Evaluation of Test Methods for

Measuring the Bond Strength of

Portland-Cement Based Repair

Materials to Concrete

L. I. Knab and C. B. Spring

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Building Technology

Building Materials Division

Gaithersburg, MD 20899

April 1988

Sponsored by:

Headquarters, U.S. Army Corps of Engineers

Washington, DC 20314-1000

U.S. Navy, Naval Facilities Engineers Command

Alexandria, Va 22322-2300

' QC ~|

nn

)rce, Air Force Engineering and Services Center

1 U U

r Force Base, FL 32403-6001

- U 5 6

88-3746

1988

C .2 J

Research Information Center

National Bureau of Standards

Gaithersburg, Maryland 20899

NBSIR 88-3746

EVALUATION OF TEST METHODS FOR

MEASURING THE BOND STRENGTH OF

PORTLAND-CEMENT BASED REPAIR

MATERIALS TO CONCRETE

AJ-gso

Q-Cioo

• LJ- /H). "IlL^

L. I. Knab and C. B. Spring

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Building Technology

Building Materials Division

Gaithersburg, MD 20899

April 1 988

Sponsored by:

Headquarters, U.S. Army Corps of Engineers

Washington, DC 2031 4-1 000

U.S. Navy, Naval Facilities Engineers Command

Alexandria, Va 22322-2300

U.S. Air Force, Air Force Engineering and Services Center

Tyndall Air Force Base, FL 32403-6001

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
.
ABSTRACT

Three bond strength test methods were evaluated for screening and

selecting repair materials used in overlaying and patching

Portland cement concrete. Bond strengths of three repair

materials to base concrete were investigated using two uniaxial

tensile bond strength test methods and a slant shear bond

strength test method. The differing strengths of the repair

materials caused different failure patterns, which had to be

considered in the analyses of the failure stresses.

Substantial differences in the failure stresses of the uniaxial

tension and slant shear test methods were attributed to their

different geometries and loading conditions. These differences

emphasized the need to select test method (s) with geometry and

loading conditions which are anticipated for the in-service

repair material.

For the two higher strength repair materials investigated, the

relative precision (repeatability) of the slant shear and one of

the uniaxial tensile test methods (pipe nipple grips) were

comparable and relatively good (coefficient of variation values

were about 5 percent) . It was concluded that both the slant

shear test method and the pipe nipple grips uniaxial tensile test

iii
method are promising methods for screening and selecting repair

materials of the type investigated (portland cement concrete or

latex-modified concrete) for overlaying or patching portland

cement concrete.

Keywords; overlaying, patching, portland-cement concrete, repair

materials, slant shear bond strength, test method, -uniaxial

tensile bond strength

iv
TABLE OF CONTENTS

Page

ABSTRACT iii

1. BACKGROUND 1

2 . PURPOSE AND SCOPE . . . .................... 2

3 . SPECIMENS AND TEST METHODS . . . . 3

4. MATERIALS, MIXING, AND CURING PROCEDURES 5

5. TEST RESULTS AND DISCUSSION 8

6. CONCLUSIONS 19

7. RECOMMENDATIONS FOR FURTHER RESEARCH 22

8 . REFERENCES -> . « 25

APPENDIX A. PROCEDURE FOR SPECIMEN PREPARATION 36

v

1 . BACKGROUND

There is a need for performance tests and performance criteria

for screening and selecting materials for overlaying and patching

Portland cement concretela . For example, there are existing ASTM

test methods and specifications for using epoxy-resin bonding

systems (C 881 2

, C 882 3, C 883 4, C 884 5) and latex bonding agents

and systems (C 1042 8

, and C 1059 7) with hardened portland cement

concrete. However, test methods and specifications are needed

for other types of repair materials, such as freshly mixed plain

Portland cement concrete or latex modified concrete bonded to

hardened portland cement concrete.

The Tri-Service (U.S. Army, Navy, and Air Force) Building

Materials Investigational Program has sponsored research at the

National Bureau of Standards (NBS) to develop performahce tests

for concrete repair materials. A previous study8 developed a

test method to determine the uniaxial tensile bond strength.

That study concentrated primarily on the bond strength of new

Portland cement paste to old portland cement paste.

a Raised numerals refer to references in Section 8.
2. PURPOSE AND SCOPE

The purpose of the current study was to evaluate three bond*3

strength test methods for use in screening and selecting repair

materials used in overlaying and patching portland cement

concrete. The current study extended the previous study (reference

8) by investigating the uniaxial tensile bond strength of

concrete (instead of cement paste) with 76 mm (3 in. ) (instead of

38 mm (1.5 in.)) diameter specimens. In the current study, two

methods of gripping uniaxial tensile specimens were investigated.

Also, a modified ASTM C 882 3 slant shear bond strength test

method was conducted concurrently with the uniaxial tensile bond

test methods. Three repair materials were investigated: (1) 13

to 14 day-old portland cement concrete (PCC) on 80 day-old base PCC,

referred to as "14 Day-Old PCC"; (2) a 7 day-old latex modified

concrete (LMC) with an excessive air content on 94 day-old base

PCC, referred to as "Excessive Air LMC"? and \ 3 ) a 10 day-old LMC

with a normal air content on 129 day-old base PCC, referred to as

"Normal Air LMC" c . The test methods were evaluated by analyzing

the failure patterns, the magnitude and relative precision of the

failure stresses, and the differences in the geometry and loading

conditions between the test methods.

k When testing for bond strength, failure . could occur in

the repair material, in the base concrete, or on the bond plane.

c Additional information on the use of styrene/butadiene

latex in concrete overlays can be found in reference 11.

2
3 . SPECIMENS AND TEST METHODS

3 . 1 Uniaxial Tensile Bond Strength Specimens and Test

Methods

The following two methods of applying uniaxial tensile stress to

bond strength specimens were used. A bond strength specimen

consisted of a 76 mm (3 in.) diameter by approximately 76 mm (3

in.) -long cylinder of repair material bonded to a 76 mm (3 in.)

diameter by approximately 76 mm (3 in.) -long cylinder of base

PCC . A screw-driven testing machine was used to conduct both

uniaxial tensile test methods.

3.1.1. Friction Grips.

The required friction around the lateral surface area of the bond

strength specimen was developed by closing together the sides of

a 76 mm (3 in.) inside diameter^ by 76 mm (3 in.) -long steel pipe

which had been split along its longitudinal axis (the pipe was

one piece with a 76 mm (3 in.) -long seam). Two identical split

pipe pieces (friction grips) were used: one to grip the repair

material and the other to grip the base concrete. Figure 1 shows

the test setup, including the split pipe friction grips and their

^ The inside diameter of the steel pipe was near 76 mm (3

in.) and allowed sufficient friction to develop around the repair

material or base concrete to prevent slippage during testing.

3
universal ball and socket connections. A rubber "o'1 -ring provided

a 4.8 mm (3/16 in.) spacing between the split pipe pieces at the

bond plane.

3.1.2. Pipe Nipple Gripse

The lateral circumference of a 76 mm (3 in.) diameter by approximately

76 mm (3 in.) -long base PCC cylinder with a sawn surface was

bonded with epoxy inside of a nominal 76 mm (3 in.) inside

diameter, black steel pipe nipple (see Appendix A, Part I and

figure Al, for details) . After the epoxy had cured, the specimen

was inverted and an empty, nominal 76 mm (3 in.) inside diameter

by 76 mm (3 in.) -long, black steel pipe nipple was mounted on top

of the base concrete-pipe nipple "0"-ring assembly, and the repair

material was poured into the empty steel pipe nipple (Appendix A,

Part II). The rubber "0"-ring provided about 4.8 mm (3/16 in.)

spacing between the pipe nipples at the bond plane. Base

concrete filled this 4.8 mm (3/16 in.) spacing. The bond plane

coincided with the plane formed by the end of the pipe nipple

that contained the repair material. After curing, the repair

material had bonded to the sawn surface of the base concrete and

to the inside of the pipe nipple into which it had been poured.

In order to attach the specimen to the testing machine, pipe caps

with special attachments, including universal ball and socket

e This method was developed at Dow Chemical Co. (see

footnote g) by L. Kuhlmann.

4
connections, were screwed on the pipe nipples at both ends

(figure 2)

.

3.2 Modified ASTM Slant Shear Bond Strength Test Method

A modification of the ASTM C 882 3 slant shear bond strength test

consisted of replacing one-half of the slant shear specimen with

repair material. That is, one-half of the specimen was repair

material bonded to the other half, which was base concrete. The

angle of the shear plane was approximately 30° with respect to

the longitudinal axis of the cylinder. Figure 3 shows a slant

shear specimen being compressed.

4. MATERIALS, MIXING, AND CURING PROCEDURES

The mix proportions of base concrete and repair materials tested

are given in table *1. A nominal 12.5 mm (1/2 in.) maximum size,

crushed dolomitic limestonef aggregate (100 percent passing a

12.5 mm (1/2 in.) sieve and approximately 9 percent retained on a 9.5 mm (3/8 in.) sieve) was used in both the base PCC and the

repair material. A concrete sand with a fineness modulus of

about 2.6 and ASTM Type I portland cement were used in both the

base PCC and repair materials. In the LMC repair material, a styrene-butadiene polymer emulsion (latex) manufactured by Dow

f As reported by the supplier.

5
Chemical^ was used in which the polymer comprised about 48

percent by weight of the total emulsion. The high air content

(about 15 percent, table 1) of the Excessive Air LMC repair

material was caused by the omission of the antifoam agent in the

latex.

4 . 1 Base Concrete

After casting, the specimens of base concrete were covered with

plastic sheeting, stripped at 2 days of age, immersed in saturated

lime water for 26 days, and then air dried until tested. The

base concrete was sawn to the required geometry (either at 90° or

30° to the cylinder's longitudinal axis) using a water-lubricated,

diamond saw blade. The sawn section was placed in either a 76 mm

(3 in.) diameter by 152 mm (6 in.) -long plastic cylinder mold (type

used for molding concrete) or epoxied in a steel pipe nipple (see

Appendix A, Part I) . All sawn surfaces were sanded using

sandpaper and then wiped with a damp towel to remove any debris.

9 Certain manufacturers' names, and names of commercial

equipment, instruments, and materials are identified in this

report to adequately specify the experimental procedure. Such an

identification does not imply recommendation or endorsement by

the National Bureau of Standards, nor does it imply that the

equipment, instruments, or materials identified are necessarily

the best available for the purpose.

6
4.2 Repair Material Specimens

Immediately prior to casting the 14 Day-Old PCC and the Excessive

Air LMC repair materials onto the sawn surface of the base

concrete, a thin layer of repair material was applied to the base

concrete surface with a brush. Immediately prior to placing the

Normal Air LMC repair material, the base concrete surface was

first dampened with water and then brushed with a thin layer of

repair material. All repair materials were placed in three

layers, with each layer rodded and then tapped as necessary on

the outside of the mold for further consolidation (except that

the Normal Air LMC was vibrated instead of being tapped) . After

casting, the repair materials were covered with plastic sheeting

and then stripped at the desired age. Stripping consisted of

removal of the plastic sheeting and the plastic molds. Plastic

molds were used in fabricating the friction grips, slant shear,

and control compression specimens. Stripping ‘the pipe nipple

grips specimens consisted of removal of the plastic sheeting, but

the lateral surfaces of the cylinders remained adhered to and

sealed by the steel pipe nipples. Specimens consisting of the 14

Day-Old PCC repair material were stripped at 12 days of age and

air dried 1 to 2 days prior to testing. Specimens consisting of

the Excessive Air LMC repair material were stripped at 1 day of

age and air dried for 6 days prior to testing. Specimens

consisting of the Normal Air LMC repair material had their

plastic sheeting removed at 1 day of age and their plastic molds

7
removed for air drying 1 day prior to testing. (The latex

manufacturer had recommended that the LMC be stripped at 1 day of

age for air drying. The Normal Air LMC repair material was cast

at the latex manufacturer's laboratory and shipped by air to NBS

for testing.) All base concrete and repair materials were cast

and cured at room temperature. Specimens were dried at approximately

40 percent relative humidity. The ages of the base concrete and

repair materials when they were tested are given in tables 2 to 4

5. TEST RESULTS AND DISCUSSION

Tables 2, 3 , and 4 list the failure stress and the location and

approximate amount of the failure surface from the bond testing

of the 14 Day-Old PCC, Excessive Air LMC, and Normal Air LMC

repair materials, respectively, for the three bond test methods

studied. The information given in tables 2 to 4 regarding the

location and amount of the failure surface is explained in

Section 5.1.

With the slant shear test method, the tables give the failure

stress based on the cross-sectional area (4.561xl0“ 3 m

2 (7.07 in. 2

))

and on the elliptical bond plane area, 9.123xl0 -3 m

2 (14.14 in. 2 )*1

, as specified by ASTM C882 3 (see below) .. The failure "bond"

stress based on the elliptical bond plane area was used when

k ASTM C 882 actually specifies 9116 mm2 (= 9.116xl0" 3 m

2

and 14.13 in. 2

)

8
"comparing" the failure stress from the slant shear test method

with that from the tensile test methods. The failure stress (not

a "bond" stress) based on the cross-sectional area was used when

comparing the strength of a slant-shear specimen with the

compressive strength of a comparable 76 mm (3 in.) diameter by

152 mm (6 in.)-long control cylinder (see Section 5.2.2)

.

The failure "bond" stress as used in this paper was calculated per

ASTM C 882 ^ by dividing the failure load (P)

,

which was Collinear

with the cylindrical axis of the slant shear specimen, by the

elliptical bond plane area (9.123xl0“ 3 m2 (14.14 in. 2 )). The

nominal shear bond stress ((cos 30°xP)/14.14 in. 2

) which acts

parallel to the bond plane, however, is lower than the ASTM stress.

Based on plots of crosshead movement versus applied load in some

of the friction grips tests, the grips appeared to "seat"

themselves by slipping slightly relative to the concrete surface

as the load was being increased to its maximum value. It is

believed that this apparent "seating" did not appreciably affect

the test results. In contrast, and as expected, no apparent

slippage of the pipe nipple grips specimens was observed.

5.1 Failure Patterns

The approximate percentages of the failure surface area which

failed in the repair material, in the base concrete, or on the

9
bond plane, are given in columns 3, 4, and 5 in tables 2, 3, and

4 (the sum of columns 3, 4, and 5 is 100 percent). The percentage

of the failure surface area which occurred on the bond plane was

further distinguished as: (i) a thin layer of repair material

which adhered on the base concrete, (ii) a thin layer of base

concrete which adhered on the repair material, or (iii) a "clean"

break, where neither the repair material nor the base concrete

adhered to the other. Also, in some of the slant shear cases (see

column 6, tables 2 and 4) , the failure process produced a

separate piece which contained both the repair material and the

base concrete bonded together. Because the determinations of the

percentages of the failure surface area were estimated visually,

they are approximate values. Additional approximation occurred

when determining whether a layer of repair material or base

concrete which was adhered on the bond plane should be treated as

a "thin" layer on the bond plane (column 5) or be treated as a

separate material. For example, a "thin" layer of repair

material on the bond plane could have been entered either in

column 5 with an "r" (designating repair material) or in column 3

as a failure in the repair material. (The repair material,

however, could always be distinguished from its base concrete)

Despite these approximations, it was considered that the percentages

and locations of the failure surfaces provided a good basis for

analyzing the failure trends. As shown in tables 2 to 4 , depending

on the repair material and the test method used, failure occurred

in the repair material, in the base concrete, on the bond plane,

10
or a combination of these. The failure patterns for each of the

three repair materials are discussed below.

5.1.1 14 Day-Old PCC Repair Material

With the 14 Day-Old PCC repair material (table 2) , preferential

failure patterns for the friction grips tensile and the slant

shear test methods were not evident. This lack of failure

patterns was not unexpected with the friction grips test method,

since the tensile strength of the control repair material

specimens (1.98 MPa (287 psi) at 13 days of age, table 1) was

about the same as that estimated for the base concrete (about

2.07 MPa (300 psi) 1

). A lack of failure patterns also was not

unexpected with the slant shear test, since the average compressive

strength of the control repair material cylinders (26 MPa (3.8

ksi) , table 1) was somewhat close to that of the control base

concrete cylinders (34 MPa (4.9 ksi), table 1).

There appeared to be a pattern of preferential failure in the 14

Day-Old PCC repair material for the pipe nipple grips test

method. (Because no pipe nipple grips tensile control tests were

conducted with specimens consisting entirely of 14 Day-Old PCC,

1 The 2.07 MPa (300 psi) stress corresponds to the failure

of primarily base concrete, based on the average of the three

friction grip failure stresses in table 4 with 75 percent or more

of the failure surface having failed in the base concrete (column

4) . 11
it was not possible to comment on the apparent failure pattern by

comparing the strength of the 14 Day-Old PCC repair material to

that of the base concrete .

)

5.1.2 Excessive Air LMC Repair Material

With all three test methods, there was a clear pattern of

preferential failure in the Excessive Air LMC repair material

That is, with each specimen, the total percentage of the failure

surface which failed in the repair material in all cases exceeded

the sum of the percentage which failed in the base concrete and

the percentage which failed as "clean*1 breaks- (The total

percentage which failed in the repair material can be found in

table 3 by adding the percentage of repair material on the bond

plane which adhered to the base concrete, denoted by "r" in

column 5, to the percentage of failure in the repair material,

given in column 3 .

)

This failure pattern was as expected for the slant shear test,

since the average compressive strength of the Excessive Air LMC

control repair material cylinders (16 MPa (2.3 ksi)

,

table 1) was

substantially below that of the control base concrete cylinders

(about 34 MPa (4.9 ksi), table 1).

This failure pattern was also expected for both tensile test

methods. With the friction grips tensile test method, the

12
estimated average tensile strength of the repair material (0.903

MPa (131 psi) , which represents the failure primarily of repair

material, table 3) was less than that estimated for the base concrete

(about 2 o 07 MPa (300 psi3 )) . Similarly, with the pipe nipple

grips tensile test method, the estimated average tensile strength

of the repair material, 1.50 MPa (217 psi), which represents the

failure primarily of repair material (table 3) , was less than

that estimated for the base concrete, 2.71 MPa (393 psi), which

represents primarily the failure of base concrete (table 4, see

Section 5.1.3)

.

5.1.3 Normal Air LMC Repair Material

There was a clear pattern of preferential failure in the base

concrete with the Normal Air LMC repair material and with the two

tensile test methods (table 4) , especially for the pipe nipple

grips method. That is, with each test specimen, the total

percentage of the failure surface which failed in the base

concrete (entries in column 4 plus "b" entries in column 5) in

almost all cases exceeded the sum of the percentage which failed

in the repair material and the percentage which failed as a "clean" break. (Because no tensile control tests were conducted

with specimens consisting entirely of Normal Air LMC, it was not

possible to comment on the failure pattern by comparing the

strength of the Normal Air LMC repair material to that of the

j See footnote "i" in Section 5.1.1.

13
I

base concrete.)

With the Normal Air LMC repair material , all the slant shear

specimens had "clean" break values of 75 percent or greater

(column 5 , table 4) . This pattern of failure along the bond plane

appeared reasonable, since the average compressive strength of

the control repair material cylinders (36 Mpa (5.2 ksi) , table

1)

j was fairly close to that of the control base concrete cylinders

(about 34 MPa (4.9 ksi), table 1). This failure trend, which differedj

from that of the tensile tests with the Normal Air LMC, may have

been caused by (i) the nature of the bond of the repair material

to its base concrete, i.e. , when subjected to slant shear, the

bond plane was weaker as compared to the repair material and the

base concrete, (ii) the possible preferential failure on the

bond plane in the slant shear test or, (iii) a combination of (i)

and (ii)

5.2 Precision and Magnitude of the Failure Stresses

Because the repair material, the base concrete, and the bond of

the repair material to the base concrete each has its characteristic

strength and variability, the amount and location of the failure

surface had to be considered when analyzing the failure stresses. I For example, and as discussed in Section 5.1.2, with the Excessive

Air LMC, there was a preferential failure in the repair material

as compared to the "remainder of the specimen" (base concrete or

14
"clean" breaks on the bond plane) . Therefore, the properties of

this repair material had a greater influence on the failure

stress statistics than the properties of the "remainder of the

specimen" for the three test methods. Similar statements can be

made regarding the other failure patterns discussed in Section 5.1.

The average and coefficient of variation values of the failure

stress for the three test methods and the three repair materials

are given in table 5.

With each of the three test methods, the average and coefficient

of variation values of the failure stress for the 14 Day-Old PCC

repair material were approximately the same as those corresponding

to the Normal Air LMC repair material (table 5) . It is worth

noting that, although the average failure stresses were approximately

the same for the 14 Day-Old PCC and the Normal Air LMC repair

materials, their failure patterns were different (see Section 5.1).

5.2 .I. Precision of the Test Methods

It was considered inappropriate to use the standard deviation to

measure the precision (repeatability about a given base line)

because of the large differences in the averages and standard

deviations of the slant shear as compared to the two tensile

tests for a given repair material (tables 2, 3, and 4). Rather,

the coefficient of variation (=(standard deviation/average) xlOO)

,

15
which is a measure of precision adjusted for the magnitude of the

average , was used as a measure of the relative precision.

The coefficient of variation values of the slant shear test

ranged from about 5 to 11 percent and were less than or equal to

those for both tensile tests when comparing with each of the

three repair materials (table 5) . This trend, though not

statistically significant^ , suggests that the relative precision

of the slant shear test was as good, and in some cases better, as

compared to the relative precision of the two uniaxial tensile test

methods

With the two higher strength repair materials, the relative

precision of the slant shear test and the pipe nipple grips test

were comparable and relatively good (coefficient of variation

values of about 5 percent, table 5)

With each of the three repair materials, the coefficient of

variation value of the pipe nipple grips test was always less

than that of the friction grips test (table 5) . This trend,

though not statistically significant (see footnote k in Section

^ In this study, the difference in the coefficient of

variation values from two samples (1 and 2) were considered to be

statistically significant if the test statistic, z, given by

Sachs9 (z = |

V

1 -V2 1 /( (v2/2n 1 ) + (v|/2n2 ) ) 1/ 2

; V = coefficient of

variation and n = sample size) was 3 or greater. Use of Sach's

test statistic was an approximation because it is for "sample

sizes not too small (n^,n2 > 30)" (compared to the sample sizes

of 7 or 8 of this study) and it was assumed that the test

statistic is normally distributed.

16
5.2.1.), suggests that the relative precision of the pipe nipple

grips test method was better than that of the friction grips test

method

.

With the 14 Day-Old PCC and the Normal Air LMC repair materials,

the coefficient of variation values were relatively low for all

three test methods and ranged from 5 to 10 percent (table 5)

.

The Excessive Air LMC repair material, however, had considerably

higher coefficient of variation values (but not statistically

significant - see footnote k in Section 5.2.1.) as compared to

the other two repair materials (table 5) for all three test

methods. Because there was a clear pattern of preferential

failure in the Excessive Air LMC repair material, it was suspected

that the higher coefficient of variation values were caused, at

least in part, by a physical property of the repair material,

such as its high air content or possibly, a lack of homogeneity.

Such a physical property could cause a greater variety of failure

locations within the repair material. The value of the coefficient

of variation is increased by an increase in the standard deviation

of the strength and by a decrease in the average strength. For a

given test method, the Excessive Air LMC had substantially

decreased average strength values (attributed to the high air

content) and increased standard deviation values as compared to

the other two repair materials (tables 2,3, and 4).

17
5,2.2 Magnitude of the Failure Stress

For each of the three repair materials , the failure stress in the

slant shear test (failure stress computed as failure load divided

by the 9ol23xl0“ 3 m2 (14,14 in, 2

) elliptical bond plane area - ASTM C 882 3

) was substantially greater1 than that for the two

tensile tests (table 5) . This substantial difference in failure

stress was attributed primarily to the different test geometry,

loading, and stresses in the slant shear test as compared to the

two tensile tests.

Values of the ratio of the slant shear average failure stress

(computed by dividing the failure load by 4.56xl0” 3 m

2 (7.07 in. 2

),

tables 2 to 4) to that of the compressive strength of the base

concrete control cylinders (about 34 MPa (4900 psi) , table 1)

were 0.81 for the 14 Day-Old PCC, 0.40 for the Excessive Air LMC,

and 0.86 for the Normal Air LMC. This ratio represents the

fraction of the strength of the slant shear composite specimen

(repair material and base concrete) relative to the compressive

strength of the base concrete control cylinders. As the strength

of the slant shear composite specimen approaches that of the base

concrete control specimen, the value of the ratio approaches unity.

A selected ratio value, then, could serve as a useful performance

1 Values of the "t" statistic (reference 10, Natrella, page

3-23) were 17 or more. These "t" values indicated that the

difference between the mean failure stress for the slant shear

test method as compared to each of the two tensile test methods

was statistically significant for each of the three repair materials.

18
criterion, provided the base concrete strength is desired to be

the basis for comparison.

The average failure stress for the pipe nipple grips test method

exceeded111 that of the friction grips test method for each of the

three repair materials (table 5) . It was believed that the

higher average failure stress was caused, at least in part, by

less eccentricity in the pipe nipple grips test method as

compared to the friction grips test method.

With each of the three test methods, the Excessive Air LMC repair

material had substantially lower average failure stresses as

compared to the other two repair materials (table 5) . The lower

strength was attributed to the excessive air content (about 15

percent)

6. CONCLUSIONS

1. Selection of Test Methods. The two types of test

methods investigated (slant shear and uniaxial tension)

had different geometry and loading conditions which

resulted in substantially different failure stresses.

These differences in failure stresses emphasized the

m Values of the "t" statistic (reference 10, Natrella, page

3-23) were 4 or more. These "t" values indicated that the

difference between the mean failure stress for the two test

methods was statistically significant for each of the three

repair materials.

19
need to select test method (s) with geometry and loading

conditions which are anticipated for the in-service

repair material.

It was concluded that both the slant shear test method

and the pipe nipple grips uniaxial tensile test method

are promising methods for screening and selecting

repair materials of the type investigated (portland

cement concrete or latex-modified concrete) for

overlaying or patching portland cement concrete. As

indicated above, the test method (s) chosen should have

geometry and loading conditions which are anticipated

for the in-service repair material.

2 . Importance of Failure Patterns. Because the repair

material, the base concrete, and the bond of the repair

material to the base concrete each has its own

characteristic failure stress and variability, failure

pattern (amount and location of the failure surface)

needs to be considered when analyzing the failure

stresses. The different characteristics of the repair

materials studied resulted in different failure

patterns. The failure pattern is important because it

indicates where the composite bond specimen (repair

material and base concrete) failed. Failure in the

20
base concrete, for example, can be desireable and

indicates that the base concrete is controlling the

strength rather than the repair material or its bond to

the base concrete.

3 . Relative Precision of the Three Test Methods. With

the three repair materials studied, the relative

precision, as measured by the coefficient of variation,

of the slant shear test method was as good, and in some

cases possibly better11 as compared to the two uniaxial

tensile test methods (table 5) . For the two higherstrength repair materials investigated, however, the

relative precision of both the slant shear and the pipe

nipple grips tensile test methods were comparable and

relatively good (coefficient of variation values of

about 5 percent)

.

4. Selection of Uniaxial Tensile Test Method. The pipe

nipple grips tensile test method was considered to be

the more promising of the two uniaxial tensile test

methods investigated because of its higher average

failure stress and possibly better11 relative precision

as compared to the friction grips test method. It was

believed that the higher average failure stress was

n The relative precision was "possibly better" because of

the trend of lower, though not statistically significant,

coefficient of variation values.

21
caused, at least in part, by less eccentricity introduced

in the pipe nipple grips test method as compared to the

friction grips test method.

5. Slant Shear Test Method Criterion. A potentially

useful criterion in establishing the minimum strength

for the slant shear test method is the fraction of the

strength of the slant shear composite specimen (repair

material and base concrete) relative to the base

concrete control specimen. Both slant shear and control

specimens need to be loaded in compression at the same

load rate and also the same cross-sectional area needs

to be used to calculate the stresses. As the strength

of the slant shear composite specimen approaches that

of the base concrete control specimen, the value of the

ratio approaches unity. A selected ratio value, then,

could serve as a useful performance criterion, provided

the base concrete strength is desired to be the basis for

comparison.

7. RECOMMENDATIONS FOR FURTHER RESEARCH ON SLANT SHEAR AND PIPE

NIPPLE GRIPS TENSILE TEST METHODS

1. Minimum strength levels related to field performance

(performance criteria) should be developed.

22
2 o The effects of the environment (e.g., temperature

or moisture cycling or both) on the bond strength of

the repair material to its base concrete should be

investigated

.

3 . The feasibility of using the test methods to

determine the bond strength of different types of

repair materials , such as polymer concrete or rapid set

concretes, should be investigated

„

4. The feasibility of using the test methods to accurately

determine the bond strength of repair materials at

early ages (e.g., 1 to 24 hours of curing) should be

evaluated.

5. The effects of surface preparation and surface

conditions of the base concrete (e.g., texture and

moisture content) on the bond strength of the repair

material should be investigated.

6. Analytical analyses, such as finite element

analyses (e.g., see reference 12), of the test methods

should be considered. These analyses, which take into

account the differences in strength and stiffness of

the components (e.g., repair material, base concrete,

pipe nipples) , should provide additional insight into

23
the failure patterns and information on the stress

distributions

7. In addition to the bond test methods investigated

in this report , other bond test methods which simulate

different types of loading conditions (e.g., flexure,

direct shear, and thermal compatibility) should be

investigated

ACKNOWLEDGMENTS

This investigation was conducted under the Tri-Service Building

Materials Investigational Program and was jointly sponsored by

the Headquarters, U.S. Army Corps of Engineers; U.S. Navy, Naval

Facilities Engineering Command; and U.S. Air Force, Air Force

Engineering and Services Center.

The authors would like to acknowledge Mr. Nat Waters of NBS for

the preparation and testing of the test specimens and Mr. Jim

Seiler of NBS for the design of the friction grips and the

uniaxial tension attachments, including the universal ball and

socket connections. The authors appreciate the statistical

consultation provided by Dr. James J. Filliben of NBS. Mr. Lou

Kuhlmann of Dow Chemical Co. is acknowledged for his assistance in

the preparation of the "Normal Air" latex modified concrete.

Ms. Denise Herbert is acknowledged for her preparation of the

tables

24
8.

REFERENCES

1. Knab, L.I., "Factors Related to the Performance of Concrete

Repair Materials," Repair, Evaluation, Maintenance, and Rehabilitation

Research Program, Technical Report REMR-CS-12, U.S. Army Corps of

Engineers, Washington D.C., March, 1988.

2. ASTM, Standard Specification for Epoxv-Resin-Base Bonding

Systems for Concrete . ASTM C 881-78 (1983) , ASTM, Philadelphia,

PA, 1978.

3. ASTM, Standard Test Method for Bond Strength of Epoxv-Resin

Systems Used with Concrete . ASTM C 882-78 (1983) , ASTM, Philadelphia,

PA, 1978.

4. ASTM, Standard Test Method for Effective Shrinkage of EpoxvResin Systems Used with Concrete . ASTM C 883-80 (1983) , ASTM,

Philadelphia, PA, 1980.

5. ASTM, Standard Test Method for Thermal Compatibility Between

Concrete and an Epoxv-Resin Overlay . ASTM C 884-78 (1983) , ASTM,

Philadelphia, PA, 1978.

6 . ASTM , Standard Test Method for Bond Strength of Latex Systems

Used with Concrete . ASTM C 1042-85, ASTM, Philadelphia, PA, 1985.

7. ASTM, Standard Specification for Latex Agents for Bonding

Fresh to Hardened Concrete . ASTM C 1059-86, ASTM, Philadelphia,

PA, 1986.

8. Struble, L. and Waters, N. , "Tensile Test to Measure Adhesion

Between Old and New Cement Paste," NBSIR 87-3685, National Bureau

of Standards, Gaithersburg, MD, January, 1988.

9. Sachs L. , Applied Statistics . Springer-Verlag New York Inc.,

1982.

10. Natrella, M. G. , "Experimental Statistics," Handbook 91,

National Bureau of Standards, Gaithersburg, MD, 1966.

11. Kuhlmann, L. A., "Using Styrene/Butadiene Latex in Concrete

Overlays," Paper Presented at the Transportation Research Board

Annual Meeting, Washington D.C., January, 1988.

12. Wall, J.S. and Shrive, N.G., "Factors Affecting Bond between

New and Old Concrete," ACI Materials Journal, March-April 1988,

pp. 117-125.

25
(T3 ja

3

S'

O "O

c -u

26
Table 2. Failure Stress and Location and Amount of Failure Surface for 14 DayOld Portland Cement Concrete Repair Material Bonded to 80-Day Old

Base Portland Cement Concrete

Bond

Test Method

Failure Stress

(psi)^ based on

7.07 in. 2 cross- sectional area.

(1)

Failure Stress

(psi)^ based on 14.14 in. 2 elliptical bond plane area.

(2)

Approximate Percentage of Failure Surface Area which Failed:

in Repair in Base on Bond in Repair Material

Material Concrete Plane+ and Base Concrete**

(3) (4) (5) (6)

Tension, 287 _ 70 30 0 0 Friction 321 - 0 95 5r 0 Grips* 281 - 75 25 0 0 256 - 25 15 30c, 30r 0 299 - 80 20 0 0 287 - • 60 40 0 0 278 - 20 30 25c, 25r 0 250 - 25 15 60c 0

Avg.- 282

Std. dev.- 22.6 COV (%) \

• 8.0

Tension, 418 - 75 5 20r 0 Pipe Nipple 412 - 90 10 0 0 Grips* 440 - 0 100 0 0 396 - 90 10 0 0 440 - 65 20 15r 0 415 - 95 5 0 0 465 - 60 40 0 0 421 - 90 10 0 0

Avg. 426

Std. dev. 21.4 COV (%) 5.0

Slant 3860 1930 45 0 20c, 30r 5 Shear** 4120 2060 10 0 25c, 25r 40 3990 2000 35 0 25c, 25r 15 4020 2010 25 0 30c, 30r 15 3580 1790 10 0 75c 15 3840 1920 80 0 20c 0 4190 2090 0 0 30c 70 4000 2000 5 0 60c 35

Avg. 3950 Std . dev. 191 COV (%) 4.8

1980

964.8

* Tested at crosshead speed of 1 mm/min.

** Loaded at approximately 89,000 N/min. (20,000 lbf./min.).

+ c = clean break, neither in repair material nor base concrete;

r = thin layer of repair material adhered on base concrete. ++ Failure process produced a separate piece which contained both

the repair material and the base concrete bonded together.

f

Avg. = average, Std. dev. = standard deviation, COV = coefficient of variation = ((standard deviation)/average) x 100.

\ 1 psi = 6895 Pa; 7.07 in. 2 = 4.56 x 10" 3 m

2

; 14.14 in. 2 = 9.123 x 10" 3 m

2 .

27
Table 3. Failure Stress and Location and Amount of Failure Surface for 7 DayOld Latex Modified Concrete ("Excessive Air") Repair Material Bonded

to 94 Day-Old Base Portland Cement Concrete

Bond

Test Method

Failure Stress

(psi)^ based on 7.07 in. ^ cross- sectional area. O)

Failure Stress

(psi)^ based on 14.14 in. 2 elliptical bond

plane area.

(2)

Approximate Percentage of Failure

in Repair in Base on Bond

Material Concrete Plane'*' (3) (A) (5)

Surface area which Failed:

in Repair Material

and Base Concrete"1""*’ (6)

Tension, 119 30 0 70r 0 Friction 128 - 30 0 70r 0 Grips* 140 - 35 0 5c,60r 0 200 - 70 0 10c, 20r 0 128 - 50 0 5c,45r 0

75 - 60 0 10c, 30r 0 128 - 30 0 70r 0 131 - 20 0 80r 0

Avg. ‘ 131 Std. dev. ' 34.1 COV (%) ir 26.0

Tension, 196 - 85 0 15r 0 Pipe Nipple 206 - 50 0 50r 0 Grips* 212 - 70 0 30r 0 203 - 10 0 90r 0 153 - 60 0 40r 0 312 - 90 0 lOr 0 234

Avg. 217

Std. dev. 48.6 COV (%) 22.4

70 0 30r 0

Slant 1900 950 0 0 lOOr 0 Shear** 1810 905 0 0 lOOr 0 1870 935 0 0 lOOr 0 2310 1155 0 0 5c, 95r 0 2340 1170 0 0 lOOr 0 1750 875 0 0 lOOr 0 1930 965 0 0 5c,95r 0 1960 980 0 0 lOOr 0

Avg. 1980 990

Std. dev. 222 111. COV (%) 11.2 11.2

* Tested at crosshead speed of 1 mm/min.

** Loaded at approximately 89,000 N/min. (20,000 lbf./min.).

+ c = clean break, neither in repair material nor base concrete;

r = thin layer of repair material adhered on base concrete. ++ Failure process produced a separate piece which contained both

the repair material and the base concrete bonded together.

-j- Avg. = average, Std. dev. = standard deviation, COV = coefficient of variation = ((standard deviation)/average) x 100.

^ 1 psi = 6895 Pa; 7.07 in. 2 = 4.56 x 10~ 2 m

2

; 14.14 in. 2 = 9.123 x 10” 2 m

2

.

28
Table 4. Failure Stress and Location and Amount of Failure Surface for 10 DayOld Latex Modified Concrete ("Normal Air") Repair Material Bonded to

129 Day-Old Base Portland Cement Concrete

Bond

Test Method

Failure Stress

(psi)^ based on

7.07 in. ^ cross sectional area.

( 1 )

Failure Stress (psi)^

based on 14.14 in.^

elliptical bond plane area.

(2)

Approximate Percentage of Failure

in Repair in Base on Bond

Material Concrete Plane+

(3) (4) (5)

Surface area which Failed:

in Repair Material

and Base Concrete’*""*’ (6)

Tension, 315 0 50 30c, 20b 0 Friction 318 - 0 5 50c, 45b 0 Grips* 306 - 0 95 5c 0 299 - 5 40 30c, 25b 0 271 - 0 75 15c, 10b 0 274 - 0 30 35c, 35b 0 237 - 0 40 40c, 20b 0 321 - 0 100 0 0

Avg. ' 293

Std. dev. ' 29.5 COV (%) 1r 10.1

Tension, 362 - 0 80 10c, 10b 0 Pipe Nipple 421 - 0 95 5b 0 Grips* 390 - 0 100 0 0 393 - 0 100 0 0 402 - 0 40 20c, 40b 0 371 - 0 100 0 0 390 - 0 85 15c 0 412 - 5 60 35c 0

Avg. 393

Std. dev. 19.6 COV (%) 5.0

Slant 4370 2185 Shear** 4200 2100

4510 2255

4100 2050

4020 2010

4280 2140

4230 2115

3880 1940

Avg. 4200 2100

Std. dev. 199. 100 COV (%) 4.7 4.7

0 0 90c 10

0 0 100c 0 0 5 95c 0

0 20 80c 0

0 15 85c 0

0 10 85c 5

0 25 75c 0

0 25 75c 0

* Tested at crosshead speed of 1 mm/min.

** Loaded at approximately 89,000 N/min. (20,000 lbf./min.).

+ c = clean break, neither in repair material nor base concrete;

b = thin layer of base concrete adhered on repair material. ++ Failure process produced a separate piece which contained both

the repair material and the base concrete bonded together.

f

Avg. = average, Std. dev. = standard deviation, COV = coefficient

of variation = ((standard deviation)/average) x 100.

\ 1 psi 6895 Pa; 7.07 in.^ = 4.56 x 10”^ m^; 14.14 in.^ = 9.123 x 10'^ m^.

29
Table

5.

Average

and

Coefficient

of

Variation

Values

for

the

Three

Test

Methods

and

Three

Repair

Materials I

o\o ' CO 03 O' > rH

flj 8

rH

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IVJ rH 8, w in o o

O' CP o o cp CP rH

Cr> rH 03 >< V o\o 9 —' o O 5a)

Q) > in 03 in rH p 03 S a — a <d o

-P °H rH X!

in Z -H

E-t si

•rHa •H £h in O' CO c 04 >- 03 rH CP 0 • 03 CO

03 Cr> >

<C o O rH

ina %

CO MO d

•H * P cu 03 rH o 1 1 •H 12 c w 0 c •H

•H 5J in -P H a 03 rH CO 0 — co co CP •H&

id 03 rH 03

tp>< ( )

tj p

pH •rH

id rH T5 p

fd rH 0 •rH P -H Q > fd •H P T •rH

fd o a-p a fd « s s

in rH 1 p Ih rH £ 5 s, 1

rHaI

rHs

•pH £•

rHrH

Q) OX

03

•S

coIo O X

co

03

o\<>

in &

in

<P

co

MO

•HWa

cps5

in8

-P

in

r—§I „(d H Q) s & o

30
Universal ball and

socket connection

Split-pipe

friction grips

Bond plane

within 4.8 mm

(3/16 in.) thick

rubber "O’-ring

Figure la. Friction-grip test setup. Friction grips attached on

a specimen, then installed in screw-driven testing machine, and

pulled in tension. Two split-pipe friction grips were used: one

gripped the repair material and the other gripped the base

concrete. A rubber "0"-ring provided a 4.8 mm (3/16 in.) spacing

between the split pipe grips at the bond plane. A universal ball

and socket connection was used at each end of the specimen - see

figure lb for details.

31
32

Figure

lb.

Split-pipe

friction

grip

attachments,

including

one

split-pipe

friction

grip

and

its

universal

ball

and

socket

connection.
Universal ball and

socket connectior

Pipe cap

Bond plane within

4.8 mm (3/16 in.)

thick rubber

"0"-ring

Figure 2a. Pipe-nipple grip test setup. Pipe caps screwed on pipe

nipples, then installed in screw-driven testing machine, and

pulled in tension. Two pipe nipples were used: one bonded to

the base concrete and the other bonded to the repair material

(Appendix A). A rubber M O

u -ring provided about 4.8 mm (3/16 in.)

spacing between the pipe nipples at the bond plane. A universal

ball and socket connection was used at each end of the specimen - see figure 2b for details.

33
34

Figure

2b.

Pipe

nipple

grip

attachments,

including

one

pipe

cap

and

its

universal

ball

and

socket

connection.
Figure 3. Slant shear specimen being compressed. One half of

the specimen is base Portland cement concrete and the other half

is repair material.

35
APPENDIX A . PROCEDURE0 FOR PREPARATION OF PIPE NIPPLE GRIPS

SPECIMENS USED IN UNIAXIAL TENSILE BOND STRENGTH TEST METHOD

Ic Method Used to Bond Base Concrete to a Nominal 76 mm (3 in.)

Inside Diameter, Black Steel, Pipe Nipple

The arrangement used to bond the base concrete to a nominal 76 mm

(3 in.) inside diameter by 76 mm (3 in.) “long, black steel, pipe

nipple is shown in figure Al. A flat, smooth, glass plate was

placed on a smooth, level working area. A thin polyethylene

sheet was placed on top of the glass surface to prevent any

excess epoxy from bonding to the glass. A 76 mm (3 in.) inside

diameter x 4 . 8 mm (3/16 in.) -thick rubber "0"-ring was placed

over the sawn end of the base concrete cylinder (figure Al) and

that end was placed on the polyethylene sheet. (The lateral

surface of the 76 mm (3 in.) diameter by 76 mm (3 in.) long base

concrete cylinder had been wiped clean and had been air dried to

insure good bonding to the epoxy. The sawn surface of the

concrete cylinder was perpendicular to the longitudinal axis of

the concrete cylinder.) Then four steps were performed in the

following order:

1. A wax seal was applied completely around the "0 M -

° Appropriate safety measures need to be followed, including

protection from acetone and the epoxy resin and its curing agent.

36
ring-polyethylene interface to prevent any excess epoxy

from contacting the sawn concrete surface (which was to

be bonded to the repair material) . The wax was applied

in its molten state and allowed to solidify by cooling

to room temperature.

2. A silicone rubber adhesive (G.E. RTV 108) seal was

applied completely around the 88 0

88 -ring-concrete

interface to insure that excess epoxy would not contact

the sawn surface of the base concrete.

3. The inside surface of a nominal 76 mm (3 in.) inside

diameterP, black steel, pipe nipple was cleaned with

acetone to provide good bonding to the epoxy. Its

entire inside surface was then coated liberally with

epoxy (Shell Oil Co. : 3 parts by mass EPON 828 epoxy

resin to 1 part by mass Shell V-25/V-125 curing agent

for epoxy resins) . Sufficient epoxy was applied so

that excess epoxy would pond between the top (non-sawn

end) of the base concrete cylinder and the pipe nipple

after the pipe nipple was placed over the base concrete

cylinder (see next step)

.

4 . To insure that the epoxy made complete contact with

P The inside diameter of the pipe nipple was slightly

greater than the 76 mm (3 in.) diameter of the base concrete cylinder.

37
the base concrete cylinder's lateral surface, the pipe

nipple was slowly and gently pushed down over the base

concrete cylinder while turning the pipe nipple until

it contacted the "0"-ring (figure Al) . The inside

diameter of the pipe nipple was large enough to fit

over the base concrete cylinder and yet close enough in

size to insure that the longitudinal axis of the

concrete cylinder was aligned with the longitudinal

axis of the pipe nipple. In some cases, after having

placed the pipe nipple (with epoxy) over the base

concrete, it was seen that the pipe nipple diameter was

a little too large to provide good alignment. In these

cases, several thin pieces of wire, fitted between the

pipe nipple and the lateral surface of the base

concrete and running parallel to the longitudinal axis

of the pipe nipple, were used to insure that the

longitudinal axes of the base concrete cylinder and the

pipe nipple were aligned. The wires were inserted

immediately after the pipe nipple was placed over the

base concrete cylinder and were spaced equally around

the circumference of the base concrete cylinder.

38
II. Mounting a Nominal 76 mm (3 in.) Inside Diameter Pipe Nipple

to Cast and Hold the Repair Material

After the epoxy in the base concrete-pipe nipple assembly (Part I.

above) had cured for at least four days at room temperature and had

attained the necessary strength to prevent slippage during

testing, the following steps were performed:

1. The base concrete-pipe nipple "O'* -ring assembly

(Part I. above) was removed from the polyethylene

sheeting and was inverted so that the sawn surface of

the base concrete was facing upward.

2. An empty, nominal 76 mm (3 in.) inside diameter, black

steel pipe nipple (inside surface of pipe nipple had

been cleaned with acetone to assure good bonding of the

repair material to the pipe nipple) was seated on the

"C'-ring and on the sawn surface end of the base

concrete. The empty seated pipe nipple was aligned

with the pipe nipple containing the base concrete and

maintained in alignment by taping with duct tape;

splints can be used, if necessary, to align and hold

both pipe nipples. After the repair material had been

cast into the empty pipe nipple and had cured, the duct

tape (and splints, if used) was removed prior to

testing.

39
Inside diameter of pipe nipple slightly

greater than the 76 mm (3 in.) diameter

of the base concrete cylinder

Threads

Nominal 76 mm (3 in.) inside diameter, 'black'

steel, pipe nipple.

Pipe nipple slowly and

gently pushed down over the concrete cylinder

while turning the pipe

nipple until it contacted

the 'O'-ring

(Appendix A, Part I, Step 4)

76 mm (3 in.) diameter x 76 mm

(3 in. ) - long

base concrete

cylinder

1

Sawn concrete

surface perpendicular to longitudinal axis

of concrete

cylinder —

Thin

polyethylene

sheet

Smooth, flat, glass plate

Lateral surface had been

wiped clean and had been

air dried to insure good

bonding to the epoxy

4.8 mm (3/16 in.) thick x 76 mm (3 in.) inside diameter

rubber "0"-ring

Silicone rubber adhesive

seal applied completely

around "O’-ring-concrete

interface

(Appendix A, Part I, Step 2)

Wax seal applied completely

around "O'-ring-polyethylene

interface

(Appendix A, Part L Step 1)

Smooth, level table/bench top

Figure Al. Sketch of setup for method to bond a nominal 76 mm (3 in.)

inside diameter, black steel pipe nipple to a 76 mm (3 in.) diameter by 76 mm

(3 in.) -long base concrete cylinder using an epoxy-resin adhesive. See

Appendix A, Part I for further details.

40
NBS-1T4A (rev. 2 »ac) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 88^3746

2. Performing Organ. Report No.| 3. Publication Date APRIL 1988

4. TITLE AND SUBTITLE

Evaluation of Test Methods for Measuring the Bond Strength of

Portland-Cement Based Repair Materials to Concrete

5. AUTHOR(S)

L.I. Knab and C.B. Spring

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8 . Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS ( Street. City , State, ZIP)

Headquarters, U.S. Army Corps of Engineers U.S. Air Force, Air Force Engineering

Washington, D.C. 20314-1000- and Services Center

TT c X7 xt j i T7 • n j Tyndall Air Force Base, FL 32403-6001

U.S. Navy, NaVal Facilities Engineers Command J * Alexandria, VA 22322-2300

10.

SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

Three bond strength test methods were evaluated for screening and selecting repair

materials used in overlaying and patching portland cement concrete. Bond strengths

of three repair materials to base concrete were investigated using two uniaxial

tensile bond strength test methods and a slant shear bond strength test method.

The differing strengths of the repair materials caused different failure patterns,

which had to be considered in the analyses of the failure stresses.

Substantial differences in the failure stresses of the uniaxial tension and slant

shear test methods were attributed to their different geometries and loading conditions. These differences emphasized the need to select test method (s) with

geometry and loading conditions which are anticipated for the in-service repair

material

.

For the two higher strength repair materials investigated, the relative precision

(repeatability) of the slant shear and one of the uniaxial tensile test methods

(pipe nipple grips) were comparable and relatively good (coef f iecient of variation

values were about 5%) . It was concluded that both the slant shear test method and

the pipe nipple grips uniaxial tensile test method are promising methods for screening and selecting repair materials of the type investigated (portland cement

concrete or latex-modified concrete) for overlaying or patching portland cement

12. KEY WORDS (Six to twelve entries ; alphabetical order; capitalize only proper names; and separate key words by semicolons)

overlaying, patching, portland-cement concrete, repair materials, slant shear bond

strength, test method, uniaxial tensile bond strength

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