安藤ハザマ研究年報 Vol.8 2020
報 告Relationship between crack width and rebar corrosion
volume in the electro galvanic corrosion experiment andin the actual structure
George Vulpe MINESAWA *1・Takuo MUROYAMA *1・Isamu SANDANBATA *1
Technologies for deterioration assessment of RC structures corrosion degradation are being
developed, but the difficulty of sampling corrosion data and the variability associated with RC
degradation had hampered the progress. In the study, results of crack and corrosion surveys of theRC slab samples extracted from the deck of a marine pier and the results of electro galvanic corrosion
experiments on RC members were reported. At first the specimen surfaces cracking condition is visuallyevaluated and then the degree of internal corrosion of the reinforcement was quantitatively assessed.
The crack width and the amount of reinforcing bar corrosion obtained by the galvanic corrosion test andfrom the actual structure was compared with data reported in previous studies. The actual structure
upper face rebars samples were showing a similar tendency between corrosion and cracking, withslightly lower corrosion in comparison to previous studies.
Keywords: RC Structure, Degradation Evaluation, Rebar Corrosion, Crack Width, Galvanic
Corrosion

1. Introduction
As part of the maintenance of social infrastructure,
the development of technologies for deterioration
det e c t ion , a ssessment , a nd pr ed ic t ion for R C
st r uc t u r es c or r osion deg rad at ion a r e ga i n i ng
attention. The RC members degradation due tocorrosion of the rebar is progressing with time andthe corrosion degree and corrosion speed is being
influenced by the environment and by factors suchas concrete permeability, concrete cover thickness
and the rebar diameter. The lack of the structuraldesign documentation and the difficulty to sample
the corroded rebars had hampered the progress of thequantitative analysis of RC degraded members.
In the study, a detailed survey is implemented,
allowing using fewer samples. The relation of surface
crack width and corrosion surveys of the RC slab
samples extracted from the deck of a marine piers andthe results of electro galvanic corrosion experimentson RC members were being compared. At first, theFig.1 Galvanic corrosion experiment specimens

specimen surface cracking condition was visuallyevaluated and then the degree of internal corrosion of
the reinforcement was quantitatively assessed.
*1 土木研究部

1安藤ハザマ研究年報 Vol.8 2020

Fig.2 Summary of crack width measurement along specimen length

2. Electro galvanic corrosion experiment
As rebar corrosion progress in time is slow, anTable.1 S ummary of crack width and corrosion loss

electro ga lva n ic exper iment was per formed i nmeasurement for each specimen

laboratory conditions, to investigate the effect ofparameters.
The RC specimen dimensions, and the layout of
the indoor experimental setup used for the electro
galvanic corrosion test are shown in Figure 1. In thegalvanic corrosion test, two types nominal diameter ofreinforcing bar (D16 / D25) and two different concrete
cover thicknesses (30 mm and 40 mm) were used forcomparison and identification of parameter effect.
In the experiment the cracking occurrence time andintegrated galvanic current values were monitored,
while the crack width distribution was measured every
10 mm along the crack after the crack fully developedon the upper surface of the specimen, the plot of crack
width is shown in Figure 2. The galvanic specimens
crack width measurement shows a large variation overthe crack length and a significant variability evenbetween the specimens under the same conditions.
After the crack inspection and measurement, the RCspecimens were cut into four 100 mm length blocks andthe amount of reinforcing bar corrosion was determined

Fig.3 C rack maximum width versus average corrosion

for each of the blocks. The Table 1 summarizes theloss for the galvanic corrosion specimens

average and maximum corrosion for eight galvanic
corrosion specimens, the average corrosion was below 5%
while the maximum crack width was 0.55 mm or less.

2

安藤ハザマ研究年報 Vol.8 2020

Table.2 Summary of corrosion loss measurement for each 100mm length block of the specimen
Specimen Ｎｏ Rebar

Cover(mm)D25-40-No4
D25
D25-40-No340
D16-40-No4
D16
D16-40-No3

D25-30-No1
D25
D25-30-No230
D16-30-No1
D16
D16-30-No2

Mass(g)391.79390.56394.86389.62389.62389.62389.62389.62152.43154.58153.05153.89153.89153.89153.89153.89389.62389.62389.62389.62389.62389.62389.62389.62
153.89153.89153.89153.89154.31
153.41155.57151.16

Uncorroded Rebar
Length Diam Unit Mass
(mm)
(mm)
(g/mm)
102.25 27.00
3.832
101.74 27.00
3.839
102.90 27.02
3.837
101.57 26.98
3.836
101.57 27.02
3.836
101.57 27.00
3.836
101.57 27.01
3.836
101.57 27.01
3.836
101.29 16.54
1.505
102.86 16.57
1.503
101.69 16.57
1.505
102.22 16.59
1.505
102.22 16.67
1.505
102.22 16.50
1.505
102.22 16.52
1.505
102.22 16.50
1.505
101.57 27.03
3.836
101.57 27.02
3.836
101.57 26.99
3.836
101.57 27.01
3.836
101.57 27.01
3.836
101.57 27.02
3.836
101.57 27.01
3.836
101.57 27.02
3.836
102.22 16.51
1.505
102.22 16.46
1.505
102.22 16.50
1.505
1.505
102.22 16.61
102.55 16.59
1.505
102.05 16.56
1.503
103.29 16.55
1.506
100.39 16.55
1.506

Mass(g)379.90373.41386.00381.51385.76375.04380.78375.30149.68147.32
142.27145.86151.87142.86144.20148.43379.70379.94
376.40382.33381.18380.82381.52379.93148.94143.75152.53146.55150.53146.72
146.30145.88Length(mm)102.28101.72102.90101.58103.19101.74102.49100.02101.26102.85101.71102.24103.51102.28102.23101.85101.70103.13101.29101.89101.42101.13102.24102.08102.69101.54103.39101.43102.53102.07103.29100.38

Corroded Rebar
Unit Mass Corrosion Corrosion(g/mm)(mg/㎜2) Loss(%)
3.714
1.370
3.06
3.671
1.988
4.37
3.751
1.014
2.24
3.756
0.942
2.09
3.738
0.441
2.54
3.6861.689
3.90
3.715
1.016
3.15
3.752
1.687
2.18
1.478
0.523
1.78
1.432
1.356
4.69
1.399
2.036
7.06
1.427
1.507
5.24
1.467
0.373
2.51
1.397
2.080
7.19
1.411
1.826
6.27
1.457
1.034
3.17
3.734
1.149
2.67
3.684
1.106
3.96
3.716
1.539
3.13
3.752
0.843
2.18
3.758
0.981
2.02
3.766
1.025
1.83
3.732
0.934
2.72
3.722
1.118
2.97
1.450
0.929
3.63
1.416
1.931
5.93
1.475
0.254
1.97
1.445
1.387
4.00
1.468
0.707
2.43
1.437
1.260
4.38
1.416
1.726
5.96
1.453
1.012
3.48

surface crack and rebar corrosion was described in 1).

The detailed galvanic experiment corrosion survey
data are listed in Table 2 for each 100 mm length block.
As for corrosion distribution along the rebar, the blocks

3. Quantitative survey of the reinforcing

near the center typically shows a larger amount ofbars corrosion in the actual marine

corrosion than the blocks at the ends. The relationshipstructure

between the crack width and the amount of corrosionshows large variability, blocks with large corrosion

Investigation and survey of the actual RC marine

shows the tendency to develop larger cracks, as shown

pier deck structure was conducted for the deck’s slabin Figure 3. An analytical relation between measured

as described in reference 2). The underside rebar

crack
crack measured
top face upper rebar

a. Survey of RC block No. 57

top face lower rebarb. Survey of RC block No. 69

Fig.4 The survey of cracks and photos of the surfaces of RC blocks extracted from the RC deck structure3安藤ハザマ研究年報 Vol.8 2020

Fig.5 Relation between crack width and rebar amount of corrosion in comparison to previous research data
cover of the slab almost collapsed due to wave erosion

The amount of corrosion was calculated by theand corrosion while upper surface shows only minor

Equation (1).

cracking. The survey was conducted on the top layers ofrebars located near the upper surface of the deck slab.

Corrosion amount (mg / mm2) = (w-w’) / s(1)

On site crack measurement was conducted followedby the extraction of two sample blocks, on different

w : Initial mass of rebar (mg)slabs. The survey of the crack pattern is shown inw’ : Mass of rebar after removal of corrosion rustFigure 4, including photos of the top surface of eachs : Total surface area of rebar (mm2)

RC block extracted from of the actual RC pier deck
structure. Measurement of chloride concentration

The corrosion mass loss was measured between 0 to

distribution in concrete indicates the exceedance of0.54%, and the amount of corrosion was 0 to 0.17 mg/

NaCl threshold for corrosion initialization including

mm2 for rebars right below the crack, which although

at deck’s upper surface bars depth location, therefore

is a small value, is indicating corrosion onset.

there is the possibility of upper surface cracks beThe data regarding crack width and the amountcaused by corrosion of the reinforcing bars.

of reinforcing bar corrosion obtained by the galvanic

The top layer of the reinforcing bars just below

corrosion test and from the actual structure survey, isthe crack was extracted and a quantitative survey

shown in Figure 5. In addition, the previous research

was conducted for the corrosion volume. The rebar

data results on the crack width and the amount ofcover thickness was 50 up to 60 mm. As result ofrebar corrosion as reported in the published references

investigation, the maximum crack width was below 0.08

3) to 7), are plotted for comparison in the Figure 5.

mm, which is very small value compared to the crack
width on the lower surface of the same deck. Since the4. Summary

crack developed along the upper reinforcing bar of thedeck slab, it was judged that most of the confirmed

The survey results of the crack width and thecracks were related to corrosion of the rebars.

amount of reinforcing bar corrosion obtained by the4安藤ハザマ研究年報 Vol.8 2020

galvanic corrosion test and from the actual RC deck

actual structure, Japan Society of Civil Engineers,

structure were compared with data reported in five74th Annual Meeting, V-233, 2019.
3) Tetsushi KIMURA, Kyuichi MARUYAMA, Hiyoshi

previous studies in relation to the crack width and theHAMADA: Evaluation of Corrosion of Reinforcing

corresponding rebar corrosion.
Galvanic corrosion experiment provided timely

Bars in Reinforced Concrete Member, Annual

detailed data and an evaluation method for assessing

Papers on Concrete Engineering, vol.18, No.1,

the effect of the concrete cover depth and of the rebar

pp.771-776, 1996.
4) K .TAKEWAK A and S.M ATSUMOTO: Effect ofsize.
As for the limited number of collected data, theReinforcement Corrosion in Concrete on Mechanicalresults of the actual RC structure samples were

Properties of RC Members, Proceedings of the 6th

show ing a simila r tendency between cor rosion

Annual Lecture Meeting on Concrete Engineering,and cracking, with slightly lower corrosion for the1984.
5) H iyoshi HAMADA, Kyuichi MARUYAMA, Takumi

corresponding upper surface rebars in comparison toSHIMOMURA, Toshiyuki AOYAMA: Deterioration

previous studies.
Corrosion survey are providing the essential data

Prediction Model of Reinforced Concrete Structuresneeded for the development of quantitative degradationin Corrosive Environment, Proceedings of Annual

evaluation methods as well as for the assessment ofLecture Meeting on Concrete Engineering, vol.19,

the structural degradation status and for the planning

No.1, 19976) M asahiro OK A Z A K I, Takumi SHI MOM U R A ,of the maintenance, repair or replacement decision.

Hiroshi MATSUO: Examination of rebar corrosion
REFERENCESand corrosion crack width in concrete focusing1) G eorge Vulpe MINESAWA, Kazuhiko URANO:

on non-uniformity in the axial direction of rebar,

MC based corrosion progress evaluation method

Annual Proceedings of Concrete Engineering,

including variability of concrete cover, Japan

Vol.25, No.1, 2003
7) K iyomi TAMORI, Kyuichi MARUYAMA, Masashi

Society of Civil Engineers, 20th International

ODAGAWA , Chikanor i H A SH I MO T O: Crack

Summer Symposium, CS2-062, 2018.
2) G eorge Vulpe MINESAWA, Takuo MARUYAMA,

Behavior of Reinforced Concrete Members due toIsamu SA NDA MBATA: Relationship between

Corrosion of Reinforcing Bars, Annual Proceedings

crack width and rebar corrosion volume in theof Concrete Engineering, 10-2, 1988.

electro galvanic corrosion experiment and in the

電食試験と実構造物の鉄筋腐食量とひび割れ幅の関係
峰沢ジョージヴゥルペ，室山拓生，三反畑勇

近年，社会資本ストックの維持管理が大きな社会問題となっている中で，特に RC 構造物の劣化診断，劣化予測技術の開発が進められている。また，鉄筋の腐食度や腐食速度は，コンクリートかぶり厚，鉄筋径，コンクリート材料の強度や浸透，RC 構造部材の暴露環境などの影響を受けることは知られている。多くの劣化構造物において設計書等の詳細データが残されておらず，また実際の RC 構造では，その機能が喪失されるような鉄筋の抽出が困難であることから，実構造物の腐食鉄筋について，定量的な要因分析は進んでいない状況である。本論では，現地でサンプリングできた海上桟橋の RC 床版のサンプルを用いたひび割れ・腐食量調査と技研室での RC 部材の電食実験の結果を比較し，目視で確認できるひび割れ状況と，内部の鉄筋腐食量の関係について示す。
キーワード：鉄筋コンクリート構造物，劣化評価，鉄筋腐食，ひび割れ幅，電食5