appropriate time considering the importanceof the structure, region or member, maintenance category, degree of defect, remaining service lifeand deterioration prediction.
In cases where the defect is a deterioration that occurred at the time identified in thedeterioration prediction and the degree of deterioration is nearly in agreement with that assumed in
the original maintenance plan, or where the deterioration progressed at a lower rate than predicted,
no detailed investigations are required and investigations should be continued in accordance withthe original maintenance plan. In cases where deterioration progressed at a higher rate than
predicted, whether detailed investigations are required or not and when investigations need to be
conducted should be considered based on the type of the deterioration mechanism and the rate ofprogress. In case of deterioration due to frost attack, chemical attack, alkali silica reaction, fatigue
and ablation, it is generally known that the defects occur on concrete surface at early stages. No
detailed investigations are therefore required immediately even when such defect is discovered. In
cases where corrosion cracks or stain of rust due to carbonation or chloride induced deterioration
have been detected, the reinforcement in concrete has already been corroded and deterioration stage
has already got to propagation stage or acceleration stage. Detailed investigations should therefore
be conducted immediately. For specific methods of detailed investigations for these types ofdeterioration, refer to Part 2 “Maintenance for Specific Deterioration Mechanisms.”
In cases where it is unknown whether the defect is ascribable to deterioration, damage or initialdefects, the cause for the defect should be determined early. Even in cases where the defect isevidently ascribable to damage or initial defects, damage or initial defects may exist that are
difficult to identify through the surface, or concurrent deterioration or poor quality of concrete or
reinforcement may also exist. To properly evaluate the influences of these conditions on the38

Chapter 4

Investigations in Assessment

structural performance, detailed investigations should be conducted.
(5) For actions in cases where the delamination of concrete or other problems that are expected
to affect third parties have been confirmed in investigations in regular assessment, refer toCommentary (4) in Section 4.2 “Investigations in Initial Assessment.”

4.5

Investigations in Extraordinary Assessment(1) Investigations in extraordinary assessment shall be conducted for the structure,region or member that may have been damaged in a disaster or accident as quickly as
possible while ensuring the safety of the investigator.
(2) Standard investigations in investigations in extraordinary assessment should
basically be conducted by visual observation or hammer tapping in principle.
(3) In cases where damage or deformation has been verified by standard
investigations, detailed investigations shall be conducted as required.
(4) In cases where a secondary disaster is likely to occur or damage that could affectthird parties has been confirmed, remedial measures shall be taken immediately.

[Commentary] (1) In numerous cases, extraordinary assessments are urgently required after adisaster or accident. There are cases where the safety of a damaged structure has been greatly
deteriorated due to a disaster or accident although the structure has not collapsed or failed. In thewake of a disaster or accident, therefore, the area around the structure should be declared off-limits
or other measures should be taken to prevent secondary disasters. At the same time, investigations
in extraordinary assessment should be conducted as quickly as possible while ensuring the safety of
the investigator. In cases where investigations in extraordinary assessment are conducted of astructure in the wake of a great earthquake in particular, aftershocks during investigations are highly
likely to cause the structure to be subjected to a new defect or damage. Greater safety should
therefore be guaranteed. Investigations in extraordinary assessment of a structure after a fire should
be conducted only after the confirmation of fire extinguishment or the removal of toxic gases.
Investigations in extraordinary assessment should be conducted for the structure, region ormember that may have suffered damage or defect due to a disaster or accident. There may be cases
where investigations in extraordinary assessment are required for regions that are likely to be
subjected to damage or defect but are difficult to investigate. Then, investigation in extraordinary
assessment methods should be examined comprehensively considering the maintenance category,
importance of the structure, region or member, type of performance affected, remaining service lifeand cost performance.
(2) In standard investigations of investigation in extraordinary assessment, visual observations
are first conducted from a distance. After the confirmation of no risk of collapse, investigations are
conducted through visual observations at close range or hammer tapping. Investigated are cracking,lack of section, delamination, peeling, spalling and water leakage, deformation, supporting
conditions, and abnormal sounds and vibrations. Nondestructive testing equipment should be used
to meet cost performance and emergency requirements in cases where such testing is consideredeffective for verifying damage or deformation.
(3) The damage to a structure, region or member due to a disaster or accident is determined bystructural factors. Then, in cases where examining remedial measures is determined easily from the39

Standard Specifications for Concrete Structures-2007, Maintenanceappearance of concrete by standard investigations, remedial measures such as repair andstrengthening should be taken without conducting detailed investigations. In cases where no
emergency measures are considered necessary from the appearance of the structure despite somedamage, crack depth should be investigated and detailed investigations should be conducted for
identifying the load bearing capacity and stiffness of the structure at an appropriate point of time
when the effects of accidental external forces have disappeared, and data for evaluating theperformance of the structure should be collected.
In cases where the structure has been subjected to the effects of a fire, detailed investigations are
required for verifying the quality of concrete and reinforcement that have been subjected to hightemperature. Tests should therefore be conducted to estimate the temperature of the heat to whichconcrete samples are exposed and verify the effect of the heat, and to examine the dynamic
characteristics of steel. In addition, investigations should be conducted to identify the area where
subjected to high temperature, because this area needs repair.
In cases where emergency measures have been taken based on the results of standard
investigations, detailed investigations should be conducted at the earliest time possible after thedisappearance of influences of external forces to place the structure in service safely and securely.
For conducting detailed investigations, refer to Section 4.7 “Investigation.”(4) In cases where defects are discovered in investigations that are likely to cause concrete
pieces to fall and damage people and property such as the delamination of cover concrete,
appropriate measures should be taken immediately. As emergency measures of investigations in
extraordinary assessment, the area under the point of defect should be declared off-limits, or netting
should be provided immediately in the area to prevent concrete pieces from falling. Trains andvehicles should be ordered to slow down and the weight of vehicles traveling in the area should be
restricted. Emergency measures should be taken continuously for a required period of time until therestoration of the structure to its original state.
In cases where emergency measures are taken in investigations in extraordinary assessment, it
should be fully understood that they are taken under different conditions from those for ordinary
emergency measures and care should be taken to prevent secondary disasters from occurring while
installing the emergency measures.

4.6

Investigations in Emergency Assessment(1) In cases where an accident has occurred due to defect of a structure orconsiderable defect has been confirmed in a structure although no accident has occurred,investigations in emergency assessment shall be conducted in the region or member of asimilar structure that is likely to suffer similar defect.
(2) In investigations in emergency assessment, investigations shall be conducted byusing an appropriate method capable of verifying the existence of defect similar to theone causing the accident.
(3) In cases where concrete defect are confirmed in an investigation in emergency
assessment that could affect third parties due to the falling of concrete pieces, remedial
measures shall be taken immediately.

40

Chapter 4

Investigations in Assessment[Commentary] (1) There is a high possibility that structures of the same type constructed in thesame period have been designed and constructed in accordance with the same standard. In cases
where an accident has occurred due to defect of a structure or where outstanding defect has been
confirmed in the structure in periodic assessment although no accidents were induced, similar
problems are highly likely to occur also in similar structures build in the same period. The objectiveof investigations in emergency assessment is to verify whether defect similar to the one that caused
the accident has occurred or not in a structure similar to the one subjected to the accident, and tocollect data required for taking remedial measures quickly.
Investigation in emergency assessment should be conducted for the region or member that isdetermined to be likely to suffer similar defect based on the previous accidents. In investigations,due attention must be given to the safety of the investigator.
(2) By investigations conducted in investigations in emergency assessment, it should be verified
whether deformation has occurred or not, data should be collected that is required for identifying
the condition of the structure and determining the need of remedial measures. To that end, not only
visual observations and hammer tapping but also investigations using non-destructive testing
equipment and chipping of concrete for observation should be combined. For structures constructedin accordance with similar design standard or using similar materials, the design standard or
existing documents concerning the structure provide useful information. Document search istherefore important. If the structure is exposed to a different environmental action, the action should
also be inspected.
(3) For actions in cases where the delamination of concrete or other problems that are expected
to affect third parties have been confirmed in investigations in emergency assessment, refer toCommentary (4) in 4.2 “Investigations in Initial Assessment.”

4.7

Investigation

4.7.1 General
Investigations shall be conducted by an appropriate method for appropriate items
selected in order to obtain specific data on the conditions of a structure, region ormember.

[Commentary] In the investigation conducted during the maintenance of a structure, thecondition of the structure should be identified as specifically and quantitatively as possible. To
achieve this objective, investigations are conducted.
Selecting more investigation items and investigation methods collecting more data, and setting
the investigation point to the more wide-ranging make it possible to obtain more detailed andaccurate information on the structure. An increased number of investigation items and more
complicated investigation methods, however, increase the time and cost required for investigations.
If an excessively high priority is given to the efficiency or simplicity of investigations, identifying
the condition and changes in condition of a structure during the maintenance period becomesdifficult in cases where inappropriate frequency and coverage of investigation, or inappropriate
investigation items and methods are selected.
In investigations conducted in the initial, periodic and extraordinary assessments, fully
understanding the objective of investigation, and properly defining the items and methods for
efficiently obtaining data required for identifying the condition of the structure are necessary.
41

Standard Specifications for Concrete Structures-2007, Maintenance

4.7.2

Investigation items

Investigation items shall be selected properly considering the type and objective of theinvestigation, condition of the structure, required information and the cause fordeterioration of the structure.

[Commentary] The general investigation items include an outline of the structure, state of serviceof the structure, defect and deformation of the appearance of the structure, conditions of concreteand steel, structural details, conditions of supplementary equipment, environmental actions andstate of existing remedial measures. The information to be obtained on the items and major
investigation methods adopted are listed in Table C4.7.1. Investigation items should be selected sothat required information may be obtained either in standard or detailed investigations. Items of thestandard investigation are basically specified in the maintenance plan. Items of the detailed
investigations should be selected properly according to the objective based on the results ofstandard investigations.

42

Chapter 4

Investigations in Assessment

Table C4.7.1 Examples of general investigation items, information to be obtained and major
investigation methods
Generalinvestigations item

Outline of structureState of service ofstructure

Defect anddeformation of theappearanceState of concreteState of steel

Conditions ofstructural details
and supplementary
equipment

Environmental
actions and loads

Conditions ofexisting remedial
measures

Information to be obtained-Specifications and design standard applied-Design documents-Construction records-Verification records-Maintenance records-Conditions while in service (loads, external forces, etc.)-Outline of surrounding environment-Supporting condition-Abnormal sounds and vibrations-Serviceability (ride quality)-Initial defects (cracks, honeycomb, cold joints, sand streaking,etc.)-Discoloring and staining of concrete-Cracking-Scaling-Delamination, peeling and spalling-Exposure, corrosion and fracture of steel-Deformation-Stain of rust
-Water leakage-free lime
-Gel
-Materials used and mix proportions-Delamination and internal voids-State of water content-Physical properties (e.g. strength and void structure)-Chemical properties (e.g. hydrates and reaction products)-Degree of penetration of deterioration factors (e.g. depth ofcarbonation and depth of chloride penetration)-amount of reinforcing steel-Locations and diameters of reinforcement, and cover depth-Reinforcing bar arrangements-State of steel corrosion-Lack of section-Sectional area of the member-Cover depth-Anchorages and joints-Joint of bema and column-State of supplementary equipment-Meteorological conditions (e.g. temperature, minimum
temperature, humidity, precipitation and insulation)-Water supplies (conditions of weathered part of building
exterior, conditions of water supplies from the ground,waterproof layers and drain facilities, etc.)-Salt supplies (e.g. amount of air-borne salt, effects of seawaterand amount of deicing agents spread)-Wind (direction and velocity)-Carbon dioxide concentration-pH of highly acid river water-Water quality in sewerage facilities-Occurrence of acid precipitation and acid fog-Alkali supplies-Loading conditions (e.g. vehicles, vibrations, water pressure)-External forces related to disasters (e.g. earthquakes and fires)
State of Repair and strengthening-State of functionality improvement-State of restriction in service

43

Major investigation method-Method based on documents-Method through interviews-Visual observations (at close range
and at a distance)-Driving feeling test
-Loading test, vibratory loading test

-Visual observations (at close range
and at a distance)-Hammer tapping-Surface hardness method-Method based on surface hardness-Method using elastic waves-Method electromagnetic waves-Local destruction (collection of coresamples, chipping of concrete,collection of drilled powder produced
while drilling a hole in concrete, etc.)-Chipping-Methodusingelectromagnetic
induction-Method using Electromagnetic waves-Measuring directly-Reviews of design documents-Method using electromagnetic waves-Measuring directly-Based on existing records-Based on meteorological data (e.g.
AMeDAS)-Measuring directly (using sensors,
etc.)-Monitoring-Visual observations (at close range
and at a distance)-Testing of repair and reinforcing
materials

Standard Specifications for Concrete Structures-2007, Maintenance

4.7.3
4.7.3.1

Investigation methods
GeneralThe investigation methods described in this section shall be used as standard
methods. Appropriate methods shall be selected to obtain information on the items
selected.

[Commentary] This Specification describes the basics of general investigation methods: (i)document search, (ii) visual observations, (iii) hammer tapping, (iv) using non-destructive test
machines, (v) investigations involving local destruction, (vi) loading and vibratory loading tests ofexisting structures, (vii) evaluation of environmental actions and (viii) testing of repair andreinforcing materials. Investigations methods used in investigation in initial, routine, regular,
extraordinary and emergency assessments should be selected appropriately so that information on
investigation items can be collected. Table C4.7.2 shows examples of investigation methods andinformation obtained. Table C4.7.3 shows examples of deterioration mechanisms and corresponding
investigation methods. For the investigation, it is important to select appropriate methods based onthese tables and Part 2 “Maintenance for Specific Deterioration Mechanisms.”
When using a method not described in this section, it should be fully examined and its validity
should be verified. In cases where the deterioration mechanism is known and more detailed
information is required, Part 2 “Maintenance for Specific Deterioration Mechanisms” should be
consulted.

Table C4.7.2a Investigation methods and information obtained
Document search

Investigation method
Collection of documents
Interviews

Visual observations and hammer
tapping

Information obtained(i) Specifications and design standard used(ii) Design documents(iii) Construction records(iv) Verification records(v) Maintenance records (e.g. investigation records andhistories of repair and strengthening)(i) Initial defects (cracks, honeycomb, cold joints, sandstreaking, etc.)(ii) Discoloring and staining of concrete (stain of rust,
germination of fungi, precipitation of gel, presence ofefflorescence, free lime, discoloring of concrete, waterleakage, etc.)(iii) Cracks (directions, patterns, quantity, widths,
lengths and stain of rust, etc.)(iv) Scaling(v) Delamination of concrete (presence, number oflocations, area, etc.)(vi) Peeling and spalling of concrete(vii) Exposure, corrosion and fracture of steel(viii) Deformation

Using the naked eye
Using binoculars
Using cameras
Hammer tapping

44

Chapter 4

Investigations in Assessment

Table C4.7.2b Investigation methods and information obtained
Using
non-destructive
test machines

Investigation method
Using a surface
Surface hardness method
hardness
Using
Using the electrical conductivity
Electromagnetic and magnetism of steel
induction
Using the electromagnetic
induction of concrete
Using elastic
Hammer tapping
waves
Ultrasonic testing
Impact elastic wave method
Acoustic emission testing

Using
electromagnetic
waves

X-ray method
Electromagnetic radar method
Infra-red devices (thermographymethod)Electrochemical
methodHalf-cell potential method
Polarization resistance method
Four electrodes method
Using optical fiber scope
Method involving local
destruction

Core sampling
Chipping
Collection of drilled powder
produced while drilling a hole inconcrete
Sampling steel

Driving a vehicle

Road alignments, driving feeling
test
Loading and vibratory loading
tests
Based on existing records
Based on meteorological data
(e.g. AMeDAS)
Measurement directly (using
sensors, etc.)
Monitoring

Investigation for evaluating
environmental actions, loads, etc.

45

Information obtained(i) Concrete strength(i) Locations and diameters of steel in concrete and cover
depth(ii) State of water content(i) Concrete quality, e.g. compressive strength and elastic
modulus(ii) Concrete crack depth(iii) Delamination, peeling and void in concrete(iv) Dimensions of members such as the thickness ofconcrete(v) Grouting in sheath (prestressed concrete structures)(i) Locations and diameters of steel in concrete andconcrete cover(ii) Delamination, peeling and void in concrete(iii) Distribution of cracks in concrete(iv) Grouting in sheath (prestressed concrete structures)(i) Tendency of Corrosion of reinforcement in concrete(ii) Rate of corrosion of reinforcement in concrete(iii) Electric resistance of concrete(i) Internal conditions of concrete(ii) Grouting in sheath (prestressed concrete structures)(i) Crack depth(ii) Compressive strength, tensile strength and elastic
modulus of concrete (loading tests)(iii) Carbonation depth of concrete(iv) Analysis of concrete (chemical analysis, fluorescence
X-ray analysis, X-ray analysis, thermal analysis, optical
microscope, polarization microscope, scanning electron
microscope and EPMA)(v) Conditions of chloride ions (concentrations of chloride
ions and distribution of concentrations)(vi) Analysis of mix proportions(vii) Released expansion and residual expansion of
concrete(viii) Air and water permeability of concrete(ix) Pore size distribution(x) Air void distribution in concrete(xi) State of corrosion of reinforcement (by chipping)(xii) Tensile strength of reinforcement (by sampling
reinforcement)(i) Section stiffness of member (static and dynamic
stiffness)(ii) Vibration characteristics(i) Meteorological conditions (e.g. temperature, minimum
temperature, humidity, precipitation and insulation)(ii) Water supplies (conditions of weathered part ofbuilding exterior, conditions of water supplies from theground, waterproof layers and drain facilities)(iii) Salt supplies (e.g. amount of air-borne salt, effects ofseawater and amount of deicing agents spread)(iv) Wind (direction, velocity and frequency)(v) Carbon dioxide concentration(vi) pH of highly acid river water(vii) Water quality in sewerage facilities(viii) Occurrence of acid precipitation and acid fog(ix) Alkali supplies(x) Loading conditions (vehicles, vibrations, waterpressure, etc.)(xi) External forces related to disasters (e.g. earthquakes
and fires)

Standard Specifications for Concrete Structures-2007, Maintenance

Table C4.7.3a Deterioration mechanisms and corresponding investigation methods

Electrochemical method

AbradedUsing electromagnetic waves

Fatigue

Using elastic waves

Alkali silica reaction

Surface hardness method
Electromagnetic induction

Chemical attack

Visual investigations*1
Hammer tapping

Information on design and construction, information
on maintenance and remedial measures
Using the naked eye, binoculars or cameras
Delamination, peeling and voids
State of corrosion of steel (when steel is exposed)
Test hammer strength
Locations and diameters of steel
Hammer tapping, ultrasonic method, impact elastic
wave method, and acoustic emission method
Steel arrangement
Rader method
Voids
Cover concrete
Infrared devices
Surface spalling(thermography method)
Steel arrangement,
X-ray method
diameter, voids and cracks
Half-cell potential method and polarization resistancemethodFour electrodes method
Inside conditions of concrete and grouting in sheath

Frost attack

Document search

Details

Chloride induced deterioration

Investigation method

Carbonation*2

Deterioration mechanism

●

●

●

●

●

●

●

●
●
●

●
●
●

●
●
●

●
●
●

●
●
●

●
●
●

●
●
-

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

-

-

-

▲

▲

▲

▲

▲

▲

▲

-

▲

▲

▲

▲

▲

▲

▲

▲

-

▲

▲

▲

▲

▲

▲

-

▲

▲

▲

▲

▲

-

-

▲
▲
▲
▲
▲
▲
▲
Using optical fiber scope
Legend●: Items for which standard investigations are conducted.
▲: Items for which standard investigations are conducted as required.
▲: Items for which detailed investigations are conducted as required.
-: Unknown whether the items is related to the deterioration mechanism or not.
*1: Deformation, discoloring, scaling and cracking are included.
*2: Corrosion of steel owing to the carbonation of concrete.
*3: TG (thermogravimetric) analysis and DTA (differential thermal analysis) make qualitative and quantitative analysis of hydrates
and carbonated materials.
*4: Electron probe microanalyzer, which makes qualitative and quantitative analysis of regions in concrete.

46Chapter 4

Investigations in Assessment

Table C4.7.3b Deterioration mechanisms and corresponding investigation methods

AbradedFatigue

Alkali silica reaction

Chemical attack

Frost attack

Details

Chloride induced deterioration

Investigation method

Carbonation*2

Deterioration mechanism

▲
▲
▲
▲
▲
▲
▲
Appearance and crack depth
▲
▲
▲
▲
▲
▲
Carbonation depth, uncarbonated depth
▲
▲
▲
▲
▲
▲
Permeation depth of chloride ion
▲
▲
▲
▲
▲
Chloride ion content
Compressive strength, tensile strength and elastic
▲
▲
▲
▲
▲
▲
▲
modulus
Method involving local destruction Analysis of mix proportions
▲
▲
▲
▲
▲
-Collection of core samples▲
Amount of alkali-Chipping▲Aggregate reaction-Collection of drilled powder▲Released and residual expansion of concrete
produced while drilling a hole in
▲
▲
▲
▲
▲
Pore size distribution
concrete▲▲
Air void distribution
▲
▲
▲
▲
▲
Air and water permeability tests▲▲
Thermal analysis (TG-DTA)*3
▲
▲
▲
▲
X-ray method (identification of hydrates)
▲
▲
▲
▲
EPMA*4▲▲▲
Scanning electron microscope
▲
▲
▲
▲
▲
▲
Method involving local destruction State of corrosion of steel-Chipping
▲
▲
▲
▲
▲
▲
Tensile strength of steel-Sampling steel
Road alignment and driving
▲
▲
▲
▲
▲
▲
Road alignment and comfort of vehicle occupants●feeling test
Loading tests (static and dynamic
▲
▲
▲
▲
Crack occurrence and stiffness
loading)
▲
▲
▲
▲
Vibratory loading tests
Natural frequency and vibration mode
▲
▲
▲
▲
▲
▲
Measurement method of stressMeasurement of strain under loading
Measurement method of
▲
▲
▲
▲
▲
▲
Measurement of deformation under loading
deformation
Legend●: Items for which standard investigations are conducted.
▲: Items for which standard investigations are conducted as required.
▲: Items for which detailed investigations are conducted as required.
-: Unknown whether the items is related to the deterioration mechanism or not.
*1: Deformation, discoloring, scaling and cracking are included.
*2: Corrosion of steel owing to the carbonation of concrete.
*3: TG (thermogravimetric) analysis and DTA (differential thermal analysis) make qualitative and quantitative analysis of hydrates
and carbonated materials.
*4: Electron probe microanalyzer, which makes qualitative and quantitative analysis of regions in concrete.

4.7.3.2

Document search

Documents concerning the design, construction and maintenance of structures shallbe examined.

[Commentary] An outline of a structure can be known by reviewing the specifications, design
criteria, design documents, construction records, investigation records, and maintenance records
such as the histories of repair and strengthening. Information can also be obtained by interviewing
47

Standard Specifications for Concrete Structures-2007, Maintenancethe people who were involved in design, construction and maintenance of the structure to beinvestigated. Obtaining effective information on the maintenance of the structure by collecting
documents may make it possible to omit other investigations. It is important in investigations totake this point into consideration and conduct reviews of document properly.

4.7.3.3

Visual observations and hammer tapping

Visual observations and hammer tapping shall be used to identify the appearance ofstructure, defects on areas near the surface such as the delamination and peeling of
concrete.

[Commentary] With the progress of concrete deterioration, the defect frequently becomesoutstanding on concrete surface. In investigations in assessment, therefore, concrete surface should
basically be observed visually. In cases where the people engaged in investigation cannot haveaccess to concrete surface, using binoculars may be effective. The items that should be visuallymonitored and details are described below.
(i)Discoloring and staining of concrete: Area where discoloring or staining occurred, color,
presence and area of white gel, efflorescence and free lime, from concrete, occurrence
and area of water leakage(ii)

Cracks in concrete: Directions of cracks, patterns of cracks, quantity of cracks, typical
widths and lengths of cracks and whether stain of rust from cracks occurred or not(iii)

Scaling: Area of scaling and scaling depth(iv)

Delamination of concrete: Presence, number of locations and area(v)

Peeling and spalling of concrete: Number of locations and area(vi)

Exposure, corrosion and fracture of steel: Concrete cover, number of locations wheresteel was exposed, length of steel exposed and degree of corrosion(vii)

Displacement and deformation of structures: Deflection, movement and subsidence

For the relationship between the item to be monitored and the characteristics of deterioration
mechanism, refer to Part2 “Maintenance for Specific Deterioration Mechanisms.” When
conducting visual testing, refer to NDIS 3418 "Visual testing methods for concrete structures" ofthe Japanese Society for Non-destructive Investigation. In cases where defect has been detected on
the surface of a structure by visual observations, crack widths, and areas and lengths of cracks
should be measured using crack scales or measuring tapes. For quantitatively assessing the positionand size of defect, analyzing the images recorded by digital cameras is effective. In addition tovisual observation, data may be extracted from the intensity of laser beam reflected by the concretesurface.
In visual observations, not only the external defects and deformations of concrete but also theconditions of structures in service including the vehicular traffic can be verified. Exploring the areas
around the structure by visual observations also enables the verification of deterioration-related
environment actions.
Hammer tapping as well as visual observations enables the identification of internal voids nearconcrete surface. In hammer tapping, concrete surface is struck with a hammer and the degree of48

Chapter 4

Investigations in Assessment

impact and sounds are interpreted to estimate the presence of deterioration in concrete. Hammer
tapping is a simple but important method for quickly identifying the presence of deterioration.
Accurately determining the presence of deterioration by hammer tapping, however, requires much
experience.

4.7.3.4

Methods using nondestructive testing equipment(1) When conducting investigations using nondestructive testing equipment, theobjective, scope and limitations of application and accuracy of measurement required
shall be identified, and an appropriate method shall be selected.
(2) Surface hardness methods should be used to estimate concrete strength.
(3) Electromagnetic induction utilizes either the electroconductive or magnetic
properties of steel or the dielectric characteristics of concrete, and should be adopted toobtain information mainly on the following items.
(a) Locations and diameters of reinforcing bars, and concrete cover(b) State of water content(4) Methods utilizing elastic waves include hammer tapping, ultrasonic testing, impact
elastic wave method and acoustic emission method, etc., and should be adopted to obtain
information mainly on the following items.
(a) Concrete quality such as compressive strength and elastic modulus(b) Concrete crack length(c) Delamination, peeling and voids(d) Member dimensions including concrete thickness(e) Grout in the sheath (prestressed concrete structures)(5) Methods utilizing electromagnetic waves include X-ray method, radar method andinfrared devices methods (thermography method), etc. and should be adopted to obtain
information mainly on the following items.
(a) Locations and diameters of steel, and concrete cover(b) Delamination, peeling and voids(c) Distribution of cracks(d) Grout in the sheath (prestressed concrete structures)(6) Electrochemical methods include half-cell potential methods, polarization
resistance methods and four electrodes methods, etc. and should be adopted to obtain
information mainly on the following items.
(a) Tendency of corrosion of reinforcement49

Standard Specifications for Concrete Structures-2007, Maintenance(b) Rate of corrosion of reinforcement(c) Electric resistance of concrete(7) Methods utilizing optical fiber scope should be adopted to obtain information
mainly on the following items.
(a) Internal conditions of concrete(b) Grout in the sheath (prestressed concrete structures)[Commentary] (1) In visual observations and hammer tapping, information can basically beobtained only on the defect on the surface and near the surface layer of a concrete structure. In cases
where grasping the internal conditions of concrete is required or where more detailed information isnecessary for estimating the deterioration mechanism and determining the degree of deterioration,
investigations should be conducted by methods using nondestructive testing equipment.
(2) Collecting core samples for testing strength is a basic and important method of measuringconcrete strength in existing structures. Frequently conducting strength tests using core samples is,however, not desirable because the structure may be damaged. Then, surface hardness method is
widely used in which concrete strength is estimated based on the results of measurement of surface
hardness on concrete surface. Surface hardness method should be conducted in accordance with JIS
A 1155 "Method of measurement for rebound number on surface of concrete" and JSCE-G
504-2007 "Test method for concrete strength by test hammer."
The surface hardness of the concrete surface is determined not only by concrete strength but
also the state of water content and carbonation of concrete. It is therefore difficult to accurately
estimate the compressive strength of concrete at ages greater than a certain level solely based on themeasurement of surface hardness. When estimating the strength of concrete of an existing structure,
therefore, surface hardness method should be combined with compressive strength tests using coresamples.
(3) The methods using electromagnetic induction include the electromagnetic induction method
for nondestructive investigation of the locations and diameters of reinforcing bars in concrete andthe cover depth, and a method for estimating the water content ratio of concrete based on therelationship between the water content ratio and induction ratio of concrete. When applying thesemethods, preparations are required such as developing calibration curves. Measuring the diameterof reinforcement or cover depth becomes difficult in cases where reinforcing bars are arranged
densely. In addition, the water content ratio of concrete is measured only in surface layers. Then, it
should be noted that measurements may sometimes be much different from the internal conditionsof concrete.
(4) Investigation methods using elastic waves propagating through concrete include hammer
tapping, ultrasonic method, impact elastic wave method and acoustic emission method.
In hammer tapping, the sound waves produced by striking concrete surface with a hammer aredetected, and the delamination of concrete and the locations of voids near concrete surface layers
are identified based on the distribution and amplitude of the sound waves obtained.
The ultrasonic method is used to identify the quality of concrete and crack depths based on the
propagation characteristics of ultrasonic waves through concrete.
In impact elastic wave method, voids in concrete or the thickness of members is assessed based
50Chapter 4

Investigations in Assessmenton the elastic waves produced by striking concrete with a hammer. Elastic waves are detected with avibration sensor installed on concrete surface.
Acoustic emission method is employed to detect acoustic emissions corresponding to cracks orother small failures using an acoustic emission sensor installed on concrete surface, and to monitor
the cracking condition based on the frequency of occurrence of acoustic emissions and thecharacteristics of acoustic emission waveforms.
When taking measurements using elastic waves, the gap between the sensor and the concretesurface on which it has been installed should be minimized by injecting grease into the gap.
(5) Available for obtaining various information using electromagnetic waves that either
permeate or are reflected by concrete are X-ray method, electromagnetic radar method and infra-red
method (thermography method).
In X-ray method, the locations and diameters of reinforcing bars in concrete, cover depth andvoids are detected based on the distribution of X rays that penetrate concrete. X-ray method
provides relatively accurate data. The penetration thickness is, however, limited and safety should
be ensured during the implementation of the method.
The electromagnetic radar method aims at inspecting the locations of reinforcing bars inconcrete and the cover depth based on the reflections of electromagnetic waves (microwaves) at theinterface between materials of different relative induction ratio. It should be noted that measurement
accuracy may be reduced in cases where concrete contains a large amount of water on its surface or
where reinforcing bars are arranged densely because no electromagnetic waves penetrate concrete.
Infra-red method (thermography method) are non-contact methods for inspecting the locationsof delamination, peeling, voids, cracks and other defects based on the distribution of concretesurface temperature. The method uses the difference in thermal conductivity between the section of
deformation and the sound section. The method involves no contacting and is applicable over awide area. The exploration depths are, however, limited and the staining of concrete surface, waterleakage and the degree of insulation have some influences. The environment for measurement
should therefore be duly prepared.
(6) Half-cell potential method, polarization resistance method and four electrodes method areused to obtain information on the state and rate of corrosion of steel based on the fact that thecorrosion of steel in concrete is an electrochemical reaction.
Half-cell potential method aims at determining the progress of corrosion of steel by identifying
the difference in potential. The potential of internal steel is measured from concrete surface
throughout the member. Sections assumed to have been subjected to corrosion can be identified
based on the distribution of potentials. Measurement by the half-cell potential method should be
conducted in accordance with JSCE-E 601 "Test method for half-cell potentials of uncoated rebars
in concrete structures".
Polarization resistance method involves the measurement of the current generated when thepotential of steel is slightly polarized (potential is forced to change), and the polarization resistance,
which is a parameter of the rate of corrosion, is obtained by dividing the amount of polarization by
the measured current. Several methods are available for measuring the polarization resistance.
Measuring equipment using the alternating current impedance method has been put to practical use
and actually adopted for field measurement at numerous sites.
Four electrodes method directly measures the electric resistivity of concrete. Corrosion currents
are generated by electrochemical reaction at the time of corrosion of steel. The lower the electric
51

Standard Specifications for Concrete Structures-2007, Maintenanceresistivity of concrete around the steel, the more likely is the corrosion current to flow and the fasterthe progress of corrosion. Measuring the electric resistivity of concrete enables the acquisition of aguideline for determining the rate of progress of steel corrosion in concrete.
(7) The condition inside the concrete can be monitored by an optical fiber scope put into a small
hole created by cracking or a drill hole. In the case of a prestressed concrete beam, the conditions
around the beam can be verified via the fiberscope inserted through a gap at the end of the beam.
The condition of grouting in the sheath can also be monitored.

4.7.3.5

Investigations involving local destruction

Investigations involving local destruction are conducted mainly by collecting coresamples, using the drilled powder produced while drilling a hole in concrete, chipping or
sampling steel. Investigations involving local destruction shall be conducted to obtain
information on the physical properties and state of deterioration of concrete and steel.

[Commentary] In cases where no adequate information can be obtained by visual observations,hammer tapping or nondestructive testing, or where highly accurate information is required,investigations are sometimes conducted that involve local destruction. Investigations involving
local destruction are conducted mainly to identify the physical properties and the condition ofdeterioration of concrete and to identify the condition of deterioration of reinforcement. To achieve
the former objective, core sampling, chipping or using of the drilled powder produced while drillinga hole in concrete is adopted. For the latter objective, observations of the state of steel corrosion
after chipping concrete cover are conducted or the steel in the structure is directly collected. When
conducting investigations involving local destruction, care should be taken not to damage theperformance of the structure.
For details of investigations involving local destruction, refer to Table C4.7.3 that lists examples
for respective deterioration mechanisms. In addition to this, investigations should be conducted inaccordance with the following standards including JIS standards.
JIS A 1107 Method of sampling and testing for compressive strength of drilled cores of concrete
JIS A 1108 Method of test for compressive strength of concrete
JIS A 1113 Method of test for splitting tensile strength of concrete
JIS A 1152 Method for measuring carbonation depth of concrete
JIS A 1154 Methods of test for chloride ion content in hardened concrete
JIS A 1149 Method of test for static modulus of elasticity of concrete
JSCE-G 573-2007 Measurement method for distribution of total chloride ion in concrete
structure
JSCE-G 574-2005 Area analysis method of elements distribution in concrete by using EPMA
NDIS 3419 Method of carbonation test for concrete structures using the drilled powder
produced while drilling a hole in concrete

52

Chapter 4

4.7.3.6

Investigations in Assessment

Loading and vibratory loading tests of existing structures

Available test method for directly evaluating the mechanical behavior or properties ofexisting structures are loading and vibratory loading tests. These methods shall be used
for obtaining information on the following items.
(a) Stiffness of cross section of the member(b) Characteristics of vibration[Commentary] For directly assessing the mechanical behavior or properties of actual structures,
loading and vibratory loading tests can be used.
In loading tests, vehicles or trains are generally used as overburdens. The tests under static andvarying loading are referred to as the static and dynamic loading tests, respectively. Hydraulic jacks
can also be used to apply loads for other members to carry.
In vibratory loading tests, forced vibration is applied to the structure using impact or vibratingmachines, or loads are applied using a hydraulic jack for the reaction of supports or other members
to carry the load and the load is later released to produce free vibration.
These methods are adopted to verify whether or not the behavior of the structure in the elastic
area deviates from prediction. When implementing tests, it is necessary to carefully investigate
whether cracks, considerable residual deformation and other defects have occurred or not that may
affect the usability and durability of the structure and to verify the validity of the test method aswell as the performance of the structure not only in the planning phase but also during and after theloading test.

4.7.3.7

Investigations for evaluating loads and environmental actions

For evaluating loads and environmental actions, investigations shall be conducted by
an appropriate method to obtain the environmental and loading conditions to which thestructure is subject to.

[Commentary] Concrete structures deteriorate as they are subjected to environmental actions ofsurrounding environment. Varying environmental actions create varying causes for deterioration.
Varying degrees of action cause the rate of deterioration progress to vary. Identifying thecharacteristics of the environment in which the structure has been placed is therefore very important
to appropriate maintenance. Necessary information should be obtained by an appropriate method.
For evaluating environmental actions, the following items should be investigated.
(i)

Meteorological conditions: Temperature (maximum, minimum and mean temperatures),humidity, precipitation and insulation(ii)

Water supplies: Conditions of weathered part of building exterior, conditions of watersupplies from the ground, waterproof layers and drain facilities)(iii) Salt supplies: Amount of air-borne salt from the sea, effects of seawater and amount ofdeicing agent spread)(iv) Loading conditions: Conditions of vehicles and other loads

53

Standard Specifications for Concrete Structures-2007, Maintenance(v)

Other: pH value of highly acid river water, water quality in sewerage facilities handlingwastewater with a high sulfate concentration and occurrence of acid precipitation andacid fog

For investigations for evaluating environmental actions, refer to Chapter 5 “Identification of
Deterioration Mechanism and Prediction of Deterioration Progress.” Investigations should be
conducted for parameters required for estimating the causes for deterioration and predicting
deterioration. Investigations are, however, not necessary for all the parameters. For parametersconcerning meteorological conditions, the data publicized by the Meteorological Agency of Japan
can be used.

4.7.3.8

Tests of materials for repair and strengthening

An appropriate method shall be selected for testing the materials for concrete
structures based on the results of full consideration of the required performances for the
structure to be repaired.

[Commentary] With the increase of concrete structures requiring repair, opportunities also
increase for conducting various tests on repair materials. Only a few methods have, however, beenstandardized concerning repair materials. Before conducting tests, therefore, testing methods should
be fully reviewed. Standards for conducting tests on repair materials are listed below.
JSCE-K 511-2007 Test method for weathering resistance of concrete surface coating materials
JSCE-K 521-1999 Test method for oxygen permeability of concrete surface coating materials
JSCE-K 522-2005 Test method for vapor permeability of concrete surface coating materials
JSCE-K 523-2005 Test method for water permeability of concrete surface coating materials
JSCE-K 524-2005 Test method for chloride ion permeability of concrete surface coating
materials
JSCE-K 531-1999 Test method for bond strength of concrete surface coating materials
JSCE-K 532-2007 Test method for elongation performance of concrete surface coating materials
over concrete crack
JSCE-K 541-2000 Test methods of organic crack injecting materials for repairing in concrete
structures
JSCE-K 542-2000 Test methods of cement crack injecting materials for repairing in concrete
structures
JSCE-K 543-2000 Test methods of polymer modified cement crack injecting materials forrepairing in concrete structures
JSCE-K 551-2000 Test method of grouting organic materials for repairing and strengthening in
concrete structures
JSCE-K 552-2000 Test methods of cement grouting materials for repairing and strengthening in
concrete structures

54

Chapter 4

Investigations in Assessment

JSCE-K 553-2000 Test methods of polymer modified cement grouting materials for repairingand strengthening in concrete structures
JSCE-K 561-2003 Test method of patching repair materials in concrete structures
JSCE-K 571-2005 Test methods of surface penetrates for concrete structures
JSCE-F 561-2005 Method of making specimens for compressive strength of sprayed concrete(mortar)JSCE-F 562-2005 Method of making specimens for durability tests of sprayed concrete (mortar)
JSCE-F 563-2005 Test method for rebound percentage of sprayed concrete (mortar)
JSCE-F 564-2005 Test method for dust concentration in air during spraying concrete (mortar)
JSCE-F 565-2005 Test methods for mechanical properties, spraying performance and durabilityof sprayed concrete (mortar)
JSCE-F 566-2005 Method of making specimens of bond strength of sprayed concrete (mortar)for repairing and strengthening
JSCE-G 564-2005 Test method for length change of sprayed concrete (mortar) for repairing andstrengthening
JSCE-G 563-2005 Test method for strength of sprayed concrete (mortar) for repairing andstrengthening using prism specimens

4.7.3.9

Monitoring investigations

Monitoring investigations shall be conducted by such a method that can provide
information that meets the objective in a designated period of time stably andcontinuously.

[Commentary] Various monitoring methods have recently been proposed and put to practicaluses that enable real-time identification of changes in condition of a structure or member. In
monitoring investigations, the displacement or deformation of the structure, strain of concrete or
reinforcing steel, penetration of deteriorating regions into concrete, or corrosion of reinforcing steel
is identified as required or continuously. Remote control or data collection without field
investigations becomes possible by controlling sensors attached to concrete surface or embedded inconcrete using computers. Monitoring investigations enable the identification of changes in
condition of the structure before the occurrence of external deformation, so they are beneficial inpreventive maintenance.
For monitoring investigations, sensors fit for obtaining required information should be used andsensors need to steadily provide information in the place where it is installed during the specified
period of time. Unless these requirements are fully achieved, no adequate maintenance can be
conducted. In monitoring, information is obtained only indirectly through sensors. In numerous
cases, therefore, whether adequate information is obtained or not needs to be verified by checking
the structure. Then, it is necessary to fully understand the characteristics of instrumentation andconfirm the significance and accuracy of information to be obtained, before conducting
investigations by monitoring.
55

Standard Specifications for Concrete Structures-2007, Maintenance

CHAPTER 5 IDENTIFICATION OF DETERIORATIONMECHANISM AND PREDICTION OF DETERIORATIONPROGRESS
5.1 Principles(1) Deterioration mechanism shall be identified based on the results of investigations
considering the design drawings, materials used, records of construction administrationand verifications, environmental conditions and service conditions.
(2) Progress of deterioration shall be predicted based on the results of investigations
using an appropriate prediction model for identified deterioration mechanism.

[Commentary] (1) Fig. C5.1.1 shows a basic sequence for identification of deterioration
mechanism. If design drawings or construction records are available, specified environmental
condition, service condition and estimated deterioration mechanism at the time of design are usefulfor identification of deterioration mechanism,. Checking the materials used, records of construction
administration and verifications can show potential deterioration factors for the structure and identify
deterioration mechanism. The actual environmental conditions and service conditions of structure
may, however, be different from those assumed in design. Investigations are therefore necessary toconfirm the actual conditions. In cases where data relating to the deterioration indexes or
distinguishing defects has been obtained by investigations, possible deterioration mechanisms can be
narrowed down by consulting 5.2 “Methods for Identification of Deterioration Mechanisms” or Part
2 “Maintenance for Specific Deterioration Mechanisms.”
START
Confirmation of deterioration mechanism andenvironmental actions assumed in design
Identification of deterioration mechanism basedon the materials used and the records ofconstruction administration and verification
Identification of deterioration mechanism basedon the environmental conditions and service
conditions
Estimation of deterioration mechanism based on
the results of investigation (deterioration indexes
and distinguishing defects)
END

Fig. C5.1.1

Basic sequence for identification of deterioration mechanism
56

Chapter 5

Identification of Deterioration Mechanism and Prediction of Deterioration Progress

The deterioration index is an index for assessing the progress or degree of deterioration.
Deteroration factor, deterioration phenomena and deterioration index of each deterioration
mechanism described in Part 2 “Maintenance for Specific Deterioration Mechanisms” are listed inTable C5.1.1. When iinvestigations are carried out to identify the deterioration mechanism,
investigation items should be selected by consulting Table C5.1.1.

Table C5.1.1 Deterioration mechanism, and cause, phenomenon and indexes of deterioration
DeterioraExamples oftion
DeterioraPhenomenon of deterioration
deterioration
mechanis tion factor
indexmDecrease of pH in pore solution due to the
Depth ofchemical reaction between carbon dioxidecarbonation
Carbonati Carbon
and cement hydrate induces the corrosion ofAmount of steelondioxidesteel and it causes the cracking or peeling of
corrosion
concrete or reducing the cross section ofCorrosion-crack
steel.
Chloride
Concentration ofCorrosion of steel in concrete is induced byinducedchloride ion
Chloridechloride ions and it causes the cracking or
deteriorati
Amount of steel
ionspeeling of concrete or reducing the crossoncorrosionsection of steel.
Corrosion-crack
Depth of frost
Freezing and thawing of water in concrete
Frost
Freezing anddeterioration
causes deterioration of concrete surface e.g.,
atackthawingAmount of steel
scaling, micro cracking and pop-outs.
corrosion
Depth ofpenetration ofHardened concrete in contact with acidic
deleterious
Acidicsubstances or sulfate ions is dissolved, or
Chemical
substances
substances
concrete deteriorates due to the expansion
attackDepth ofSulfate ionspressure due to the formation of chemical
carbonation
substances
Amount of steel
corrosion
Reactive silicate minerals contained in
Alkali-sili
aggregates or carbonate rocks chemicallyDegree ofReactiveca
combines with pore solution whose pH isexpansion
aggregates
reactionhigh and it causes irregular expansion or(cracking)cracking in concrete.
Volume of
Cyclic wheel loading on highway bridge
Fatigue of traffic ofDensity of cracks
decks causes cracking or caving-in ofdeck slab large
Deflection
reinforced concrete.
vehiclesCyclic loading on railway bridge causes
Cumulative
Fatigue of
Cycliccracking in tensile steel reinforcements indamagebeam
loadingbeams and it leads fracture of steel
Lengths of cracks
memberreinforcement.
in steel57

Standard Specifications for Concrete Structures-2007, Maintenance

Abrasion

Wearing

Wearing by flowing water or wheel causes
the loss of concrete gradually with time.

Amount ofabrasion
Rate of abrasion

When deterioration mechanism can not be identified by the basic sequence shown in Fig. C5.1.1,
for instance the case in which concurrent deterioration should be considered, detailed investigation
should be conducted focusiong on the deterioration indexes that are relating to the observed
deterioration phenomenon shown in Table C5.1.1. With the results of detailed investigation, eachdeterioration index should be examined whether or not it can explain the deterioration of thestructure refering to Part 2 “Maintenance for Specific Deterioration Mechanisms”. in order to
identify deterioration mechanism.
(2) Prediction of deterioration progress are carried out to estimate future deterioration of thestructure caused by identified deterioration mechanism based on the results of investigations. The
prediction of deterioration progress is essential to the performance evaluation of the structure during
its planned service period and to the judgment of necessity for remedial measures.
Deterioration progress should be predicted quantitatively by using an appropriate model for
deterioration progress based on the existing research results and data obtained by investigations, forinstance the section of the structure, placement of reinforcing bar, quality of concrete and conditionsof steel. For quantitative prediction, the accuracy of the model for deterioration progress appropriate
data in quantity and quality are needed.
In actual situations, investigations are frequently conducted mainly by visual observation andinvestigations are conducted to obtain quantitative data as required. Then, a semi-quantitative
prediction model may be used for prediction in which deterioration may be classified into several
grades and the periods of respective grades can be predicted.

5.2 Methods for Identification of Deterioration Mechanisms(1) In cases where deterioration phenomena has not been observed, deterioration
mechanism should be identified based on the investigation results relating to the extrinsic
deterioration factors of region or member such as the environmental conditions andservice conditions, design drawings and records of construction administrations of thestructure.
(2) In cases where deterioration phenomenon has been observed, defects caused bydeterioration shall be identified and then the deterioration mechanism shall be idenitified
from the characteristics of defects and extrinsic deterioration factors of the region ormember.

[Commentary] (1) In cases where significant deterioration phenomena has not been observed in
the region or member by visual observation or hammer tapping, may be difficult to predict future
deterioration phenomena due to the few available information. However, in cases where ezternal
factors, such as environmental conditions and conditions for using the structure, are specified byinvestigations, or where assumed environmental conditions and service conditions in design havebeen confirmed using design documents, the deterioration mechanism can be estimated to someextent using Table C5.2.1 that lists the relationships between the external factors and deterioration
58

Chapter 5

Identification of Deterioration Mechanism and Prediction of Deterioration Progressmechanisms. For example, in cases where no initial defects or damage has been detected ininvestigation in the initial assessment of a newly constructed structure, no detailed investigation isrequired, and the methods described above may be adopted for estimating the deterioration
mechanism for the time being. Then, however, it should be assumed that the modification of thedeterioration mechanism may be required during the service period.

Table C5.2.1 Possible deterioration mechanisms relationg to the location, environmental
conditions and service conditions of the structure
Extrinsic deterioration factor
Possible deterioration mechanism
Location ofthestructure

Coastal area

Chloride induced deterioration
Frost attack
Chloride induced deterioration
Chemical attack
Alkali-silica reaction
Chloride induced deterioration
Frost attack
Chemical attack
Alkali-silica reaction
Fatigue
Abrasion
Carbonation

Cold district
Spa
Cyclic wetting anddryingEnvironme
ntal
conditions
and service
conditionsof thestructure

Use of de-icing salt
Cyclic loading
Carbon dioxide
Acidic water
Flowing water,
vehicles, etc.

Chemical attack
Abrasion

It is also important that internal factors of concrete structures are reviewed. Because thestructures constructed at the time when there was less awareness of the durability of structures thanat the present are likely to deteriorate because of internal factors. For example, in the years when
the control of standards concerning the use of alkali-reactive aggregate and the desalination of sea
sand were different from today, inappropriate materials may have been used. Existing structures
therefore have deteriorated by alkali-silica reaction and chloride attack, etc. because of the use of
inappropriate materials in some cases. In cases where the quality of concrete is lower than specified
as a design prerequisite because of poor compaction or curing during construction, or whereconcrete cover of steel is not enough, these internal factors can cause deterioration of structures oraccelerate deterioration. Internal factors are closely related to the deteriorations that accelerate thecorrosion of steel with thin concrete covering, for instance chloride attack, carbonation andchemical intrusion.
In cases where defects has not been observed in a periodic assessment during the maintenanceperiod and it is in agreement with the initial prediction of deterioration progress, the deterioration
mechanism estimated in the initial assessment may basically be considered appropriate. External
factors, however, may change with time from those assumed in the initial stage. For structures ormembers to which maintenance type A has been applied, for example, causes for deterioration
should be investigated in each periodic assessment and verified the validity of the estimateddeterioration mechanism.
59Standard Specifications for Concrete Structures-2007, Maintenance(2) In cases where defects have been confirmed in investigations, the defects caused bydeterioration mechanisms should be identified. Then, excluding the types of defects related to theinitial defects and damages from the detected defects such as the cracking, swelling, peeling andspalling, staining and discoloring of concrete and exposure of reinforcing bars, by the following
procedures, defects related to the deterioration can be extracted.
(i) Initial defects
Cracks, honeycombs, cold joints, sand streaking and others those occur during or shortly after
construction are referred to as initial defects. Honeycombs and cold joints can be detected by visualobservatio or hammer tapping even long after the structure is in service.
Whether or not cracking is related to initial defects can be detemined by classyfing the major
causes of cracking: materials, heat of hydration, drying shrinkage, construction and structure, basedon the cracking patterns. For example, as shown in Table C5.2.2, if the cause of cracking can be
estimated from the regularity or shape of cracking, the initiation time of cracking can sometimes be
estimated.

Crackpatterns

Initiation
stage ofcracking

Table C5.2.2 Relationship between cracking and the causes
Inappropriate Heat ofShrinka Conaggregate
hydrationge
struction
Irregular○――○cracking
Regular―○○―cracking
Map cracking○―○○
Early ages
Afterappropriate
aging

○
○

○
―

○
○

○
―

Structure
―
○
○
―
○

When it is estimated that caracks occurs due to the structural cause by the Table C5.2.2, the load
bearing capacity and section force under external forces at the cracked cross section should be
calculated by using the design drawings and investigation results. Based on the calculations, thetype, magnitude and direction of the force, which generates cracks, should be compared with theactual crack patterns. It is fundamental issue to find the cause of the cracking and to investigate theeffects on the safety performance. When the location, width and patter of the cracks are measured,
the cause of cracking during construction can be estimated by consulting Figure C5.2.1 and Table
C5.2.3.
(ii) Damage
The defective events that leads to cracking and peeling occurring when a structure is subject toexcessive forces, such as an earthquake or collision, can be easily distinguished from deterioration
phenomena when the cause of such events is known. When the cause is unknown, the involvementof damage can be recognized by inspecting similar structures near the structure to find similar
defects in them or by assuming that the defects are kinds of damage and assessing the relevance of60

Chapter 5

Identification of Deterioration Mechanism and Prediction of Deterioration Progress

the locations and size of defects as damages.
The seismic performance of a structure can generally be evaluated by checking the standards
conformed to in the design phase.
After the defects due to deteriorations have been identified from the above procedures, thedeterioration mechanism should be estimated based on the relationship between the characteristic ofdefects obtained in the investigations and distinctive phenomena of deterioration mechanisms listed
in Table C51.1.1 considering external factors such as the environmental conditions and service
conditions, and internal factors such as the materials used and construction. For details, it should berefered that the "Apparent grades and deterioration state of structures" provided in the relevant
maintenance standard in Part 2 “Maintenance for Specific Deterioration Mechanisms.”
Fatigue occurs on reinforced concrete slabs of highway bridges and on beams of railway bridges
only in cases where loading effects are significant. When maintaining such members, fatigue should
be first considered as a deterioration mechanism. When adequate consideration have been taken indesign or where outstanding deterioration-related environmental action affects, other deterioration
mechanism should be considered.
When the degree of deterioration of a structure is in phase to significantly affect the safety
performance of the structure, not only physical tests of concrete and analysis of hazardous
substances using core samples but also the investigations of steel arrangement and corrosion
condition are required. Based on the relationship of the investigation results and the environmental
actions, identification of the deterioration mechanism judgment of necessity for remedial measures
should be carried out. Since multiple mechanisms are normaly related to deterioration at this phase,
all the deteriorationg mechanisms involved should be identified, with their contributions to theperformance degradation assessed.

61

Standard Specifications for Concrete Structures-2007, MaintenanceDue to heat of hydration (2)Due to heat of hydration (1)Cracks generated due to the restrained
thermal deformation of newly placed
concrete by existing concrete.

Cracks generated by the difference between
temperature of inside and that of surface area of thestructure, due to cement hydration.

Cracking due to shrinkage caused by inferior materials orpoor mixing

Due to drying shrinkage
Large diagonal cracks occur at theedge of a large wall structure.

Map cracking occurs due to the delay of concrete placement,
the poor quality of cement or aggregate, etc.

Deformation of
formwork

Bleeding

Subsidence

CrackHorizontal
reinforcement

Subsidence cracking

Due to deformation of formwork

Cracks generated by the subsidence of concretearound fixed reinforcement during hardening processof concrete.

Cracks generated by the deformation andmovement of the formwork during
hardening process of concrete.

Due to inappropriate placement oflayers of concreteDue to rapid placement
Cracks generated by thesubsidence of fresh concrete.

Cold joints generated by theinappropriate construction.

Fig. C5.2.1 Examples of initial cracks occurring during construction
62

Chapter 5

Identification of Deterioration Mechanism and Prediction of Deterioration Progress

Table C5.2.3 Causes of cracking
Major
category

Medium category

Minor category

Causes of cracking

Abnormal setting of cement
Heat of cement hydration
Abnormal expansion of cement
Material used
Mud contained in aggregate
Material
Aggregate
Low-quality aggregate
Reactive aggregate
Chloride ions contained in concrete
Concrete―
Subsidence and bleeding of concrete
Shrinkage of concrete
Bathing
Critical betching error
Heterogeneous dispersion of admixtures
MixingLong-time mixing
Change in mix proportion during concrete
Transport
pumping
Inappropriate sequence of placement
Placement
Concrete
Rapid placement
Compaction
Insufficient compaction
Vibration or loading before hardening
Constructio
CuringSettlement and bleeding of concretenFrost attack at early age of concrete
Placement of layers of Inappropriate placement of layers ofconcreteconcrete
Inappropriate arrangement of reinforcing
Arrangementof
Reinforcing bar
bar
reinforcing bar
Insufficient concrete cover
Heaving of formwork
Formwork
Water leakage from formwork to roadbed
Formwork
Early removal of formwork
Supports
Settlement of supports
Difference in temperature and humidity on
Temperature andboth sides of the member
humidity
Cyclic freezing and thawing
PhysicalFire
Environmen
WearingAbrasiontal condition
Chemical action of acid and chloride
Corrosion of internal reinforcement due toChemicalChemical action
carbonation
Corrosion of internal reinforcement due tochloride ions
Dead load
Action while concrete strength is still low
Variable load
Excessive loading in scale and frequency
Loading
Excessive Loading that is not considered as
Accidental load
design load
Structureand external
Lack of cross sectional area and reinforcing―
Structural designforcesbars
Uneven subsidenceDifferential settlement
Support condition―of structure
Frost heaving
Other
Other
Cement63

Standard Specifications for Concrete Structures-2007, Maintenance

5.3 Prediction of Deterioration Progress(1) In the maintenance of a structure, deterioration progress shall be properly predicted
to understand the change in structural performance.
(2) Deterioration progress shall be predicted using an appropriate model in accordancewith identified deterioration mechanism.

[Commentary] (1) The degradation of performance of a structure or a structural member
constituting the structure is caused mainly by deterioration. For properly maintaining structures,
therefore, it is important that proper prediction of deterioration progress of the structure, region ormember according to the deterioration mechanism under service condition. Reflecting the predictionof deterioration progress in performance evaluation or judgement of the necessity and appropriate
time for remedial measures enables effective maintenance.
(2) For predicting deterioration, an appropriate deterioration prediction model should be built
based on the existing research results or knowledge. Described below are the basic ideas forbuilding a deterioration prediction model according to each deterioration mechanism, carbonation,
chloride attack, frost atack, chemical atack, alkali-silica reaction and fatigue. The structural
maintenance methods for respective deterioration mechanisms, and deterioration prediction models
are explained more detail in Part 2 “Maintenance for Specific Deterioration Mechanisms.”
When it is affected by carbonation and chloride attack, the corrosion of steel is a serious issue.
For predicting deterioration induced by carbonation or chloride attack, a model has been proposedthat can predict relatively accurately the intrusion of steel-corroding factors such as carbon depth
and chloride ions ingress. In actual structures, however, the corrosion of steel is frequently
accompanied by cracking or peeling of concrete. Predicting the progress of steel corrosion istherefore also important. Prediction models for corrosion rate are, however, generally less accurate
than the model for predicting the intrusion of carbon dioxides and chloride ions. In maintenance,data can be obtained on actual steel corrosion by investigations. Then, accuracy of prediction can be
improved.
Frost action, chemical intrusion and wear cause deterioration to progress from the surface to theinside of concrete. Though the rate of progress of these deterioration mechanisms has not been fully
grasped, deterioration rate in each structure can be predicted based on the relationship between theelapsed service period and the depth of deteriorated area identified by investigation.
When cracking due to alkali-silica reaction has been confirmed, the reaction has alreadyprogressed to some extent. It is important to determine whether alkali-silica reaction has nearlyceased at the time of investigation or the reaction will continue. To that end, concrete cores are
generally sampled for testing. However, prediction of the deterioration progress of ASR is generally
difficult.
In the case of fatigue of a deck slab, cracking on the deck slab increases by the cyclic loading.
Deterioration progress can therefore be identified qualitatively based on the relationship between
the elapsed service period and the state of cracking.
Predictions vary according to the degree of external forces causing deterioration. Properly
64Chapter 5

Identification of Deterioration Mechanism and Prediction of Deterioration Progress

specifying the deterioration-causing external force acting on the structure, region or member isimportant. In actual structures, multiple deterioration mechanisms may sometimes cause aconcurrent deterioration. When predicting the progress of the deterioration caused by multiple
deterioration mechanisms, it should be noted that the concurrent deterioration is not simply a totalof deteriorations caused by individual deterioration mechanisms. It should also be noted that theaccuracy of prediction is determined by the deterioration of the structure, region or member or by
the performance to be evaluated.
In cases where past maintenance data has been accumulated and adequate information isavailable on a structure in service under similar conditions as the structure to be examined,
deterioration can be predicted relatively easily based on the data. For more efficient and accurate
prediction of deterioration progress, sufficient knowledge is required on the deterioration of thestructure to be studied. Then, deterioration should be predicted under the supervision of aprofessional or.
In the initial stages of maintenance, only insufficient data is obtained and the accuracy of
prediction is inevitably low. In the prediction of deterioration progress, therefore, prediction should
be modified based on the accumulated data obtained in investigations to improve the accuracy of
prediction (Fig. C5.3.1).

構造物の性能の変化（実際）Change in performance of structure (actual)

構造物の性能Performance of structure

Range of predicted

維持管理の初期で行なった
performance of structure at
劣化予測の精度の幅
the initial stage of

maintenance

Mean ofpredicted
performance

Range of predicted
維持管理期間中の点検結果
performance of structureに基づき，修正を行なった
with investigation results
劣化予測の精度の幅
during maintenance

Service period
供用期間

Initial stages of
維持管理の初期段階
maintenance（初期点検）(Initial assessment)

Investigation
during maintenance
維持管理期間中の点検(Routine and/or periodic（日常点検，定期点検等）
assessment)

Fig. C5.3.1 Accuracy of deterioration prediction

65

Standard Specifications for Concrete Structures-2007, Maintenance

CHAPTER 6 EVALUATION AND JUDGMENT
6.1 Principles(1) Performance of the structure shall be evaluated based on the results of investigations.
Idendification of deterioration mechanism and prediction of deterioration progress shall bedone when they are needed.
(2) Necessity for remedial measures shall be judged based on the evaluation of structural
performance considering the remaining planned service period, importance andmaintenance category of the structure.

[Commentary] (1) In the maintenance of structures, it should be needed that constantattention to the change in performance of the structure or a region or member that constitutes the
structure throughout the service period of the structure. In the assessment of a structure, the present
state of deterioration should be identified by standard investigations that are generally conducted ininitial, daily, routine or extraordinary assessments, and by detailed investigations that are conducted
as required and future deterioration should be predicted. Based on the results, the performance ofthe structure, region or member at the time of investigation and at the end of planned service period
should be evaluated quantitatively, and the necessity for remedial measures should be judged.
Evaluation methods, however, vary according to the quality and quantity of data obtained ininvestigations. It should also be noted when evaluating structural performance that the required
performances can vary according to the regions or members that constitute the structure.
No evaluation methods have been established for the hazards for third party, or aesthetic
appearance and landscape. For safety and serviceability, equations for evaluation are not fully
accurate and quantitative evaluation is frequently difficult. As a more practical method, therefore,
condition of a structure at the time of investigations and condition during the remaining service life
can be predicted based on the investigation results by comparing them with the grades that havebeen specified in advance. Poorer grades should be selected when evaluation is difficult.
The performance of a structure should basically be evaluated both at the time of investigation(at present) and at the end of remaining service life. When a long service life is remained, theevaluation of performance can be carried out with a specified evaluation period as tentative target(Fig. C6.1.1). Repeating the process enables performance evaluation during the service period.
In cases where emergency measures are required, performance may be evaluated frominvestigations without predicting of deterioration progress. There also may be cases where
structural performance can not be evaluated properly because of the difficulty in estimating thedeterioration mechanism. After remedial measures are taken in these cases, the effect of emergency
measures should be identified properly by conducting an increased number of investigations, anddata should be collected for evaluating the performance of the structure more properly.
Evaluation of performance of a structure should be done by a professional engineer, responsible
engineer or engineer who has equivalents knowledge about the design, construction andmaintenance of concrete structures.
(2) Necessity for remedial measures shall be judged based on the performance of the structure,region or member evaluated properly in respective investigations. In cases where the performance66Chapter 6

Evaluation and Judgmentof the structure fails to meet the required performances at the time of investigation, remedial
measures are determined to be necessary.
When future performance of a structure will fail to meet the requirements though no remedial
measures are needed at the time of investigation, the need of remedial measures should bedetermined considering the prediction of deterioration progress, remaining planned service life,
importance of the structure, maintenance category and higher level maintenance plans for a groupof structures or throughout an area. In this case judgment should be done by a responsible engineer.

Prediction of change inperformancebased on
点検結果に基づく保有
investigation
results
性能の変化の予測

性能

Performance

Performance

性能

Change in performance
expectedat the time of initial
初回点検時に予測されinvestigation
Prediction of change in
た保有性能の変化
performance based on
点検結果に基づく保有
investigation results
性能の変化の予測

Required
performances
要求性能
At点検時
the time of
予定供用期間終了時
At the end of planned
investigation
service period
供用期間
Serviceperiod(Performance evaluation undernormal conditions)

Required
performances at
目標として設定した時点での要求性能point in timea designatedRequired
performances
要求性能

Initial
初回点検
assessment(維持管理開始）(start ofmaintenance)

目標として設specified 予定供用期間終了時
At thetime of PointAt the end of
点検時
定した時点
as a target
investigation
planned service
供用期間
periodService period(Performance evaluation in the caseof a long planned service period)

Fig. C6.1.1 Planned service period and performance evaluation (conceptual view)

6.2 Evaluation and Judgment in Initial Assessment
6.2.1 GeneralIn the initial assessment, performance of structure shall be evaluated and necessity for
remedial measures shall be judged using appropriate methods in accordance with theobjective of the initial assessment.

[Commentary] The initial assessment is the first assessment conducted at the start ofmaintenance based on an established maintenance plan. The objectives of the initial assessment are
not only to identify the condition of the structure before maintenance but also to obtain initial values
for evaluating structural performance in subsequent periodic assessments and to verify the validityof the prepared maintenance plan and amend it when it is needed. The results of the evaluation of
performance and judgment of the necessity for remedial measures in the initial assessment
determine the basic approach to subsequent maintenance of the structure. Performance should be
evaluated as quantitatively as possible.

6.2.2 Evaluation based on investigations in initial assessment
Performance of the structure at the start of maintenance and during the remaining
67

Standard Specifications for Concrete Structures-2007, Maintenanceplanned service life shall be evaluated based on the condition of the structure confirmed in
the initial assessment. Idenitification of deterioration mechanism and prediction ofdeterioration progress shall be done when they are needed.

[Commentary] Performance has rarely been deteriorated at the time of initial assessment for a
newly constructed structure or a structure for which remedial measures have been taken on a large
scale. Then, in cases where it has been verified in the initial assessment from records that no initialdefects, damage or deterioration was detected or the structure is free from any problem in designand construction owing to appropriate repair, the performance of the structure at the time ofinvestigation, or at the start of maintenance, can be evaluated to be equivalent to the performance
assumed in the design phase (or when remedial measures were taken). The performance of astructure up to the end of the planned service period can be evaluated somewhat quantitatively byusing a verification method described in design documents and considering the data obtained instandard investigations such as the state of the structure, environmental conditions and service
conditions.
For existing structures, it may be evaluated that the required performances have been met atleast at the start of maintenance if it has been confirmed that the structure is free from any initialdefects, damage or deterioration. There are, however, cases where some defects are observed in anexisting structure. In this case, the causes of defects should be identified by investigations. If thedefects are ascribed to damage or initial defects, the affects of defects on the required performancesof the structure should be examined. If the defects are ascribed to deterioration mechanisms, thedeterioration mechanism should be identified and deterioration progress should be predicted, andthe performance of the structure, its region or member at the time of investigation and during theremaining planned service life should be evaluated as quantitatively as possible.
For many cases in existing structures, durability performance was not verified in the designphase, and records of design and construction was lost. Then, by the standard investigation in theinitial assessment, it is difficult to identify the cause of defects and predict the performance properlyat the time of investigation and during the planned service period. In this case, detailed
investigations should be conducted as required to evaluate the performance quantitatively. Recordsof structures with environmental or service conditions similar to those of the structure to be
examined may also be considered for reference. For details of performance evaluation in cases
where detailed investigations are conducted, refer to 6.5 “Evaluation and judgment based on thedetailed investigations.”

6.2.3 Judgment based on investigations in initial assessment(1) In cases where deterioration phenomenon has been observed in the initialassessment, necessity for remedial measures shall be judged considering the evaluatedperformance of the structure in the period between the initial assessment and the end of theplanned service period, and the content of the maintenance planning.
(2) In cases where initial defects or damage has been observed in investigations in theinitial assessment, the effect of the defects on the structure shall be reviewed andappropriate actions shall be taken.

[Commentary] (1) In cases where deterioration has been confirmed in the initial assessment, thenecessity for remedial measures shall be judged based on the results of performance evaluation at
68

Chapter 6

Evaluation and Judgment

the time of initial assessment and the end of the planned service period of the structure conductedbased on 6.2.2 “Evaluation based on the investigations in the initial assessment”, remained planned
service period, importance and maintenance category of the structure. When detailed investigations
are carried out, the necessity for remedial measures should be judged in accordance with 6.5“Evaluation and judgment based on the detailed investigations.”
In the initial assessment, the accuracy of performance evaluation at the end of the planned
service period is not so high because the remaining service life is long generally. In cases where theperformance at the end of the planned service period is lower than the requirement, therefore, noremedial measures need to be taken immediately. Periodic assessments should be conducted inaccordance with the maintenance plan that has been reviewed based on the results of investigationsin the initial assessment, and actual performance degradation should be confirmed to review thenecessity for remedial measures.
(2) In cases where initial defects or damages such as cracks, honeycombs, cold joints and sandstreaks have been found in a structure, region or member in investigations in the initial assessment,
the effects of the defectsion on the structure should be properly examined. In cases where the initialdefect or damage can facilitate deterioration, or exert a bad influence on the performance of thestructure, appropriate remedial measures should be taken. The "Design" and "Construction"
volumes of the Standard Specifications, and the Practical Guideline for Investigation, Repair andStrengthening of Cracked Concrete Structures prepared by the Japan Concrete Institute. can berefered in the investigations or identification of defects and judgment of the necessity for remedial
measures.
When hazard for third party caused by the falling of concrete pieces is concerned, emergency
measures should be taken immediately after investigation (4.2 “Investigations in the Initial
Assessment”).

6.2.4 Review of maintenance plan based on results of initial assessment
In cases when performance of the structure can not be evaluated or necessity for
remedial measures can not be judge properly based on the results of initial assessment, themaintenance plan shall be reviewed.

[Commentary] If it has been confirmed by the initial assessment that the performance of astructure can properly be evaluated during its planned service period in accordance with the
prepared maintenance plan, the structure will be maintained in accordance with this maintenanceplan. In cases when it has been found that the condition of the structure is different from that in
preparing maintenance plan, regardless of the necessity for remedial measures, the maintenanceplan shall be reviewed so that the performance of the structure can be evaluated more properly.
In cases when initial defects and damages have been found in investigations in the initialassessment, raegardless of the remedial measures, review of the maintenance plan will be required
depending on the degree of the defects.

6.3 Evaluation and Judgment in Periodic Assessments

69

Standard Specifications for Concrete Structures-2007, Maintenance6.3.1 GeneralIn periodic assessments, performance of structure shall be evaluated and the necessity
for remedial measures shall be judged using appropriate methods in accordance with theobjective of periodic assessments.

[Commentary] In periodic assessments, routine and periodic assessments are conducted to verify
the change in performance of the structure with time.
In investigations in routine assessments, the effect of defects on the structure is evaluated basedon the newly found defects or the change of existing defects observed in routine assessments.
Investigations in routine assessments are conducted at short intervals and help finding defects inearly stage. Performance may therefore be evaluated qualitatively by a rapid and simple method.
Investigations in regular assessments are conducted at intervals of several months to years as
designated in the maintenance plan. Comparing investigation results with the results of preceding
investigations enables quantitative evaluation of the performance at the time and the degree ofchange in performance.
Since periodic assessments are conducted to periodically verify the state of the structure, region
or member in accordance with the maintenance plan, results of investigations should be comparedwith the state assumed in the maintenance plan. If the rate of performance degradation can be
confirmed based on the results of investigations at different time, the performance in the remaining
service life can be quantitatively evaluated.

6.3.2 Evaluation and judgment based on investigations in routine assessments(1) Performance of the structure shall be evaluated and the necessity for remedial
measures should be judged based on the change in performance of the structure, region
and member observed by comparison of results of investigations in routine assessments.
(2) In cases where defects have been observed by investigations in routine assessment,
identification of deterioration mechanism, prediction of deterioration progress andjudgment of necessity for remedial measures shall be carried out.

[Commentary] The objective of investigations in routine assessments is to find the change ofthe structure in its early stage by conducting simple tests (e.g. visual observations and hammer
tapping) at short intervals. If no change has been found by investigations in routine assessments, thestructure can be evaluated as in the assumed condition in the maintenance plan and no remedial
measure is needed..
In cases when new deterioration phenomena, damages or initial defects have been found byinvestigations in routine assessments, the cause should be identified and the degree of defects
should be evaluated considering the following.
Identification of causes of deterioration phenomena, damages and initial defects: Defects that
occurs on concrete surface as time elapses include cracks, stain of rust, separating out of substancesfrom concrete and deformation that are ascribed to specific deterioration mechanisms, ascarbonation, chloride attack, frost attack, chemical attack, alkali-silica reaction, fatigue and wear.
70

Chapter 6

Evaluation and Judgment

Also included are structural damage due to the action of accidental load or uneven subsidence offoundations, exposed initial defects owing to poor materials or construction, and cracks in repaired
sections due to re-deterioration.
Deterioration can occur in all structures due to environmental actions or material properties, andprogresses with time. It is important to evaluate the progress of deterioration and maintaining thestructure considering the degree of deterioration. On the other hand, neither damages nor initialdefects is planned to occur in structures. Once damages and initial defects are found, appropriate
remedial measures should be taken corresponding to the degree of its effect on the functions of thestructure. In cases when any defects has been confirmed, whether the deformation is deterioration,
damage or initial defect should first be identified. Deteriorationg mechanism should be also
identified in case of deterioration. Cracks or deformation that has been predicted in design is notincluded in defects.
Identification of the cause of defects should be carried out in accordance with 5.2 “Methods for
identification of deterioration mechanism.” The deterioration mechanism should be estimatedconsidering external and internal factors and based on the condition of defects (pattern and width ofcracks, existing of stain of rust, water leakage, calcium carbonate and scaling of concrete, range andtone of discoloration, etc.). The characteristics of defects found in major deterioration mechanisms
are shown in Part 2 “Maintenance for Specific Deterioration Mechanisms.”
Evaluation of the degree of deterioration phenomena, damages and initial defects: Standard
investigations in periodic assessments mainly consist of visual observations. The degree ofdeterioration phenomena, damages and initial defects should therefore be evaluated by those
appearances. Then, evaluating the degree of defects according to its grade is useful. The degree of
defects identified by investigations in routine assessments can be evaluated by grading of thefollowing characteristic appearances on the structure.
-Location, pattern, quantity, length and width of cracks-Location and area of delamination, peeling, spalling and a section where abnormal sound is
heard-Location and area of a section subject to scaling or deterioration-Existence and degree of stain of rust, calcium carbonate and water leakage
It is efficient that the degrees of defects are classified into (i) allowable, (ii) whether allowable
or not is uncertain or (iii) not allowable, from the point of veew to ensure the required performancesof the structure in the manual for investigations in routine assessments. Criteria should be specified
by the authority considering the service conditions and required performances of the structure,region or member.
When detailed investigations are conducted, evaluation of performance and judgment of thenecessity for remedial measures should be carried out in accordance with 6.5 “Evaluation andjudgment based on the detailed investigations.”
When defects are identified as initial defects or damages, or hazard for third party should beconsidered, evaluation of performance and judgment of the necessity for remedial measures should
be carried out in accordance with 6.2.3 “Judgment based on the investigations in the initialassessment.”71

Standard Specifications for Concrete Structures-2007, Maintenance6.3.3 Evaluation of performance based on investigations in regular assessments
In cases where defects have been observed in investigations in regular assessments, thecause of defects shall be identified and the effect of defects shall be evaluated. If the defectis regarded as deterioration, the performance of the structure, region or member shall be
evaluated based on the change of condition identified by comparing investigation resultswith records of past investigation.

[Commentary] The advantage of investigations in regular assessments is more extensive
information at the different time of investigations than that of routine assessments. More detailed
and quanitative information can be obtained by investigations in regular assessments, because not
only visual observations and hammer tapping but also by tests with non-destructive test machinesand core samples can be carried out with temporary scaffold. When defects are found in periodic
investigations, cause of defects and the degree of defects should be evaluated as quantitatively as
possible by the method described in 6.3.2 “Evaluation and judgment based on the investigations inroutine assessments.” When deterioration phenomena are found, identification of deterioration
mechanism and prediction of deterioration progress should be carried out by comparing
investigation results with past results, and the performance of the structure at the time ofinvestigation and during the remaining planned service period should be evaluated as quantitatively
as possible.
When detailed investigations are conducted in regular assessments, evaluation of performance
should be carried out in accordance with 6.5 “Evaluation and judgment based on the detailed
investigations.”

6.3.4 Judgment based on investigations in regular assessments(1) In cases where deterioration has been observed in investigations in regularassessments, necessity for remedial measures should be judged considering the evaluatedperformance of the structure, region or member from the time of investigation till the end of
the planned service period; and importance, maintenance category and economic efficiencyof the structure.
(2) In cases where the initial defects or damage has been observed in investigations inregular assessments, it shall be examined and appropriate measures shall be taken
considering the effect of defects or damage on the structure.

[Commentary] (1) Judgment of necessity for remedial measures based on the results of periodic
investigations should be carried out based on the results of performance evaluation of the structure,region or member at the time of investigation and at the end of planned service period, and theimportance of the structure, maintenance category, higher level maintenance plans for a group of
structures or throughout an area, and cost-effectiveness. When detailed investigations are conducted,
judgment of necessity for remedial measures should be carried out in accordance with 6.5“Evaluation and judgment based on the detailed investigations.”(2) When defects are identified as initial defects or damages, or hazard for third party should beconsidered in periodic investigations, consideration should be done in accordance with thecommentary (1) in 6.2.3 “Judgment based on the investigations in the initial assessment.”72

Chapter 6

Evaluation and Judgment

6.4 Evaluation and Judgment in Extraordinary Assessments
6.4.1 General
In extraordinary assessments, performance of structure shall be evaluated and necessity
for remedial measures shall be judged immediately using appropriate methods inaccordance with the objective of extraordinary assessments.

[Commentary] Investigatons in extraordinary assessments and emergency assessments are
conducted in extraordinary assessments. Investigations in extraordinary assessments are conducted
mainly in structures that have been subjected to accidental external forces such as natural disasters
and fire. Investigations in emergency assessments are conducted in structures that have specificcharacteristics which cause defects in similar structures and need to be examined. Investigations in
extraordinary and emergency assessments are not pre-planned, but they should be implemented
quickly in case of necessity. It is important that evaluation of structural performance and thejudgment of necessity for remedial measures are carried out immediately using suitable methods forthe objective of each assessment. To that end, investigations in estraordinary and emergency
assessments should be conducted by a professional engineeror the responsible engineer.

6.4.2 Evaluation based on investigations in extraordinary assessments
Performance of the structure at the time of an extraordinary assessment shall be
immediately evaluated properly based on the results of investigations in order to quick
implement of remedial measures preventing injury, death, great social and economic impact
caused by collaps and destruction.

[Commentary] Structures can collapse in the worst case when extraordinal force affects in anatural disaster or an accident. Though structures can avoide their collapse or fail, safety
performance can be lost by a natural disaster or accident. It is difficult to avoid risk in the midst of anatural disaster or an accident, social and economic impacts by secondary disasters or the disruptionof lifeline can be prevented with quick countermeasures, designated off limits to the adjacent area tothe damaged structure, extraordinary supports for the damaged structure. In order to takeappropriate measures for a damaged structure, performance to be restored should be identified as
quickly as possible evaluationg the present safety performance, serviceability and hazards for third
party of the structure and considering the condition around the structure.
In investigations in the extraordinary assessment conducted due to revision of design standards
during the service period of a structure, present compliance of the structure with standards shouldbe evaluated and the performance at the end of the planned service period should also be evaluated.
When detailed investigations are required in extraordinary assessments, the evaluation of
structural performance in orde to judge the necessity for remedial measures should be conducted as
quickly as possible. When detailed investigations are conducted in a structure for which
extraordinary remedial measures have already been taken, to ensure the safety of subsequent
services, the performance in service conditions should be evaluated. When detailed investigations
are conducted in extraordinally assessments, evaluation of performance should be carried out inaccordance with 6.5 “Evaluation and judgment based on the detailed investigations.”73

Standard Specifications for Concrete Structures-2007, Maintenance6.4.3 Judgment based on investigations in extraordinary assessments(1) In cases where defects that can cause hazards for third parties or affect the service ofthe structure has been observed, remedial measures shall be reviewed immediately.
(2) In cases where no problem has been observed in structural performance at the time ofan extraordinary assessment, it may be considered as no immediate remedial measures areneeded.

[Commentary] (1) Structures damaged under accidental loading during an earthquake or othernatural disaster plaied an important role in the phase of regional restoration in many cases. On theother hand, collapse of structures due to damage can be hazardous to numerous people in thevicinity. The needs of emergency measures to damaged structures are, therefore, eztremely high instricken areas. When the necessity for remedial measures can be judged solely by visualobservations, appropriate repair or strengthening should be applied immediately. Whne no remedial
measures can achieve the required performances, service should be restricted immediately or the
structure should be removed. It is important to introduce alternative methods quickly that have
similar functions.
(2) In extraordinary assessments, top priority is given to prompt action. When structural
performance at the time of assessments is sufficient, it can be judged as no remedial measure isnecessary. Detailed investigations should, however, be conducted at an appropriate time after
extraordinaly situation has finished, to evaluate structural performance in the period between the
point of investigation and the end of planned service period and to judge the necessity for remedial
measures while the structure is under normal service conditions. When detailed investigations are
conducted in extraordinally assessments, the necessity for remedial measures should be judged inaccordance with 6.5 “Evaluation and judgment based on the detailed investigations.”
When the performance of an existing structure at the time of investigation or in the period up to
the end of the planned service period can not conform to the standards after design standards wererevised, appropriate remedial measures should be taken. In case of inadequate seismic resistance,
basic idea for maintenance is shown in Chapter 17 “Basics of Seismic Retrofit.”

6.4.4 Evaluation and judgment based on investigations in emergency assessments
In cases where defects have been observed in a structure similar to the one that was
subject to the defects causing an accident in investigations in emergency assessments,
remedial measures shall be reviewed immediately. In cases where defects have not been
observed, necessity for remedial measures shall be judged considering possibility ofoccurrence of defects by the end of the planned service period.

[Commentary] Investigations in emergency assessments are conducted when defects of astructure has caused an accident or serious defects has been found in a structure by periodic
assessments, to verify whether or not similar defects has occurred in similar structures. Whensimilar defects are found in another structure, remedial measures should be taken immediately. In
cases there is a risk of hazard for third parties, emergency measures should be taken.
When no deformation has been confirmed in investigations in emergency assessments, it is74

Chapter 6

Evaluation and Judgment

determined that no risk is involved at present. Even in such cases, however, data should be collectedon the design standards applied to the structure, materials used and construction methods ininvestigations, the possibility of change in performance in the period up to the end of the planned
service period should be evaluated, and the necessity for remedial measures including intensified
investigations should be judged.

6.5 Evaluation and Judgment based on Detailed Investigations(1) Performance of the structure should be evaluated and necessity for remedial
measures should be judged based on the quantitative results of detailed investigations.
(2) Performance of the structure at the time of investigations shall be evaluated based on
the results of the detailed investigations in order to confirm that the required performance isachieved.
(3) Performance of the structure at the end of its planned service period shall be
evaluated using the predicted deterioration progress based on the results of the detailed
investigations in order to confirm that the required performance is achieved.
(4) In cases where the required performance is not achieved in the performance
evaluation described in (2) and (3), adoption of remedial measures shall be considered.

[Commentary] (1) Detailed investigations conducted in respective assessments provide detailed
data on the structure, region or member to be examined. Evaluaton of performance and judgment of
the necessity for remedial measures based on the results of detailed investigations should be
conducted quantitatively in principle. The obtained data should be first used to identify the cause of
defects. If the defects are caused by deterioration, the deterioration mechanism should be identified
and deterioration progress should be predicted quantitatively. Then, using the results, theperformance of the structure, region or member at the time of investigation and during its planned
service period should be evaluated quantitatively. Finally the necessity and timing of remedial
measures should be judged.
However, for some attributes of performance, quantitative evaluation can not be applied becauseof absence or inaccuracyof proposed evaluation equation. Then, the performance of the structure
should be evaluated as quantitatively as possible with semi-quantitative evaluation by the grading of
the appearance of the structure and other results in detailed investigations.
Evaluation of performance and the judgment of necessity for remedial measures should be
conducted by a professional engineer or the responsible engineer because the results may
sometimes greatly change the maintenance plan of the structure.
(2) Detailed investigations help identify the condition of a structure, region or member in detail.
Then, various performance attributes should be evaluated based on the results of investigations, andwhether required performances have been achieved or not should be verified. Described below are
the methods for evaluating the structure, region or member at the time of detailed investigation.
Sagety Performance: The load bearing capacity of the region or member should be calculatedusing appropriate equations for evaluation. Then, whether performance will be evaluated in crosssection, member or throughout the structural system should first be estimated. When making
evaluations concerning the loss of load bearing capacity due to the corrosion of steel, for example,
75

Standard Specifications for Concrete Structures-2007, Maintenancethe effect of steel corrosion can be evaluated by the loss of cross section of steel. Then, however,
evaluation can be made only in extremely local sections of the structure. On the member or
structural level, however, evaluation and judgment should be made in close consideration of tthe
effects of complicated change s in the bond properties. On the structural level, the condition ofdeterioration or how loads are carried varies from member to member. The fact that these effects
greatly influence the load bearing capacity should be considered when making evaluations. The
range of evaluation should be selected properly by considering the degree of deterioration, details ofinvestigations, reliability of evaluation equations, importance of the structure, maintenance category
and remaining service life.
Once the range of evaluation has been determined, an equation for evaluating the load bearing
capacity should be specified in view of the equation used in design standards, to calculate the load
bearing capacity. Whether or not the calculated load bearing capacity sufficiently exceeds the acting
loads or stress resultant should be determined to evaluate the load bearing capacity of the structure,region or member. The parameters in the equation for evaluating the load bearing capacity need toexpress the state of deterioration properly. It should be made possible to specify the loss of effective
cross section of concrete as a parameter in cases of frost action or chemical attack, or the loss ofsteel cross section due to steel corrosion or change in bond characteristics as parameters in cases ofcarbonation or chloride attack.
The safety factors throughout performance check can be considered to be nearly equivalent tothose assumed in design. The values of safety factors should be specified fully considering thevolume and accuracy of data collected during detailed investigations, and the degree ofdeterioration of the structure, region or member, importance of the structure, maintenance category
and remaining service life.
Safety performance other than load bearing capacity, such as stability and ductility, should be
evaluated and judged based on the same policy as for the load bearing capacity.
Serviceability performance: In regard to the serviceability performance, the required
percormance can be verified directly by using indices obtained from investigations, such as
deflection, vibration properties, inclination and water leakage. Then, serviceability can be evaluatedby determining whether investigation results satisfy the evaluation criteria or not. The stiffness of amember may be evaluated using evaluation equations like the safety of the member.
Hazards for third party and Aesthetic appearance and landscape: The hazards for third party
should be evaluated and judged as the risk of delamination, cold joints, etc. of concrete that cancouse injury people and/or property by falling concrete fragments. For the safest evaluation andjudgment, it may be assumed that cracking can impair the performance related to hazards for third
party. When defects have occurred such as concrete swelling and cold joints with people or property
located below, the performance requirements related to hazards for third party are as a rule notsatisfied, requiring emergency treatment and remedial measures.
Aesthetic appearance and landscape should be evaluated from the aspect of the possibility ofcracking, scaling, stain or rust or stain of leakage damages aesthetic appearance of the structure orlandscape, or causes discomfort to viewers or make them feel insecure. Aesthetic appearance andlandscape are evaluated subjectively. Evaluation is therefore difficult in numerous cases. People
engaged in maintenance should evaluate aesthetic appearance and landscape considering thecondition of deterioration of the structure, maintenance category, importance and location of thestructure and remaining service life.

76

Chapter 6

Evaluation and Judgment

Grading:
All types of performance to be evaluated should be evaluated quantitatively based on the resultsof detailed investigations as described above. No evaluation equations may, however, be available
for some performance attributes, or evaluation equations may not be sufficiently accurate for otherattributes. Then, using highly practical semi-quantitative evaluation methods according to grading
instead of methods based on the results of performance check has been considered allowable.
Evaluation can be made as described below using a semi-quantitative method.
First, the relationship of the grade of external deformation with the progress of deterioration to
the stage of deterioration (initial, progressing, accelerating and deterioration), and the relationshipof the grade of deformation to the performance deteriorated at the stage should be identified. For the
relationships for respective types of deterioration, refer to Part 2 “Maintenance for Specific
Deterioration mechanisms.” Then, the degree of deterioration of the structure inspected should be
evaluated according to the grade based on the results of detailed investigations. The present
condition of performance degradation should be evaluated based on the relationship between thegrade of deformation and the performance damaged.
(3) Deterioration progress should be predicted based on the quantitative data obtained indetailed investigations. Based on the prediction, safety performance, serviceability, hazards for third
party, and aesthetic appearance and landscape at the end of planned service period should be
evaluated, and the degradation of performance of the structure should be predicted.
Performance at the end of planned service period may be evaluated by estimating the values ofparameters in the evaluation equation at the end of planned service period based on the prediction ofdeterioration progress if an evaluation equation is available. In reality, however, sufficientknowledge has not yet been accumulated on deterioration prediction and parameters used in
evaluation equation can not be estimated with sufficient accuracy. Then, performance may beevaluated according to the grading.
(4) When it is found by performance evaluation conducted as described in (2) and (3) that therequired performances will not be achieved at the time of investigation or at the end of planned
service period, remedial measures should be considered. When considering the implementation ofremedial measures, it is important to comprehensively consider maintenance category, performance
attribute to be evaluated and the degree of performance degradation, importance of the structure,importance of the region or member subject to deterioration or damage, cost-effectiveness, andhigher level maintenance plans for a group of structures or throughout an area. When taking
remedial measures such as repair and strengthening, the appropriate time of implementation should
also be examined.

77

Standard Specifications for Concrete Structures-2007, Maintenance

CHAPTER 7 REMEDIAL MEASURES

7.1

Principles(1) In cases where remedial measures are considered necessary, the performance to beachieved shall be determined considering the importance of the structure, maintenancecategories, remaining planned service period, deterioration mechanism and the degree of
performance degradation of the structure. Then, appropriate remedial measures shall betaken considering the ease of maintenance and cost performance after the remedial
measures.
(2) When taking remedial measures, plans shall be prepared for enforcement andpost-implementation maintenance. In cases where the deterioration mechanism has been
identified explicitly for the structure, Part 2 should be consulted before taking remedial
measures.
(3) In cases where defect that is likely to cause problems immediately has beenrecognized such as the hazards for third party, appropriate emergency measures shall betaken promptly.

[Commentary] (1) In cases where remedial measures have been found necessary because thedegradation of present or future performance of a structure is an issue, the authority engaged in themaintenance of the structure should determine the performance to be achieved and take appropriate
remedial measures. Remedial measures are required in the following cases: (i) cases where thepresent performance of the structure is below the allowable limit, (ii) cases where the performanceof the structure is expected to fall below the allowable limit during the remaining planned service
period based on deterioration prediction although the structure is free from any problem at present,
and preventive measures are required, and (iii) cases where remedial measures are necessary tomeet revised design criteria concerning the loading and seismic resistance.
Remedial measures include the intensified investigation, repair, strengthening, functional
improvement, restriction in service, and dismantling/removal (7.2 “Types and Selection of
Remedial Measures”). The performance to be achieved should be determined considering theimportance of the structure, maintenance categories, remaining service life, and the condition ofdeterioration or performance degradation of the structure, and remedial measures should be selectedconsidering the ease of maintenance after the implementation of measures and life-cycle cost.
In cases where the deterioration mechanism has been explicitly identified, appropriate
measures should be taken consulting Part 2.
Performance should be (i) restored to a level midway between the time of construction andpresent, or maintained at the present level, (ii) restored to the level at the time of construction or(iii) carried out to a level higher that at the time of construction.

78

Remedial Measures

Performance to be achieved≈
Performance at the time of
construction

Performance to be achieved ＞
Performance at the time of
construction

Performance at thetime of construction

Performance at thetime of construction

Performance at thetime of construction

Performance tobe achieved

Performance tobe achievedTime(i)Restoration of performance to a levelmidway between the time of construction
and present, or maintenance of present levelof performance

Performanceof structure

Performance to be achieved <Performance at the time of
construction
Performanceof structure

Performanceof structure

Chapter 7

Time

Performance tobe achievedTime(ii)Restoration of performance to the level at (iii)Carring out to a level higher that at thetime of construction
the time of construction

Fig. C7.1.1 Levels of performance to be achieved(2) When taking remedial measures, the deterioration mechanism or the degree of
performance degradation of the structure should first be identified, and plans for enforcing remedial
measures and for maintaining the structure after remedial measures are taken should be prepared.
Approaches to the enforcement of remedial measures according to the type of remedial
measure are described below. For intensified investigation or restriction in service, the maintenanceplan should be reviewed and the reviewed plan should be used for enforcing remedial measures. For
repair, strengthening, functional improvement or the dismantling/removal of the structure, thedesign and construction plans for the remedial measure should be used for enforcement.
Approaches to the preparation of a maintenance plan after the enforcement of remedial
measures are described below. For intensified investigation or restriction in service, the plan for
enforcement the remedial measure is the same as the maintenance plan after the enforcement of themeasure. In cases of repair, strengthening or functional improvement, a maintenance plan should be
prepared that explicitly shows the frequency of investigation, items and methods of investigation
and remedial measures to be taken in cases where performance is deteriorated to a level below therequirements, to ensure that the required performances may be maintained during the remaining
planned service period. If only a short remaining service life has been left, materials and methods
can be selected from among numerous types, and a maintenance plan can be prepared relatively
easily after the enforcement of remedial measures. If a long remaining service life is available,
however, a maintenance plan should be prepared considering the life-cycle cost because remedial
measures are taken several times. In cases where the structure is demolished or removed, nomaintenance plan is required.
The plans for enforcement remedial measures and for maintaining the structure after theenforcement of remedial measures vary according to the deterioration mechanism even where thedegree of performance degradation is the same. In cases where the deterioration mechanism has
been explicitly identified, plans for enforcement remedial measures and for maintaining thestructure after the enforcement of remedial measures should be prepared consulting Part 2.

79

Standard Specifications for Concrete Structures-2007, Maintenance(3) Selecting remedial measures, preparing plans for enforcement remedial measures and formaintaining the structure after the enforcement of remedial measures, and enforcement remedial
measures require certain time. In cases where adverse hazards for third party are expected due to thefalling of concrete pieces, for example, appropriate emergency measures should be taken quickly
such as the restriction in service, placement of the affected area off limits and application of
spalling-proof netting.

7.2
7.2.1

Types and Selection of Remedial Measures
GeneralRemedial measures shall be selected properly from the intensified investigation, repair,strengthening, functional improvement, restriction in service and dismantling/removal of
the structure.

[Commentary] This Specification classifies remedial measures during the period of maintenanceinto six categories. The types of remedial measures that are selected based on the performance ofthe structure and the level of performance to be achieved after the enforcement of remedial
measures are listed in Table C7.2.1. Table C7.2.2 shows examples of relationships between the
result of structural evaluation and the remedial measure that can be selected. The table shows thatthe intensified investigation, repair, strengthening, restriction in service, or dismantling/removal of
the structure is selected as a remedial measure in cases where safety is an issue, and that theintensified investigation, repair, functional improvement, restriction in service, ordismantling/removal of the structure is selected as a remedial measure in cases where serviceability
is an issue. In cases where traffic lanes are increased as a result of an increase of traffic volume orwhere the function of the structure is carried out by installing sound proofing walls, strengthening islikely to be selected.
In cases where a problem has an adverse effect on pedestrians or vehicles like the falling of
concrete pieces, repair is generally selected as a remedial measure. In cases where the aesthetic
effect of the structure has been deteriorated by cracking or peeling, rust stain or staining, theappearance is restored or improved by repair. Maintenance category C is applicable to structuresthat need to be maintained only through indirect observation because direct investigation are
difficult. For these structures, repair or strengthening should be carried out according to thecondition of the structure.

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Chapter 7

Remedial Measures

Table C7.2.1 Types of remedial measures according to performance
Level of performance to be achieved and type of remedial measure
Structural
performance(i)Level midway between thetime of construction and present,or present level of performance(ii) Level at the time of
construction(iii) Level higher than at
the time of construction

SafetyIntensified investigation, repair
or restriction in service

RepairStrengthening

Serviceability

Intensified investigation, repair
or restriction in service

RepairFunctional improvement or
strengthening

Hazards for third
party

Intensified investigation, repair
or restriction in service

Repair－Aesthetic
appearance andlandscapeIntensified investigation or repair

RepairRepairDurability

Intensified investigation, repair
or restriction in service

RepairRepairTable C7.2.2 Examples of remedial measures selected based on the results of evaluation
Remedial measure
Structural
performance

SafetyResult ofevaluation

I

Intensified
investigation

RepairStrengthening

Functional
improvement

Restriction
in service

Dismantling/removalof structure

Maintenancecategories

Maintenancecategories

Maintenancecategories

Maintenancecategories

Maintenancecategories

Maintenancecategories

A

A

A

A

A

Serviceability

Aesthetic
appearance
andlandscapeDurability

I

O

O

O

O3

O

O

O

O

O

O
O

I

O
O

II

II

C

O3

O1,3

B

C

O

O

O

O

O

O1

O2

O

II

I

B

B

C

B

C

A

B

C

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O

O
O

II
Hazards forthird party

C

O

II
I

B

O

O

O1

O2

O

O
O2

O

O

O1

O

O
O

O

O

O

O:Remedial measure that can be selected
Result of evaluation I:Likely to cause a problem，II:A problem is involved
Notes 1:Classified as C because no direct investigation is possible， 2:In cases where the objective is to improve functions
3:In cases where safety is increased to the level at the time of construction81Standard Specifications for Concrete Structures-2007, Maintenance

7.2.2

Intensified investigation

Intensified investigation shall be carried out by reviewing the maintenance planconsidering the results of evaluation and judgment of the necessity for remedial measures,
remaining planned service period and specifying the appropriate frequency and items ofinvestigation.

[Commentary] Intensified investigation involves the increase of investigation frequency and ofinvestigation items in cases where repair or strengthening has been considered necessary but cannot
be enforced immediately or where the present state is observed without enforcement any measures.
When intensified investigation, the maintenance plan should be reviewed considering the results ofevaluation and judgment of the necessity for remedial measures or the remaining planned service
period, and appropriate investigation frequency and items should be determined.

7.2.3

RepairRepair shall be carried out so that the designated performance can be achieved,
based on the appropriate implementation plan for repair and the post-repair maintenanceplan. For details, refer to 7.3 Repair and Strengthening.

[Commentary] The objectives of repair in this Specification are to remove the hazards for third
party, restore or improve aesthetic appearance or landscape or durability, and restore the mechanicalperformance related to safety or serviceability to the level at the time of construction.
The objectives of repair are described below.
(i) To restore concrete structures deformed by cracking or peeling(ii) To remove concrete that has incorporated deterioration factors due to chloride ion
permeation or carbonation(iii) To prevent the permeation of hazardous substances by surface coating or to prevent
damage to third parties due to the falling of concrete pieces(iv) To guarantee the aesthetic appearance or landscape of the structure(v) To restore the serviceability of structures requiring watertightness by preventing leakage ortaking other measures
Repairing the structure to intercept deterioration factors or control the progress of deterioration
while the deterioration is still hidden reduces the burden of maintenance after the repair.
When repairing a structure, preparing plans for enforcement and post-repair maintenance isimportant. Then, materials and methods should be selected considering the durability of thestructure after the repair.

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Chapter 7

7.2.4

Remedial Measures

Strengthening

Appropriate plans shall be prepared for strengthening and post-strengthening
maintenance. For details, refer to 7.3 “Repair and Strengthening.”[Commentary] In this Specification, the objective of strengthening is to improve the mechanicalperformance related to safety or serviceability above the level at the time of construction.
Methods of strengthening are described below.
(i) Replacing concrete members(ii) Increasing the sectional area of concrete(iii) Adding members(iv) Increasing support points(v) Adding reinforcing materials(vi) Applying prestress
Appropriate plans should be prepared for strengthening the structure and maintaining thestructure after the strengthening in accordance with the “Design” volumes of the Standard
Specifications and “Guidelines for Strengthening of Concrete Structures (draft),” or based on otherstandards carried out to the design of the structure, so as to meet the designated mechanical required
performances. Then, materials and methods should be selected considering the durability of thestructure after the strengthening.

7.2.5

Functional improvement

When improving the functions of the structure, the required functions shall be
determined, and appropriate implementation plans and maintenance plans after thefunctional improvement shall be prepared.

[Commentary] Functions of a structure are carried out by adding new functions by increasing
traffic lanes to carry increased traffic volume or by installing sound proofing walls. Functional
improvement may sometimes involve strengthening. For functional improvement, appropriate plansfor enforcement and for maintenance after the functional improvement should be prepared inaccordance with the standards carried out to the design of the structure or other standards so as tomeet the designated required performances. Then, materials and methods should be selectedconsidering the durability of the structure after the functional improvement.

83

Standard Specifications for Concrete Structures-2007, Maintenance

7.2.6

Restriction in service

When restricting the service of a structure, the degree and method of restricting loads
shall be determined based on the results of evaluation and judgment of the necessity for
remedial measures. Appropriate implementation plans and maintenance plans after the
implementation shall be prepared and executed.

[Commentary] Restriction in service involves restricting loads or vehicle velocity without
repairing or strengthening the structure. Service is generally restricted simultaneously with theintensified investigation until the change of use (e.g. from a pedestrian sidewalk to a roadway),
repair, strengthening or dismantling/removal of the structure.
When restriction in service, it is important to determine the load or speed limits according to
the deterioration mechanism of the structure or the degree of performance degradation. To that end,loading tests or vibratory loading tests should be conducted. When restriction in service as well as
when intensified investigation, the maintenance plan should be reviewed based on the results ofstructural evaluation and judgment of the necessity for remedial measures, and the remaining
planned service period, and the frequency and items of investigation should be specified properly.

7.2.7

Dismantling/removal of structure

Structures shall be demolished or removed in accordance with appropriate
enforcement plans considering the effects on the surrounding environment, work safety,
disposal of waster after dismantling, team of construction and cost performance.

[Commentary] Structures are demolished or removed in cases of obsolescence due todeterioration, removal or renovation as a result of functional loss, river improvement, improvementof highway or railway alignment, enforcement of redevelopment projects, etc.
For dismantling or removing a structure, a method fit for the structure should be selected. The
method should be selected fully considering the effects on the surrounding environment, worksafety, waste recycling or reusing methods, construction period and cost performance.
When dismantling/removal, it is desirable to investigation in detail by loading tests or othermeans the relationship of structural performance degradation and material deterioration for the
purpose of improvement of engineering level of maintenance.

7.3
7.3.1

Repair and Strengthening
Principles(1) When repairing or strengthening a structure, design shall be performed for repair orstrengthening based on the results of assessments and preliminary investigation, andappropriate plans should be prepared for proper enforcement and for maintenance after84

Chapter 7

Remedial Measures

the repair or strengthening.
(2) Structures shall be repaired or strengthened in accordance with an enforcement
plan, and shall be managed and verified properly during and after the repair orstrengthening.
(3) When repairing or strengthening a structure, region or member for which thedeterioration mechanism has been explicitly identified, Part2 should be consulted.

[Commentary] (1) When repairing or strengthening a structure, the state of the structure shouldbe verified by investigation. Design and construction, and post-enforcement maintenance plans
should be prepared. Construction, administration and verification should be carried out inaccordance with the plans.
In preliminary investigation, it is important not only to check design documents, construction
reports or maintenance records but also to verify design conditions, state of construction, defect of
the structure and environmental actions and loading by directly investigating the structure, and to
identify the restrictions and problems during construction.
In the design of repair or strengthening, the performance to be achieved and the area of repair
or strengthening should be determined, and the method, materials and specifications that satisfy therequired performances should be selected. The enforcement plan should specify the area, procedureand method of construction fully considering the objective of design and field enforcement
conditions in order to implement the repair or strengthening measure properly.
In repair or strengthening, the state of the structure may sometimes change because additional
materials are carried out to an existing structure. Installing additional monitoring equipment may
become necessary to identify the progress of defect. The above points should be taken into
consideration when a plan for maintenance after repair or strengthening is prepared.
(2) Structures should be repaired or strengthened properly in accordance with an enforcement
plan. Materials and the construction method should be managed and verified during construction. At
the completion of repair or strengthening, verifications should be conducted to check the results ofadministrative testing for materials and construction method and to confirm whether repair orstrengthening has been completed as planned or not.

7.3.2

Design of repair or strengthening(1) In the design of repair or strengthening, principles of repair or strengthening tomeet designated required performances shall be defined, and appropriate materials andmethod should be selected.
(2) In the design of repair or strengthening, whether or not the structure, region ormember repaired or strengthened meets the designated required performances shall beverified by an appropriate method.

[Commentary](1) When repairing or strengthening a structure, the principle, area, method and85

Standard Specifications for Concrete Structures-2007, Maintenancematerial should be selected, and the structure should be repaired or strengthened considering thefollowing points.
(i) Present condition of the structure to be repaired or strengthened: Dimensions, arrangementand diameter of steel, etc.
(ii) Results of evaluation of the structure and judgment of the necessity for remedial measuresin assessments(iii) Deterioration mechanism(iv) Importance of the structure: E.g. a bridge on a route important for living(v) Environmental condition: Meteorological condition and the location of the structure, e.g. ina mountainous or coastal area(vi) Load condition: E.g. cyclic traffic load is predominant on bridge deck slabs and seismic
load is predominant on bridge piers(vii) Restrictions on construction: Time of construction, period, time available for construction
and construction environment (securing work space at the site, noise, vibration, odor, etc.)(viii) Combinations of repair or reinforcing materials, thickness of surface coating, crosssectional area after repair or strengthening, construction method, etc.
(ix) Maintenance: Ease of maintenance after repair or strengthening(x) Remaining planned service period
Table C7.3.1 lists principles of repair or strengthening, components of repair or strengthening
work and factors to be considered for meeting required performances for respective deterioration
mechanisms.
In the design of repair or strengthening to restore or improve the mechanical performance suchas safety and serviceability, it is important to ensure that the required performances for the structure
are met throughout the remaining service life in accordance with “Design” volumes of the Standard
Specifications, “Guidelines for Strengthening of Concrete Structures (draft)” and design standards
for the structure. The design for repair or strengthening is different from the design of a new
structure. Considerations for construction unique to the design for repair or strengthening should
therefore be identified in advance. The method and materials should be selected also considering
maintenance after the repair or strengthening.
Table C7.3.2 lists major methods for restoring or improving the mechanical performance ofstructures in accordance with “Guidelines for Strengthening of Concrete Structures (draft).”
Various researches are now being conducted and case studies of applications are now being
accumulated. No techniques may therefore be yet available that fully satisfy designated required
performances. Then, the methods or materials should be selected on the assumption of re-repair or86

Chapter 7

Remedial Measures

re-strengthening. The characteristics of methods or materials should be identified in detail, andmethods or materials should be selected based on test results or records of applications.
Major repair or strengthening methods currently put into practice are listed in Fig. C7.3.1.

Table C7.3.1 Principles and methods of repair according to deterioration mechanism
Deterioration
mechanism

Carbonation

Chloride attack

Frost attack

Chemical attack

Alkali-silica
reaction

Fatigue (concrete
deck slabs on
highway bridges)

Abrasion

Principle of repair

Components ofrepair method-Remove concrete in whichcarbonation occurred-Control the infiltration of CO2
and water after repair-Patching-Surface
treatment-Re-alkalization-Patching-Remove Cl- that intruded-Surface-Control the permeation of Cl-, treatment
water and oxygen after repair-Desalination

Factors to be considered for meeting
required performances-Degree of removal of sections ofconcrete in which carbonation occurred-Prevention of corrosion of reinforcing
bars-Quality of materials for patching-Quality and thickness of materials forsurface treatment-Alkali amount in concrete-Degree of removal of sections subjected
to permeation-Prevention of corrosion of reinforcing
bars-Quality of materials for patching-Quality and thickness of materials forsurface treatment-Anode materials -Quality of anode materials
Potential control for reinforcing-Electric power -Amount of polarization
bars
unit
-Resistance of patching materials tofreezing and thawing-Remove deteriorated concrete-Patchingof corrosion of reinforcing-Control water infiltration after -Crack injection -Prevention
bars
repair-Materials and method for crack injection-Improve the resistance of concrete -Surface
treatment
to freezing and thawing-Quality and thickness of materials forsurface treatment-Quality of materials for patching-Remove deteriorated concrete-Patching-Quality and thickness of materials forsurface treatment-Control the permeation of -Surface
hazardous substances
treatment-Degree of removal of deteriorated
concrete-Water treatment-Control water supplies(starlingand-Accelerating the diffusion of drainage)-Materials and method for crack injection
internal water-Crack injection-Quality and thickness of materials for-Control alkali supplies-Surface
surface treatment-Control expansion
treatment-Restore member stiffness-Jacketing-Water treatment(drainage)-Control the progress of cracking-Waterproofing-Restore member stiffness-Integration with existing concreteof deck slabs
members-Restore shearing load bearing -Adhesion
capacity-Increaseofthickness-Quality of materials for patching-Restore lost cross section-Patching-Bond-Restore or improve roughness -Surface-Resistance to abrasion
coefficient
treatment-Roughness coefficient87Standard Specifications for Concrete Structures-2007, Maintenance

Table C7.3.2 Examples of methods for restoring or improving mechanical performance
Applicable member
Wall*Beam Colu
Slab
mn
2
OO
O
OO
O
OO
O
OO
O
O

Carried out toMethodMajor
method*1

Concrete member

Adhesion
JacketingPrestressing
Increase of
sectional thickness
Replacement ofmembers

Adhesion
JacketingExternal cable
Increase of
thickness
ReplacingO

Addition of beams

Additional
installation
Additional
installation
Additional
installation
Seismic
isolation

OO

Addition of walls
Structure

Addition of
support points
Seismic isolation

Gener
al

O

Bear
ing

OO
O

OO

OO

OO
OO

OO

OO

OO

OO

OO:Put to practical use in numerous cases，O: Considered applicable*1: Adhesion: Steel plate adhesion and FRP (fiber reinforced plastic) adhesion (continuous fiber reinforced sheetadhesion and continuous fiber reinforced plate adhesion)Jacketing: Steel plate jacketing, FRP jacketing (continuous fiber reinforced sheet jacketing and continuous fiber
reinforced plate jacketing), reinforced concrete jacketing, mortar shotcrete and precast panel jacketing
Prestressing: External cable and internal cable
Increase of thickness: Increase of top surface thickness, increase of bottom surface thickness and bottom surface
shotcrete
Additional installation: Addition installation of beams, earthquake-resistant walls and support points*2:Wall-type bridge piers are included(2) In the design for repair or strengthening, the performance of the repaired or strengthened
structure should be checked using an appropriate method and whether the performance can beachieved or not should be verified.
In the inspection of the design for repair for restoring or improving durability, numerically
identifying the performance to be achieved is difficult at the present technological level unlike forthe load bearing capacity or stiffness. Then, the period of guarantee of durability determined by the
repair method, material configuration, specifications and other parameters may be categorized into(i) long period equivalent to the remaining service life of the structure, (ii) intermediate period or(iii) short period, for the purpose of inspecting the design for repair.
Post-repair or -strengthening mechanical performance of the structure should basically beinspected in accordance with “Design” volumes of the Standard Specifications using the loading
conditions, material properties and structural specifications related to the performance to bechecked. Then, the state and area of defect, and structural specifications should be fully identified
by conducting investigation in advance, and the effective section or area to be repaired orstrengthened should be specified properly. The loads to be carried out should be properly selectedconsidering investigation results and the performance to be inspected.

88Chapter 7

Remedial Measures

Panel installation
Embedded form
SurfaceOrganic coating

Coating

Inorganic coating

Coating

Sheet application

coating

Surfaceprotection

Silane-type impregnation

Surface
impregnant

Mesh application

Silicate-type impregnation
Other type of impregnation
Plastering
Shotcrete

Patchimg

Dry shotcrete
Wet shotcrete

Major repair or strengthening method

Repair method for restoring or
improving durability

Mortar
FillingPre-packed
Planar anode
Impressed
current system

Electricalprotection

Galvanic anodesystemUsing fiberElectrochemicalcorrosion
protection

Attaching panels

Desalination

Ponding
Using fiber
Re-alkalization

Attaching panels
Using sheets
Underwater construction
Supplying waterElectrodii

Surface coating

Crack
repairInjection

Replacement
Additional
installation

Beams
Support points

Increase of
thickness

Top surface

JacketingFiber reinforced plastic

Lower part
Concrete

Steel plate
Adhesion
Prestressing

Organic injection
Inorganic injection

Filling
Impregnation

Repair or strengthening method for restoringor improving dynamic performance

Concrete

Fiber reinforced plastic
Steel plate
External cable

89

Linear anode
Rod anode
Planar anode
Rod AnodeStandard Specifications for Concrete Structures-2007, MaintenanceFig. C7.3.1 Major repair or strengthening methods applied for concrete structures
The performance of a repaired or strengthened structure becomes effective through the
integration of the repair or reinforcing material and the existing structure. The degree of integration
should therefore be inspected properly. The performance not only of the repaired or strengthened
region or member but also of the structure system should be inspected. This is because repairing or
strengthening the region or member is likely to cause the behavior of the structure system to change
considerably from that before the repair or strengthening.

7.3.3

Execution of repair or strengthening(1) The execution plan for repair or strengthening shall be prepared based on thedesign fully considering construction restrictions.
(2) Repair or strengthening shall be carried out carefully in accordance with theexecution plan considering the characteristics of the method and materials to be adopted,
specifications and considerations.
(3) When carrying out repair or strengthening, the items and methods for effective andeconomical construction management or verification during construction or at thecompletion of work shall be specified to verify whether the designated required
performances have been met or not.

[Commentary] (1) When carrying out repair or strengthening, an appropriate execution planshould be prepared in accordance with 7.3.2 “Design of Repair or Strengthening” fully considering
construction restrictions. In cases where repair or strengthening has not been carried out inaccordance with the execution plan, not only the designated required performances may not be met
but also maintenance after the completion of work is likely to be greatly affected. The purpose ofdesign should therefore be fully understood and an appropriate execution plan should be prepared.
Typical jobs included in the execution plan for repair or strengthening are listed in Fig. C7.3.2.
(2) Repair or strengthening should be carried out carefully by professional engineers withadequate construction technical expertise in accordance with the execution plan. When carrying out
repair or strengthening, understanding the characteristics of the method and materials used and thepoints to remember is necessary because the preparation work and construction method vary
according to the method, material or specification of repair or strengthening.
(3) When carrying out repair or strengthening, the items and methods for effective andeconomical construction management or verification fit for the method, material and specification
should be defined. In cases where verifications have found that no required performances have beenmet, appropriate measures should be taken to achieve the objective.

90

Chapter 7

Remedial Measures

Investigation for construction

Investigate the present state of the structure, construction
restrictions, etc.

Preparation of execution plan

Prepare an execution plan in accordance with the design
and the results of investigations

Preparations

Carry out preliminary work required before repair orstrengthening, e.g. assembly of scaffolding

Repair or strengthening

Carry out repair or strengthening following thepredetermined steps in accordance with the execution plan

Verification

Conduct investigation to verify whether repair orstrengthening work has been completed as designed
based on the items and methods of verifications

Fig. C7.3.2 Typical jobs included in execution plan for repair or strengthening

7.3.4

Maintenance after repair or strengthening(1) After repair or strengthening, the structure shall be maintained properly so that it
can maintain the designated performance throughout the remaining planned service
period.
(2) Even in cases where a region or member of the structure has been repaired orstrengthened, the entire structure shall be maintained properly.

[Commentary] (1) After repair or strengthening, the designated required performances of thestructure should be satisfied during the remaining planned service period or during the service
period specified in the design for repair or strengthening. The continuity of the effect of the repair
or strengthening needs to be verified. To that end, the maintenance of the repaired or strengthened
structure is important. The maintenance plan before remedial measures are taken should be
reviewed and a new maintenance plan should be prepared also considering the repair orstrengthening that has been performed. Then, the new maintenance plan should be used as a basis
for diagnosing the structure using an appropriate method (investigation deterioration prediction,
evaluation of structural performance and judgment of the necessity for remedial measures), records
the results of assessments and taking new remedial measures as required.
After repair or strengthening, visual observations of an existing structure may sometimes
become impossible in cases where a certain method, e.g. surface treatment, adhesion or jacket, hasbeen enforced. Methods should therefore be considered that enable direct or indirect investigationof existing structures. Installing monitoring equipment may sometimes be effective.

91

Standard Specifications for Concrete Structures-2007, Maintenance

Deterioration after repair or strengthening should be predicted comprehensively based on theinvestigation results considering the process of deterioration after repair or strengthening including
the deterioration of the materials constituting existing structures, and of the deterioration of theintegration of the materials used for repair or strengthening and the existing structure. In cases
where the structure has been deformed again during the remaining planned service period or during
the service period specified in the design for repair or strengthening, and it has been determined thatthe designated performance requirement would not be met and that taking additional remedial
measures would be required, the design and construction method for repair or strengthening that has
been carried out should be reviewed (area, method, materials and specifications), and appropriate
remedial measures should be taken to maintain the designated required performances.
(2) Repairing or strengthening some members or a limited number of regions may partly
change the environmental or loading actions on the structure. As a result, stress distribution, water
distribution in concrete, objects transfer characteristics and electrochemical balance may change
and defect is likely to occur that is different from that in cases where no repair or strengthening has
been carried out. There is also a possibility that new defect may occur in a member or region thathas not been repaired or strengthened and that the progress of defect may become a major cause of
performance degradation for the structure system. In cases where a member or region has been
repaired or strengthened, not only the repaired or strengthened member or region but also thestructure system should be maintained properly.

92Chapter 8

Recording

CHAPTER 8 RECORDING

8.1 Principle
In the maintenance of a structure, the results of assessments and the remedial
measures taken shall be appropriately recorded and stored in accordance with themaintenance plan.

[Commentary] In order to maintain a structure efficiently and rationally, necessary information
should be made accessible as reference data for future use. Such information should contain basic
data of structures, standards and specifications applied to design and construction of structure, theresults of a series of assessments conducted while the structure is in service such as investigations,prediction of deterioration progress, evaluation and judgment,; or the results of remedial measurestaken such as repair and strengthening.
The maintenance records can be used for verifying the validity of the maintenance plan or
maintenance technology adopted. Moreover, analysis of the records by clarifying problems andrequired improvements in design and construction from a viewpoint of maintenance, can contributeto progress in technology which can be reflected in design, construction and maintenance plans for
similar structure in future. Records constitute a database on the condition of structures. Structures
should be diagnosed and remedial measures should be taken after studying the past records in detail.
After completing such a task, the results should additionally be incorporated into the records tokeep them up to date.

8.2 Method of Recording
Recording shall be preserved using appropriate method(s) in a fixed format such thatthey can be easily referred to.

［Commentary］Structures are in service for a long period of time. It should therefore be noted thatthe change of maintenance organization or replacement of person in charge during the period. Then,
records should be kept in such a format as to facilitate the understanding of the history of
maintenance. Consequently, the records should provide as accurate and objective data as possible.
The results of a series of assessments from investigation to prediction of deterioration progress,
evaluation of structural performance and judgment of necessity of remedial measures should berecorded using a certain method. To that end, a method fit for the structure should be designated inadvance.
For recording, an intelligible format should be used according to the maintenance category,
the kind and detail of maintenance and the kind of the structure. Records on the maintenance of astructure may sometimes constitute a large volume of data. In cases where numerous structures aremaintained collectively, even larger volumes of data may be managed. Building an efficient
database system and keeping it in a digital format for easy access are desirable. Records need to be
kept for a long time, during which the system may be modified. It should be made sure that records
can be used even in case of system modification. Writing the history of maintenance directly on the
structure may be effective.

93

Standard Specifications for Concrete Structures-2007, Maintenance

8.3 Items to be Recorded(1) The items to be recorded during the assessment of a structure should include thenames of persons maintaining the structure and of those conducting the assessment on acontractual basis, basic data of the structure, loading and other environmental conditions,
category of maintenance, method and results of investigations in the assessment, method
and results of deterioration prediction, the results of evaluation of structural performanceand judgment of necessity of remedial measures.
(2) In cases where remedial measures have been taken such as repair and strengthening,the details of design and construction for repair or strengthening, and the names of
persons maintaining the structure and of those conducting assessment on a contractual
basis shall be recorded.

[Commentary] (1) Examples of typical items to be recorded during maintenance are listed in Table
C8.3.1. Points to remember in respective types of investigations are described below.
Recording in initial assessment: In the investigations in initial assessment, in case initial defects arefound, the location and state of an initial defect, contents of evaluation and judgment (identified
deterioration mechanism, condition of segments, members and structure, judgment of necessity fordetailed investigation) should be recorded in addition to the items given in Table C8.3.1. In cases
where a detailed investigation has been conducted, the items, method, scope and results of theinvestigation; and the results of evaluation and judgment of necessity for remedial measures should
be recorded.
Recording in periodic assessment: In investigations in routine assessment, the date of investigation,
name of investigator and whether there is any defect or not generally need to be recorded. In cases
where defect has been recognized, the type, location and condition, and the results of evaluation andjudgment of necessity for detailed investigation should be recorded. In investigations in regularassessment, in case any defect is found, the type and location of defect, whether it is in progress ornot, contents of evaluation and judgment (identified deterioration mechanism, condition ofsegments, members and structure, judgment of necessity for detailed investigation) should berecorded in addition to the items given in Table C8.3.1.
In cases where the detailed investigation has been conducted in routine or regular assessment,
the methods of investigation (e.g. method and location of collecting samples, equipment used andanalysis method and the location and method of nondestructive testing), and the type, location andcondition of detect should be recorded as in as much detail as possible. The prediction of thedeterioration progress basing on the investigation (discussions on the variance from the predicted
deterioration progress in the initial assessment), results of evaluation and judgment (conditions of
the region or member and results of examination of remedial measures), names of the maintenanceengineers (chief manager, responsible engineers, professional engineers and investigators) and of
the people conducting assessment on a contractual basis, if any, should be recorded.
Recording in extraordinary assessment: Investigations in extraordinary or emergency assessment
are conducted in case of an accidental event such as earthquake, fire and collision. The items to berecorded in standard investigations in extraordinary or emergency assessment are the details of theaccidental phenomenon, objective of investigation, location and condition of damage, results ofevaluation and judgment (condition of segments, members and structure, judgment of necessity fordetailed investigation) in addition to the items given in Table C8.3.1. In cases where detailed
investigations have been conducted, the same items should be recorded as those in detailed
94

Chapter 8

Recordinginvestigations in regular assessment.
(2) In cases where repair, strengthening or other remedial measure has been taken, thedeterioration of the structure before the measure was taken, timing of implementation, weather, airtemperature, method and region of construction, kinds and specifications of materials used, curingmethods, quality management methods, and inspection methods and results should be recorded. The
names of maintenance engineers (chief manager, responsible engineers and professional engineers)and people conducting assessments on a contractual basis (responsible engineers and professional
engineers) should also be recorded.

8.4 Storage of Records
Records should be stored during the service period of the structure.

[Commentary] The maintenance records of a structure should be stored while it is in service
because the records serve as a basis for efficient and rational maintenance. Records should desirably
be stored beyond the service period of the structure inasmuch as possible because they may be
useful for maintenance of maintaining other similar structures.

95

Standard Specifications for Concrete Structures-2007, Maintenance

Table C8.3.1 Examples of typical items to be recorded during assessment
and application of remedial measures

GeneralItem to be recorded
Name of people
in charge

Maintenance manager(e.g., chief manager, responsible engineers, professional
engineers and investigators)

Specifications
for structure

Name, loads, surrounding environmental conditions,planned service period, maintenance type and maintenancerecords for the structure
In initial, routine, regular, extraordinary or emergency
assessment

Type

Remedial measureevaluation
andJudgment

prediction

Assessment

Investigation

Timing
Location
Item
MethodTiming of conducting investigation-Maintenance manager
Chief manager
Detailed location of the structure or member to be investigatedResponsible engineers
Professional engineers
Items to be investigated
Investigators
For respective items(detailed descriptions are required for non-standard methods)

ResultFor respective items, testing and judgment

MethodModel, equations or parameters used

ResultInitial, progressing, accelerating and deterioration periods

MethodCalculating methods, standard and criterion used

Grading

Grading of the appearance of the structure

ResultResults of evaluation and judgment for region, member or
structure
Maintenance manager (e.g., chief manager, responsible
engineers, professional engineers and investigators)
Contractor taking remedial measure (e.g. responsible
engineers and professional engineers)
Enhancement of investigations, repair, strengthening,
restrictions on service and demolition or removal

Name of people
in charge
Type

People held
responsible

MethodConstruction plan documents and drawings

RecordTiming, drawings, execution reports and history

96-Contractor conducting
Assessment
Responsible engineers
Professional engineers-Maintenance manager
Chief manager
Responsible engineers
Professional engineers
Investigators-Contractor
takingremedial measures
Responsible engineers
Professional engineersPart 2
Maintenance for Specific Deterioration Mechanisms

Chapter 9

Maintenance of Structures Subject to Carbonation

CHAPTER 9 MAINTENANCE OF STRUCTURES SUBJECT TO
CARBONATION
9.1 General(1) This chapter provides standard methods for the maintenance planning,assessment, remedial measures and recording for structures that have been or are
highly likely to be subject to performance degradation due to carbonation. The
items common to all deterioration mechanisms are shown in Part 1.
(2) This chapter shall be applied to structures of the maintenance categories A(preventive maintenance) and B (corrective maintenance).

[Commentary] (1) Carbonation in concrete structures means the carbonation reaction of the
carbon dioxide and cement hydrate as a result of the penetration of the carbon dioxide of the air into
concrete, which causes the pH value in voids of concrete to fall. Carbonation destroys thepassivation film on the steel surface in concrete, and corrosion progresses with supplies of oxygenand moisture. The corrosion of steel then induces cracking, peeling of concrete cover and reductionof the load bearing capacity. Carbonation transforms all types of hydrates including calcium silicate
hydrate. It has also been known that the change of the structure of voids in hardened cement causes
the change in strength and shrinkage due to carbonation.
This chapter discusses only carbonation attributable to carbon dioxide. Carbonation caused byother acidic substances is discussed in "Chemical Attack."
This chapter refers to reinforced concrete, prestressed concrete and steel-concrete composite
structures subject to carbonation and the description focuses on carbonation mainly related toreinforced concrete. Structures with protective layers on concrete surface such as mortar and surface
coatings or structures used in formwork are also intended. The deterioration of the protective layer
itself is not included. It should, however, be noted that such performance attributes as aesthetic
appearance and landscape, and hazards for third party of the entire structure including the protective
layer may be considerably degraded due to the deterioration of protective layers.
Deterioration due to carbonation and steel corrosion progresses during the initiation stage,
propagation stage, acceleration stage and deterioration stage (Fig. C9.1.1 and Table C9.1.1). In eachstage, deterioration has varying influences on the structure. The degree of performance degradation
with the progress of deterioration also varies according to the performance attribute. The methodsof assessment (investigation, deterioration prediction, evaluation or determination), remedial
measures implementation and recording vary in respective deterioration stages.
A standard maintenance procedure against carbonation is shown in Fig. C9.1.2.
In composite deterioration due to carbonation and chloride attack, the deterioration due tochloride attack is accelerated by carbonation. For the maintenance against the composite
deterioration, refer to Part2, Chapter 2 "Maintenance of Structures Subject to Chloride Attack."

97

Deterioration
Performancedegradation of member due to carbonation

Performance
Deterioration
degradation of member due to carbonation

Standard Specifications for Concrete Structures-2007, MaintenanceFig. C9.1.1

Conceptual view of deterioration progress due to carbonation

Table C9.1.1
Stage ofdeterioration

Definition of deterioration stages
Definition

Factor determining
the stage

Initiation stage

Until the depth of carbonation reaches thelimit state for the occurrence of corrosion

Rate of carbonation

Propagation stage

From the initiation of corrosion of steel until
cracking due to corrosion

Rate of steel
corrosionAcceleration stage

Stage in which steel corrodes at a high rate
due to cracking due to corrosion

Deterioration stage

Stage in which load bearing capacity is
reduced considerably due to increased steel
corrosion

Rate of corrosion ofsteel with cracks(2) Maintenance category B (corrective maintenance) has been designated for numerous
existing structures. In the future, maintenance category A (preventive maintenance) is expected to
be designated for more structures. In maintenance category A, remedial measures are taken early
before performance degradation due to deterioration in view of the life-cycle cost. This chapter
therefore mainly discusses structures to which maintenance category A or B is applied. Structures towhich maintenance category C (observation-based maintenance) is applied should also be
maintained by a basic method described in this chapter wherever possible.

For the matters that should be considered when determining the maintenance category forstructures that have been or are expected to be subject to deterioration due to carbonation, refer to9.2.2 "Maintenance Category." Special matters to be considered for respective maintenancecategories are also described in this chapter.
98

Chapter 9(9.2)

Possibility ofcarbonation(9.3)

Maintenance of Structures Subject to Carbonation

Maintenanceplan for the
structure

Assessment(9.3.2.2)
Investigations ininitial assessment
Standard
investigation(9.3.2.5)
Detailed
investigation(9.4)(9.3.3)(9.3.4)

Deterioration
prediction

Remedial
measures(9.5)
Recording

Evaluation andjudgment(9.3.2.3, 4)
Investigations inroutine/regularassessment
Standard
investigation(9.3.3)(9.3.4)(9.3.2.5)
Detailed
investigation

Deterioration
prediction
Evaluation andjudgment

Fig. C9.1.2 Standard maintenance procedure against carbonation

9.2 Maintenance Planning
9.2.1 Basis of planning
In order to maintain a structure subject to carbonation, the category of maintenanceshall be selected, the service period planned, and a maintenance planning for activities
including assessment, remedial measures and recording drawn up in advance in view ofthe service and environmental conditions such as the concrete drying conditions andwater supplies.

[Commentary] When drawing up a maintenance planning, it is necessary to cover such details ascheck items and procedures for initial assessment and check items, procedures, timing andfrequency for the investigations in routine and regular assessment, evaluation and judgment
methods, actions to be taken in the event of deterioration, and recording methods, taking into
consideration the type, degree of importance and planned service period of the structure, category of
maintenance, and the quality of materials.
The type of structure, size and environmental conditions of concrete structures vary fromstructure to structure. A maintenance planning must be optimized for each structure. The progress ofdeterioration of structures subject to carbonation in particular is greatly affected by the depth of99

Standard Specifications for Concrete Structures-2007, Maintenancecarbonation in concrete cover, and humidity and oxygen supplies that cause steel to corrode. An
appropriate maintenance planning needs to be drawn up, therefore, in view of these factors.
It is usually difficult, at the stage of maintenance planning, to accurately predict the state of astructure during its service period. It is therefore good practice to draw up a maintenance planningwith reference to the deterioration of a similar structure or a structure in a similar environment.

9.2.2 Determination of maintenance category
The category of maintenance of a structure subject to carbonation shall be selected inview of the degree of importance of the structure, the type of structure, hazards for third
party, the planned service period and the characteristics of deterioration due tocarbonation.

[Commentary] The determination of the category of maintenance is very important because
maintenance planning varies widely depending on the category of maintenance. The progress ofdeterioration and performance degradation due to carbonation is conceptually illustrated in Fig.
C9.1.1.
Structures to which maintenance category A (preventive maintenance) is applied should bemaintained so that they might be placed under the condition during the initiation stage with no steel
corrosion, to prevent performance degradation. The state of the structure should therefore be
identified as accurately as possible. Requirements include the following.
(i) Quantitative identification and prediction of the depth of carbonation(ii) Quantitative identification and prediction of the corrosion of reinforcing bars in concrete
For structures with maintenance category A, remedial measures are taken before reinforcing
bars corrode due to deterioration. Thus, large-scale repair or strengthening can be eliminated andthe maintenance cost can be reduced accordingly in numerous cases.
Structures to which maintenance category B (corrective maintenance) is applied should bemaintained so as to prevent the performance of the structure from failing to meet the requirements.
Structures should be maintained to prevent deterioration from reaching the stage of deterioration toensure safety, the latter half of the acceleration stage to achieve serviceability or the former half of
the acceleration stage to keep aesthetic appearance and landscape. Certain actions should be taken
when any of the following types of deterioration has been detected.
(i) The corrosion of reinforcing bars in concrete(ii) The leaching of corrosion rust on concrete surface(iii) Cracking in the direction of axis of reinforcement on concrete surface(iv) The spalling of concrete cover
For structures to which maintenance category B is applied, remedial measures should be taken
in phase (i) or (ii) above because it is extremely difficult to stop the progress of corrosion ofreinforcing bars in concrete once started. It should be noted that large-scale measures will be
required if deterioration reaches phase (iii) or (iv).
There have been few cases in which steel corrosion due to carbonation affected performance100Chapter 9

Maintenance of Structures Subject to Carbonation

attributes in short time of occurrence. For ordinary structures that are expected to be subject tocarbonation, therefore, maintenance category B (corrective maintenance) may be designated in mostcases. Once steel has started corroding, however, investigations are conducted more frequently andremedial measures of larger scale and more costly than before corrosion are needed. For structuresof great importance, with a long planned service period, or with high required performances interms of hazards for third party or aesthetic appearance, therefore, maintenance category A(preventive maintenance) should preferably be selected.
One maintenance category is generally applied to one structure. In cases where theenvironmental conditions vary from region to region or from member to member, however,
applying different maintenance categories to different regions or members may sometimes be
effective.

9.2.3 Preparation of maintenance manuals
A maintenance manual describing methods, procedures and frequency requirements
should be prepared for each structure in accordance with the maintenance planning, taking
the structure-specific conditions into consideration.

[Commentary] The service period of civil engineering structures is long, and maintenance of
those structures is performed over a long period of time. It is recommended, therefore, that in order
to inform investigators of maintenance concepts and policies, a maintenance manual be prepared sothat detailed procedures and methods can be communicated accurately even to newly assigned
responsible engineers.
Under certain circumstances such as in cases where the original maintenance planning isaltered because the actual progress of deterioration turned out to differ from that assumed in theoriginal maintenance planning, it is necessary to modify the maintenance manual and takeappropriate maintenance measures accordingly.
When preparing maintenance manuals, "The Maintenance Manual for Structures Subjected to
Carbonation Prepared in Accordance with the Standard Specifications for Design and Constructionof Concrete Structures: Maintenance (draft) " may be consulted.

9.3 Assessment
9.3.1 GeneralIn the assessment of a structure whose performance has declined or is highly likely todecline because of carbonation, investigation, evaluation of the present state, prediction ofdeterioration and judgment of the necessity for remedial measures shall be appropriately
conducted in accordance with the maintenance planning.

[Commentary] In order to maintain concrete structures appropriately, this specification requires
three types of assessment: initial assessment, periodic assessment and extraordinary assessment.
Because the initial and periodic assessments are essential for the maintenance of structures subject
to carbonation, this chapter stipulates that those assessments must be conducted. Extraordinary
assessments are regarded as assessments to be conducted on an as-needed basis and are therefore
not dealt with in this chapter. By conducting periodic assessments during the maintenance period,
defect in appearance of structures can be discovered before they occur or in early stages, and101

Standard Specifications for Concrete Structures-2007, Maintenanceremedial measures including preventive measures and repairs can be taken systematically.

9.3.2 Investigation in assessment
9.3.2.1 General
Investigations in initial, routine and regular assessment of a structure subject tocarbonation shall be conducted appropriately according to the category of maintenancerequired for the structure. Prior to investigation, check items, methods, frequency andscope of standard investigation shall be determined appropriately. For each type ofassessment, detailed investigation shall also be conducted on an as-needed basis.

[Commentary] It is important to select check items, methods, frequency and scope ofinvestigation appropriately according to the purpose of investigation in accordance with themaintenance planning.
The major parameters that should be identified in investigations of structures subject tocarbonation are the depth of carbonation and the corrosion of internal steel. In cases where
deterioration has progressed considerably, investigations should be conducted to directly evaluate
performance.
The items to be examined in investigations vary according to the degree of deterioration. In
cases where it has been determined or assumed that the deterioration was in the initiation stage,investigations should be conducted mainly to identify the progress of carbonation. In cases where it
has been determined or assumed that the deterioration was in or beyond the propagation stage,investigations should be conducted mainly to identify the progress of steel corrosion. Table C9.3.1
shows major items to be examined in the respective stages. Data on the items related todeterioration prediction such as the environmental action, depth of carbonation, steel corrosion andlocation of steel should be collected in as early a stage as possible. Monitoring may be conducted
for continuously identifying the depth of carbonation or corrosion of internal steel for structures towhich maintenance category A (protective maintenance) is applied.
Carbonation progresses quickly where concrete is dry, and steel corrodes where concrete iswet. Thus, the rate of deterioration may vary from region to region of a structure. The efficiency ofsubsequent maintenance may be improved by confirming in the initial stages the locations where
deterioration is likely to progress.
The frequency and range of investigation should be determined considering the maintenancecategory, environmental conditions, structural format and the state of deterioration for the structure.
Deterioration due to carbonation is likely to occur at locations e.g. overhanging slabs, railings,
intermediate slabs and cracking-prone places on bridges. Carbonation is generally likely to progresson the southern rather than northern face. These points should be taken into consideration whenselecting the location of examinations.
Regardless of the category of maintenance, it is important to go through the design drawings
and specifications, construction records, investigation results and the repair history prior to theinvestigation of a structure.
If the state of a structure cannot be judged appropriately by standard investigation, detailed
investigation must be conducted.

102

Chapter 9

Maintenance of Structures Subject to Carbonation

Table C9.3.1

Main check items in investigation

Stage of Deterioration

Initiation

Propagation

Acceleration

Deterioration

Change of appearance

O

O

O

O

Depth of carbonation

O

▲

▲

▲

Chloride ion concentration

▲*

▲*

▲*

▲*

Steel corrosion

▲

O

O

O

Concrete strength

▲*

▲*

▲

O

Load bearing capacity

▲*

▲*

▲

▲

Location of steel

O

▲

▲*

▲*

Environmental action

▲*

▲

▲

▲

Monitoring

▲*

▲*

▲*

▲*

Weathering and leakage

O

O

▲*

▲*

O

: Items to be investigated on a priority basis▲ : Items that should preferably be investigated▲* : Items to be investigated on an as-needed basis

9.3.2.2 Investigation in initial assessment(1) In initial assessment, appropriate check items for standard investigation shall beselected for newly constructed structures, existing structures, large-scale repairs
and strengthened structures.
(2) If deterioration prediction, evaluation or judgment is difficult to make through astandard investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigation in initial assessment is the first investigation conducted whenthe maintenance of a concrete structure is started. Investigation in initial assessment includes not
only the first investigation of a newly constructed structure conducted before it goes into service but
also the first investigation of an existing structure or a structure for which remedial measures havebeen taken in response to deterioration. Check items for the investigation may vary from structure
to structure. Basic check items for standard investigations in initial assessment of a newly
constructed structure are the document search on the design drawings and specifications andconstruction records and observation. It is good practice to check on such details as concrete cover,the state of steel and porosity through nondestructive testing on an as-needed basis. When103

Standard Specifications for Concrete Structures-2007, Maintenanceinvestigating a structure for which remedial measures have been taken, it is also important to checkfor problems in repaired or reinforced parts of the structure. These should be included in check
items of standard investigation. When an existing structure is investigated, check items are similar
to those for a newly constructed structure if design drawings and specifications and construction
records exist. If there is no such document or record, it is necessary to select check items ofstandard investigation with reference to Section 1.3.2.5 “Detailed investigation.” In cases where a
prediction needs to be made with high accuracy about a structure to which maintenance category A(preventive maintenance) is applied, it is necessary to conduct investigations concerning theparameters used for the method described in Section 1.3.3 “Methods for predicting degradation of
performance degradation of structures.”
Extremely important items in the investigation in initial assessment of a structure subject tocarbonation are listed below.
(i) Concrete mix proportions, water-cement ratio (water-binder ratio) in particular(ii) Type of cement, and existence, type and volume of additive(iii) Concrete cover(iv) Environmental condition(v) Existence of initial defects(vi) Condition of repaired or strengthened sections
Items (i) and (ii) are input values for equation (Eq. C9.3.2) and essential to the prediction ofprogress of carbonation. For newly constructed structures, data on these items can be obtained bysearching construction records or other documents. For existing structures, however, acquiring data
is frequently difficult because of unavailability of design and construction records. Then, estimation
should be made based on the existing data on similar structures. Item (iii) is very important for
estimating the time of start and rate of steel corrosion and sometimes may not be as specified indesign. Verification is therefore necessary. In relation to item (iv), temperature, humidity,
weathering and leakage should be identified. Carbonation generally progresses rapidly in wet
sections. Steel may corrode and concrete composition may change in sections placed alternately
under dry and wet conditions. It has also been reported that steel corrosion due to carbonation andresultant concrete peeling and spalling are greatly affected by weathering and leakage of water.
Effects of water ascribable to poor bonding, waterproofing or starling have similar impact to that ofweathering or leakage. Item (v) greatly affects the durability of structures regardless of carbonation.
Detecting this item in the investigation in initial assessment is important. Investigating thedeformation in repaired or strengthened sections and the condition of deformation (e.g. swelling or
peeling of surface coating) (item (vi)) is also important.
(2) If evaluation and judgment cannot be made with high accuracy by standard investigation
alone or if a highly deteriorated part of a structure is to be investigated, detailed investigation isnecessary. Check items of detailed investigation are indicated in Section 1.3.2.5 “Detailed
investigation.”

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9.3.2.3 Investigation in routine assessment(1) In routine assessment, standard investigation shall be conducted to detect not only
the defect of concrete surface such as cracking in concrete, peeling and spalling of
concrete covering, leaching of rebar rust, efflorescence and discoloring but also
the leakage and the deterioration in appearance such as displacement anddeformation.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) The purpose of investigation in routine assessment is to detect deterioration at
an early stage by checking on defect in the state of a structure over time. The determination of thetime at which deterioration began in order to obtain information that is useful for predicting
deterioration is another important purpose of the investigation. In the investigation focus should beplaced on deterioration phenomena or their indicators such as cracking in concrete, peeling andspalling of concrete covering, leaching of rebar rust, efflorescence, discoloring, leakage,displacement and deformation. As for the structures to which maintenance category A (preventive
maintenance) is applied, the evaluation of their performance and also the judgment whether
remedial measures should be applied is generally difficult if they are in the initial stage, because
investigation in routine assessment is conducted mainly by observation. Then, appropriatemonitoring should also be employed and more items should be investigated as required. Specificmonitoring methods include the measurement of corrosion of internal steel by an electrochemical
method e.g. measuring half-cell potential and monitoring polarization resistance. Also effective isregularly measuring the depth of carbonation and steel corrosion in specimens made of the same
concrete as the structure to be examined and exposed under the same condition. Exclusively
inspecting the sections where deterioration was expected to progress as a result of initial assessment
is also effective.
(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone or if severe deterioration has already occurred, detailed investigation is conducted. Checkitems of detailed investigation are described in detail in Section 1.3.2.5 “Detailed investigation.”

9.3.2.4 Investigation in regular assessment(1) The purpose of investigation in regular assessment is to obtain information that isdifficult to obtain in routine assessment. In regular assessment, standard
investigation consisting of detailed observation of defects shall be conducted as inroutine assessment.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigation in regular assessment is conducted for obtaining the information
more detailed than that in routine assessment. Areas where signs of defects or deterioration havebeen detected in initial or routine assessment need to be examined intensively. The appearance ofthe structure should basically be examined as in routine assessment. Investigations of the depth ofcarbonation in concrete or steel corrosion may sometimes become necessary in addition to theexamination of the appearance of the structure.
In the investigation in regular assessment, the depth of carbonation should be measured three
to five times at equal intervals during the initiation stage. The volume of corroded steel is nearly in105

Standard Specifications for Concrete Structures-2007, Maintenanceproportion to time. Steel corrosion should therefore be measured twice each in the progressing,acceleration and deterioration stages.
In the structures to which maintenance category A (preventive maintenance) is applied, theprogress of carbonation is in proportion to the square root of time. Then, the depth of carbonation
should be measured at the specified interval so that the increase in depth of carbonation between
every measurement should be identical. The executing year of measurement can be given bymultiplying the number of years in service from the initial measurement by X2 (X = 2, 3 ...).
(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone or if severe deterioration has already occurred, detailed investigation is conducted. Checkitems of detailed investigation are described in detail in Section 1.3.2.5 “Detailed investigation.”

9.3.2.5 Detailed Investigation
Detailed investigation shall be conducted to obtain detailed information on a structure
subject to carbonation in cases where the deterioration of the structure is difficult topredict, evaluate or judge by standard investigation alone in initial, routine or regularassessment. Check items, methods and location of a detailed investigation shall beselected appropriately taking into consideration such factors as the purpose ofinvestigation and the accuracy of obtained results.

[Commentary] When the determination of the present state of a structure and the deterioration
prediction of the structure are difficult by standard investigation alone, detailed investigation isconducted in order to obtain the information necessary for those purposes. Examples ofinvestigation items for structures subject to carbonation, and of data on the condition of thestructure at the time of investigation and those in the future estimated from the investigation results
are listed in Table C9.3.2. The evaluation items estimated from data in the table are evaluated after
deterioration is predicted.
Major check items are outlined below. For other measurement items or testing methods thanthose described below, refer to 4.7 "Investigation."(i) Depth of carbonation
The area of carbonation is defined as the uncolored portion of concrete when a solution ofphenolphthalein (JIS K 8001) is applied to a fracture side of concrete. The depth from the concretesurface to the boundary between colored and uncolored portions is measured at several locations
and the mean value is defined as the depth of carbonation. Measurement should be conducted
immediately after core samples are collected. Concrete should be fractured in dry condition forinvestigation because using water for splitting concrete results in inaccurate measurement of thedepth of carbonation. For the method of measuring the depth of carbonation, refer to JIS A 1152
“Methods for Measuring the Depth of Carbonation in Concrete.”
The area of carbonation specified by the phenolphthalein test is not always identical to thearea where calcium carbonate is generated due to carbonation. The testing method has, however,been generally adopted, and also the initiation of steel corrosion has been discussed in relation to
the depth of carbonation. Note that employing measurement methods using samples of powder
collected from drill holes has also been proposed recently.

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Table C9.3.2

Maintenance of Structures Subject to Carbonation

Examples of evaluation items in detailed investigation

Measurement item

Data obtained byinvestigation

Evaluation items predicablefrom obtained data

Temperature, humidity, carbon
dioxide concentration, weatheringand insulation

Temperature, humidity andwater content

Rate of carbonation andrate of corrosion

Cracking (width, depth and density)

Grade of corrosion andaesthetic appearance

Grade of corrosion andaesthetic appearance

Concrete strength and modulus ofelasticity

Concrete strength andstiffness

Depth of carbonation

Depth of carbonation

Rate of carbonation andinitiation of corrosion

Water content

Water content

Water content

Rate of corrosion

Location and corrosion of steel (area Grade of corrosion,
corrosion amount of steel
and volume) and leaching of rustand load bearing capacity

Rate of corrosion and load
bearing capacity

Electrochemical indicators (e.g.
half-cell potential, polarization
resistance and electric resistivity)

Grade of corrosion and rate Grade of corrosion, rate ofcorrosion and load bearingof corrosion
capacity

Deflection and displacement

Stiffness and load bearing
capacity

Note: For the grade of corrosion, refer to Table C9.3.3.

(ii) Cracking
Cracking accelerates carbonation or steel corrosion by encouraging the transfer of substances.
If the crack width is below an allowable value, there will be no problem. Excessive cracking,however, is likely to greatly accelerate deterioration and structural performance degradation. The
reason for or degree of deterioration may be estimated at certain levels of cracking. In cases ofcracking in concrete, therefore, data useful for determining the deterioration and predicting
subsequent deterioration should be collected such as the location, spacing, pattern, width and depthof cracking.
(iii) Steel corrosion
Steel corrosion has a direct impact on the performance of the structure in numerous cases. In
tests, therefore, the concrete cover should be chipped and whether corrosion has occurred or notshould be determined and the location, area, weight and depth of pitting corrosion should bemeasured directly. Obtaining quantitative data on corrosion could enable the quantitative evaluationof the reduction of physical property values and degradation of structural performance. Detailed
investigations are therefore necessary. To simplify the method of measurement, the state of steel
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Standard Specifications for Concrete Structures-2007, Maintenancecorrosion may be graded for evaluation (Fig. C9.3.3).
Grades I through IV roughly correspond to grades I-1, I-2, II and III for structural appearance
shown in Table C9.3.4. If no crack occurs due to corrosion and the location of corrosion is invisible
from outside, decision should be made using a half-cell potential distribution map or by othermeans.

Table C9.3.3

Grades of corrosion and state of steel

Grade of corrosion

State of steel

IMill scale. Thin and compact rust layer all over the steel. No rustadhesion on concrete surface.

II

Swelling rust exists at some locations but is spotty in small areas.

III

No lack of section can be visually recognized. Swelling rust exists allaround the reinforcement or throughout the length of reinforcement.

IV

Lack of section of reinforcement.

When monitoring steel corrosion by nondestructive testing, electrochemical indicators such as
half-cell potential and polarization resistance should be measured. The values of these indicators are,however, affected by the state of concrete such as the water content and the degree of carbonation.
Measurements should therefore be made in accordance with 4.7.3 “Investigation methods.”
Electrochemical methods have been applied to steel corrosion due to carbonation in fewer cases
than to chloride attack, and no evaluation standards have yet to be established. Then, care should be
exercised.
(iv) Appearance of structures
In cases where performance of structure cannot be evaluated direct from the state of concreteand steel, the defect of appearance provides important data for performance evaluation. The gradesof appearance of structures deteriorated due to carbonation are shown in Table C9.3.4. Grades II-1
and II-2 are differentiated by the quantity of corroded steel. Differentiation is, however, difficult at
the present technological level for deterioration prediction. For differentiation, observation istherefore essential.

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Table C9.3.4

Maintenance of Structures Subject to Carbonation

Grades of structural appearance and stage of deterioration

Grade of structural appearanceState of deterioration

I-1 (initiation stage)

No defect found in appearance. Remaining carbonation is at
or more than the limit for rust development.

I-2 (propagation stage)

No defect found in appearance. Remaining carbonation is
below the limit for rust development. Corrosion starts.

II-1 (first half of acceleration
stage)

Cracking occurs due to corrosion.

II-2 (second half ofacceleration stage)

With the progress of cracking due to corrosion, peeling or
spalling is found. No lack of section of steel.

III (deterioration stage)

Peeling and spalling are found with cracking due tocorrosion. Lack of section of steel.

9.3.3 Methods for predicting performance degradation of structures
9.3.3.1 General(1) In the maintenance of a structure subject to carbonation the performance of thestructure shall be evaluated quantitatively at the time of investigation, and futuredegradation shall be predicted.
(2) In order to predict the performance degradation of a structure, deterioration due tocarbonation shall be predicted quantitatively.
(3) If (2) is difficult, an alternative method is to predict performance degradation by
estimating the length of the initiation, propagation, acceleration and deterioration
stages, taking the progress of carbonation into consideration.
(4) Deterioration shall be predicted on the basis of investigation results.

[Commentary] (1) and (2) In the performance verification based maintenance system, changes(deterioration) in various performance attributes inherent in the structure should be predicted. To
that end, the progress of material deterioration should be predicted quantitatively. The performanceof the structure and the degree of deterioration of materials constituting the structure should be
evaluated quantitatively at the time of investigation and the end of planned service period.
Performance degradation of the structure or the degree of deterioration of materials constituting thestructure at the time of investigation may be evaluated quantitatively by an appropriate method
based on investigation results. The performance or the degree of deterioration at the end of theplanned service period should be predicted quantitatively based on the previous periodic
assessments. The prediction of deterioration progress is not always in agreement with actual
progress of deterioration. The method of prediction should therefore be reviewed based on the
results of investigations to be conducted later.
(3) When evaluating various performance attributes of a structure by combining the results ofprediction of deterioration progress of concrete and steel, quantitative prediction is difficult at thepresent technological level. Then, the performance degradation of a structure due to carbonation is109

Standard Specifications for Concrete Structures-2007, Maintenanceexamined during the initiation stage (in which the depth of carbonation reaches the limit for theoccurrence of steel corrosion), propagation stage from the initiation of corrosion to cracking due tocorrosion, acceleration stage (in which the rate of corrosion increases due to cracking), anddeterioration stage (in which load bearing capacity decreases remarkably with the progress of steel
corrosion). Each process of deterioration basically corresponds to the state (performance) of thestructure, so deterioration may be predicted quantitatively by predicting the length of each stage.
The length of the initiation stage is calculated using the rate of carbonation. The length of the
propagation stage is calculated using the rate of steel corrosion and the quantity of corroded steel at
the time of cracking due to corrosion. The length of the acceleration stage is calculated using therate of corrosion of steel subject to corrosion-induced cracking. The length of the deterioration stage
is calculated using the rate of corrosion of steel subject to corrosion-induced cracking and thequantity of corroded steel at which load bearing capacity is reduced. The calculation methods aredescribed in 1.3.3.2 "Prediction of carbonation" and 1.3.3.3 "Prediction of steel corrosion."
The “Design” volume of the standard specification stipulates that structures should bedesigned so that no steel may corrode, or so that deterioration may not reach the propagation stage
by conducting performance check. The “Maintenance” volume of the standard specification
discusses the propagation, acceleration and deterioration stages after the steel corrosion as wellbecause it deals with the structures designed and constructed before the revision of specifications
and because unexpected deterioration may progress even in the structures designed and constructedin accordance with the present specification.
(4) Investigation results are related to either the quality of concrete of the structure or theenvironment in which the structure is placed while in service. These parameters should be used as abasis for predicting deterioration. If no investigation result is available because the structure is now
being planned or because the structure is already in existence, investigation results or deterioration
conditions of similar structures under the similar environment may be consulted.

9.3.3.2 Prediction of carbonation(1) The progress of carbonation shall be predicted properly considering the quality ofconcrete and the environment in which the structure is in service.
(2) The progress of carbonation may be predicted by one of the following methods.
(i) t rule(ii) Use of accelerated test(iii) Use of physico-chemical models[Commentary] (1) Predicting the rate of progress of carbonation is important to accurate
estimation of the length of the initiation stage. The rate of progress of carbonation is determined by
the velocity of movement of carbon dioxide in concrete and the capacity of retaining pH of water invoids. The velocity of movement of carbon dioxide is affected by hardened cement and the quantity
and structure of voids in aggregate. Thus, cement, admixtures, type of aggregate, water-cement ratio(water-binder ratio), and the degree of hydration of binder affect the rate of carbonation. Carbon
dioxide moves at a much lower rate in the liquid phase than in the gaseous phase. In cases where
voids are fully filled with water, therefore, the progress of carbonation can virtually be ignored.
Under highly dry conditions, on the other hand, no carbonation occurs. Then, the rate of110Chapter 9

Maintenance of Structures Subject to Carbonation

carbonation is affected by the water content of concrete, and temperature, humidity, frequency of
precipitation, insulation and traffic volume (gas emissions) should be taken into consideration asenvironmental conditions. The capacity of retaining pH of water in voids of concrete is determinedby the quantity of calcium hydroxide. Then, cement, type of admixture, water-cement ratio, cement
content and the degree of hydration of binder affect the rate of carbonation. The effects should be
evaluated properly for prediction.
(2) Three major methods for predicting the progress of carbonation are described below.
(i) t rule
Numerous works have confirmed that the depth of carbonation is in proportion to the squareroot of the period of carbonation.

yb t(Eq. C9.3.1)

where,

y: depth of carbonation (mm)t: period of carbonation (years)
b: coefficient of the rate of carbonation (mm/ year )In cases where the depth of carbonation has been measured, the coefficient of the rate ofcarbonation should be obtained based on the measurement for subsequent prediction. The
coefficient of the rate of carbonation can be obtained principally using the data of one measurement.
To enhance the reliability, however, the coefficient should be calculated by the least square method
after conducting two or three measurements every few years. In cases where the depth ofcarbonation and the coefficient of rate of carbonation vary greatly according to the measurement
location in a structure, the rate of carbonation may vary from region to region.
If no investigation result is available, the rate of carbonation should be predicted using a
reliable equation for calculating the rate of carbonation properly considering the materials and mix
proportions of concrete and the environmental conditions under which the structure is in service. As
described in "Commentary (1)," the rate of carbonation is subject to various factors. Most equations
for calculating the rate of carbonation use water-cement (water-binder) ratio and compressive
strength as indicators of concrete quality. For predicting the rate of carbonation, using an equation
for the same materials, mix proportions and environmental conditions as those for the structure
under study is desirable. If no such equation is available, the following equation may be adopted.

y   3.57  9.0W / B  t(Eq. C9.3.2)

where,
W/B: effective water-binder ratio= W/(Cp + kAd)
W: unit-area mass of water
B: unit-area mass of effective binder
Cp: unit-area mass of Portland cement
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Standard Specifications for Concrete Structures-2007, Maintenance

Ad: unit-area mass of admixture
k: coefficient indicating the effect of admixture
For fly ash: k = 0
For ground blast furnace slag: k = 0.7(ii) Use of accelerated test
Accelerated test is convenient for evaluating the relative rate of carbonation in a short periodof time. Absolute evaluation is, however, difficult because the factor of acceleration (ratio of therate of carbonation in accelerated testing to that under natural condition) depends on the materials,
mix proportions, initial curing conditions before the initiation of acceleration and the dimensions ofspecimens. When estimating the rate of carbonation in accelerated test, therefore, not only theconcrete in question but also concrete specimens with the same mix proportions as the concretewith a depth of carbonation found in natural weathering or in an actual structure should also be
tested. It should be confirmed that the rate of carbonation in accelerated test does not exceed that ofnatural condition.
(iii) Calculation using physico-chemical models
Methods have recently been evaluated for modeling the movement and reaction ofcarbonation-related substances in concrete such as water, carbon dioxide and calcium hydroxide andpredicting the progress of carbonation by numerical calculations. The methods are beneficial inaccurately predicting the progress of carbonation and in increasing the efficiency of maintenance if
the parameters required for calculation can be specified satisfactorily. Then, parameters should bespecified carefully based on the results of various tests.

9.3.3.3 Prediction of steel corrosion(1) The progress of steel corrosion due to carbonation shall be predicted properly
considering the concrete quality and the environment in which the structure is inservice.
(2) The initiation of steel corrosion should be determined based on the remaining
concrete cover after carbonation(3) The progress of steel corrosion before cracking occurs due to corrosion may be
predicted by either of the following methods.
(i) Method based on the quantity of corroded steel obtained from the investigation(ii) Method based on the rate of reaction of steel to corrosion(4) Cracking due to corrosion may be predicted by either of the following methods.
(i) Predicting from the quantity of corroded steel(ii) Predicting using a mechanical model(5) The progress of steel corrosion after cracking due to corrosion should be predictedby properly evaluating the effects of cracking on the mobility of substances.

[Commentary](1) Steel corrosion due to carbonation accelerates the performance degradation of112

Chapter 9

Maintenance of Structures Subject to Carbonation

the structure. Predicting steel corrosion is therefore important as well as predicting carbonation.
Steel corrosion is affected by such factors as pH of water in voids in concrete at the location of steel,rate of oxygen supply and water content of concrete. The lower the pH is, the higher the rate ofcorrosion is. The rate of corrosion, however, remains constant in the range between pH 4 and 10 at
atmospheric temperature. In the area where carbonation occurs, pH is said to be 8.2 to 10. Whencarbonation has progressed to some extent, the rate of corrosion may be at a constant level under thesame conditions, which has been confirmed by previous experiments.
Since corrosion is attributed to oxygen, the rate of oxygen supply to the steel therefore
naturally affects the rate of corrosion. The velocity of oxygen movement in concrete is affected bycement, admixtures, type of aggregate, water-cement (water-binder) ratio and degree of hydration ofbinder, and water content as for carbon dioxide. As the water content of concrete decreases, oxygen
supply increases. In an excessively dry condition, because the progress of corrosion requires water,
the rate of corrosion decreases. Then, predicting steel corrosion like the rate of carbonation requires
proper evaluation of environmental conditions that affect the water content of concrete. In case of
concurrent deterioration by steel corrosion and chloride attack, the rate of corrosion increases.
Prediction therefore should be made carefully.
(2) Steel is corroded as pH drops around the steel. The rate of corrosion is not exactly zeroeven when pH is in the alkali area. Defining an indicator for determining the initiation of corrosionis therefore difficult. Numerous works and researches of structures have revealed that corrosion due
to carbonation generally starts before carbonation reaches the steel. The initiation of corrosion isfrequently identified using the thickness of remaining concrete cover, or the variance between the
thickness of concrete covering and the depth of carbonation. The previous researches concluded that
corrosion occurs as the thickness of remaining concrete cover falls below 10 mm. Actually, however,steel corrosion is affected not only by the thickness of remaining concrete cover but also by
numerous other factors including the quality of concrete and environmental conditions. It cannot be
therefore said that no steel corrodes under any condition as long as the thickness of remaining
concrete cover exceeds 10 mm. There have been few cases of serious steel corrosion causing
functional deterioration of a structure where the thickness of remaining concrete cover exceeded 10
mm. Then, carbonation can be assumed to start when the thickness of remaining concrete coverreaches 10 mm. In cases where concrete contains chloride ions, the chloride ions immobilized in thehydrate of cement are dissociated as carbonation progresses and are concentrated in the area freefrom carbonation. Then, corrosion starts earlier. The results of investigations of structures that
contained chloride ions from sea sand and had progressed carbonation show that steel often
corroded when the thickness of remaining concrete cover falls below approximately 15 mm. The
value may vary according to the quantity of chloride ions or water content of concrete. The rate ofsteel corrosion in cases where chloride ions exist is higher than the rate of steel corrosion ascribableonly to carbonation. The thickness of remaining concrete cover to determine the initiation of steel
corrosion should therefore be specified properly by analyzing the results of investigations of thestructure. The thickness of remaining concrete cover can be obtained using the predicted depth ofcarbonation shown in 1.3.3.2 "Prediction of carbonation."
In cases where cracking has occurred in concrete, the progress of carbonation should be
predicted in cracked sections. If carbonation has occurred in the concrete at the interface with steel,corrosion occurs even if the crack width is small. The maximum depth of carbonation in the cracked
area should be compared with the concrete cover.
When predicting the initiation of corrosion direct from pH of water in voids of concrete notusing the thickness of remaining concrete cover, the ion composition of water in voids of concreteand the electrochemical mechanism of steel corrosion in concrete should be evaluated properly.

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Standard Specifications for Concrete Structures-2007, Maintenance(3) Steel corrosion due to carbonation may sometimes progress relatively slowly. Few works
are therefore available. Methods of predicting steel corrosion may not be highly reliable. Morestudies need to be done. The present prediction methods are outlined below.
(i) Method based on the volume of corroded steel obtained from investigation results
In cases where the change in volume of corroded steel has been measured in investigations,the progress of corrosion may be predicted through the regression analysis of the result. The resultsof past researches show that most of the curves representing the time-based change in volume ofsteel corroded by carbonation are nearly linear. The result has been verified by analyses using
electrochemical models. In cases where the volume of corroded steel and the initiation of steel
corrosion are known as a result of investigations, subsequent corrosion can be predicted relatively
easily. Even where the initiation of corrosion is unknown, curves representing time-based change
can be estimated if the results of measurement of the volume of corroded steel at two or more ages
are available.
(ii) Method based on the velocity of reaction of steel to corrosion
In cases where no measurement of the volume of corroded steel are available, the progress ofcorrosion may be predicted by properly evaluating the rate of corrosion using an existing equation
for calculating the rate of corrosion. As described in "Commentary (1)", the rate of steel corrosion isaffected by the quantities of water and oxygen. Using electrochemical models considering thevelocity of oxygen supply to concrete or the water content of concrete, and properly specifying
parameters for models may increase the accuracy of estimation. It has been reported that the rate ofsteel corrosion under ordinary conditions (at a temperature of 20ºC and a relative humidity of 60 to70%) is 2 x 10-3 mm/year, which can be referred when estimating the volume of corroded steel.
(4) Cracking of concrete due to steel corrosion increases the mobility of substances andaccelerates the progress of corrosion, resulting in aesthetic problems. For predicting the crack
appearance, determining the volume of steel corroded at the time of cracking is required. The
following methods may be used to determine the volume of steel corroded at the time of cracking.
(i) Method based on the volume of corroded steel
Carbonation unlike chloride attack frequently causes general corrosion. The results ofelectrolytic corrosion testing can be used for reference because corrosion progresses uniformly
around the rebar in the testing. As a result of electrolytic testing using deformed steel bars, it was
found that cracking occurs due to corrosion where the volume of corroded steel is approximately 10
mg/cm2 or greater. If the volume of steel corroded at the time of cracking due to corrosion isassumed to be 10 mg/cm2, the timing of cracking due to corrosion can be estimated on the safe side.
(ii) Method using a mechanical model
It has been known that the volume of steel corroded at the time of cracking is affected by
concrete cover, concrete strength and steel bar diameter. Various elastic and elasto-plastic analysis
methods considering the effects have been proposed. These methods may be used by specifying
model parameters properly.
(5) Researches are now being made on the methods for predicting steel corrosion after thecrack appearance due to corrosion but none have yet been established. Among the parameters forvarious models of corrosion with no corrosion-induced cracking, it is better to replace the values
related to the mobility of substances such as the velocities of movement of oxygen and water withthose with cracking. The validity of methods should be verified by experiments.
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Maintenance of Structures Subject to Carbonation

9.3.3.4 Modification of prediction
If the state of deterioration determined in an investigation differs from a predicted stateof deterioration, the cause of the difference shall be identified and the prediction shall berevised accordingly. If necessary, the maintenance planning shall be altered.

[Commentary] When the deterioration confirmed in investigations is different from theprediction, appropriate investigations should be conducted using the deterioration prediction
methods shown in 9.3.3.2 "Prediction of carbonation" and 9.3.3.3 "Prediction of steel corrosion"and based on Table C9.3.2 to examine the cause for the difference, and the prediction should be
modified. Then, the results of several investigations conducted until that are useful to theexamination of causes and the modification of the prediction. Revising the subsequent maintenanceplans including a review of investigation frequency based on the modified prediction is also
important.

9.3.4 Evaluation and judgment(1) The evaluation of performance and judgment as to whether remedial measuresneed to be taken based on the results of the investigation in initial, routine andregular assessment shall be made in accordance with Part 1 and Item (2) andsubsequent items in this section.
(2) The performance of a structure subject to carbonation shall be evaluated byappropriately selecting performance attributes to be evaluated in view of the stageof deterioration of the structure.
(3) The evaluation of performance attributes at the time of investigation and at the endof the planned service period of the structure should be made by a quantitative
method.
(4) If Item (3) is difficult to achieve, the evaluation of performance attributes at the timeof investigation and at the end of the planned service period of the structure may
be made by a semi-quantitative grading-based method.
(5) Judgment as to whether remedial measures need to be taken shall be made in viewof the degree of performance degradation due to carbonation, the degree ofimportance of the structure, category of maintenance, and the remaining service
life.

[Commentary] (1) The evaluation of performance and judgment of necessity for remedial
measures in initial, routine and regular assessment for structures in which little progress ofdeterioration has been recognized are frequently more or less the same regardless of thedeterioration mechanism. For details, refer to Part 1. The evaluation of performance and judgmentof necessity for remedial measures for structures in which deterioration may have or has progressedvary according to the deterioration mechanism. When discussing the performance degradation due
to carbonation, the descriptions in this chapter should be consulted.

(2) In structures subject to carbonation, the performance attribute to be affected bydeterioration varies depending on whether deterioration is in the initiation, propagation, acceleration
or deterioration stage. The performance attribute to be evaluated should be properly selected foreach stage of deterioration. In the initiation stage, steel is likely to corrode with the progress ofcarbonation, and in the propagation stage, steel corrosion progresses due to the supply of oxygen
115

Standard Specifications for Concrete Structures-2007, Maintenancethrough the concrete cover. The steel protection, one of the durability parameters, should therefore
be evaluated. In the acceleration stage, the volume of corroded steel remarkably increases due to thecracking caused by corrosion. Then, the steel protection performance, serviceability in such terms
as the stiffness and ductility of members, hazards for third party such as peeling and spalling of
concrete due to cracking, and aesthetic appearance should be evaluated. In the deterioration stage,corrosion progresses further. In addition to the performance attributes to be evaluated in theacceleration stage, safety performance including load bearing capacity should be evaluated.
In cases where the steel has corroded and has been subject to cyclic loading, the hazards forthird party including the spalling of concrete may be an issue in early stages like the propagation
stage.
(3) The performance of a structure at the time of investigation and at the end of the planned
service period should be evaluated after quantitatively evaluating the deterioration of concrete andsteel.
For evaluating the performance of a structure at the time of investigation, safety andserviceability are verified by obtaining the load bearing capacity and deformation by, for example,
substituting the mechanical properties of materials obtained from investigation results into a
structural calculation formula. Also conceivable is the verifying of the hazards for third party andaesthetic appearance and landscape based on the range and density of cracking or peeling and thedegree of steel corrosion. Performance can be evaluated relatively explicitly at the time ofinvestigation by such verifications in cases where deterioration is not serious. In cases whereserious deterioration has occurred and the expansion of steel or the deterioration of bond withconcrete is large, or in cases where concrete cover has been delaminated or spalled, appropriate
methods reflecting these effects should be examined.
Performance at the end of the planned service period should be evaluated based on the resultsof performance evaluation at the time of investigation and the results of deterioration prediction.
Evaluating performance with sufficient accuracy is difficult in numerous cases. As a supplementarymeasure, deterioration is generally predicted based on the rate of carbonation and the rate of steel
corrosion using the methods shown in 1.3.3 "Methods for predicting performance degradation of
structure." Then, the accuracy of the deterioration prediction method as well as the accuracy of theperformance verification method is important. Prediction methods should therefore be selected
carefully. Adequate safety should be guaranteed.
(4) In the performance verification type design system, structural performance should ideallybe evaluated quantitatively. At present, however, there is no established method of quantitative
estimation. As a practical method, the performance of a structure can be evaluatedsemi-quantitatively, with reference to Table C9.3.5, by performing appearance grading inaccordance with Table C9.3.4.
The purpose of grading is to classify the present degree of deterioration of a structuresemi-quantitatively instead of predicting and evaluating the degree of deterioration in future. It isalso possible, however, to predict the performance of a structure at the end of the planned service
period in accordance with Table C9.3.5 by estimating the stage of deterioration at the end of theplanned service period on the basis of investigation results such as the rate of carbonation and steel
corrosion. The method of estimating the degree of deterioration at a certain point of time in future
by constructing a deterioration grade model based on a stochastic theory such as a Markov model
has also been proposed.
If detailed maintenance records for a similar structure (type of structure, materials,

116

Chapter 9

Maintenance of Structures Subject to Carbonation

construction, environment, state of use) are available and its progress of deterioration is also similar
to that of the evaluated structure, then the evaluation results for the similar structure provide useful
information.
(5) Because judgment is the act of deciding whether remedial measures need to be taken on thebasis of structural performance evaluation results, there is no difference depending on deterioration
factors. Therefore, refer to Part 1.

Table C9.3.5 Grades of appearance of structures and typical performance degradation

Grade ofappearance ofstructure

Serviceability

Hazards for third
party

Aesthetic
appearance andlandscape

SafetyI-1 (initiation
stage)

-

-

-

-

I-2
(propagation
stage)----

II-1 (first halfof acceleration
stage)-

II-2 (second
half ofacceleration
stage)-

Deterioration of load
bearing capacity andductility-Lack of section of
steel
III
(deterioration
stage)-Reduction of
concrete crosssection due toswelling or peelingof concrete--

Deterioration of
stiffness(increase of
deformationand occurrenceof vibration)

Aesthetic
deterioration-Cracking-Lack of sectionof steel

Hazards for third
party-Deterioration ofbond between
steel and concrete-Peeling-Reduction of
concrete crosssection due toswelling or
peeling of
concrete

117-Spalling-Leaching ofsteel rust
-Exposure ofsteelStandard Specifications for Concrete Structures-2007, Maintenance

9.4 Remedial Measures
9.4.1 Selection of remedial measures(1) If it has been judged that remedial measures need to be taken in connection withperformance degradation of a structure subject to carbonation, remedial measuresby which the corrected structure meets the required performances shall beselected.
(2) If it is difficult to select remedial measures for a structure on the basis ofperformance verification, remedial measures may be selected from the measurescorresponding to the grade of appearance.

[Commentary] (1) If it has been judged, as a result of evaluation, that remedial measures need tobe taken, it is necessary to select one or more of the following measures: (i) intensified investigation,(ii) repair, (iii) strengthening, (iv) functional improvement, (v) restriction in service or (vi)dismantling/removal. Basically, decisions as to which measures to take should be made by the
maintenance manager of the structure, but it is good practice to refer to Part 1 for information on
typical relationships between evaluation and judgment results and remedial measures.

(2) If it is difficult to select remedial measures for a structure through quantitative evaluationor judgment, remedial measures are selected from the measures corresponding to the deterioration
grade of the structure. Remedial measures to be taken vary depending on the type of structure, thedegree of importance of the structure, deterioration rate and the category of maintenance, but
recommended standard measures are shown in Table C9.4.1.

Table C9.4.1 Grades of appearance of structure and remedial measures

Grade ofappearance ofstructure

Intensified
investigation

RepairI-1 (initiation
stage)

O**

I-2(propagation
stage)

Strength-ening**

Functional
improvement

O**

(X)

X

O

O

X

X

II-1 (first halfof acceleration
stage)

OO

OO

X

X

II-2 (second
half ofacceleration
stage)

OO

OO*

X

X

III
(deterioration

118

Restriction
in service

O

Dismantling/removalChapter 9

Maintenance of Structures Subject to Carbonation

stage)OO: Standard remedial measures (OO*: Including the restoration of mechanical performance), O:
Remedial measures in some cases,
O*: Preventive measure
X:

Remedial measure taken based on other criterion than the grade of appearance.
Strengthening**: Enhancing the mechanical performance above the initiation level

9.4.2 Repair and strengthening
Methods and materials for the repair or strengthening of a structure shall be selectedtaking into consideration the performance degradation of the structure due to carbonationand life cycle cost, so that the required effect can be achieved.

[Commentary] In cases where repair or strengthening is carried out as a remedial measure, it isnecessary to define the expected effect of repair or strengthening and the required performance(what level of performance to be maintained for how many years?). Ideally, it is desirable that
remedial measures be taken after constructing a deterioration formula (for repair) or structural
calculation formula (for strengthening) in view of such factors as the properties of the materials
used and verifying the calculation results obtained from those formulas. In this case, it is also
important to take life cycle cost into consideration according to the remaining planned service
period.

When taking preventive measures for a structure to which maintenance category A(preventive maintenance) is applied, an appropriate method should be selected fully considering theeffect that should be achieved by the method.
The methods of repair or strengthening for structures subject to performance degradation due
to carbonation are listed in Table C9.4.2 by expected effect.

Table C9.4.2 Expected effects and methods of repair or strengthening

Expected effectControl the
progress ofcarbonation

Examples of methods
Surface treatment and grout injection into cracks

Reduce the depth of Repair of cross section (corrosion protection and coating arecarbonation to none included) and re-alkalization
Control the
progress of steel
corrosion

Surface treatment, (electrical protection), repair of crosssection, re-alkalization, corrosion protection and water
treatment

Restore or enhanceload bearing
capacity(Adhesion of steel or fiber reinforced plastic plates), (use of
external cable), (lining) and (increase of thickness)

119Standard Specifications for Concrete Structures-2007, Maintenance( ): Method in the parenthesis is selected in cases with a high rate of steel corrosion or a highvolume of corroded steel where the concentration of chloride ion is high.
Table C9.4. 3 Grades of structural appearance and methods of repair or strengthening

Grade of structuralappearanceStandard methods

I-1 (initiation stage)

Surface treatment* and Re-alkalinization*

I-2 (propagation stage)

Surface treatment, (Patching) and Re-alkalization

II-1 (first half ofacceleration stage)

Surface treatment, (Electrical protection), Re-alkalization andPatching

II-2 (second half ofacceleration stage)

Patching

III (deterioration stage)

Patching, (Adhesion of steel or PRP), (External cable),(Jacketing) and (thickness increasing )*: Preventive method( ): Method in the parenthesis is selected in cases with a high rate of steel corrosion or a highvolume of corroded steel where the concentration of chloride ion is high.

In weathering or leakage, water encourages steel corrosion due to carbonation. In order tocontrol the progress of steel corrosion, therefore, water treatment measures such as dewatering,
jointing and waterproofing should also be taken. When selecting the method, Table C9.4.2 and thepresent performance degradation of the structure should be considered. For the deterioration gradeof appearance and remedial measures, refer to Table C9.4.3.
In the initiation stage, neither performance degradation nor deterioration has occurred in the
structure. In this period, remedial measures are taken only for structures to which maintenancecategory A (preventive maintenance) is applied. Then, remedial measures are expected to control
the progress of carbonation in concrete cover. Surface treatment should therefore be applied toprevent carbon dioxide from entering the concrete. Restoring pH in the concrete cover byimplementing the re-alkalinization method is also effective.
In the propagation stage, steel has corroded but the volume of corrosion amount of steel isstill low and little performance degradation has occurred. In this stage as in the initiation stage,
surface treatment is generally selected. Patching or re-alkalinization may be considered.
In the first half of the acceleration stage, the deterioration of mechanical performance is not
yet outstanding. Cracks have occurred in concrete cover due to steel corrosion. Applying
re-alkalinization for restoring pH in the concrete cover or patching for removing the sections subject
to carbonation should be considered. In order to prevent re-deterioration, surface treatment after thepatching should also be considered.
In the second half of the acceleration stage, serviceability is reduced due to the deteriorationof stiffness, and the concrete cover either is delaminated or spalls, resulting in serious hazards forthird party. In this period, the concrete cover is removed and patching is applied to compensate for120

Chapter 9

Maintenance of Structures Subject to Carbonation

the deterioration of monolithic characteristics of members due to carbonation. Surface treatment
after the patching, and the addition or replacement of reinforcing bars should also be considered.
In few cases, deterioration due to only carbonation has reached the deterioration stage.
Concurrent deterioration due to carbonation and chloride attack sometimes reaches the deterioration
stage and reduces load bearing capacity. Then, methods for restoring load bearing capacity such as
the adhesion of steel or FRP, external cable, jacketing and thickness increasing should be applied inaddition to the patching including the addition or replacement of reinforcing bars. These methods
should be implemented after removing the concrete cover and patching, for preventing
re-deterioration.
If the entry of carbon dioxide is blocked, which is a cause of carbonation, by surface coatingor other means, no subsequent carbonation may be assumed. Many of the repair or strengthening
methods applied have been developed only recently and few have been applied to actual structures.
If such methods are adopted, the structure may be re-deteriorated and its performance may be
degraded due to the factors not expected in the design phase. Measures should therefore be takensuch as increasing the frequency of investigations after the repair or strengthening.
For details of the methods of repair and strengthening, refer to the "Guidelines ofStrengthening Concrete Structures (draft)," "Guidelines for Repairing or Strengthening Concrete
Structures Using Continuous Fiber Reinforced Membrane," "Guidelines for Design and
Implementation of Electrochemical Protection (draft)," "Guidelines for Design and Implementationof Surface Protection (draft)," "Shotcreting Guidelines (draft) - Repair and Strengthening" and the"Reports of Concrete Structures Repair Method Committee I, II and III" and "Reports of Concrete
Structures Restoration Committee" prepared by the Japan Concrete Institute. Applying there-alkalinization or electrical protection method to a structure using reactive aggregate is likely tohelp deteriorate the structure due to alkali silica reaction. Then, the "Guidelines Concerning theApplication of Electrochemical Protection Considering Alkali-silica Reaction" prepared by theSociety of Materials Science, Japan should be consulted and the applicability of a repair method
and the method of implementation should be determined carefully.

9.5 Recording(1) Investigation, deterioration estimation, evaluation and judgment, and remedial
measures shall be recorded in accordance with Part 1.
(2) Items relevant to carbonation shall be recorded.

[Commentary] As a general rule, the results of investigations, deterioration estimations,evaluations and remedial measures must be recorded in accordance with Part 1. Items relevant tocarbonation require careful attention, particularly with respect to record keeping. Items to berecorded are indicated in Section 1.3.2 “Investigation in assessment" and the evaluation items
indicated in Section 1.3.4 “Evaluation and judgment.”121

Standard Specifications for Concrete Structures-2007, Maintenance

CHAPTER 10 MAINTENANCE OF STRUCTURES SUBJECTTO CHLORIDE ATTACK
10.1 General(1) This chapter provides standard methods for the maintenance planning,assessment, remedial measures and recording for structures that have been or are highly
likely to be subject to performance degradation due to chloride attack. The items common
to all the deterioration mechanisms are shown in Part 1.
(2) This chapter shall be applied to structures of the maintenance categories A(preventive maintenance) and B (corrective maintenance).

[Commentary] (1) Chloride attack that occurs in concrete structures means the progress of steel
corrosion in concrete due to the existence of chloride ions in concrete, causing cracking or peelingin concrete due to the volume expansion of corrosion products or the lack of section of steel.
Chloride attack also means the performance degradation of the structure caused by above
phenomenons. Chloride ions not only accelerate steel corrosion but also change the composition of
concrete. This chapter discusses the matters related to steel corrosion. Chloride ions are supplied
either from external environments of the structure such as seawater and deicing agents or from thematerials used for producing concrete. Any type of deterioration attributable to the steel corrosion
accelerated by chloride ions is discussed in this chapter regardless of the source of supply ofchloride ions.

Deterioration due tochloride attack

Cracking occurs inconcrete due to corrosion
Steel starts
corrodingService period
Acceleration
Initiation
stage Propagation stage
Deterioration
stage
stage

- Deterioration ofaesthetic appearance

Performancedegradation of
structure

Performancedegradation of
structure

Deterioration due tochloride attack

Deterioration due to chloride attack and steel corrosion progresses during the initiation stage,
propagation stage, acceleration stage and deterioration stage (Fig. C10.1.1 and Table C10.1.1). In
each stage, deterioration has varying influences on the structure. The degree of performancedegradation with the progress of deterioration also varies according to the performance attribute.
The methods of assessment (investigation, deterioration prediction, evaluation or determination),
remedial measures implementation and recording vary in respective deterioration stages. A standard
maintenance procedure against chloride attack is shown in Fig. C10.1.2.

(a) Focused on aesthetic
appearance and landscape

Cracking occurs inconcrete due to corrosion
Steel starts
corrodingService period
Initiation
stage

Propagation
Deterioration
stage Acceleration
stage
stage
Reduction of-Load bearing capacity-Stiffness(b) Focused on safety

Fig. C10.1.1 Progress of deterioration progress due to chloride attack

122Chapter 10

Maintenance of Structures Subject to Chloride Attack

Table C10.1.1 Definitions of deterioration stages
Stage of deterioration
Initiation stage

Propagation stage
Acceleration stage
Deterioration stage

Definition
Until the chloride ion concentration on
the surface of steel reaches themarginal
concentrationfortheoccurrence of corrosion*
From the initiation of steel corrosion
until cracking due to corrosion
Stage in which steel corrodes at a highrate due to cracking due to corrosion
Stage in which load bearing capacity is
reduced considerably due to theincrease of corrosion amountStage determined by
Diffusion of chloride ions
Initially contained chloride ion
concentration
Rate of steel corrosion
Rate of corrosion of steel withcracks*The standard value is 1.2 kg/m3.

Possibility ofchloride
attack

(10.2)(10.3)

Maintenanceplan for the
structure

Assessment(10.3.2.2)
Investigations ininitial assessment(10.3.2.5)
Detailed
investigation

Standard
investigation(10.4)(10.3.3)(10.3.4)

Deterioration
prediction

Remedial
measures

Evaluation andjudgment(10.5)
Recording(10.3.2.3, 4)
Investigations inroutine/regularassessment(10.3.2.5)
Detailed
investigation

Standard
investigation(10.3.3)(10.3.4)

Deterioration
prediction
Evaluation andjudgment

Fig. C10.1.2 Standard maintenance procedure against chloride attack
There have been cases where concurrent deterioration due to carbonation and chloride attack
seriously damaged structures. This is because the movement and condensation of chloride ions in
concrete with the progress of carbonation in concrete accelerates steel corrosion. In thephenomenon, deterioration due to chloride attack was accelerated by carbonation. The structures123

Standard Specifications for Concrete Structures-2007, Maintenancesubjected to concurrent deterioration due to carbonation and chloride attack should be maintained inaccordance with the descriptions in this chapter.
(2) Maintenance category B (corrective maintenance) has been designated for numerous
existing structures. In the future, maintenance category A (preventive maintenance) is expected to
be designated for more structures. In maintenance category A, remedial measures are taken early
before performance degradation due to deterioration in view of the life-cycle cost. This chapter
therefore mainly discusses structures for which maintenance category A or B has been designated.
Structures for which maintenance category C (observational maintenance) has been designatedshould also be maintained by a basic method described in this chapter wherever possible.
For the matters that should be considered when specifying the maintenance category forstructures that have been or are expected to be subjected to deterioration due to chloride attack,refer to 10.2.2 “Maintenance Categories.” Special matters to be considered for respective
maintenance categories are also described in the section.

10.2 Maintenance Planning
10.2.1 Basis of planning
In order to maintain a structure subject to chloride attack, the category of maintenanceshall be selected, the service period planned, and a maintenance planning for activities
including assessment, remedial measures and recording drawn up in advance in view ofthe service and environmental conditions such as the concrete drying conditions andwater supplies.

[Commentary] When drawing up a maintenance planning, it is necessary to cover such details ascheck items and procedures for initial assessment and check items, procedures, timing andfrequency for the investigations in routine and regular assessment, evaluation and judgment
methods, actions to be taken in the event of deterioration, and recording methods, taking into
consideration the type, degree of importance and planned service period of the structure, category of
maintenance, and the quality of materials.
The type of structure, size and environmental conditions of concrete structures vary fromstructure to structure. A maintenance planning must be optimized for each structure. In a structure
subjected to chloride attack in particular, chloride ions are supplied either from external
environments of the structure such as seawater and deicing agents or from the materials used for
producing concrete. The progress of deterioration of structures subjected to chloride attack varies
greatly according to how chloride ions are supplied to concrete or how chloride ions exist in
concrete. These points should be taken into consideration for preparing an appropriate maintenanceplan.
It is usually difficult, at the stage of maintenance planning, to accurately predict the state of astructure during its service period. It is therefore good practice to draw up a maintenance planningwith reference to the deterioration of a similar structure or a structure in a similar environment.

10.2.2 Determination of maintenance category
The category of maintenance of a structure subject to chloride attack shall be selectedin view of the degree of importance of the structure, the type of structure, hazards for third
party, the planned service period and the characteristics of deterioration due to chloride
attack.

[Commentary] The determination of the category of maintenance is very important because
maintenance planning varies widely depending on the category of maintenance. The progress of124

Chapter 10

Maintenance of Structures Subject to Chloride Attack

deterioration and performance degradation due to chloride attack is conceptually illustrated in Fig.
C10.1.1.
Structures to which maintenance category A (preventive maintenance) is applied should bemaintained so that they might be placed under the condition during the initiation stage with no steel
corrosion, to prevent performance degradation. The state of the structure should therefore be
identified as accurately as possible. Requirements include the following.
(i) Quantitative identification of supply of chloride ions to the surface of the structure(ii) Quantitative identification and future prediction of chloride ion penetration into or
accumulation in concrete(iii) Verification and future prediction of steel corrosion in concrete
For structures with maintenance category A, remedial measures are taken before reinforcing
bars corrode due to deterioration. Thus, large-scale repair or strengthening can be eliminated andthe maintenance cost can be reduced accordingly in numerous cases.
Structures to which maintenance category B (corrective maintenance) is applied should bemaintained so as to prevent the performance of the structure from failing to meet the requirements.
Structures should be maintained to prevent deterioration from reaching the deterioration stage toensure safety, the latter half of the acceleration stage to achieve serviceability or the former half of
the acceleration stage to keep aesthetic appearance and landscape. Certain actions should be taken
when any of the following types of deterioration has been detected.
(i)

The corrosion of reinforcing bars in concrete(ii)

The leaching of corrosion rust on concrete surface(iii)

Cracking in the direction of axis of reinforcement on concrete surface(iv)

The spalling of concrete cover

For structures to which maintenance category B is applied, remedial measures should be taken
in phase (i) or (ii) above because it is extremely difficult to stop the progress of corrosion ofreinforcing bars in concrete once started. It should be noted that large-scale measures will be
required if deterioration reaches phase (iii) or (iv).
One maintenance category is generally applied to one structure. In cases where theenvironmental conditions vary from region to region or from member to member, however,
applying different maintenance categories to different regions or members may sometimes be
effective. For example, in a bridge located along the seashore, maintenance category A(preventive maintenance) is applied to beams and category B (corrective maintenance) is applied tosupplementary equipment including railings.

10.2.3 Preparation of maintenance manuals
A maintenance manual describing methods, procedures and frequency requirements
should be prepared for each structure in accordance with the maintenance planning,taking the structure-specific conditions into consideration.

[Commentary] The service period of civil engineering structures is long, and maintenance of
those structures is performed over a long period of time. It is recommended, therefore, that in order
to inform investigators of maintenance concepts and policies, a maintenance manual be prepared sothat detailed procedures and methods can be communicated accurately even to newly assigned
responsible engineers.
Under certain circumstances such as in cases where the original maintenance planning is alteredbecause the actual progress of deterioration turned out to differ from that assumed in the original
125

Standard Specifications for Concrete Structures-2007, Maintenancemaintenance planning, it is necessary to modify the maintenance manual and take appropriate
maintenance measures accordingly.
When preparing maintenance manuals, "The Maintenance Manual for Structures Subjected to
Chloride Attack Prepared in Accordance with the Standard Specifications for Design andConstruction of Concrete Structures: Maintenance (draft) " may be consulted.

10.3 Assessment
10.3.1 GeneralIn the assessment of a structure whose performance has declined or is highly likely todecline because of chloride attack, investigation, evaluation of the present state,prediction of deterioration and judgment of necessity for remedial measures shall beappropriately conducted in accordance with the maintenance planning.

[Commentary] In order to maintain concrete structures appropriately, this specification requires
three types of assessment: initial assessment, periodic assessment and extraordinary assessment.
Because the initial and periodic assessments are essential for the maintenance of structures, thischapter stipulates that those assessments must be conducted. Extraordinary assessments are
regarded as assessments to be conducted on an as-needed basis and are therefore not dealt with in
this chapter. By conducting periodic assessments during the maintenance period, defect inappearance of structures can be discovered before they occur or in early stages, and remedial
measures including preventive measures and repairs can be taken systematically.

10.3.2 Investigation in assessment
10.3.2.1 General
Investigations in initial, routine and regular assessment of a structure subject tochloride attack shall be conducted appropriately according to the category of maintenancerequired for the structure. Prior to investigation, check items, methods, frequency andscope of standard investigation shall be determined appropriately. For each type ofassessment, detailed investigation shall also be conducted on an as-needed basis.

[Commentary] It is important to select check items, methods, frequency and scope ofinvestigation appropriately according to the purpose of investigation in accordance with themaintenance planning.
The major parameters that should be identified in investigations of structures subjected tochloride attack are the distribution of chloride ion concentrations and the corrosion of internal steel
in concrete cover. In cases where deterioration has progressed considerably, investigations should
be conducted to directly evaluate performance.
The items to be examined in investigations vary according to the degree of deterioration. In
cases where it has been determined or assumed that the deterioration was in the initiation stage,investigations should be conducted mainly to identify the penetration of chloride ions. In cases
where it has been determined or assumed that the deterioration was in or beyond the propagation
stage, investigations should be conducted mainly to identify the progress of steel corrosion. Table
C10.3.1 shows major items to be examined in respective stages of deterioration. Data on the items
related to deterioration prediction such as the environmental action, chloride ion concentration,
depth of carbonation, steel corrosion and location of steel should be collected in as early a stage as
possible. Monitoring may be made for continuously identifying the penetration of chloride ions orwhether steel corrodes or not in concrete for structures for which maintenance category A(protective maintenance) has been designated126Chapter 10

Maintenance of Structures Subject to Chloride Attack

Table C10.3.1 Main check items in investigation
Stage of deterioration
Initiation Propagation Acceleration Deterioration
stage
stage
stage
stage
Defective appearanceO
OOO
Chloride ion concentration▲O
OO
Carbonation depth▲OO▲Steel corrosion
▲
O
O
O
▲
Concrete strength
O
▲
▲
▲
Load bearing capacity▲▲▲
Rebar alignment
▲
O
▲
▲
Environmental action
▲
O
▲
▲
Monitoring
▲
▲
▲
▲
O: Items to be investigated on a priority basis▲ Items that should preferably be investigated▲ Items to be investigated on an as-needed basis
The frequency and range of investigation should be determined considering the maintenancecategory, environmental conditions, structural format and the state of deterioration for the structure.
Deterioration due to chloride attack is likely to occur on the beams on the side providing access toships and on the side protected by revetment at piers; and bottom surface of the slab, beam ends,
structurally cracking-prone sections and sections accepting wastewater from road surface on bridges
in cases where bridges are subjected to the effect of deicing agents. These sections should be
investigated.
Regardless of the category of maintenance, it is important to go through the design drawings
and specifications, construction records, investigation results and the repair history prior to theinvestigation of a structure.
If the state of a structure cannot be judged appropriately by standard investigation, detailed
investigation must be conducted.

10.3.2.2 Investigation in initial assessment(1) In initial assessment, appropriate check items for standard investigation shall beselected for newly constructed structures, existing structures, large-scale repairs andstrengthened structures.
(2) If deterioration prediction, evaluation or judgment is difficult to make through astandard investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigation in initial assessment is the first investigation conducted when themaintenance of a concrete structure is started. Investigation in initial assessment includes not only
the first investigation of a newly constructed structure conducted before it goes into service but also
the first investigation of an existing structure or a structure for which remedial measures have beentaken in response to deterioration. Check items for the investigation may vary from structure to
structure. Basic check items for standard investigations in initial assessment of a newly constructedstructure are the document search on the design drawings and specifications and construction
records and observation. It is good practice to check on such details as concrete cover, the state ofsteel and porosity through nondestructive testing on an as-needed basis. When investigating a127

Standard Specifications for Concrete Structures-2007, Maintenancestructure for which remedial measures have been taken, it is also important to check for problems inrepaired or reinforced parts of the structure. These should be included in check items of standard
investigation. When an existing structure is investigated, check items are similar to those for a
newly constructed structure if design drawings and specifications and construction records exist. If
there is no such document or record, it is necessary to select check items of standard investigation
with reference to Section 10.3.2.5 “Detailed Investigation.” In cases where a prediction needs to bemade with high accuracy about a structure to which maintenance category A (preventive
maintenance) is applied, it is necessary to conduct investigations concerning the parameters used forthe method described in Section 10.3.3 “Method for Estimating Degradation of Performance ofStructure.”
Extremely important items in the investigation in initial assessment of a structure subject tochloride attack are listed below.
(i) Concrete mix proportions, water-cement ratio (water-binder ratio) in particular(ii) Type of cement(iii) Whether an additive is used or not, and type and volume of the additive(iv) Initial chloride ion content(v) Concrete cover(vi) Environmental condition(vii) Whether there are initial defects or not(viii) Condition of repaired or strengthened sections
Items (i), (ii) and (iii) are input values for equations (Eq. C10.3.4) and (Eq. C10.3.5) andessential to the prediction of chloride ion diffusion. Item (iv) is important when obtaining thechloride ion concentration in concrete cover. Item (v) is a very important factor affecting theinitiation and rate of steel corrosion and sometimes may not be as specified in design. Verification istherefore necessary. For item (vi), the volume of incoming chloride and cyclic wetting and drying
conditions should be identified under the marine environment. In cases where deicing agents are
sprayed, the frequency of application and the volume of agents should be identified. Item (vii)
greatly affects the durability of structures not only in chloride attack but also in other phenomenon.
Detecting defects in the initial investigation is important. Investigating the deformation in repaired
or strengthened sections and the condition of deformation (e.g. swelling or peeling of surface
coating) (item (viii)) is also important.
(2) If evaluation and judgment cannot be made with high accuracy by standard investigation
alone or if a highly deteriorated part of a structure is to be investigated, detailed investigation isnecessary. Check items of detailed investigation are indicated in Section 10.3.2.5 “Detailed
Investigation.”

10.3.2.3 Investigation in routine assessment(1) In routine assessment, standard investigation shall be conducted to detect not
only the defect of concrete surface such as cracking in concrete, peeling and spalling of
concrete covering, leaching of rebar rust, efflorescence and discoloring but also theleakage and the deterioration in appearance such as displacement and deformation.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) The purpose of investigation in routine assessment is to detect deterioration at
an early stage by checking on defect in the state of a structure over time. The determination of the128

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Maintenance of Structures Subject to Chloride Attack

time at which deterioration began in order to obtain information that is useful for predicting
deterioration is another important purpose of the investigation. In the investigation focus should beplaced on deterioration phenomena or their indicators such as cracking in concrete, peeling andspalling of concrete covering, leaching of rebar rust, efflorescence, discoloring, leakage,displacement and deformation. As for the structures to which maintenance category A (preventive
maintenance) is applied, the evaluation of their performance and also the judgment whether
remedial measures should be applied is generally difficult if they are in the initial stage, because
investigation in routine assessment is conducted mainly by observation. Then, appropriatemonitoring should also be employed and more items should be investigated as required. Specificmethods include the measurement of corrosion of internal steel by an electrochemical method e.g.
measuring half-cell potential and monitoring polarization resistance, and the installation of sensors
for estimating the penetration of chloride ions into concrete covering. Also effective is measuring
the chloride ion concentration, apparent chloride ion diffusion coefficient or steel corrosion in
specimens made of the same concrete as the structure to be examined and exposed under the same
condition. Exclusively inspecting the sections where deterioration was expected to progress as aresult of initial assessment is also effective.
(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone or if severe deterioration has already occurred, detailed investigation is conducted. Checkitems of detailed investigation are described in detail in Section 10.3.2.5 “Detailed Investigation.”

10.3.2.4 Investigation in regular assessment(1) The purpose of investigation in regular assessment is to obtain information that isdifficult to obtain in routine assessment. In regular assessment, standard investigationconsisting of detailed observation of defects shall be conducted as in routine assessment.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigation in regular assessment is conducted for obtaining the information
more detailed than that in routine assessment. Areas where signs of defects or deterioration havebeen detected in initial or routine assessment need to be examined intensively. The appearance ofthe structure should basically be examined as in routine assessment. Investigations of the
distribution of chloride concentration in concrete or steel corrosion may sometimes become
necessary in addition to the inspection of the appearance of the structure.
For predicting the initiation of corrosion accurately in periodic investigations, chloride ion
concentration should be measured at least twice during the initiation stage. For predicting the rate ofsteel corrosion during the propagation or acceleration stage, the corrosion amount of steel should bemeasured at least twice in each stage because the increase of the corrosion amount of steel is nearlyin proportion to the elapse of time.
For the structures for which maintenance category A (preventive maintenance) has been
designated, the frequency of measurement should be increased during the expected initiation stage
and propagation stage.
(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone or if severe deterioration has already occurred, detailed investigation is conducted. Checkitems of detailed investigation are described in detail in Section 10.3.2.5 “Detailed Investigation.”

129

Standard Specifications for Concrete Structures-2007, Maintenance10.3.2.5 Detailed investigation
Detailed investigation shall be conducted to obtain detailed information on a structure
subject to chloride attack in cases where the deterioration of the structure is difficult topredict, evaluate or judge by standard investigation alone in initial, routine or regularassessment. Check items, methods and location of a detailed investigation shall beselected appropriately taking into consideration such factors as the purpose ofinvestigation and the accuracy of obtained results.

[Commentary] When the determination of the present state of a structure and the deterioration
prediction of the structure are difficult by standard investigation alone, detailed investigation isconducted in order to obtain the information necessary for those purposes. Examples ofinvestigation items for structures subject to chloride attack, and of data on the condition of thestructure at the time of investigation and those in the future estimated from the investigation results
are listed in Table C10.3.2. The evaluation items estimated from data in the table are evaluated after
deterioration is predicted.
Table C10.3.2 Examples of evaluation items in detailed investigation
Measurement item

Data obtained by investigation

Temperature, humidity,
weathering and insulation
Amount of air-born chloride

Temperature, humidity and watercontent
Amount of air-born chloride

Cracking (width, depth anddensity)Concrete strength andmodulus of elasticity
Carbonation depth

Grade of corrosion and aesthetic
appearance
Concrete strength and stiffness

Distribution of chloride ion
concentrations

Water content
Location and corrosion ofsteel (area and volume) andleaching of rustElectrochemical indicators(e.g. half-cell potential,
polarization resistance andelectric resistivity)

Carbonation depth and carbonation
rate
Apparent chloride ion diffusion
coefficient, surface chloride ion
concentration, initial chloride ion
concentration and chloride ion
concentration at the location of steel
Water content
Grade of corrosion, corrosion
amount of steel and load bearing
capacity
Whether corrosion occurred or not
and rate of corrosion

Deflection and displacement Stiffness and load bearing capacity

Evaluation items
predicable from obtained
data
Qualitative corrosion rate
Chloride ion concentrationon concrete surface
Grade of corrosion,
aesthetic appearance
Future depth ofcarbonation
Chloride ion concentration
at the location of steel

Qualitative corrosion rate
Corrosion rate, load
bearing capacity
Future grade of corrosion
and corrosion rate-

Note: For the grade of corrosion, refer to Table C10.3.3.
Major investigation items are outlined below. For other investigation items, refer to 4.7“Investigations in Assessment.”
130

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Maintenance of Structures Subject to Chloride Attack(i) Chloride ion concentration
For the methods of collecting concrete cores or concrete granulated by drilling for measuring
the distribution on chloride ion concentrations in concrete, and for the methods for measuring the
distributions of total chloride ion concentrations in concrete using the samples, refer to JSCE-G 573"Measurement method for distribution of total chloride ion in concrete structure.”(ii) Steel corrosion
Steel corrosion has a direct impact on the performance of the structure in numerous cases. In
tests, therefore, the concrete cover should be chipped and whether corrosion has occurred or notshould be determined and the location, area, weight and depth of pitting corrosion should bemeasured directly. Obtaining quantitative data on corrosion could enable the quantitative evaluationof the reduction of physical property values and degradation of structural performance. Detailed
investigations are therefore necessary. To simplify the method of measurement, the state of steel
corrosion may be graded for evaluation as shown in Table C10.3.3.
Table C10.3.3 Grades of corrosion and state of steel
Grade of corrosion
I
II
III

IV

State of steel
Mill scale. Thin, compact rust layer all over the steel. No rustadhesion to concrete surface.
Swelling rust exists at some locations but is spotty in small
areas.
No lack of section is visually recognized. Swelling rust,
however, exists all around the reinforcement or throughout thelength of reinforcement.
Lack of section of reinforcement.

Grades I through IV roughly correspond to grades I-1, I-2, II and III for structural appearance
shown in Table C10.3.4. If no crack occurs due to corrosion and the location of corrosion isinvisible from outside, decision should be made using a half-cell potential distribution map or byother means.
When monitoring steel corrosion by nondestructive testing, electrochemical indicators such as
half-cell potential and polarization resistance should be measured. The values of these indicators are,however, affected by the state of concrete such as the water content and the degree of penetration ofchloride ions. Measurements should therefore be made in accordance with 4.7.3 “Inspection
Methods.”(iii) Appearance of Structures
In cases where performance of structure cannot be evaluated direct from the state of concreteand steel, the defect of appearance provides important data for performance evaluation. The gradesof appearance of structures deteriorated due to chloride attack are shown in Table C10.3.4. Grades
II-1 and II-2 are differentiated by the quantity of corroded steel. Differentiation is, however,difficult at the present technological level for deterioration prediction. For differentiation,observation is therefore essential.

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Standard Specifications for Concrete Structures-2007, Maintenance

Table C10.3.4 Grades of appearance of structure and state of deterioration
Grade of structural appearance
I-1 (initiation stage)

State of deterioration
No defect of appearance is found. The marginal chloride
ion concentration for the occurrence of corrosion has notbeen exceeded.
I-2 (propagation stage)
No defect of appearance is found. The marginal chloride
ion concentration for the occurrence of corrosion has been
exceeded. Corrosion initiates.
II-1 (first half of acceleration Cracking occurs due to corrosion. Leaching of rust is
stage)
observed.
II-2 (second half of acceleration Numerous cracks occur due to corrosion. Leaching of ruststage)
is observed. Partial peeling or spalling is found. The
corrosion amount of steel increases.
III (deterioration stage)
Numerous cracks occur due to corrosion. Crack width islarge. Leaching of rust is observed. Peeling and spalling arefound. Great displacement and deflection are observed.

10.3.3 Methods for predicting performance degradation of structures
10.3.3.1 General(1) In the maintenance of a structure subject to chloride attack, the performance of thestructure shall be evaluated quantitatively at the time of investigation, and futuredegradation shall be predicted.
(2) In order to predict the performance degradation of a structure, deterioration due tochloride attack shall be predicted quantitatively.
(3) If (2) is difficult, an alternative method is to predict performance degradation by
estimating the length of the initiation, propagation, acceleration and deterioration stages,
taking the penetration of chloride ions into consideration.
(4) Deterioration shall be predicted on the basis of investigation results.

[Commentary] (1) and (2) In the performance verification based maintenance system, changes(deterioration) in various performance attributes inherent in the structure should be predicted. To
that end, the progress of material deterioration should be predicted quantitatively. The performanceof the structure and the degree of deterioration of materials constituting the structure should be
evaluated quantitatively at the time of investigation and the end of planned service period.
Performance degradation of the structure or the degree of deterioration of materials constituting thestructure at the time of investigation may be evaluated quantitatively by an appropriate method
based on investigation results. The performance or the degree of deterioration at the end of theplanned service period should be predicted quantitatively based on the previous periodic
assessments. The prediction of deterioration progress is not always in agreement with actual
progress of deterioration. The method of prediction should therefore be reviewed based on the
results of investigations to be conducted later.
(3) When evaluating various performance attributes of a structure by combining the results ofprediction of deterioration progress of concrete and steel, quantitative prediction is difficult at thepresent technological level. Then, deterioration may be predicted quantitatively by predicting thelengths of initiation, propagation, acceleration and deterioration stages considering the penetrationof chloride ions into concrete and the progress of steel corrosion. The respective stages ofdeterioration and the factors determining their lengths are shown in Table C10.1.1.
132Chapter 10

Maintenance of Structures Subject to Chloride Attack

The length of the initiation stage is calculated using the chloride ion diffusion or initial chloride
ion concentration. The length of the propagation stage is calculated using the rate of corrosion andthe corrosion amount of steel at the time of cracking. The length of the acceleration stage iscalculated using the rate of corrosion of steel subjected to cracking due to corrosion. The length ofdeteriorating stage is calculated using the rate of corrosion of steel subjected to cracking due tocorrosion and the corrosion amount of steel when the load bearing capacity is reduced. The
calculation methods are described in 10.3.3.2 “Prediction of Chloride Ion Diffusion” and 10.3.3.3“Prediction of Progress of Steel Corrosion.”(4) Investigation results are related either to the quality of materials of the structure or to theenvironment in which the structure is placed while in service. These parameters should be used as abasis for predicting deterioration. If no data is available on the chloride ions in concrete for a newly
constructed structure or no investigation results are available for an existing structure, investigation
results or deterioration conditions for adjacent structures or for structures under the similar
environment may be consulted.

10.3.3.2 Prediction of chloride ion diffusion(1) Chloride ion diffusion shall be predicted properly considering the quality ofconcrete and the environment in which the structure is in service.
(2) Chloride ion diffusion may be predicted by one of the following methods.
(i) Obtaining an apparent chloride ion diffusion coefficient by applying a diffusion
equation.
(ii) Obtaining the diffusion coefficient of the material by conducting accelerated test.
(iii) Making a numerical analysis considering the reaction of chloride ions or the
movement of chloride ions at the boundary with the environment(iv) Using investigation results[Commentary] (1) Predicting chloride ion diffusion is important to accurate estimation of thelength of the initiation stage. Chloride ions transfer in concrete using the concentration gradient inwater existing in continuous fine pores as the driving force, or with the transfer of water. The
transfer of chloride ions is greatly affected by the composition of concrete or the transfer of water
under cyclic wetting and drying conditions. In cases where concrete has a high water-cement ratio
or is cured poorly, concrete is no longer sufficiently tight and chloride ions may transfer easily. The
transfer of chloride ions is also affected by the type of the cement or additive used. Under a severe
condition with cyclic wetting and drying like in seawater splash zones, chloride ions penetrate into
concrete substantially near the surface, greatly increasing the surface chloride ion concentration. In
cases of concurrent deterioration attributable to carbonation and chloride attack, chloride ions areconcentrated inside the carbonation front. Chloride ion diffusion should therefore be predicted byproperly considering the method for specifying the parameters, the variations of quality of concrete
cover and concrete and the effects of environmental conditions.
When predicting chloride ion diffusion, an appropriate safety factor should be specified
considering the method for specifying parameters, variations of the quality in the structure to bestudied and the effects of environmental conditions.
(2) Four major methods available for predicting chloride ion diffusion are described below.
(i) Obtaining an apparent diffusion coefficient by applying a diffusion equation
One method is to use a solution obtained by solving a diffusion equation known as Fick's second
law of diffusion equation (Eq. C10.3.1) under an appropriate boundary condition while regarding
the transfer of chloride ions in concrete as a simple diffusion process. Equation (Eq. C10.3.2) is a133

Standard Specifications for Concrete Structures-2007, Maintenancesolution of equation (Eq. C10.3.1) obtained based on the assumption that the surface chloride ion
concentration is constant. Equation (Eq. C10.3.2) has been generally used for analyzing the rate ofpenetration of chloride.
The chloride ion concentration in equation (Eq. C10.3.2) is not the liquid phase chloride ion
concentration in concrete but the total chloride amount per unit volume of concrete. The mechanismof transfer of chloride in concrete in the form of chloride ion is not precisely represented. The
chloride ion diffusion coefficient in equation (Eq. C10.3.2) is therefore referred to as an apparent
diffusion coefficient.
  2C 
C Dc 2 t
 x 

(Eq. C10.3.1)

where,
C: Chloride ion concentration in the liquid phase
Dc: Chloride ion diffusion coefficientx: Depth from concrete surface
t: time.
x
C ( x, t )   cl  Co 1  erf


2
D

t
ap



(Eq. C10.3.2)

where,
C(x, t): Chloride ion concentration (kg/m3) at depth x (cm) and time t (years)
C0: Chloride ion concentration at the surface (kg/m3)
Dap: Apparent chloride ion diffusion coefficient (cm2/year)
erf: Error function

cl: Safety factor for prediction precision
cl is generally related to the precision of prediction, and should be specified considering thevariations of the depth of concrete cover of the structure and of C0 and Dap, which are affected byenvironmental conditions. A value of 1.0 may generally be used.
Surface chloride ion concentration C0 in equation (Eq. C10.3.2) is a boundary condition forsolving equation (Eq. C10.3.1). Surface chloride ion concentration C0 is determined by the external
environment. Standard values are listed in Table C10.3.5. In addition to the values shown in thetable, the amount of chloride ions mixed during the production of concrete should be considered insolving the equation.
The surface chloride ion concentration and apparent chloride ion diffusion coefficient should beobtained based on the investigation results by regression analysis of the distribution of chloride ion
concentrations using equation (Eq. C10.3.2). In cases where initial chloride ions are involved, thevalue obtained by subtracting the initial chloride ion concentration from the measured chloride ion
concentration should be used for regression analysis. The apparent chloride ion diffusion coefficient
can be obtained from the distribution of chloride ion concentrations in the structure in accordancewith JSCE-G 573 "Measurement method for distribution of total chloride ion in concrete structure.”
In cases where no investigation results are available or where neither the apparent chloride ion
diffusion coefficient nor the surface chloride ion concentration can be obtained based on theinvestigation results, equations (Eq. C10.3.4) and (Eq. C10.3.5), and values in Table C10.3.5. may
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Maintenance of Structures Subject to Chloride Attack

be used. In the structures on which deicing agents are sprayed, however, the surface chloride ion
concentration should basically be obtained based on the investigation results. The concentration ofchloride ions mixed into concrete from materials should be considered as Ci in equation (Eq.
C10.3.3).
xC  x, t    cl・C（）
 Ci 
0 1 - erf
2 D t(Eq. C10.3.3)

where,
Ci: Initially contained chloride ion concentration (kg/m3)

cl: Safety factor for prediction precision
About apparent chloride ion diffusion coefficient: When using ordinary Portland cement,
equation (Eq. C10.3.4) may be used. When using Portland blast furnace slag cement, equation (Eq.
C10.3.5) may be used.
log10D = -3.9(W/C)2 + 7.2(W/C) – 2.5(Eq. C10.3.4)

log10D = -3.0(W/C)2 + 5.4(W/C) – 2.2(Eq. C10.3.5)

where,
D: Apparent chloride ion diffusion coefficient (cm2/year)
W/C: Water-cement ratio
About surface chloride ion concentration C0: For the structures subjected to the effects ofchloride ions in seawater, values in Table C10.3.5 may be used as surface chloride ion
concentrations.
Table C10.3.5 Surface chloride ion concentration C0 (kg/m3)
SplashDistance from seashore (km)zone
Near the
0.1
0.25
0.5
shoreline
Areas with a highvolume of
air-born salt
Areas with a low
volume of
air-born salt

Hokkaido, Tohoku,
Hokuriku andOkinawa
Kanto, Tokai, Kinki,
Chugoku, Shikoku
and Kyushu

1.0

9.0

4.5

3.0

2.0

1.5

4.5

2.5

2.0

1.5

1.0

13

C0 may be obtained near the seashore based on the assumption that a height of 1 m
corresponds to a distance of 25 m from the shoreline.
(ii) Obtaining the diffusion coefficient of the material by conducting accelerated testing
Methods of accelerated test concerning the penetration of chloride ions include increasing thechloride ion concentration in the environment, exposing concrete to alternate wetting and drying
conditions and forcing chloride ions to transfer using the potential difference. Methods forcalculating the apparent chloride ion diffusion coefficient using these methods have beenstandardized as the standards of the Japan Society of Civil Engineers (JSCE standards). Whenestimating the apparent chloride ion diffusion coefficient based on the results of accelerated test,
135

Standard Specifications for Concrete Structures-2007, Maintenancetesting both the concrete to be examined and the concrete specimen with the same mix proportions
as the concrete for which the apparent chloride ion diffusion coefficient has been identified innatural exposure tests or in investigations for actual structures for comparison is useful when
applying the results of accelerated testing to actual structures. The JSCE standards mentioned above
are JSCE-G571 2007 "Test method for effective diffusion coefficient of chloride ion in concrete by
migration" and JSCE-G572 2007 A "Test method for apparent diffusion coefficient of chloride ion
in concrete by submergence in salt water." The diffusion coefficient obtained in accelerated testing
may be used as the apparent diffusion coefficient in equation (Eq. C10.3.2) or (Eq. C10.3.3) when
an appropriate safety factor is taken into consideration.
(iii) Making a numerical analysis considering the reaction of chloride ions or the transfer ofchloride ions at the boundary with the environment
Researches have been conducted concerning the binding or adhesion of chloride ions to hydrateof cement, or the transfer of chloride ions with capillary water due to alternate wetting and drying.
In the methods based on these mechanisms, no chloride ion concentration is calculated as an
amount in unit volume of concrete but liquid phase chloride ion concentration is basically used.
(iv) Using investigation results
Simple method is to measure the chloride content using chipped concrete pieces during chipping
tests to examine steel corrosion in an actual structure. When using such methods, accurately
calculating the chloride diffusion coefficient is difficult but estimating the diffusion coefficient ispossible based on some assumptions.
In cases where cracking has occurred in concrete due to corrosion, chloride ions penetrating thecracks have direct impact on reinforcing bars. Then, corrosion is highly likely to be accelerated.
When calculating the chloride ion diffusion coefficient in the affected section, cracking should betaken into consideration. In concrete in which carbonation has progressed, the distribution ofchloride ion concentrations varies. Chloride ion concentration decreases at concrete surface andincreases inside the carbonation front. When calculating the apparent chloride ion diffusion
coefficient, the effects of carbonation should be fully taken into consideration if the concrete is
subjected to carbonation.

10.3.3.3 Prediction of steel corrosion(1) The progress of steel corrosion due to chloride attack shall be predicted properly
considering the concrete quality and the environment in which the structure is in service.
(2) The initiation of steel corrosion should be determined based on the chloride ion
concentration in the concrete cover.
(3)The progress of steel corrosion before cracking occurs due to corrosion may be
predicted by either of the following methods.
(i) Method based on the quantity of corroded steel obtained from the investigation(ii) Method based on the rate of reaction of steel to corrosion(4) Cracking due to corrosion may be predicted by either of the following methods.
(i) Predicting from the quantity of corroded steel(ii) Predicting using a mechanical model(5) The progress of steel corrosion after cracking due to corrosion should be
predicted by properly evaluating the effects of cracking on the mobility of substances.

[Commentary] (1) Regarding the factors affecting the corrosion of steel reinforcement, chloride
ion content, pH value in the pore solution at the position of reinforcement and amount of oxygen
supply to steel surface and water content in concrete can be listed. However, the effects of these136

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Maintenance of Structures Subject to Chloride Attack

factors on the corrosion rate is not clarified quantitatively enough to achieve precise prediction
Corrosion reaction requires oxygen. The rate of oxygen supply to the steel therefore affects therate of corrosion. The oxygen transfer rate in concrete is affected by the types of cement, admixture
and aggregate, water-cement (water-binder) ratio, degree of hydration of binder and water content.
As the water content of concrete decreases, oxygen supply increases. In an excessively dry
condition, the rate of corrosion decreases because the corrosion reaction requires water. When
predicting corrosion, therefore, environmental actions such as cyclic wetting and drying should be
evaluated properly. No effects on environmental actions have, however, yet been quantitatively
identified.
(2) The pore solution in concrete with a pH of 12 or higher is highly alkaline. Steel is in a
passive state in a highly alkaline environment and is unlikely to corrode. The mechanism causing
steel to turn passive is generally explained as the formation of a passive coating due to the chemical
absorption of oxygen on the surface of steel and subsequent generation of a compact oxide layer. If
chloride ions exist beyond the marginal chloride ion concentration for causing corrosion, thepassive coating is destroyed and steel starts corroding.
If the marginal chloride ion concentration for causing corrosion can be obtained based on theinvestigation results for the structure, the value should in principle be used for predicting theinitiation of steel corrosion. Otherwise, the marginal chloride ion concentration for causing
corrosion may be set to be 1.2 kg/m3 in accordance with “Standard Specification [Design].”(3) Methods of predicting the progress of steel corrosion up to the crack appearance aredescribed below.
(i) Method based on the corrosion amount of steel obtained from investigation results
In cases where the time-based change in corrosion amount of steel has been identified byinvestigations, the progress of corrosion should be predicted based on the result.
If the corrosion amount of steel and the initiation of steel corrosion are known as a result ofinvestigations, for example, subsequent corrosion can be predicted by assuming a curve
representing the time-based change in corrosion amount of steel. Even where the initiation of
corrosion is unknown, curves representing time-based change can be estimated if the results ofmeasurement of the corrosion amount of steel at two or more ages are available. Then, the progressof deterioration should be properly predicted considering that chloride attack causes severe partial
corrosion of steel.
For chloride attack, the degree of deterioration can be evaluated in several grades of corrosion.
If the relationship between the chloride ion concentration at the location of steel and the degree ofsteel corrosion is identified in advance, the grade of corrosion can be predicted by predicting
chloride ion diffusion.
(ii) Method based on the reaction rate of steel to corrosion
A method for estimating the rate of reaction of steel to corrosion using amount of oxygen supply
as well as chloride ion diffusion as parameters has been studied. The precision of prediction will
increase if parameters in a model can be set properly based on the results of investigations.
(4) Cracking of concrete due to steel corrosion not only causes aesthetic deterioration but also
lets more deterioration factors intrude into the structure and accelerates the progress of corrosion. If
the progress of corrosion is predicted and the corrosion amount at the time of the crack appearance
has been determined, the timing of crack appearance can be predicted. The following methods may
be used for prediction.
(i) Method based on the volume of corroded steel
The timing of crack appearance is predicted by obtaining the corrosion amount of steel thattriggers cracking by using test results on steel corrosion in concrete. One method for obtaining test137

Standard Specifications for Concrete Structures-2007, Maintenanceresults in a relatively short period of time is to accelerate steel corrosion by electrolytic corrosion
test. Corrosion progresses homogeneously in steel in electrolytic corrosion testing unlike under thecondition in chloride attack under which steel is subjected to serious partial corrosion. The
mechanism is, however, the same that causes cracking in concrete due to corrosion with the
expansion of corrosion products. The results of electrolytic corrosion test may be used for reference
if investigations are conducted simultaneously.
(ii) Method using a mechanical model
The corrosion amount at the time of cracking is affected by concrete cover, concrete strengthand steel bar diameter. Various elastic and elastoplastic analysis methods considering the effects
have been proposed. These methods may be used by specifying model parameters properly.
(5) No methods have yet been established for predicting steel corrosion after the crack
appearance due to corrosion. Of the parameters for various models of corrosion with nocorrosion-induced cracking, replacing the values of parameters such as the apparent chloride ion
diffusion coefficient, transfer rate of oxygen and water with the values of parameters for models
subjected to cracking due to corrosion is realistic. The validity of methods should be verified by
testing.
In the acceleration stage and deteriorating stage, load-bearing capacity should be evaluated byproperly evaluating the reduction ratio of steel cross section, depth of pitting and bond strength.

10.3.3.4 Modification of prediction
If the state of deterioration determined in an investigation differs from a predicted stateof deterioration, the cause of the difference shall be identified and the prediction shall berevised accordingly. If necessary, the maintenance planning shall be altered.

[Commentary] When the deterioration confirmed in investigations is different from the prediction,
appropriate investigations should be conducted using the deterioration prediction methods shown in
10.3.3.2 “Prediction of Chloride Ion Diffusion” and 10.3.3.3 “Prediction of Progress of SteelCorrosion” and based on Table C10.3.2 in 10.3.2.5 “Detailed examinations” to examine the cause
for the difference, and the prediction should be modified. Then, the results of several investigations
conducted until that are useful to the examination of causes and the modification of the prediction.
Revising the subsequent maintenance plans including a review of investigation frequency based on
the modified prediction is also important.

10.3.4 Evaluation and judgment(1) The evaluation of performance and judgment as to whether remedial measuresneed to be taken based on the results of the investigation in initial, routine and regularassessment shall be made in accordance with Part 1 and Item (2) and subsequent items inthis section.
(2) The performance of a structure subject to chloride attack shall be evaluated byappropriately selecting performance attributes to be evaluated in view of the stage ofdeterioration of the structure.
(3) The evaluation of performance attributes at the time of investigation and at the endof the planned service period of the structure should be made by a quantitative method.
(4) If Item (3) is difficult to achieve, the evaluation of performance attributes at the timeof investigation and at the end of the planned service period of the structure may be made138

Chapter 10

Maintenance of Structures Subject to Chloride Attackby a semi-quantitative grading-based method.
(5) Judgment as to whether remedial measures need to be taken shall be made in viewof the degree of performance degradation due to chloride attack, the degree of importanceof the structure, category of maintenance, and the remaining service life.

[Commentary] (1) The evaluation of performance and judgment of necessity for remedial
measures in initial, routine and regular assessment for structures in which little progress ofdeterioration has been recognized are frequently more or less the same regardless of thedeterioration mechanism. For details, refer to Part 1. The evaluation of performance and judgmentof necessity for remedial measures for structures in which deterioration may have or has progressedvary according to the deterioration mechanism. When discussing the performance degradation due
to chloride attack, the descriptions in this chapter should be consulted.
(2) In structures subjected to chloride attack, the performance attribute to be affected bydeterioration varies depending on whether deterioration is in the initiation, propagation, acceleration
or deterioration stage. The performance attribute to be evaluated should be properly selected foreach stage of deterioration. In the initiation stage, steel is likely to corrode due to chloride ions, andin the propagation stage, steel corrosion progresses due to the supply of oxygen through theconcrete cover. The steel protection performance, one of the durability parameters, should therefore
be evaluated. In the acceleration stage, the corrosion amount of steel remarkably increases due tothe cracking ascribable to corrosion. Then, the steel protection performance, serviceability in suchterms as the stiffness and ductility of members, hazards for third party such as peeling and spallingof concrete due to cracking, and aesthetic appearance should be evaluated. In the deterioration stage,corrosion progresses further. In addition to the performance attributes to be evaluated in theacceleration stage, safety performance including load-bearing capacity should be evaluated.
In cases where the steel has corroded and has been subjected to cyclic loading, the hazards forthird party including the spalling of concrete may be an issue in early stages like the propagation
stage.
(3) The performance of a structure at the time of investigation and at the end of the planned
service period should be evaluated after quantitatively evaluating the deterioration of concrete andsteel.
For evaluating the performance of a structure at the time of investigation, safety andserviceability are verified by obtaining the load bearing capacity and deformation by, for example,
substituting the mechanical properties of materials obtained from investigation results into a
structural calculation formula. Also conceivable is the verifying of the hazards for third party andaesthetic appearance and landscape based on the range and density of cracking or peeling and thedegree of steel corrosion. Performance can be evaluated relatively explicitly at the time ofinvestigation by such verifications in cases where deterioration is not serious. In cases whereserious deterioration has occurred and the expansion of steel or the deterioration of bond withconcrete is large, or in cases where concrete cover has been delaminated or spalled, appropriate
methods reflecting these effects should be examined.
Performance at the end of the planned service period should be evaluated based on the results ofperformance evaluation at the time of investigation and the results of deterioration prediction.
Evaluating performance with sufficient accuracy is difficult in numerous cases. As a supplementarymeasure, deterioration is generally predicted based on the apparent diffusion coefficient of chloride
and the rate of steel corrosion using the methods shown in 10.3.3 "Methods for Predicting
Performance Degradation of Structure." Then, the accuracy of the deterioration prediction method
as well as the accuracy of the performance verification method is important. Prediction methods
should therefore be selected carefully. Adequate safety should be guaranteed.
(4) In the performance verification type design system, structural performance should ideally be
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Standard Specifications for Concrete Structures-2007, Maintenanceevaluated quantitatively. At present, however, there is no established method of quantitative
estimation. As a practical method, the performance of a structure can be evaluatedsemi-quantitatively, with reference to Table C10.3.6, by performing appearance grading inaccordance with Table C10.3.4.
The purpose of grading is to classify the present degree of deterioration of a structuresemi-quantitatively instead of predicting and evaluating the degree of deterioration in future. It isalso possible, however, to predict the performance of a structure at the end of the planned service
period in accordance with Table C10.3.6 by estimating the stage of deterioration at the end of theplanned service period on the basis of investigation results such as the apparent diffusion coefficientof chloride and steel corrosion. The method of estimating the degree of deterioration at a certain
point of time in future by constructing a deterioration grade model based on a stochastic theory suchas a Markov model has also been proposed.
If detailed maintenance records for a similar structure (type of structure, materials, construction,
environment, state of use) are available and its progress of deterioration is also similar to that of theevaluated structure, then the evaluation results for the similar structure provide useful information.
Table C10.3.6 Grades of appearance of structures and typical performance degradation
Grade ofappearance ofstructure

SafetyServiceability

Hazards
for third
party

I-1 (initiation
stage)
I-2(propagation
stage)
II-1 (first halfofacceleration
stage)
II-2 (second
half ofacceleration
stage)
III(deterioration
stage)---

Aesthetic
appearance
andlandscape
-

-

-

-

-

-

-

-

Aesthetic
deterioration-CrackingDeterioration of load
bearing capacity andductility

Deterioration of stiffness(increase of deformationand occurrence of vibration)

Hazards
for third
party-Lack of section ofsteel-Lack of section of steel-Peeling-Deterioration of bond
between steel and concrete-Spalling-Reduction of
concrete crosssection due toswelling or peelingof concrete-Leaching ofsteel rust
-Exposure ofsteel-Reduction of concrete crosssection due to swelling or
peeling of concrete(5) Because judgment is the act of deciding whether remedial measures need to be taken on thebasis of structural performance evaluation results, there is no difference depending on deterioration
factors. Therefore, refer to Part 1.

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Maintenance of Structures Subject to Chloride Attack

10.4 Remedial Measures
10.4.1 Selection of remedial measures(1) If it has been judged that remedial measures need to be taken in connection withperformance degradation of a structure subject to chloride attack, remedial measures bywhich the corrected structure meets the required performances shall be selected.
(2) If it is difficult to select remedial measures for a structure on the basis ofperformance verification, remedial measures may be selected from the measurescorresponding to the grade of appearance.

[Commentary] (1) If it has been judged, as a result of evaluation, that remedial measures need tobe taken, it is necessary to select one or more of the following measures: (i) intensified investigation,(ii) repair, (iii) strengthening, (iv) functional improvement, (v) restriction in service or (vi)dismantling/removal. Basically, decisions as to which measures to take should be made by the
maintenance manager of the structure, but it is good practice to refer to Part 1 for information on
typical relationships between evaluation and judgment results and remedial measures.
(2) If it is difficult to select remedial measures for a structure through quantitative evaluation or
judgment, remedial measures are selected from the measures corresponding to the deterioration
grade of the structure. Remedial measures to be taken vary depending on the type of structure, thedegree of importance of the structure, deterioration rate and the category of maintenance, but
recommended standard measures are shown in Table C10.4.1.
Table C10.4.1 Grades of appearance of structure and remedial measures
Grade of appearanceof structure
Grade I-1 (initiation
stage)
Grade I-2
(propagation stage)
Grade II-1 (first halfof acceleration
stage)
Grade II-2 (second
half of acceleration
stage)
Grades III(deteriorating stage)

Restriction Dismantlingin service /removal

Intensified
investigation

RepairStrengthening**

Functional
improvement

O

O**

X

X

O

O

X

X

OO

OO

X

X

OO

OO*

X

X

O

O*

X

X

OO

OO

OO : Standard remedial measures (OO*:Including the restoration of mechanical performance)
O : Remedial measures in some cases(O*: Including the restoration of mechanical performance)
O**: Preventive measure
X : Remedial measure taken based on other criterion than the grade of appearance
Strengthening**: Enhancing the mechanical performance above the initial level

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Standard Specifications for Concrete Structures-2007, Maintenance10.4.2 Repair and strengthening
For repair or strengthening, methods and materials should be selected so as toachieve the designated required performances, considering the performance degradation
due to chloride attack and the life-cycle cost.

[Commentary] In cases where repair or strengthening is carried out as a remedial measure, it isnecessary to define the expected effect of repair or strengthening and the required performance(what level of performance to be maintained for how many years?). Ideally, it is desirable that
remedial measures be taken after constructing a deterioration formula (for repair) or structural
calculation formula (for strengthening) in view of such factors as the properties of the materials
used and verifying the calculation results obtained from those formulas. In this case, it is also
important to take life cycle cost into consideration according to the remaining planned service
period.
When taking preventive measures for a structure to which maintenance category A (preventive
maintenance) is applied, an appropriate method should be selected fully considering the effect thatshould be achieved by the method.
The methods of repair or strengthening for structures subject to performance degradation due tochloride attack are listed in Table C10.4.2 by expected effect. When selecting the method, Table
C10.4.2 and the present performance degradation of the structure should be considered. For thegrades of appearance deterioration of structure and remedial measures, refer to Table C10.4.3.
Table C10.4.2 Expected effects and methods of repair or strengthening
Expected effectReduce the supply of
corroding-factors
Remove the corroding-factors
Control the progress of steel
corrosion
Increase the load bearing capacity

Examples of methods
Surface treatment
Patching and electrochemical desalination
Surface treatment, Cathodic protection,
Patching and Rust-preventing coating
FRP adhesion, patching, external cable,
Jacketing and Thickness increasing

Table C10.4.3 Grades of structural appearance and standard methods of repair orstrengthening
Grade of structural appearance
I-1 (initiation stage)I-2 (propagation stage)

Standard method

Surface treatment*
Surface treatment, patching, Cathodic protection andelectrochemical desalination
II-1 (first half of acceleration Surface treatment, patching, cathodic protection andstage)
electrochemical desalination
II-2 (second half of acceleration Patchingstage)III (deteriorating stage)
FRP bonding, patching, external cable, Jacketing and Thickness
increasing*: Preventive method
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Maintenance of Structures Subject to Chloride Attack

In the initiation stage due to chloride attack, neither performance degradation nor deterioration
has occurred in the structure. In the period, remedial measures are taken only for structures to which
maintenance category A (preventive maintenance) is applied. Then, remedial measures are expected
to prevent chloride ions from intruding into concrete and diffusing. Surface treatment should
therefore be applied to prevent chloride ions from entering the concrete from the external
environment.
In the propagation stage, steel has corroded but the corrosion amount of steel is still low andlittle performance degradation has occurred. In the stage as in the initiation stage, surface treatment
is generally selected. Patching or electrochemical desalination may sometimes be applied to remove
chloride ions that intruded into the concrete. A cathodic protection method may be applied toprevent steel corrosion from progressing.
In the first half of the deterioration acceleration stage, the deterioration of mechanicalperformance is not yet outstanding. Cracks occur in concrete cover due to steel corrosion. An
electrochemical desalination method for removing the chloride ions from concrete or the patchingfor removing the concrete cover may be considered. As a part of the patching, surface treatment
may also be applied after the repair. In order to prevent further progress of steel corrosion, applying
cathodic protection should also be considered.
In the second half of the acceleration stage, serviceability is reduced due to the deterioration of
stiffness, and the concrete cover either is delaminated or spalls, resulting in serious hazards for third
party. In this stage, the concrete cover is removed and the patching is applied. As a part of thepatching, simultaneously applying surface treatment should be considered, and the addition or
replacement of reinforcing bars should also be considered.
In cases where the deterioration stage has been reached and the load bearing capacity has been
reduced, methods for restoring the load bearing capacity by such means as the adhesion of steel or
FRP plates/sheets, use of external cable, jacketing and the thickness increasing should be applied inaddition to the patching through the addition or replacement of reinforcing bars. These methods
should be implemented after removing the concrete cover and applying surface treatment, forpreventing re-deterioration.
When selecting a method that has been applied in few cases, the frequency of post-repair or-strengthening investigations should be increased. Many of the repair or strengthening methods
applied have been developed only recently and few have been applied to actual structures. If suchmethods are adopted, the structure may be re-deteriorated and its performance may be degraded dueto the factors not expected in the design phase. Measures should therefore be taken such asincreasing the frequency of investigations after the repair or strengthening.
For details of the methods of repair and strengthening, refer to the "Guidelines for Strengthening
Concrete Structures (draft)," "Guidelines for Repairing or Strengthening Concrete Structures Using
Continuous Fiber Reinforced Membrane," "Guidelines for Design and Implementation ofElectrochemical Protection (draft)," "Guidelines for Design and Implementation of Surface
Protection (draft)," "Shotcreting Guidelines (draft) - Repair and Strengthening," "Reports ofConcrete Structures Repair Method Committee I, II and III" and "Reports of Concrete Structures
Restoration Committee" prepared by the Japan Concrete Institute. Applying the re-alkalization orelectrical protection method to a structure using reactive aggregate is likely to encourage thedeterioration of the structure due to alkali silica reaction. Then, the "Guidelines Concerning theApplication of Electrochemical Protection Considering Alkali-silica Reaction" prepared by theSociety of Materials Science, Japan should be consulted and the applicability of the repair method
and the method of implementation should be determined carefully.

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Standard Specifications for Concrete Structures-2007, Maintenance10.5 Recording(1) Investigation, deterioration estimation, evaluation and judgment, and remedial
measures shall be recorded in accordance with Part 1.
(2) Items relevant to chloride attack shall be recorded.

[Commentary] As a general rule, the results of investigations, deterioration estimations,evaluations and remedial measures must be recorded in accordance with Part 1. Items relevant tochloride attack require careful attention, particularly with respect to record keeping. Items to berecorded are the investigation items indicated in Section 10.3.2 “Investigation in Assessment", andthe evaluation items indicated in Section 10.3.4 “Evaluation and Judgment.”

144

Chapter 11

Maintenance of Structures Subject to Frost Attack

CHAPTER 11 MAINTENANCE OF STRUCTURES SUBJECT TO
FROST ATTACK

11.1 General(1) This chapter provides standard methods for the maintenance planning,assessment, remedial measures and recording for structures that have beenor are highly likely to be subject to performance degradation due to frost
attack. The items common to all deterioration mechanisms are shown in Part
1.
(2) This chapter shall be applied to structures of the maintenance categories A(preventive maintenance) and B (corrective maintenance).

- Corrosion of steel- Exposure of aggregate- Spalling of aggregate
Beginning of scaling

Initiation
stage

Freezing andthawing cycles

Propagation Acceleration Deterioration
stage
stage
stage

- Aesthetic deterioration

Frost attack deteriorationof concrete- Exposure of steel

Performance degradationof member

Performance degradationof member

Frost attack deteriorationof concrete[Commentary] (1) Frost attack damage, which is caused by the freezing expansion of water inconcrete, is the deterioration of concrete resulting from the freezing and thawing cycles occurring
over a long period of time. Typically, micro crack, scaling, pop-out, and the like occur at theconcrete surfaces of structures subjected to frost attack. Micro cracks and scaling often occur incases where the quality of concrete is low or air bubbles have not been entrained appropriately.
Pop-outs are often seen in cases where the quality of aggregate is low. The degree of deterioration
due to frost attack is determined by various factors, namely, factors related to materials such as themix proportions (e.g., cement content, water/cementitious material ratio, air content) of concreteand the quality of aggregates, factors related to structures such as the shape of cross section and theamount of reinforcing steel, and factors related to the environmental conditions under which
structures are used such as the degree of water supply, the influence of insulation, ambient
temperature (especially the lowest temperature) and the number of freezing and thawing cycles.

- Exposure of steel- Corrosion of steel- Exposure of aggregate- Spalling of aggregate
Beginning of scaling

Initiation
stage

Freezing andthawing cycles

Propagation Acceleration
stage
stage

- Reduction of load bearing capacity- Reduction of stiffness(b) Focus on safety(a) Focus on aesthetic appearance and landscapeFig. C11.1.1 Conceptual view of deterioration progress due to frost attack

145

Deterioration
stage

Standard Specifications for Concrete Structures-2007, Maintenance

Table C11.1.1 Definition of deterioration stages
Stage of
Deterioration

Definition

Factor determining the stage

Initiation
stage

Until concrete begins to scale under the Possibility of frost attack damage,influence of freezing and thawing lowest temperature, frozen water
cyclescontent, freezing and thawing cycles

Propagation
stage

Until aggregate exposure or spalling
Lowest temperature, frozen water
occurs due topropagations ofcontent, freezing and thawing cycles
concrete surface deterioration

Acceleration
stage

Until steel exposure occurs or steel Deterioration depth by frost attack,corrosion begins
rate of steel corrosion

Deterioration
stage

Stage in which load bearing capacity is
Deterioration depth by frost attack,reduced considerably due to increased
rate of steel corrosion
steel corrosion

Frost attack deterioration not only mars the appearance of structures but also reduces the masstransfer resistance of concrete. In areas where chloride attack as well as frost attack damage isproblematic, steel corrosion could begin earlier under the influence of frost attack. A method for its
prediction, however, is yet to be developed.
As shown in Fig. C11.1.1(a), degradation in appearance due to frost attack can be classified into
four stages, namely, the initiation stage until the beginning of concrete surface scaling caused byfreezing and thawing cycles, the propagation stage until the beginning of , the acceleration stage
until steel exposure occurs due to lack of concrete cover, and the deterioration stage after
occurrence of steel corrosion. From the viewpoint of the safety performance of structural members
including resistance to steel corrosion, deterioration in terms of decreases in the strength andstiffness of structural members due to frost attack can also be classified, as shown in Fig. C11.1.1(b),into the initiation stage until the beginning of deterioration such as concrete surface scaling due tofreezing and thawing cycles, the propagation stage until the occurrence of aggregate spalling, theacceleration stage until the occurrence of steel corrosion due to decreases in cover concrete, and thedeterioration stage in which deteriorations such as decreases in load-carrying capacity result fromsteel corrosion.
Table C11.1.1 shows the definitions of deterioration from the viewpoints of decreases instrength and stiffness of structural members and lists factors determining the stage of deterioration.
In the management of structures in non-freezing environment, however, it is not advisable to leave astructure in the frost attack deterioration process unrepaired until the acceleration or deterioration
stage defined in Table C11.1.1.
Fig. C11.1.2 shows standard procedures for the maintenance of structures in a frost attack
environment.
(2) This maintenance standard is applicable to maintenance category A and B. Maintenancecategory B(corrective maintenance) is applied to many of existing ordinary structures. It is also
likely, however, that if, for example, waterproofing measures such as surface treatment are taken forstructures constructed in the coming years, structures requiring maintenance category A (preventive
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Chapter 11

Maintenance of Structures Subject to Frost Attack

maintenance) will increase. Even in the maintenance of structures to which maintenance category C(observational maintenance) is applied, it is necessary to carry out maintenance as described in thischapter.
For the matters that should be considered when determining the maintenance category forstructures that have been or are expected to be subject to deterioration due to frost attack, refer to
11.2.2 "Maintenance Category." Special matters to be considered for respective maintenancecategories are also described in this chapter.

Possibility offrost attack(11.2)(11.3)

Maintenanceplan for the
structure

Assessment(11.3.2.2)
Investigations ininitial assessment
Standard
investigation(11.3.2.5)
Detailed
investigation(11.4)(11.3.3)(11.3.4)

Deterioration
prediction

Remedial
measures(11.5)
Recording

Evaluation andjudgment(11.3.2.3, 4)
Investigations inroutine/regularassessment
Standard
investigation(11.3.3)(11.3.4)(11.3.2.5)
Detailed
investigation

Deterioration
prediction
Evaluation andjudgment

Note: The numbers in parentheses indicate the relevant sections or subsections in this chapter.
Fig. C11.1.2 Standard maintenance procedure against frost attack

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Standard Specifications for Concrete Structures-2007, Maintenance11.2 Maintenance Planning
11.2.1 Basis of planning
In order to maintain a structure subject to frost attack, the category of maintenanceshall be selected, the service period planned, and a maintenance planning for activities
including assessment, remedial measures and recording drawn up in advance in view ofthe service and environmental conditions such as the water supplies.

[Commentary] When drawing up a maintenance planning, it is necessary to cover such details ascheck items and procedures for initial assessment and check items, procedures, timing andfrequency for the investigations in routine and regular assessment, evaluation and judgment
methods, actions to be taken in the event of deterioration, and recording methods, taking into
consideration the type, degree of importance and planned service period of the structure, category of
maintenance, and the quality of materials.
The type of structure, size and environmental conditions of concrete structures vary fromstructure to structure. A maintenance planning must be optimized for each structure. The progress ofdeterioration due to frost attack varies considerably depending on the degree to which water is
supplied, the influence of insulation, ambient temperature (especially the lowest temperature) andthe number of freezing and thawing cycles. It is therefore necessary to draw up an appropriate
maintenance plan, taking these factors into consideration. When measures such as surface
protection are taken at the construction stage, it is also necessary to perform maintenance, taking
into consideration the duration of the protection effect.
It is usually difficult, at the stage of maintenance planning, to accurately predict the state of astructure during its service period. It is therefore good practice to draw up a maintenance planningwith reference to the deterioration of a similar structure or a structure in a similar environment.

11.2.2 Determination of maintenance category
The category of maintenance of a structure subject to frost attack shall be selected inview of the degree of importance of the structure, the type of structure, hazards for third
party, the planned service period and the characteristics of deterioration due to frost
attack.

[Commentary] The determination of the category of maintenance is very important because
maintenance planning varies widely depending on the category of maintenance. The progress ofdeterioration and performance degradation due to frost attack is conceptually illustrated in Fig.
C11.1.1.
Structures to which maintenance category A (preventive maintenance) is applied should bemaintained so that they might be placed under the condition during the initiation stage with noscaling, to prevent performance degradation. The state of the structure should therefore be identified
as accurately as possible. Requirements include the following.
(i)

Evaluation of environmental conditions such as the supply of water and the lowest
temperature(ii)

Quantitative evaluation and prediction of deterioration progress due to scaling of the148Chapter 11

Maintenance of Structures Subject to Frost Attack

surface layer of concrete
Structures to which maintenance category B (corrective maintenance) is applied should bemaintained so as to prevent the performance of the structure from failing to meet the requirements.
In the event of frost attack damage, the following stages of deterioration can be observed:(i)Concrete surface deterioration is observed.

(ii)

Exposed aggregates can be observed.

(iii)

Aggregate spalling can be observed.

Once deterioration due to frost attack has started, it is extremely difficult to stop the progress ofdeterioration. It is desirable, therefore, that remedial measures be taken at Stage (i) or Stage (ii)mentioned above even in the case of a structure to which maintenance category B (corrective
maintenance) is applied. It should also be kept in mind that large-scale remedial measures need tobe taken if deterioration progresses to Stage (iii).
It is common practice to apply a single category of maintenance to a single structure. There arecases, however, where it is more reasonable to apply different types of maintenance to different
parts or members of a structure. For example, it may be reasonable to apply maintenance category A(preventive maintenance) to the parts of a structure where appearance is important andmaintenance category B (corrective maintenance) to the rest of the structure.

11.2.3 Preparation of maintenance manuals
A maintenance manual describing methods, procedures and frequency requirements
should be prepared for each structure in accordance with the maintenance planning,taking the structure-specific conditions into consideration.

[Commentary] The service period of civil engineering structures is long, and maintenance of
those structures is performed over a long period of time. It is recommended, therefore, that in order
to inform investigators of maintenance concepts and policies, a maintenance manual be prepared sothat detailed procedures and methods can be communicated accurately even to newly assigned
responsible engineers.
Under certain circumstances such as in cases where the original maintenance planning is alteredbecause the actual progress of deterioration turned out to differ from that assumed in the original
maintenance planning, it is necessary to modify the maintenance manual and take appropriate
maintenance measures accordingly.

11.3 Assessment
11.3.1 GeneralIn the assessment of a structure whose performance has declined or is highly likely todecline because of frost attack, investigation, evaluation of the present state, prediction ofdeterioration and judgment of the necessity for remedial measures shall be appropriately
conducted in accordance with the maintenance planning.

149

Standard Specifications for Concrete Structures-2007, Maintenance[Commentary] In order to maintain concrete structures appropriately, this specification requires
three types of assessment: initial assessment, periodic assessment and extraordinary assessment.
Because the initial and periodic assessments are essential for the maintenance of structures subject
to frost attack, this chapter stipulates that those assessments must be conducted. Extraordinary
assessments are regarded as assessments to be conducted on an as-needed basis and are therefore
not dealt with in this chapter. By conducting periodic assessments during the maintenance period,
defect in appearance of structures can be discovered before they occur or in early stages, andremedial measures including preventive measures and repairs can be taken systematically.

11.3.2 Investigation in assessment
11.3.2.1 General
Investigations in initial, routine and regular assessment of a structure subject to frost
attack shall be conducted appropriately according to the category of maintenancerequired for the structure. Prior to investigation, check items, methods, frequency andscope of standard investigation shall be determined appropriately. For each type ofassessment, detailed investigation shall also be conducted on an as-needed basis.

[Commentary] It is important to select check items, methods, frequency and scope ofinvestigation appropriately according to the purpose of investigation in accordance with themaintenance planning.
The major parameters that should be identified in investigations of structures subject to frost
attack are the state of water supply, the degree of saturation, anomalies in appearance, and depth ofdeterioration by frost attack. In cases where deterioration has progressed considerably,
investigations should be conducted to directly evaluate performance.
The items to be examined in investigations vary according to the degree of deterioration. In
cases where it has been determined or assumed that the deterioration was in the initiation stage,investigations should be conducted mainly to identify the progress of defects on concrete. In cases
where it has been determined or assumed that the deterioration was in or beyond the propagation
stage, investigations should be conducted mainly to identify the depth of deterioration by frost
attack. Table C11.3.1 shows major items to be examined in the respective stages. Data on the items
related to deterioration prediction such as the state of scaling and the environmental action should
be collected in as early a stage as possible.
The frequency and range of investigation should be determined considering the maintenancecategory, environmental conditions, structural format and the state of deterioration for the structure.
Frost attack damage tends to occur at places that are supplied with a large amount of moisture andare exposed to sunlight. It is desirable, therefore, that the entire structure is investigated and a planbe drawn up so that the parts of the structure where the conditions mentioned above should be met
be investigated intensively.
Regardless of the category of maintenance, it is important to go through the design drawings
and specifications, construction records, investigation results and the repair history prior to theinvestigation of a structure.
If the state of a structure cannot be judged appropriately by standard investigation, detailed
investigation must be conducted.

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Chapter 11

Maintenance of Structures Subject to Frost Attack

Table C11.3.1 Main check items in investigation
Stage of Deterioration

Initiation
Stage

PropagationStage

Acceleration
Stage

Deterioration
Stage

Change of appearance

O

O

O

O

Depth of deterioration by
frost attack*

▲

O

O

O

State of water supply anddegree of saturation

O

O

O

O

Concrete strength

▲

▲

▲

▲*

O: Items to be investigated on a priority basis▲: Item to be investigated on an as-needed basis▲*: Items that should preferably be investigated* See Section 11.3.3.3.

11.3.2.2 Investigation in initial assessment(1) In initial assessment, appropriate check items for standard investigation shall beselected for newly constructed structures, existing structures, large-scale repairs
and strengthened structures.
(2) If deterioration prediction, evaluation or judgment is difficult to make through astandard investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigation in initial assessment is the first investigation conducted whenthe maintenance of a concrete structure is started. Investigation in initial assessment includes not
only the first investigation of a newly constructed structure conducted before it goes into service but
also the first investigation of an existing structure or a structure for which remedial measures havebeen taken in response to deterioration. Check items for the investigation may vary from structure
to structure. Basic check items for standard investigations in initial assessment of a newly
constructed structure are the document search on the design drawings and specifications andconstruction records and observation. It is good practice to check on such details as concrete cover,the state of steel and porosity through nondestructive testing on an as-needed basis. Wheninvestigating a structure for which remedial measures have been taken, it is also important to checkfor problems in repaired or reinforced parts of the structure. These should be included in check
items of standard investigation. When an existing structure is investigated, check items are similar
to those for a newly constructed structure if design drawings and specifications and construction
records exist. If there is no such document or record, it is necessary to select check items ofstandard investigation with reference to Section 11.3.2.5 “Detailed Investigation.” In cases where a
prediction needs to be made with high accuracy about a structure to which maintenance category A(preventive maintenance) is applied, it is necessary to conduct investigations concerning theparameters used for the method described in Section 11.3.3 “Methods for Predicting Degradation of
Performance Degradation of Structures.”
Extremely important items in the investigation in initial assessment of a structure subject to151

Standard Specifications for Concrete Structures-2007, Maintenancefrost attack are listed below.
I. Items related to the quality of concrete(i)

Quality of aggregate (absorption, loss of mass)(ii)

Mix proportion of concrete(iii) Air content (air void spacing factor)(iv) Degree of saturation of concrete (water content)
II. Items related to the quality of construction(i)

Cover concrete(ii)

Initial defects

III. Items related to environmental deterioration factors(i)Lowest temperature(ii)

Number of freezing and thawing cycles

Among the items listed above, I–(i), (ii) and (iii) are essential for predicting the occurrence offrost attack damage, but these are used only in cases where mix proportion records are available.
II–(i) needs to be checked because it affects the time of initiation and rate of steel corrosion, and its
actual values tend to differ from design values. I–(iv) and III–(i) and III–(ii) are items necessary for
estimating depth of deterioration by frost attack. Among these items, the lowest temperature and thenumber of freezing and thawing cycles are important for the prediction of the rate of deterioration.
II–(ii) needs to be checked during the investigation in initial assessment because it greatly affects
the durability—durability against not only frost attack but also other deterioration factors— ofstructures.
Basically, investigation is made through the examination of design and construction records andvisual observation. It is good practice, however, to check surface temperature, the locations andstate of steel, etc., through non-destructive testing on an as-needed basis.
In the investigation in initial assessment of a structure for which remedial measures have beentaken, it is also important to check for defects (for example, peeling or detachment of concretesurface coating materials) in the repairing or strengthening areas.
(2) If evaluation and judgment cannot be made with high accuracy by standard investigation
alone, detailed investigation is necessary. Check items of detailed investigation are indicated in
Section 11.3.2.5 “Detailed Investigation.”

11.3.2.3 Investigation in routine assessment(1) In routine assessment, standard investigation shall be conducted to detect thestate of water supply (wettedness of concrete) and the defect of concrete surface
such as micro cracking of concrete, scaling and pop-outs.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.
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Chapter 11

Maintenance of Structures Subject to Frost Attack[Commentary] (1) The purpose of investigation in routine assessment is to detect deterioration at
an early stage by checking on defect in the state of a structure over time. The determination of thetime at which deterioration began in order to obtain information that is useful for predicting
deterioration is another important purpose of the investigation. A main check item is the observationof anomalies in the state of concrete surface due to phenomena peculiar to frost attack damage suchas pop-outs, micro crack and scaling. Even if concrete deterioration is not detected, deterioration
may occur at places where water is supplied to the concrete surface. It is therefore desirable that thestate of water supply be checked during investigation. It is also good practice to intensively
investigate the regions that were identified during the investigation in initial assessment as being
prone to deterioration.
(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone or if severe deterioration has already occurred, detailed investigation is conducted. Checkitems of detailed investigation are described in detail in Section 9.3.2.5 “Detailed Investigation.”

11.3.2.4 Investigation in regular assessment(1) The purpose of investigation in regular assessment is to obtain information that isdifficult to obtain in routine assessment. In regular assessment, standard
investigation consisting of detailed observation of visible properties, the state ofwater supply, etc., shall be conducted as in routine assessment.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigation in regular assessment is conducted for obtaining the information
more detailed than that in routine assessment. Areas where signs of defects or deterioration havebeen detected in initial or routine assessment need to be examined intensively. The appearance ofthe structure should basically be examined as in routine assessment. It is also necessary to keep
track of changes over time by measuring the depth of deterioration by frost attack in concrete,
preparing a deterioration map or conducting ultrasonic wave propagation speed, surface strength orother tests using non-destructive testing equipment in addition to the examination of the appearanceof the structure.
Frost attack damage occurs in winter, in which the water in concrete freezes. If the progress ofdeterioration is to be predicted with high accuracy in an investigation in regular assessment,
therefore, it is desirable that investigations be conducted in summer, in which deterioration is not inprogress. If depth of deterioration by frost attack is measured in an investigation in regularassessment, it is good practice to take measurements three to five times at equal intervals during theperiod in which deterioration is expected to occur. If maintenance category A (preventive
maintenance) is applied, it is advisable to increase the frequency of measurement.
(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone or if severe deterioration has already occurred, detailed investigation is conducted. Checkitems of detailed investigation are described in detail in Section 11.3.2.5 “Detailed Investigation.”

153

Standard Specifications for Concrete Structures-2007, Maintenance11.3.2.5 Detailed investigation
Detailed investigation shall be conducted to obtain detailed information on a structure
subject to frost attack in cases where the deterioration of the structure is difficult topredict, evaluate or judge by standard investigation alone in initial, routine or regularassessment. Check items, methods and location of a detailed investigation shall beselected appropriately taking into consideration such factors as the purpose ofinvestigation and the accuracy of obtained results.

[Commentary] When the determination of the present state of a structure and the deterioration
prediction of the structure are difficult by standard investigation alone, detailed investigation isconducted in order to obtain the information necessary for those purposes. Examples ofinvestigation items for structures subject to frost attack, and of data on the condition of the structure
at the time of investigation and those in the future predicted from the investigation results are listed
in Table C11.3.2. The evaluation items estimated from data in the table are evaluated after
deterioration is predicted.
Table C11.3.2 lists check items for evaluating anomalies in the state of concrete and steel. It is
recommended that evaluators of anomalies in the state of concrete structures with surface protectionrefer to the investigation and evaluation items indicated in the Recommendation for Concrete
Repair and Surface Protection of Concrete Structures.

Table C11.3.2 Examples of evaluation items in detailed investigation
Measurement item

Data obtained by investigation

Evaluation items predictable fromobtained data

Depth of deterioration by frost
Depth of deterioration by frost
attack, frost attack deterioration Frost attack deterioration rate
attackrate
Crack (width, depth, density)

Aesthetic appearance

Aesthetic appearance

Scaling

Aesthetic appearance

Aesthetic appearance

Pop-out

Aesthetic appearance, quality of
Aesthetic appearance
aggregate

Concrete strength, elastic modulus Concrete strength, stiffness

Concrete strength

Steel location (cover concrete) and Corrosion grade, amount of steel
Corrosion rate, corrosion gradestate of corrosion
corrosion, load bearing capacity
Deflection, deformation

Stiffness, load bearing capacity---

Pore structure (pore volume, pore Depth of deterioration by frost
Frost attack deterioration rate
size distribution)
attack, concrete strength
Void structure (air content, air void Depth of deterioration by frost
Frost attack deterioration ratespacing factor)
attackWater content rate (degree of
Water content rate
saturation)
Temperature,supplyinsulation,

Frost attack deterioration ratewater Temperature, humidity, state of
Frost attack deterioration rate
moisture

Note: For the grade of corrosion, refer to Table C9.3.3.

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Chapter 11

Maintenance of Structures Subject to Frost Attack

Major check items are outlined below. For other measurement items or testing methods thanthose described below, refer to 4.7 "Investigation."(i) Environmental conditions: The degree and type of deterioration of a structure varies withthe lowest temperature to which the structure is subjected, the number of freezing and thawing
cycles and the degree of water supply. This means that frost attack damage to a structure does notoccur even if the structure is under severe environmental conditions and water is supplied as long as
the quality of concrete is sufficiently high. Even in cases where the quality of concrete is low, thedegree of frost attack damage is low if environmental conditions are mild or there is no supply ofwater. In other words, severe frost attack damage to a structure occurs if the structure is in a harshenvironment, water is supplied and the quality of concrete is low. It is desirable, therefore, thatcollected data on the environmental conditions be used for the prediction of deterioration progressby comparing the data with the performance degradation of the structure under consideration.
(ii) Depth of deterioration by frost attack: Depth of deterioration by frost attack should be
evaluated comprehensively by measuring scaling depth and depth of deterioration due to micro
crack. Scaling depth is measured at the surface of the structure, and the maximum and minimum
values are determined. Depth of deterioration due to micro crack is determined by taking coresamples from the place where frost attack damage was observed and evaluating, for example,
measured ultrasonic wave propagation speeds at different depths.
(iii) Steel corrosion: Corrosion of reinforcing steel used in a structure tends to directly affectthe performance of the structure. It is therefore important to chip off the cover concrete so that thereinforcing steel is exposed and measure the state, location, area and mass of corrosion, pitting
corrosion depth, etc. By obtaining quantitative data on corrosion, the performance degradation of
the structure can be evaluated quantitatively.
(iv) Appearance of structures: Anomalies in appearance of a structure deteriorated because of
frost attack may provide information that is highly helpful in performance evaluation. It is therefore
necessary to investigate the parts of the structure showing anomalies and the degree of change as
quantitatively as possible. For reference purposes, Table C11.3.3 shows the relationship between theappearance grade of a structure and the state of deterioration involving steel corrosion.

Table C11.3.3 Relationship between appearance grade of a structure and the state ofdeterioration taking into account steel corrosion
Appearance grade ofstructure

State of deterioration

State I
(initiation stage)

Stage at which the structure is subjected to freezing and thawing
cycles, but there has been no performance degradation and the initialstructural soundness is retained

State II(propagation stage)

Stage at which depth of deterioration by frost attack is so small as tohave little impact on stiffness and steel corrosion has not occurred,
but appearance is being affectedState III
(acceleration stage)

Stage at which depth of deterioration by frost attack has become solarge as to affect third parties through spalling, etc., and steel
corrosion occurs

Stage IV
(deterioration stage)

Stage at which depth of deterioration by frost attack is greater thancover concrete, and corrosion is so severe as to affect serviceability
and safety performance

155

Standard Specifications for Concrete Structures-2007, Maintenance11.3.3 Methods of predicting performance degradation of structures
11.3.3.1 General(1) In the maintenance of a structure subject to frost attack the performance of thestructure shall be evaluated quantitatively at the time of investigation, and futuredegradation shall be predicted.
(2) In order to predict the performance degradation of a structure, deterioration due tofrost attack shall be predicted quantitatively.
(3) If (2) is difficult, an alternative method is to predict performance degradation by
estimating the length of the initiation, propagation, acceleration and deterioration
stages, taking the progress of concrete deterioration by frost attack into
consideration.
(4) Deterioration shall be predicted on the basis of investigation results. If
investigation results are not available, the quality of the concrete protection layer
and the quality of the concrete, and the environmental conditions under which thestructure is used shall be evaluated appropriately, and a prediction shall be madeby allowing for an appropriate margin of safety.

[Commentary] (1) and (2) In the performance verification based maintenance system, changes(deterioration) in various performance attributes inherent in the structure should be predicted. Inorder to predict the performance degradation of a structure in a frost attack environment, it isnecessary to quantitatively predict the deterioration of the materials, namely, decreases in the crosssectional area of the concrete and the progress of corrosion of the steel in the concrete. The
performance of the structure and the degree of deterioration of materials constituting the structure
should be evaluated quantitatively at the time of investigation and the end of planned service period.
Performance degradation of the structure or the degree of deterioration of materials constituting thestructure at the time of investigation may be evaluated quantitatively by an appropriate method
based on investigation results. The performance or the degree of deterioration at the end of theplanned service period should be predicted quantitatively based on the previous periodic
assessments. The prediction of deterioration progress is not always in agreement with actual
progress of deterioration. The method of prediction should therefore be reviewed based on the
results of investigations to be conducted later.
(3) When evaluating various performances attributes of a structure by combining the results ofprediction of deterioration progress of concrete and steel, quantitative prediction is difficult at thepresent technological level. A practical method, therefore, is to predict the length of the initial,
propagation, acceleration and deterioration stages by taking into consideration depth ofdeterioration by frost attack and the progress of steel corrosion. Table C11.1.1 shows examples offactors determining the length of stages of deterioration when the deterioration process is
considered in terms of decreases in the load-carrying capacity and stiffness of structural members at
each stage of deterioration. In this case, the length of the initiation stage can be roughly predictedfrom the period until the occurrence of frost attack damage, and the duration of the deterioration
process from the propagation stage can be roughly predicted from depth of deterioration by frost
attack. The prediction of the period until the occurrence of frost attack damage and depth ofdeterioration by frost attack is described in Section 11.3.3.2 “Prediction of Occurrence of Frost
Attack,” and Section 11.3.3.3 “Prediction of Depth of Deterioration by Frost Attack.”(4) Investigation results are related to either the quality of concrete of the structure or theenvironment in which the structure is placed while in service. These parameters should be used as a156

Chapter 11

Maintenance of Structures Subject to Frost Attack

basis for predicting deterioration. Many of the frost attack damage prediction methods currently inuse, however, are based on the results of experiments conducted under controlled concrete quality
and environmental conditions. In cases where the deterioration of a real structure is predicted, theaccuracy of prediction may not be sufficiently high.
If no information is available on environmental conditions as in the case of a newly constructedstructure or if investigation results are not available for an existing structure, investigation results
for adjacent structures or structures in similar environments may be used for reference purposes.

11.3.3.2 Prediction of occurrence of frost attack
The occurrence of deterioration by frost attack shall be predicted according to theenvironmental conditions under which the structure and the investigation results
concerning the quality of aggregate and the frost attack resistance of concrete.

[Commentary] The occurrence of frost attack damage to a structure must be predicted
comprehensively in view of the used materials, the mix proportions and air content of the concrete,the environment of the structure and the degree of water supply. Since, however, it is difficult underpresent conditions to quantitatively evaluate the environment in which a structure is to be placed,common practice is to evaluate the possibility of occurrence of frost attack damage in view of a
frost attack damage hazard map based on the weather conditions, such as the lowest temperature, towhich the structure is to be subjected, of the properties of aggregate or of the results of freezing andthawing tests conducted under certain conditions. As a guide concerning the degree of vulnerability
to frost attack damage, JASS 5 “Reinforced Concrete Work 2003” (Fig. 26.1, Frost attack Risk
Distribution in Section 26) may be used.
From the viewpoint of materials, it is necessary to predict the occurrence of frost attack damage
to both aggregate and concrete. Representative anomalies attributable to the quality of aggregate
include pop-outs. Pop-outs occur when the surface mortar layer spalls because of expansion
pressure generated by the freezing of water in the aggregates. The "Construction" volume of theStandard Specifications suggests an absorption of 3% or less and a loss of weight as determined byaggregate soundness testing of 12% or less as limit values of aggregate properties that meet the
frost attack resistance requirements.
One way to evaluate the frost attack resistance of concrete is to conduct a freezing and thawing
test on the concrete to be used or concrete designed to simulate it in accordance with JIS A 1148
“Method of test for resistance of concrete to freezing and thawing.” It is possible, to a certain extent,
to evaluate the possibility of occurrence of frost attack damage from the test results thus obtained.
Since, however, the environment of a real structure varies widely; it is difficult to predict thedeterioration of a real structure quantitatively. For an existing structure, it is possible to conduct afreezing and thawing test using core specimens. For a similar reason, it is difficult to predict
deterioration in a real-world environment. Regardless of the type of concrete specimens used (i.e.,
concrete to be used, concrete designed to simulate it, or core specimens), therefore, it is desirable
that freezing and thawing test results be used for reference purposes only in evaluating thepossibility of occurrence of frost attack damage.

157

Standard Specifications for Concrete Structures-2007, Maintenance11.3.3.3 Prediction of depth of deterioration by frost attack
The depth of deterioration by frost attack should be predicted on the basis of the depth
and rate of deterioration by frost attack obtained from investigations.

[Commentary] Frost attack damage increases the porosity of concrete, causing adverse effects
such as decreases in compressive strength and increases in the rate of chloride ion penetration andthe rate of carbonation. It is therefore necessary to predict the depth and amount of textural
alteration of concrete. A simulation model capable of predicting depth of deterioration by frost
attack has not yet been developed. A practical approach, therefore, is to measure and analyze core
specimens taken from a structure and use the obtained results for the prediction of the deteriorationof the structure or the prediction of structures in adjacent areas.
Measurement and analysis methods currently under study include the method of determining
depth of deterioration by frost attack from the distribution of ultrasonic wave propagation velocity
at different depths from the concrete surface or the pore size distribution measured by mercury
porosimetry. In the case of evaluation based on ultrasonic wave propagation velocity, evaluation byuse of core specimens may be difficult because propagation velocity is greatly affected by aggregate.
It is important to directly measure the structure on an as-needed basis. In the case of evaluation
based on the pore size distribution, there are a number of areas in which further study is needed toachieve high-accuracy evaluation such as the variability of measurement results and the necessity of
special measuring equipment, so much more data needs to be accumulated.
A method for estimating depth of deterioration by frost attack currently under development is
the method of determining changes in the degree of deterioration such as the number of freezing
and thawing cycles and the relative dynamic modulus of elasticity from the distribution oftemperature and the degree of saturation in different parts of the concrete. At the present stage ofdevelopment, freezing and thawing test results can be model, but further accumulation of data isneeded in order to achieve agreement with real structures.
Studded tires were banned in March 1991, and the use of deicing agents has increased sincethen. Usually, the use of deicing agents increases scaling. When evaluating depth of deterioration by
frost attack, therefore, it is necessary to take the use of deicing agents into consideration.

11.3.3.4 Modification of prediction
If the state of deterioration determined in an investigation differs from a predicted stateof deterioration, the cause of the difference shall be identified and the prediction shall berevised accordingly. If necessary, the maintenance plan shall be altered.

[Commentary] When the deterioration confirmed in investigations is different from theprediction, appropriate investigations should be conducted using the deterioration prediction
methods shown in 11.3.3.2 “Prediction of Occurrence of Frost Attack” and 11.3.3.3 “Prediction of
Depth of Deterioration by Frost Attack” and based on Table C11.3.2 to examine the cause for thedifference, and the prediction should be modified. Then, the results of several investigations
conducted until that are useful to the examination of causes and the modification of the prediction.
Revising the subsequent maintenance plans including a review of investigation frequency based on
the modified prediction is also important.

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Maintenance of Structures Subject to Frost Attack

11.3.4 Evaluation and judgment(1) The evaluation of performance and judgment as to whether remedial measuresneed to be taken based on the results of the investigation in initial, routine andregular assessment shall be made in accordance with Part 1 and Item (2) andsubsequent items in this section.
(2) The performance of a structure subject to frost attack shall be evaluated byappropriately selecting performance attributes to be evaluated in view of the stageof deterioration of the structure.
(3) The evaluation of performance attributes at the time of investigation and at theend of the planned service period of the structure should be made by aquantitative method.
(4) If Item (3) is difficult to achieve, the evaluation of performance attributes at thetime of investigation and at the end of the planned service period of the structure
may be made by a semi-quantitative grading-based method.
(5) Judgment as to whether remedial measures need to be taken shall be made inview of the degree of performance degradation due to frost attack, the degree ofimportance of the structure, category of maintenance, and the remaining service
life.

[Commentary] (1) The evaluation of performance and judgment of necessity for remedial
measures in initial, routine and regular assessment for structures in which little progress ofdeterioration has been recognized are frequently more or less the same regardless of thedeterioration mechanism. For details, refer to Part 1. The evaluation of performance and judgmentof necessity for remedial measures for structures in which deterioration may have or has progressedvary according to the deterioration mechanism. When discussing the performance degradation due
to frost attack, the descriptions in this chapter should be consulted.
(2) As shown in Fig. C11.1.1, in structures subject to carbonation, the performance attribute tobe affected by deterioration varies depending on whether deterioration is in the initiation,
propagation, acceleration or deterioration stage. The performance attribute to be evaluated should
be properly selected for each stage of deterioration. At the initiation stage, for example, basicallydeterioration has not become apparent, so degradation does not occur in any of the performance
attributes. At the propagation stage, deterioration occurs at the concrete surface so that degradation
occurs in appearance-related performance. At the acceleration stage, depth of deterioration by frost
attack increases and degradation occurs in appearance, and degradation may occur in performance
attributes related to third party impact due to spalling of concrete or other forms of degradation.
Because the cross-sectional area of concrete begins to decrease considerably, decreases inload-carrying capacity or other performance attributes become a concern in the case of a structuralmember with a small cross-sectional area although such phenomena do not pose a serious problem
in the case of a massive structure. At the deterioration stage, the deterioration of concrete due tofrost attack becomes even more apparent, and steel corrosion begins. In the case of a structuralmember, therefore, degradation of serviceability due to deformation or degradation of safety
performance due to a decrease in load-carrying capacity becomes a concern. If steel corrosion has
occurred and the steel is under fatigue loading, it is necessary to consider third party impacts suchas spalling of concrete in addition to safety and serviceability.
(3) and (4) In order to quantitatively evaluate the performance of a structure subjected to frost
attack, taking into consideration the influence of steel corrosion, it is necessary to quantitatively
evaluate the degradation of each performance attribute after quantifying the state of concrete
159

Standard Specifications for Concrete Structures-2007, Maintenancedeterioration and steel corrosion due to frost attack. One way to do this is to substitute the property
values for each material at the time of investigation and at the end of the planned service period in
the structural calculation equations, verify safety and serviceability from the calculated values ofsuch attributes as load-carrying capacity and deformation and check on third party impact andappearance by examining the ranges and degrees of cracking, scaling, pop-out, etc. If, however,structural calculation equations are applied, it must be confirmed in advance that the preconditions
for the equations, such as bond properties and structural details, are satisfied. There are cases where
evaluation at the time of investigation can be made with a certain level of accuracy, but it is not easy
to predict property values at the end of the planned service period. A practical method, therefore, is
to classify the states of deterioration into a number of grades as shown in Table C11.3.3 according
to structural appearance investigation results and evaluate the degraded performance at the time ofinvestigation semi quantitatively with reference to Table C11.3.4. The aim of deterioration grading
is to evaluate the present degree of deterioration of a structure on a semi quantitative scale, insteadof evaluating the future progress of deterioration. Performance evaluation, however, can be made if
the state of deterioration at the end of the planned service period is predicted by, for example,
estimating deterioration from the relationship between the service period and depth of deterioration
by frost attack determined through a detailed investigation. In this case, however, it is important toallow for an appropriate factor of safety according to the accuracy of deterioration prediction.
If detailed maintenance records for a similar structure (type of structure, materials, construction,
environment, state of use) are available and the progress of deterioration to date is similar to that of
the similar structure, the evaluation results for that structure can be used as a guide.
(5) Because judgment is the act of deciding whether remedial measures need to be taken on thebasis of structural performance evaluation results, there is no difference depending on deterioration
factors. Therefore, refer to Part 1.

Table C11.3.4 Grades of appearance of structures and typical performance degradation
Grade of appearanceof structureState I
(initiation stage)
State II(propagation stage)
State III
(acceleration stage)

SafetyServiceability

Hazards for third
party

Aesthetic
appearance andlandscape

-

-

-

-

-

-

-

Degradation ofaesthetic
appearance

Decrease instiffness

Decrease in load -Decrease inbearing capacity cross-sectional
area of concrete-Decrease incross-sectional-Deterioration ofState IV
area of concrete bond between(deterioration stage)steel and
-Steel corrosion
concrete-Steel corrosion

160-Scaling-Pop-out
Hazards for third
party-Peeling-Spalling-CrackChapter 11

Maintenance of Structures Subject to Frost Attack

11.4 Remedial Measures
11.4.1 Selection of remedial measures(1) If it has been judged that remedial measures need to be taken in connection withperformance degradation of a structure subject to frost attack, remedial measuresby which the corrected structure meets the required performances shall beselected.
(2) If it is difficult to select remedial measures for a structure on the basis ofperformance verification, remedial measures may be selected from the measurescorresponding to the grade of appearance.

[Commentary] (1) If it has been judged, as a result of evaluation, that remedial measures need tobe taken, it is necessary to select one or more of the following measures: (i) intensified investigation,(ii) repair, (iii) strengthening, (iv) functional improvement, (v) restriction in service or (vi)dismantling/removal. Basically, decisions as to which measures to take should be made by the
maintenance manager of the structure, but it is good practice to refer to Part 1 for information on
typical relationships between evaluation and judgment results and remedial measures.
(2) If it is difficult to select remedial measures for a structure through quantitative evaluationor judgment, remedial measures are selected from the measures corresponding to the deterioration
grade of the structure. Remedial measures to be taken vary depending on the type of structure, thedegree of importance of the structure, deterioration rate and the category of maintenance, but
recommended standard measures are shown in Table C11.4.1.

Table C11.4.1 Grades of appearance of structure and remedial measures
Grade of appearance of structure

Intensified
investigation

RepairStrengthening**

I (initiation stage)

(O)

(O)

(X)

II (propagation stage)

OO

OO

X

O

III (acceleration stage)

O

OO *

X

OO

O*

X

OO

IV (deterioration stage)

Restriction inserviceOO: Standard remedial measures (OO*: Including the restoration of mechanicalperformance), O: Remedial measures in some cases (O*: including the restoration of
mechanical performance), X: Remedial measure taken based on other criterion than the grade ofappearance. Strengthening**: Enhancing the mechanical performance above the initiation level

11.4.2 Repair and strengthening
Methods and materials for the repair or strengthening of a structure shall be selected,
taking into consideration the performance degradation of the structure due to frost attack
and life cycle cost, so that the required effect can be achieved.

[Commentary] In cases where repair or strengthening is carried out as a remedial measure, it isnecessary to define the expected effect of repair or strengthening and the required performance(what level of performance to be maintained for how many years?). Ideally, it is desirable that161

Standard Specifications for Concrete Structures-2007, Maintenanceremedial measures be taken after constructing a deterioration formula (for repair) or structural
calculation formula (for strengthening) in view of such factors as the properties of the materials
used and verifying the calculation results obtained from those formulas. In this case, it is also
important to take life cycle cost into consideration according to the remaining planned service
period.
When taking preventive measures for a structure to which maintenance category A(preventive maintenance) is applied, an appropriate method should be selected fully considering theeffect that should be achieved by the method.
The purposes of repair or reinforcement carried out in response to frost attack damage are to
remove the deteriorated parts and restore the load-carrying capacity and stiffness of structuralmembers. Table C11.4.2 shows examples of repair or reinforcement methods for achieving these
purposes. Deterioration due to frost attack damage consists mainly of the deterioration of concrete.
The properties of concrete damaged by frost attack, therefore, are in many cases alteredconsiderably. Basically, therefore, an effective method is to replace the damaged part of concrete
although the effectiveness of the method depends on the degree of deterioration. Wherever possible,
remedial measures should be taken when the structure is dry. As shown in Table C11.4.3, repair orreinforcement methods to be used vary depending on the degree of deterioration. Usually, repair andreinforcement goals can be achieved with relatively simple remedial measures if taken at an earlystage of deterioration. It is therefore necessary to decide on the timing for taking remedial measuresappropriately according to the maintenance plan.

Table C11.4.2 Expected effects and methods of repair or strengthening(including preventive maintenance)
Expected effect

Examples of methods

Control of water supply

Surface treatment, grout injection into cracks,
drainage

Removal of deteriorated part

Repair of cross section, grout injection into cracks

Increase in load bearing capacity

Increase of thickness, replacing, lining

Table C11.4.3 Grades of appearance of structure and examples of standard
repair/strengthening methods
Grade of appearance of structureStandard repair/strengthening method

I (initiation stage)

Surface treatment*

II (propagation stage)

Surface treatment

III (acceleration stage)

Surface treatment, grout injection into cracks,
repair of cross section

IV (deterioration stage)

grout injection into cracks, increase of thickness,
replacing, lining*: preventive maintenance method162

Chapter 11

Maintenance of Structures Subject to Frost Attack

Deterioration due to frost attack damage does not occur if the supply of water is cut off. In thecase of a structure with high frost attack damage risk, therefore, deterioration can be prevented bytaking such measures as covering the concrete surface with a protective material when a new
structure is constructed. In the case of a structure to which maintenance category A (preventive
maintenance) is applied, if drying shrinkage or structural cracks are observed even when frost attack
damage has not occurred, measures such as grout injection into cracks or taking water-related
maintenance measures (e.g., drainage) help prevent frost attack damage.
In the case of frost attack damage, the post-repair/reinforcement frost attack deterioration ratevaries depending on the quality of repair materials or reinforcement materials rather than the qualityof existing concrete. This necessitates deterioration prediction in view of the frost attack resistanceof repair materials or reinforcement materials. It is also necessary to pay attention to details andintervals of investigations in regular assessment after remedial measures are taken and to theselection of priority observation items.
For more details of repair and reinforcement methods, it is advisable to refer to the“Recommendations for Strengthening of Concrete Structures,” “Recommendations for Concrete
Repair and Surface Protection of Concrete Structures,” Report of JCI Committee on “Rehabilitationof Concrete Structures (Japan Concrete Institute),” etc.

11.5 Recording(1) Investigation, deterioration estimation, evaluation and judgment, and remedial
measures shall be recorded in accordance with Part 1.
(2) Items relevant to frost attack shall be recorded.

[Commentary] As a general rule, the results of investigations, deterioration estimations,evaluations and remedial measures must be recorded in accordance with Part 1. Items relevant tocarbonation require careful attention, particularly with respect to record keeping. Items to berecorded are indicated in Section 11.3.2 “Investigation in Assessment" and the evaluation items
indicated in Section 11.3.4 “Evaluation and Judgment.”163

Chapter 12

Maintenance of Structures Subject to Chemical Attack

CHAPTER 12 MAINTENANCE OF STRUCTURES SUBJECT TO
CHEMICAL ATTACK
12.1 General(1) This chapter provides standard methods for the maintenance planning, assessment,
remedial measures and recording for structures that have been or are highly likely to be
subject to performance degradation due to chemical attack. The items common to all
deterioration mechanisms are shown in Part 1.
(2) This chapter shall be applied to structures of the maintenance categories A(preventive maintenance) and B (corrective maintenance).

Initialstage

Propagation
stage

Initiation ofsteel corrosion

Service period
Accelerati Deterioration
on stagestage• Degradation of appearance

Deterioration of
concrete due tochemical attack

Cracking
Aggregate
Initiation of exposureattack on
concrete

Performancedegradation of
structural member

Performancedegradation of
structural member

Deterioration of
concrete due tochemical attack[Commentary] (1) Chemical attack can be classified, according to the mechanism of chemical
attack, into major two types. One is the deterioration mechanism of concrete that occurs when
cement hydrates and chemically aggressive substances react and turn hydrates into soluble
substances. This type of chemical attack is caused by a majority of acids, inorganic salts, andcorrosive gases such as hydrogen sulfide and sulfurous acid gas. The other is the deterioration
mechanism of concrete caused by expansion pressure generated by expansive compounds produced
when cement hydrates in the concrete react with substances that cause chemical attack. This type ofchemical attack is caused by sulfate salts. Deterioration phenomena occur in sewer systems,
chemical plants, other structures located in hot spring resorts, acidic rivers and acidic/sulfuric soil
areas, water treatment facilities and water utilization facilities where leaching of alkalis fromconcrete is caused by contact with soft water, structures where de-icing salts are applied, andstructures exposed to seawater. As chemically aggressive environments, this chapter deals mainlywith sewer-related facilities, hot spring resorts, acidic rivers, etc., that are subject to acidic
deterioration by sulfuric acid and soils subject to deterioration by sulfate salts. For information
about structures subject to chloride attack caused by deicing agents, it is advisable to refer to
Chapter 10 “Maintenance of Structures Subject to Chloride Attack.”(a) Deterioration in terms of appearance

Cracking
Aggregate
Initiation of exposureattack on
concrete
Initialstage

Initiation ofsteel corrosion

Propagation Accelerati
stage
on stage

Service period
Deteriorati
on stage• Decrease in load-carrying capacity• Decrease in stiffness(b) Deterioration in terms of safety

Fig. C12.1.1 Conceptual view of deterioration progress due to chemical attack

164

Standard Specifications for Concrete Structures-2007, MaintenanceAs shown in Fig. C12.1.1 and Table C12.1.1, the deterioration process of a structure due tochemical attack and resultant steel corrosion can be divided into the initiation, propagation,
acceleration and deterioration stages. Because the influence of deterioration phenomena on
structural performance varies according to the deterioration progress, methods for assessment(investigation, prediction of deterioration progress, evaluation and judgment), remedial measuresand recording also vary from stage to stage. A structure in a chemically aggressive environment
may have a protective layer over its concrete surface. The deterioration stages are defineddifferently, therefore, depending on the presence or nonpresence of protective layers.
Fig. C12.1.2 shows a standard procedure for maintenance in a chemically aggressive
environment.

Deterioration
stageStage ofdeterioration

Initial stage

Propagation
stage
Acceleration
stage
Deterioration
stage

Table C12.1.1 Definition of deterioration stages
Definition in a
Definition in a structure
Factors determining
structure withoutwith protective layer overthe stage
protect layer
concrete
Period until the
Period until the alteration ofRate of ingress ofalteration of concrete
underlying concrete due tochemically aggressive
due to ingress ofingress of chemically
substances into
chemically aggressive
aggressive substances
concrete or protective
substances into
through the protective layer
layer over concrete
concrete
Period until the aggregates in the concrete areRate of concrete
exposed and begin to peel off
erosion
Period until initiation of steel corrosion due to theRate of concrete
increase of deteriorated depth by chemical attack anderosionreach of deterioration factors to steel reinforcement
Rate of concrete
Stage in which load bearing capacity is reduced
erosionconsiderably due to loss of cross sectionof concrete or
Rate of corrosion ofsteel, etc.
steel

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Chapter 12
Possibility ofchemical
attackMaintenance of Structures Subject to Chemical Attack(12.2)(12.3)

Maintenanceplan for the
structure

Assessment(12.3.2.2)
Investigations ininitial assessment
Standard
investigation(12.3.2.5)
Detailed
investigation(12.3.3)
Deterioration prediction(12.3.4)
Evaluation and judgment(12.4)
Remedial
measures(12.5)
Recording(12.3.2.3,4)
Investigations inroutine/regularassessment
Standard
investigation(12.3.2.5)
Detailed
investigation(12.3.3)
Deterioration prediction(12.3.4)
Evaluation and judgment

Fig. C12.1.2 Standard maintenance procedure against chemical attack

In the application of this chapter, it should be refered to Present State of and Upcoming Trends
in Research on Reinforcing Steel Corrosion and Corrosion-proofing and Repairs I/II (ConcreteEngineering Series 26), Present State of Research on Chemical Attack on Concrete and Leaching(Concrete Engineering Series 53), Report of the Committee on Material Design Support Systems(Japan Concrete Institute), Report of the Committee on Long-term Performance Verification
Support Model for Concrete Structures (Japan Concrete Institute) and Guidelines for Corrosion
Control Technology and Corrosion Prevention Technology for Concrete Structures of Sewerage
Systems (Japan Sewage Works Agency).
(2) This maintenance standard is applicable to Type A maintenance (preventive maintenance)
and Type B maintenance (corrective maintenance). At present, Type B maintenance is applied tomany existing structures. In the coming years, however, structures in the Type A maintenancecategory (for example, sewerage facilities for which corrosion prevention measures such as surface
protection are taken from the construction stage) are expected to increase. Structures in the Type C
maintenance category (observational maintenance) should also be maintained with reference to thischapter.

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Standard Specifications for Concrete Structures-2007, Maintenance12.2 Maintenance Planning
12.2.1 Basis of planning
In order to maintain a structure subject to chemical attack, the category of maintenanceplan shall be selected, the service period planned, and a maintenance planning for activities
including assessment, remedial measures and recording drawn up in advance in view of theservice and environmental conditions such as the condition for supplying substances
causing chemical attack.

[Commentary] When drawing up a maintenance plan, it is necessary to cover such details ascheck items and procedures for the initial assessment and check items, procedures, timing andfrequency for routine and rugular assessments, methods for evaluation and judgment, action to betaken in the event of deterioration, and recording methods, taking into consideration the type,
degree of importance and planned service period of the structure, category of maintenance, and thequality of materials.
The structure formalization, size and environmental conditions of concrete structures vary fromstructure to structure. A maintenance plan to be applied to a structure must be optimized for eachstructure. Drainage and exhaust equipment at chemical plants or sewer system often creates closed
environments that could be filled with harmful gases or steam because vents and other ventilation
devices could release obnoxious odors to cause complaints from neighbors. In those facilities, it isdifficult to inspect frequently because ventilation or drainage of incoming water is necessary to
carry out investigations, and sometimes considerable performance degradation has already beenfound when an investigation is conducted. Surface protection measures are often taken for astructure in a chemically aggressive environment, so the deterioration of protective materials should
be considered in the maintenance.
It is usually difficult, at the stage of maintenance planning, to accurately predict the state of astructure during its service period. It is, therefore, good practice to draw up a maintenance planningwith reference to the deterioration of a similar structure or a structure in a similar environment.

12.2.2 Determination of maintenance category
The category of maintenance of a structure subject to chemical attack shall be selectedin view of importance of the structure, the type of structure, hazards for third party, theplanned service period and the characteristics of deterioration due to chemical attack.

[Commentary] The determination of the category of maintenance is very important because
maintenance plans vary widely depending on the category of maintenance. The progress ofdeterioration and the performance degradation due to chemical attack are conceptually illustrated inFig. C12.1.1.
Structures to which maintenance category A (preventive maintenance) is applied should by
maintained to prevent alteration of concrete, that is, at the initiation stage, regardless of the presenceof a protective layer over the concrete. The state of the structure should therefore be identified as
accurately as possible. To cope with deterioration due to chemical attack, requirements include thefollowing:167

Chapter 12

Maintenance of Structures Subject to Chemical Attack(i) Quantitative evaluation of the supply of substances that cause chemical attack on the surfaceof the structure(ii) Quantitative determination and prediction of the deterioration of the protective layer overthe concrete(iii) Quantitative determination and prediction of the intrusion and accumulation of substancesthat cause chemical attack in the concrete(iv) Determination and prediction of the occurrence or nonoccurrence of corrosion of the steel inthe concrete
Structures to which maintenance category B (corrective maintenance) is applied should bemaintained so as to prevent tthe performance of the structure from failing to meet the requirements.
For example, maintenance is performed so that deterioration can be prevented until the deterioration
stage if attention is paid to safety and serviceability, until the acceleration stage if attention is paid
to third party impact or until the propagation stage if attention is paid to appearance. Certain actions
should be taken when any of the following types of deterioration has been detected:(i) Deterioration of the protective layer over the concrete is observed.
(ii) Concrete surface deterioration is observed.
(iii) A loss in cross-sectional area or cracking is observed at the concrete surface.
(iv) Corrosion of steel in the concrete is observed.
Once concrete erosion is initiated, it is extremely difficult to stop the progress of deterioration.
It is desirable, therefore, that repair is done at phase (i) or phase (ii) mentioned above even in thecase of a structure to which maintenance category B (corrective maintenance) is applied. It should
be noted that large-scale measures will be required if deterioration reaches phase (iii) or (iv).
It is common practice to apply a single category of maintenance to a single structure. There arecases, however, where it is more reasonable to apply different types of maintenance to different
parts or members of a structure. For example, there may be a case where maintenance category A(preventive maintenance) is applied to the piers of a bridge located at a site where soil contains
sulfate salts, and maintenance category B (corrective maintenance) is applied to the girders.

12.2.3 Preparation of maintenance manuals
A maintenance manual describing methods, procedures and frequency requirements
should be prepared for each structure in accordance with the maintenance planning, taking
the structure-specific conditions into consideration.

[Commentary] The service period of civil engineering structures is long, and maintenance of
those structures is performed over a long period of time. It is recommended, therefore, that in order
to inform investigation personnel of maintenance concepts and policies, a maintenance manual be
prepared so that detailed procedures and methods can be communicated accurately even to newly
assigned maintenance engineers.
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Standard Specifications for Concrete Structures-2007, Maintenance

Under certain circumstances such as in cases where the original maintenance plan is alteredbecause the actual progress of deterioration turned out to differ from that assumed in the original
maintenance plan, it may be necessary to modify the maintenance manual and take appropriate
maintenance measures accordingly.

12.3 Assessment
12.3.1 GeneralIn the assessment of a structure whose performance has been declined or is highly likely
to decline because of chemical attack, investigation, evaluation of the present state,prediction of deterioration and judgment of the necessity for remedial measures shall beappropriately conducted in accordance with the maintenance planning.

[Commentary] In order to maintain concrete structures appropriately, this Specification requires
three types of assessment: initial assessment, periodic assessment and extraordinary assessment.
Because the initial and periodic assessments are essential for the maintenance of structures in achemically aggressive environment, this chapter stipulates that those assessments must be
conducted. Extraordinary assessments are regarded as assessments to be conducted on an as-neededbasis and are therefore not dealt with in this chapter. By conducting periodic assessments during themaintenance period, anomalies in appearance of structures can be discovered before they occur orin early stages, and remedial measures including preventive measures and repairs can be taken
systematically.

12.3.2 Investigation in assessment
12.3.2.1 General
Investigations in initial, routine and regular assessment of a structure subject tochemical attack shall be conducted appropriately according to the category of maintenancerequired for the structure. Prior to investigation, check items, methods, frequency andscope of standard investigations shall be determined appropriately. For each type ofassessment, detailed investigations shall also be conducted on as-needed basis.

[Commentary] It is important to select check items, methods, frequency and scope ofinvestigation appropriately according to the purpose of investigation in accordance with themaintenance planning.
Items that need to be ascertained through investigation in connection with a structure in achemically aggressive environment are the type and concentration of chemically aggressive
substances, the infiltration depth of chemically aggressive substances, the depth of concrete erosion,
the depth of carbonation, and the corrosion of internal steel. In the event of severe deterioration,
investigation for the purpose of directly evaluating structural performance needs to be conducted.
Check items in investigation varies with the degree of deterioration. If the deterioration of thestructure is judged or inferred to be at the initiation stage, mainly investigations for determining theinfiltration of chemically aggressive substances or the progress of chemical attack on the protective
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Maintenance of Structures Subject to Chemical Attack

layer over the concrete need to be conducted. If the deterioration of the structure is judged orinferred to be at the propagation stage, mainly investigations for determining the progress ofchemical attack on the concrete need to be conducted. If the deterioration of the structure is judged
or inferred to be at the deterioration stage, mainly investigations for determining the progress ofsteel corrosion need to be conducted. Table C12.3.1 lists main check items at different stages ofdeterioration. It is desirable that data concerning check items related to deterioration prediction,such as the type, concentration and infiltration depth of chemically aggressive substances,anomalies in appearance, and reinforcing steel locations, among the check items necessary for
deterioration prediction be collected at the earliest possible stage. Monitoring of a structure towhich Type A maintenance (preventive maintenance) is applied may be conducted to continuallycheck on the occurrence of hydrogen sulfide gas or the occurrence of rust on the steel in theconcrete.
The frequency and scope of investigation must be determined in view of such factors as thecategory of maintenance required for the structure, environmental conditions, the type of structure
and the state of deterioration. For example, places prone to the generation of hydrogen sulfide gas
such as the gas-phase and mixed-phase zones and diameter-change sections of sewer conduits areprone to chemical attack.
Regardless of the category of maintenance, it is important to go through the design drawings
and specifications, construction records, investigation results and the repair history prior to theinvestigation of a structure.
If the state of a structure cannot be judged appropriately, a detailed investigation must be
conducted.

Table C12.3.1 Main check items in investigation
Stage of deterioration
Initiation
Propagation Acceleration Deterioration
Defective appearanceO
OOO
Type and concentration ofOOO▲chemically aggressive substance
Depth of deterioration byOOO▲chemical attack
Carbonation depthO
OO▲
Steel corrosion
▲ *
▲ *
▲
O
Concrete strength▲▲
O
O
Load bearing capacity
▲ *
▲ *
▲
Bar location
O
▲ *
▲ *
Monitoring
▲ *
▲ *
▲ *
▲ *
O: Itemes to be investigated on a priority basis▲: Items that should preferably be investigated▲ * : Items to be investigated on an as-needed basis

12.3.2.2 Investigaion in iitial assessment(1) In initial assessment, appropriate check items for standard investigation shall beselected for newly constructed structures, existing structures, large-scale repairs and170

Standard Specifications for Concrete Structures-2007, Maintenancestrengthned stuructures.
(2) If deterioration prediction, evaluation or judgment is difficult to make through astandard investigation alone, detailed investigations shall be conducted.

[Commentary] (1) Investigation in the initial assessment is the first investigation conductedwhen the maintenance of a concrete structure is started. Investigation in the initial assessment
includes not only the first investigation of a newly constructed structure conducted before it goes
into service but also the first investigation of an existing structure or a structure for which remedial
measures have been taken in response to deterioration. Check items for the investigation may varyfrom structure to structure. Basic check items for standard investigations in the initial assessment of
a newly constructed structure are the document serch on the design drawings, specifications andconstruction records, and visual ovservation. It is good practice to check on such details as concrete
cover, the state of steel and porosity through nondestructive testing on an as-needed basis. Wheninvestigating a structure for which remedial measures have been taken, it is also important to checkfor problems in repaired or strengthened parts of the structure. These should be included in chckitems of standard investigations. When an existing structure is inspected, check items are similar to
those for a newly constructed structure if design and construction records exist. If there is no suchrecord, it is necessary to select check items of standard investigation with reference to 12.3.2.5“Detailed Investigation.” In cases where a prediction needs to be made with high accuracy about astructure to which Type maintenance category A (preventive maintenance) is applied, it is necessary
to conduct investigations concerning the parameters used for the method described in 12.3.3“Methods for Estimating Degradation of Performance of Structures.”
Extremely important items in the investigation in the initial assessment of a structure subject tochemical attack are listed below.
(i) Environmental conditions(ii) Presence or nonpresence and type of protective layer over concrete(iii) Type of cement(iv) Mix proportions for concrete, particularly water/cementitious material ratio(v) Use or nonuse, type and quantity of admixture(vi) Concrete cover(vii) Initial defects(viii) The condition of repaired or reinforced parts
Among the items listed above, Item (i) is an item essential for the prediction of the progress ofchemical attack, and it is necessary to check on the type and concentration of the chemicallyaggressive substance in addition to temperature and humidity. It is also important to identify theconfiguration of the structure and the environmental conditions. In the case of an unventilated sewer
system, for example, the ceiling of the conduit becomes prone to condensation as humidity rises
under the influence of sewage, and the deterioration of the ceiling zone is accelerated because thecondensate contains sulfuric acid. In sewers, deterioration tends to become intense in the171Chapter 12

Maintenance of Structures Subject to Chemical Attack

mixed-phase zone and in diameter-change sections. Item (ii) is important for predicting the progressof deterioration at the initiation stage. Items (iii), (iv) and (v) are important for evaluating
predictions of the infiltration rate of a chemically aggressive substance and the rate of carbonation.
Item (vi) is important as a factor affecting the initiation and rate of steel corrosion. Concrete coverneeds to be checked because cover concrete may not have been placed as designed. Item (vii)
greatly affects the durability of the structure with or without chemical attack, so it is important todiscover initial defects during the investigation. For Item (viii), it is important to check whether
there is any change in the state of a repaired or reinforced part and, if any, determine the state of thatchange (for example, peeling or detachment of surface protection materials).
(2) If evaluation and judgment cannot be made with high accuracy by standard investigations
alone, detailed investigations are necessary. Check items of detailed investigations are indicated in
12.3.2.5 “Detailed Investigation.”12.3.2.3 Investigation in routine assessment(1) In routine assessment, standard investigation shall be conducted to detect not only
the defect of protect layer over concrete such as deterioration, cracking, scaling, spalling
and the defect of concrete surface such as cracking, scaling, spalling, stain of rust,
efflorescence, but also water leakage, deterioration in appearance such as displacementand deformation, and abnormal odors.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) The purpose of investigation in routine assessment is to detect deterioration at
an early stage by checking on anomalies in the state of a structure over time. The determination of
the time at which deterioration began in order to obtain information that is useful for predicting
deterioration is another important purpose of the investigation. In the investigation, focus should beplaced on deterioration phenomena or signs of deterioration, such as anomalies of the surface of theprotective layer over the concrete (e.g., alteration, cracking, scaling, spalling), concrete surface
anomalies (e.g., alteration, cracking, scaling, spalling, rusty water, free lime), water leaks,
displacement and deformation, and obnoxious odors.
In the case of chemical plant facilities and underground structures, deterioration may betriggered by synthesized organic acids or organic acids generated by the metabolism of
microorganisms. The presence of organic acids can often be detected by odors. Since, however,organic acids, hydrogen sulfide and sulfuric acid could have adverse effects on human health, gasconcentration must be measured prior to the investigation in a closed environment. Depending on
circumstances, it may be necessary to install ventilation equipment or wear a gas mask andprotective clothing.
Because a protective layer over concrete is by far more resistant to chemical attack thanconcrete, it is desirable that the occurrence of deterioration due to chemical attack be detected prior
to the propagation stage. However, investigation in routine assessments usually depends mainly on
visual observation, and it is difficult to make evaluation or judgment on the basis of investigation
results. As for the structures to which maintenance category A (preventive maintenance) is applied,the evaluation of their performance should be conducted in conjunction with appropriate monitoring.
It is important to determine whether chemically aggressive substances exist in advance by, for172

Standard Specifications for Concrete Structures-2007, Maintenanceexample, measuring changes in the type and concentration of the gases and liquids in contact withthe structure with gas concentration meters or ion concentration meters. In the case of sewer-related
facilities, the timing of monitoring needs to be determined appropriately because the type andconcentration of the gases and liquids in the structure vary considerably depending on the rate of
inflow and time. It is good practice to make a test specimen with a protective layer and concrete
identical to those of a real structure, expose the specimen to the same environment as theenvironment of the real structure and measure the infiltration depth of chemically aggressive
substances, chemical penetration depth, and the progress of steel corrosion. Intensive investigationin the sections where deterioration was expected to progress as a result of the initial assessment isalso effective.
(2) If high-accuracy evaluation or judgment is difficult to make by results of standard
investigations or if severe deterioration has already occurred, a detailed investigation is conducted.
Check items of a detailed investigation are described in detail in Section 12.3.2.5 “Detailed
Investigation.”12.3.2.4 Investigation in regular assessment(1) The purpose of investigation in regular assessment is to obtain information that isdifficult to obtain in routine assessment. In regular assessment, standard investigationconsisting of detailed observation of defects shall be conducted as in routine assessment.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigations in regular assessment is conducted for obtaining information
more detailed than the in routine assessment. Areas where signs of defects or deterioration havebeen detected in the initial or a routine assessment need to be examined intensively. The appearanceof the structure should basically be examined as in routine assessment. Investigations oftheinfiltration depth of chemically aggressive substances, the depth of carbonation and the state ofsteel corrosion may sometimes become necessary in addition to the examination of the appearanceof the structure.
In order to predict the progress of deterioration due to chemical attack with high accuracy inrugular assessment, it is good practice to take measurements three to five times at equal intervals
during the expected stages of initiation, propagation, acceleration and deterioration.
In the structures to which maintenance category A (preventive maintenance) is applied, it isgood practice to increase measurement frequency during the expected stages of initiation andpropagation.
(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone, detailed investigations are conducted. Check items of detailed investigations are described indetail in 12.3.2.5 “Detailed Investigation.”12.3.2.5 Detailed investigation

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Maintenance of Structures Subject to Chemical Attack

Detailed investigation shall be conducted to obtain detailed information on a structure
subject to chemical attack in cases where the deterioration of the structure is difficult topredict, evaluate or judge by standard investigation alone in initial, routine or regularassessment. Check items, methods and location of detailed investigation shall be selected
appropriately taking into consideration such factors as the purpose of investigation and theaccuracy of obtained results.

[Commentary] A detailed investigation is conducted when the determination of the present stateof a structure and the deterioration of the structure are difficult by results of standard investigations
in order to obtain information necessary for those purposes. Examples of investigation items forstructures subject to chemical attack, and of data on the condition of the structure at the time ofinvestigation and those in the future estimated from the investigation results are listed in Table
C12.3.2. The "evaluation item predictable from obtained data" in the table can be evaluated after
deterioration is predicted.
Table C12.3.2 lists check items for evaluating anomalies in the state of concrete and steel. It is
recommended that evaluators of anomalies in the state of concrete structures with surface protectionrefer to the investigation and evaluation items indicated in the Recommendations for Concrete
Repair and Surface Protection of Concrete Structures.
Major check items are outlined below. For other measurement items and test methods than thosedescribed below, refer 4.7.3 “Methods for Investigation.”(i) pH and concentration of a solution containing a chemically aggressive substanceIn cases where liquid in contact with a structure is causing chemical attack, pH can be measured
with a pH meter and the concentration of the chemically aggressive substance can be measured byhigh performance liquid chromatography or ion chromatography by taking liquid samples. In thecase of liquid containing sulfuric acid ions, concentration measurement can be done with relative
ease by the settling process using barium chloride.

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Standard Specifications for Concrete Structures-2007, Maintenance

Table C12.3.2 Examples of evaluation items in detailed investigation
Data obtainable by
Evaluation items predicable from
Measurement item
investigation
obtained data
Chemical substances pH, Rate of ingress ofRate of ingress of chemicallytemperature and humidity chemically aggressive
aggressive substances,in underground water,
substances and deterioration Deterioration depth by chemicalsoil and air
by chemical attack
attack, Corrosion rate
Rate of ingress ofRate of ingress of chemicallyDepth of ingress ofchemically aggressive
aggressive substances,chemically aggressive
substances (e.g., EPMA),
Deterioration depth by chemical
substances
grade in appearance
attacak, Corrosion rate
Rate of deterioration by
Rate of ingress of chemically
Cracking (width, depth
chemical attack, grade inaggressive substances, Carbonationand density)
appearance, and aesthetic
rate, Corrosion rate and Aesthetic
appearance
appearance
Rate of ingress ofRate of ingress of chemicallychemically aggressive
aggressive substances,
Lack of section ofsubstances and deterioration Deterioration depth by chemical
concreteby chemical attack,andattack, Time of initiation ofaesthetic appearance
corrosion
hammer tapping test
Grade in appearance, defect Concrete strength
Discoloration,
Grade in appearance,
Aesthetic appearance
efflorescenceaesthetic appearance
Carbonation rate, rate ofCarbonation rate, Rate of ingress ofCarbonation depth
ingress of chemicallychemically aggressive substances,aggressive substances
Time of initiation of corrosion
Grade in appearance,
Locations and state ofCorrosion rate, Load bearing
amount of corrosion, load
steel (area, quantity)
capacity
bearing capacity
Electrochemical
indicators (e.g., half-cell
Initiation of corrosion,
Future grade of corrosion, corrosion
potential, polarization
corrosion rate
rate
resistance, electric
resistance)
Concrete strength andConcrete strength andConcrete strength, Load bearing
modulus of elasticity
stiffness
capacity
Deflection andStiffness and load bearing
Stiffness, Load bearing capacity
displacement
capacity(ii) Infiltration depth of chemically aggressive substance
It is desirable that the infiltration depth of chemically aggressive substances be determined
qualitatively and quantitatively through chemical analysis or instrumental analysis. The reason isthat performing an analysis by using an electron probe micro-analyzer (EPMA) is an effective
method of investigating the type and distribution of chemically aggressive substances. For example,
the distribution of ettringite can be evaluated through image processing from the distribution of
calcium (Ca), aluminum (Al) and sulfur (S). Further information on EPMA analysis can be found in
JSCE-G 574-2005, Method of Area Analysis of Regions in Concrete by the EPMA Method.

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Chapter 12

Maintenance of Structures Subject to Chemical Attack(iii) Appearance of structure

If the state of concrete and steel is not directly related to the performance of the structure,anomalies in appearance provide useful information for performance evaluation. It is necessary toinvestigate not only anomalies in the state of the protective layer over the concrete, cracks in theconcrete, loss of concrete cross section, discoloration, efflorescence and the state of steel corrosion
but also anomalies in the state of the environment such as land subsidence. When estimating the
progress of deterioration, it is desirable that not only anomalies in appearance but also chemical
penetration depth as indicated by cross-sectional loss, cracks, etc., be investigated. Appearance
grades of a structure whose performance has deteriorated because of chemical attack are shown in
Table C12.3.3.

Table C12.3.3 Grades of structural appearance and stagte of deterioration
Grade of appearance of structure

I (initiation stage)

II (0ropagation stage)
III (acceleration stage)
IV (deterioration stage)

States of deterioration of astructure without protective layer
Period until the deterioration of
surface concrete begins; no
defect of appearance is found.

States of deterioration of astructure with protective layer
While chemically aggressive
substances have entered theprotective layer, no defect ofappeareance is found.
Rough or cracked concrete
Defects of the protective layer
surface is found.
have been found anddeterioration of underlying
concrete has been initiated.
Cracking or lack of cross section of concrete is so severe as to cause
the aggregate to be exposed or to be peeled off.
Cracking or lack of cross section of concrete has reached thereinforcing steel, and displacement and deflection of the structure isconsiderable due to decreases of cross-sectional area of steel, etc.

(iv) Carbonation depth
In the case of chemical attack by acids, the carbonation depth of concrete can be used as anindicator of penetration depth. It should be kept in mind, however, that a chemical aggressive
substance has already penetrated to a level deeper than the carbonation zone. The measuringmethod must be in accordance with Chapter 9 “Maintenance of Structures Subject to Carbonation.”
The ph of a typical carbonation zone identified through measurement in a structure subject tocarbonation ranges from about 8.2 to 10. In the case of carbonation due to chemical attack, pH
levels of pore solutions of 7 and lower are measured.
(v) Steel corrosion
Corrosion of reinforcing steel used in a structure tends to affect the performance of the structure.
It is therefore good practice to chip off the cover concrete so that the reinforcing steel is exposed
and measure the state, location, area and mass of corrosion, pitting corrosion depth, etc. By
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Standard Specifications for Concrete Structures-2007, Maintenanceobtaining quantitative data on corrosion, the performance degradation of the structure can beevaluated quantitatively.
In cases where steel corrosion is monitored, electrochemical indicators such as self-potential
and polarization resistance are measured. These values, however, are affected by the state ofconcrete including the water content and the composition of pore solutions. Information helpful indetermining the measuring method can be found in Section 4.7.3 “Methods for Investigation.” Careshould be taken when applying an electrochemical method to steel corrosion due to chemical attack
because application to chemical attack is less proven than application to chloride attack or
carbonation and there are no established evaluation criteria.

12.3.3 Methods for predicting performance degradation of structures
12.3.3.1 General(1) In the maintenance of a structure subject to chemical attack, the performance of thestructure shall be evaluated quantitatively at the time of investigation, and futuredegradation shall be predicted.
(2) In order to predict the performance degradation of a structure, deterioration due tochemical attack shall be predicted quantitatively.
(3) If (2) is difficult, an alternative method is to predict performance degradation by
estimating the length of initiation, propagation, acceleration and deterioration stages, taking
the progress of erosion in the protective layer and concrete due to chemical attack and thesteel corrosion into consideration.
(4) Deterioration shall be predicted on the basis of investigation results.

[Commentary] (1) and (2) In the performance-verification type maintenance method, anomalies(degradation) in various performance attributes of a structure are to be predicted. In order to do that,
it is necessary to quantitatively predict the deterioration of the materials used in the structure subject
to chemical attack, namely, chemical penetration into the concrete and the progress of corrosion of
the steel in the concrete. It is also necessary to quantitatively evaluate the performance of thestructure and the degree of deterioration of the materials used in the structure at the time ofinvestigation and at the end of the planned service period on the basis of investigation results. The
performance degradation of the structure or the degree of deterioration of the constituent materials
at the time of investigation can be evaluated by using an appropriate method on the basis of theinvestigation results. Performance and the degree of deterioration at the end of the planned service
period are estimated on the basis of the investigation results in periodic assessments. Because thedeterioration estimation results do not necessarily agree with the actual progress of deterioration, it
is important to review the estimation method on the basis of the results of multiple investigations
conducted thereafter.
(3) In cases where the deterioration of the concrete and steel used in a structure are predicted,
and various performance attributes of the structure are evaluated by combining the results thus
obtained, it is not easy, at the present level of technology, to make quantitative predictions. A
practical method, therefore, is to estimate the length of the initiation, propagation, acceleration anddeterioration stages by taking into consideration the infiltration of chemically aggressive substances
177Chapter 12

Maintenance of Structures Subject to Chemical Attack

into the concrete and the progress of concrete penetration and steel corrosion. The deterioration
stages and factors determining their length are listed in Table C12.1.1.
The length of the initiation stage is calculated from the rate of penetration of the protective layeror the underlying concrete by the gas or liquid containing a chemically aggressive substance; thelength of the propagation stage and the acceleration stage, from the rate of penetration of theconcrete by a chemically aggressive substance; and the length of the deterioration stage, from therate of steel corrosion and the amount of corrosion of the steel whose load-carrying capacity
decreases. These calculations must be made in accordance with Section 12.3.3.2 “Prediction ofChemical Erosion”, and Section 12.3.3.3 “Prediction of Steel Corrosion.”(4) Investigation results can be classified into two types: one type concerns the quality of theprotective layer and the underlying concrete used in the inspected structure and the other concerns
the environment in which the structure is used. As a general rule, deterioration must be estimated byanalyzing these investigation results. If no information is available on environmental conditions asin the case of a newly constructed structure or if investigation results are not available for an
existing structure, investigation results for adjacent structures or structures in similar environments
may be used for reference purposes.

12.3.3.2 Prediction of chemical erosion(1) The progress of chemical erosion shall be predicted considering the quality ofprotective layer and concrete and the environment in which the structure is in service.
(2) The progress of chemical erosion may be predicted by one of the following methods.
(i) Use of investigation results(ii) Use of accelerated tests(iii)Use of numerical analyses considering the reaction of chemically aggressive
substances and their movement at the boundary with the environment[Commentary] (1) The prediction of chemical erosion is important for accurate estimation of theinitiation, propagation and acceleration stages. The rate of chemical erosion varies considerably
depending on the type and concentration of the chemically aggressive substance concerned and thequality of concrete. Usually, the chemically aggressive substance has already reached a region
deeper than the altered region and exists in high concentrations. When predicting the progress ofchemical erosion, therefore, it is necessary to distinguish the penetration depth in the concrete fromthe infiltration depth of the chemically aggressive substance. Since, however, what can be observed
visually or otherwise are anomalies in appearance of the concrete, it is desirable that the penetration
depth in the concrete be estimated in order to predict the progress of chemical erosion. If a moredetailed prediction is to be made, other indicators such as the infiltration depth of the chemicallyaggressive substance and the depth of carbonation should also be estimated. In the case of anunderground structure, the environment of the structure needs to be appropriately taken into
consideration because other chemically aggressive substances of different types and concentrations
may infiltrate from the inner and outer parts of the structure.
In cases where a resin or other protective layer is provided over the concrete surface, not only178

Standard Specifications for Concrete Structures-2007, Maintenancethe quality of concrete but also the quality of the protective layer material must be taken into
consideration when estimating the progress of deterioration.
When making a prediction, it is necessary to use an appropriate factor of safety, taking into
consideration the setting methods for the parameters used, the variability of the quality of thestructure and the influence of the environmental conditions.
(2) Commonly used methods for predicting the progress of chemical erosion can be broadlyclassified into three types:(i) Use of investigation results
Penetration depth of chemically aggressive substance in concrete may be proportional to thesquare root of time or to time, depending on the type and quantity of the chemically aggressive
substance concerned.
Under conditions not conducive to separation or in the case of deterioration due to sulfate salts
in a soil environment or in an environment without water flow, the penetration rate is in many cases
proportional to the square root of time, as in the case of the infiltration rate of a chemicallyaggressive substance. Penetration depth in such cases can be expressed asy   c ( a  t  b)

(Eq. C12.3.1)

where
y: penetration depth in concrete (mm)t: duration of exposure to chemically aggressive substance (year)
a: concrete penetration rate factor (mm/ year )b: coefficient (deterioration from initial stage: b =0)
γc: factor of safety related to accuracy of prediction

In the equation shown above, γc, which is a factor of safety related to prediction accuracy, needs
to be determined taking into account the variability of structures and the variability of thecoefficient a, which is affected by environmental conditions. In general, 1.0 may be used.
Under conditions conducive to separation or in the case of deterioration due to acidic substancesin an environment with water flow such as a water channel, the penetration rate is in many cases
proportional to time. It is generally known that in the case of a sewer pipe, the concentration ofhydrogen sulfide in the gas phase in the pipe is proportional to the penetration rate. The penetration
depth in such cases can be expressed asy   c (c  t  d )(Eq. C12.3.2)

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where
y: penetration depth in concrete (mm)t: duration of exposure to chemically aggressive substance (year)
c: concrete penetration rate factor (mm/year), c = e [H2S] + f[H2S]: hydrogen sulfide concentration (ppm)d, e, f: coefficients (deterioration from initial stage: d = 0)
γc: factor of safety related to accuracy of prediction
If investigation results include measured values of penetration depth, recommended practice isto determine the concrete penetration rate factor from the measurement results and make subsequentpredictions accordingly. In theory, the concrete penetration rate factor can be calculated throughone-time measurement. If a highly reliable value is to be obtained, however, it is desirable that theconcrete penetration rate factor be calculated by the least squares method after conducting two or
three measurements at intervals of several years. It should also be kept in mind that if concrete
penetration depth and the penetration rate factor vary considerably with measurement locations inthe structure, the penetration rate also varies among different parts of the structure.
If the pH of the solution is close to neutral even in the case of acid-induced deterioration,
deterioration-related deposits may delay deterioration by clogging the pores. Chemical attack,therefore, does not necessarily occur as mentioned above. In chemical attack by sulfate salts,
penetration depth is not necessarily proportional to the square root of time because the progress ofdeterioration may be greatly affected, for example, by cracks caused by the expansion of reaction
products. If such deterioration is expected, it is necessary to conduct appropriate accelerated
deterioration tests.
(ii) Use of accelerated test
In many cases, chemical erosion gradually occurs from the surface of the protective layer or theunderlying concrete. Deterioration, therefore, can be easily detected visually. So far, however, nosystematic method for predicting the progress of chemical erosion has been proposed. It is therefore
desirable that accelerated deterioration tests be conducted under conditions that do not alter thedeterioration mechanism of the chemically aggressive substance expected to come into contact withthe structure, taking into consideration the environment of the structure, and concrete penetration
depth, the infiltration depth of the chemically aggressive substance, etc., be estimated accordingly.
This method enables highly reliable estimation but may require long time to obtain results. Methodof Test for Chemical Resistance of Concrete in Aggressive Solution proposed by Japan Testing
Center for Construction Materials is an informative reference on a test method of this kind.
If an accelerated deterioration test is conducted for a protective layer over concrete, it isdesirable that the test be conducted on a protective layer integrated with the concrete. This is for the
purpose of accurately evaluating the effect of the interface between the protective layer and theconcrete.
(iii) Use numerical analyses considering the reaction of chemically aggressive substances and180

Standard Specifications for Concrete Structures-2007, Maintenancetheir movement at the boundary with the environment
A method for predicting the progress of chemical erosion by using a numerical analysis
technique that enables quantitative evaluation of the chemical reaction between a chemicallyaggressive substance and cement hydrates and the resultant changes in properties has been proposed.
At present, however, there are not many numerical analysis methods related to chemical erosion on
concrete. In the case of sewer conduits, for example, the generation of hydrogen sulfide gas and thequantities of dissolved oxygen and sludge in sewage are among the factors governing thedeterioration rate of concrete. In pipe sections with uneven bottoms or in areas where wastewater
drops into a pit, a considerable amount of hydrogen sulfide gas is emitted so that the concrete
penetration rate increases. It is desirable that an analysis technique capable of allowing for these
conditions be used. When analyzing phenomena involving cracking caused by the expansion ofreaction products as in deterioration caused by sulfate salts, it is desirable that an analysis capableof allowing for the effect of such phenomena be conducted.

12.3.3.3 Prediction of steel corrosion(1) The progress of steel corrosion due to chemical attack shall be predicted properly
considering the concrete quality and the environment in which the structure is in service.
(2) The initiation of steel corrosion should be determined based on the remaining
uncarbonated depth.
(3) The progress of steel corrosion may be predicted by one of the following methods.
(i) Predicting from the investigation results(ii) Predicting using accelerated tests[Commentary] (1) In general, chemical attack occurs first at the surface of steel. In a state inwhich there is concern about steel corrosion, chemical attack has already occurred in the protective
layer and the underlying concrete, so the protective layer and the underlying concrete cannot be
expected to function as protective shields against steel corrosion. The prediction of steel corrosion
due to chemical attack, therefore, is actually the prediction of steel corrosion due to a chemicallyaggressive substance. Factors affecting the rate of steel corrosion due to chemical attack include theconcentration of the chemically aggressive substance at the steel location and the water content of
concrete. It is not yet possible, however, to quantitatively evaluate the relationship between thesefactors and the corrosion rate.
(2) In the case of acid-induced deterioration, deterioration occurs as concrete is attacked by anacid and altered. In general, when concrete is attacked by an acid, the cross-sectional area of theattacked region decreases and carbonation occurs. In the case of deterioration caused by sulfuric
acid, therefore, carbonation depth is often used as an easy-to-measure indicator of the infiltration
depth of sulfuric acid ions. In the case of deterioration caused by sulfate salts, steel corrosion occurs
as the concrete is porositized to cause early carbonation. In both cases, prediction should be basedon the penetration depth of the chemically aggressive substance. Since, however, there seems tohave been no steel corrosion research focusing on chemical attack and the infiltration depth of achemically aggressive substance is difficult to measure by a simple method, this specification
basically requires that the time of initiation of steel corrosion be judged in terms of the remaining
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non-carbonated cover thickness.
There seems, however, to have been no research, either, on the relationship between theremaining non-carbonated cover thickness and the initiation of steel corrosion from the viewpointof chemical attack. It is therefore necessary to identify the relationship between the remaining
non-carbonated cover thickness and the time of initiation of steel corrosion through investigationsor through accelerated deterioration tests that appropriately take into consideration the type of steel
and the environmental conditions under which the structure of interest is to be used.
(3) Steel corrosion due to chemical attack tends to be by far faster than steel corrosion due toother deterioration mechanisms. The progress of steel corrosion due to chemical attack, therefore,
must be estimated by one or more of the following methods:(i) Method based on corrosion rates obtained as investigation results
If the rate of corrosion has been measured over time, the progress of corrosion can be predictedby regressing the measurement results. The shape of curves showing time-dependent changes in therate of steel corrosion due to chemical attack varies depending on the type and concentration of thechemically aggressive substance concerned. It is desirable, therefore, that the corrosion rate be
estimated from the corrosion rate–time curves by using corrosion rate measurements taken at threeor more material ages.
(ii) Method using accelerated tests
If investigation results are not available, it is desirable that the corrosion rate be predicted
through accelerated deterioration testing in due consideration of the type of steel and theenvironmental conditions under which the structure is placed.
At the deterioration stage, it is necessary to evaluate load-carrying capacity by appropriately
evaluating the loss of the cross-sectional area of concrete, the steel corrosion rate, anchoring, etc.

12.3.3.4 Modification of prediction
If the state of deterioration determined in an investigation differs from a predicted state ofdeterioration, the cause of the difference shall be identified and the prediction shall berevised accordingly. If necessary, the maintenance planning shall be altered.

[Commentary] If the state of deterioration determined in an investigation differs from a predictedstate of deterioration, an appropriate investigation must be conducted with reference to thedeterioration prediction methods described in Section 12.3.3.2 “Prediction of Chemical Erosion”,
and Section 12.3.3.3 “Prediction of Steel Corrosion”, and Table C12.3.2 in Section 12.3.2.5“Detailed Investigaiton”, to identify the cause of the difference from the prediction and revise theprediction accordingly. The results of a number of investigations conducted are useful for
identifying the cause of the difference and revising the prediction. It is also important to reconsider
such details as the frequency of investigation in view of the revised prediction and alter the
maintenance plan if necessary.

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Standard Specifications for Concrete Structures-2007, Maintenance12.3.4 Evaluation and judgment(1) The performance of a structure shall be evaluated and the necessity for remedial
measures shall be judged based on the results of the investigation in initial, routine andregular assessments in accordance with Part 1 and Item (2) and subsequent Items in thissection.
(2) The performance of a structure subject to chemical attack shall be evaluated byappropriately selecting performance attributes to be evaluated in view of the deterioration
stagestage of deterioration of the structure.
(3) The evaluation of performance attributes at the time of investigation and at the end of
the planned service period of the structure should be made by a quantitative method.
(4) If Item (3) is difficult to achieve, the evaluation of performance attributes at the time ofinvestigation and at the end of the planned service period of the structure may be made by asemi quantitative grading-based method.
(5) The necessity for remedial measures shall be judged in view of the degress of
performance degradation due to chemical attack, the degree of importance of the structure,category of maintenance, and the remaining planned service life.

[Commentary] (1) The evaluation of the performance and judgment of necessity for remedial
measures in initial, routine and regular assessment for stuructures in which littlie progress ofdeterioration has been recognized are frequently more ore less the same, regardless of deterioration
mechanisms. For details, refer to Part 1. The evaluation and judgment for a structure that may be
deteriorated to some extent vary with deterioration mechanisms. Evaluation and judgment, therefore,
concerning performance degradation due to chemical attack need to be made in accordance with theprovisions of this chapter.
(2) In the case of a structure in a chemically aggressive environment, performance attributes
affected by deterioration vary depending on the stage of deterioration (initiation stage, propagation
stage, acceleration stage or deterioration stage). Performance attributes to be evaluated, therefore,
need to be selected appropriately for each stage of deterioration. At the initiation stage, for example,
either chemical attack is not visible or the chemically affected zone is within the protective layerover the concrete. The performance attribute to be evaluated, therefore, is the capability of theprotective layer, etc., in preventing chemical attack on the concrete. At the propagation stage,appearance and third party impact due to the spalling of the concrete surface or other forms ofdeterioration need to be evaluated. At the acceleration stage, chemical attack on concrete occurs, so
performance attributes such as the stiffness and ductility of structural members under the influenceof decreases in cross-sectional area, the serviceability of water channels such as discharge capacity,and the capability of the cover concrete to protect the reinforcing steel are evaluated. In addition, it
is also necessary to evaluate third party impact and appearance because deterioration becomessevere. At the deterioration stage, the cross-sectional area of the concrete decreases considerably,and steel corrosion occurs. It is therefore necessary to pay attention to decreases in stiffness andductility of structural members and safety performance items such as load-carrying capacity. third
party impact and appearance degradation due to a partial loss of the cross section of concrete andsteel corrosion also need to be evaluated.
(3) The performance of a structure at the time of investigation and at the end of the planned
service period needs to be evaluated after the state of deterioration of the constituent materials of183

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Maintenance of Structures Subject to Chemical Attack

the structure, namely, the concrete protection materials, concrete and steel, is evaluatedquantitatively. For example, in the performance evaluation at the time of investigation, safety andserviceability are checked by determining load-carrying capacity, the amount of deflection and theamount of deformation by substituting the dynamic properties obtained from investigation results inthe structural calculation equations. It is also possible to verify third party impact and appearance by,for example, evaluating cracks, the extent and density of scaling and spalling and the degree of steel
corrosion. By these verification methods, it may be possible to evaluate performance in a relatively
straightforward manner at the time of investigation. It is usually difficult, however, to evaluate
performance at the end of the planned service period with sufficient accuracy. A reasonable method,
therefore, is to supplement such evaluation by verifying durability through deterioration prediction
based on the chemical attack rate coefficient and the steel corrosion rate with reference, for example,
to the method described in Section 12.3.3 “Methods for Predicting Performance Degradation of
Structures.” In this case, not only the accuracy of the performance verification method used at thetime of investigation but also the accuracy of the deterioration prediction method are importantconsiderations. Prediction methods, therefore, need to be carefully selected, and it is important toallow for a reasonable factor of safety.
(4) In the performance verification type design system, structural performance should ideally beevaluated quantitatively. At present, however, there is no established method for doing it. As apractical method, the performance of a structure at the time of investigation can be evaluatedsemiquantitatively, with reference to Table C12.3.4, by performing grading in accordance with
Table C12.3.3.
The purpose of grading is to classify the present degree of deterioration of a structure
semiquantitatively instead of predicting and evaluating the degree of deterioration in future. It isalso possible, however, to predict the performance of a structure at the end of the planned service
period in accordance with Table C12.3.4 by estimating the stage of deterioration at the end of theplanned service period on the basis of investigation results such as the chemical attack rate, theinfiltration rate of the chemically aggressive substance, the carbonation rate and the steel corrosion
rate.
If detailed maintenance records for a similar structure (type of structure, materials, construction,
environment, state of use) are available and the progress of deterioration thus far of the structure ofinterest is similar to that of the similar structure, then the evaluation results for that structure
provide useful information.
(5) Because judgment is the act of deciding whether remedial measures need to be taken on thebasis of structural performance evaluation results, there is no difference depending on deterioration
factors. Therefore, refer to Part 1.

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Table C12.3.4 Grades of appearance of structures and typical performance degradation
Grade of
Hazards for Aesthetic appearance
appearance
SafetyServiceability
third party
and landscapeof structure
I (initiation－－－－
stage)
Degradation ofaesthetic appearance• Peeling ofII (propaga
protective layer over－－tion stage)
concrete• Deterionration andcracking of concrete
Decrease in stiffness(increase in
deformation,
Decrease in loadDegradation ofIII
occurrence ofbearing capacity
aesthetic appearance
Hazards for(acceleration
vibration)• Decrease of cross• Deterioration andthird party
stage)• Decrease in crosssection of concrete
cracking of concrete
section of concrete• Decrease in flow
• Peelingrate, etc.
and spallingof concrete
Decrease in stiffness(increase in
deformation,
Decrease in load
occurrence ofDegradation of
bearing capacity
vibration)
aesthetic appearanceIVand ductility• Deterioration of bond
• Deterioaration and(deterioration • Decrease in crossbetween steel andcracking of concrete
stage)
section of concrete
concrete• Stain of rust
• Decrease in cross• Decrease in cross• Exposure of steel
section of steel
section of concrete• Decrease in crosssection of steel
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12.4 Remedial Measures
12.4.1 Selection of remedial measures(1) If it has been judged that remedial measures need to be taken in consideration withperformance degradation of a structure subject to chemical attack, remedial measures bywhich the the corrected structure meets the required performances shall be selected.
(2) If it is difficult to select remedial measures for a structure on the basis of performanceverification, remedial measures may be selected from the measures corresponding to thegrade of appearance.

[Commentary] (1) If it has been judged, as a result of evaluation, that remedial measures need tobe taken, it is necessary to select one or more of the following measures: (i) intensified investigation,(ii) repair, (iii) strengthening, (iv) functional improvement, (v) restriction in service or (vi)dismantling/removal. Basically, decisions as to which measures to take should be made by the
maintenance manager of the structure, but it is good practice to refer to Part 1 for information on
typical relationships between evaluation and judgment results and remedial measures.
(2) If it is difficult to select remedial measures for a structure through quantitative evaluation or
judgment, remedial measures are selected from the measures corresponding to the deterioration
grade of the structure. Remedial measures to be taken vary depending on the type of structure, thedegree of importance of the structure, deterioration rate and the category of maintenance, but
recommended standard measures are shown in Table C12.4.1.

Table C12.4.1 Grades of appearance of structures and remedial measures
Dismantli
Intensified
Grade ofStrength
Functional
Restriction
ng/remova
appearance ofinvsetigati Repair
ening** improvement in service
onlstructure
I (initiation stage)
O
O**
X
X
II (propagation
OO
OO
X
X
stage)III (acceleration
OO
OO*
X
X
O
stage)IV (deterioration
O*
X
X
OO
OO
stage)
OO: standard remedial measures [OO*: including the restoration of mechanical performance]
O: remedial measures in some cases[O*: including restoration of mechanical performance, O**: preventive measures]
X: remedial measures taken based of other criteria other than the grade of appearance
Strengthening**: Enhancing the mechanical performance above the initial level

12.4.2 Repair and strengthening
Methods and materials for the repair or strengthening of a structure shall be selectedtaking into consideration the performance degradation of the structure due to chemical
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Standard Specifications for Concrete Structures-2007, Maintenanceattack and life cycle cost, so that the required effect can be achieved.

[Commentary] In cases where repair or strengthening is carried out as a remedial measure, it isnecessary to define the expected effect of repair or strengthening and the required performance(what level of performance to be maintained for how many years?). Ideally, it is desirable that
remedial measures be taken after constructing a deterioration formula (for repair) or structural
calculation formula (for strengthening) in view of such factors as the properties of the materials
used and verifying the calculation results obtained from those formulas. In this case, it is also
important to take life cycle cost into consideration according to the remaining service life. In cases
where preventive maintenance measures are taken for a structure to which Type A maintenance(preventive maintenance) is applied, it is necessary to select an appropriate method in due
consideration of the effect expected of the method.
Repair and strengthening methods for structures deteriorated by chemical attack can beclassified, according to expected effects, as shown in Table C12.4.2. When deciding on which
method to use, it is necessary to take into consideration the present state of performance degradationof the structure concerned besides Table C12.4.2. For the correspondence between appearance
deterioration grades and remedial methods, refer to Table C12.4.3.

Table C12.4.2 Expected effects and methods of repair or strengthening
Expected effectExamle of methods
Control the progress Surface treatment (resin lining, sheet lining), FRP adhesion,of chemical erosion
Embedded form, Ventilation, Washing
Control the progress Surface treatment, Patching, Rust-preventing coatingof steel corrosion
Restore or enhance FRP adhesion, Thickness increasing, Jacketingload-bearing
capacity

Table C12.4.3 Grades of structural appearance and methods of repair or strenghening
Grade of appearance Standard methodsof structure
I (initiation stage) Surface treatment, Ventilation, Washing
II (propagation
Surface treatment, Patching, Embedded form,
stage)
Ventilation, Washing
III (acceleration
Patching, Surface treatment, Thickness increasing,stage)
Embedded form, ventilation & washingIV (deterioration
FRP sheet bonding, Patching, Surface treatment,
stage)
Thickness increasing, Jacketing, Embedded form,
Ventilation, Washing

If a structure is at the initiation stage of deterioration due to chemical attack, performancedegradation or deterioration has not yet occurred. Structures for which remedial measures are taken
at this stage, therefore, are only those to which Type A maintenance (preventive maintenance) is
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applied. The expected effect in this case is to prevent the infiltration and diffusion of chemicallyaggressive substances into the concrete. This means that it is necessary to devise surface treatment
methods for preventing the penetration of chemically aggressive substances and ventilation andwashing methods for preventing the occurrence or attachment of chemically aggressive substances.
If a structure is at the propagation stage, penetration into the concrete has already begun. The
degree of penetration, however, is still low, and little degradation of performance has occurred.
Remedial measures taken at this stage, therefore, consist mainly of surface treatment as in the caseof a structure at the initiation stage.
If a structure is at the acceleration stage, the degradation of mechanical performance is not yet
substantial, but the exposure of aggregates near the concrete surface and cracking of concrete havealready occurred. It is therefore necessary to consider the use of such measures as cross-sectional
restoration and left-in-place form installation.
If a structure is at the deterioration stage and the load-carrying capacity has already decreased, it
is necessary to use repair methods for restoring cross sections and load-carrying capacity by, forexample, increasing or replacing reinforcing bars, such as FRP sheet bonding, jacketing, overlay orleft-in-place formwork methods. In order to prevent the recurrence of deterioration, it is also
necessary to apply such methods after removing the deteriorated portions and restoring crosssections.
Many of the repair and strengthening methods in use today were developed in recent years, andsome of them have not been field-tested extensively. Those methods might fail to prevent therecurrence of deterioration or achieve the required performance because of factors that could not be
expected at the design stage. It is desirable, therefore, that precautionary measures such asincreasing investigation frequency be taken after repair or strengthening work is done.
For details of various repair and strengthening methods, refer to, for example,
Recommendations for Strengthening of Concrete Structures, Recommendations for Concrete Repair
and Surface Protection of Concrete Structures, Report of the Committee on Repair Methods forConcrete Structures (I, II and III) (Japan Concrete Institute), Report of JCI Committee on
Rehabilitation of Concrete Structures (Japan Concrete Institute) and Guidelines for Corrosion
Control Technology and Corrosion Prevention Technology for Concrete Structures of Sewerage
Systems (Japan Sewage Works Agency).

12.5 Recording(1) Investigation, deterioration estimation, evaluation and judgment, and remedial
measures shall be recorded in accordance with Part 1.
(2) Items relevant to chemical attack shall be recorded.

[Commentary] As a general rule, the results of investigations, deterioration estimations,evaluations and remedial measures must be recorded in accordance with Part 1. Items relecant tochemical attack require careful attention, particularly with respect to record keeping. Items to berecorded are the investigation items indicated in Section 12.3.2 “Investigation in Assessment”, andthe evaluation items indicated in Section 12.3.4 “Evaluation and Judgment.”

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Chapter 13

Maintenance of Structures Subject to Alkali-Silica Reaction

CHAPTER 13 MAINTENANCE OF STRUCTURES SUBJECT TO
ALKALI–SILICA REACTION
13.1 General(1) This chapter provides standard methods for the maintenance planning,assessment, remedial measures and recording for structures that have been or are
highly likely to be subject to performance degradation due to ASR. The items
common to all deterioration mechanisms are shown in Part 1.
(2) This chapter shall be applied to structures of the maintenance categories A(preventive maintenance) and B (corrective maintenance).

[Commentary] (1) Alkali–aggregate reaction and ASR: The alkalis (Na2SO4 and K2SO4)
contained in cement are dissolved in the pore water solution in the concrete during the hydration of
cement to become a strong alkali (pH = 13 to 13.5) water solution composed mainly of alkalihydroxides (NaOH and KOH). Aggregates containing certain types of silica minerals may reactwith the strong alkali water solution in the concrete to cause abnormal expansion and resultant
cracking of concrete. Reaction of this kind is referred to collectively as alkali–aggregate reaction. In
Japan, in the second half of the 1970s, deterioration due to alkali–aggregate reaction due toalkali–aggregate reaction was found in structures built mainly by using crushed andesite aggregate
in the Kansai, Chugoku and Hokuriku regions. It is generally said that such alkali–aggregate
reaction can be classified into two types, namely, alkali–silica reaction (ASR) and alkali–carbonate
reaction, and alkali–aggregate reaction problems reported in Japan concern mainly ASR. This
chapter, therefore, deals the maintenance of structures subject to ASR.
A hypothesis that has come to be widely accepted as a result of recent research is that what
used to be termed "alkali–carbonate reaction" is actually ASR involving microcrystalline silica
contained in limestone.
Defect caused by ASR and contributing factors: This chapter is applicable to structures consistingof reinforced concrete, prestressed concrete or steel–concrete composite structures subject to ASR,
but it is intended mainly for application to reinforced concrete structures.
In structures subject to ASR, defect becomes visible in the form of concrete cracks several
years after construction. Defect of structures caused by ASR usually occurs over a long period oftime in the presence of moisture and alkalis. It is generally known that the degree of change caused
by ASR varies considerably depending on (1) factors related to concrete such as the type andcontent of reactive aggregate, the type and alkali content of cement and concrete mix proportions(cement content, water/cementitious material ratio, air content, and the type and content of
admixtures), (2) factors related to concrete structures such as the cross-sectional shapes of structuralmembers, the amount of reinforcing steel and constraint conditions and (3) factors related to theservice environmental conditions under which the structure is placed such as the supply of moistureand alkalis, insulation, and exposure to rain.
It is also generally known that in cold regions in Japan, ASR is accelerated by salts (e.g.,
NaCl) widely used as deicing agents.
ASR-induced deterioration: As shown in Fig. C13.1.1 and Table C13.1.1, the deterioration
process of a structure due to ASR can be divided into the initiation, propagation, acceleration anddeterioration stages. The influence of deterioration phenomena on the performance of structures
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Standard Specifications for Concrete Structures-2007, Maintenancevaries among these deterioration stages, and the degree of performance degradation due to theprogress of deterioration at each stage also varies depending on the performance attributeconcerned.
The reason why two types of deterioration process are shown in Fig. C13.1.1 is that the
progress of deterioration due to ASR is affected by various factors as mentioned above, and thatcannot be expressed with a single illustration. Fig. C13.1.1(a) shows a case in which the
expansibility of concrete is high and the concrete is cracked so severely that the integrity of thestructural members is lost or expansion continues until the reinforcing steel is damaged (yielding,cracking or fracture). Fig. C13.1.1(b) shows a case in which cracking occurs because of ASR, but
ASR-induced expansion converges at a certain point in time for some reason (e.g., the reactive
material on the aggregate surface has been used up) and, consequently, the transition from the
propagation stage of deterioration to the acceleration stage does not occur. Although not shown here,
there may be a case in which ASR-induced deterioration stops at the acceleration stage. Thus, one
characteristic of ASR is that a single deterioration process cannot be identified, and identification ofdeterioration stages and deterioration prediction are difficult to make.
(2) Currently known characteristics of a structure that has deteriorated or is likely to deteriorate
because of ASR and remedial measures taken for the structure are as follows:(i) It is difficult to detect deterioration, even by monitoring, before expansion cracks occur.
Even if reactive aggregate is used or there is a large amount of alkalis, whether expansion
actually occurs is unpredictable.
(ii) Even if deterioration as mentioned in (i) is detected, there is no established method forpreventing further progress of deterioration from the initiation stage.
(iii) For the reasons mentioned in (i) and (ii), there are too many uncertain factors to takeremedial measures for structures at the initiation stage of ASR-induced deterioration (i.e., all
structures that have not shown any sign of ASR-induced deterioration) merely because
ASR-induced deterioration could occur in future.
Because of these characteristics, in the case of an ordinary structure, it is common practice toperform maintenance while checking on defect in the state of the structure. This chapter, therefore,
focuses mainly on structures in the maintenance category B.
In the case of a structure that is highly likely, judging from the results of a fact-finding
investigation of a nearby structure or a structure built with similar materials, to be affected by ASR,
if requirements related to hazards for third party or appearance are demanding or if remedial
measures are difficult to take, it is desirable that a maintenance plan based mainly on concepts andmethods in the maintenance category A be drawn up on an as-needed basis. It should also be kept inmind that structures in the maintenance category C (observational maintenance) are notmaintenance-free. Instead, it is necessary to take maintenance measures consistent with the basic
concepts and methods described in this chapter as much as possible.
For considerations in deciding on the category of maintenance for a structure that hasdeteriorated or is likely to deteriorate because of ASR, refer to Section 13.2.2, “Determination of
Category of Maintenance.” Fig. C13.1.2 illustrates a standard procedure for maintenance inconnection with ASR.
In connection with the application of this chapter, it is advisable to refer to Report of the
Subcommittee on Alkali–Aggregate Reaction Control Measures (Japan Society of Civil Engineers),
Ministry of Construction Comprehensive Technology Development Project: Development of190

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Maintenance of Structures Subject to Alkali-Silica Reaction

Performancedegradation of member

Deterioration
due to ASR

Deterioration
Performancedegradation of member due to carbonation

Concrete Durability Improvement Technology (Public Works Research Center), Report of theCommittee on Alkali–Aggregate Reaction (Japan Concrete Institute) or Report of the Subcommittee
on Deterioration of Concrete Structures Due to Deicing Agents (Japan Concrete Institute).

Fig. C13.1.1

Conceptual view of deterioration progress due to ASR

Table C13.1.1
Stage ofdeterioration

Definition of deterioration stages
Definition

Factor determining the stage

Period in which ASR occurs but neither
expansion nor resultant cracking has not
yet occurred

Rate of alkali–silica gelformation (type and quantityof reactive minerals, quantityof alkalis)

Propagation stage

Period in which expansion occurs
continuously and cracking occurs in thepresence of water and alkalis, but steel
corrosion does not occur

Water-induced expansion rateof alkali–silica gel (supply ofwater and alkalis)

Acceleration stage

Period in which water-induced expansion
is maximized, crack propagate and steel
corrosion may or may not occur

Water-induced expansion rateof alkali–silica gel (supply ofwater and alkalis)
Water-induced expansion rateof alkali–silica gel (supply ofwater and alkalis)

Deterioration stage

Period in which the width and density ofcracks increase and the integrity ofstructural members is lost, thecross-section area decreases because ofsteel corrosion or the load-carrying
capacity decreases considerably becauseof steel damage, etc.

Initiation stage

191

Steel corrosion rate
Rate of increase in tensilestress in steel

Standard Specifications for Concrete Structures-2007, Maintenance(13.2)

Possibility ofASR(13.3)

Maintenanceplan for the
structure

Assessment(13.3.2.2)
Investigations ininitial assessment
Standard
investigation(13.3.2.5)
Detailed
investigation(13.4)(13.3.3)(13.3.4)

Deterioration
prediction

Remedial
measures

Evaluation andjudgment(13.5)
Recording(13.3.2.3, 4)
Investigations inroutine/regularassessment
Standard
investigation(13.3.3)(13.3.4)(13.3.2.5)
Detailed
investigation

Deterioration
prediction
Evaluation andjudgment

Fig. C13.1.2 Standard maintenance procedure against ASR

13.2 Maintenance Planning
13.2.1 Basis of planning
In order to maintain a structure subject to ASR, the category of maintenance shall beselected, the service period planned, and a maintenance planning for activities including
assessment, remedial measures and recording drawn up in advance in view of the service
and environmental conditions[Commentary] When drawing up a maintenance planning, it is necessary to cover such details ascheck items and procedures for initial assessment and check items, procedures, timing andfrequency for the investigations in routine and regular assessment, evaluation and judgment
methods, actions to be taken in the event of deterioration, and recording methods, taking into
consideration the type, degree of importance and planned service period of the structure, category of
maintenance, and the quality of materials.
The type of structure, size and environmental conditions of concrete structures vary fromstructure to structure. A maintenance planning to be applied to a structure must be optimized for
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each structure. Deterioration of a structure due to ASR varies considerably depending on the service
and environmental conditions for the structure such as the supply of water and alkalis, insulation,and exposure to rain. An appropriate maintenance planning needs to be drawn up, therefore, in viewof these factors.
It is usually difficult, at the stage of maintenance planning, to accurately predict the state of astructure during its service period. It is therefore good practice to draw up a maintenance planningwith reference to the deterioration of a similar structure or a structure in a similar environment.

13.2.2 Determination of maintenance category
The category of maintenance of a structure subject to ASR shall be selected in viewof the degree of importance of the structure, the type of structure, hazards for third party,
the planned service period and the characteristics of deterioration due to ASR.

[Commentary] The determination of the category of maintenance is very important because
maintenance planning varies widely depending on the category of maintenance. The progress ofdeterioration and performance degradation due to ASR is conceptually illustrated in Fig. C13.1.1.
Structures to which maintenance category B (corrective maintenance) is applied should bemaintained so that performance of structure does not fail to meet the required performances. For
example, maintenance needs to be performed in view of performance degradation at and after theacceleration stage if attention is paid to safety and at and after the propagation stage if attention ispaid to serviceability, hazards for third party and appearance. Indicators of deterioration due to ASR
include the following:(i) Cracking, discoloration and bleeding of alkali–silica gel have occurred.
(ii) The width and density of cracks have increased, and there is rusty water due to steel
corrosion.
(iii) The width and density of cracks have further increased, and surface unevenness,
displacement and local scaling and spalling occur.
(iv) There is rusty water indicating further corrosion of steel.
(v) There are cracks and steel damage due to environmental deterioration factors.
(vi) Displacement and deformation have increased.
Because it is extremely difficult to stop the progress of deterioration after the reinforcing steel
in the concrete begins to be corroded, it is desirable that even in cases where maintenance category
B (corrective maintenance) is applied, repair should be carried out at the stage of (i) or (ii)mentioned above. It should be kept in mind that if stage (iii), (iv) or (v) is reached, very large-scalemeasures such as cross-sectional restoration need to be taken. Thus, it is necessary to fully
understand the target level of maintenance, the characteristics of ASR-induced deterioration and thecharacteristics of maintenance methods required for different categories of maintenance, and to
determine the category of maintenance, taking life cycle cost into consideration.

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Standard Specifications for Concrete Structures-2007, Maintenance13.2.3 Preparation of maintenance manuals
A maintenance manual describing methods, procedures and frequency requirements
should be prepared for each structure in accordance with the maintenance planning, taking
the structure-specific conditions into consideration.

[Commentary] The service period of civil engineering structures is long, and maintenance of
those structures is performed over a long period of time. It is recommended, therefore, that in order
to inform investigators of maintenance concepts and policies, a maintenance manual be prepared sothat detailed procedures and methods can be communicated accurately even to newly assigned
responsible engineers.
Under certain circumstances such as in cases where the original maintenance planning isaltered because the actual progress of deterioration turned out to differ from that assumed in theoriginal maintenance planning, it is necessary to modify the maintenance manual and takeappropriate maintenance measures accordingly.

13.3 Assessment
13.3.1 GeneralIn the assessment of a structure whose performance has declined or is highly likely
to decline because of ASR, investigation, evaluation of the present state, prediction ofdeterioration and judgment of the necessity for remedial measures shall be appropriately
conducted in accordance with the maintenance planning.

[Commentary] In order to maintain concrete structures appropriately, this specification requires
three types of assessment: initial assessment, periodic assessment and extraordinary assessment.
Because the initial and periodic assessments are essential for the maintenance of structures subject
to ASR, this chapter stipulates that those assessments must be conducted. Extraordinary
assessments are regarded as assessments to be conducted on an as-needed basis and are therefore
not dealt with in this chapter. By conducting periodic assessments during the maintenance period,
defect in appearance of structures can be discovered before they occur or in early stages, andremedial measures including preventive measures and repairs can be taken systematically.

13.3.2 Investigation in assessment
13.3.2.1 General
Investigations in initial, routine and regular assessment of a structure subject to ASR
shall be conducted appropriately according to the category of maintenance required forthe structure. Prior to investigation, check items, methods, frequency and scope ofstandard investigation shall be determined appropriately. For each type of assessment,
detailed investigation shall also be conducted on an as-needed basis.

[Commentary] It is important to select check items, methods, frequency and scope ofinvestigation appropriately according to the purpose of investigation in accordance with themaintenance planning.
Defect due to ASR include cracking, discoloration, bleeding of alkali–silica gel, pop-out,
displacement, deformation and localized surface unevenness. Different investigations focusing on
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these items are conducted to determine whether defect occurring in a structure have been caused by
ASR. In practice, the standard procedure is as follows: on-site visual observation, core sampling,indoor investigations, the evaluation of investigation results, and the prediction of the possibility of
expansion. Items to be checked in an investigation of a structure affected by ASR are the amount ofexpansion of concrete and the resultant cracking and steel corrosion and damage (yielding, cracking,fracture). In the event of severe deterioration, it may be necessary to consider conducting an
investigation in which the performance of the structure such as load-carrying capacity can beevaluated directly.
Check items in investigation varies with the degree of deterioration, but defects in appearance
including cracking due to the expansion of concrete are necessary check items, regardless of thedegree of deterioration. If deterioration is judged or estimated to be at or after the acceleration stage,
an investigation in which steel corrosion and damage can be checked also needs to be conducted.
Table C13.3.1 lists main check items at different stages of deterioration.

Table C13.3.1

Main check items in investigation

Stage of Deterioration

Initiation

Propagation

Acceleration

Deterioration

Change of appearance

O

O

O

O

Reactivity of aggregate

▲

▲

▲

▲

Residual expansion

▲*

▲

O

O

Steel corrosion/damage

▲*

▲*

▲

O

Concrete strength

▲*

▲

O

O

Load bearing capacity

▲*

▲*

▲

O

Environmental action

O

O

O

O

O: Items to be investigated on a priority basis▲: Items that should preferably be investigated▲*: Items to be investigated as required

The frequency and scope of investigation must be determined in view of such factors as thecategory of maintenance required for the structure, environmental conditions, the type of structure
and the state of deterioration. ASR becomes faster at places subject to the influence of insulation,
exposure to rain, deicing agents, etc., and steel corrosion occurs in a humid condition. Although asufficient amount of data on steel damage are not available, steel damage tends to occur in cases
where the amount of expansion is large. Consequently, the rate of deterioration may vary among
different parts of the structure. By identifying such deterioration-prone portions at an early stage,
maintenance at subsequent stages can be performed efficiently.
Regardless of the category of maintenance, it is important to go through the design drawings
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Standard Specifications for Concrete Structures-2007, Maintenanceand specifications, construction records, investigation results and the repair history prior to theinvestigation of a structure.
If the state of a structure cannot be judged appropriately by standard investigation, detailed
investigation must be conducted.

13.3.2.2 Investigation in initial assessment(1) In initial assessment, appropriate check items for standard investigation shall beselected for newly constructed structures, existing structures, large-scale repairs
and strengthened structures.
(2) If deterioration prediction, evaluation or judgment is difficult to make through astandard investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigation in initial assessment is the first investigation conducted whenthe maintenance of a concrete structure is started. Investigation in initial assessment includes not
only the first investigation of a newly constructed structure conducted before it goes into service but
also the first investigation of an existing structure or a structure for which remedial measures havebeen taken in response to deterioration. Check items for the investigation may vary from structure
to structure. Basic check items for standard investigations in initial assessment of a newly
constructed structure are the document search on the design drawings and specifications andconstruction records and observation. It is good practice to check on such details as concrete cover,the state of steel and porosity through nondestructive testing on an as-needed basis. Wheninvestigating a structure for which remedial measures have been taken, it is also important to checkfor problems in repaired or reinforced parts of the structure. These should be included in check
items of standard investigation. When an existing structure is investigated, check items are similar
to those for a newly constructed structure if design drawings and specifications and construction
records exist. If there is no such document or record, it is necessary to select check items ofstandard investigation with reference to Section 13.3.2.5 “Detailed Investigation.” In cases where a
prediction needs to be made with high accuracy about a structure to which maintenance category A(preventive maintenance) is applied, it is necessary to conduct investigations concerning theparameters used for the method described in Section 13.3.3 “Methods for Predicting Degradation of
Performance Degradation of Structures.”Check items that are very important in the initial investigation of a structure subject to ASR
are listed below.
(i)

Source area of aggregate used(ii)

Total alkali content of concrete(iii)State of cracking, discoloration, bleeding of alkali–silica gel, etc.

(iv)

Repair or reinforcement status

Among the items listed above, information on Item (i) can be found on the geological maps ofJapan showing the distribution of reactive stone because the distribution of ASR-causing stone isdependent on geological conditions. It is difficult, however, to judge whether rocks in a particulararea are reactive from the rock type and geologic age information shown on the geological maps
alone. Surveys on the distribution of reactive aggregates in Japan have been conducted by a numberof institutions. If alkali– silica reactivity is suspected, therefore, it is advisable to refer to the results
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Chapter 13

Maintenance of Structures Subject to Alkali-Silica Reactionof these surveys. Concerning Item (ii), it is good practice to check, from the alkali content of theconcrete used and the cement content of the concrete, whether the total alkali content exceeds thelimit value (3 kg/m3) of total alkali content. Item (iii) is necessary for the investigation of an
existing structure in initial assessment. In cases where an investigation of a structure for which
remedial measures have been taken is conducted in initial assessment, Item (iv) should be added tothe check items of normal examinations because it is important to check on defect (e.g., peeling or
detachment of covering materials) of repaired or reinforced parts.
Signs of ASR cannot be detected at the time of final investigation because at least several
years will pass before ASR-induced cracks become visible. If reactive aggregate is used in concrete,
expansion might occur after many years of use even if no sign of deterioration such as cracks isdetected in the initial assessment. Because it is extremely difficult to estimate the amount ofexpansion of concrete used in a real structure, (1) reactivity of aggregate, (2) possibility of
expansion and (3) the actual amount of expansion as a quantitative indicator need to be checked inthat order in subsequent investigations. Although it is not possible at present to predict the progressof deterioration quantitatively even by using the investigation results in initial assessment, it ispossible to evaluate deterioration potential qualitatively.
(2) If evaluation and judgment cannot be made with high accuracy by standard investigation
alone or if a highly deteriorated part of a structure is to be investigated, detailed investigation isnecessary. Check items of detailed investigation are indicated in Section 13.3.2.5 “Detailed
Investigation.”13.3.2.3 Investigation in routine assessment(1) In routine assessment, standard investigation shall be conducted to detect not only
the defect of concrete surface such as cracking, discoloration, bleeding ofalkali–silica gel, rusty water, scaling and spalling, but also appearance deteriorationsuch as displacement, deformation, localized surface unevenness and joint filler
defect, water supply conditions, etc.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) The purpose of investigation in routine assessment is to detect deterioration at
an early stage by checking on defect in the state of a structure over time. The determination of thetime at which deterioration began in order to obtain information that is useful for predicting
deterioration is another important purpose of the investigation in routine assessment. In a routine
assessment, therefore, attention should be paid to deterioration phenomena and signs ofdeterioration, namely, concrete surface defect such as cracking, discoloration, bleeding ofalkali–silica gel, rusty water, scaling and spalling, and other defect such as displacement,
deformation, localized surface unevenness and joint filler defect. In areas where water is suppliedsuch as wet concrete surfaces, deterioration, whether caused by ASR or otherwise, is expected in thenear future. It is desirable, therefore, that water supply conditions be investigated.
ASR-induced cracks are not uniform. Instead, cracks occurring in a structure varyconsiderably depending on the environmental conditions (temperature, humidity, insulation andexposure to rain) and the constraint conditions (the amount and arrangement of steel, presence of
external constraints). In the case of a plain concrete structure or a structure with a small amount ofreinforcing steel, mesh cracks or map cracks occur over the entire structure. If ASR-induced
expansion is constrained by longitudinal reinforcing steel or prestressing tendons, cracks
perpendicular to the constraint are effectively prevented, so directional cracks along the longitudinal197

Standard Specifications for Concrete Structures-2007, Maintenancesteel reinforcement or prestressing tendons often result along with map cracks.
Normal examinations depend mainly on visual investigation. If, therefore, deterioration isdetected, ASR is already at a highly advanced stage, and it is difficult to evaluate or judge astructure at the initiation stage on the basis of investigation results in routine assessment. In the caseof a structure to which maintenance category A is applied, therefore, it is necessary to add check
items as appropriate by, for example, using an appropriate monitoring method.
It is also important to conduct intensive investigations of deterioration-prone areas identified
in the initial assessment.
(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone or if severe deterioration has already occurred, detailed investigation is conducted. Checkitems of detailed investigation are described in detail in Section 13.3.2.5 “Detailed Investigation.”13.3.2.4 Investigation in regular assessment(1) The purpose of investigation in regular assessment is to obtain information that isdifficult to obtain in routine assessment. In regular assessment, standard
investigation consisting of detailed observation of defects shall be conducted as inroutine assessment.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigation in regular assessment is conducted for obtaining the information
more detailed than that in routine assessment. Areas where signs of defects or deterioration havebeen detected in the initial assessment or the routine assessment need to be inspected intensively.
Check items consist mainly of observatory items as in the routine assessment, but check items thatmake it possible to determine changes over time in the width, number and density of cracks bypaying attention to the location and direction of ASR-induced cracks should be added. In the case ofa structure to which maintenance category A is applied, it is necessary to increase check items as
appropriate, such as using an appropriate monitoring method.
Measuring crack propagation and expansion behavior of a structure by installing chips forcontact gauges by which to measure the propagation of cracks in the concrete and displacement
meters by which to measure the deformation of structural members is helpful in maintaining a
structure and deciding on repair and reinforcement measures. In the case of an ASR-affectedstructure, stepped patterns of expansion, in which expansion increases in spring to summer andremains unchanged in autumn to winter, tend to occur because of the temperature dependence ofASR. The amount of expansion in future, therefore, can be estimated by measuring the expansion
behavior of a real structure over a period of one year.
(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone or if severe deterioration has already occurred, detailed investigation is conducted. Checkitems of detailed investigation are described in detail in Section 13.3.2.5 “Detailed Investigation.”

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13.3.2.5 Detailed investigation
Detailed investigation shall be conducted to obtain detailed information on a
structure subject to ASR in cases where the deterioration of the structure is difficult topredict, evaluate or judge by standard investigation alone in initial, routine or regularassessment. Check items, methods and location of a detailed investigation shall beselected appropriately taking into consideration such factors as the purpose ofinvestigation and the accuracy of obtained results.

[Commentary] A detailed investigation is conducted when the determination of the present stateof a structure and the deterioration of the structure are difficult by normal examination results alone
in order to obtain information necessary for those purposes.
A detailed investigation of an ASR-affected structure should cover check items that make itpossible to evaluate the degree of influence of cracking on the steel corrosion, load-carrying
capacity, stiffness, etc., of the structure and the residual expansion concerned with future
performance degradation. A detailed investigation of a structure is conducted to evaluate the degreeof performance degradation due to ASR, make judgments as the necessity of repair or reinforcement
and the scope of repair or reinforcement, and obtain information necessary for selecting repair orreinforcement methods and materials. On-site tests conducted for a structure include themeasurement of crack width and amount of expansion of a real structure and investigations using
core samples. Because the performance degradation of a concrete structure due to ASR is greatly
affected by the environmental conditions, it is necessary not only to investigate the environmental
conditions under the influence of insulation and exposure to rain in detail but also to investigate theinfluence of seawater, deicing agents and deterioration due to the combined effect of freeze–thaw
cycles and chemical attack. Core samples taken from a structure are used, for example, for theprediction of residual expansion, compressive strength testing, alkali–silica gel detection byscanning electron microscope, chemical analysis, concrete texture observation by use of thin
specimens, the evaluation of alkali–silica reactivity of aggregate used, and petrological testing. In
general, ASR-affected concrete is characterized by a considerable decrease in the modulus ofelasticity, compared with compressive strength, indicating that the modulus of elasticity is moresensitive than compressive strength to changes in the dynamic properties of concrete. A method for
estimating the degree of ASR-induced deterioration from this relationship has been proposed. Whena detailed investigation is conducted, the investigation results should be used to re-evaluate
deterioration prediction and the investigation results in regular assessment. If the results differ fromthe initial predictions, it is necessary to reconsider the service and environmental conditions for the
structure that contribute to deterioration, such as the supply of moisture and alkalis, insulation andexposure to rain.
Depending on the circumstances, a structure that has undergone excessive ASR-induced
expansion may have not only defect of the concrete surface such as cracking and alkali–silica gel
bleeding, but also a decrease in the load-carrying capacity due to a decreased in concrete strength or
steel corrosion or damage (yielding, cracking, fracture). It is therefore necessary to investigate thedeformation properties of the structure or its members or steel strains through loading tests or byother means. In areas with localized surface unevennesses or displacements, the state of steel
corrosion and steel damage need to be investigated by appropriate nondestructive testing or bychipping away the cover concrete.
Table C13.3.2 shows investigation check items for a structure subject to ASR and examples of
information obtainable from investigation results concerning the estimated state of the structure at
the time of investigation and in future. The "evaluation item predictable from obtained information"in the table can be evaluated after deterioration prediction is made. The measuring methods formain investigation items are briefly described below. For other details, refer to Section 4.7.3,
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Standard Specifications for Concrete Structures-2007, Maintenance“Investigation Methods”.

Table C13.3.2

Examples of evaluation items in detailed investigation

Measurement item

Data obtained byexaminations

Evaluation items predicablefrom obtained data

Alkali–silica reactivity of aggregate Deterioration rate of ASR

Deterioration rate of ASR

Residual expansion

Deterioration rate of ASR

Deterioration rate of ASR

Crack (width, depth, density)

Deterioration rate of ASR,
appearance

Deterioration rate of ASR,
appearance

Location and state of corrosion ofsteel (area, amount)

Corrosion grade,load-carrying capacity

Corrosion rate, load-carrying
capacity

Steel damage

Load-carrying capacity

Load-carrying capacity

Discoloration, alkali–silica gel
bleeding

Appearance

Concrete strength, modulus ofelasticity

Concrete strength, modulus ofelasticity

Concrete strength, stiffness,
alkali–silica reaction rate

Concrete strength

Displacement, deformation

Stiffness

Load-carrying capacity

Rock type of aggregate (type andcontent of reactive minerals)

Alkali–silica reactivity ofdeterioration rate of ASR

Deterioration rate of ASR

Alkali content of concrete

Deterioration rate of ASR

Deterioration rate of ASR

Temperature, humidity, insulation,
exposure to rain

Deterioration rate of ASR

Deterioration rate of ASR

Influence of seawater and deicing
agentsDeterioration rate of ASR

Deterioration rate of ASR

Density indicators (e.g., ultrasonicwave propagation velocity)

Cracking, strength, stiffness

Note: For the grade of corrosion, refer to Table C10.3.3.

(i) Appearance of structure
If the state of the concrete or steel used in a structure is not directly related to the performance ofthe structure, defect in appearance may provide useful information necessary for performance
evaluation. The appearance grades of structures whose performance has deteriorated because of
ASR are tabulated in Table C13.3.3.

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Table C13.3.3

Maintenance of Structures Subject to Alkali-Silica Reaction

Grades of structural appearance and stage of deterioration

Grade of structural appearanceState of deterioration

I (initiation stage)

ASR-induced expansion and resultant cracking have not yet
occurred, and there is no anomaly in appearance.

II (propagation stage)

Expansion occurs continuously in the presence of moistureand alkalis, cracking occurs, and discoloration andalkali–silica gel bleeding can be seen. There is no rusty water
due to steel corrosion.

III (acceleration stage)

This is the stage at which the rate of expansion due to ASR is
maximized. Cracking occurs and crack with and density
increase. Rusty water due to steel corrosion may be seen.

IV (deterioration stage)

Crack width and density increase further, and localized
surface unevenness, displacement and localized scaling andspalling occur. Steel corrosion continues and rusty water canbe seen. Cracks or steel damage due to environmental
deterioration factors may be seen. Displacement anddeformation increase.

(ii) Alkali–silica reactivity of aggregate
The alkali–silica reactivity of aggregate is tested by the chemical method specified in JIS A 1145
and the mortar-bar method specified in JIS A 1146. These test methods, however, are not suitable
for the evaluation of the alkali–silica reactivity of all types of aggregate, and there are certain typesof aggregate that cannot be evaluated by those methods. Another problem is that evaluation by themortar-bar method takes as long as three to six months. Because of these circumstances, test
methods for obtaining results quickly are used in other countries.
(iii) ASR resistance of concrete
The most reliable method for checking the ASR resistance of concrete is to expose concrete
specimens prepared by using the same mix proportions and other conditions as will be used for areal structure under the same environmental conditions as those under which a real structure will beplaced and check whether cracking occurs. This approach, however, is not realistic. A commonlyused method is to evaluate the ASR resistance of concrete specimens through accelerated curing
tests. An example is a method conforming to JCI AAR-3, Test for Alkali–Silica Reactivity ofConcrete. It has been confirmed experimentally and empirically that a six-month expansion of 0.1%
determined by this method can be used as a threshold for the occurrence of ASR-induced damage.
In cases where alkalis are supplied from an external source, the method of curing concrete
specimens by reproducing the conditions under which alkalis are expected to be supplied to a real
structure and checking the six-month expansion similarly may be used.
(iv) Residual expansion of concrete
A commonly used method of residual expansion measurement by use of core samples is the methodof using a humid air chamber kept at a temperature of 40°C and a relative humidity of 100%
(JCI-DD2). Other methods include a method using a 1M NaOH solution at 80°C (Canadian method,
ASTM C 1260-94) and a method using a saturated NaCl solution at 50°C (Danish method).
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Standard Specifications for Concrete Structures-2007, MaintenanceThreshold values used for accelerated expansion testing are often determined in accordance with thecriteria for the test of the alkali–silica reactivity of aggregate. The threshold values used to judge
residual expansion in accelerated expansion tests on core samples, however, are not based on
accumulated research findings. It should be kept in mind, therefore, that at least at present, therelationship of those threshold values with the future expansion behavior of real structures is notnecessarily clear.

13.3.3 Methods for predicting performance degradation of structures
13.3.3.1 General(1) In the maintenance of a structure subject to ASR the performance of the structure
shall be evaluated quantitatively at the time of investigation, and future degradation
shall be predicted.
(2) In order to predict the performance degradation of a structure, deterioration due to
ASR shall be predicted quantitatively.
(3) If (2) is difficult, an alternative method is to predict performance degradation by
estimating the length of the initiation, propagation, acceleration and deterioration
stages, taking the progress of ASR into consideration.
(4) Deterioration shall be predicted on the basis of investigation results.

[Commentary] (1) and (2) In the performance verification based maintenance system, changes(degradation) in various performance attributes of a structure are to be predicted. In order toestimate the performance of a structure subject to ASR, it is necessary to quantitatively predict thedeterioration of the materials used in the structure. It is also necessary to quantitatively evaluate theperformance of the structure and the degree of deterioration of the materials used in the structure at
the time of investigation and at the end of the planned service period on the basis of investigation
results. The performance of the structure or the degree of deterioration of the constituent materials
at the time of investigation can be evaluated by using an appropriate method on the basis of theinvestigation results. Performance and deterioration at the end of the planned service period are
predicted on the basis of the investigation results in regular assessment by estimating thesubsequent progress of deterioration over time.
Anomalous expansion of concrete due to ASR results from the water-induced expansion of
the alkali–silica gel formed by the chemical reaction of the reactive silica minerals contained in theaggregate with a water solution composed mainly of alkali hydroxides in the concrete. Alkali–silica
gel formed in reactive aggregate absorbs water, and the aggregate expands. The expansion of thereactive aggregate generates internal stress not only to cause in aggregate particles but also todestroy the cement paste around the aggregate particles. With further progress of ASR, microscopic
cracks grow to cause macroscopic cracks to appear at the surface of the structure. ASR-affectedconcrete, therefore, has not only relatively large cracks but also many microscopic cracks in andaround the aggregate particles.
The temperature and humidity of the surface layer of an ASR-affected concrete member differ
from those of the inner concrete. Consequently, a difference in the amount of expansion occurs
between the surface layer and the inner concrete. The stress caused by such differences in theamount of expansion among different parts of the concrete and the restraining effect of reinforcing
steel and the stress caused by differential deformation of different members also cause cracking.

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ASR-induced cracking could cause steel corrosion in the presence of water and oxygen
supplied through cracks. It has also been found that in the event of extreme expansion of concretedue to ASR, part of the reinforcing steel in the concrete may be damaged (yielding, cracking,fracture).
This chapter assumes, therefore, that items to be predicted are the expansion of concrete (andresultant crack propagation), the progress of steel corrosion, and the occurrence of steel damage.
(3) In cases where the deterioration of the concrete and steel used in a structure are predicted,
and various performance attributes of the structure are evaluated by combining the results thus
obtained, it is not easy, at the present level of technology, to make quantitative predictions. A
practical method, therefore, is to estimate the length of the initiation, propagation, acceleration anddeterioration stages by taking the progress of the ASR of concrete into consideration. The
deterioration stages and factors determining their length are listed in Table C13.1.1. As shown in
Fig. C13.1.1 with two types of illustrations, the ASR-induced deterioration process can be modeleddifferently depending on the expansibility of concrete. If the quantity of reactive minerals containedin the aggregate is large and the expansibility of the formed alkali–silica gel is high, the
ASR-induced expansion of concrete may occur over a long period of time so that severe
deterioration results because the large amount of expansion is large. If the quantity of reactive
minerals contained in the aggregate is relatively small, the ASR-induced expansion of concrete may
converge at a certain stage, and further change may not occur even after a sufficiently long periodof time. This means that as far as ASR-induced deterioration is concerned, not all structures reachthe deterioration stage. It is not easy, however, to derive performance degradation curves from suchinformation as the investigation results for the structure. Predicted values of residual expansion due
to ASR will contain large errors. Even if the structure to be maintained is considered to be relatively
free from expansion, therefore, it is necessary to maintain the structure appropriately by, forexample, carefully checking for ASR-induced defect.
(4) The results of investigation of a structure be classified into two types: one concerns thequality of concrete used in the structure and the other concerns the environment in which thestructure is used. As a general rule, deterioration prediction must be based on these investigation
results. For example, in the case of a structure in which the number, length, width, etc., of
ASR-induced cracks have changed very little for a long period of time, ASR-induced expansion
may have largely converged. In that case, the state of deterioration can be expected to remainunchanged for a while as shown in Fig. C13.1.1(b). At the present level of technology, however, it isdifficult to accurately predict changes in various performance attributes of a structure even if
information is available about ASR-induced cracking, etc., through investigation. It is advisable,
therefore, even in cases where deterioration prediction is made on the basis of investigation results,
to evaluate the performance attributes of a structure by appropriately evaluating investigation
results about the reactivity of aggregate, concrete mix proportions and the environmental conditions
under which the structure is used and allowing for an appropriate factor of safety in making
predictions.
If no information is available on the ASR of concrete as in the case of a newly constructedstructure or if investigation results for an existing structure are not available, investigation results
for an adjacent structure or a structure in a similar environment can be used as a guide. It is goodpractice to refer to investigation results for an adjacent structure on an as-needed basis because
there may be similarities to the concrete (especially aggregate) used for an adjacent structure or theenvironment in which the structure is used. For example, if it is known that severe ASR-induced
deterioration has occurred at a structure built with the same type of concrete, care must be taken
because ASR-induced deterioration may occur when certain environmental conditions (e.g., supplyof water) are met even if little or no sign of ASR-induced deterioration has been observed thus far.
203

Standard Specifications for Concrete Structures-2007, Maintenance13.3.3.2 Prediction of ASR-induced expansion of concrete(1) The progress of ASR-induced expansion of concrete used in a structure shall be
predicted in due consideration of the influence of the environmental conditions
under which the structure is used.
(2) The amount of ASR-induced expansion of concrete may be predicted by one ormore of the following methods.
(i) Use of investigation results(ii)Use of accelerated curing test on core samples[Commentary] (1) If the aggregate used is reactive, expansion may occur after a long period ofuse even if no sign of ASR is found at the time of investigation. It is generally known that theprocess of ASR-induced expansion consists of a chemical reaction process in which alkali–silica gel
is formed by chemical reaction and a physical process in which alkali–silica gel absorbs water andexpands. These processes do not occur simultaneously. Instead, the expansion process begins after
chemical reaction progresses sufficiently. It is thought that the rate of progress of the chemical
reaction process is determined mainly by the type and content of reactive minerals, the type andalkali content of cement, and concrete mix proportions. The rate of progress of the physical process
is affected by the environmental conditions (e.g., supply of water, temperature) under which thestructure is used. The rate of progress of ASR-induced expansion of concrete needs to be estimatedby taking these factors into consideration.
(2) Experiment results have shown that the rate of formation of alkali–silica gel in thechemical reaction process and the amount of expansion of concrete are not necessarily related
proportionally. Thus, it is difficult to predict with high accuracy the progress of ASR-induced
expansion of concrete because there are still many unknowns about the rate of progress of the twoprocesses mentioned above. In maintaining a structure that has deteriorated because of ASR,
however, it is necessary to conduct a study on the possibility of concrete expansion by some kind of
method in advance. Current practice is to use one or more of the methods described below in orderto predict the progress of ASR-induced expansion of concrete.
(i) Method based on investigation results
The progress of deformation and cracking of structural members is measured, for example by thecontact gauge method, in advance, and the progress of future cracking of the members is estimatedfrom the measured changes over time. It is therefore necessary to obtain investigation data required
for estimation. The occurrence of ASR-induced expansion and resultant cracking is greatly affectedby the environmental conditions of the structure. Measuring both heavily crack parts and relatively
intact parts of the structure in an investigation is helpful in estimating the expansion behavior of theentire structure. The use of data on the expansion of the real structure makes it possible to estimate
the rate of expansion so as to provide information useful for repair and reinforcement.
It is desirable that investigation results used here be ones obtained over a long period of time.
Studies have shown that the progress of ASR-induced expansion is greatly affected by such factors
as seasonal changes in atmospheric temperature. It is therefore necessary to use investigation results
obtained from investigations conducted over a period of at least one year.
(ii) Method using accelerated curing tests on core samples

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Maintenance of Structures Subject to Alkali-Silica Reaction

The possibility of expansion of concrete is estimated by storing core samples taken from a structure
in an environment conducive to ASR and measuring the amount of expansion in that accelerated
curing environment. A number of accelerated curing test methods have been proposed, and different
accelerate curing environments are used in different test methods. From the experiences with past
projects in Japan, many have concluded that concrete with an expansion as determined byaccelerated curing testing of 0.1% or more might expand in a harmful manner in future to cause
degradation in serviceability and durability. Many have also concluded that concrete with an
expansion as determined by accelerated curing testing of less than 0.05% is unlikely to expand in a
harmful manner in future. Conclusions are divided, however, about concrete with expansions of
0.05 to 0.1%, and it is difficult to evaluate the possibility of expansion.
What is to be kept in mind here is that the amount of expansion obtained by the method using
accelerated curing tests on core samples is a result obtained in an accelerated curing environment
specified by each test method, and that result is not necessarily the same as the actual amount ofexpansion in future in the real-world environment. In other words, what can be done throughaccelerated curing tests is merely to predict the possibility of the structure's moving onto the nextstage of deterioration (in this example the acceleration stage) sometime in future, and predicting thetime of such transition is difficult under the present circumstances. It is also difficult to estimate therate of expansion occurring at a real structure from the results of accelerated curing tests. Careshould be taken, therefore, when trying to predict the amount of ASR-induced expansion of
concrete by this method and decide what to do in connection with repair or reinforcement.

13.3.3.3 Prediction of steel corrosion
The progress of steel corrosion due to ASR shall be predicted properly considering
the influence of ASR-induced defect and the environment in which the structure is inservice.

[Commentary] Deterioration due to ASR may cause cracking and other adverse effects on the
structure due to the expansion of concrete, but ASR-induced deterioration itself does not directly
affect steel corrosion. It has also been reported that the influence of ASR-induced cracks on steel
corrosion is smaller than that of cracks caused by other factors mainly because cracks are filled up
with alkali–silica gel. It has also been reported, however, that in regions prone to chloride attack,severe steel corrosion resulted under the influence of chloride ions that have infiltrated throughcracks. The influence of ASR-induced defect on steel corrosion must be studied, taking into
consideration all relevant factors including the locations and degrees of defect and theenvironmental conditions under which the structure is used.

13.3.3.4 Prediction of steel damage
The occurrence of ASR-induced damage to the reinforcing steel in a structure shallbe predicted in due consideration of the influence of the quality of concrete, reinforcement
patterns, the type and shape of structural members and the environmental conditions
under which the structure is used.

[Commentary] If ASR causes severe deterioration, steel damage (yielding, cracking, fracture)
may result. It is difficult to detect steel damage or estimate the possibility of future steel damage
simply by observing the outside appearance of the structure. It is nevertheless necessary to be very
careful because steel damage is highly likely to affect the load-carrying capacity of the structure.

205

Standard Specifications for Concrete Structures-2007, MaintenanceAccording to damage reports, all reported cases of reinforcing bar fracture occurred at bends
in reinforcing bars. It has been inferred, therefore, that the fractures were caused by fine cracks that
may have occurred in the inner region at a bend in a reinforcing bar formed when reinforcing bars
conforming to a now-defunct standard, which specified material and rib configuration requirementsthat differ from the requirements under the current standard, were bent. In many cases, fracture
occurred in poorly reinforced regions, such as beams of T-shaped piers and the upper surfaces offootings, where reinforcing bars had to span 10 mm or wider cracks along longitudinal
reinforcement.
In a structure that has deteriorated severely because of ASR, therefore, it is good practice toevaluate the possibility of occurrence of steel damage with reference to investigation results for
similar structures, conduct an appropriate nondestructive testing and, if necessary, investigate
possible damage regions by chipping away the cover concrete to expose the reinforcing bars.

13.3.3.5 Modification of prediction
If the state of deterioration determined in an investigation differs from a predictedstate of deterioration, the cause of the difference shall be identified and the prediction shallbe revised accordingly. If necessary, the maintenance planning should be altered.

[Commentary] If the state of deterioration determined in an investigation differs from a predictedstate of deterioration, an appropriate investigation must be conducted with reference to thedeterioration prediction methods described in Section 13.3.3.2, “Prediction of ASR-induced
Expansion of Concrete,” and Section 13.3.3.3, “Prediction of Steel Corrosion,” Section 13.3.3.4,“Prediction of Steel Damage” and Table C13.3.2 in Section 13.3.2.5, “Detailed Investigation,” toidentify the cause of the difference from the prediction and revise the prediction accordingly. The
results of a number of investigations conducted are useful for identifying the cause of the difference
and revising the prediction. It is also important to reconsider such details as the frequency ofinvestigation in view of the revised prediction and alter the maintenance planning if necessary.

13.3.4 Evaluation and judgment(1) The evaluation of performance and judgment as to whether remedial measuresneed to be taken based on the results of the investigation in initial, routine andregular assessment shall be made in accordance with Part 1 and Item (2) andsubsequent items in this section.
(2) The performance of a structure subject to ASR shall be evaluated by appropriately
selecting performance attributes to be evaluated in view of the stage ofdeterioration of the structure.
(3) The evaluation of performance attributes at the time of investigation and at the endof the planned service period of the structure should be made by a quantitative
method.
(4) If Item (3) is difficult to achieve, the evaluation of performance attributes at the timeof investigation and at the end of the planned service period of the structure may
be made by a semi-quantitative grading-based method.
(5) Judgment as to whether remedial measures need to be taken shall be made in viewof the degree of performance degradation due to ASR, the degree of importance of206

Chapter 13

Maintenance of Structures Subject to Alkali-Silica Reaction

the structure, category of maintenance, and the remaining service life.

[Commentary] (1) The evaluation of performance and judgment of necessity for remedial
measures in initial, routine and regular assessment are frequently more or less the same regardlessof the deterioration mechanism. For details, refer to Part 1. The evaluation of performance andjudgment of necessity for remedial measures for structures in which deterioration may have or has
progressed vary according to the deterioration mechanism. When discussing the performancedegradation due to ASR, the descriptions in this chapter should be consulted.
(2) In the case of a structure subject to ASR, performance attributes affected by deteriorationvary depending on the stage of deterioration (initiation stage, propagation stage, acceleration stage
or deterioration stage). Performance attributes to be evaluated, therefore, need to be selected
appropriately for each stage of deterioration.
Basically, evaluation and judgment concerning a structure subject to ASR must be madethrough investigations of cracks in the structure and accelerated curing tests on core samples.
ASR-induced cracks are usually as deep as concrete cover, and few cracks are deeper than thereinforcing steel. It is generally said that if reinforcing bars are arranged appropriately in theconcrete, the influence of ASR on the load-carrying capacity of the concrete structure is small. If
cracks in the concrete exist only in the cover concrete zone, in many cases degradation inserviceability, hazads for third party and appearance causes problems such as cracking-induced steel
corrosion, cracking and discoloration. Recent investigations of structures that had undergone
excessive expansion due to ASR revealed decreases in concrete strength and bond between steel andcover concrete, and damage in bent steel bar regions. In these cases, the load-carrying capacity ofthe structure needs to be evaluated.
(3) The performance of a structure at the time of investigation and at the end of the planned
service period needs to be evaluated quantitatively after the state of deterioration of the constituent
materials of the structure, namely, the concrete protection materials, concrete and steel, is evaluatedquantitatively. For example, in the performance evaluation at the time of investigation, safety andserviceability may be checked by determining load-carrying capacity, the amount of deflection andthe amount of deformation by substituting the dynamic properties obtained from investigation
results in the structural calculation equations. It is also possible to verify appearance by evaluatingcracks, the extent and density of scaling and spalling, etc. By these verification methods, it may bepossible to evaluate performance in a relatively straightforward manner at the time of investigation.
It is difficult, however, to evaluate performance at the end of the planned service period with
sufficient accuracy. A reasonable method, therefore, is to supplement such evaluation by verifying
durability through deterioration prediction based on the rate of progress of ASR with reference, forexample, to the method described in Section 13.3.3, “Method for Predicting Performance
Degradation of Structures”. In this case, not only the accuracy of the performance verification
method used at the time of investigation but also the accuracy of the deterioration prediction
method are important considerations. Prediction methods, therefore, need to be carefully selected,
and it is important to allow for a reasonable factor of safety.
(4) In the performance verification type design system, structural performance should ideallybe evaluated quantitatively. At present, however, there is no established method of quantitative
estimation. As a practical method, the performance of a structure can be evaluatedsemi-quantitatively, with reference to Table C13.3.5, by performing appearance grading inaccordance with Table C13.3.4.
The purpose of grading is to classify the present degree of deterioration of a structuresemi-quantitatively instead of predicting and evaluating the degree of deterioration in future. It isalso possible, however, to predict the performance of a structure at the end of the planned service
207

Standard Specifications for Concrete Structures-2007, Maintenanceperiod in accordance with Table C13.3.4 by estimating the stage of deterioration at the end of theplanned service period on the basis of investigation results such as the rate of crack propagation.
The method of estimating the degree of deterioration at a certain point of time in future by
constructing a deterioration grade model based on a stochastic theory such as a Markov model has
also been proposed.
If detailed maintenance records for a similar structure (type of structure, materials,
construction, environment, state of use) are available and the progress of deterioration thus far of
the structure of interest is similar to that of the similar structure, then the evaluation results for thatstructure provide useful information.

Table C13.3.4 Grades of appearance of structures and typical performance degradation
Grade ofappearance ofstructure

Serviceability

Hazards
for third
party

Aesthetic
appearance andlandscapeI (initiation stage) -

-

-

-

II (propagation
stage)-

Decrease inwatertightness

Degradation inappearance

Decrease in ductility• Cracking

Hazards
for third
party

・Steel corrosion

Steel corrosion

Decrease inload-carrying capacity• Cracking

III (acceleration
stage)IV (deterioration
stage)

Safety・Detailed verification:load-carrying capacity
Simple verification:
decrease in concrete
strength, decrease inbond with steel, steel
damageDisplacement/defor
mation of structure

・ Scaling・ Spalling・ Cracking
・ Discoloration
・ Bleeding ofalkali–silica
gel• Deflection• Relative
displacement• Localized
surface unevenness(5) Because judgment is the act of deciding whether remedial measures need to be taken on thebasis of structural performance evaluation results, there is no difference depending on deterioration
factors. Therefore, refer to Part 1.

208Chapter 13

Maintenance of Structures Subject to Alkali-Silica Reaction

13.4 Remedial Measures
13.4.1 Selection of remedial measures(1) If it has been judged that remedial measures need to be taken in connection withperformance degradation of a structure subject to ASR, remedial measures bywhich the corrected structure meets the required performances shall be selected.
(2) If it is difficult to select remedial measures for a structure on the basis ofperformance verification, remedial measures may be selected from the measurescorresponding to the grade of appearance.

[Commentary] (1) If it has been judged, as a result of evaluation, that remedial measures need tobe taken, it is necessary to select one or more of the following measures: (i) intensified investigation,(ii) repair, (iii) strengthening, (iv) functional improvement, (v) restriction in service or (vi)dismantling/removal. Basically, decisions as to which measures to take should be made by the
maintenance manager of the structure, but it is good practice to refer to Part 1 for information on
typical relationships between evaluation and judgment results and remedial measures.
(2) If it is difficult to select remedial measures for a structure through quantitative evaluation or
judgment, remedial measures are selected from the measures corresponding to the deterioration
grade of the structure. Remedial measures to be taken vary depending on the type of structure, thedegree of importance of the structure, deterioration rate and the category of maintenance, but
recommended standard measures are shown in Table C13.4.1.

Table C13.4.1 Grades of appearance of structure and remedial measures
Grade ofappearanceof structure

Intensified
investigation

RepairI (initiation
stage)O

II(propagation
stage)

Strength-ening**

Functional
improvement

Restriction
in service

O**

X

X

O

OO

X

X

III
(acceleration
stage)

OO

OO

X

X

O

IV
(deterioration
stage)

OO

OO*

X

X

OO

Dismantling/removalOO

OO: Standard remedial measures (OO*: Including the restoration of mechanical performance), O:
Remedial measures in some cases, O**: Preventive measure, X: Remedial measure taken based onother criterion than the grade of appearance.
Strengthening**: Enhancing the mechanical performance above the initiation level209

Standard Specifications for Concrete Structures-2007, Maintenance13.4.2 Repair and strengthening
Methods and materials for the repair or strengthening of a structure shall be selectedtaking into consideration the performance degradation of the structure due to ASR and life
cycle cost, so that the required effect can be achieved.

[Commentary] In cases where repair or strengthening is carried out as a remedial measure, it isnecessary to define the expected effect of repair or strengthening and the required performance(what level of performance to be maintained for how many years?). Ideally, it is desirable that
remedial measures be taken after constructing a deterioration formula (for repair) or structural
calculation formula (for strengthening) in view of such factors as the properties of the materials
used and verifying the calculation results obtained from those formulas. In this case, it is also
important to take life cycle cost into consideration according to the remaining planned service
period.
Repair and reinforcement methods for structures deteriorated by ASR can be classified,according to expected effects, as shown in Table C13.4.2.

Table C13.4.2 Expected effects and methods of repair or strengthening
Expected effect

Examples of methods

Control of progress of
ASR

Water control (cutoff, drainage), crack injection, surface
treatment (covering, impregnation)

Restraining of
ASR-induced expansion

Prestressing, steel/PC/FRP jacketing

Removal of deteriorated
portionCross-sectional restoration

Steel corrosion control

Crack injection, crack filling, surface treatment (covering,
impregnation)

Elimination of third
party impact

Prevention of spalling

Restoration/enhancement Steel plate/FRP sheet bonding, prestressing, overlay,of load-carrying capacity steel/PC/FRP jacketing, external tendon

In order to control the progress of ASR, it is important to control water (cutoff, drainage) sothat water is not supplied to the structure from an outside source. Among the regions involved in
ASR, namely, reactive aggregate, alkalis and water, the regions other than reactive aggregate (i.e.,alkalis and water) exist in the concrete from the beginning, and they are also supplied from theenvironment through, for example, the back side of the structure. It is therefore difficult, even if the
supply of water and alkalis can somehow be cut off, to completely stop the progress of ASR whenwater and alkalis are present in quantities needed to cause ASR in the concrete. It is necessary tokeep this characteristic of ASR in mind.
When deciding on which method to use, it is necessary to take into consideration the present
210Chapter 13

Maintenance of Structures Subject to Alkali-Silica Reaction

state of performance degradation of the structure concerned besides Table C13.4.2. For thecorrespondence between appearance deterioration grades and repair and reinforcement methods,
refer to Table C13.4.3. Many of the repair and reinforcement methods in use today were developed
in recent years, and some of them have not been field-tested extensively. Those methods might failto prevent the recurrence of deterioration or achieve the required performance because of factorsthat could not be expected at the design stage. It is desirable, therefore, that precautionary measures
such as increasing investigation frequency be taken after repair or reinforcement work is done. In
the event of the recurrence of deterioration, repair or reinforcement measures need to be taken again.
In such cases, it is important to carefully investigate the extent, state, cause, etc., of re-deteriorationand select appropriate control measures and materials. For example, when applying theelectrochemical corrosion control method (electrochemical desalination, electrochemical so
notification) to a concrete structure that has been obviously affected by ASR, care needs to be taken
so as not to accelerate ASR.

Table C13.4. 3 Appearance degradation grades of structure and examples of standard
repair/reinforcement methods
Grade of structuralappearance
I (initiation stage)

Expected
expansion-

Water control (cutoff, drainage)*

Small

Water control (cutoff, drainage), crack injection, surface
treatment (covering, impregnation), prevention of
spalling

Large

Water control (cutoff, drainage), crack injection, surface
treatment (covering, impregnation), prevention of
spalling, cross-sectional restoration, prestressing, steel
plate/FRP sheet bonding, overlay, steel/PC/FRP
jacketing, external tendon

Small

Water control (cutoff, drainage), cross-sectional
restoration, surface treatment (covering), prevention of
spalling, prestressing, steel plate/FRP sheet bonding,overlay, steel/PC/FRP jacketing, external tendon

II (propagation stage)
III (acceleration stage)

IV(deterioration stage)

Standard repair/reinforcement method*: Preventive method

For details of various repair and reinforcement methods, refer to, for example, the Report of
the Subcommittee on Alkali–Aggregate Reaction Control (Japan Society of Civil Engineers),
Recommendations for Concrete Repair and Surface Protection of Concrete Structures (Japan
Society of Civil Engineers), Recommendations for Strengthening of Concrete Structures (Japan
Society of Civil Engineers), Report of JCI Committee on Rehabilitation of Concrete Structures(Japan Concrete Institute) and the Guideline for Electrochemical Corrosion Control Methods
Considering ASR (The Society of Materials Science, Japan).
Considerations in selecting repair and reinforcement methods and materials are as follows:211

Standard Specifications for Concrete Structures-2007, Maintenance(i) Progress of ASR and appearance grades
The rate of progress of ASR does not necessarily correspond to the appearance grade of thestructure. As shown in Fig. C13.1.1, if the quantity of reactive minerals contained in the aggregate
is relatively small, the amount of expansion due to ASR may be relatively small so that
deterioration does not progress very much for many years. When making decisions on repair orreinforcement, therefore, it is important to take into consideration both the present rate of progressof ASR and the appearance grade of the structure. The rate of progress of ASR is judged from theresults of regular assessment of the structure or residual expansion results obtained from accelerated
curing tests on core samples. If the appearance grade of the structure is at the propagation stage or
the acceleration stage and a considerable amount of expansion is expected in future, it is necessary
to think of taking measures such as water control (cutoff, drainage), surface treatment (covering,
impregnation), crack injection, prevention of spalling, cross-sectional restoration and measures toprovide restraint against expansion such as prestressing and steel/PC/FRP jacketing.
(ii) Water control (cutoff, drainage)Before selecting repair/reinforcement methods and materials, it is necessary, as a basic
approach, to take water control (cutoff, drainage) measures so that water is not supplied to thestructure from external sources. Because these measures are important in order to control the
progress of ASR, they must be implemented regardless of the appearance grade of the structure. If
there is a deteriorated bridge pier or abutment, possible sources of water such as expansion devices,
drainage pipes, deck slab drainage pipes, etc., are investigated. If water from such sources has beenfound, water control measures, such as making expansion joints non-draining and drainage end
treatment (drainage treatment) measures for drains and drain pipes, must be implemented in a
reliable manner. It is also necessary to take such precautionary measures as sloping and draining the
top faces of piers and abutments to prevent water from collecting there. In regions where deicing
agents are used, these measures are particularly important in order to prevent deterioration due tothe combined effects of water and other deterioration factors such as freeze–thaw cycles or chloride
attack. If drains in structural parts or members such as abutments or retaining walls that are under
the influence of backside water are clogged, the drainage holes must be cleared, and additional
drainage holes must be installed on an as-needed basis.
(iii) Repairs related to hazards for third party or appearance
Structures whose performance has been degraded by ASR are prone to not only cracking but also
bleeding of alkali–silica gel. If alkali–silica gel is polluted by vehicle exhaust gases, surface
discoloration may also occur to ASR-affected structures. Repairs may be carried out, therefore, forreasons related to the appearance of concrete structures. Repairs may also be carried out in view ofimpacts on third parties such as scaling or spalling of concrete.
(iv) Performance of surface lining materials
Performance attributes required of surface lining materials used for structures deteriorated by ASR
include crack bridging ability, impermeability, water vapor permeability, weather resistance, alkali
resistance, bondability with concrete, carbon dioxide impermeability, oxygen impermeability,
freeze–thaw resistance and chloride impermeability. Among these, crack bridging ability, water
impermeability and water vapor impermeability are particularly important. Since, however,deterioration due to the combined effects of deterioration factors related to other attributes such as
freeze–thaw cycles and chloride attack may result depending on the environmental conditions
surrounding the ASR-affected structure, it is also necessary to carefully consider other performance
attributes.

212

Chapter 13

Maintenance of Structures Subject to Alkali-Silica Reaction(v) Surface lining materials expected to contribute mainly to water impermeability
In the case of a structure whose performance has been degraded by ASR, ASR-induced expansion
can be controlled by preventing the intrusion of water from external sources or by adjusting thewater content of concrete by dissipating water from internal sources. Surface lining materials
expected to contribute mainly to water impermeability are effective in controlling ASR if theconcrete is in a dry state or if water intrusion from an outside source is expected. In this case, it isnecessary to completely cover the structural members. If the water content of the concrete is high or
the members cannot be covered completely, the use of surface lining materials might not only fail toachieve the expected repair effect but also cause water to be confined and accumulated in the
structure. It is therefore necessary to carefully study the state of the structure such as the presence ofbackside water and, if necessary, install drainage holes. If it is difficult to judge whether the surface
treatment method using surface lining materials is appropriate, it is good practice to make combined
use of the surface treatment method using a silane impregnation agent mentioned in Item (iv) andthe crack injection method and observe the state of the structure after the surface treatment
measures are taken.
(vi) Silane surface impregnant agents expected to contribute mainly to water repellency
This method is a very effective ASR control method if the environmental conditions are such thatwater intrusion can be prevented and water in the concrete can be dissipated. Water intrusion
through cracks is prevented by means of crack injection or crack filling. It is important to use asurface lining material that does not hamper water dissipation to cover the surface impregnant
material.
(vii) Lithium nitrite or other surface impregnant agents
ASR can be controlled by impregnating concrete with lithium ions in a quantity corresponding to
the quantity of alkali metal ions in the concrete. When applying this method, it is necessary to study
details such as the quantity of lithium ions to be used for impregnation, the depth and extent ofimpregnation and impregnation methods. After impregnation, it is necessary to cover the surface toprevent lithium ions and nitrite ions from being washed out by rainwater, etc. It is necessary to pay
careful attention to the outflow of nitrite ions during construction work as well as before and afterit.
(viii) Repair and reinforcement to achieve safety and serviceability goals
It has been generally believed that ASR-induced cracks in a structure do not affect the load-carrying
capacity of the structure. There are cases, however, in which repair or reinforcement was carried out
for a structure in which excessive expansion occurred because of ASR. Also, in cases where
expansion occurs over a long period of time and excessive expansion of concrete occurs during that
period, large tensile forces act on the reinforcing bars used to restrain the concrete against
expansion. Consequently, in a structure always under the influence of water and with a low steel
ratio, reinforcing steel damage (yielding, cracking, breaking) may occur in the bent-bar zones.
Repair or reinforcement is necessary in these cases, too.
In cases where measures are taken to enhance the mechanical performance of an existing
structure, usually large-scale construction work needs to be carried out because scaffolding andheavy construction equipment are used. It is possible, therefore, to conduct a detailed investigation
during that construction period and decide on and carry out large-scale repair or reinforcement
against ASR on the basis of the investigation results. Even if the purpose is to enhance mechanicalperformance, repair or reinforcement must be carried out, taking into consideration not only themechanical performance but also ASR-induced deterioration, so that the required performances can
213

Standard Specifications for Concrete Structures-2007, Maintenancebe met throughout the specified service period. For example, in cases where steel jacketing iscarried out for the purpose of seismic strengthening, the water impermeability of the steel plates
enhances the effectiveness of steel jacketing as an ASR control method.

13.5 Recording(1) Investigation, deterioration estimation, evaluation and judgment, and remedial
measures shall be recorded in accordance with Part 1.
(2) Items relevant to ASR shall be recorded.

[Commentary] As a general rule, the results of investigations, deterioration estimations,evaluations and remedial measures must be recorded in accordance with Part 1. Items relevant to
ASR require careful attention, particularly with respect to record keeping. Items to be recorded are
indicated in Section 13.3.2 “Investigation in Assessment" and the evaluation items indicated in
Section 13.3.4 “Evaluation and Judgment.”214

Chapter14

Maintenance of Reinforced Concrete Slabs Subject to Fatigue

CHAPTER 14 MAINTENANCE OF REINFORCED CONCRETESLABS SUBJECT TO FATIGUE

14.1 General(1) This chapter provides standard methods for maintenance planning, assessment,
remedial measures and recording for reinforced concrete slabs whose performance has
deteriorated or is likely to deteriorate because of fatigue. The items common to all
deterioration mechanisms are shown in Part 1.
(2) This chapter shall be applied to structures of the maintenance category A(preventive maintenance) and B (corrective maintenance).

[Commentary] (1) Reinforced concrete slabs for road bridges (hereafter referred to as "slabs") arethin for their span lengths (girder spacings). Because slabs are members that directly support wheelloads, they are representative structures whose performance is degraded by fatigue caused by cyclicloading.
Because bending moment is a governing factor in the design of slabs, inspection is made by
the allowable stress method based on the elastic thin plate bending theory, and it has generally been
believed that slabs are sufficiently safe against cyclic loads. Cracking of the underside of the slab
and spalling of concrete, however, began to be seen in the first half of the 1970s, and in some cases
concrete slabs caved in even though the reinforcing bars were in a sound condition. Studies haveshown that the main cause of slab fatigue was the passing of overloaded vehicles. It has also beenshown, however, that deterioration is accelerated by the combined effect of a number of factors,
such as the infiltration of rainwater into the slabs because of the lack of waterproof layers and thenonconformity of existing structures to the current design standard (e.g., thin slab thickness, large
span length) until the slabs fail in punching shear. Today, various types of slabs that are highly
durable against fatigue are already in use. Since, however, the fatigue resistance of slabs has
improved, it is now possible that fatigue-induced deterioration occurs in steel materials and joints
with girders instead of in concrete. In order to prevent fatigue-induced deterioration in these parts ofstructures, therefore, structural details and joints that are highly durable against fatigue have been
put to practical use. When managing slabs, it is necessary to pay attention to these vulnerable partsof structures.
On the basis of examples of slabs severely deteriorated because of fatigue and the results ofstudies on the causes of such deterioration, the process of fatigue-induced deterioration of slabs canbe divided into the initiation stage, propagation stage, acceleration stage and the deterioration stage
as shown in Fig. C14.1.1 and Table C14.1.1. The performance of a structure is affected differently
at different stage of deterioration, and the degree of performance degradation due to deterioration
also varies among different deterioration stages. Methods, therefore, for assessment (investigation,
deterioration prediction, evaluation and judgment), remedial measures and recording varies among
different deterioration stages.

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Performancedegradation of slab

Deterioration due
to fatigue

Standard Specifications for Concrete Structures-2007, MaintenanceCave-in ofslab

Occurrenceof flexural
cracking

Initiation
stage

Bidirectional
propagationof crack

Propagation
stage

Opening/closingofcracks,etc.

Acceleration
stage

Crack
penetrationand sever waterleakage
Deterioration
stage

Fatiguecharacteristics
of slabFig. C14.1.1 Conceptual view of deterioration progress due to fatigue of concrete slab

Table C14.1.1 Definitions of deterioration stages
Stage ofdeterioration

Initiation stage(state I)

Propagation stage(state II)

Acceleration stage(state III)

Deterioration
stage(state IV)

Definition
Several unidirectional cracks along the main
reinforcement due to drying shrinkage and loading canbe seen. Depending on the girder restraint conditions,cracks perpendicular to the bridge axis may develop
because of drying shrinkage or changes in girder
temperature.
Flexural cracks along the main reinforcement grow,and at the same time cracks along the distribution
reinforcement begin to grow and map cracking occurs.
Crack density visibly increases considerably, but thecontinuity of the reinforced slab (tow way plate) has not
yet been lost.

Factor determining thestage
Applied design standards:
slab thickness,amount of
distribution reinforcement,slab span length
Construction:
drying shrinkage
Service conditions:traffic volume, vehicle
weight(axleload),
vehicle location

Interconnection of cracks into fine networks increases,
and opening/closing of cracks and crack surfaces begin
to rub one another. After cracks form slits and corners
fall, the resistance of the concrete cross section is nolonger dependable. Consequently, the punching shear
capacity of the concrete slab begins to decrease.

In addition to the factors
mentioned above:
Environmental conditions:influence of seepage water
Remedial measures taken:
bridge deck waterproof
membrane;repair/strengthening

The occurrence of penetrating cracks in the crosssection of the slab causes the continuity of the slab to belost, and the resultant beam-like members separated by
the penetrating cracks have to resist wheel loads. The
ultimate strength of the member is affected by suchfactors as penetrating crack spacing, concrete strength

All factors
above

216

mentioned

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Maintenance of Reinforced Concrete Slabs Subject to Fatigue

and the amount of reinforcement steel.

(2) The performance of the slabs of an existing bridge varies mainly with the environment inwhich the structure is placed (e.g., load history, rainfall and snowfall) and the design standards
applied. In cases where a bridge has no bridge deck waterproof membrane, the effects of fatigue areunavoidable, so maintenance category B is applied to many slabs. If waterproofed slabs are properly
constructed, performance degradation due to fatigue is not likely to become a problem for about 50
years. Maintenance category A can also be applied if traffic loads (axle loads), vehicle locations on
the bridge, cracks, etc., can be monitored. This chapter, therefore, applies to structures in themaintenance category A and B.
Matters to consider when deciding on the maintenance category for a slab that has deteriorated
or is likely to be deteriorated because of fatigue are described in 14.2.2 “Determination of
Maintenance Category.” Important considerations for different types of maintenance are also
described in this chapter.

Possibility offatigue(14.2)(14.3)

Maintenanceplan for the
structure

Assessment(14.3.2.2)
Investigations ininitial assessment
Standard
investigation(14.3.2.5)
Detailed
investigation(14.4)(14.3.3)(14.3.4)

Deterioration
prediction

Remedial
measures(14.5)
Recording

Evaluation andjudgment(14.3.2.3, 4)
Investigations inroutine/regularassessment
Standard
investigation(14.3.3)(14.3.4)(14.3.2.5)
Detailed
investigation

Deterioration
prediction
Evaluation andjudgment

Fig. C14.1.2 Standard maintenance procedure of reinforced concrete slabs under fatigue stress217

Standard Specifications for Concrete Structures-2007, Maintenance14.2 Maintenance Planning
14.2.1 Basis of planning
In order to maintain reinforced concrete slabs under fatigue stress, the maintenancecategory shall be selected, the service period planned, and a maintenance planning foractivities including assessment, remedial measures and recording drawn up in advance inview of the service conditions such as the magnitude and frequency of live loads and theenvironmental conditions such as the supply of rainwater.

［Commentary］When drawing up a maintenance planning for reinforced concrete slabs under
fatigue stress, it is necessary to cover such details as check items and procedures for the initialassessment and check items, procedures, timing and frequency for routine and regular assessment,
evaluation and judgment methods, actions to be taken in the event of deterioration, and recording
methods, taking into consideration the service conditions such as the type of structure, applicablestandards, degree of importance, planned service period, maintenance category, large vehicle traffic
volume and vehicle locations, the environmental conditions such as the supply of rainwater to theupper surface of the slab, and other factors such as the quality of materials and the existence ornonexistence of a bridge deck waterproof membrane.
It is usually difficult, at the stage of maintenance planning, to accurately predict the state of astructure during its service period. It is therefore good practice to draw up a maintenance planningwith reference to the deterioration of a similar structure or a structure in a similar environment.

14.2.2 Determination of maintenance category
The maintenance category of reinforced concrete slabs under fatigue stress shall beselected in view of the degree of importance of the structure, the type of structure,
hazards for third party, the planned service period and the characteristics of deterioration
due to fatigue.

[Commentary] The determination of the maintenance category is very important because
maintenance planning vary widely depending on the maintenance category. The progress ofdeterioration and performance degradation of reinforced concrete slabs due to fatigue isconceptually illustrated in Fig. C14.1.1.
In order to apply maintenance category A (preventive maintenance), it is necessary to perform
maintenance at the initiation stage, in which map cracking has not yet occurred, in order to preventthe performance degradation of the structure due to fatigue. This makes it necessary to investigate
the state of the structure as accurately as possible and carry out the following:(i) Quantitative evaluation and prediction of the axle weight of passing vehicles, total weight,
the number of loading cycles, vehicle location, etc.

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Maintenance of Reinforced Concrete Slabs Subject to Fatigue(ii) Determination of the influence of water such as rainwater
If maintenance category A is applied, in many cases large-scale repair and reinforcement can
be avoided so that the maintenance cost can be kept low.
If maintenance category B (corrective maintenance) is applied, it is necessary to conduct
investigation relying mainly on visual observation periodically in order to check on the progress ofdeterioration from the state of cracking at the underside of the slab. To be more specific, some kindof action is taken after the following types of deterioration are found:(i) Initiation of map cracking at the underside of the slab(ii) Initiation of opening/closing of cracks and rubbing between crack surfaces(iii) Penetrating cracks in the slab cross section and occurrence of water leaks or free lime
Even when maintenance category B (corrective maintenance) is applied, it is desirable that
repair be carried out at Stage (i). It should be kept in mind that if deterioration reaches Stage (ii) or(iii), large-scale remedial measures need to be taken.

14.2.3 Preparation of maintenance manuals
A maintenance manual describing methods, procedures and frequency requirements
should be prepared for each structure in accordance with the maintenance planning,taking the structure-specific conditions into consideration.

[Commentary] The service period of civil engineering structures is long, and maintenance of
those structures is performed over a long period of time. It is recommended, therefore, that in order
to inform investigators of maintenance concepts and policies, a maintenance manual be prepared sothat detailed procedures and methods can be communicated accurately even to newly assigned
maintenance engineers.
Under certain circumstances such as in cases where the original maintenance planning isaltered because the actual progress of deterioration turned out to differ from that assumed in theoriginal maintenance planning, it is necessary to modify the maintenance manual and takeappropriate maintenance measures accordingly.
Manuals such as “Maintenance Manual for Reinforced Concrete Slabs under Fatigue StressConforming to Standard Specifications for Concrete Structures: Maintenance” can be used as areference when preparing a maintenance manual.

14.3 Assessment
14.3.1 GeneralIn the assessment of a reinforced concrete slab whose performance has declined or
is highly likely to decline because of fatigue, investigation, evaluation of the present state,deterioration prediction and judgment of necessity for remedial measures shall beappropriately conducted in accordance with the maintenance planning.

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Standard Specifications for Concrete Structures-2007, Maintenance[Commentary] In order to maintain concrete structures appropriately, this specification requires
three types of assessment: initial assessment, regular assessment and extraordinary assessment.
Because the initial and periodic assessments are essential for the maintenance of reinforced concreteslabs under fatigue stress, this chapter stipulates that those assessments must be conducted.
Extraordinary assessments are regarded as assessments to be conducted on an as-needed basis andare therefore not dealt with in this chapter. By conducting periodic assessments during themaintenance period, defects in appearance of structures can be discovered before they occur or inearly stages, and remedial measures including preventive measures and repairs can be taken
systematically.

14.3.2 Investigation in assessment
14.3.2.1 General
Investigations in initial, routine and regular assessment of a reinforced concrete slab
under fatigue stress shall be conducted appropriately according to the maintenancecategory required for the structure. Prior to investigation, check items, methods,
frequency and scope of standard investigation shall be determined appropriately. For
each type of assessment, detailed investigation shall also be conducted on an as-neededbasis.

[Commentary] It is important to select check items, methods, frequency and scope ofinvestigation appropriately according to the purpose of investigation in accordance with themaintenance planning.
Defects peculiar to the fatigue of slabs include the map cracking of the underside of theconcrete slab and map crack densification. If defects of these types have been found, the slab has
been deteriorated because of fatigue. Check items and checking methods in investigation of a slab,
therefore, consist mainly of a visual observation of defects in appearance. Table C14.3.1 lists main
check items at each stage of fatigue-induced deterioration of slabs. If evaluation or judgment basedon defects in appearance or the road surface condition is difficult, it is necessary to conduct
investigation for items such as crack behavior, cross-sectional quantities, load-carrying capacities
and traffic characteristics. Table C14.3.2 lists main investigation methods for different check items.
Investigation concerning the service conditions and environmental conditions that affect thefatigue of slabs are also important. For example, the degree of fatigue increases as the number ofpassing large vehicles increases. Even among identical structures, if large vehicles are allowed topass, through lanes are more prone to fatigue than passing lanes. If the slab concrete surface is in a
wet condition as in rainy regions, fatigue is accelerated. In areas under the influence of seawatersuch as coastal areas or in cold regions where deicing agents are applied to roads on a daily basis in
winter, it is necessary to take into consideration not only fatigue-induced deterioration but also
deterioration due to chloride attack.

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Table C14.3.1 Main check items in investigation
Stage of
Deterioration

Defects inappearanceRoad
surface
defects

Crackbehavior

Initiation
stage
Propagation
stage
Acceleration
stage
Deterioration
stage

O

▲

▲

▲*

▲*

▲*

▲

O

▲*

▲

▲*

▲*

▲*

▲

O

▲*

▲*

▲*

▲*

▲*

▲*

O

O

O

▲*

▲*

▲*

▲*

Cross-sectional Load-carrying
Traffic
Monitoring
quantities
capacity
characteristics

O:priority check item,▲:item preferably to be checked,▲*:item to be checked on an as-needed basis

Table C14.3.2 Investigation methods of reinforced concrete slab
Investigation item

Investigation Method

State of crack (direction, density, width, corner
falls), water leakage, free lime, discolorationof concrete

Visual observation, simple
measurement, photography

Abnormal soundSounding

Road surface
defects

Crack, cave-in

Visual observation, photography

Crack behavior

Depth, opening/closing, surface unevenness

Contact gauge, etc.

Concrete strength

Test hammer, core test

Rebar arrangement

Electromagnetic radar method,
ultrasonic radar method, etc.

Slab thickness

Ultrasonic method, etc.

Load-carrying
capacity

Deflection

Loading test

Traffic
characteristics

Traffic volume, large vehicle percentage,lane-by-lane traffic volume percentages, type of
vehicle, axle load

Traffic volume survey, load
measurement

Defects inappearance

Cross-sectional
quantities

14.3.2.2 Investigation in initial assessment(1) In initial assessment, appropriate check items for standard investigation shall beselected for newly constructed structures, existing structures, large-scale repairs andstrengthened structures.
(2) If deterioration prediction, evaluation or judgment is difficult to make through astandard investigation alone, a detailed investigation shall be conducted.

[Commentary] (1) Investigation in initial assessment is the first investigation conducted when themaintenance of a concrete structure is started. Investigation in initial assessment includes not only
the first investigation of a newly constructed structure conducted before it goes into service but also
the first investigation of an existing structure or a structure for which remedial measures have beentaken in response to deterioration. Investigation items may vary from structure to structure.
In the case of a newly constructed slab, it is necessary to record, as part of investigation results,
not only records on the quality of materials and construction such as the quality of concrete, slab
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Standard Specifications for Concrete Structures-2007, Maintenancethickness and concrete cover but also records on initial defects such as drying shrinkage anddefective construction joints and remedial measures taken in connection with those initial defects.
In the case of an existing slab or a slab for which remedial measures have been taken, records on
quality control and investigation at the construction stage may not exist, and the load history to date
may not be clear, either. For these types of slabs, therefore, the investigation conducted after
fatigue-induced deterioration is discovered is usually regarded as the investigation in initialassessment. In such cases, standard investigation items need to be determined with reference to
14.3.2.5 “Detailed Investigation.”(2) If evaluation and judgment cannot be made with high accuracy by standard investigation
alone or if a highly deteriorated part of a structure needs to be investigated, a detailed investigationis necessary. Check items of a detailed investigation are indicated in 14.3.2.5 “Detailed
Investigation.”

14.3.2.3 Investigation in routine assessment(1) In routine assessment, standard investigation designed basically to check on
concrete surface defects such as cracking, peeling and spalling, rust stain, free lime anddiscoloration and appearance deterioration such as water leakage, and displacement anddeformation shall be conducted.
(2) If deterioration prediction, evaluation or judgment is difficult to make by standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) The purpose of investigation in routine assessment is to detect deterioration at
an early stage by checking on defects in the state of a structure over time and, if necessary, takeremedial measures while the deterioration is still a minor problem. The determination of details
such as the time and place of occurrence also yield information that may be helpful in predicting
future deterioration.
Because slabs are always under harsh service conditions, it is necessary to check on changes inthe state of slabs on a daily basis and detect the progress of deterioration at the earliest possible
stage. Investigation in routine assessment of a slab consists mainly of the investigation of the stateof the underside of the slab such as the state of cracks, spalling of concrete, water leaks and freelime.
The purpose of investigation in routine assessment conducted by the manager of slabs is not
only to check on the occurrence or signs of occurrence of performance degradation but also tocheck on serviceability and hazards for third party such as safety of passing vehicles and spalling of
concrete. If maintenance category A is applied, monitoring shown in Table C14.3.3 may be
conducted as part of investigation in routine assessment.
(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone or if severe deterioration has occurred, detailed investigation is conducted. Check items ofdetailed investigation are described in detail in 14.3.2.5 “Detailed Investigation.”

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14.3.2.4 Investigation in regular assessment(1) The purpose of investigation in regular assessment is to obtain information that isdifficult to obtain in routine assessment. In regular assessment, standard investigationconsisting of detailed observation of defects in appearance such as cracks shall be
conducted as in routine assessment.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) and (2) The purpose of investigation in regular assessment, which is
conducted once in one to several years, is to obtain information that is difficult to obtain in a routine
assessment. In regular assessment, areas where the progress of deterioration has been identified inroutine assessment are investigated in greater detail.
In the investigation in regular assessment of a slab, standard investigation of the slab are
conducted at close range to observe the state of the underside of the slab, measure crack density andcrack width, check for corner falls, check on crack behavior such as crack opening/closing anddisplacement, and evaluate the quality of concrete by the sounding method. Regular assessment
intervals are determined by the maintenance manager in view of the service conditions andenvironmental conditions. It is difficult to quantify the state of deterioration by simple investigation
methods such as visual observation and sounding. After fatigue-induced deterioration has been
detected, therefore, it is good practice to monitor not only the density (direction), width andbehavior of cracks, deflection, etc., but also traffic characteristics such as traffic volume and vehicleloads by using such devices as traffic flow monitoring cameras and axle load measurement systems
in order to monitor the progress of deterioration and take preventive measures accordingly.
Examples of traffic characteristics monitoring are shown in Table C14.3.3.

Table C14.3.3 Examples of monitoring items and methods for traffic characteristics
Monitoring item related to trafficcharacteristics

MethodTraffic volume survey
Traffic volume, large vehicle percentage, Traffic volume survey, records by use of
traffic flow monitoring system, etc.
lane-by-lane traffic volume percentage,
vehicle type surveys, etc.
Axle load measurement, back analysis ofdeflection measurement results, etc.

Vehicle load survey(2) If high-accuracy evaluation or judgment is difficult even after the standard investigation or
if deterioration is severe, detailed investigation is conducted. Detailed investigation is described indetail in 14.3.2.5 “Detailed Investigation.”

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Standard Specifications for Concrete Structures-2007, Maintenance14.3.2.5 Detailed investigation
Detailed investigation shall be conducted to obtain detailed information on a structure
in cases where the deterioration of a reinforced concrete slab deteriorated because of
fatigue is difficult to predict, evaluate or judge by standard investigation alone conducted
as part of the initial, routine or regular assessment. Check items, methods and location ofdetailed investigation shall be selected appropriately taking into consideration suchfactors as the purpose of investigation and the accuracy of obtained results.

[Commentary] Detailed investigation is conducted when the determination of the present state ofa structure and the deterioration of the structure are difficult by standard investigation results alone
or when anomalous deterioration of a slab has occurred in order to obtain information necessary for
purposes such as detailed evaluation of the degree of deterioration, studies on the cause ofdeterioration, and studies on subsequent progress of deterioration and repair or reinforcement
methods to be used.
Main check items and investigation methods for detailed investigation and items that can beevaluated through that investigation are shown in Table C14.3.4.

Table C14.3.4 Examples of evaluation items in detailed investigation
Investigation item

Items related todisplacement

Items related tomaterials

Items related totraffic
characteristics

Investigation Method

Evaluation item

Deflection

Loading test

Degree ofdeterioration

Crack behavior

Loading test

Degree ofdeterioration

Crack depth

Ultrasonic method, core sampling

Degree ofdeterioration

Concretestrength

Test hammer, core strength test

Prediction ofprogress ofdeterioration

Concrete
quality

Laboratory test on core samples

Prediction ofprogress ofdeterioration

Concrete crosssectionCore sampling, etc.

Prediction ofprogress ofdeterioration

State of rebar
arrangement

Electromagnetic radar method,
ultrasonic method, chipping survey

Prediction ofprogress ofdeterioration

State of load

Traffic volume survey, vehicle weight(axle load) measurement, etc.

Prediction ofprogress ofdeterioration

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14.3.3 Methods for predicting performance degradation of structures
14.3.3.1 General(1) In the maintenance of a reinforced concrete slab under fatigue stress, theperformance degradation of the slab shall be evaluated quantitatively at the time ofinvestigation, and future degradation shall be predicted.
(2) In order to predict the performance degradation of a reinforced concrete slab, it isnecessary to predict deterioration due to fatigue quantitatively.
(3) If (2) is difficult, an alternative method is to predict performance degradation by
predicting the length of the initiation, propagation, acceleration and deterioration stages,
taking into consideration the progress of cracking at the underside of the slab.
(4) As a general rule, deterioration shall be predicted on the basis of investigation
results.

[Commentary] (1) and (2) In the performance-verification type maintenance method, changes(deterioration) in various performance of a structure are to be predicted. To do that, it is necessary to
predict the progress of deterioration of the materials constituting the slab, especially the cracking of
concrete, quantitatively. It is also necessary to quantitatively evaluate the performance of the slab
and the degree of deterioration of the materials constituting the slab at the time of investigation andat the end of the planned service period on the basis of investigation results. The performancedegradation of the structure or the degree of deterioration of the constituent materials at the time ofinvestigation can be evaluated by using an appropriate method on the basis of the investigation
results. Performance and the degree of deterioration at the end of the planned service period are
predicted on the basis of the regular investigation results by predicting the subsequent progress ofdeterioration over time.
An example of a method for quantitatively predicting the progress of deterioration of a slab
under fatigue stress is to use the S–N relation derived from a punching shear fatigue test using awheel tracking machine. If the structural conditions of the structure under consideration and theload conditions can be reproduced accurately from the investigation results, quantitative fatigue
prediction can be made by using the S–N relation. The actual rate of progress of slab fatigue,
however, is affected by many conditions such as design and construction conditions including slab
thickness, concrete strength and the amount of distribution steel, service conditions including
passing traffic volume, axle loads of large vehicles and vehicle locations and environmental
conditions including the supply of rainwater to the upper surface of the slab. It is not easy toidentify these conditions. In winter, attention needs to be paid to the progress of steel corrosion, too,because deicing agents may be used. When trying to predict the progress of fatigue of a slab, it isnecessary to take into consideration the factors affecting deterioration mentioned above and allow
for an appropriate factor of safety.
(3) and (4) In order to predict fatigue-induced deterioration of a slab, it is necessary to identify
the environmental conditions, such as cross-sectional performance, axle loads of passing large
vehicles, vehicle locations and water, for each structure. Since, however, these conditions are
difficult to determine by the prediction methods in use today, predictions are inherently uncertain.
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Standard Specifications for Concrete Structures-2007, Maintenance

Deterioration may be predicted semiquantitatively, therefore, from the visually observed state of theunderside of the slab and factors affecting the progress of deterioration. As shown in Fig. C14.3.1,
fatigue-induced cracks at the underside of the slab can be classified, according to the stage ofdeterioration, into the initiation stage, at which unidirectional flexural cracks occur at the undersideof the slab, the propagation stage, at which cracks become bidirectional, the acceleration stage, atwhich cracks begin to open and close, and the deterioration stage, at which penetrating cracks andconsiderable water leaks occur, and the punching shear resistance of the slab decreases. At thedeterioration stage, bleeding of white powdery substance may be seen at the pavement surface as aprecursor of falling of blocks. Also, the deterioration of the cover concrete along the upper surfaceof the slab may result in the occurrence of pot holes at the pavement surface. These stages of slab
deterioration and factors determining their duration of each stage are summarized in Table C14.1.1.
It is relatively easy to identify the stage of deterioration of a slab by observing the state ofcracking at the underside of the slab with reference to the descriptions shown above. Since, however,crack density may not increase beyond a certain limit, it is risky to try to determine the duration of astage of deterioration according to the amount of cracking alone. In this case, it is necessary toobserve the width and depth of cracks, crack behavior such as the amount of crack opening, closing
and faulting, water leaks, bleeding of free lime, road surface defects, etc.

State I
状態Ⅰ（潜伏期）(initiation stage)
一方向ひび割れUnidirectional
cracking

State II
状態Ⅱ（進展期）(propagation stage)
二方向ひび割れBidirectional
cracking

State III
状態Ⅲ（加速期）(acceleration stage)
ひび割れの網細化
Densificationofと角落ち
cracks andcornerfalls

State IV状態Ⅳ（劣化期）(deterioration stage)
床版の陥没
Cave-inof slabFig. C14.3.1 Progress of cracking at underside of reinforced concrete slab

14.3.3.2 Modification of prediction
If the state of deterioration determined in investigation differs from a predicted stateof deterioration, the cause of the difference shall be identified and the prediction shall berevised accordingly. If necessary, the maintenance planning shall be altered.

[Commentary] When the deterioration confirmed in investigation is different from theprediction, appropriate investigation should be conducted with reference to the deterioration
prediction methods described in 14.3.3.1 “General,” and the explanation table in 14.3.2.5 “Detailed
Investigation,” to identify the cause of the difference from the prediction and revise the prediction
accordingly. It is also important to reconsider such details as the frequency of investigation in view
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14.3.4 Evaluation and judgment(1) The evaluation of performance and judgment as to whether remedial measuresneed to be taken based on the results of the investigation in initial, routine and regularassessment shall be made in accordance with Part 1 and Item (2) and subsequent items inthis section.
(2) The performance of a reinforced concrete slab under fatigue stress shall be
evaluated by appropriately selecting performance to be evaluated in view of the stage ofdeterioration of the reinforced concrete slab.
(3) The evaluation of performance at the time of investigation and at the end of theplanned service period of the reinforced concrete slab should be made by a quantitative
method.
(4) If Item (3) is difficult to achieve, the evaluation of performance at the time ofinvestigation and at the end of the planned service period of the reinforced concrete slab
may be made by a semiquantitative grading-based method.
(5) Judgment as to whether remedial measures need to be taken shall be made in viewof the degree of performance degradation of the reinforced concrete slab due to fatigue,
the degree of importance of the structure, maintenance category, and the remaining
service life.

[Commentary] (1) The evaluation of performance and judgment of necessity for remedial
measures in initial, routine and regular assessment for structures in which little progress ofdeterioration has been recognized are frequently more or less the same regardless of thedeterioration mechanism. For details, refer to Part 1. The evaluation of performance and judgmentof necessity for remedial measures for structures in which deterioration may have or has progressedvary according to the deterioration mechanism. When discussing the performance degradation of areinforced concrete slab due to fatigue, the descriptions in this chapter should be consulted.
(2) In the case of a slab under fatigue stress, performance affected by deterioration and thedegree of performance degradation vary depending on the stage of deterioration (initiation stage,
propagation stage, acceleration stage or deterioration stage). Performance to be evaluated at eachstage of deterioration, therefore, needs to be selected on the basis of the state of cracking at theunderside of the slab as shown in Fig. C14.3.1. For example, at the initiation or propagation stage,
serious problems related to safety or serviceability do not occur, but it may be necessary to evaluate
steel protection performance, which is a durability-related performance attribute because regions
causing steel corrosion may enter through cracks depending on the environment in which thestructure is placed. At the propagation stage, appearance begins to be a performance attributes to beevaluated. At the acceleration stage, hazards for third party associated with peeling, spalling, etc.,
also needs to be evaluated in addition to appearance because cracks begin to form slits and corners
begin to fall. Safety and serviceability also need to be evaluated because the dynamic properties ofconcrete cross sections begin to decline. At the deterioration stage, map cracks grow into

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Standard Specifications for Concrete Structures-2007, Maintenancepenetrating cracks and, depending on the circumstances, the slab may caves in. Because of these
forms of degradation associated with safety, serviceability and hazards for third party, theevaluation of these performances is very important.
(3) and (4) Under the present conditions, quantitative evaluation to determine to what extent
the performance of a slab declines since the initiation of maintenance and when the allowable limit
state is reached is difficult. For example, safety can be evaluated by checking on load-carrying
capacity through a loading test conducted at the time of investigation, but safety in future is difficult
to predict. There are also performances that are difficult to evaluate quantitatively at the time ofinvestigation. An alternative, therefore, is semiquantitative evaluation made by the method
described below. As the first step, the stage of deterioration at the time of investigation isdetermined from the state of the underside of the slab by using Table C14.1.1. At the same time, thestage of deterioration at the end of the service period is estimated through deterioration prediction,and the stage of deterioration and the appearance grade are related. The degree of performancedegradation of the structure can be judged or estimated to some extent from the appearance of thestructure with reference to Table C14.3.5. If, therefore, the stage of deterioration can be determinedor predicted by using these tables, the performance of the structure can be evaluatedsemiquantitatively.
(5) Because judgment is the act of deciding whether remedial measures need to be taken on thebasis of the results of performance evaluation of slabs, there is no difference depending on
deterioration factors. Therefore, refer to Part 1.

Table C14.3.5 Structural appearance grading and typical performance degradations
Structuralappearance
grade

Safety performance

Serviceability
performance

Hazards for third party
Appearance

－

－

－

(propagation
stage)－－－

State III

Decrease in shear stiffness

State I
(initiation stage)
State II

(acceleration
stage)
State IV
(deterioration
stage)

Degradation in appearance－•Slit formation by cracks,
corner falls• Cracking• Free lime
Decrease in load-carrying Road surface damage due • Cave-in of concrete
capacity
surfaceto fatigue• Penetrating cracks
Hazards for third party• Cracking and cave-in ofroad surface• Infiltration of rainwater• Peeling• Steel corrosion• Spalling

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14.4 Remedial Measures
14.4.1 Selection of remedial measures(1) If it has been judged that remedial measures need to be taken in connection withperformance degradation due to fatigue, remedial measures shall be taken so that thestructure after the measures meets the required performances.
(2) If it is difficult to select remedial measures on the basis of performanceverification, remedial measures may be selected from the measures corresponding to theappearance grade for the fatigue of a slab.

[Commentary] (1) If it has been judged, as a result of evaluation, that remedial measures need tobe taken, it is necessary to select one or more of the following measures: (i) intensified investigation,(ii) repair, (iii) strengthening, (iv) functional improvement, (v) restriction in service or (vi)dismantling/removal. Basically, decisions as to which measures to take should be made by the
maintenance manager of the structure, but it is good practice to refer to Part 1 for information on
typical relationships between evaluation and judgment results and remedial measures.
(2) If it is difficult to select remedial measures through quantitative evaluation or judgment,
remedial measures are selected from the measures corresponding to the grade of fatigue-induced
deterioration of the slab. Remedial measures to be taken vary depending on the type of structure,
the degree of importance of the structure, deterioration rate and the maintenance category, but
recommended standard measures are shown in Table C14.4.1. Measures related to functional
improvement are not shown in the table because it is not related to the grade of fatigue-induced
deterioration.
At the initiation or propagation stage, at which the degree of deterioration of the slab due tofatigue is relatively low, intensified investigation suffices. At and after the acceleration stage,
however, appropriate repair or strengthening measures need to be selected, taking into consideration
the service conditions and the environmental conditions. An alternative is to select a number ofremedial measures or take remedial measures by stages in view of the service conditions of the slab
and the environmental conditions. Because the fatigue of slabs is greatly affected by water, it isdesirable that remedial measures be taken in conjunction with bridge deck waterproofing. If
remedial measures are taken for the underside of a slab, bridge deck waterproofing should be
carried out first before other remedial measures are taken. The reason is that if remedial measures
for the underside of the slab are taken first, rainwater and other water retained in the slab would
have adverse effects on fatigue and other deterioration mechanisms (chloride attack, freeze–thaw
damage, alkali–silica reaction).
Because of the possibility of recurrence of deterioration, investigation in routine and regularassessment need to be conducted even after remedial measures are taken. In one example, after the
steel plate adhesion method and the overlay method were applied to a deteriorated slab, the cracks
in the slab grew because of increases in traffic volume and in the number of overloaded vehicles,
and the required performance was not maintained until the end of the of the structure.

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Standard Specifications for Concrete Structures-2007, Maintenance

Table C14.4.1 Appearance grades of reinforced concrete slabs and remedial measures
Appearance grade of reinforced
concrete slab

Intensified
Restriction
Repair Strengthening**
Dismantling/removal
investigationin service

I(initiation stage)

O

(O)

X

II(propagation stage)

OO

OO

X

III(acceleration stage)

OO

OO*

X

IV(deterioration stage)

O

OO*

X

O

O

OO:standard measures(OO*:including restoration of mechanical performance）,O:measures to be taken under certain
circumstances,(O):preventive measures, Strengthening**:designed to achieve performance level higher than initial level,
X:measures taken in accordance with criteria other than appearance grade

14.4.2 Prevention measures
If a reinforced concrete slab is at high risk of performance degradation due to fatigue,
deterioration shall be prevented by installing a bridge deck waterproof membrane over theupper surface of the reinforced concrete slab so that water such as rainwater does notenter the slab.

[Commentary] If a reinforced concrete slab is at high risk of performance degradation due tofatigue, installing a bridge deck waterproof membrane over the upper surface of the slab is effective
in preventing the progress of fatigue due to abrasion resulting from the intrusion of rainwater orother water into the slab. From many types of bridge deck waterproof membrane, an appropriate
type needs to be selected in view of the waterproofing effect, constructibility, economy and thedegree of contact with the asphalt pavement. In cases where a waterproof membrane with a highwaterproofing effect is used, the space between the asphalt pavement and the waterproof membrane
is easily infiltrated by water. It is therefore necessary to carefully consider ways to drain such water.

14.4.3 Repair and strengthening
Methods and materials for the repair or strengthening of a reinforced concrete slab
shall be selected taking into consideration performance degradation due to fatigue andlife cycle cost, so that the required effect can be achieved.

[Commentary] In cases where repair or strengthening is carried out as a remedial measures, it isnecessary to define the expected effect of repair or strengthening and the required performance(what level of performance to be maintained for how many years?).
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Repair or strengthening methods can be classified, according to expected effects, as shown in
Table C14.4.2.
When deciding on which method to use, it is necessary to take into consideration the present
state of performance degradation of the structure concerned besides the expected effect. For thecorrespondence between appearance deterioration grades and standard repair and strengthening
methods, refer to Table C14.4.3. The repair or strengthening methods listed in the table are
well-proven methods. If poorly field-tested materials are used, it is desirable that investigation
frequency be increased after the repair or strengthening is done.
For details of various repair or strengthening methods, refer to, for example,“Recommendations for Strengthening of Concrete Structures,” “Report of the Committee on Repair
Methods for Concrete Structures (I, II and III) (Japan Concrete Institute)” and “Report of JCI
Committee on Rehabilitation of Concrete Structures (Japan Concrete Institute).”Many of the repair or strengthening methods in use today were developed in recent years, andsome of them have not been field-tested extensively. Those methods might fail to prevent therecurrence of deterioration or achieve the required performance because of factors that could not be
expected at the design stage. In the event of the recurrence of deterioration, repair or strengthening
measures need to be taken again. In such cases, it is important to carefully investigate the extent,
state, cause, etc., of re-deterioration, select appropriate control measures and materials and carry out
repair or strengthening again.

Table C14.4.2 Examples of repair or strengthening methods and expected effects
Expected effect

Example of repair/strengthening method

Improvement in terms of hazards for third party
and appearance

Surface treatment (lining)

Improvement in fatigue durability achieved byeliminating the influence of water

Installation of bridge deck waterproof membrane

Improvement in fatigue durability achieved bycontrolling crack opening

FRP sheet adhesion, prestressing

Restoration of cross-sectional stiffness achievedby installing members at extreme tension fiber

Adhesion of steel plates, etc., on underside of slab,
overlay to enlarge cross section of reinforced concrete,installation of additional girders

Improvement of fatigue durability achieved by
improving shear stiffness of compression zone of Overlay on upper surface of slab
cross section

Table C14.4.3 Appearance grades of slabs deteriorated by fatigue and examples of standard
repair/strengthening methods
Appearance grade of slab
I (initiation stage)

Standard repair/strengthening method
Bridge deck waterproof membrane*

II (propagation stage)

Bridge deck waterproof membrane, Steel plate/FRP
sheet adhesion, overlay on upper surface, overlay on
underside, additional girder

III (acceleration stage with

Bridge deck waterproof membrane, steel plate
231

Standard Specifications for Concrete Structures-2007, Maintenanceinfluence of water)
III (acceleration stage without
influence of water)IV (deterioration stage)adhesion, overlay on upper surface
Bridge deck waterproof membrane, steel plate
adhesion, overlay on upper surface, additional girder
Restriction in service, dismantling/removal*:preventive maintenance method

14.5 Recording(1) Investigation, deterioration prediction, evaluation and judgment, and remedial
measures shall be recorded in accordance with Part 1.
(2) Items relevant to the fatigue of reinforced concrete slabs shall be recorded.

[Commentary] As a general rule, the results of investigation, deterioration prediction, evaluation
and remedial measures must be recorded in accordance with Part 1. Items relevant to fatigue
require careful attention, particularly with respect to record keeping. Items to be recorded are
indicated in 14.3.2 “Investigation in Assessment” and 14.3.4 “Evaluation and Judgment.”

232Chapter15

Maintenance of Reinforced Concrete Beams Subject to Fatigue

CHAPTER 15 MAINTENANCE OF REINFORCED CONCRETE
BEAMS SUBJECT TO FATIGUE

15.1 General(1) This chapter provides standard methods for maintenance planning, assessment,
remedial measures and recording for reinforced concrete beams whose performance has
deteriorated or is likely to deteriorate because of fatigue. The items common to all
deterioration mechanisms are shown in Part 1.
(2) This chapter shall be applied to structures of the maintenance category A(preventive maintenance) and B (corrective maintenance).

[Commentary] (1) Failure of a material resulting from cyclic applications of loads usually smaller
than the static strength of the material is referred to as "fatigue" or "fatigue failure." Fatigue of aconcrete structure refers to the phenomenon in which the performance of the structural members ofa concrete structure deteriorates as cracks occur in the reinforcing steel (e.g., reinforcing bars,
prestressing tendons) or concrete constituting the structure because of cyclic loading, and eventually
the structure fails under normal loads.
This chapter provides standard methods of maintaining beams that are highly likely to be
subjected to cyclic application of relatively large variable loads.
Fatigue-induced performance degradation of beams occurs in various forms including (1)decrease in safety due to fatigue breaking of tensile reinforcing steel, (2) decrease in safety due tocompression fatigue failure of concrete, (3) decrease in stiffness or degradation in terms of hazards
for third party or appearance due to propagation or enlargement of flexural cracks, (4) decrease insafety due to shear fatigue failure (propagation of diagonal cracks) of concrete and (5) decrease insafety due to fatigue breaking of shear reinforcing bars.
Because of typical service conditions (loading effects) for a structure and its cross-sectional
details, investigation and evaluation of the fatigue of beams focus mainly on decreases in stiffness
due to fatigue breaking of tensile and shear reinforcing steel and propagation and enlargement of
flexural cracks and shear cracks in concrete and hazards for third party due to spalling, etc., ofcracked concrete. This chapter, therefore, provides maintenance methods for beams whose
durability is determined by fatigue breaking of reinforcing steel. Maintenance methods for beams
whose durability is determined by fatigue of concrete must be determined separately in due
consideration of the environmental conditions and other factors.
In one recent incident, flexural cracks in the concrete of a girder of an express railway bridge
grew past the neutral axis of the member because of resonance. In another incident, severe cracking
of a road bridge was caused by large vehicles passing the bridge. In recent years, however, there has
been no reported incidence of structural member failure caused by the fatigue of reinforcing steel
even in the case of a long-used structure. Likely reasons are that actual loads are usually smaller
than design loads, and actual loads in reinforcing steel are reduced to levels smaller than design
values by the dissipation of loads in the beams, the contribution of nonstructural members to the233Standard Specifications for Concrete Structures-2007, Maintenancestiffness of girders and the bearing of part of tensile stress by concrete. For example, it has beenreported that actual stresses measured at rapid transit bridge girders were smaller than half of thedesign values. Another likely reason is that design values for fatigue strength contain a margin ofsafety. The investigation and evaluation provided in this chapter may be omitted if it can be clearly
judged, on the basis of a sufficient amount of information, that even members subjected to cyclicloading are highly unlikely to be subject to fatigue. In prestressed concrete members, the amplitudeof stress in prestressing steel due to variable loads is very small unless cracking occurs. In cases
where prestressing steel are bonded to concrete, studies on fatigue may be omitted unless crackingof concrete occurs. Depending on the circumstances, however, prestressed concrete members withunbonded prestressing steel may require investigation and evaluation paying attention to anchorage
zones.
Fig. C15.1.1 illustrates the relationship between the deterioration stages of a beam under
fatigue stress and performance degradation. Table C15.1.1 lists definitions of each stages ofdeterioration in the load-carrying capacity of members and factors determining the stage ofdeterioration.

Performancedegradation of beam

Deterioration due
to fatigue

Fig. C15.1.2 shows a standard procedure for fatigue-related maintenance of beams.

Partial breakingof reinforcing steel
Initial cracking

Initiation
stage

Propagation Acceleration
stage
stage

Deterioration
stage

Fig. C15.1.1 Conceptual view of deterioration progress due to fatigue-induced of beam234

Chapter15

Maintenance of Reinforced Concrete Beams Subject to Fatigue

Table C15.1.1 Definitions of deterioration stages
Stage ofdeterioration
Initiation stage

Propagation stage

Acceleration stage
Deterioration
stage

Possibility offatigue

Factor determining the
stage

Definition• Stage at which metallic crystal level slip is occurring in
the reinforcing steel because of cyclic loading, but
usually detectable initial cracks have not yet occurred• Stage at which initial cracks occur in the reinforcing
steel, and early-stage cracks become large enough to be
detected by magnetic particle investigation• Stage at which crack propagation occurs at a ratedependent on the material composition of steel• Stage at which the loss of cross section due to fatigue
cracking of the steel is minor and has little impact onload-carrying capacity• Stage at which fatigue cracks in the steel become close
to critical crack length, part of the steel is on the verge of
fatigue breaking, and load-carrying capacity might
decrease

Fatigue crack propagationrate• Stage at which fatigue breaking of the reinforcing steel
in the beam occurs locally, and stresses are redistributedin the reinforcing steel to induce further fatigue breaking(15.2)(15.3)

Maintenanceplan for the
structure

Assessment(15.3.2.2)
Investigations ininitial assessment
Standard
investigation(15.3.2.5)
Detailed
investigation(15.4)(15.3.3)(15.3.4)

Deterioration
prediction

Remedial
measures

Evaluation andjudgment(15.5)
Recording(15.3.2.3, 4)
Investigations inroutine/regularassessment
Standard
investigation(15.3.3)(15.3.4)(15.3.2.5)
Detailed
investigation

Deterioration
prediction
Evaluation andjudgment

Fig. C15.1.2 Standard maintenance procedure of beam under fatigue stress235

Standard Specifications for Concrete Structures-2007, Maintenance(2) This chapter applies to beams in the maintenance category A and B.
As mentioned earlier, in the case of a normally designed structure, studies on fatigue may beomitted if there is no anomaly. Although not clearly known because no information is available on
examples of fatigue failures of beams, initial cracking of reinforcing steel does not occur
immediately after an anomaly in appearance occurs. Instead, the member fails only after a certain
amount of time has passed following the initial breaking of steel. It has also been reported that evenafter initial cracking of reinforcing steel occurs, a number of reinforcing bars placed in the beam
break sequentially instead of all at once.
These indicate that maintenance category A may be applied to a beam to be maintained before
fatigue cracking of reinforcing steel occurs. It is difficult, however, to detect initial cracking of
reinforcing steel by nondestructive testing. It is recommended, therefore, that in cases where thewidth of cracks (e.g., cracks caused by other factors, flexural cracks allowed for at the design stage)in the concrete exceeds the critical value considered at the design stage or in cases where cracks or
deflections are too large, fatigue-related maintenance be performed indirectly by ascertaining
through measurement, etc., that reinforcing steel strains are not greater than the critical strain forcracking.
If cracking of reinforcing steel has already occurred, maintenance category B is applied.

15.2 Maintenance Planning
15.2.1 Basis of planning
In order to maintain beams under fatigue stress, the maintenance category shall beselected, the service period planned, and a maintenance planning for activities including
assessment, remedial measures and recording drawn up in advance in view of the service
conditions such as the magnitude and frequency of variable loads.

［Commentary］When drawing up a maintenance planning, it is necessary to cover such details ascheck items and procedures for the initial assessment and check items, procedures, timing andfrequency for routine and regular assessment, evaluation and judgment methods, actions to be takenin the event of deterioration, and recording methods, taking into consideration the type of structure,
the degree of importance of the structure, planned service period, maintenance category, service
conditions and the quality of materials.
It is usually difficult, at the stage of maintenance planning, to accurately predict the state of astructure during its service period. It is therefore good practice to draw up a maintenance planningwith reference to the deterioration of a similar structure or a structure in a similar environment.

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15.2.2 Determination of maintenance category
The maintenance category of beams under fatigue stress shall be selected in view ofthe degree of importance of the structure, the type of structure, hazards for third party, theplanned service period and the characteristics of deterioration due to fatigue.

[Commentary] The determination of the maintenance category is very important because
maintenance plannings vary widely depending on the maintenance category. The progress ofdeterioration and performance degradation of beams due to fatigue is conceptually illustrated in Fig.
C15.1.1.
In order to apply maintenance category A (preventive maintenance) to a structure, it isnecessary to perform maintenance at the initiation stage, in which initial cracking of the steel in theconcrete has not yet occurred, in order to prevent the performance degradation of the structure. This
makes it necessary to investigate the state of the structure as accurately as possible and carry out thefollowing:(i) Quantitative evaluation of concrete surface crack width(ii) Quantitative evaluation and prediction of the magnitude of variable loads, the number ofloading cycles, load locations, etc.
(iii) Amplitude of stress in reinforcing steel
Structures to which maintenance category B (corrective maintenance) is applied need to be
maintained so that structural performance does not fail to meet the required performances. For
example, maintenance is performed so that deterioration can be prevented until the deterioration
stage if attention is paid to safety and until the latter half of the acceleration stage if attention is paid
to serviceability. In this case, some kind of action is taken after the following deterioration is
identified:(i) Initial cracking of steel has been observed.
(ii) Fatigue cracks in steel are close to critical crack length.
(iii) Breaking of steel has been observed.
It is desirable that repair is done at Stage (i) or Stage (ii) mentioned above even in the case of astructure to which maintenance category B (corrective maintenance) is applied. Large-scale
remedial measures need to be taken if deterioration make progress to Stage (iii). In investigation,
therefore, checks must be made on not only the service conditions (e.g., load conditions andfrequency) and changes in appearance such as the state of cracks but also other details such as (a)fatigue cracks, (b) length of fatigue cracks in reinforcing steel and (c) amplitude of stress inreinforcing steel.

237

Standard Specifications for Concrete Structures-2007, Maintenance15.2.3 Preparation of maintenance manuals
A maintenance manual describing methods, procedures and frequency requirements
should be prepared for each structure in accordance with the maintenance planning,taking the structure-specific conditions into consideration.

[Commentary] The service period of civil engineering structures is long, and maintenance of
those structures is performed over a long period of time. It is recommended, therefore, that in order
to inform investigators of maintenance concepts and policies, a maintenance manual be prepared sothat detailed procedures and methods can be communicated accurately even to newly assigned
maintenance engineers.
Under certain circumstances such as in cases where the original maintenance planning isaltered because the actual prediction of deterioration turned out to differ from that assumed in theoriginal maintenance planning, it may be necessary to modify the maintenance manual and takeappropriate remedial measures accordingly.

15.3 Assessment
15.3.1 GeneralIn the assessment of a beam whose performance has declined or is highly likely todecline because of fatigue, investigation, evaluation of the present state, deterioration
prediction and judgment of necessity for remedial measures shall be appropriately
conducted in accordance with the maintenance planning.

[Commentary] In order to maintain concrete structures appropriately, this specification requires
three types of assessment: initial assessment, periodic assessment and extraordinary assessment.
Because the initial and periodic assessments are essential for the maintenance of beams under
fatigue stress, this chapter stipulates that those assessments must be conducted. Extraordinary
assessments are regarded as assessments to be conducted on an as-needed basis and are therefore
not dealt with in this chapter. By conducting periodic assessments during the maintenance period,changes in appearance of structures can be discovered before they occur or in early stages, andremedial measures including preventive measures and repairs can be taken systematically.

15.3.2 Investigation in assessment
15.3.2.1 General
Investigation in initial, routine and regular assessment of a beam under fatigue stressshall be conducted appropriately according to the maintenance category required for the
structure. Prior to investigation, check items, methods, frequency and scope of standard
investigation shall be determined appropriately. For each type of assessment, detailed

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investigation shall also be conducted on an as-needed basis.

[Commentary] It is important to select check items, methods, frequency and scope ofinvestigation appropriately according to the purpose of investigation in accordance with themaintenance planning.
In order to evaluate the fatigue-induced deterioration of a beam and accurately predict thedeterioration, it is necessary, for example, to measure the amplitude of reinforcing steel stresses
under variable loads with strain gauges attached to the beam and checking for fatigue cracks in thereinforcing steel. These can be done, however, only by removing the cover concrete and using
precision measuring instruments. If there are many beams under similar conditions, it is possible todetermine the relationship between deflections, etc., of relatively easy-to-measure beams undervariable loads and the amplitude of reinforcing steel stresses in advance and estimate, by using therelationship thus determined, the amplitude of stresses in the reinforcing steel in the members to be
maintained. This is an indirect method of estimation but it is useful in deterioration prediction withrelatively high accuracy.
In general, investigation vary depending on the stage of deterioration. Table C15.3.1 lists main
check items at each stage of fatigue-induced deterioration. The state at the initiation stage can beroughly evaluated mainly by referring to the design drawings and specifications and conducting
visual observation. If the design conditions and service conditions indicated in the drawings andspecifications can be identified through monitoring, sampling, etc., the information thus obtained isuseful for deterioration prediction. At and after the propagation stage, investigation that make itpossible to directly determine the prediction of fatigue of the reinforcing steel are necessary.
If the state of the structure cannot be identified appropriately through standard investigation,
detailed investigation must be conducted.

Table C15.3.1 Main check items in investigation
Stage of
Deterioration
Initiation
stage
Propagationstage
Accelerati
onstage
Deteriorati
on
stage

DesignconditionsServiceconditions(load,frequ
ency)

State
of
cracking

Crack
openingwidth

Memberdeflection

SteelstressamplitudeFatiguecrack(scan)

ConcretestrainMonitori
ng

O

O

O

▲*

▲*

▲*

▲*

▲*

▲*

▲

O

O

O

O

▲

▲

▲*

▲*

▲*

O

O

O

O

O

O

▲

▲*

▲*

O

O

O

O

O

O

▲

▲*

239

Standard Specifications for Concrete Structures-2007, Maintenance15.3.2.2 Investigation in initial assessment(1) In initial assessment, appropriate check items for standard investigation shall beselected for newly constructed structures, existing structures, large-scale repairs andstrengthened structures.
(2) If deterioration prediction, evaluation or judgment is difficult to make throughstandard investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigation in initial assessment is the first investigation conducted when themaintenance of a concrete structure is started. Investigation in initial assessment includes not only
the first investigation of a newly constructed structure conducted before it goes into service but also
the first investigation of an existing structure or a structure for which remedial measures have beentaken in response to deterioration. Investigation items may vary from structure to structure.
Information needed to predict the progress of fatigue of a beam includes the amplitude ofstress acting on the reinforcing steel and the number of loading cycles. When selecting investigation
items in initial assessment, it is necessary to take into consideration the service conditions for themember and the relationship with the investigation items in routine or regular assessment .
When conducting the investigation in initial assessment of a newly constructed structure, it ispossible to predict the deterioration from the information obtained from the design drawings andspecifications. The goal here is to check whether the load conditions are not more severe than thedesign assumptions and whether the applied loads are not too large in view of the state of cracking,etc. It is also important to identify the members to monitor at the subsequent stages.
In cases where the investigation in initial assessment of an existing structure is conducted,
deterioration can be predicted as in the case of a newly constructed structure if the design drawings
and specifications exist and the service conditions, etc., have been identified through monitoring. If
the design drawings and specifications are not available and the service conditions, etc., are notclearly known, it is necessary to estimate the load history by investigating the service conditions ormeasuring the amplitude of stress in the reinforcing steel directly or indirectly. If such investigation
are conducted, it is advisable to obtain data necessary for deterioration prediction indicated in
15.3.3.2 “Prediction of Fatigue,” with reference to 15.3.2.5 “Detailed Investigation.”
In cases where investigation in initial assessment of a structure for which remedial measures
have been taken is conducted, usually a study on the mechanical aspects of the structure has alreadybeen conducted, and therefore necessary data are available from the drawings and specifications
used for the study. If the remedial measures taken are not related to fatigue, it is good practice topredict the deterioration by a method similar to the method used for a newly constructed structure.

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Table C15.3.2 Typical investigation items in initial assessment
Inspection item
Service conditions (e.g., loadconditions, frequency)
State of cracking
Crack opening amplitude
Member deflection
Reinforcing steel stress

Inspection Method
Design drawings and specifications ormonitoring
Visual inspection
Measurement by use of π gauge
Measurement by use of displacement meter
Measurement by use of strain gauge

Necessity
O
O
▲
▲
▲

(2) If high-accuracy evaluation or judgment is difficult to make by conducting standard
investigation alone or if severe deterioration has already occurred, detailed investigation isconducted. Check items of detailed investigation are described in 15.3.2.5 “Detailed Investigation.”

15.3.2.3 Investigation in routine assessment(1) In routine assessment, standard investigation designed basically to check on
appearance deterioration such as the state of cracking shall be conducted.
(2) If deterioration prediction, evaluation or judgment is difficult to make by standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) It is difficult to predict the fatigue of reinforcing steel from changes inappearance such as the state of cracking. If, however, the deterioration is predicted with sufficientaccuracy at the time of the initial assessment and it is judged that the initiation stage is sufficiently
long compared with the design service period or the planned service period, the present state of thestructure can be identified through appearance investigation on the state of cracking, etc., conductedduring investigation in routine assessment. In such cases, the identification of the state ofdeterioration in appearance is the basic purpose of standard investigation. In investigation in routine
assessment, however, of a structure to which maintenance category A is applied, it is good practice
to conduct monitoring in order to indirectly or directly check on the service conditions such as themagnitude and frequency of working loads, the amplitude of stress in the reinforcing steel, etc.,
depending on the circumstances.

Table C15.3.3 Typical investigation items in routine assessment
Investigation item

Investigation method

Necessity

Service conditions (e.g., load conditions, frequency)

Monitoring▲

Visual inspection

O

State of cracking(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone or if severe deterioration has occurred, detailed investigation is conducted. Check items ofdetailed investigation are described in detail in 15.3.2.5 “Detailed Investigation.”

241

Standard Specifications for Concrete Structures-2007, Maintenance15.3.2.4 Investigation in regular assessment(1) The purpose of investigation in regular assessment is to obtain information that isdifficult to obtain in routine assessment. In regular assessment, standard investigationconsisting of detailed observation of defects in appearance such as cracks shall be
conducted as in routine assessment.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigation in regular assessment is conducted for the purpose of obtaining
information that is more detailed than the information obtainable from a routine assessment.
Members that have been identified as requiring attention in the initial or routine assessment need to
be investigated intensively.
Check items consist mainly of appearance items such as the state of cracking as in a routine
assessment, but it is good practice to combine those check items with other check items dependingon the stage of deterioration on an as-needed basis so that the stage of deterioration can be
identified with higher accuracy.
Table C15.3.4 lists typical check items of investigation conducted as part of a regularassessment of a beam under fatigue stress. Intervals between regular assessment must be determined
appropriately by the maintenance manager in view of the service conditions.
In cases where the deterioration needs to be predicted with high accuracy through regularinvestigation of a structure to which maintenance category A is applied, it is good practice to selectcheck items by which the amplitude of stress in the reinforcing steel can be determined directly or
indirectly from the check items of detailed investigation.

Table C15.3.4 Typical investigation items in regular assessment
Inspection item

Inspection method

Necessity

Service conditions (e.g., load Design drawings and specifications or monitoring
conditions, frequency)▲

State of cracking

Visual inspection

O

Crack opening amplitude

Measurement by use of π gauge▲

Member deflection

Measurement by use of displacement meter▲

O:priority check item,▲:item to be checked on an as-needed basis(2) If high-accuracy evaluation or judgment is difficult even after standard investigation or if
deterioration is severe, detailed investigation is conducted. Detailed investigation is described indetail in 15.3.2.5 “Detailed Investigation.”
If deterioration such as rapid propagation or enlargement of cracks due to fatigue of242

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reinforcing steel has been found by visual observation, detailed investigation needs to be conductedurgently because the fatigue of the reinforcing steel is thought to be at an advanced stage.

15.3.2.5 Detailed investigation
Detailed investigation shall be conducted to obtain detailed information on a
structure in cases where the deterioration of a beam under fatigue stress is difficult topredict, evaluate or judge by standard investigation alone conducted as part of the initial,
routine or regular assessment. Check items, methods and location of detailed
investigation shall be selected appropriately taking into consideration such factors as the
purpose of investigation and the accuracy of obtained results.

[Commentary] Detailed investigation is conducted when the determination of the present state ofa structure and the deterioration of the structure are difficult by standard investigation results alone
in order to obtain information necessary for those purposes. In detailed investigation of a beam
subject to fatigue stress, direct determination of the amplitude of stress acting on the reinforcing
steel and checking on fatigue cracks at the steel surface are important for accurate prediction of the
progress of fatigue. It is also good practice to quantitatively relate the investigation items checked
during routine and regular assessment with the amplitude of stress acting on the reinforcing steel.
Loads considered in connection with stress amplitude measurement are in many cases loads
that are acting under normal conditions. If it is difficult to measure the magnitude of loads
accurately or if high-accuracy measurement needs to be conducted, it is good practice to takemeasurements by letting controllable, predetermined loads (e.g., test vehicle, loading apparatus) act.
Table C15.3.5 shows detailed investigation items and methods for a beam under fatigue stress.
Table C15.3.6 lists important considerations in measuring the amplitude of stress in the reinforcing
steel and checking for fatigue cracks at the steel surface.

Table C15.3.5 Detailed investigation items and methods
Investigation item

Investigation method

Service conditions (e.g., load Design drawings and specifications or monitoring
conditions, frequency)
State of cracking

Visual inspection

Crack opening amplitude

Measurement by use of π gauge

Member deflection

Measurement by use of displacement meter

Reinforcing steel stressMeasurement by use of strain gauge

Checks for fatigue crack

Magnetic particle inspection method, fluorescent penetrate method,
eddy current method, ultrasonic method, radiation method

Steel arrangement

Electromagnetic radar method, electromagnetic induction method

Quality of concreteCore sampling, surface hardness method, ultrasonic method243

Standard Specifications for Concrete Structures-2007, Maintenance

Table C15.3.6 Investigation methods and important considerations
Investigation item

Method and considerations

To measure stress in the reinforcing steel of a simple beam, a high-stress region
such as a center span region is selected, the cover concrete in an appropriate
section is removed, and a strain gauge is bonded to the steel surface for strain
Amplitude of stress in measurement.
If steel stress cannot be measured directly because exposing reinforcing steel
reinforcing steel
would create a maintenance problem, the steel arrangement and concrete cover
are investigated by an appropriate method, concrete strain is measured, and steel
stress is calculated by an appropriate method.
To check for fatigue cracks in the reinforcing steel, a high-stress region is
Fatigue cracking of in selected as in the stress amplitude measurement, the cover concrete in an
appropriate section is removed, and inspection is conducted by a nondestructive
reinforcing steel
testing method such as the magnetic particle inspection method.

15.3.3 Methods for predicting performance degradation of structures
15.3.3.1 General(1) In the maintenance of a beam under fatigue stress, the performance degradationof the beam shall be evaluated quantitatively at the time of investigation, and futuredegradation shall be predicted.
(2) In order to predict the performance degradation of a beam, it is necessary to
predict deterioration due to fatigue quantitatively.
(3) If (2) is difficult, an alternative method is to predict performance degradation by
predicting the length of the initiation, propagation, acceleration and deterioration stages,
taking into consideration the progress of fatigue of the reinforcing steel.
(4) As a general rule, deterioration shall be predicted on the basis of investigation
results.

[Commentary] (1) and (2) In the performance-verification type maintenance method, changes(deterioration) in various performance of a structure are to be predicted. To do that, it is necessary to
predict the progress of deterioration of the materials constituting the beam, especially the predictionof fatigue of the reinforcing steel, quantitatively. It is also necessary to quantitatively evaluate theperformance of the beam and the degree of deterioration of the materials constituting the beam at
the time of investigation and at the end of the planned service period on the basis of investigation
results. The performance degradation of the beam or the degree of deterioration of the constituent
materials at the time of investigation can be evaluated by using an appropriate method on the basisof the investigation results. Performance and the degree of deterioration at the end of the planned
service period are predicted on the basis of the periodic assessment results. Since, however,deterioration prediction results do not necessarily agree with the actual progress of deterioration, it
is important to review the prediction method on the basis of the results of two or more investigation
conducted subsequently.
(3) In cases where high-accuracy measurement is conducted continuously in a laboratory or

244

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Maintenance of Reinforced Concrete Beams Subject to Fatigue

other controlled environment, it is possible to determine the process of deterioration throughappearance observation, but in the case of a real structure, that is not possible except at the final
stage of the deterioration process. If, however, attention is paid to the fatigue process of thereinforcing steel, which is a main factor contributing to the fatigue failure of the member, theprocess leading to the fatigue breaking can be divided, as in other deterioration predictions, into theinitiation, propagation, acceleration and deterioration stages.
There is a crack propagation law based on destruction dynamics is a steel crack propagation
model. The relationship between fatigue crack length and the number of loading cycles is illustrated
in Fig. C15.3.1.
By using this model, the deterioration process can be divided into the initiation stage, which isthe period until the occurrence of the first visible crack, the propagation stage, which is the period
during which fatigue cracks grow relatively stably, the acceleration stage, which is the period inwhich openings of cracks begin to appear at the fracture sides until breaking occurs, and thedeterioration stage, which is the period in which part of the reinforcing steel in the beam begins to
break and the load-carrying capacity of the beam decreases. The relationship between thedeterioration stages and performance degradation is shown in Fig. C15.1.1, and the factor
determining the deterioration stages and their durations is indicated in Table C15.1.1. The amplitudeof stress in a structure tends to be relatively small, and the initiation stage is usually longer than theother stages.
Crack length
Initiation stage

Propagation stage

Acceleration/
deterioration stages

Occurrence of firstvisible crack
Initiation of cleaving of
fracture sides
Number of loading
cyclesFig. C15.3.1 Model of fatigue crack propagation in reinforcing steel(4) Investigation results include data related to the state of the investigated members and theservice conditions of the structure. As a general rule, deterioration prediction must be made on thebasis of those investigation results. If, however, such investigation results are not available because
prediction is to be made at the planning stage or for members of an existing structure, it is necessary
to make conservative predictions, taking uncertain factors into consideration. The factor of safety to
be used in this case should be determined with reference to, for example, the “Design” volumes of
the Standard Specifications. It is also possible to refer to investigation results or the state ofdeterioration of similar members under identical environmental conditions.

245

Standard Specifications for Concrete Structures-2007, Maintenance15.3.3.2 Prediction of fatigue(1) The progress of fatigue of a beam shall be predicted in due consideration of theinfluence of the design conditions and the service conditions.
(2) The progress of fatigue of a beam may be predicted by applying the crack
propagation law for reinforcing steel or the linear cumulative damage law.

[Commentary] The prediction of fatigue of a beam is affected by the variable load (stressamplitude) level and the number of stress cycles. In order to predict the progress of fatigue,
therefore, it is important to allow for the service conditions and the design conditions such as
cross-sectional details and the quality of reinforcing steel appropriately. With respect to service
conditions, in the case of a railway bridge, it may be possible to predict working loads and their
history with relatively high accuracy. In the case of a road bridge or an offshore structure, working
loads vary widely, so monitoring should be conducted to enhance prediction accuracy.
Because stress waves in a structure are irregular instead of repetitions of constant stresses,
those waves need to be converted to repetitions of independent stress waves. There are many
conversion methods, and it is necessary to select an appropriate method depending on loadconditions and characteristics of the structure. The range pair method and the rainflow method areoften used for railway bridges, and the zero-up crossing method is widely used for offshore
structures. From independent waves obtained by these methods, the equivalent number of cycles
corresponding to a constant stress amplitude by using, for example, the modified Miner's rule.
Stresses due to not only variable loads but also permanent loads occur in beams. If stresses due topermanent loads are taken into account, tools such as the figure of Goodman relations are used.
(2) There is no established method of predicting the fatigue of beams. There are simple
methods, however, using laws such as the crack propagation law, which uses fatigue crack length inreinforcing steel, a main factor contributing to the fatigue failure of a member, as an indicator, andthe linear cumulative damage law as described below.
(i) Prediction based on the crack propagation law
According the crack propagation law, the relationship between the fatigue crack propagation
rate (da/aN) in reinforcing steel and stress can be expressed asda C  K m
dN

(Eq.C15.3.1)

wherea: crack length
N: number of stress cycles
ΔK: stress intensity factor (=    a )Δσ: stress amplitude
C, m: coefficients (usually determined by the properties of reinforcing steel)246

Chapter15

Maintenance of Reinforced Concrete Beams Subject to Fatigue

On the basis of the relation shown above, the crack length aN after N loading cycles at a stressamplitude of Δσ can be calculated from the equation shown below Eq. (C15.3.2) to estimate thefatigue crack length in the reinforcing steel.

aN 

1
m
1
2



m  m

 1
 m 1  N  C  F       2  1  a i 2




1



(Eq.C15.3.2)

whereai: initial crack length
F: correction factor (for example, 1.12 for a surface crack)

If the reinforcing steel in the beam is exposed in investigation and crack length is measured by,for example, the magnetic particle inspection method, the prediction of fatigue cracking after theinvestigation can be estimated by replacing the initial crack length with the measured crack length.
(ii) Prediction based on the linear cumulative damage law
The method using degree of cumulative fatigue damage expressed in Eq. (C 15.3.3) is a simple
method for predicting the fatigue.

M 
i

ni
Ni

(Eq.C15.3.3)

where
M: degree of cumulative fatigue damage
ni: number of stress cycles with amplitude of Sri
Ni: fatigue life due to stress with amplitude of Sri

Unlike the crack propagation law described in (i) above, the degree of cumulative fatigue
damage is not designed for direct evaluation of fatigue-induced deterioration. The progress ofdeterioration, however, can be predicted qualitatively by determining thresholds for identifying
deterioration stages. Table C15.3.7 shows examples of relationship of deterioration stages with
fatigue crack length and degree of cumulative fatigue damage. Although varying depending on theinvestigation method, the initial crack length ranges roughly from 0.05 mm to 0.5 mm. Criticalcrack length varies depending on the reinforcing steel diameter, working stress and strength(destruction ductility). The thresholds for the deterioration stages based on degree of cumulative
fatigue damage shown in the table are reference only values based mainly on structural soundness
grading for the maintenance of steel railway bridges. Thresholds, therefore, should be determined
appropriately in view of such factors as the service conditions and the method and frequency of247

Standard Specifications for Concrete Structures-2007, Maintenanceinvestigation.
Table C15.3.7 Stages of fatigue-induced deterioration and prediction of deterioration
State
Ⅰ
Ⅱ
Ⅲ
Ⅳ
ai:initial crack
length，Stage ofdeterioration
Initiation stage
Propagation stage
Acceleration stage
Deterioration
stage
af::critical crack
lengtha  aiai < a  af

Degree of cumulative
fatigue damage M
M 0.8
0.8 <M  1

a > afM>1

Crack length a

15.3.3.3 Modification of prediction
If the state of deterioration determined in investigation differs from predicted state ofdeterioration, the cause of the difference shall be identified and the prediction shall berevised accordingly. If necessary, the maintenance planning shall be altered.

[Commentary] When the deterioration confirmed in investigation is different from theprediction, appropriate investigation should be conducted with reference to the deterioration
prediction methods described in15.3.3.2 “Prediction of Fatigue,” and Table 15.3.5 in 15.3.2.5“Detailed Investigation,” to identify the cause of the difference from the prediction and revise theprediction accordingly. For example, if predictions for degree of cumulative fatigue damage differ
from detailed investigation results, the deterioration stages may be modified on the basis of fatigue
crack length predictions. It is also important to reconsider such details as the frequency ofinvestigation in view of the revised prediction and alter the maintenance planning if necessary.

14.3.4 Evaluation and judgment(1) The evaluation of performance and judgment as to whether remedial measuresneed to be taken based on the results of the investigation in initial, routine and regularassessment shall be made in accordance with Part 1 and Item (2) and subsequent items inthis section.
(2) The performance of a beam under fatigue stress shall be evaluated byappropriately selecting performance to be evaluated in view of the stage of deteriorationof the beam.
(3) The evaluation of performance at the time of investigation and at the end of theplanned service period of the structure should be made by a quantitative method.
(4) If Item (3) is difficult to achieve, the evaluation of performance at the time ofinvestigation and at the end of the planned service period of the structure may be madeby a semiquantitative grading-based method.
(5) Judgment as to whether remedial measures need to be taken shall be made in248

Chapter15

Maintenance of Reinforced Concrete Beams Subject to Fatigue

view of the degree of performance degradation due to fatigue, the degree of importance ofthe structure, maintenance category, and the remaining planned service period.

[Commentary] (1) The evaluation of performance and judgment of necessity for remedial
measures in initial, routine and regular assessment for structures in which little progress ofdeterioration has been recognized are frequently more or less the same regardless of thedeterioration mechanism. For details, refer to Part 1. The evaluation of performance and judgmentof necessity for remedial measures for structures in which deterioration may have or has progressedvary according to the deterioration mechanism. When discussing the performance degradation of areinforced concrete beam due to fatigue, the descriptions in this chapter should be consulted.
(2), (3) and (4) In the case of a beam under fatigue stress, performance affected bydeterioration vary depending on the stage of deterioration (initiation stage, propagation stage,acceleration stage or deterioration stage). Performance to be evaluated at each stage of deterioration,
therefore, need to be selected appropriately. For example, it can be said that at the initiation stage
and the propagation stage, little performance degradation occurs in safety performance,serviceability, hazards for third party or appearance. At and after the acceleration stage, fatigue
cracks occur in the reinforcing steel and some of the reinforcing bars may come into a state close to
breaking in fatigue or actually break. As a result, safety and serviceability deteriorate asload-carrying capacity, stiffness, etc., decrease because the cross section of the reinforcing steel
becomes smaller. These performance, therefore, need to be evaluated.
There is as yet no established method, however, for quantitatively evaluating various
performances of beams under fatigue stress. A more realistic approach, therefore, may be toevaluate the performance of a structure semiquantitatively by performing grading as shown in Table
C15.3.8 for appearance grades of beams.

249

Standard Specifications for Concrete Structures-2007, Maintenance

Table C15.3.8 Appearance grades, degree of cumulative fatigue damage and typicalperformance degradations
Appearance
grade of beam

Classification by degreeofcumulative
fatiguedamageState I–1
(initiation stage)M < 0.2

State I–2
(initiation stage)
State I–3
(initiation stage)
State II(propagation
stage)

0.2 < M <0.5
0.5 < M <0.8
0.8 < M <1.0

Classification byappearance

Safety performance

Serviceability
performance

Hazards for third
party Appearance

Crackinghas
occurred, but thereisnovisibleanomalyinappearance.
〃

－

－

－

－

－

－

〃

－

－

－

〃

－

－

－

Decreaseinload-carrying
capacity
Crack propagation •Decreaseincan be seen.
cross-sectional area
due to fatigue cracks
in reinforcing steel

State III
(acceleration
stage)

Decrease
stiffness•Crackpropagation

Degradationin appearance•CrackpropagationinM > 1.0
State IV
(deterioration
stage)

Decreaseinload-carrying
Crack propagation capacityand growth can be •Fatigue breaking of
seen.
some
of
the
reinforcing bars inthe beam

Decreasein
stiffness•Breakingofreinforcing steel

Hazards for third
party•Scalingandspallingofconcretenear
brokenreinforcing bars

15.4 Remedial Measures
15.4.1 Selection of remedial measures(1) If it has been judged that remedial measures need to be taken in connection withthe performance degradation of a beam due to fatigue, remedial measures shall be taken
so that the structure after the measures meets the required performances.
(2) If it is difficult to select remedial measures on the basis of performanceverification, remedial measures may be selected from the measures corresponding to theappearance grade for the fatigue of a beam.

[Commentary] (1) If it has been judged, as a result of evaluation, that remedial measures need tobe taken, it is necessary to select one or more of the following measures: (i) intensified investigation,(ii) repair, (iii) strengthening, (iv) functional improvement, (v) restriction in service or (vi)dismantling/removal. Basically, decisions as to which measures to take should be made by the
maintenance manager of the structure, but it is good practice to refer to Part 1 for information on
typical relationships between evaluation and judgment results and remedial measures.
(2) If it is difficult to select remedial measures through quantitative evaluation or judgment,
250

Chapter15

Maintenance of Reinforced Concrete Beams Subject to Fatigue

remedial measures are selected from the measures corresponding to the grade of deterioration of thestructure. Remedial measures to be taken vary depending on the type of structure, the degree ofimportance of the structure, deterioration rate and the maintenance category, but recommended
standard measures are shown in Table C15.4.1.
Table C15.4.1 Appearance grades of beams and remedial measures
Appearance grade ofreinforced concrete
beamIntensified
investigation

RepairStrengthening Functional Restriction Dismantling/**
improvement in service
removalI-1(initiation stage)

X

X

X

X

I-2(initiation stage)O

I-3(initiation stage)

O

O**

X

X

O

II(propagation stage)

OO

O*

X

X

O

III(acceleration stage)

OO

OO*

X

X

OO

IV(deterioration stage)

OO

OO*

X

X

OO

O

O:standard measures（OO*:including restoration of mechanical performance）
O:measures to be taken under certain circumstances,(O):preventive measures
Strengthening**:designed to achieve performance level higher than initial level*:measures taken in accordance with criteria other than appearance grade

15.4.2 Repair and strengthening
Methods and materials for the repair or strengthening of a reinforced concrete beam
shall be selected taking into consideration performance degradation due to fatigue andlife cycle cost, so that the required effect can be achieved.

[Commentary] In cases where repair or strengthening is carried out as a remedial measure, it isnecessary to define the expected effect of repair or strengthening and the required performance(what level of performance to be maintained for how many years?). Ideally, it is desirable that
remedial measures be taken by constructing a deterioration formula (for durability) or structural
calculation formula (for load-carrying capacity and stiffness) in view of such factors as theproperties of the materials used and verifying the calculation results obtained from those formulas.
In this case, it is also important to take life cycle cost into consideration according to the remaining
service life.
In cases where preventive remedial measures are taken for a structure to which maintenancecategory A (preventive maintenance) is applied, it is necessary to select an appropriate method indue consideration of the effect expected of the method.
Repair or strengthening methods for beams deteriorated by fatigue can be classified,according to expected effects, as shown in Table C15.4.2. When deciding on which method ormaterial to use, it is necessary to take into consideration the present state of performancedegradation of the members concerned. For the correspondence between appearance grades andremedial methods, refer to Table C15.4.3.
In cases where a beam whose performance has deteriorated because of fatigue is to be251Standard Specifications for Concrete Structures-2007, Maintenancerepaired or strengthened, it must be ascertained in advance that the repair or strengthening method
and materials to be used are sufficiently safe under cyclically applied loads that will act on the beam
after the repair or strengthening is carried out. For details of various repair and strengthening
methods, refer to, for example, “Recommendations for Strengthening of Concrete Structures,”“Recommendations for Repair and Strengthening of Concrete Structures with Continuous Fiber
Sheets,” “Recommendations for Concrete Repair and Surface Protection of Concrete Structures(Japan Society of Civil Engineers)” and “Report of JCI Committee on Rehabilitation of Concrete
Structures (Japan Concrete Institute).”Table C15.4.2 Expected effects and methods of repair or strengthening
Expected effect

Example of repair/strengthening method

Restoration of safety (improvement Steel plate/FRP sheet adhesion, additional girder,of load-carrying capacity)
external cable
Restoration of serviceability

Steel plate adhesion, additional girder(improvement of stiffness)
Elimination of hazards for third party

FRP sheet adhesion

Table C15.4.3 Appearance grades and methods of repair or strengthening
Appearance grade ofbeam
I-1(initiation stage)I-2(initiation stage)I-3(initiation stage)II(propagation stage)
III(acceleration stage)
IV(deterioration stage)

Standard repair/strengthening
method－－Steel plate/FRP sheet adhesion
Steel plate/FRP sheet adhesion
Steelplate/FRP
sheet
adhesion, additional girder,
external cable

15.5 Recording(1) Investigation, deterioration prediction, evaluation and judgment, and remedial
measures shall be recorded in accordance with Part 1.
(2) Items relevant to the fatigue of reinforced concrete beams shall be recorded.

[Commentary] As a general rule, the results of investigation, deterioration prediction, evaluations
and remedial measures must be recorded in accordance with Part 1. Items relevant to fatigue
require careful attention, particularly with respect to record keeping. Items to be recorded are
indicated in 15.3.2 “Investigation in Assessment,” and 15.3.4 “Evaluation and Judgment.”252

Chapter16

Maintenance of Structures Subject to Abrasion

CHAPTER 16 MAINTENANCE OF STRUCTURES SUBJECT TOABRASION

16.1 General(1) This chapter provides standard methods for the maintenance planning,assessments, remedial measures and recording for structures that have been or are
highly likely to be subject to performance degradation due to abrasion. The items
common to all the deterioration mechanisms are shown in Part 1.
(2) This chapter shall be applied to structures of the maintenance categories A(preventive maintenance) and B (corrective maintenance).

[Commentary] (1) Abrasion means a phenomenon in which concrete cross section is gradually
reduced due to the friction caused by water flowing or wheels. Firstly, in the structures subject toabrasion, coarse aggregate is exposed owing to the reduction of mortar. With the progress ofdeterioration, coarse aggregate falls off and steel is exposed or corrodes and the cross sections ofsteel and concrete are reduced.
Abrasion is a problem in such structures as pavements, floors, underwater bridge piers, ports
and hydraulic facilities including dams and channels. In pavements and floors, abrasion occurs due
to wheel loads. In underwater bridge piers, ports or channels, abrasion occurs due to flow andimpact of water or waves. Concrete cracking, peeling and spalling sometimes occur at a certain
level of impact. Structures near the coastlines may be subject to abrasion due to come flying sand.
In cold areas, floating masses of ice sometimes induce the abrasion of offshore structures.
This chapter refers to unreinforced concrete, reinforced concrete, prestressed concrete andsteel-concrete composite structures subject to abrasion and the description focuses on concrete
structures that are deteriorated by flowing water. Descriptions concerning pavements and floors
subject to abrasion due to abrasion by wheels are given in “Standard Specifications for Pavements.”
If abrasion progresses extraordinarily, steel is exposed, corroded and reduced its cross section
as described earlier, however, in actual case few structures can be left until such a deterioration
stage without any remedial measures. This chapter refers, therefore, to the maintenance before thedeterioration reaches the deterioration level in which steel is affected. As shown in Fig.C16.1.1 andTable C16.1.1, the deterioration progress due to abrasion is divided into four stages such as, initialstage which up to the occurrence of abrasion, propagation stage which up to the exposure of coarse
aggregate, acceleration stage which up to the falling of coarse aggregate, and deterioration stage inwhich the cross section is greatly reduced and outstanding performance degradation occurs. This
chapter focuses on concrete members. In cases where only the surface coating materials forpreventing concrete abrasion including protective concrete and mortar are subject to abrasion, it isdetermined that deterioration is in the initial stage. In each stage, deterioration has varying influenceon the performance of the structure. The assessment (investigation, deterioration prediction,
evaluation or determination), and the remedial measures vary in respective deterioration stages.
Deterioration due to abrasion affects such performance attributes as serviceability and aesthetic
appearance and landscape because of the reduction of discharge owing to the increase of roughness
coefficient. Safety that is determined by load bearing capacity or other factors is not seriously
affected except for members of small cross section. Fig.C16.1.1 therefore shows performancedegradation focusing on serviceability and aesthetic appearance and landscape.
253

Performance degradationof member

Deterioration due
to abrasion

Standard Specifications for Concrete Structures-2007, MaintenanceOutcrop of coarse
aggregates

Falling of coarse
aggregate

Occurrence ofabrasion

Initiation
stage

Propagation
stage

Acceleration
stage

Deterioration
stage

Fig. C16.1.1 Conceptual view of deterioration progress due to abrasion

Table C16.1.1 Definition of deterioration stages
Stage of deterioration

Definition

Initiation stage

Until the occurrence of abrasion of concrete

Propagation stage

From the occurrence of abrasion to the exposure of coarse aggregate

Acceleration stage

From the exposure to the falling of coarse aggregate

Deterioration stage

Outstanding degradation of performance due to the reduction of crosssection caused by abrasion

Major factor
determining duration

Abrasion rate(2) Maintenance category B (corrective maintenance) has been designated for numerous
existing structures. In the future, maintenance category A (preventive maintenance) is expected to
be designated for more structures. In maintenance category A, remedial measures are taken early
before performance degradation due to deterioration in view of the life-cycle cost. This chapter
therefore mainly discusses structures to which maintenance category A or B is applied. Structures towhich maintenance category C (observation-based maintenance) is applied should also be
maintained by a basic method described in this chapter wherever possible.
For the matters that should be considered when determining the maintenance category forstructures that have been or are expected to be subject to deterioration due to abrasion, refer to
16.2.2 "Determination of Maintenance Category." Special matters to be considered for respective
maintenance categories are also described in this chapter.

254

Chapter16

Possibility ofabrasion(16.2)

Maintenance of Structures Subject to Abrasion

Maintenance plan forthe structures(16.3)
Assessment(16.3.2.2)
Investigations ininitial assessment
Standard
investigation(16.3.2.5)
Detailed
investigation(16.4)

Deterioration
prediction(16.3.3)

Remedial
measure(16.5)

Evaluation andjudgment(16.3.4)

Recording(16.3.2.3,4)
Investigations in
Routine/ regularassessment
Normalexamination(16.3.3)(16.3.4)(16.3.2.5)
Detailed
inspection

Deterioration
prediction

Evaluation andjudgment

Figures in the parentheses indicate the related section or paragraph of this chapter.

Fig.C16.1.2 Standard maintenance procedure against abrasion

16.2 Maintenance Planning
16.2.1 Basics of planning
In order to maintain a structure subject to abrasion, the category of maintenance shallbe selected, the service period planned, and a maintenance planning for activities
including assessment, remedial measures and recording drawn up in advance in view ofthe service and environmental conditions such as the flowing water.

[Commentary] When drawing up a maintenance planning, it is necessary to cover such details ascheck items and procedures for initial assessment and check items, procedures, timing andfrequency for the investigations in routine and regular assessment, evaluation and judgment
255

Standard Specifications for Concrete Structures-2007, Maintenancemethods, actions to be taken in the event of deterioration, and recording methods, taking into
consideration the type, degree of importance and planned service period of the structure, category of
maintenance, and the quality of materials.
The type of structure, size and environmental conditions of concrete structures vary fromstructure to structure. A maintenance planning must be optimized for each structure. The progress ofdeterioration of structures subject to abrasion is greatly affected by the flow velocity, sedimentcontent in flowing water and the quality of concrete. An appropriate maintenance planning needs tobe drawn up, therefore, in view of these factors.
It is usually difficult, at the stage of maintenance planning, to accurately predict the state of astructure during its service period. It is therefore good practice to draw up a maintenance planningwith reference to the deterioration of a similar structure or a structure in a similar environment.

16.2.2 Determination of maintenance category
The category of maintenance of a structure subject to abrasion shall be selected inview of the degree of importance of the structure, the type of structure, hazards for third
party, the planned service period and the characteristics of deterioration due to abrasion.

[Commentary] The determination of the category of maintenance is very important because
maintenance planning varies widely depending on the category of maintenance. The progress ofdeterioration and performance degradation due to abrasion is conceptually illustrated in Fig.
C16.1.1.
Structures to which maintenance category A (preventive maintenance) is applied should bemaintained so that they might be placed under the condition during the initiation stage withdeterioration only of the protection layers or concrete abrasion not yet starting, to prevent
performance degradation. The state of the structure should therefore be identified as accurately as
possible. Requirements include the following.
(i) Identification of the effects of abrasion factors on the structure surface(ii) Quantitative evaluation and prediction of the abrasion of the protection layer
Elimination of large-scale repair or strengthening is also important objective.
Structures to which maintenance category B (corrective maintenance) is applied should bemaintained so as to prevent the performance of the structure from failing to meet the requirements.
Structures should be maintained to prevent deterioration from reaching the deterioration stage toensure safety, the propagation stage to achieve serviceability or to keep aesthetic appearance andlandscape. Certain actions should be taken when any of the following types of deterioration has
been detected.
(i) Abrasion of concrete surface(ii) Exposure of coarse aggregate(iii) Falling of coarse aggregate
For structures to which maintenance category B is applied, remedial measures should be taken
256Chapter16

Maintenance of Structures Subject to Abrasionin phase (i) or (ii) above because it is extremely difficult to stop the progress of abrasion once
started. It should be noted that large-scale measures will be required if deterioration reaches phase(iii) .
One maintenance category is generally applied to one structure. In cases where theenvironmental conditions vary from region to region or from member to member, however,
applying different maintenance categories to different regions or members may sometimes be
effective. For example, in a channel, maintenance category A (preventive maintenance) is applied tothe invert, which is vulnerable to abrasion and category B (remedial maintenance) is applied to sidewalls.

16.2.3 Preparation of maintenance manuals
A maintenance manual describing methods, procedures and frequency requirements
should be prepared for each structure in accordance with the maintenance planning,taking the structure-specific conditions into consideration.

[Commentary] The service period of civil engineering structures is long, and maintenance of
those structures is performed over a long period of time. It is recommended, therefore, that in order
to inform investigators of maintenance concepts and policies, a maintenance manual be prepared sothat detailed procedures and methods can be communicated accurately even to newly assigned
responsible engineers.
Under certain circumstances such as in cases where the original maintenance planning isaltered because the actual progress of deterioration turned out to differ from that assumed in theoriginal maintenance planning, it is necessary to modify the maintenance manual and takeappropriate maintenance measures accordingly.

16.3 Assessment
16.3.1 GeneralIn the assessment of a structure whose performance has declined or is highly likely todecline because of abrasion, investigation, evaluation of the present state, prediction ofdeterioration and judgment of necessity for remedial measures shall be appropriately
conducted in accordance with the maintenance planning.

[Commentary] In order to maintain concrete structures appropriately, this specification requires
three types of assessment: initial assessment, periodic assessment and extraordinary assessment.
Because the initial and periodic assessments are essential for the maintenance of structures subject
to abrasion, this chapter stipulates that those assessments must be conducted. Extraordinary
assessments are regarded as assessments to be conducted on an as-needed basis and are therefore
not dealt with in this chapter. By conducting periodic assessments during the maintenance period,change of appearance of structures can be discovered before they occur or in early stages, andremedial measures including preventive measures and repairs can be taken systematically.

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Standard Specifications for Concrete Structures-2007, Maintenance16.3.2 Investigation in assessment
16.3.2.1 General
Investigations in initial, routine and regular assessment of a structure subject toabrasion shall be conducted appropriately according to the category of maintenancerequired for the structure. Prior to investigation, check items, methods, frequency andscope of standard investigation shall be determined appropriately. For each type ofassessment, detailed investigation shall also be conducted on an as-needed basis.

[Commentary] It is important to select check items, methods, frequency and scope ofinvestigation appropriately according to the purpose of investigation in accordance with themaintenance planning.
The major parameters that should be identified in investigations of structures subject toabrasion are the degree of abrasion (depth and area) and the abrasion rate. In cases where
deterioration has progressed considerably, investigations should be conducted to directly evaluate
performance. Here, the abrasion rate means the progress rate of sectional reduction depth from theconcrete surface.
The items to be examined in investigations vary according to the degree of deterioration. In
cases where it has been determined or assumed that the deterioration was in the initiation stage,investigations should be conducted mainly to identify the progress of change of appearance. In
cases where it has been determined or assumed that the deterioration was in or beyond the
propagation stage, investigations should be conducted mainly to identify the progress of abrasion.
Table C16.3.1 shows major items to be examined in the respective stages. Data on the items related
to deterioration prediction such as the degree of abrasion and the environmental action (e.g. flow
velocity, sediment content and head) should be collected in as early a stage as possible.
The frequency and range of investigation should be determined considering the maintenancecategory, environmental conditions, structural format and the state of deterioration for the structure.
Abrasion is likely to occur at the points of cross-sectional change, in curves where velocity changes
or at locations subject to impact loads due to high head. Intensive investigation should be made atthese points as well as investigations throughout the structure.
Regardless of the category of maintenance, it is important to go through the design drawings
and specifications, construction records, investigation results and the repair history prior to theinvestigation of a structure.
If the state of a structure cannot be judged appropriately by standard investigation, detailed
investigation must be conducted.

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Table C16.3.1 Main check items in investigation
Stage of Deterioration

Initiation

Propagation

Acceleration

Deterioration

Change of appearance

O

O

O

O

Degree of abrasion

▲

O

O

O

Environmental action

▲

▲*

▲*

O

Concrete strength

▲

▲

▲

▲*

O

: Items to be investigated on a priority basis▲: Items that should preferably be investigated▲* : Items to be investigated on an as-needed basis

16.3.2.2 Investigation in initial assessment(1) In initial assessment, appropriate check items for standard investigation shall beselected for newly constructed structures, existing structures, large-scale repairs
and strengthened structures.
(2) If deterioration prediction, evaluation or judgment is difficult to make through astandard investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigation in initial assessment is the first investigation conducted when themaintenance of a concrete structure is started. Investigation in initial assessment includes not only
the first investigation of a newly constructed structure conducted before it goes into service but also
the first investigation of an existing structure or a structure for which remedial measures have beentaken in response to deterioration. Check items for the investigation may vary from structure to
structure. Basic check items for standard investigations in initial assessment of a newly constructedstructure are the document search on the design drawings and specifications and construction
records and observation. It is good practice to check on such details as concrete cover, the state ofsteel and porosity through nondestructive testing on an as-needed basis. When investigating a
structure for which remedial measures have been taken, it is also important to check for problems inrepaired or reinforced parts of the structure. These should be included in check items of standard
investigation. When an existing structure is investigated, check items are similar to those for a
newly constructed structure if design drawings and specifications and construction records exist. If
there is no such document or record, it is necessary to select check items of standard investigation
with reference to 16.3.2.5 “Detailed Investigation.” In cases where a prediction needs to be madewith high accuracy about a structure to which maintenance category A (preventive maintenance) is
applied, it is necessary to conduct investigations concerning the parameters used for the method
described in 16.3.3 “Methods for Predicting Degradation of Performance Degradation of
Structures.”
Extremely important items in the investigation in initial assessment of a structure subject toabrasion are listed below.

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Standard Specifications for Concrete Structures-2007, Maintenance(i) Environmental and loading conditions(ii) Concrete strength (or water-cement ratio)(iii) Type and volume of the additive(iv) Initial defect(v) Condition of abrasion (depth and area)(vi) Condition of repaired or strengthened sections
Item (i) is essential to the prediction of progress of abrasion. Identifying the flow velocity,
sediment content and head is required. Items (ii) and (iii) are important when evaluating theabrasion resistance of concrete, or the abrasion rate. Item (v) greatly affects the durability ofstructures regardless of abrasion. Detecting this item in the investigation in initial assessment isimportant. In sections with poor concrete filling in particular, the velocity of abrasion increases andthe performance of the structure is greatly affected.
When investigating an existing structure, identifying the degree of abrasion (depth and area)(item (v)) in addition to items (i) through (iv) is important. Investigating the deformation in repaired
or strengthened sections and the condition of deformation (e.g. swelling or peeling of surface
coating) (item (vi)) is also important.
(2) If evaluation and judgment cannot be made with high accuracy by standard investigation
alone, detailed investigation is necessary. Check items of detailed investigation are indicated in
16.3.2.5 “Detailed Investigation.”

16.3.2.3 Investigation in routine assessment(1) In routine assessment, investigation shall be conducted to detect not only thedefect of concrete surface such as degree of abrasion (depth and area), cracking
in concrete, peeling and spalling of concrete covering but also the deterioration inappearance such as displacement and deformation.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) The purpose of investigation in routine assessment is to detect deterioration at
an early stage by checking on defect in the state of a structure over time. The determination of thetime at which deterioration began in order to obtain information that is useful for predicting
deterioration is another important purpose of the investigation. In the investigation focus should beplaced on deterioration phenomena or their indicators such as abrasion, cracking, peeling andspalling of concrete covering, displacement and deformation.
Exclusively inspecting the sections where deterioration was expected to progress as a result of
initial assessment is also effective.
(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone or if severe deterioration has already occurred, detailed investigation is conducted. Check260

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items of detailed investigation are described in detail in 16.3.2.5 “Detailed Investigation.”

16.3.2.4 Investigation in regular assessment(1) The purpose of investigation in regular assessment is to obtain information that isdifficult to obtain in routine assessment. In regular assessment, standard
investigation consisting of detailed observation of defects shall be conducted as
in routine assessment. Addition to that environmental action should be identified.
(2) If deterioration prediction, evaluation or judgment is difficult through standard
investigation alone, detailed investigation shall be conducted.

[Commentary] (1) Investigation in regular assessment is conducted for obtaining the information
more detailed than that in routine assessment. Areas where signs of defects or deterioration havebeen detected in initial or routine assessment need to be examined intensively. The appearance ofthe structure should basically be examined as in routine assessment. Identifying the locations whereabrasion is likely to occur based on the investigation results and preparing a deterioration map are
effective for grasping time-based change in deterioration.
In some cases, the service environment or use condition of a structure may change. It istherefore important to regularly identify the changes in discharge and sediment content.
When measuring the depth and area of abrasion in regular assessment, measurements should
be taken three or more frequently during the expected stage of deterioration.
For the structures for which maintenance category A (preventive maintenance) is designated,the frequency of measurement should be increased during the expected initiation stage andpropagation stage.
(2) If high-accuracy evaluation or judgment is difficult by conducting standard investigation
alone or if severe deterioration has already occurred, detailed investigation is conducted. Checkitems of detailed investigation are described in detail in 16.3.2.5 “Detailed Investigation.”

16.3.2.5 Detailed investigation
Detailed investigation shall be conducted to obtain detailed information on a structure
subject to abrasion in cases where the deterioration of the structure is difficult to predict,evaluate or judge by standard investigation alone in initial, routine or regular assessment.
Check items, methods and location of a detailed investigation shall be selected
appropriately taking into consideration such factors as the purpose of investigation andthe accuracy of obtained results.

[Commentary] When the determination of the present state of a structure and the deterioration
prediction of the structure are difficult by standard investigation alone, detailed investigation isconducted in order to obtain the information necessary for those purposes. Examples ofinvestigation items for structures subject to abrasion, and of data on the condition of the structure at
the time of investigation and those in the future estimated from the investigation results are listed in
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Table C16.3.2. The evaluation items estimated from data in the table are evaluated after
deterioration is predicted.
Major check items are outlined below. For other measurement items or testing methods thanthose described below, refer to 4.7 "Investigation."(i) Degree of abrasion (depth and area)
The depth of abrasion is defined as the variance between the level of concrete surface at thetime of construction and that at the time of investigation. The depth from the concrete surface
without abrasion to the concrete surface subject to abrasion is measured at several points. The
maximum, minimum and mean values are obtained. For obtaining the area of abrasion, the area isrecorded using photographs and sketches and the lengths of long and short sides are measured.
Before the measurement, the weakened surface portion should be removed until the sound concrete
is exposed.
(ii) Environmental action
The progress of abrasion varies greatly according to the environmental actions of flowing
water, waves and other factors. Even where concrete of the same quality is used, deterioration
progresses slowly under moderate environmental actions and quickly under severe conditions.
Factors of actual environmental actions such as flow velocity, discharge, head, sediment content,
wave force and height, etc. should be identified for evaluating the performance and predicting thedeterioration of the structure.
(iii) Appearance of structures
In cases where performance of structure cannot be evaluated direct from the state of concrete,
the defect of appearance provides important data for performance evaluation. The grades ofappearance of structures deteriorated due to abrasion are shown in Table C16.3.3.

Table C16.3.2 Examples of evaluation items in detailed investigation
Measurement item

Data obtained by investigation

Evaluation items predicable fromobtained data

Degree of abrasion(depth and area)

Degree of abrasion (depth and area)
abrasion rate, load carrying capacity,
permeability and aesthetic appearance

Degree of abrasion (depth and area),load carrying capacity, permeability
and aesthetic appearance

Cracking(width, depth and density)

Cracking (width, depth and density),rate of progress of cracking andaesthetic appearance

Cracking (width, depth and density)and aesthetic appearance

Concrete strength andmodulus of elasticity

Concrete strength, stiffness and load
carrying capacity

Condition of abrasion (depth and area),
stiffness and load carrying capacity

Environmental action(discharge, flow velocity,
sediment content and wave
condition)

Environmental conditions, abrasion
rate and permeability

Condition of abrasion (depth and area)and permeability

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Table 16.3.3 Grades of structural appearance and stage of deterioration
Grade of appearanceState of deterioration

I(Initiation stage)

No abrasion of concrete

II(Propagation stage)

exposure of coarse aggregate, but no falling of coarse aggregate

III(Acceleration stage)

Falling of coarse aggregate falls

IV(Deterioration stage)

Coarse aggregate falls remarkably and the cross section is reduced over a widearea.

16.3.3 Methods for predicting performance degradation of structures
16.3.3.1 General(1) In the maintenance of a structure subject to abrasion the performance of thestructure shall be evaluated quantitatively at the time of investigation, and futuredegradation shall be predicted.
(2) In order to predict the performance degradation of a structure, deterioration due toabrasion shall be predicted quantitatively.
(3) If (2) is difficult, an alternative method is to predict performance degradation by
estimating the length of the initiation, propagation, acceleration and deterioration
stages, taking the progress of abrasion into consideration.
(4) Deterioration shall be predicted on the basis of investigation results.

[Commentary] (1) and (2) In the performance verification based maintenance system, changes(deterioration) in various performance attributes inherent in the structure should be predicted. To
that end, the progress of material deterioration should be predicted quantitatively. The performanceof the structure and the degree of deterioration of materials constituting the structure should be
evaluated quantitatively at the time of investigation and the end of planned service period.
Performance degradation of the structure or the degree of deterioration of materials constituting thestructure at the time of investigation may be evaluated quantitatively by an appropriate method
based on investigation results. The performance or the degree of deterioration at the end of theplanned service period should be predicted quantitatively based on the previous periodic
assessments. The prediction of deterioration progress is not always in agreement with actual
progress of deterioration. The method of prediction should therefore be reviewed based on the
results of investigations to be conducted later.
(3) When evaluating various performance attributes of a structure by combining the results ofprediction of deterioration progress of concrete and steel that constitute the structure, quantitative
prediction is difficult at the present technological level. Then, predicting the lengths of initiation,
propagation, acceleration and deterioration stages considering the progress of concrete abrasion is arealistic approach. The respective stages of deterioration and the factors determining their lengths263

Standard Specifications for Concrete Structures-2007, Maintenanceare shown in Table C16.1.1. The prediction methods are described in 16.3.3.2 "Prediction ofabrasion."(4) Investigation results are related to either the quality of concrete of the structure or theenvironment in which the structure is placed while in service. These parameters should be used as abasis for predicting deterioration. If the structure is now being planned or no investigation result isavailable for the existing structure, investigation results or deterioration conditions of similar
structures under the similar environment may be consulted.

16.3.3.2 Prediction of abrasion(1) The progress of abrasion shall be predicted properly considering the quality ofconcrete and the environment in which the structure is in service.
(2) The progress of abrasion may be predicted by one of the following methods.
(i) Method based on the degree of abrasion obtained from investigation results(ii) Method based on the investigation results for a similar structure under the sameenvironment(iii) Evaluation in an abrasion test

[Commentary] (1) The abrasion rate is determined by the mix proportions and strength of
concrete, flow velocity and sediment content, strength and frequency of waves and whether impact
is applied or not. Generally, the lower the water-cement ratio of concrete, the more dense andstronger the concrete. Then, abrasion progresses slowly. Surface treatment using materials thatdensify concrete surface is also expected to increase abrasion resistance. Even for concrete of thesame quality, the abrasion rate naturally varies according to the acting load. The higher the flow
velocity, the higher the abrasion rate. In cases where the flowing water contains deposit, theabrasion rate increases even at the same flow velocity owing to the force of abrasion. Deterioration
may sometimes progresses considerably on an apron of a weir with a head owing to impact loads.
When predicting the progress of abrasion, therefore, both the physical properties of concrete and theenvironmental actions should be evaluated properly.
(2) Three major methods for predicting the progress of abrasion are described below.
(i) Methods based on the degree of abrasion obtained in investigations
In cases where the time-based change in degree of abrasion has been predicted ininvestigations, the progress of abrasion may be predicted through the regression of the result. Under
the same loading conditions, it may be assumed that the abrasion rate is nearly constant and that thedegree of abrasion is in proportion to time. The abrasion rate should be estimated based on themeasurements taken at three or more ages.
(ii) Method based on the investigation results for a similar structure under the sameenvironment
If no investigation results are available for the structure, the progress of abrasion may be
predicted based on the investigation results for a similar structure under the same environment.

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Maintenance of Structures Subject to Abrasion(iii) Evaluation in abrasion testing
No method has yet been established for quantitatively predicting abrasion. If no investigation
results are available, therefore, the abrasion rate should be predicted in abrasion testing properly
considering the concrete mix proportions and environmental actions (e.g. flow velocity andsediment content).

16.3.3.3 Modification of prediction
If the state of deterioration determined in an investigation differs from a predictedstate of deterioration, the cause of the difference shall be identified and the prediction
shall be revised accordingly. If necessary, the maintenance planning shall be altered.

[Commentary] When the deterioration confirmed in investigations is different from the prediction,
appropriate investigations should be conducted using the deterioration prediction methods shown in
16.3.3.2 "Prediction of abrasion" and based on Table C16.3.2 to examine the cause for thedifference, and the prediction should be modified. Then, the results of several investigations
conducted until that are useful to the examination of causes and the modification of the prediction.
Revising the subsequent maintenance plans including a review of investigation frequency based on
the modified prediction is also important.

16.3.4 Evaluation and judgment(1) The evaluation of performance and judgment as to whether remedial measuresneed to be taken based on the results of the investigation in initial, routine andregular assessment shall be made in accordance with Part 1 and Item (2) andsubsequent items in this section.
(2) The performance of a structure subject to abrasion shall be evaluated byappropriately selecting performance attributes to be evaluated in view of the stageof deterioration of the structure.
(3) The evaluation of performance attributes at the time of investigation and at theend of the planned service period of the structure should be made by aquantitative method.
(4) If Item (3) is difficult to achieve, the evaluation of performance attributes at thetime of investigation and at the end of the planned service period of the structure
may be made by a semi-quantitative grading-based method.
(5) Judgment as to whether remedial measures need to be taken shall be made inview of the degree of performance degradation due to abrasion, the degree ofimportance of the structure, category of maintenance, and the remaining service
life.

[Commentary] (1) The evaluation of performance and judgment of necessity for remedial
measures in initial, routine and regular assessment for structures in which little progress ofdeterioration has been recognized are frequently more or less the same regardless of thedeterioration mechanism. For details, refer to Part 1. The evaluation of performance and judgmentof necessity for remedial measures for structures in which deterioration may have or has progressed265Standard Specifications for Concrete Structures-2007, Maintenancevary according to the deterioration mechanism. When discussing the performance degradation due
to abrasion, the descriptions in this chapter should be consulted.
(2) In the structures subject to abrasion, the performance attribute to be affected bydeterioration varies depending on whether deterioration is in the initiation, propagation, acceleration
or deterioration stage. The performance attribute to be evaluated should be properly selected foreach stage of deterioration. In the propagation stage for example, the cross section is likely to be
reduced with the progress of abrasion. In hydraulic structures, the water permeability capacity
determined by the change in roughness coefficient should be evaluated. In the acceleration stage,
the cross section is likely to be reduced as coarse aggregate is exposed. Evaluations should be madeto verify further deterioration of water permeability capacity due to the increase of roughness
coefficient, or aesthetic deterioration. In the deterioration stage, relatively large cross sections are
reduced as a result of falling of coarse aggregate. Attention should be paid not only to the items
worth noting in the acceleration stage but also to safety that is determined by such factors as load
bearing capacity, and to the deterioration of serviceability due to water leakage through the reduced
cross section.
(3) The performance of a structure at the time of investigation and at the end of the planned
service period should be evaluated after evaluating the deterioration of concrete and steel. For
evaluating the performance of a structure at the time of investigation, safety is checked by obtaining
the load bearing capacity, etc. by, for example, substituting the dynamic properties of materials
obtained from investigation results into a structural calculation formula. Also conceivable is thechecking of serviceability by obtaining the discharge and the checking of aesthetic appearance andlandscape by examining the exposure of coarse aggregate and the range and density of cracking,peeling and spalling. Performance can be evaluated relatively explicitly at the time of investigationby checking the effects in cases where deterioration is not serious. Evaluating performance at theend of the planned service period fully accurately is, however, difficult. As a supplementarymeasure, deterioration is generally predicted based on the abrasion rate using the methods shown in
16.3.3 “Methods for Predicting Performance Degradation of Structure”. Then, the accuracy of thedeterioration prediction method as well as the accuracy of the performance checking method isimportant. Prediction methods should therefore be selected carefully. Adequate safety should beguaranteed.
(4) In the performance verification type design system, structural performance should ideallybe evaluated quantitatively. At present, however, there is no established method of quantitative
estimation. As a practical method, the performance of a structure can be evaluatedsemi-quantitatively, with reference to Table C16.3.3, by performing appearance grading inaccordance with Table C16.3.4.
The purpose of grading is to classify the present degree of deterioration of a structuresemi-quantitatively instead of predicting and evaluating the degree of deterioration in future. It isalso possible, however, to predict the performance of a structure at the end of the planned service
period in accordance with Table C16.3.4 by estimating the stage of deterioration at the end of theplanned service period on the basis of investigation results such as the abrasion rate. The method of
estimating the degree of deterioration at a certain point of time in future by constructing adeterioration grade model based on a stochastic theory such as a Markov model has also been
proposed.
If detailed maintenance records for a similar structure (type of structure, materials,
construction, environment, state of use) are available and its progress of deterioration is also similar
to that of the evaluated structure, then the evaluation results for the similar structure provide useful266

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information.
(5) Because judgment is the act of deciding whether remedial measures need to be taken on thebasis of structural performance evaluation results, there is no difference depending on deterioration
factors. Therefore, refer to Part 1.

Table C16.3.4 Grades of appearance of structures and typical performance degradation
Grade of appearance ofstructure

SafetyServiceability

Aesthetic appearance
and landscape

I(Initiation stage)

-

-

-

II
(Propagation stage)-

III(Acceleration stage)-IV(Deterioration stage)- exposure of coarse
aggregate

Degradation of load
carrying capacity andductility

Reduction of discharge-Increase of roughness
coefficient-Leakage-Cracking-Peeling-Spalling-Reduction cross sectionof concrete

16.4 Remedial Measures
16.4.1 Selection of remedial measures(1) If it has been judged that remedial measures need to be taken in connection withperformance degradation of a structure subject to abrasion, remedial measures bywhich the corrected structure meets the required performances shall be selected.
(2) If it is difficult to select remedial measures for a structure on the basis ofperformance verification, remedial measures may be selected from the measurescorresponding to the grade of appearance.

[Commentary] (1) If it has been judged, as a result of evaluation, that remedial measures need tobe taken, it is necessary to select one or more of the following measures: (i) intensified investigation,(ii) repair, (iii) strengthening, (iv) functional improvement or (v) restriction in service. Basically,
decisions as to which measures to take should be made by the maintenance manager of the structure,but it is good practice to refer to Part 1 for information on typical relationships between evaluationand judgment results and remedial measures.
(2) If it is difficult to select remedial measures for a structure through quantitative evaluationor judgment, remedial measures are selected from the measures corresponding to the deterioration
grade of the structure. Remedial measures to be taken vary depending on the type of structure, thedegree of importance of the structure, deterioration rate and the category of maintenance, but
recommended standard measures are shown in Table C16.4.1. Taking remedial measures forstructures to which maintenance category A (preventive maintenance) is designated in the initiation
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Standard Specifications for Concrete Structures-2007, Maintenancestage in which no outstanding abrasion occurs is important from a preventive viewpoint. It is also
important to take remedial measures for structures to which maintenance category B (corrective
maintenance) is designated, for preventing deterioration before it becomes outstanding, considering
the rate of progress of deterioration.

Table C16.4.1 Grades of appearance of structure and remedial measures
Stage of deterioration
I (Initiation stage)
II (Propagation stage)

Intensified
investigation

OOO

III (Acceleration stage)
IV (Deterioration stage)

Repair

O*
OO
OO
OO*

Strengthening**
X

Functional
improvement
X

X

X

X

X

X

X

Restriction inserviceO

OO: Standard remedial measures [OO*: Including the restoration of mechanical performance]
O: Remedial measures in some cases [OO*: Preventative measures]
X: Remedial measure taken based on other criterion than the grade of appearance
Strengthening** : Enhancing the mechanical performance above the initial level

16.4.2 Repair and strengthening
Methods and materials for the repair or strengthening of a structure shall be selectedtaking into consideration the performance degradation of the structure due to abrasion
and life cycle cost, so that the required effect can be achieved.

[Commentary] In cases where repair or strengthening is carried out as a remedial measure, it isnecessary to define the expected effect of repair or strengthening and the required performance(what level of performance to be maintained for how many years?). Ideally, it is desirable that
remedial measures be taken after constructing a deterioration formula (for repair) or structural
calculation formula (for strengthening) in view of such factors as the properties of the materials
used and verifying the calculation results obtained from those formulas. In this case, it is also
important to take life cycle cost into consideration according to the remaining planned service
period.
When taking preventive measures for a structure to which maintenance category A(preventive maintenance) is applied, an appropriate method should be selected fully considering theeffect that should be achieved by the method.
The methods of repair or strengthening for structures subject to performance degradation due
to abrasion are listed in Table C16.4.2 by expected effect.

Table C16.4.2 Expected effects and methods of repair or strengthening
Expected effect

Example of method268

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Control the progress of abrasion

Surface treatment(including coating, adhesion of abrasive-resistant materials and impregnation)

Reduce roughness coefficient

Surface treatment and repair of cross section

Secure member cross section

Surface treatment

Enhance load carrying capacity

Adhesion of steel or fiber reinforced plastic plates, lining and replacing

When selecting the method, Table C16.4.2 and the present performance degradation of thestructure should be considered. For the grades of deterioration of appearance and remedial measures,refer to Table C16.4.3.
In the initiation stage, surface treatment may be applied to prevent the abrasion of concretesurface. In the propagation or acceleration stage, repairing the cross section reduced by abrasion iseffective. Then, surface treatment may be applied to prevent abrasion in the section of cross section
to be repaired. In the deterioration stage, dynamic properties may have been deteriorated in suchterms as load bearing capacity and roughness. Then, enhancing the dynamic properties by adhering
steel or fiber reinforced plastic plates or applying lining is important. Also in this case, surface
treatment for preventing abrasion after the implementation of remedial measures is desirable.
Many of the repair or strengthening methods applied have been developed only recently andfew have been applied to actual structures. If such methods are adopted, the structure may be
re-deteriorated and its performance may be degraded due to the factors not expected in the designphase. Measures should therefore be taken such as increasing the frequency of investigations after
the repair or strengthening.
For details of the methods of repair and strengthening, refer to the “Guidelines forStrengthening Concrete Structures (draft),” “Guidelines for Design and Implementation of Surface
Protection (draft),” “Shotcreting Guidelines(draft) - Repair and Strengthening” and otherdocuments.

Table C16.4.3 Appearance grades of structural and standard methods of repair orstrengthening
Appearance grade of structure

Example of method

I (Initiation stage)

Surface treatment*

II (Propagation stage)

Repair of cross section and surface treatment*

III (Acceleration stage)

Repair of cross section and surface treatment*

IV (Deterioration stage)

Adhesion of steel or fiber reinforced plastic plates, lining, replacing
and surface treatment*

16.5 Recording(1) Investigation, deterioration estimation, evaluation and judgment, and remedial
measures shall be recorded in accordance with Part 1.
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Standard Specifications for Concrete Structures-2007, Maintenance(2) Items relevant to abrasion shall be recorded.

[Commentary] As a general rule, the results of investigations, deterioration estimations,evaluations and remedial measures must be recorded in accordance with Part 1. Items relevant toabrasion require careful attention, particularly with respect to record keeping. Items to be recorded
are indicated in Section 16.3.2 “Investigation in Assessment" and the evaluation items indicated in
Section 16.3.4 “Evaluation and Judgment.”

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Chapter 17 Seismic Retrofit

CHAPTER 17 SEISMIC RETROFIT

17.1 General
This chapter provides basic matters concerning the planning, assessments, selectionof methods, design, construction, post-retrofit maintenance and recording for seismic
retrofit of existing structures.

[Commentary] Seismic design standards for structures stipulate the levels of earthquake motions
to be considered and required seismic performance according to the technical level at the time when
the standards were established. Seismic design standards have undergone revisions as earthquake
motions stronger than the design level frequently damaged structures or caused structures tocollapse and new technologies were developed. Each time the standards were revised, theearthquake motions to be considered or seismic required performances for structures and members
were upgraded. In the Hyogoken-Nambu Earthquake of 1995, numerous structures were damaged
or collapsed. As a result, the levels of earthquake motions to be considered were raised considerably
in highway and railway design standards including the “Standard Specifications for Concrete
Structures.” The structures that were designed before the revision of seismic standards therefore nolonger meet the latest seismic standards. The seismic retrofit of non-conforming structures is an
important issue in maintenance. Existing structures are in large numbers and many are not incompliance with standards. When applying seismic retrofit, therefore, it is important to prepare aplan for effective retrofit considering the importance of the structure and the level of retrofit.
This chapter provides a basic idea of seismic retrofit for improving the seismic performance ofexisting structures. The restoration of structures damaged by earthquakes is, however, discussed inPart 1 because repair or strengthening is applied based on the results of extraordinary assessments
conducted after accidental loads are applied.

17.2 Seismic Retrofit Planning(1) The seismic retrofit plan shall be prepared considering the characteristics of thestructure or member to be strengthened, objective of service, available seismic
performance, seismic performance to be provided, importance, emergency and cost
performance.
(2) The seismic retrofit plan should generally present information concerning theselection of methods of seismic assessment and seismic retrofit, retrofit design,
construction and recording.

[Commentary]

The seismic retrofit plan should be prepared properly to retrofit a structure or member inconformity with its conditions that are identified in advance. To that end, the characteristics of the structure
or member to be strengthened, objective of service, available seismic performance, seismic performance tobe provided, importance, emergency and cost performance should be identified. Various types of concrete
structures exist such as bridges, port facilities, tunnels and plant facilities and have unique characteristics.
Seismic retrofit of ground-level structures is relatively easy. On the other hand, retrofit is not so easy forunderwater structures such as piers and other port facilities, and bridge piers installed in rivers, orunderground structures such as tunnels and foundations because the building of a coffer dam or large-scale

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Standard Specifications for Concrete Structures-2007, Maintenanceexcavation is involved. When preparing a seismic retrofit plan, these points and social impacts described
below should be taken into consideration.

(i) The suspension of service due to the damage to a structure or collapse of a structure impacts
the escape, relief and rescue activities during a disaster and the prevention of secondary disasters.
The delay of restoration influences the regional life and economic activities. Not only the difficulty
in restoration and the construction cost but also the social impacts of structural damage should beconsidered.
(ii) In cooperation with a plan for escape and relief activities during a great earthquake,developing a plan for retrofit emergency required important structures such as the key
transportation hubs like airports and seaports and channels between these facilities is important.
(iii) Infrastructure systems such as highways, railways, and water and power supply systems
function as a network. Infrastructure can keep working if an alternative route is available tocompensate for the suspension of a route. In view of such a condition, structures should beprioritized for seismic retrofit.
(iv) The leakage of the contents of oil or gas tanks at the time of serious damage to thefacilities during an earthquake has great influences in the vicinity. Seismic retrofit of the structures
involving high risk or facilities required for power generation or gas supply should be given a highpriority.

17.3 Seismic Assessment
17.3.1 General
When planning seismic retrofit, the seismic performance of the structure shall be
evaluated properly considering the importance of the structure, emergency and cost
performance for the purpose of identifying the currently available seismic performance ofthe structure and judging the necessity for seismic retrofit.

[Commentary] When planning seismic retrofit, seismic performance of the structure should be
evaluated to judge seismic performance before seismic retrofit. In simple assessment, seismic
performance is estimated based on the design concept at the time of design and construction of thestructure. Detailed assessment is conducted based on the results of directly investigation of thestructure. Seismic performance should be judged fully considering the importance of the structure,
emergency and cost performance, and the opinions of the responsible or professional engineer.

17.3.2 Investigation for seismic assessment
Literature surveys shall be basically conducted to evaluate seismic performance. In
cases where available data are inadequate or insufficiently accurate, or the structure has
been deteriorated, detailed investigation shall be conducted.

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Chapter 17 Seismic Retrofit[Commentary] For evaluating the present seismic performance of a structure or member, theequation for evaluation used in structural design is generally employed. Then, data such as thedimensions of members, arrangement of reinforcing bars and the strength of members is required.
In the inspections for seismic performance evaluation, surveying literature such as design drawingsand completed building drawings is a basic practice.
Detailed investigation should be conducted to evaluate seismic performance in the following
cases.
(i) Where evaluating seismic performance is difficult because of a lack of design or completedbuilding drawings(ii) Where the structure has been deteriorated
In case (i), the arrangement of reinforcing bars should be verified by nondestructive or small scale
destructive testing. The shape of the hook at the anchorage of reinforcement, arrangement of shear
reinforcement and whether the main reinforcement has intermediate anchorages or not influence theductility or flexural strength of members, which is important to seismic performance. Detailed
investigation should be conducted if details of reinforcing bar arrangement are unknown.
In case (ii), detailed investigation should be conducted to examine whether or not the equationfor evaluating the seismic performance of sound members used in design is applicable todeteriorated structures, and to collect quantitative data for input into the equation. In cases where
detailed investigation have been conducted in routine or other assessment to identify the conditionof deterioration, the results may be used for evaluating seismic performance. In cases where no
outstanding deterioration has been found by visual observation but initial deterioration has or may
have occurred, detailed investigation should be conducted. Then, whether detailed investigation are
required or not should be judged by a responsible or professional engineer considering theimportance of the structure, cost performance and other factors.

17.3.3 Evaluation of seismic performance and judgment of necessity for seismic retrofit(1) In principle, seismic performance of a structure should be evaluated and thenecessity for seismic retrofit should be judged in accordance with Chapter 6 “Evaluation
and Judgment” and (2) below.
(2) In cases where no outstanding deformation of a structure due to deterioration isfound, seismic performance may be evaluated and the necessity for seismic retrofit may
be judged using the method for inspecting seismic performance stipulated in the“Design” volumes of the Standard Specifications.

[Commentary] (1) Seismic performance of a structure should be evaluated and the necessity ofseismic retrofit should be judged quantitatively by the methods of structural performance evaluationand judgment of the necessity of remedial measures based on the investigation results shown in
Chapter 6 “Evaluation and Judgment.”273

Standard Specifications for Concrete Structures-2007, Maintenance(2) In cases where no outstanding deformation of a structure due to deterioration is found,seismic performance may be evaluated and the necessity of seismic retrofit may be judged using themethod for inspecting seismic performance shown in the “Design” volumes of the Standard
Specifications.” The standards for specific types of structures may be applied at the discretion of the
responsible engineer, e.g. “Specifications for Highway Bridges: Seismic Design,” “DesignStandards for Railway Structures: Seismic Design” and “Technical Standards for Port and Harbor
Facilities.” The performance evaluation equation used in design is oriented toward sound members
and applicable to cases with no outstanding deterioration of an existing structure or member. The
performance evaluation equation used in design is inapplicable to cases with the corrosion ofreinforcing bars and cracking along the bars because the strength and expansibility of reinforcing
bars are deteriorated and because the bond between reinforcing bars and concrete is reduced. The
performance evaluation equation is applicable to cases where structural requirements are met insuch terms as concrete cover, shape of the hook of reinforcement, and arrangements of joints andhoops. Whether structural requirements are met or not should therefore be verified. Unless therequirements are met, the seismic performance calculated should be reduced according to thecondition or other measures should be taken.
In cases of outstanding deterioration, repair or strengthening in response to deterioration isrequired as well as seismic retrofit.

17.4 Selection of Seismic Retrofit Method
The seismic retrofit method shall be selected properly considering the present
seismic performance of the structure or member to be strengthened and the seismic
performance to be achieved, importance of the structure, cost performance, environment
in which the structure is placed in service, and the site conditions.

[Commentary] Methods for improving seismic performance include improving the strength ofthe member, improving ductility and reducing the inertial force during an earthquake. Various
seismic retrofit methods have been executed such as the increase of member thickness, jacket withreinforced concrete or steel plates, application of reinforcement, adhesion of steel or fiber
reinforced plastic plates and installation of dampers. An appropriate method of seismic retrofit
should be selected considering the present seismic performance of the structure or member to bestrengthened and the seismic performance to be achieved, importance of the structure, cost
performance, environment in which the structure is placed while in service and site conditions.
Seismic retrofit methods should be selected in accordance with Chapter 7 “Remedial Measures”
because seismic retrofit methods have much in common with ordinary retrofit methods.
Existing structures to be retrofitted have generally been in service such as railways, highways,
ports, plants and power or gas supply facilities. In cases where stores or facilities are located undera viaduct, where only narrow space is available in a river or at the construction site, or where
enforcing traffic regulations is difficult; large-scale work for removing obstacles, temporary work or
security measures are required before the commencement of construction. Methods have recently274

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been developed and put to practical use that enable construction in narrow space, manually apply
light-weight reinforcement, enable construction in cases where only small surface of members is
exposed, eliminate the construction of a temporary coffer dam in the river or eliminate the need of
temporary earth retaining or excavation. These methods may be selected considering theconstruction conditions. Described below are typical retrofit methods for structures.
(i) Seismic retrofit of reinforced concrete rigid frame viaducts-Jacket with steel plates-Jacket with fiber reinforced plastic plates-Installation of reinforcement or divided steel plates on the outer side of the column-Adhesion of multiple layers of thin steel plates-Jacket with concrete segments and steel strands-Construction on one side of the column using steel plates and reinforcement-Installation of damper braces(ii) Seismic retrofit of reinforced concrete bridge piers-Jacket with reinforced concrete-Jacket with steel plates-Jacket with fiber reinforced plastic plates-Underwater construction using mechanical joints-Installation of concrete filled steel piles from above the ground-Jacket by erecting straight sheet piles from above the ground-Insertion of steel into the frame of bridge pier(iii) Seismic retrofit of underground box culverts (construction from inside)-Inner jacket with reinforced concrete-Inner jacket with steel plates-Inner jacket with fiber reinforced plastic plates-Installation of supports-Insertion of shear reinforcement275

Standard Specifications for Concrete Structures-2007, Maintenance17.5 Design of Seismic Retrofit
Seismic retrofit shall be designed by an appropriate method to meet the required
seismic performances.

[Commentary] Seismic retrofit should be designed properly following the retrofit design
procedure shown in Chapter 7 “Remedial Measures.” Seismic performance may be inspected after
seismic retrofit in accordance with the “Design” volumes of the Standard Specifications. Standards
such as the “Specifications for Highway Bridges: Seismic Design,” “Design Standards for Railway
Structures: Seismic Design” and “Technical Standards for Port and Harbor Facilities” may be
applied at the discretion of the responsible engineer. Details of the retrofit method may be specified,
the retrofit method may be selected and the performance of the strengthened member may beinspected in accordance with the “Guidelines for Strengthening of Concrete Structures (draft),”“Guidelines for Repair and Strengthening of Concrete Structures Using Continuous Fiber Sheets”
and other documents.
With the increase of strength of bridge piers by retrofit, foundations instead of piers may bedamaged. When retrofitting a structure, the sections requiring retrofit should be identified fully
considering the balance throughout the structure and performance should be improved properly inthe sections. For foundation members, identifying damage or repairing is difficult. Improving
ductility rather than strength of piers so as not to cause damage to foundation members facilitates
restoration.

17.6 Execution of Seismic Retrofit(1) Structures shall be retrofitted properly using materials of verified quality.
(2) When retrofitting a structure, an effective verification plan shall be developed andappropriate verification shall be conducted during and after construction to verify seismic
retrofit has been constructed so that the designated effect of retrofit may be achieved.

[Commentary] (1) Structures should be retrofitted properly in accordance with Chapter 7“Remedial Measures” and using materials of verified quality. For matters unique to retrofit, refer tothe “Guidelines for Strengthening of Concrete Structures (draft)” and the “Guidelines for Repair
and Strengthening of Concrete Structures Using Continuous Fiber Sheets.”
For seismic retrofit, such methods are frequently adopted as the increase of member thickness,jacket with reinforced concrete or steel plates, application of reinforcement and adhesion of steel orfiber reinforced plastic plates. Drilling is frequently in existing members. Appropriate construction
is required to prevent damage to reinforcement by verifying the locations of reinforcement inexisting members. In cases where reinforcement is actually located at positions far different fromthose assumed in design, actions are required including the review of the design. In order to ensure
the installation of anchors at appropriate locations and the provision of adequate bond, surface
treatment is important at the construction joints between existing and reinforcing concrete or on thesurface of adhesion of steel or fiber reinforced plastic plates. To that end, the weak department or276

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adhesion objects to concrete surface shall be removed. Methods have recently been developed forchipping concrete without damaging reinforcement or internal concrete (water jet method) or
shotcrete concrete or mortar.
(2) In seismic retrofit, verifications should be conducted to judge whether or not thestrengthened structure or member meets the required performances specified in seismic retrofit
design. At the end of retrofit, only a limited number of items may be verified, e.g. the surface
condition of the structure, dimensions of the member and locations of reinforcement. Appropriate
interim verifications shall therefore be conducted in each phase of construction.
The method of verification varies according to the structure to be strengthened or the methodof retrofit. In order to ensure efficient and reliable verification , items, method and frequency ofverification in each construction phase should be examined and a verification plan should be
prepared. The time and cost required for the verification and the reliability of the verification should
also be examined in advance. Specific verification items include general items in the construction of
concrete structures such as the arrangement of reinforcing bars in sections where member thickness
is increased (strength, diameter, location and the degree of fixation of reinforcement), physicalproperties and thickness of concrete or mortar to be placed, and items unique to seismic retrofit likethe strength of anchors to be installed and the bond between existing and reinforcing concrete. For
the method of adhering steel or fiber reinforced plastic plates, items such as material strength andadhesion should be verified whether adequate reinforcing effect is provided or not. Theseverification items should be fully examined when preparing the verification plan.
In verifications, whether construction has been carried out properly or not and whether thestrengthened structure provides the designated seismic performance or not are judged. The methodof verification and standard of judgment should be objective and stipulated in the special mention
specifications prepared at the time of signing the agreement. Strictly conducting tests in accordancewith the Japan Industrial Standards and the standards of Japan Society of Civil Engineers is a basis
for making objective decisions. Comparison with past construction is facilitated and failure may be
prevented based on the results of comparison. Thus, construction is carried out more effectively.

17.7 Maintenance after Seismic Retrofit
A retrofitted structure shall be maintained so that the required performances for the
structure are within the allowable range throughout the remaining planned service period.

[Commentary] A retrofitted structure shall be maintained so that the designated performance forthe structure may be within the allowable range throughout the planned service period assumed in
retrofit design. The retrofitted structure should be maintained by following the maintenanceprocedure described in this Specification. For seismic retrofit, large-scale remedial measures are
frequently taken. In cases where the state of the structure or member changes greatly before andafter the retrofit, the maintenance procedure for newly constructed structures should be taken.

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Standard Specifications for Concrete Structures-2007, Maintenance17.8 Recording
Data of the retrofit shall be recorded by an appropriate method and stored for arequired period.

[Commentary] Records on the planning, design and construction of seismic retrofit not only
serves as a basic material for the maintenance of the strengthened structure but also is important forevaluating subsequent seismic retrofit methods or materials to be used. Data shall therefore berecorded in a way that facilitates reference, and kept at least as long as the strengthened structure isin service. For details of recording, refer to Chapter 8 “Recording.”

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