NBSIR 87-3685

Tensile Test to Measure Adhesion

Between Old and New Cen^ent

Paste

L. Struble and N. Waters

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

October 1987

Issued January 1988

Progress Report

Prepared for: Headquarters, U.S. Army Corps of Engineers

Washington, DC 20314-2300

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

NBSIR 87-3685

TENSILE TEST TO MEASURE ADHESION

BETWEEN OLD AND NEW CEMENT

PASTE

L. Struble and N. Waters

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

October 1987

Issued January 1988

Progress Report

Prepaced for: Headquarters, U.S. Army Corps of Engineers

Washington, DC 20314-2300

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

Table of Contents

Page

ABSTRACT iv

INTRODUCTION 1

EXPERIMENTAL APPROACH 2

RESULTS 5

DISCUSSION 6

CONCLUSIONS 10

ACKNOWLEDGEMENTS 11

REFERENCES 12

LIST OF FIGURES

Page

Figure 1. Schematic diagram of loading configuration,

showing inner material (cement paste used as

a model for cementitious repair material)

cast between two cylinders of substrate

material (cement paste used as a model for

hardened concrete) 13

Figure 2. Saw and jig for preparing surface of substrate

material 14

Figure 3. Grips; (a) Grip No, 1, and (b) Grip No, 2 15

Figure 4, Schematic diagram showing Grip No, 1 16

Figure 5, Tank for immersing specimens during tensile loading 17

Figure 6, Tensile strength data for each of the 14 treatments 18

Figure 7, Tensile strength versus age of inner material

for the 4 treatments determined to have no

affect on strength level and variance 19

LIST OF TABLES

Page

Table 1, Summary of Treatments 20

Table 2, Tensile Strength Data 21

Table 3, Values Assigned to Parameters for Pairing Test

Treatments , 2 3

Table 4. Treatments Paired for Statistical Analysis ,,,,,,, 24

Table 5, Results of Statistical Analyses Comparing each

Pair of Treatments for Variance (F-test) and mean

(t-test) 25

Table 6, Summary of Test Parameters 26

iii
ABSTRACT

A tensile test has been developed to measure the adhesion of

repair material to hardened concrete using specimens of repair

material cast between two cylinders of hardened substrate

material. Cement paste was used as the model material for both

the repair material and the hardened substrate. Aspects of the

test procedure that appeared to affect the strength data included

the jig used to cut the hardened substrate surface in preparing

the composite specimen, the grips used during the tensile test,

the crosshead speed, exposure condition during loading, and

possibly the age of the repair material. The adhesion of cement

paste to a hardened cement paste substrate was approximately 2.7

MPa, with a coefficient of variation of 15 percent. The test

provides a method for measuring tensile strength of the bond

between repair material and concrete substrate under controlled,

laboratory conditions, for use in evaluating materials, surface

preparation methods, and application procedures.

Key words: adhesion, bond, cement, concrete, tensile strength,

test me tho d

.

iv
INTRODUCTION

Repair and rehabilitation of concrete are becoming increasingly important as the nation seeks to extend the life of

existing concrete structures. Therefore, increased attention

should be given to the technology and practice of concrete

repair. The goal of this project is to contribute to understanding

the factors controlling the performance of cementitious materials

for concrete repair, and the formation of a technical basis for

developing guidelines for selection of repair materials.

Strong adhesion of repair material to the underlying

concrete is considered essential to the repair of concrete

structures. Achieving strong adhesion generally involves both

effective preparation of the old concrete surface, and proper

selection and application of the repair material. Typical

cementitious repair materials are concrete or mortar containing

some organic polymer. Measuring strength of adhesion between the

repair material and its concrete substrate can be used to

evaluate both effectiveness of the surface preparation and

performance of the repair material.

Test methods for adhesion strength, reviewed by Sasse and

Fiebrich [1]

,

and more recently by Knab [2]

,

include measurements

of shear strength [3-5] and tensile strength [5-7] . The shear

methods are variants of the slant-shear test, in which the

concrete is bonded on a plane oblique to the loading axis and

loaded in compression to attain an indirect shear loading. The

slant-shear test has been adopted by ASTM for me’asuring strength

of the bond between epoxy-resin materials and concrete [3] . However, no similar standard test exists based on tensile

strength. It is considered that an available method for measuring

tensile test strength would contribute to understanding adhesion

and to assessing material performance.

The objective of the present investigation is development of

a method for measuring the uniaxial tensile strength of the

adhesion of repair material to a concrete substrate, and to carry

out preliminary studies to assess the method. There appears to

be little information concerning expected levels of strength and

variance for the test being developed. Mindess and Struble [8]

measured the strength between cement paste and aggregate using a tensile test, and reported strength values of 2 to 4 MPa at 7

days, a slightly higher value at 28 days, and a coefficient of

variation (la/mean) of ~30 percent. This coefficient of variation

is probably excessive if the test is to allow assessing the

performances of materials. The strength of concrete in a direct

tensile test has a coefficient of variation of approximately 7

percent [9]

,

probably a reasonable target level for a bond

tens ile test.

1
EXPERIMENTAL APPROACH

The experimental approach consisted of developing a general

test procedure, then varying certain test parameters to evaluate

their effect on the strength level and on the precision of strength

data. Finally, preliminary tests were carried out using a

commercially available repair material.

The loading configuration, shown schematically in Fig, 1,

involved composite specimens with repair material sandwiched

between two cylinders of substrate, loaded in uniaxial tension.

In these preliminary studies, cement paste was used as a model

material for both cementitious repair material and concrete

substrate. In addition to the cement paste, one commercially

available repair material, a cementitious grout^’^, was tested to

determine whether the procedure may be suitable for repair materials

All cement pastes were prepared from the same Type I^ portland

cement with a wa t e r - to - c ement ratio of 0,35 (by weight). The

grout was mixed with water using a wa t e r - t o - s o 1 i d ratio of 0.20,

following the manufacturer's instructions. The pastes and grout

were mixed according to a standard procedure [10]

.

Substrate paste was cast in cylindrical molds of waxed

cardboard, 38 mm (1-1/2 in) diameter and 76 mm (3 in) height.

Paste was placed in the mold and consolidated using a vibrating

table until no further air bubbles were observed. Specimens were

cured for 24 hours in a moist cabinet, at 27°C and 92 percent

relative humidity. They were then demolded and cured at room

temperature (~23°C) until the desired age, usually 7 to 14 days.

Samples were immersed in an aqueous solution saturated with

Ca(0H)2 so solid Ca(0H)2 from the hydrated cement would not

dissolve during curing.

One face of each hardened cement-paste substrate cylinder

was prepared for casting fresh cement paste. This face was cut

to form a smooth, planar surface normal to the loading axis,

using a low-speed, diamond saw^ lubricated with water during

^Certain trade names and company products are identified to

specify adequately the experimental procedure. In no case does

such identification imply recommendation or endorsement by the

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

are necessarily the best available for the purpose.

^Masterflow 713, obtained from Master Builders, Inc.,

C 1 eve 1 and , OH

.

^As defined by ASTM C 150-85, Standard Specification for

Portland Cement.

^Buehler Isomet with low-density blade.

2
cutting. One of two jigs was used to hold the cylinder during

cutting: Jig No. 1, supplied with the saw, and Jig No. 2

(Fig. 2), designed in the course of these studies (See results).

The composite specimens were prepared as a sandwich of

cement paste or other repair material between two cylinders of

hardened cement paste. A mold was utilized such that fresh paste

or other repair material of desired thickness could be cast

between the two cylinders. Cement paste was prepared as described

previously, and inserted into the mold. The composite specimens

were vibrated to consolidate, as described previously, with the

axis of the cylinder horizontal to avoid weakening the bond by

entrapping air bubbles at the interface. Specimens were allowed

to harden in the mold for 24 hours in the moist cabinet, then

demolded and immersed in a solution saturated with Ca(0H)2 for

the desired curing time, usually 7 to 30 days.

An objective of this investigation was to identify grips for

the tensile test that would provide uniaxial tension with minimum

shear or torque, would hold specimens tightly enough to prevent

slippage, and would not cause stress concentrations that affect

the strength measurement. We initially considered using a cable

puller, a wire mesh tube designed to grip cable in order to pull

it through conduit, which had been used in an earlier study of

the bond between cement paste and aggregate [8]

.

This grip

appeared to provide adequate gripping but only moderate precision

of tensile strength data (as discussed previously, the typical

coefficient of variation was ~30 percent). Two grips were used

in the present study. Grip No. 1 (Figs. 3 and 4) was based on a grip designed in our laboratory for calibrating a pneumatic testing

device [11] . Key features of the design included clamps to

prevent slippage and universal joints to maintain a loading axis

free of shear and torque. This design was modified in Grip No, 2

(Fig. 3) to allow more convenient mounting of the specimen,

retaining the univeral joints but replacing the clamps with rigid

brackets. This grip, however, showed evidence of slipping (See

results )

.

Composite specimens were loaded using a universal testing

machine^ equipped with an electronic load cell and monitored using

an XY recorder. The crosshead speed (loading rate) was varied

between 0.1 and 100 mm/min. For most tests, specimens were

immersed in a solution saturated with Ca(0H)2 during the tensile

loading, using a tank designed for this purpose (Fig, 5); for

comparison, a few specimens were tested in laboratory air.

With only one exception, all specimens failed at the

interface between the inner material and one of the cylinders of

^ Ins tr on 112 5.

3
hardened paste. Little inner material was observed adhering to

the substrate material after specimens were tested.

To calculate tensile strength, the load at failure is

divided by the cross-sectional area of the specimen. Measurements

of the diameters of 10 specimens provided a cross-sectional area

of 895 mm^ with coefficient of variation of only 0.3 percent.

Based on this low variance, the cross-sectional area was assumed

to be the same for all specimens.

4
RESULTS

The experimental test design consisted of seven variables

with fourteen different data sets (Table 1), The tensile

strength data are presented in Table 2 and Fig. 6. Both the

strength level and the standard deviation varied among the

treatments. Strength values ranged from 0.83 MPa to 3.31 MPa,

and standard deviation values ranged from 0.21 to 0.78 MPa, with

coefficient of variation between 10 percent and 68 percent,

depending on the specific treatment.

Assessments of certain test procedures were made during the

course of the study. Procedures appeared satisfactory except for

problems with one jig used to hold the substrate material while

cutting the face against which the inner material was subsequently

cast, and one type of grip used during tensile loading. The

surface of the substrate materials using Jig No. 1 was not always

normal to the cylindrical axis. A new jig, designated Jig No. 2,

was designed and constructed to hold this cylinder such that the

surface was more nearly normal. Slipping of the grips, indicated

by abrupt and transient decreases in load, was often observed

when using Grip No. 2, while Grip No. 1 showed no evidence of

s 1 ipp ing

.

5
DISCUSSION

Procedures to Analyze Test Data

Test data were analyzed using statistical methods to

determine which treatments appeared to influence either the level 1 or the precision of the tensile strength. In order to determine

whether the strength data of any treatment were significantly

different from the overall strength data, an analysis of variance

was performed on all data. The F-ratio of 2.04 calculated in

this analysis is significant at the 0.05 level^, indicating that

there are significant differences in strength data for one or

more treatment. Another statistical test, Bartlett's test, was

performed to determine whether the standard deviation of any one

treatment is significantly different from the standard deviation

of all data. The Barilett parameter, which is tested for significar

using a Chi-squared distribution, is 22.17, significant at the

0.05 level, indicating that one or more procedures have standard

deviation levels that are significantly different from the levels

of the overall strength data.

Neither the analysis of variance nor the Bartlett's test

indicate which specific procedures affect the strength level or

standard deviation. In order to determine which procedures

affect the test results, pairs of treatments were compared using

statistical methods. The pairs of procedures for these analyses |

were selected so as to vary only one parameter within each pair.

To pair the treatments for this comparison, each test parameter

was assigned a binary value (Table 3) for convenience in selecting ® treatment pairs (Table 4). It should be noted that two parameters, | spec.imen age and crosshead speed, were tested at more than two

levels, so analysis of test data using this binary approach providesj

only a preliminary indication of their effect. | Each pair of treatments was tested for equality of variance

using an F-test and for equality of mean using a pooled or j unpooled variance t-test^. The pooled variance t-test assumes i equality of variance, so those pairs of treatments that were

found to be unequal in variance were tested for equality of mean ! using an unpooled variance t-test. Since both tests assume a normal}

distribution, data for each treatment were first tested for

normality using the Wilk-Shapiro test. This test indicated that

the distribution of data for each treatment was normal. 1

^That is, there is a 95% probability that the null hypothesis of no significant diffarence may be rejected.

^The statistical analyses were carried out using RS/1 , a data

analysis system for personal computers from BBN Software Products

C o rp .

6
Results of Analysis of Test Data

Results of the statistical analysis are listed in Table 5.

Many of the parameters were varied in more than one pair of

tests, sometimes with conflicting results in terms of equality of

variance or mean. As summarized in Table 5, a few treatment

parameters appeared to affect the variance of the test results, and

a number of treatment parameters appeared to affect the mean

s t r eng th

.

One treatment parameter that clearly influenced the mean

strength was the cutting jig. In nearly every case. Jig No. 2

produced a lower mean strength than Jig No. 1. There was no

apparent effect of the jig on variance. As discussed previously,

it was observed that Jig No. 2 provided a bonding surface more

nearly and consistently normal to the central axis of the

specimen. Thus the jig appears to be an important aspect of the

tensile test procedure.

The exposure condition, whether or not the specimen is

immersed in Ca(0H)2 solution during loading, affected the mean and

possibly the variance. It was considered from previous studies

that the specimens should not be allowed to dry. Drying is known

to cause microcracks; and if the two materials dry at different

rates, the cracks may occur in paste near the interface and

reduce the measured bond strength. Thus loading in air was

expected to decrease strength level and increase variance.

However, the results were not entirely consistent with this

expectation. The tests with the specimen loaded in air produced

a higher variance, but also a higher mean strength, compared to

two similar treatments with the specimen immersed, though the

difference in variance was significant only for one of the

immersed treatments. So exposure condition appears to be an

important parameter.

The crosshead speed did not affect variance, but affected

the mean strength in some treatment pairs. Most tests were run

using a crosshead speed of 1 mm/min. When crosshead speed was

increased to 10 or 20 mm/min or decreased to 0.1 mm/min, there

was no effect on mean strength. However, increasing crosshead

speed to 100 mm/min did appear to increase significantly the

strength level.

The two grips did not affect either the variance or the mean

strength. Since Grip No. 2 tended to slip. Grip No. 1 was

preferred

.

It is not clear from the statistical results whether the age

of the sample affected the bond strength. Ages of both the inner

cement paste, used to model a repair material, and the outer

paste, used to model the concrete substrate, were not varied

appreciably or systematically in these tests. The variation of

7
age of the inner paste did not affect either the mean or variance

of bond strength. There was an indication that variation of age

of the outer paste affected the mean strength in one pair of

tests. Age of the inner material is expected to have a significant

effect on bond strength if varied more widely, e.g. between a few

days and several months. However, such a wide variation in age

was not included in the present study, and additional tests are

required to confirm any age effect.

In addition to the tests utilizing cement paste as the inner

material, one test utilized a cementitious grout. The grout did

not affect the variance, but may have affected the mean. The

mean strength using the grout was 3.14 MPa, significantly higher

than the mean strength using cement paste for one comparable

treatment, but not significantly different than the mean strength

for the other comparable treatment. The test using grout

provided a preliminary indication that the test can be used to

assess performance of cementitious repair materials.

Recommended Testing Procedures

Based on these statistical analyses, procedures for measuring

tensile strength of the bond between old and new concrete may be

described. Test parameters that appear to be important, based on

qualitative assessments and on the statistical analysis, and the

recommended procedures (Table 6) are as follows: cutting the

surface of the hardened substrate material using Jig No. 2,

loading the composite specimen using Grip No. 1, keeping the

specimens immersed in saturated Ca(0H)2 solution while loading,

and loading at a constant crosshead speed, e.g. 1.0 mm/min.

Four treatments (Numbers 4, 6, 11, and 13) utilized these

parameters. Data in these four treatments had a total sample

size of 24, an overall mean of 2.39 MPa, and a standard deviation

of 0.51 MPa, for a coefficient of variation of 26 percent. This

variance is still considered excessively high. An analysis of

variance produced an F-ratio of 7.51, which is significant at

0.05, indicating that there are still unexplained differences in

strength data between one or more individual treatment.

The difference may be due to variation in specimen age.

Strength data plotted against age of the inner material (Fig. 7)

indicate that results at the two intermediate ages, 15 and 21

days, are higher than the results at the lowest age, 7 days, and

the highest age, 28 days. As discussed previously, an effect of

age was expected, but the binary analysis showed no age effect,

perhaps as a result of that particular statistical approach. If

there is an effect of age, either of the substrate material or

the inner material, then the bond test should be carried out at a single specimen age. In that case, the test results may better

be estimated from data of each individual treatment: the mean

strength levels of these four treatments ranged from 1.9 to 2.7

8
MPa, the standard deviations ranged from 0.2 to 0.5 MPa, and the

coefficient of variation levels from 11 to 17 percent. This

range of variance is lower than the 26 percent obtained with

treatments at various ages, and closer to the 7 percent reported

by Neville [9] for the tensile strength of concrete. The effect

of specimen age on strength level and variance needs additional

s tudy

.

AddI icat ions of the Tensile Test

The test developed in the present study allows direct

determination of tensile strength of the bond between new

concrete or repair material and old concrete. This bond is more

typically evaluated using a shear test. The present work

provides a method for measuring tensile strength in addition to

shear strength of this bond. Although additional studies are

needed, it appears that under controlled, laboratory conditions,

the test can be used to evaluate materials, surface preparation

methods, or application procedures. In particular, a combination

of a tensile test, such as described in this study, and a shear

test, such as ASTM C 882, would allow selection of repair

material based on strength of adhesion to the concrete substrate.

If the substrate material is found to affect adhesion of a particular repair material, then the test can be used with a specific concrete substrate to select a repair material.

The tensile adhesion test was developed for cementitious

repair materials. In the preliminary studyes, the test appeared

to provide a satisfactory method to measure adhesion of cement

paste or grout to hardened cement paste. The test has not been

applied to repair materials that are based on materials other

than cement. It may not be suitable for materials that exhibit

substantial elastic or plastic deformation.

9
CONCLUSIONS

A tensile test has been developed to measure adhesion

strength of cementitious repair material to concrete substrate.

A preliminary study of the tensile test indicates that certain test

parameters affect strength results: the jig used to cut the

substrate surface, the grips, crosshead speed, exposure condition,

and possibly age of the inner material. Recommended procedures

are summarized in Table 6. From those tests in which these

parameters were not varied, the adhesion of cement paste to a

hardened cement paste substrate was 2.7 MPa, with a coefficient

of variation of 15 percent. Although the strength data were

scattered, the test appears to provide an acceptably low variance.

It offers a potential method for assessing the adhesion of repair

materials to the concrete substrate. Additional studies are

needed to better define test parameters that affect precision and

accuracy

.

10
ACKNOWLEDGEMENTS

This work was conducted under the Tri-Service Building

Materials Investigation 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 gratefully acknowledge the contribution of J. Seiler in the grip design.

11
REFERENCES

1. H.R. Sasse and M. Fiebrich, Bonding of polymer materials to

concrete. Materials and Structures, 16 (94) . 293- 301 (1983).

2. L.I. Knab . Performance of repair materials for concrete - a

status report. To be published (1987).

3. American Society for Testing and Materials. C882-78,

Standard Test Method for Bond Strength of Epoxy-Resin

Systems Used with Concrete. Annual Book of ASTM Standards,

Vol. 04.02, Concrete and Mineral Aggregates. Philadelphia:

ASTM ( 1986) .

4. American Society for Testing and Materials. C1042-85,

Standard Test Method for Bond S t r eng th of Latex Systems Used

with Concrete. Annual Book of ASTM Standards, Vol. 04.02,

Concrete and Mineral Aggregates. Philadelphia: ASTM

(1986) .

5. American Association of State Highway and Transportation

Officials. T237, Standard Method for Testing Epoxy Resin

Adhesive. AASHTO Materials, Part I, Tests. Washington:

AASHTO ( 1986) .

6. American Concrete Institute. 503R-80, Use of Epoxy Compounds

with Concrete, Appendix A. 1985 ACI Manual of Concrete

Practice - Part 5. Detroit: ACI (1985).

7. Japanese Industrial Standard. JIS A 6024-1981, Epoxy

Injuction Adhesives for Repairing in Buildings. Tokyo: JIS

(1981) .

8. S. Mindess and L. Struble. Preliminary data on the cementaggregate bond. Presented at the 84th Annual Meeting of the

American Ceramic Society, Cincinnati, OH (1982).

9. A.M. Neville. Properties of Concrete. 2nd Edition, 687

pages. London: Pitman Publishing Ltd (1973).

10. American Society for Testing and Materials. C305-82,

Standard Method for Mechanical mixing of Hydraulic Cement

Pastes and Mortars of Plastic Consistency. Annual Book of

ASTM Standards, Vol. 04.01, Cement; Lime; Gypsum. Philadelphi

ASTM ( 1986 ) .

11. J.F. Seiler, M.E. McKnight, and L.W. Masters. Development

of a Test Apparatus and Method for Measuring Adhesion of

Protective Coatings. NBSIR 82-2535, 36 pages. Washington:

US Department of Commerce (1982).

12
Substrate

material

Figure 1. Schematic diagram of loading configuration, showing

inner material (cement paste used as a model for

cementitious repair material) cast between two cylinders

of substrate material (cement paste used as a model for

hardened concrete).

13
fi///f///l/i/f

F i gur e 2

,

S aw and jig for preparing surface of substrate material.

14
"

-„„,7 "•"<4 s

'

(a)

15
Figure 4

Universal Joint

Nose clamp

-Outer material

Strap, 3 each,

evenly spaced

Inner material

Strap, 3 each,

evenly spaced

Outer material

Universal joint

Bolt attaches to

testing machine

. Schematic diagram showing Grip No. 1.

16
Figure 5. Tank for immersing specimens during tensile loading.

17
Figure 6. Tensile strength data for each of the 14 treatments.

18
AGE OF INNER MATERIALS (days)

Figure 7. Tensile strength versus age of inner material for the 4

treatments determined to have no affect on strength

level and variance.

19
Table 1. Summary of treatments.

Numb e r S amp 1

e

( Inner

)

Cutting

Jig

Age

Inner

( Days

)

Outer

Grip Exposure

Condition

Crosshea

Speed

( mm/m in

)

1 PASTE 1 30 42 2 IMMERSED 1

2 PASTE 1 31 43 1 IMMERSED 1

3 PASTE 1 14 28 1 IMMERSED 1

4 PASTE 2 15 22 1 IMMERSED 1

5 PASTE 2 15 22 1 IMMERSED 100

6 PASTE 2 7 14 1 IMMERSED 1

7 PASTE 1 7 14 1 IMMERSED 0 .

1

8 PASTE 1 15 22 1 IMMERSED 1

9 PASTE 1 15 22 1 IMMERSED 10

10 PASTE 1 14 21 1 IN AIR 1

11 PASTE 2 21 28 1 IMMERSED 1

12 PASTE 2 28 35 1 IMMERSED 20

13 PASTE 2 28 35 1 IMMERSED 1

14 GROUT 2 14 24 1 IMMERSED 1

20
Table 2. Tensile strength data.

Procedure

Numb e r Spec imen

Numb e r Load S tr ength

Mean

S t r eng th

S tandar

d

Deviation

Coefficient

o f

(kg) (MPa) (MPa) (MPa)

Variation

(%)

1 S27 - 29 168 1 . 44 0.83 0 . 57 68

S16-19 12 0 . 10

S35 - 37 171 1 . 47

S17-21 52 0 . 45

S31-39 145 1 .25

S18 - 32 34 0 . 29

2 S28-22 129 1 . 11 1.31 0 , 40 31

S26 - 33 131 1 , 13

S30 -40 95 0 . 82

S23 - 38 177 1 . 52

S34 230 1 . 98

3 S42 - 54 325 2 . 79 1.97 0.78 40

S43 - 52 285 2 .45

S48 -49 155 1.33

S 4 7 - 5 6 330 2 . 84

S44-45 195 1 . 68

S41- 53 85 0.73

S46 - 55 465 4 . 00

4 S74-76 320 2 .75 2 . 71 0 . 31 11

S57-72 345 2.97

S62 - 75 350 3 .01

S61-67 360 3 .09

S59-66 320 2.75

S58 - 71 290 2 . 49

S63 - 64 275 2 . 36

S60-68 245 2 . 11

S69 - 73 335 2.88

5 S65- 70 385 3 . 31 3 . 31

6 S118-128 250 2 , 15 1.86 0.21 11

S136-153 175 1 . 50

S130-137 215 1.85

S146 - 151 220 1 . 89 - S142 - 154 220 1 . 89

7 S78 - 85 60 0 . 52 0.83 0 . 24 29

S91- 103 120 1 .03

S89 - 95 135 1 . 16

S84- 92 75 0 . 64

S81- 88 90 0 . 77

21
(Table 2, cont.)

8 S96-101 105 0 . 90 1 . 32 0 .49 37

S77 - 110 95 0 . 82

S87-100 155 1 . 33

S102-108 155 1 . 33

S88-93 255 2 .19

9 S82-97 200 1 .72 1 . 74 0 . 76 44

S94- 105 140 1 . 20

S80- 90 80 0 . 69

S99-109 255 2 . 19

10 S116-120 335 2 .88 2 . 19 0 . 64 29

S133 - 138 260 2 . 23

S134-144 135 1 . 16

S124-131 290 2.49

S117-119 425 3.65

11 S129-143 415 3 . 57 2.72 0 .45 17

S123-126 280 2 .41

S148-152 320 2 . 75

S127-141 305 2 . 62

S115-147 265 2 . 28

12 S121-145 275 2 . 36 2.36

13 S122-125 200 1 . 72 1 . 94 0 .25 13

S139-140 210 1 .81

S132-149 275 2 . 36

S135-150 220 1 . 89

14 S190-203 350 3 . 01 3 . 14 0.33 10

S176-197 425 3 . 65

S193 - 201 365 3 . 14

S198 - 202 320 2 . 75

S175-200 DID NOT BREAK AT INTERFACE

22
Table 3. Values assigned to parameters for pairing test treatments.

Par ame ter Value = 1 Value = 2

Sample (inner material)

Cutting jig

Grips

Age of inner specimen

Age of outer specimen

Crosshead speed

Exposure condition

paste

No . 1

No . 1

<=18 days

<=26 days

<=1 mm/min

imme r s e d

grout

No . 2

No . 2

>18 days

>26 days

>1 mm/min

in air

23
Table 4, Treatments paired for statistical analysis.

Numbers of Paired Treatments Parameter Values

Varied parameter Test 1 Test 2 Test 1 Test 2

Age inner 2 3 31 14

Age outer 3 8 28 22

3 7 28 14

Crosshead speed 8 9 1 10

12 13 20 1

7 9 0 .

1

10

11 12 1 20

5 6 100 1

4 5 1 100

Cutting jig 2 11 1 2

4 8 2 1

5 9 2 1

2 13 1 2

6 8 2 1

4 7 2 1

6 7 2 1

Grips 1 2 2 1

Exposure condition 8 10 imme r s e d air

7 10 imme r s e d air

S amp 1

e

4 14 paste grout

6 14 paste grout

24
Table 5. Results of statistical analyses comparing each pair of

treatments for variance (F-test) and mean (t-test).

Treatment Pair

Varied parameter Test 1 Test 2 Variance Mean

Age inner 2 3 Equal Equal

Age outer 3 8 Equal Equal

3 7 Not equal Not equal

Crosshead speed 8 9 Equal Equal

12 13 _ _ _ a Equal^

7 9 Equal Equa 1

11 12 ... a Equal^

5 6 a Unequal^

4 5 a Unequal^

Cutting j ig 2 11 Equal Unequal

4 8 Equal Unequal

5 9 ... a Unequal^

2 13 Equal Unequal

6 8 Equal Equal

4 7 Equal Unequal

6 7 Equal Unequal

Grips 1 2 Equal Equal

Exposure condition 8 10 Equal Not equal

7 10 Not equal Not equal

S amp 1

e

4 14 Equal Equal

6 14 Equal Not equal

^One treatment had a for equal variance.

s amp 1

e

size of one

,

s o this pair was not tested

^One treatment had a s amp 1

e

size of one

,

s o its single value was

compared to the mean of the other treatment

.

25
Table 6. Summary of test parameters.

Parameter Recommended procedurii

Jig for cutting surface of substrate material

Grip

Crosshead speed

Exposure Condition

Age of inner material

Jig No . 2

Grip No . 1

1 . 0 mm/min

Imme r s e d

Cons t an

t

26
NBS«114A (REV. 2-80 - U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date

BIBLIOGRAPHIC DATA

REPORT NO.

SHEET (See instructions) NBSIR 87-3685 JANUARY 1988

4. TITLE AND SUBTITLE

Tensile Test to Measure Adhesion Between Old and New Cement Paste

5. AUTHOR(S)

L. Struble and N. Waters

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

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8 . Type of Report & Period Covered

Progress

9

.

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

Headquarters, U.S. Amy Corps of Engineers

Washington, D.C. 20314-2300

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

10.

SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11.

ABSTRACT (A ZOO^word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

A tensile test has been developed to measure the adhesion of repair material to

hardened concrete using specimens of repair material cast between two cylinders

of hardened substrate material. Cement paste was used as the model material for

both the repair material and the hardened substrate. Aspects of the test procedure

that appeared to affect the strength data included the jig used to cut the hardened

substrate surface in preparing the composite specimen, the grips used during the

tensile test, the crosshead speed, exposure condition during loading, and possibly

the age of the repair material. The adhesion of cement paste to a hardened

cement paste substrate was approximately 2.7 MPa, with a coefficient of variation

of 15 percent. The test provides a method for measuring tensile strength of the

bond between repair material and concrete substrate under controlled, laboratory

conditions, for use in evaluating materials, surface preparation methods, and

application procedures.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) adhesion, bond, cement, concrete, tensile strength, test method

13. AVAILABILITY

Unlimited

I I For Official Distribution. Do Not Release to NTIS

I I Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

QX] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

32

15. Price

$11.95

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