NISTIR 6402

Predicting the Performance of

Concrete Repair Materials

Summary of Workshop

April 26 and 27, 1999

Durham, New Hampshire

Alexander M. Vaysburd

Nicholas J. Carino

Benoît Bissonette

United states Department of Commerce

Technology Administration

National Institute of Standards and Technology

NISTIR 6402

Predicting the Performance of

Concrete Repair Materials

Summary of Workshop

April 26 and 27, 1999

Durham, New Hampshire

Alexander M. Vaysburd

Structural Preservation Systems, Inc.

Nicholas J. Carino

National Institute of Standards and Technology

Benoît Bissonette

Laval University

Workshop Sponsors:

Conproco Corp.

Master Builders, Inc.

Sika Corp.

Structural Preservation Systems, Inc.

W.R. Grace & Co.

January 2000

U.S. Department of Commerce

William M. Daley, Secretary

Technology Administration

Dr. Cheryl L. Shaver, Under Secretary of Commerce for Technology

National Institute of Standards and Technology

Raymond G. Kammer, Director

iii

ABSTRACT

On April 26 and 27, 1999 a workshop on Predicting the Performance of Concrete Repair

Materials was held at the New England Conference Center in Durham, New Hampshire.

This workshop was a follow up of a previous workshop held in 1995 at the National

Institute of Standards and Technology which dealt with research needs to minimize

cracking in concrete repair materials. The focus of the 1999 workshop was on test

methods and modeling techniques for predicting the performance of concrete repairs.

The two-day workshop included a half-day of presentations to define the problems and

review current knowledge. The presentations were followed by working group sessions

on the following topics: (1) modeling material performance; (2) repair design,

specification, and application; and (3) repair materials and systems. The conclusions of

the working groups were presented at a plenary session on the second day. The

workshop concluded with recommendations for action. This report provides

summaries of the working group discussions and concludes with the recommended

actions.

Keywords: Building technology; concrete repair; drying shrinkage; modeling;

performance criteria; tensile creep; tensile strength; test methods.
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v

TABLE OF CONTENTS

ABSTRACT.............................................................................................................................iii

ACKNOWLEDGEMENTS ....................................................................................................vi

1. INTRODUCTION .............................................................................................................1

1.1 Cracking of Repair Materials..................................................................................1

1.2 Workshop Objectives and Format..........................................................................2

2. WORKING GROUP REPORTS........................................................................................5

2.1 Working Group 1  Modeling Material Performance ........................................5

2.2 Working Group 2  Repair Design, Specification, and Application .................10

2.3 Working Group 3  Repair Materials and Systems ............................................16

3. SUMMARY AND RECOMMENDED ACTIONS..........................................................21

4. REFERENCES...................................................................................................................23

3.1 Cited References ......................................................................................................23

3.2 Suggested References..............................................................................................24

APPENDIX A  Workshop Program..................................................................................25

APPENDIX B  Workshop Participants and Working Group Members ........................29
vi

ACKNOWLEDGEMENTS

The workshop would not have been possible without the support of several sponsoring

organizations. The authors wish to thank the following organizations and individuals:

Conproco Corporation (C. Brown and D. Pinelle), International Concrete Repair

Institute (M. Collins), U.S. Army Corps of Engineers (J. McDonald), National Research

Council of Canada (N. Mailvaganam), Master Builders Inc. (R. Meyers), Sika

Corporation (T. Gillespie), and W.R. Grace & Co. (P. Tourney). Milt Collins is also

acknowledged for providing photographs of workshop activities.

It would be inappropriate to conclude without acknowledging that the success of this

workshop, and the interest generated thereby, were due in large part to the attendees

themselves who participated enthusiastically during the working group sessions.
1

1. INTRODUCTION

1.1 Cracking of Repair Materials

The concrete industry of the 21st Century is facing two major challenges:

ß How to design and construct new concrete structures that will perform during

their design service life with minimum maintenance and repair; and

ß How to maintain the desired service life of distressed or deteriorated existing

concrete structures; how to rehabilitate, repair, and protect them so they

continue to serve their intended purpose.

The performance of a repaired concrete structure, and thus its service life, depends on

the quality of the composite system formed by the repair material and the existing

concrete substrate. The behavior of these two components must be compatible if the

repaired structure is to maintain its integrity. Compared with other characteristics, the

absence of cracking of the repair phase has a major impact on the long-term durability

of a repair system. While development of tensile cracks may be favorable from the point

of view of stress distribution in the repair material, the situation is different when

judged from the point of view of the permeability of the materialits ability to retard

penetration of aggressive elements into the concrete.

Cracking in the repair phase, caused by restrained volume changes, is one of the most

common causes of poor performance in repaired structures. Cracking initiates and

promotes corrosion, especially in severe environments, and corrosion, in turn, causes

enlargement of cracks. Increased cracking aggravates any one of a number of other

mechanisms of deterioration. For example, in repeated cycles of freezing and thawing in

a wet environment, water enters the cracks during the thawing portion of the cycle and,

during subsequent freezing, the expansive stress results in progressive deterioration.

The sensitivity to cracking of repair materials used in a repair project is one of the most

critical factors affecting the durability of the repaired structure. It must be emphasized,

however, that repair problems cannot be resolved simply by specifying and using

crack-resistant repair materials. Evaluation of existing concrete conditions, design

details and specifications, and quality of on-site workmanship are also of fundamental

importance in ensuring durability of repaired structures.

The intent of the workshop summarized in this report was to examine the tools needed

by the repair industry to ensure that materials specified and used for concrete repairs

are dimensionally compatible with existing concrete substrates so as to minimize

cracking during the desired service life. The workshop focused on modeling techniques

for predicting the service life of concrete repairs, and on test methods and performance

criteria for selecting repair materials with low likelihood of cracking in service.
2
3

1.2 Workshop Objectives and Format

At the September 1995 workshop, “Research Needs for Establishing Material Properties

to Minimize Cracking in Concrete Repairs” (Vaysburd 1996), held at the National

Institute of Standards and Technology (NIST), the following needs were identified for

the concrete repair industry:

ß The need to enhance our understanding of causes and properties affecting

cracking in repairs;

ß The need for reliable prediction of performance of concrete repairs based on

short-term tests; and

ß The need for developing mathematical models for predicting the future service

life of concrete repairs.

The workshop outlined the necessary research to be conducted to transform concrete

repair from “art” to a technology based on engineering and material science. It was

recommended that the workshop process be continued on a regular basis in order to

improve the quality of the North American concrete repair industry and increase its

international competitiveness.

The steering committee of the second workshop, “Predicting the Performance of

Concrete Repair Materials,” was composed of the following individuals:

- Christopher Brown, Conproco, Corp. (Chairman)

- James McDonald, U.S. Army Corps of Engineers (USACE) (Co-chairman)

- Noel Mailvaganam, National Research Council of Canada (NRC-CNRC) (Cochairman)

- Douglas Burke, Naval Facilities Engineering Service Center

- Nicholas Carino, NIST

- Terence Holland, Consultant

- Dennis Pinelle, Conproco, Corp.

- Alexander Vaysburd, Structural Preservation Systems, Inc.

The workshop was held at the New England Hotel and Conference Center, Durham,

New Hampshire on April 26 and 27, 1999. It was co-sponsored by the International

Concrete Repair Institute (ICRI), the National Institute of Standards and Technology,

the National Research Council of Canada, Conproco Corp., Structural Preservation

Systems Inc., Master Builders Inc., Sika Corp., and W.R. Grace & Co. The workshop

program and a list of the participants are included in Appendices A and B, respectively.

The objectives of the workshop were as follows:

ß To review current methods for determining the service life of repair systems;
4

ß To identify new studies, new test methods, and data needed to develop

guidelines for determining the service life of repairs;

ß To adopt or develop performance criteria for the selection of repair materials;

ß To adopt or develop standard protocol for repair material data sheets;

ß To reach agreement on how to develop a reliable model to predict the service

life of concrete repairs; and

ß To recommend actions necessary to develop the model.

To achieve these objectives, the 1999 workshop was arranged according to the following

format:

ß Attendance was by invitation in order to obtain a balance among material

manufacturers, researchers, structural engineers and specifiers, constructors,

and those working on mathematical modeling of material performance.

ß The workshop started with a General Session where problem-statement papers

were presented as indicated in the Program (Appendix A). The presentations

were given by individuals actively involved in significant work. These papers

were intended to give the latest information and points of view on the subject

of cracking of repair materials.

ß The workshop participants were divided into three working groups reflecting

the participants’ expertise and interests.

- Group 1: Modeling Material Performance;

- Group 2. Repair Design, Specification and Application (Users of repair

materials);

- Group 3. Repair Materials and Systems (Material manufacturers and

researchers).

Each working group had a chairman (or facilitator) and co-chairman as

indicated in Appendix B. All discussions took place in working groups.

Subsequent to the group discussions, the chairman and co-chairman of each

working group prepared a summary report for the plenary session.

ß The Workshop was concluded with a final discussion and recommendations

for action.

The remainder of this report is based upon discussions and conclusions of the working

groups. Chapter 2 summarizes the working group discussions; Chapter 3 lists the

recommended action items; and Chapter 4 includes pertinent references.

The authors have exercised their prerogatives to limit the length of this summary. Much

of the original floor discussions are omitted and only those items of direct significance

to the objectives of this workshop are summarized.
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2. WORKING GROUP REPORTS

2.1 Working Group 1  Modeling Material Performance

Objectives

The group’s discussion focused on answering the following questions:

ß What are we trying to model?

ß What is the uncertainty in analytical results?

ß Who are the users of these analytical models?

ß What models are available?

ß What action items should be recommended to advance our modeling

capabilities?

Purpose of Modeling

The ultimate objective of modeling is to be able to estimate the service life of the

repaired concrete structure. However, this is a difficult problem, and it was the

consensus of the group that this long-term objective will be achieved by incremental

advances in our modeling capabilities. Therefore, it was decided to consider the

requirements for three levels of models:

Level 1 —Evaluate the susceptibility of a given repair material to cracking under

standardized conditions. This might serve as a screening tool for

comparing the performance of alternative materials.

Level 2 —Predict the “short-term” performance of a specific repair under

anticipated field conditions.

Level 3 —Predict the service life of repaired structures.

These are discussed in more detail.

Level 1 model—The objective of this model is to evaluate the susceptibility to cracking of

a given repair material under standard (isothermal) conditions of restraint and drying.

Basically, this model estimates the increase of restraint-induced tensile stress in the test

specimen as a function of time and compares that stress with the developing tensile

strength. The strength-to-stress ratio would be a measure of the likelihood of cracking

under the given conditions. A value significantly greater than 1 would indicate low

likelihood of cracking, and a value significantly less than 1 would indicate a high

likelihood of cracking. Figure 1 is a schematic to illustrate hypothetical results for three

materials: A, B, and C. In this example, material A would have the greatest cracking

tendency, while material C would have the least. For each material, the strength-tostress ratio is shown as a band to reflect the uncertainty of the analysis. One of the

challenges in the development of a Level 1 model will be to determine how to represent

the uncertainty in the results.
7

To implement a Level 1 model requires knowing the following information about the

repair material:

ß The development of the elastic modulus;

ß The development of tensile strength; and

ß The development of autogenous shrinkage and drying shrinkage.

In addition, it is necessary to account for stress relaxation, which is beneficial in

reducing the tensile stress that develops under restrained shrinkage. Standard test

methods will be required to measure these basic properties of the material. A key

question that needs to be answered is whether the stress relaxation (or creep) properties

under tensile loading are significantly different from those under compressive loading.

The answer to this question will dictate the complexity of the testing needed to measure

the key properties. The measurement of these properties has to begin at early ages that

correspond to when volume reductions would begin to occur (drying shrinkage and

autogenous shrinkage) in the test specimen. Another important characteristic that must

be understood is the tensile strength of the repair material under sustained stress. There

are indications that the sustained strength may be a fraction of that measured in a shortterm tensile test (Poston et al. 1998).

An important aspect of model development is the verification of the results by

comparison with carefully controlled tests that replicate the analytical conditions. Two

Figure 1 Schematic of strength-stress ratio as a function of time for specimens of three

repair materials subjected to standard conditions of restraint and drying

Strength/Stress

(Safety Margin)

1.0

Cracking is unlikely

Cracking is likely

Time

A

B

C
8

types of restrained shrinkage conditions might be considered. One involves axial

restraint of a prism, as shown in Fig. 2(a). This would involve the adoption of a

standard test frame with fixed stiffness, kr. A difficulty with this approach is the

transfer of the tensile force from the restraining fixture to the specimen. The problem

may be overcome by the second type of test, as shown in Fig. 2(b). In this case, an inner

steel ring restrains the shrinkage of the outer ring of repair material. The ring of repair

material is, in effect, subjected to loading equivalent to a uniform pressure at the

interface with the steel ring. This uniform pressure leads to a tensile stress in the

circumferential direction and a compressive stress in the radial direction. These stresses

vary in magnitude with radial distance, as shown in Fig. 3. For a uniform

circumferential shrinkage strain, the critical tension-compression state of stress occurs

at the inside radius of the ring of repair material (Shah et al. 1998).

Level 2 model—The next level of modeling would predict the short-term performance of

the repair material under anticipated field conditions. In this context, “short term”

refers to the time duration after which there are small changes in material properties,

and it may include a duration that encompasses one complete cycle of extremes in

environmental conditions. The analysis would consider the actual three-dimensional

ks(t) kr

Repair

material

(a) Axial restraint of prism

(b) Restraint by ring

Steel ring

Figure 2 Restrained shrinkage tests: (a) axial restraint and (b) ring restraint
9

shape of the repair in relation to the base concrete. It would consider not only the

stresses within the repair materials but also the conditions at the interface with the

substrate. The model would simulate the temperature history of the repair by taking

into account the initial temperatures of the substrate and repair material, the heat of

hydration, the anticipated ambient conditions, and the effects of insulation (if used). A

Level 2 model might rely on some of the techniques used for a Level 1 model, but it

would have to include additional capabilities such as moisture transport as affected by

the porosity of the repair material and the ambient conditions. As in the case of the

Level 1 model, there is a need to determine the very early-age properties of repair

materials and how they change as a function of time and temperature (maturity).

Level 3 model—The ultimate goal of a model would be to predict the performance of the

repaired structure. It would have to simulate the long-term interaction of the repair

with the structure for a given environmental exposure. To standardize some of the

parameters that will be used in Level 3 modeling, it will be necessary to define

“standard” exposure conditions (such as number of cycles of freezing and thawing,

relative humidity and temperature ranges, and presence of deleterious chemicals). It

would also be necessary to define the applicable “failure” criterion that signals the end

of satisfactory performance. This would in turn require understanding the controlling

degradation mechanism (freezing and thawing damage, corrosion, chemical attack, and

so forth). Since this level of modeling would involve predictions based on assumptions

and simplifications, consideration of the sensitivity of the predictions to the assumed

conditions would be essential. Because of this, modeling should be based on stochastic

analysis. The output of Level 3 modeling would provide the expected service life (and

its confidence interval) of the repaired structure, which would be vital for life cycle cost

analyses of alternative repair strategies.

Users

σθ

σr

σr σθ

Figure 3 Equivalent uniform pressure loading and biaxial stresses in ring test
10

Any model development effort should consider carefully the potential users. Key

factors to consider are the quantities needed as model input and the nature of the

output. Depending on the user, the required model input can be quite simple or

complex. The model may include sub-models that use simple input values to estimate

the material characteristics required to run the main model. In general, the simplicity of

the input and output is related to the user’s level of understanding of the underlying

principles of the model. Thus models intended for practical use by designers and

contractors would require simpler input and output interfaces than models intended for

researchers. However, complex models could be used to generate useful design tools

such as graphs and tables. An example that was cited is the well-known series of graphs

used to predict the evaporation rate of a free water surface as a function of ambient

conditions.

Existing Models:

The working group identified a number of existing models that have been developed to

predict the potential for cracking due to volume changes under restrained conditions.

Some have been developed specifically for analyzing repair materials, while others may

be modified to make them applicable to modeling concrete repairs. The models that

were identified are as follows:

ß Conproco procedure (Pinelle 1995)

ß ACI Committee 209 procedure (ACI 209R-92) with new Comité International

du Béton (CIB) equations for time-dependent properties

ß Laval University (Pigeon and Bissonette 1999)

ß Chidiac et al. (1997)

ß The University of Texas model for polymer concrete repairs1

ß 4C-Temp & Stress Model (Danish Technical University; Pedersen et al. 1997)

ß HIPERPAV (McCullough and Rasmussen 1999)

ß Warsaw University of Technology (polymer concrete repairs; Czarnecki et al.

1999)

Most of the above are basically “load-resistance” models that compare the computed

stresses in a particular structural configuration with the available strength as a function

of time. In addition to these models, a fracture mechanics based model was developed

at Northwestern University to analyze the ring test (Shah et al. 1998).

Action Items

The working group concluded its discussion by identifying six action items:

ß A synthesis should be carried out of operational Level 1 models. The synthesis

 

1 Zalatimo, J.A., and Fowler, D.W., “Designing Durable Polymer Concrete Overlays,” manuscript

distributed at workshop
11

should identify the underlying mechanistic model, the required input,

assumptions and simplifications that are used, and the nature of the output.

ß A comparison of the predictions by the functioning Level 1 models should be

carried out. Test problems should be designed that are within the scope of as

many models as possible.

ß A similar review and synthesis of available Level 2 and Level 3 models should

be carried out.

ß Experimental studies should be carried out of time-dependent properties of

repair materials under tensile stress and comparison with properties measured

under compression. These studies should be planned using the principles of

experiment design to ensure statistically valid results. This information is vital

for determining the standard test methods needed to measure the material

properties required as input to numerical models.

ß Test methods are needed to measure early-age properties of repair materials.

These methods should be reliable, robust, and relatively simple to perform.

ß A modeling subcommittee should be established within existing ACI and ICRI

committees. The subcommittee will provide a focus for sharing the latest

developments and for publication of documents on the state-of-the-art and

design practices as they evolve.

Interested parties should seek to establish consortia within the ACI Strategic

Development Council to fund needed research.

2.2 Working Group 2  Repair Design, Specification, and Application

Objectives

The working group discussion was mainly directed to the following topics:

ß The practical applicability of the U.S. Army Corps of Engineers (USACE)

proposed Performance Criteria for Selection of Repair Materials for NonStructural (Protective) Repairs (Vaysburd et al. 1999).

ß The adoption of the USACE proposed Repair Material Data Sheet Protocol

(Vaysburd et al. 1999).

ß Test methods for sensitivity to cracking of repair materials.

The ultimate objective of this group’s discussion was to identify those properties of

cement-based repair materials and the corresponding test methods to provide the basis

for a quantitative approach for predicting cracking in concrete repairs and for selection

of crack-resistant repair materials. The members agreed that appropriate material

properties are critical for crack resistance and durability of concrete repairs, but equally

important are the quality of the design and construction practices, which are beyond the

scope of the present workshop.
12

It was recognized that to predict the useful life of repaired structures requires

knowledge of more than basic material properties measured under standard conditions.

To predict crack related-failures, as a function of the variables involved in repair

material systems, requires more knowledge, at a fundamental level, about the complex

interrelationships between properties and environment.

The working group discussed the proposed USACE performance criteria for the

selection of non-structural repair materials (Table 1) and the proposed USACE repair

material data sheet protocol (Table 2).

It was recognized that many repair materials presently manufactured do not satisfy the

proposed performance criteria. The working group did not reach a consensus on the

need and merit of all the performance requirements and test methods. However, it

concluded that performance criteria and standard data sheet protocols are necessary

and that those proposed by the USACE provide good starting points.

The group noted that the ring test shows promise as an indicator of the cracking

tendency of repair materials. Further research has to be focused on factors such as

specimen geometry, test instrumentation, and environmental conditions.

Although the USACE study (Vaysburd et al. 1999) did not show definitive correlations

between tensile creep, creep relaxation, and crack resistance of the material, it was

agreed that tensile creep merits further study in the context of establishing performance

Table 1  Proposed USACE Performance Criteria for the Selection of Repair Materials

(Vaysburd et al. 1999)

Property Test Method Requirement

Tensile strength, minimum 28 d CRD-C 164 (WES 1949b) 2.8 MPa (400 psi)

Modulus of elasticity, maximum ASTM C 469 24 GPa (3.5 x 106 psi)

Coefficient of thermal expansion CRD-C 39 (WES 1949a) 13 μm/m/°C

(7 x10-6/°F)

Drying shrinkage, maximum

- 28 d

- 1 year

ASTM C 157 (1949e) (Modified).

For modifications to the standard,

see “Data Sheet Protocol,” Table 2 400 μm/m

1,000 μm/m

Restrained shrinkage

- -cracking

- implied strain at 1 year, maximum

Ring Method. For test description,

see “Data Sheet Protocol,” Table 2 No cracks within 14 d

1,000 μm/m
13

criteria. A simplified and reproducible test method for tensile creep of repair materials

needs to be developed.
14

Table 2  USACE Recommended Repair Material Data Sheet Protocol with Commentary

(Vaysburd et al. 1999)

1. Repair Material Description

• Recommended use

• Benefits

• Limitations

2. Composition Data

• Base material(s)

Example: This repair mortar is composed of a precise blend of portland cement, microsilica, graded aggregates,

dry acrylic polymer and fine fibers.

• Sulfur trioxide (SO3), % - ASTM C 563

• Alkali content, kg/m3 (lbs/yd3 )

The typical means by which the alkali content has been controlled with concrete mixtures in the U.S. has been to

establish a maximum limit only on the portland cement. Cement with an alkali content smaller than 0.6 %,

expressed as equivalent Na2O, is referred to as low alkali cement. This provision proved satisfactory for concrete.

The disadvantage of establishing an alkali limit based on the alkali of the portland cement alone for repair

materials is that many proprietary repair materials contain blends of different cements, additives, admixtures and

other constituents that contain alkali. It is the sum of the alkalis from all sources that is pertinent to the potential

reaction with a reactive aggregate.

 Past research conducted first in Germany, and then in Canada, led to the conclusion that when the alkali in a

mixture is kept below a maximum of 3.0 kg/m3 (5.0 lbs/yd3), there will be no ASR (Publication No. FHWA-SA-97-

045, Gress, D., “Early Distress of Concrete Pavements,” January 1997).

• pH

• Air content

3. Physical Properties

• Unit weight of material, kg/m3 (lb/ft3)

• Fresh wet density, kg/m3 (lb/ft3) – ASTM C 138

• Strengths

Age, days

Property and Test Method 1 3 7 28

Compressive strength

- Mortar – ASTM C 109

51 mm (2-in.) cubes

- Concrete mortar extended with coarse aggregate

– ASTM C 39

76 x 152 mm (3 x 6-in.) cylinders

Flexural Strength – ASTM C 78

- Mortar

- Concrete; mortar extended with coarse aggregate

Direct tensile strength – CRD-C 164

- Mortar

- Concrete; mortar extended with coarse aggregate

• Modulus of elasticity – ASTM C 469

- Mortar

- Concrete; mortar extended with coarse aggregate
15

4. Performance Properties

• Drying shrinkage - ASTM C 157 (Modified)

Modifications to ASTM C 157 “Length Change of Hardened Hydraulic Cement Mortar and Concrete”:

a. Standard specimen size is 76 x 76 x 275 mm (3 x 3 x 11-1⁄4 in.) for mortar, mortar extended with coarse

aggregate, and concrete.

b. Remove specimen from mold at 23 ± 1⁄2 hours and make initial comparator reading immediately. (For

rapid hardening materials, remove specimen from mold at 3 hours and make initial comparator reading).

c. The specimens are then stored under the standard conditions of 23.0 ± 1.7°C (73.4 ± 3°C) and 50 ± 4 %

RH.

Subsequent comparator readings are to be taken at ages of 3 days, 7 days, 14 days, 1 month, and 2 months;

measurements shall continue until 90 % of ultimate drying shrinkage is reached. Ultimate shrinkage is to be

determined as described in ASTM C 596, Drying Shrinkage of Mortar Containing Portland Cement.

- Mortar

- Concrete; mortar extended with coarse aggregate

• Coefficient of thermal expansion – CRD C 39

- Mortar

- Concrete; mortar extended with coarse aggregate

• Freezing and thawing resistance – ASTM C 666 (Procedure A)

• Compressive creep – ASTM C 512

- Mortar

- Concrete; mortar extended with coarse aggregate

• Rapid chloride permeability – ASTM C 1202

- Mortar

- Concrete; mortar extended with coarse aggregate

• Sulfate resistance – ASTM C 1012

• Cracking resistance – Ring Test (see description below)

- Age at first crack

- Implied strain

(Sum of average crack widths at the end of test divided by the ring circumference)

- Age at the end of the test

Description of the Ring Test

This method allows the determination of a material’s sensitivity to cracking caused by restrained volume

changes. Figure A shows the mold and specimen for the ring test. The material is cast around a 254-mm (10-

in.) outside diameter and 25.4 mm (1 in.) thick steel pipe. The thickness of the tested material ring is 32 mm

(1.25-in) and the height is 102 mm (4 in.). The freshly-mixed material should be consolidated in the mold as

recommended by the manufacturer. The material rings are to be kept in their molds and covered with plastic

for the first 24 hours after they are cast. After removal of the outer rings of the molds, the top surfaces of the

material rings should be sealed with epoxy (the rings are not removed from the bottom plates of the molds).

The material rings should then be wet cured for 48 hours. After the completion of the recommended curing

period, the specimens shall be kept for at least 60 days under standard laboratory conditions of 23.0 °C ± 1.7

°C (73.4 °F ± 3°F) and 50 % ± 4 % RH. The rings should be monitored daily for evidence of cracking. The day

that cracking is observed should be recorded and the initial crack width should be measured and recorded to

the nearest 0.02 mm (0.001 in). The width of each crack should be measured periodically at the quarter points

and mid-height along the crack, and the average width should be recorded. The computed strain, or implied

strain, associated with the crack widths at the end of testing is reported in the data sheet. The implied strain

is computed by taking the sum of the average crack widths of all cracks in the specimen and dividing by the

ring circumference – approximately 1000 mm (39.4 in.)
16

Figure A. Ring test mold and test specimen

254 mm O.D. Steel Pipe

25.4 mm thick

318 mm I.D. Rolled Steel Plate

3.2 mm thick

102 mm

12.7 mm Square Steel

Positioning Bar

3.2 mm Thick Rolled Steel

Plate

25.4 mm Thick Steel

Pipe

32 mm Thick

Repair Material

SECTION

PLAN
17

Cracking resistance – German Angle Test (modified)

- Age at first crack

- Number and average width of cracks at end of test

Description of the German Angle Test

This test was originally developed by the Technical Academy, Aachen, Germany and was adopted by the

Highway Construction Department of the German Federal Ministry of Transport as part of the Technical Test

Regulations (TR BE-PCC) for concrete substitution systems made of cement mortar or concrete with a plastic

additive. The mold and specimen used for this test are shown in Figure B.

The following is the modification of this test:

Apply epoxy bonding compound before placing repair mixture into the angle. Unless the manufacturer

recommends otherwise, the mixture is to be compacted by external vibration, and then leveled off and

smoothed. The specimen should be wet cured for 72 hours, then stored under the intended service

conditions, or stored in the laboratory under conditions that simulate intended service conditions. Conditions

of the test shall be described in the data sheet. The specimens shall be monitored for cracking for at least 90

days. The time to cracking, number of cracks at the end of the test, and average crack width should be

recorded.

Figure B. German Angle Test specimen

5. Packaging, storage

• Packaging

• Volume yield

• Shelf life

• Storage requirements

6. How the Material Works

Example: This product is a medium slump, two-component, trowel grade mortar. The product’s portland

cement base and low water-to-cement ratio provide the foundation for the system’s strength, durability and

basic physical properties. To improve its properties, the product utilizes the advantages of an acrylic polymer

emulsion. The fine particle size of the acrylic emulsion allows it to penetrate and form a polymer film

throughout the C-S-H matrix and microvoids. This filling of the voids reduces shrinkage, permeability and

moisture absorption. Additionally, the polymer increases adhesion, flexibility, and freeze-thaw and abrasion

resistance.

7. How to Use the Material

• Concrete surface preparation

• Mixing

• Application and finish

• Curing

• Cleanup

• Safety

70 mm 70 mm

1000 mm

7 mm

Steel Angle

Mortar
18

A consensus was reached that the proposed performance criteria are only for protective

(non-structural) repairs. Performance criteria for structural, load-carrying repairs need

to be developed. A feedback mechanism and database need to be established to

evaluate the merits of the proposed criteria in practice.

It was noted that research at Laval University is also directed to the development of

performance criteria and test methods. A technology transfer mechanism is urgently

needed to review the research results and ensure timely implementation. The

International Concrete Repair Institute (ICRI) and others should provide the leadership

role to establish this mechanism.

Action Items:

In conclusion, the working group identified the following action items:

ß The development of performance criteria for structural repairs should be

carried out. ACI and ICRI should take the leadership in this direction.

Interested parties should consider the establishment of a partnership or

consortia to fund the needed research.

ß Test methods are needed to measure the sensitivity to cracking of repair

materials. The methods should be reliable, short-term, and reproducible.

ß ICRI should consider including the USACE performance criteria for protective

repair materials and the recommended material data sheet protocol in their

consensus guidelines.

ß The ring test method and Structural Preservation Systems, Inc. stress/strain

indicator technique should be further researched as a practical procedure to

evaluate crack resistance of repair materials.

ß A centralized technology transfer mechanism needs to be established to review,

coordinate the research, and publish the results as they develop.

ß A joint repair materials committee or subcommittee should be considered

within ICRI and ACI to focus on issues discussed by the Workshop.

2.3 Working Group 3 — Repair Materials and Systems

Objectives

The group’s discussion focused mainly on addressing the following questions:

ß What are the critical material properties affecting cracking in concrete repairs?

ß How to design a test method for predicting a material’s in-place performance

considering all variables involved in field applications?

ß How to define standards for the evaluation of material performance in a

selected test?
19

There is presently no generally accepted test method or methods to determine the longterm performance of a material to be used for surface repairs. The most important

material properties in this respect are likely to be those related to the various types of

deformation: shrinkage, creep, modulus of elasticity, and coefficient of thermal

expansion. However, there is no agreement on the relative influence of each of these

properties. Furthermore, there are insufficient field and laboratory data, both on the

properties of repair materials and on the performance of repaired elements subjected to

different exposures, to correlate any single property or a combination of these

properties to observed long-term field performance.

After an open discussion on the subject, the members of the working group agreed on a

number of basic points:

ß Considering the complexity of the problem and all the variables involved

(material properties, substrate properties, exposure conditions, etc.), it will take

many years before a sound design method based on theoretical considerations

as well as empirical relationships is developed.

ß Industry, both for marketing purposes and for construction, needs relatively

simple test methods that can be easily used, and, better still, a unique method

that would generate one single index or value describing the expected

durability, that is, a “number.”

ß Any test method or design method will have to take into account the variability

of the exposure conditions (variations in relative humidity and temperature,

with or without freezing).

ß The basic material properties (mechanical, thermal, visco-elastic, and

shrinkage) will always be required for characterization purposes and modeling,

and will, therefore, always have to be measured using standardized

procedures.

In view of the above, and considering the urgent need for more rational design methods

in the field of surface repairs, the members of the working group discussed a

standardized test method that would rapidly yield sound information on the long-term

performance of a given repair material subjected to various types of exposure

conditions. It was agreed that such a test method would necessarily have to use a

composite specimen in order to represent as much as possible the actual conditions

under which repair materials are placed. Test specimens should also be sufficiently

small in order to be suitable for both laboratory and field testing. The test should allow

the influence of various exposure conditions to be investigated. Like any other test

method, it should be repeatable, and it should be designed to ensure that both the

material and the application method adequately represent what occurs in the field.

A number of points concerning the scope of the required test method were discussed

and agreed upon. It was decided that only materials with proper rheology, suitable for

the intended environment, free of early-age problems, properly cured, well bonded to
20

the substrate, and non load bearing should be tested with this method. It was also

agreed that the relative thickness of the surface repair was the most significant

geometrical parameter, since the basic problem is one of restrained shrinkage, and the

repair thickness has a large influence on the overall shrinkage of the repair layer. The

test method should not be intended to simulate various patch shapes, because the test

results in terms of cracking would then be too complex to analyze and comparisons

between different test results would be difficult.

The working group considered the “box test,” used in the USACE field study (Emmons

et al. 1998), to be the type of test needed, although, as previously mentioned, the test

specimen would have to be sufficiently small to allow it to be used also in the

laboratory. The test specimen used in the USACE field study is shown in Fig. 4; it is a

precast concrete slab with a cavity to be filled with the repair material. The bottom of

the cavity contains grooves to provide mechanical interlock between the repair material

and substrate. This test could be used to generate laboratory and field data, under

known exposure conditions, which could then be correlated to observed field

performance, using whatever possible basic material properties and models. One of the

interesting possibilities with such a test would be to measure the performance of a

reference material under various types of exposure conditions, and then correlate, as

just mentioned, the results obtained with the observed field performance. Such a

standardized test method would allow the development of a database from both

laboratory and field tests under known exposure conditions, including, when available,

the relationships with observed field performance.

The members of the working group suggested that a small number of persons be

selected and given the task of defining precisely the required characteristics of the “box

test” before considering its standardization. In addition to the size of the box, it will be

necessary to define exactly the preparation of the substrate, since absorption of water by

the substrate can influence the characteristics of the interface and the performance of

the repair material. It will also be necessary to define standards for the evaluation of

performance (type and intensity of cracking as a function of time of appearance),

including the possibility of in-place tests (such as a pull-out test) to evaluate the residual

mechanical strength.

At the conclusion of the workshop, representatives from Conproco, the Corps of

Engineers, Structural Preservation Systems, and Laval University agreed to meet in the

near future to outline the scope of work to be done for further development of the “box

test.” A major part of this work could be performed by the Industrial Chair on Shotcrete

and Concrete Repairs at Laval University, which has an objective to provide technical

support to the concrete repair industry.
21

In addition to the development of a field performance test, it was suggested that one of

the most important ways to improve the durability of surface repairs would be to

disseminate as much information as possible, in the following areas:

ß Available test data (both field and laboratory);

ß On-going and planned studies; and

ß Current and new types of repair materials available.

This could be done through ICRI. It is vital to remember that many, if not most, of the

surface repair durability problems observed in the field are due to improper selection

and use of repair materials.
22

Action Items

The working group concluded its report by highlighting four action items:

ß A simple test method is needed that can be used easily under different

exposure conditions. The method should account for all in-situ variables, and

should be able to generate one single value or index describing the expected

performance.

ß The “box test” developed by Structural Preservation Systems, Inc. and

described in the Corps of Engineers report (Emmons et al. 1998) should be

studied to define precisely the required characteristics of the test. The test

180 mm

2000 mm

1820 mm

20 mm x 20 mm

Grooves

@ 150 mm

635 mm

455 mm

75 mm Deep

90 mm

90 mm

100 mm x 00 mm

Welded Wire Fabric

Figure 4 Precast concrete slab with 75 mm deep cavity to evaluate the field cracking

performance of repair material (Emmons et al. 1998)
23

should be modified as needed and considered for development as a standard

test method.

ß Interested parties should consider establishing consortia to join their efforts

and fund needed studies.

ß Dissemination of information on field and laboratory test data for current and

new repair materials, and on ongoing research studies in the concrete repair

field. This could be implemented through ICRI.
24

3. SUMMARY AND RECOMMENDED ACTIONS

In the course of their discussions, the three working groups, especially Groups 2 and 3,

found that their approaches to dealing with these challenges often were similar. In some

circumstances, the working group discussions revealed that, although the participants

share similar concerns, they proposed different approaches for addressing the same

challenges. This reflects the different perspectives and expertise of the participants and

highlights the need for a regular exchange of opinions. These exchanges provide

opportunities to further coordinate and consolidate activities to improve the quality of

the concrete repair industry.

In brief, this workshop yielded a high quality attack on the problem of cracking of

concrete repairs. While it proved to be difficult to arrive at quantitative conclusions,

nonetheless, most of the critical issues were defined. This summary of the workshop

should provide useful information to those already working in this field, as well as to

those entering it for the first time.

To succeed, the concrete repair industry will need to change attitudes toward research,

design, material manufacture, construction, quality control, and education. The action

plan resulting from this workshop is a step in this direction, providing a list of

necessary tasks to be undertaken and serving as a catalyst for improvements in the

concrete repair industry.

Enhancing the industry knowledge base is essential for appropriate design and

construction and to make sound decisions. This activity requires creating improved

mechanisms to share the knowledge that is available, as well as developing additional

knowledge.

The following short-term action items, in addition to the items emphasized in the

working group discussions, were adopted at the plenary session of the 1999 Workshop:

ß A test method for evaluating the field performance of concrete repair materials

is to be designed, evaluated, and introduced into practice by a partnership of

the following organizations:

- Laval University

- U.S. Army Corps of Engineers

- Structural Preservation Systems, Inc.

- Conproco, Corp.

- Sika Corp.

ß Organize a joint ICRI/ACI Repair and Rehabilitation Task Force (RRTF) to

address and coordinate issues related to performance of concrete repairs.
25

ß Proceed with establishing consensus “Performance Criteria for Selection of

Repair Materials” and a standard “Repair Material Data Sheet Protocol”

(ICRI/ACI RRTF)

ß Establish a centralized site for compilation and storage of performance data on

repair materials (USACE, NIST, Laval University). The ACI Concrete Research

Council (CRC) may provide funding.

ß Develop guidelines on the use of ring test method to evaluate resistance to

cracking of repair materials (ICRI).

ß Organize a Symposium on Performance of Repair Materials during the 2001

ICRI International Congress.

ß The next workshop, with the theme “Improving the Performance of Concrete

Repairs,” will take place in 2001, in Quebec, Canada.

The 1999 Workshop speaks directly to the concrete repair community: to the owners,

designers, and contractors; to manufacturers; to research laboratories; to universities; to

professional societies and trade associations. This workshop summary also speaks to

the government agencies who have responsibilities to help provide quality public

structures for their citizens.

Finally, the discussions and summary of this workshop do not give the final solution for

predicting the field performance of concrete repairs. However, they do delineate the

critical issues that must be addressed to reach such a solution. It is hoped that

subsequent work will benefit from this workshop.
26

4. REFERENCES

4.1 Cited References

ACI Committee 209, “Prediction of Creep, Shrinkage, and Temperature Effects in

Concrete Structures,” ACI 209R-92 (1997), ACI Manual of Concrete Practice, American

Concrete Institute, Farmington Hills, Mich.

Czarnecki, L., Garbacz, A., Lukowski, P., and Clifton, J. R., “Polymer Composites for

Repairing Portland Cement Concrete: Compatibility Project,” Technical Report

NISTIR 6394, National Institute of Standards and Technology, 1999.

Emmons, P. H., Vaysburd, A. M., Poston, R. W., and McDonald, J.E., “Performance

Criteria for Concrete Repair Materials, Phase II, Field Studies,” Technical Report

REMR-CS-60, U.S. Army Waterways Experiment Station, Vicksburg, MS, September

1998, 98 p.

McCullough, B. F. and Rasmussen, R. O., “Fast-Track Paving: Concrete Temperature

Control and Traffic Opening Criteria for Bonded Concrete Overlays,” Vol. IIHIPERPAV User’s Manual, FHWA-RD-98-168, 1999 , Federal Highway

Administration, 76 p.

Pigeon, M and Bissonnette, B., “Bonded Concrete Repairs: Tensile Creep and Cracking

Potential,” Concrete International, Vol. 21, No. 11, November 1999,, pp. 31-35.

Pinelle, D. J., “Curing Stresses in Polymer Modified Repair Mortars,” Cement, Concrete,

and Aggregates, Vol. 17, No. 2, December 1995.

Poston, R. W., Kesner, K. E., Emmons, P. H., and Vaysburd, A. M., Performance of

Concrete Repair Materials, Phase II Laboratory Results,” Technical Report, REMRCS-57, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS, April

1998, 299 p.

Shah, S. P., Ouyang, C., Marikunte, S, Yang, W, and Becq-Giraudon, E, “A Method to

Predict Shrinkage Cracking of Concrete,” ACI Materials Journal, Vol. 95, No. 4, JulyAugust 1998, p. 339-346.

Vaysburd, A. M., “Research Needs for Establishing Material Properties to Minimize

Cracking in Concrete Repairs, Summary of a Workshop,” ICRI Publication No.

Y320001, 1996, 32 p.

Vaysburd, A. M., Emmons, P. H., McDonald, J. E., Poston, R. W., and Kesner, K. E.,

“Performance Criteria for Concrete Repair Materials, Phase II Summary Report,”

Technical Report REMR-CS-62, U.S. Army Engineers Waterways Experiment

Station, Vicksburg, MS, March 1999, 72 p.
27

4.2 Suggested References

Bissonnette, B., and Pigeon, M. E., “Tensile Creep at Early Ages of Ordinary, Silica-fume

and Fiber-reinforced Concretes,” Cement and Concrete Research, 25 (5), 1995, pp. 1075-

1085.

Carino, N. J., and Clifton, J. R., “Prediction of Cracking in Reinforced Concrete

Structures,” Technical Report NISTIR-5634, National Institute of Standards and

Technology, 1995.

Chidiac, S. E., Cheung, M. S., and Mailvaganam, N., “Service Life of Patches in Concrete

Flat Slabs,” Trends in Structural Mechanics, J. Roorda and N.K. Srivastava, Eds.,

Kluwer Academic Publishers, 1997, pp. 299-308.

Emmons, P. H., Vaysburd, A. M., Pinelle, D. J., and McDonald, J. E., “Crack Resistant

Materials – The Origin of Durability of Concrete Repairs,” (ICRI) Concrete Repair

Bulletin, Vol. 10, No. 5, September/October 1997, pp. 20-23.

Krauss, P. D., and Rogalla, E. A., “Transverse Cracking in Newly Constructed Bridge

Decks,” NCHRP Report 380, Transportation Research Board, National Research

Council, Washington, DC, 1996, 126 p.

Pedersen, E. S., Spange, H., Pedersen, E. J., Jensen, H. E., Andersen, M. E., Jensen, P. F.,

and Knudsen, J. G., “HETEK, Control of Cracking in Concrete—Guidelines,” The

Danish Road Directorate, Report 120, 1997, Copenhagen, Denmark

Radocea, A, “Autogenous Volume Change of Concrete at Very Early Ages,” Magazine of

Concrete Research, Vol. 50, No. 2, June 1998, pp. 107-113.

Shah S. P., Weiss, W. J., and Yang, W., “Shrinkage Cracking—Can It Be Prevented?”

Concrete International, Vol. 20, No. 4, April 1998, pp. 51-55.

Torrenti, J. M., Granger, L., Biruy, M, and Genin, P., “Modeling Concrete Shrinkage

under Variable Ambient Conditions,” ACI Materials Journal, Vol. 96, No. 1, JanuaryFebruary 1999, pp. 35-39.

U.K. Concrete Society Working Party, “Non-structural Cracks in Concrete,” Technical

Report No. 22, 1982.

Kovler, K., Igarashi, S., and Bentur, A, “Tensile Creep Behavior of High Strength

Concretes at Early Ages,” Materials and Structures, Vol. 32, June 1999, pp. 383-387.

Yang, W., Wang, K., and Shah, S. P., “Prediction of Concrete Cracking Under Coupled

Shrinkage and Creep Conditions,” Proceedings 4th Materials Engineering Conference,

ASCE, Nov. 10-14, 1996, Washington, DC, pp. 564-573.
28

APPENDIX A

WORKSHOP PROGRAM
29

WORKSHOP ON PREDICTING THE PERFORMANCE

OF CONCRETE REPAIR MATERIALS

April 26 and 27, 1999

New England Conference Center and Hotel

Durham, New Hampshire

DAY 1

7:15 AM Registration

7:30 AM Continental Breakfast

General Session Chairman: David Fowler

The University of Texas

8:00 AM Welcome and Review of Christopher Brown

the Workshop Goals Conproco, Corp.

8:10 AM Welcome Noel Mailvaganam

NRC Canada

8:15 AM An Overview of the Research Study, Jim McDonald

“Performance Criteria for U.S. Army Corps of Engineers

Selection of Repair Materials”

8:20 AM “Performance Criteria for Selection Randall Poston

of Repair Materials: Laboratory WDP Associates

Testing”

8:50 AM “Performance Criteria for Selection Alexander Vaysburd

of Repair Materials: Field Testing” Structural Preservation Systems

9:20 AM “Performance Criteria for Selection Jim McDonald

of Repair Materials: Summary” U.S. Army Corps of Engineers

9:50 AM Coffee Break

10:00 AM “Considerations on the Dimensional Benoît Bissonnette

Compatibility of Concrete Repairs” Laval University
30

10:30 AM “Modeling the Short- and Long-Term Samir Chidiac

Behavior of Concrete Repair” Chidiac & Associates

11:00 AM “Modeling Dimensional Behavior Dennis Pinelle

of Repair Materials” Conproco, Corp.

11:30 AM “Premature Cracking in Reconstructed Daniel Cusson and

Concrete Bridge Barrier Walls” Wellington Repette

IRC/CNRC

12:00 PM “Methods for Crack Prediction of David Scott

Cementitious Repair Materials” U.S. Army Corps of Engineers

12:35 PM Lunch

1:40 PM Instructions to Working Groups Alexander Vaysburd

Structural Preservation Systems

1:50 PM Break

2:00 PM Working Group Discussions

5:00 PM Adjournment

DAY 2

7:30 AM Continental Breakfast

8:00 AM Working Group Discussions

10:00 AM Conproco Plant Tour Dennis Pinelle

Conproco, Corp.

12:00 PM Lunch

1:00 PM Plenary Session Chairman: Peter Emmons

Reports from Chairs of Working Groups Structural Preservation

Systems

2:30 PM Final Discussions and Recommendations

for Action
31

3:00 PM Adjournment
32

APPENDIX B

WORKSHOP PARTICIPANTS

AND WORKING GROUP MEMBERS
33

WORKSHOP PARTICIPANTS

Name Company

Benoît Bissonnette Laval University, Canada

Christopher Brown Conproco, Corp.

Douglas Burke Naval Facilities Engineering Service Center

Nicholas Carino NIST

Samir Chidiac Chidiac & Associates

Ian Christopher Conproco, Corp.

Milt Collins ICRI

Daniel Cusson NRC Canada

Peter Emmons Structural Preservation Systems

David Fowler The University of Texas

Tim Gillespie Sika Corporation

Paul Kelley Simpson, Gumpertz and Heger

Noel Mailvaganam NRC Canada

Beatrice Martin-Perez NRC Canada

David McDonald U.S. Gypsum

James McDonald U.S. Army Corps of Engineers

Rod Meyers Master Builders, Inc.

Matt Miltenberger Master Builders, Inc.

Christopher Piecos Five Star Industries

Michel Pigeon Laval University, Canada

Dennis Pinelle Conproco, Corp.

Randall Poston WDP & Associates

Gajanan Sabnis Howard University

David Scott U.S. Army Corps of Engineers

Heather See Master Builders, Inc.

Ken Snyder NIST

Paul Tourney W.R. Grace & Co.

Alexander Vaysburd Structural Preservation Systems

James Warner Consultant

Daniel Webber NY/NJ Port Authority
34

Workshop Participants at Opening Session

Dennis Pinelle hosts tour of Conproco Laboratory
35

Samir Chidiac during Working

Group 1 discussion

David McDonald during Working

Group 3 discussion

Gajanan Sabnis (L) and

Noel Mailvaganam (R)

during Working Group 3

discussion

Heather See, Chris Brown, and David Fowler (L to R) during Working

Group 3 discussion
36

WORKING GROUP 1

MODELING

Chairman: Nicholas Carino, NIST, USA

Co-chairman: Beatrice Martin-Perez, NRC, Canada

Benoît Bissonnette Laval University, Canada

Samir Chidiac Chidiac & Associates, Canada

Ian Christopher Conproco, Corp., USA

Rod Meyers Master Builders, Inc., USA

Matt Miltenberger Master Builders, Inc., USA

Dennis Pinelle Conproco, Corp., USA

David Scott U.S. Army Corps of Engineers, USA

Ken Snyder NIST, USA

Paul Tourney W.R. Grace & Co., USA
37

WORKING GROUP 2

REPAIR, DESIGN, SPECIFICATION AND APPLICATION

(USERS OF REPAIR MATERIALS)

Chairman: Randall Poston, WDP & Associates, USA

Co-chairman: Alexander Vaysburd, Structural Preservation Systems, Inc., USA

Douglas Burke Naval Facilities Engineering Service Center, USA

Daniel Cusson NRC, Canada

Peter Emmons Structural Preservation Systems, USA

Paul Kelley Simpson, Gumpertz and Heger, USA

James McDonald U.S. Army Corps of Engineers, USA

James Warner Consultant, USA

Daniel Webber NY/NJ Port Authority, USA
38

WORKING GROUP 3

REPAIR MATERIALS AND SYSTEMS

(MATERIAL MANUFACTURERS AND RESEARCHERS)

Chairman: Michel Pigeon, University of Laval, Canada

Co-chairman: Tim Gillespie, Sika Corp., USA

Christopher Brown Conproco, Corp., USA

Milt Collins ICRI, USA

David Fowler The University of Texas, USA

Noel Mailvaganam NRC, Canada

David McDonald U.S. Gypsum, USA

Christopher Piecos Five Star Industries, USA

Gajanan Sabnis Howard University, USA

Heather See Master Builders, Inc., USA