uniaxial tensile tests to measure the bond of in situ

NISTIR 4648

NAT L INST. OF STAND & TECH R.I.C.

A11103 7iabE2

mUniaxial Tensile Tests toMeasure the Bond of in

Situ Concrete Overlays

^QC-

100

U56

//46i»8

1991

Robert G. Mathey^Lawrence I. Knab^

^Guest Researcher, NIST

^Research Civil Engineer, NIST

U.S. DEPARTMENT OF COMMERCENational Institute of Standards

and Technology

Building and Fire Research Laboratory

Building Materials Division

Gaithersburg, MD 20899

Sponsored by:

TrI-ServIce Building Materials

Investigational ProgramHeadquarters,

U.S. Army Corps of Engineers

Washington, DC 20314-1000

U.S. Navy,

Naval Facilities Engineering CommandAlexandria, VA 22332-1000

Headquarters, U.S. Air Force,

Engineering and Services

Boiling Air Force Base, DC 20332-5000

U.S. DEPARTMENT OF COMMERCERobert A. Mosbacher, Secretary

NATIONAL INSTITUTE OF STANDARDSAND TECHNOLOGYJohn W. Lyons, Director

NIST

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\

NISTIR 4648

Uniaxial Tensile Tests toMeasure the Bond of In

Situ Concrete Overlays

Robert G. Mathey^Lawrence I. Knab^

^Guest Researcher, NIST

^Research Civil Engineer, NIST

U.S. DEPARTMENT OF COMMERCENational Institute of Standards

and Technology

Building and Fire Research Laboratory

Building Materials Division

Gaithersburg, MD 20899

Sponsored by:

TrkServIce Building Materials

Investigational ProgramHeadquarters,

U.S. Army Corps of Engineers

Washington, DC 20314-1000U.S. Navy,

Naval Facilities Engineering CommandAlexandria, VA 22332-1000Headquarters, U.S. Air Force,

Engineering and Services

Bolling Air Force Base, DC 20332-5000

October 1991

U.S. DEPARTMENT OF COMMERCERobert A. Mosbacher, Secretary

NATIONAL INSTITUTE OF STANDARDSAND TECHNOLOGYJohn W. Lyons, Director

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Abstract

The feasibility of two in situ tensile test methods for use in thefield to measure the bond of concrete overlays was investigated inthe laboratory. The two test methods used pneumatic and hydraulicloading apparatuses. The uniaxial tensile tests were conductedusing partial-depth in situ cores drilled through overlay concreteand into previously cast slabs. Comparisons of the magnitude andrepeatability of the tensile strength results for the two testmethods indicated that they were comparable. The studydemonstrated that both the pneumatic and hydraulic test methods areapplicable for field use for measuring the tensile strength of thebond between a relatively thick overlay and its base concrete.

Key Words: bond, concrete, in situ, overlays, repair materials,tensile strength, test methods

111

Table of Contents1.

Introduction 1

2. Bond Strength Test Methods for Repair Materials .... 1

3

.

Laboratory Study 3

3.1 Materials3.2 Concrete Slabs3 . 3 Test Apparatus and Procedures

3.3.1 Pneumatic3.3.2 Hydraulic

4 . Test Results

4.1 Tensile Test Data4.2 Data Analysis and Discussion

5. Summary and Conclusions 9

6. Recommendations 11

7. Acknowledgments 11

8. References 12

V

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List of Tables and Figures

Table 1. Mix Proportions and Properties of Fresh Baseand Overlay Concrete 14

Table 2. Compressive Strength and Age of Base andOverlay Concrete 15

Table 3. Tensile Test Data for Slab Number 1 16Table 4. Tensile Test Data for Slab Number 2 17Table 5. Tensile Test Data for Slab Number 3 18Table 6. Summary of Tensile Test Data 19

Figure 1. Typical Concrete Slab Used for the TensileTests of Drilled Cores 20

Figure 2 . Sketch of Cross-Section of PneumaticApparatus Attached to an Isolated Core 21

Figure 3a. Pneuamtic Apparatus Positioned for Testing . . 22Figure 3b. Pneumatic Apparatus with Attached Rubber

Sheet to Reduce Movement at Failure andPrevent Damage to Piston 22

Figure 4. Heise Air Pressure Gauge with Pacing Dialused to Pressurize Piston Air Chamber ata Uniform Rate 23

Figure 5. Sketch of Cross-Section of CalibrationSetup for Pneumatic Appratus 24

Figure 6. Hydraulic Apparatus Positioned for Testing .. 25Figure 7. Tensile Core Strength Data for Overlay Over

Base Concrete (0/B)

,

Overlay ConcreteOnly (O )

,

and Base Concrete Only (B) 26Figure 8. Failed Cores from Slab No. 1 27Figure 9. Failed Cores from Slab No. 2 28Figure 10. Failed Cores from Slab No. 3 29

VI

1. Introduction

The strength of the bond between repair materials and existingconcrete is a major factor in the performance of repaired concretestructures. There is a need for a repeatable field test method tomeasure the tensile strength of this bond. Two in situ testmethods to measure the uniaxial tensile bond strength of concreteoverlays were investigated in the laboratory to determine theirfeasibility for field use. Comparisons were made of the magnitudeand repeatability of the bond strength results for the two testmethods. It is noted that the feasibility of using anotherhydraulic apparatus, similar to the one investigated in thisreport, has been demonstrated to measure tensile bond strength ofconcrete overlays (see Section 2)

.

In this report, "in situ” refers to drilling a core through anoverlay and a small distance into its base concrete and thentesting the tensile strength of the intact core, rather thanremoving the core and testing it elsewhere. These in situ testmethods have the advantage of providing results in the fieldcompared with the presently used method of drilling cores andtesting them in shear in the laboratory.

The two methods investigated were based on either a hydraulic orpneumatic apparatus. The hydraulic uniaxial tensile test apparatuswas a modification of the ACI 503R field test apparatus [1] formeasuring the adhesion between cured epoxy or other polymericcompounds and concrete. A small, portable, pneumatic apparatus wasdeveloped at the National Institute of Standards and Technology(NIST) for measuring the adhesion of protective coatings tosubstrates [2,3]. This apparatus was modified for in situmeasurements of the tensile bond strength of concrete cores whichwere drilled through concrete overlays and into base concrete.

Compared with the hydraulic test apparatus, the pneumatic testapparatus offers the potential of minimizing or eliminating theeffects of eccentric load and of more accurately controlling therate of load application. Both of the test methods investigated inthis laboratory study can potentially be used to develop orvalidate performance criteria, to accept or reject an overlayinstallation, to gain information on the possible deterioration ofthe overlay-substrate bond with time, to evaluate differentoverlays in the laboratory, and to correlate laboratory test datawith field performance of overlays.

2. Bond Strength Test Methods for Repair Materials

A brief review of some of the test methods for determining the bondof repair or overlay concrete materials to existing concrete ispresented. Some of these test methods are used extensively whileothers have had little use in the field.

1

In recent years there have been a number of reports dealing withtest methods to assess or evaluate the bond between repairmaterials and existing concrete. Included in this category of testmethods are procedures for measuring the bond between concreteoverlay materials and existing or base concrete in pavements. Bondstrength of repair and overlay concrete materials have beenmeasured both in laboratory and field tests. These tests haveincluded taking field core samples and measuring the bond by meansof shear tests in the laboratory, or by an in situ tensile bondtest performed in the field. Currently the bond between concreteoverlay materials and existing concrete pavement is generallydetermined in the laboratory using shear tests of concrete cores[4,5,6].

In a recent evaluation of repair materials with regard to selectioncriteria, a number of currently used adhesion/bond test methodswere considered, including direct tension, direct pull-off,flexure, direct shear, and slant shear [7]. The slant-shear testwas viewed as the most reliable method. It is noted that theslant-shear test is a laboratory test and is not applicable as anin situ field bond test. In another study [8], four test methodswere evaluated: slant shear, indirect tension, and two flexuraltest methods. It was found that the slant shear test method wasthe most appropriate and was therefore used to assess the effectsof various parameters on the bond strength between new and oldconcrete. In a study to evaluate spall repairs [9], specimens weredamaged by pullout testing of a metal insert embedded in concrete.The concrete was repaired with epoxy mortar and subjected topullout testing again. The study showed that the overriding factorgoverning successful repairs to concrete was the soundness of therepair plane. Knab and Spring [10] investigated the bond strengthof concrete repair materials using a slant-shear test method andtwo methods for measuring the uniaxial tensile bond strength oflaboratory-prepared specimens.

Various test methods were reviewed by Knab [11] with regard totheir use in standards, specifications, and investigations ofconcrete repair materials. All of the tests reviewed are conductedin the laboratory, except the in situ tensile bond or adhesion testmethod [1,12]. Preliminary performance criteria were developed forscreening and selecting portland cement concrete (PCC) and latex-modified concrete (LMC) materials to be overlaid on PCC pavementsand bridge decks [6]. The criteria were developed using the directshear bond test method and were based on direct shear bondstrengths of PCC and LMC overlays using cores from pavements andbridge decks and laboratory- and field-cast specimens. Two commondirect shear bond test methods are described in Reference Nos. 4

and 13.

A light, portable, hydraulic apparatus, similar to the ACI 503Rapparatus, was applied by Causey [14] to measure the bond ofconcrete overlay repair materials. The tests were intended to

2

evaluate the quality of concrete repair materials. The overlaysincluded portland cement and polymer modified concretes, which wereconsiderably thicker than the relatively thin epoxy concreteoverlays described in ACI 503R [1]. Hindo [15] used the same typeof apparatus as Causey in carrying out in situ direct tensile teststo evaluate the bond strength between overlay concrete and theexisting base concrete. A somewhat similar in situ hydraulic testmethod has been used to evaluate the bond of repair materials tosurfaces at any angle, including horizontal and vertical surfaces[16]. Examples of the use of mechanical in situ tensile bond orpull off test methods are given in Reference Nos. 17-19.

Another pneumatic apparatus, in addition to the one developed atNIST [2,3], was a device used to measure the tensile bond betweenplaster and concrete and between grout and masonry block [20].

3

.

Laboratory Study

Three concrete slabs with overlays of different compressivestrengths were cast and cured. Cores were drilled through theoverlay concrete and a small distance into the base concrete. Asteel disk was adhered to the top of the intact core using a highstrength, quick-set epoxy. The disk was attached to the hydraulicor pneumatic apparatus and the core was pulled uniaxially bysteadily increasing the hydraulic or air pressure. The failureoccurred either at the bond line, in the overlay concrete or in thebase concrete. A failure occurring at a location other than at thebond plane indicated that the bond strength of the overlay to itsbase concrete exceeded the tensile strength at the location offailure. Also, cores were drilled into overlay concrete only andbase concrete only, and the uniaxial tensile strengths of theoverlay and the base concretes were determined.

The materials and procedures used to cast the slabs, a descriptionof the slabs, and the test apparatus and procedures used to conductthe tensile tests are presented in this section of the report.

3.1 Materials

The base concrete in the three slabs was portland cement concrete(PCC) . The overlay concrete in two of the slabs was PCC and latexmodified concrete (LMC) was used in the other slab. A sketch of atypical concrete slab is shown in Figure 1. At the time oftesting, the age of the base concrete in the three slabs rangedfrom 48 to 76 days and the age of the overlay concrete ranged from7 to 28 days. The ranges in strength of the base and overlayconcretes in the three slabs were 30.3 to 31.8 MPa (4390 to 4620psi) and 24.4 to 32.9 MPa (3540 to 4770 psi)

,

respectively. Mixproportions and properties of the fresh base and overlay concretesare given in Table 1. The compressive strengths of the base and

3

overlay concrete are given in Table 2 . The base and overlayconcretes were made using ASTM Type I portland cement, siliceousconcrete sand, and 19 mm (3/4 in.) maximum size crushed stonecoarse aggregate. The concrete was mixed in a 0.25-m^ (9-ft^)capacity drum type mixer. Batch volumes for the base and overlayconcretes were 0.18 and 0.15 m^ (6.5 and 5.3 ft^) , respectively.Mixing time was about 7 minutes. The density of the fresh baseconcrete in Slab No. 1 was 2280 kg/m^ (142 Ibm/ft^) . A waterreducing admixture was used only in the first base concrete cast(Slab No. 3) , and it was found that it was not needed in subseguentbase and overlay concrete batches.

3.2 Concrete Slabs

One half of each of the three slabs had overlay concrete cast overbase concrete, one quarter of the slab had base concrete only,while the other quarter of the slab had overlay concrete only(Figure 1)

.

Base concrete was cast in wood forms that were 1400 x 1400 mm (56X 56 in.) in length and width and 100 mm (4 in.) deep. Onequadrant of the wood form, 710 x 710 mm (28 x 28 in.), did notcontain base concrete but was reserved to be used later for overlayconcrete. Reinforcing bars. No. 4 size, were spaced 200 mm (8 in.)apart in both directions of the forms as shown in Figure 1. Thebars were placed at mid depth of the forms and they extended theentire length and width of the forms (1400 mm (56 in.)).

A 50-mm (2-in.) thick overlay was cast over an area of baseconcrete of 710 x 1400 mm (28 x 56 in.) . The overlays of Slab Nos.2 and 3 were PCC and the overlay of Slab No. 1 was LMC. Prior tocasting the overlay, the surface of the base concrete was sandblasted, and the surface of the base concrete was kept wet for aperiod of about 2 hours before placing the overlay. The overlayconcrete materials were also cast in the 100 mm (4 in.) deepquarter sections (710 x 710 mm (28 x 28 in.)) of the wood forms.A sketch of a typical slab showing areas where tensile tests wereconducted for overlay over base concrete (0/B)

,

overlay concreteonly (O)

,

and base concrete only (B) is given in Figure 1.

Concrete cylinders, 150 by 300 mm (6 by 12 in.), were cast, stored,and cured along with the concrete slabs at room temperature. Thefresh concrete cylinders and slabs were moist cured for about sevendays and air dried until tested.

The compressive cylinder strengths of the overlay concrete at thetime of the tensile bond tests were 103, 86, and 81 percent of thecompressive cylinder strengths of the base concrete in Slabs No. 1,

2, and 3, respectively. Table 2 gives the compressive cylinderstrengths of concretes and their ages when tested.

4

From 1 to 3 days prior to conducting the tensile tests, 57.2 mm(2.25 in.) diameter cores 64 mm (2.5 in.) deep were drilled in theslabs using a nominal 64 mm (2.5 in.) diameter core barrel. Thecenters of the cores were spaced 200 mm (8 in.) apart in both thelength and width directions of the slabs. The cores were alsolocated in the centers of the sections determined from theintersection of the reinforcing bars. Eighteen cores were drilledin the areas where overlay concrete was placed over base concrete,and nine cores were drilled in each of the overlay concrete onlyand base concrete only areas of the slabs (see Figure 1) . Aftercoring, ground concrete and sediment were washed out of the coreholes with water using a hose.

3 . 3 Test Apparatus and Procedures

Tensile tests were performed on in situ cores drilled in theconcrete slabs using pneumatic and hydraulic test methods.Alternate pneumatic and hydraulic test locations on the concreteslabs were adjacent to each other for purposes of comparing testresults. The duration of each test was measured using a stopwatchto compute the rate of load application.

3.3.1 Pneumatic Apparatus

The pneumatic apparatus used in this study was a modification of anapparatus used to test the bond strength of coatings [2,3]. Themajor component of the pneumatic apparatus was a stainless steelpiston with an air chamber. When the piston was pressurized, itprovided a tensile force to the concrete core. A smaller diameterpiston was used in previous studies for adhesion tests of coatings.The larger diameter piston used in this study was designed for thesame maximum value of air pressure as in previous studies. In thisstudy, the inside diameter of the piston was increased to 127 mm (5in.) in order to provide a greater tensile force needed to test theconcrete cores. A sketch of the pneumatic apparatus is shown inFigure 2. By controlling the air flow into the air chamber of thepiston, the rate of applying the tensile force to the drilled corewas controlled. The tensile force that could be applied waslimited by the 0.690 MPa (100 psi) air pressure in the piston airchamber, which corresponded to a maximum load of about 9800 N (2200Ibf )

.

This value of maximum load was determined by calibration ofthe piston.

The following procedures were used for preparing the surface of theconcrete core and for adhering a steel disk through which a tensileforce was applied to the concrete core. The top surface of eachcore was cleaned with sand paper and then wiped with acetone andthe surface was allowed to dry. Proper precautions were taken withthe acetone, including care to prevent ignition of the acetone andproper handling procedures. Then a 12.7 mm (1/2 in.) thick by

5

50.8 inin (2 in.) diameter steel disk, containing a threaded steelstud, was adhered to the top surface of the core using a quick-setting, high-strength epoxy system^*^. The surface of the steeldisk to be adhered was sandblasted to provide improved bond.Heaters with a blower and a capacity of 1500 Watts were used toapply heat to the surface of the cores to assure that they were dryprior to applying epoxy. About 30 minutes of additional heatingwas applied to the epoxy system to accelerate the cure. A plasticenclosure was used to confine the heat to dry the tops of theconcrete cores to enhance bonding and to further accelerate thecure of the epoxy. The steel disks were also heated prior toapplying the epoxy.

The pneumatic test apparatus was assembled and attached to a coreas shown in Figures 2 and 3 . This apparatus included a brassbearing plate positioned over the steel disk, a rubber gasketmoistened with water, and a piston screwed onto a threaded stud.As a safety precaution, a rubber sheet was secured over theassembled pneumatic apparatus to reduce the movement of the pistonat failure (Figure 3b) and prevent damage to the piston.Introduction of air at the valve (Figure 2) resulted in (i) thesilicone^ gasket being compressed and sealed on the rubber gasket,thus sealing the piston and (ii) the air chamber in the pistonbeing pressurized, causing an upward tensile force on the threadedstud, the steel disk, and the core. After entering the intakechannel, the air travelled over the compressed gasket to adiametrically opposite position from the air intake channel, whereit entered the piston air chamber through another air channel(Figure 2) . The chamber air pressure was increased at a uniformrate of 0.0076 MPa (1.1 psi)/sec, monitored with a pacing dialattached to a calibrated Heise air pressure gauge (Figure 4) .

^ Certain manufacturers' names and names of commercialequipment, instruments, and materials are identified in this reportto adequately describe the experimental procedure. Such anidentification does not imply recommendation or endorsement by theNational Institute of Standards and Technology, nor does it implythat the equipment, instruments, or materials identified arenecessarily the best available for the purpose.

^ An epoxy-resin bonding system, Poly-Carb Mark-198, was used,and according to the manufacturer, it met the ASTM C 881Specification for Type I, II, and III, Grade 3, Class A, B, or Ctype material and was a two-component 100% solids, moistureinsensitive, epoxy-based system for use as a high-strength, non-shrink grouting material.

^ The silicone gasket was made from RTVll, a General Electricsilicone rubber compound.

6

Failure of the core occurred in the overlay, at the bond plane, orin the base concrete. The average load rate applied to the coreitself was 5690 N (1280 lbf)/inin. The load was applied until thecore failed; the air pressure at failure was recorded.

The pneumatic apparatus was calibrated to obtain the relationshipbetween air pressure in the piston and tensile force applied to thecore. This relationship was used in determining the tensile corestrengths. The setup for calibration is shown in Figure 5. Duringcalibration, care was taken to assure that the threaded rod hadample clearance along its length.

3.3.2 Hydraulic Apparatus

The equipment described in ACI 503 R [1] was modified from amechanical to a hydraulic loading apparatus by the VirginiaTransportation Research Council (VTRC) and this modified apparatuswas used in this study. The VTRC used the modified ACI 503Rapparatus to test polymer concrete overlays which were 10 to 13 mm(0.4 to 0.5 in.) thick [4].

Similar procedures for surface preparation and adhesion of steelpipe caps for tensile load application were followed as describedfor the pneumatic device (Section 3.3.1). A steel pipe cap with aflat, 50.8 mm (2 in.) diameter, machined bottom surface(sandblasted to provide better bond)

,was adhered with epoxy to the

top of the core.

The hydraulic apparatus was positioned as shown in Figure 6, witha template used to center the core with respect to the hydraulicapparatus. A plug with an attached hook was screwed into a pipecap adhered to the top of a core. The hook was connected to acalibrated dynamometer and the dynamometer was connected to ahydraulic jack. The load was carefully applied manually using alever attached to the hydraulic jack (Figure 6) . However, due tolimitations of the apparatus, the load rate varied somewhat,particularly at higher loads near failure. A stopwatch was used tocontrol the rate of applied load at regular time and loadintervals. The average load rate applied to the cores was 5340N/min. (1200 Ibf/min.). The load at failure was recorded from aload-tracking hand on the calibrated dynamometer, which had a 8896N (2000 Ibf) capacity.

4. Test Results

4.1 Tensile Test Data

Data are presented in Tables 3 to 5 for individual core specimensand the data are graphically shown in Figure 7. These tablesinclude tensile core strengths for overlay over base concrete

7

(0/B) , overlay concrete only (O) , and base concrete only (B) .

Table 6, which is a summary of tensile test data, includes theconcrete compressive strength and test age of overlay and baseconcrete for each of the three slabs.

Failure locations in the concrete cores are included in Tables 3 to5. Figures 8 to 10 are photographs of the failed cores. Ingeneral, there was little difference in the failed core lengthsusing the pneumatic compared with the hydraulic test method forcomparable tests for each of the slabs. It is noted that coresdesignated with "R" were retested and only the initial values wereincluded in the data analysis, except for one case (Table 5) . Aretest was performed only for those cases where failure occurred inthe initial test at the interface of the epoxy and the surface ofthe core. Since the surface of the core experienced little damage,the steel disk or pipe cap was adhered again using epoxy and thetensile test was repeated. The initial values had the highestfailure load values and were considered to be the mostrepresentative of the core strength. Retesting confirmed that theinitial values be selected for data analysis.

Failure information for 0/B tensile core bond tests for the threeslabs is summarized as follows. In Slab No. 1 (LMC overlay) , thelocation of the failure almost always occurred in the baseconcrete. In Slabs Nos. 2 and 3 (PCC overlay) , failure locationgenerally occurred either in the overlay concrete or at the bondinterface. When comparing the pneumatic and hydraulic test methodswith regard to failure locations in the 0/B concrete cores, therewas little difference in the failure locations in each of the threeslabs

.

4.2 Data Analysis and Discussion

The average, standard deviation, and coefficient of variationvalues for each set of specimens corresponding to 0/B, O, and Bconcretes for each slab tested are given in Table 6.

Because the failure location almost always occurred in the baseconcrete in Slab No. 1, the average tensile core strengthsrepresent minimum bond strengths. Although the data do notrepresent the maximum bond strengths, the data are applicable forcomparing the two test methods.

For Slab Nos. 2 and 3, the number of failures at the bond interfacewere about the same as the number of failures not at the bondinterface for each test method of each slab. In the data analysis,the average tensile core strength and variability were based onfailures at both locations. Thus, the average tensile corestrengths for Slab Nos. 2 and 3 represent minimum bond strengths.As with Slab No. 1, the data do not represent maximum bondstrengths, but are applicable for comparing the two test methods.

8

The relatively close agreement between average strengths for thepneumatic and hydraulic test results, for each of the nine sets ofdata, is shown in Figure 7. Although the differences in theaverage strengths between the two test methods were onlystatistically significant in one"^ of the nine cases, the averagetensile strengths from all nine cases using the pneumatic methodwere slightly greater than those of the hydraulic method. Theratio of the average pneumatic to hydraulic strengths for all ninesets of data (Table 6) ranged from 1.04 to 1.22, with an average of1.10. An explanation for the higher average pneumatic strengths isthat the pneumatic method provided a more uniform and controlledrate of loading and possibly less eccentricity than the hydraulicmethod.

With regard to precision, the coefficient of variation values oftensile core strength, with one exception, were less than 20percent for both test methods and, in most cases, were notsubstantially different when comparing the two test methods (Table6) . The overall range of coefficient of variation values for thepneumatic method (6.0-19.9) was about the same as for the hydraulicmethod (6.1-22.7)

.

The laboratory study demonstrated that the pneumatic and hydraulictest methods are viable methods for measuring the bond strengthbetween a relatively thick (about 50 mm (2 in.)) overlay and itsbase concrete. The results of the pneumatic test method werejudged to be comparable to the hydraulic test method since forequivalent sets of data:

o the average tensile strengths were not judged to besubstantially different from an engineering viewpoint(ratio of average tensile strengths of the pneumatic tohydraulic test methods ranged from 1.04 to 1.22),

o the differences in the average strengths between the twotest methods, with one exception, were not statisticallysignificant, and

o in most cases, the coefficient of variation values were notsubstantially different, and thus the precision(repeatability) of the two test methods was consideredcomparable.

5. Summary and Conclusions

A laboratory study was conducted to investigate the feasibility oftwo tensile test methods as in situ field tests to measure the bond

^ The 0/B data from Slab No. 3. This case had the highestratio of the average pneumatic to hydraulic strengths of 1.22.

9

between overlay concrete and base concrete. Tests were performedon slabs having overlay concrete cast over previously cast baseconcrete. The compressive strength of the overlay concrete wasvaried while the base concrete had about the same compressivestrength. Uniaxial hydraulic and pneumatic tensile tests wereconducted using in situ cores drilled in the slabs to measure thetensile bond strength between the overlay concrete and baseconcrete, and to measure the tensile strength of the overlay andbase concretes.

The conclusions from this laboratory study to investigate thefeasibility of using hydraulic and pneumatic uniaxial tensile testmethods as in situ field test methods are as follows:

1. A pneumatic apparatus, originally developed for measuring theadhesion of protective coatings, was modified successfully tomeasure the tensile bond strength of 57.2 mm (2.25 in.) diameterconcrete cores.

2. The pneumatic and hydraulic test methods are feasible methodsfor use in the field for measuring the tensile bond strengthbetween a relatively thick (about 50 mm (2 in.)) overlay and itsbase concrete. Although the test methods are feasible for fielduse, their applicability under varying field conditions needs to bedemonstrated

.

3. The results of the pneumatic test method were judged to becomparable to the hydraulic test method since for equivalent datasets

:

o the average tensile strengths were not judged to besubstantially different from an engineering viewpoint(ratio of average tensile strengths of the pneumatic tohydraulic test methods ranged from 1.04 to 1.22),

o the differences in the average strengths between the twotest methods, with one exception, were not statisticallysignificant, and

o with one exception, the coefficient of variation valueswere less than 20 percent for both test methods and, inmost cases, were not substantially different.

4 . Advantages of the pneumatic test method compared with thehydraulic test method are:

o the rate of load application was better controlled for thepneumatic test method, and

o the pneumatic test method has the potential to be used onhorizontal, vertical or overhead surfaces. Hydraulic testmethods [14-16] other than the one investigated and

10

mechanical test methods [17-19] have potential for use onvertical and overhead surfaces.

5.

Both test methods investigated were judged to be applicable foroverlay materials other than those included in this study, providedadequate bonding can be developed between the steel disk or pipecap and the top of the overlay. Factors affecting the bond of thesteel disk or pipe cap to the overlay need to be considered,including the effects of the water used for coring and theapplication of heat (if used) to cure the epoxy.

6.

Recommendations

1. The feasibility of using the pneumatic and hydraulic testmethods to measure in situ the tensile bond strength of overlays tobase concrete in the field should be evaluated, particularly inadverse environmental conditions (e.g., wet surfaces, or cool orcold temperatures) . It is noted that preliminary field data havebeen obtained by NIST to evaluate the feasibility of both testmethods to measure the tensile bond strength of portland cementconcrete and latex modified concrete bridge deck overlays but thedata are as yet unpublished.

2. Use of the test methods to measure the tensile bond strength ofoverlay thicknesses in excess of about 50 mm (2 in.) needs to beinvestigated, since other factors, such as eccentricity, may affectthe magnitude or precision or both. For example, methods orapparatus should be developed for reducing the eccentricity.

3. In situ, uniaxial test methods to evaluate the tensile bondstrength of repair materials on surfaces other than horizontalshould be evaluated.

7

.

Acknowledgments

This investigation was conducted under the Tri-Service BuildingMaterials Investigational Program and was jointly sponsored by theHeadquarters, U.S. Army Corps of Engineers; U.S. Navy, NavalFacilities Engineering Command; and Headquarters, U.S. Air Force,Engineering and Services.

The authors gratefully acknowledge the assistance of Frankie Davis,Nathaniel E. Waters, Edgardo Colon, and Curtis Spring for castingand preparing slabs and performing tests. Special thanks areexpressed to Frankie Davis and James Seiler who provided ideas andsuggestions for improving the test procedures. The authors alsothank their NIST colleagues, James Clifton, Geoffrey Frohnsdorff,James Pielert, and Nicholas Carino, who gave important reviewcomments. The statistical consultation provided by James J.Filliben of NIST is also acknowledged. Finally, the authors

11

appreciate the support of Denise Herbert for typing the tables.8.

References

1. "Use of Epoxy Compounds with Concrete,” Appendix A, ACI 503R-89,1990 ACI Manual of Concrete Practice - Part 5 . American ConcreteInstitute, Detroit, Michigan, 1990.

2. Seiler, J. F. , McKnight, M. E. and Masters, L. W. "Developmentof a Test Apparatus and Method for Measuring Adhesion of ProtectiveCoatings," NBSIR 82-2535, National Bureau of Standards, July 1982.

3. U. S. Patents: No. 4,393, 699 Pneumatic Adhesion Tester . July19, 1983; No. 4,491,014 Bond Testing Apparatus . Jan. 1, 1985; No.4,494,563 Fluid Safety Valve . Jan. 22, 1985.

4. Sprinkel, M. M. , "Evaluation of the Construction and Performanceof Multiple Layer Polymer Concrete Overlays, Interim Report No. 2,Condition of the Overlays after Five Years in Service," VirginiaTransportation Research Council, Report VTRC 87-R28, May, 1987.

5. Hutchinson , R. L. , "Resurfacing with Portland Cement Concrete,"NCHRP Synthesis of Highway Practice 99, Transportation ResearchBoard, Dec., 1982.

6. Knab, L. I., Sprinkel, M. M. , and Lane, O. J. , "PreliminaryPerformance Criteria for the Bond of Portland-Cement and Latex-Modified Concrete Overlays," NISTIR 89-4156, National Institute ofStandards and Technology, Nov., 1989.

7. Rizzo, E. M. and Sobelman, M. B. , "Selection Criteria forConcrete Repair Materials," ACI Concrete International, Sept.,1989.

8. Wall, J.S. and Shrive, N. G. , "Factors Affecting Bond BetweenNew and Old Concrete," ACI Materials Journal, March-April, 1988,pp. 117-125.

9. Collins, F. G. and Roper, H. , "Evaluation of Concrete SpallRepairs by Pullout Test," RILEM, Materials and Structures, 22

,

1989, pp. 280-286.

10. Knab, L. I. and Spring, C. B. , "Evaluation of Test Methods forMeasuring the Bond Strength of Portland Cement Based RepairMaterials to Concrete," Cement, Concrete, and Aggregates, Summer1989, ASTM, Phil. PA. pp.3-14.

11. Knab, L. I., "Factors Related to the Performance of ConcreteRepair Materials," Repair, Evaluation, Maintenance, andRehabilitation Research Program, Technical Report REMR-CS-12, U. S.

Army Corps of Engineers, Wash DC, 20314-1000, March, 1988.

12

12. AASHTO, Standard Method for Testing Epoxy Resin Adhesive,AASHTO T 237-73 (1982), AASHTO, Wash. D.C.

13. "Method of Test for Determining the Shearing Strength of BondedConcrete," Test Method No. Iowa 406-B, September 1984, IowaDepartment of Transportation, Highway Division (2 pages)

.

14. Causey, F. E. , "Preliminary Evaluation of a Tension Test forConcrete Repairs," Report No. GR-83-14, Bureau of Reclamation,Denver CO., Dec. 1984.

15. Hindo, K. R. ,"In-Place Bond Testing and Surface Preparation of

Concrete," ACI, Concrete International, Apr. 1990, pp. 46-48.

16. Peterson, C. G.,"New Bond Testing Method Developed," ConcreteRepair Bulletin, International Association of Concrete RepairSpecialists, Sept. 1990.

17. Murray A. McC. and Long, A. E.,"A Study of the In-SituVariability of Concrete Using the Pull-Off Method," Proc. Instn.Civ. Engrs., Part 2,^, Dec. 1987, pp. 731-745.

18. Long, A. E. and Murray, A. McC., "The 'Pull-Off 'PartiallyDestructive Test for Concrete," ACI SP-82, American ConcreteInstitute, Detroit Michigan, 1984, pp. 327-350.

19. Schulz, R.-R., "Repair Work - Criteria for Planning andTendering," Betonwerk und Fertigteil-Technik, Vol. 53, No. 8, 1987,pp. 574-582.

20.

Davey, R. A. and Boserio, I. M. , "Expansion Admixture forMasonry Wall Grouts," Ministry of Works and Development, Report No.4-78/1, Central Laboratories, New Zealand, August 1978.

13

Water

Sand

Coarse

Aggregate

(0

0)

t:0)aouaT3c(0

oco-Huuoaoua

oaoua

OMp(0

DQ)

Wi

O PD C< 0)

sV 0)(A U(0

oo

pM c

P 6

VO CNJ on If) in

o o o

paauX0)

U)

J1la

a o

oc(0

*0c10

n

Vj:p>1ia

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J3uoto

J310

p(0

jCp(0

0)

TS3pHuc

o2

•O tJI

c“

op0)

uucou

pc0s0)

u1

•oc(0

pHpoa

oppc«BVu

D»

oo

Hho

oO'10

ao•o

p10

V0)

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pc0)

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U 0) V10 s Pa V (0

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a <0

V aIh pH0) in» 0 pHP •

«P c

O0) 0 aSh -H u0 P 0)

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(Q iH

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0) X jC•pH Q) HP P•pH (0

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X <0

0) ^P Q>

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c PP w cp V

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01 -O pH ‘mc c 01

0 10 0 10

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a PUBc ^ -P VQ • (0 1h oa u a 10" TJ apm "pH pH UC pH VO «u o o ^ a

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Pc0)

B0)

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<t>

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•o0)

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0) 01 p kl gO' <0 O' tJ ti 0 0) '0

c 10 C <0 g a 0)

00) c

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p<0 01

'0 010) ^ « TJ P *0

o u O P (U 0 P0)

01 (0 u o ij 2 p p 4J(0 o U <0 TJ 0 (QCQ u < ^ a (0

•o

(0 01

14

Table 2. Compressive Cylinder Strength and Age of Base and Overlay Concrete

Base Concrete Overlay Concrete

Compressive CompressiveSlab No. Type Age

(days)Strength

MPa (psi)Type Age

(days)Strength

MPa (psi)

1 PCC^ 76 31.8 (4610) LMC^ 14 32.9 (4770)

2 PCC 69 31.8 (4620) PCC 28 27.4 (3980)

3 PCC 48 30.3 (4390) PCC 7-8 24.4 (3540)

^PCC denotes portland cement concrete.

^LMC denotes latex modified concrete.

15

Core^Number

Table 3

Concrete^

. Tensile Test

TensilePneumaticMPa fosi)

Data for Slab Number 1

StrengthHydraulicMPa fDsi) Failure Location

1 0/B 2.39 (346) base concrete15 0/B 2.72 (394) 80% base concrete^3 0/B 2.83 (411) 95% base concrete^

10 0/B 1.88 (272) base concrete12 0/B 2.17 (315) base concrete5 0/B 2.11 (306) base concrete

7 0/B 1.73 (251) base concrete14 0/B 2.36 (342) base concrete2 0/B 2.12 (307) base concrete6 0/B 1.97 (286) base concrete4 0/B 2.43 (352) 95% overlay concrete^

11 0/B 2.46 (357) base concrete16 0/B 1.59 (231) base concrete

25 0 3.05 (442) overlay concrete19 0 3.57 (518) overlay concrete23 0 3.05 (442) overlay concrete21 0 3.52 (511) overlay concrete27 0 2.93 (425) overlay concrete

22 0 3.39 (492) overlay concrete26 0 2.98 (432) overlay concrete24 0 2.94 (427) overlay concrete20 0 2.84 (412) overlay concrete

34 B 2.17 (315) base concrete28 B 2.30 (334) base concrete30 B 1.79 (259) base concrete32 B 1.49 (216) base concrete36 B 2.28 (330) base concrete

31 B 1.72 (249) top of concrete31R^ B 1.59 (231) base concrete33 B 1.70 (246) base concrete29 B 1.80 (261) base concrete35 B 1.94 (281) base concrete

^Failed cores shown in Figure 8.

“Compressive strengths of LMC overlay and PCC base were 32.9 and 31.8 MPa(4770 and 4610 psi)

,

respectively. Ages when tested of overlay and basewere 14 and 76 days, respectively. 0/B represents tensile bond tests ofoverlay on base concrete; 0 represents tensile tests of overlay concreteonly; B represents tensile tests of base concrete only.

^Remainder failed at bond/interface.^31R was a retest of 31; since the strength of 31 was higher than 31R, thestrength of 31 was included in the data analysis and 31R was omitted.

16

Table 4. Tensile Test Data for Slab Number 2

Tensile StrengthCore^Number Concrete^

PneumaticMPa fosi)

HydraulicMPa (TDsi) Failure Location

5 0/B 1.95 (283) bond/ interface17 0/B 2 . 63 (381) c10 0/B 2 . 17 (315) bond/ interface3 0/B 1.66 (241) bond/ interface

15 0/B 1.71 (248) c1 0/B 2 . 14 (311) overlay concrete8 0/B 1.79 (260) mostly bond/interface

18 0/B 2.36 (342) overlay concrete18R^ 0/B 1.80 (261) overlay concrete6 0/B 1.18 (171) bond/ interface

11 0/B 1.79 (260) mostly bond/interface4 0/B 1.70 (246) bond/ interface

16 0/B 2 . 15 (312) bond/ interface9 0/B 2 .32 (337) overlay concrete2 0/B 1.87 (271) mostly bond/interface7 0/B 1.83 (266) overlay concrete

14 0/B 1.28 (185) base concrete



21 B 1.82 (264) base concrete19 B 1.53 (222) base concrete23 B 1.75 (254) base concrete25 B 1.64 (238) base concrete

24 B 1.56 (226) base concrete26 B 1.45 (211) base concrete22 B 1.87 (271) base concrete

^Failed cores shown in Figure 9.

^Compressive strengths of PCC overlay and PCC base were 27.4 and 31.8 MPa(3980 and 4620 psi)

,

respectively

.

Ages when tested of overlay and basewere 28 and 69 days, respectively. 0/B represents tensile bond tests ofoverlay on base concrete; O represents tensile tests of overlay concreteonly; B represents tensile tests of base concrete only.

^For core number 17, failure occurred at two locations in overlay concrete;for core number 15, combination bond/interface and base concrete failure.

"^ISR was a retest of 18; since the strength of 18 was higher than 18R, thestrength of 18 was included in the data analysis and 18R was omitted.

17

Table 5. Tensile Test Data for Slab Number 3

Core^Number Concrete^

TensilePneumaticMPa Tosi)

StrengthHydraulicMPa fosi) Failure Location

5 0/B 2.45 (355) bond/ interface17 0/B 1.98 (287) overlay concrete8 0/B 1.90 (275) bond/ interface

13 0/B 1.63 (236) overlay concrete15 0/B 1.84 (267) overlay concrete10 0/B 2.08 (301) overlay concrete12 0/B 1.61 (234) bond/ interface3 0/B 2.07 (300) bond/interface1 0/B 1.75 (254) c

4 0/B 1.70 (246) bond/interface18 0/B 1.59 (231) bond/ interface2 0/B 1.63 (236) base concrete9 0/B 1.42 (206) overlay concrete7 0/B 1.66 (241) overlay concrete6 0/B 1.70 (246) bond/ interface

11 0/B 1.42 (206) overlay concrete16 0/B 1.11 (161) bond/ interface14 0/B 1.90 (276) bond/ interface



32 B 2.09 (303) base concrete34 B (d d34R® B 2.58 (374) epoxy/concrete34RR® B 2.36 (343) base concrete30 B 2.04 (296) base concrete36 B 1.79 (259) base concrete28 B 2.27 (329) epoxy/concrete

35 B 1.80 (261) base concrete31^ B 2.19 (317) epoxy/concrete31R^ B 2.01 (291) base concrete33 B 2.12 (307) base concrete29 B 1.45 (211) base concrete

^Failed cores shown in Figure 10.“Compressive strengths of PCC overlay and PCC base were 24.4 and 30.3 MPa(3540 and 4390 psi)

,

respectively. Ages when1 tested of overlay and basewere 7-8 and 48 days, respectively. 0/B represents tensile bond tests ofoverlay on base concrete; O represents tensile tests of overlay concreteonly; B represents tensile tests of base concrete only.

^Combination bond/interface and base concrete.^No data.®34R was a retest of 34; 34RR was a retest of 34R. Since the strength of34R was higher than 34RR and data were not obtained for 34, 34R wasincluded in the data analysis and the other two omitted.

^31R was a retest of 31; since the strength of 31 was higher than that of31R, the strength of 31 was included in the data analysis and 31R wasomitted.

18

Table

6.

Summary

of

Tensile

Test

Data

to

4)

P •

0 PO V

>1 r*P X0

p4) •

JQ 31 4)

3 C VO ID ID

Z a

p in o H•d • • •

• >1 VO 00 VO

P X(0

>. .

P 3 r) r*4) 4) • • •

0 C in O'O a ip rH

p m o n nj O O'*0 ^ • ^ • P •

• >1 n o fM in p in

> X • in • <n • pm —

*

o ^ o ^ o ^Q <0 Pa to

• s a-d wp • o O' ^ in mCO 3 r* • O' • m •

4) n n n pC • m • ^ • ina O o ^ o ^

Xp

^ dv 0 •

4) X C -H d p (N VO <NrH p 4) P 4) •o p o rH•H O' p <0 c >1 • • •

CO c p X al X p «PC 4) CO4) Pp «-s

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• • • • • •

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1

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0)

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(A

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c0Si

u to

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to to

4) 4)

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4) 4)

to to

C C4) 4)

P Pto to

P PC C4) 4)

to to

4) 4)

P P

PC T34) 4)

E0) PO

to to

4) 4)

P P0 OC C4) 4)

a a-o -o<U 4)

P P o uygo o cQ a

1x:p4)

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Pto

4)

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pfl

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poc4)

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p•d>1X•dc(0

34)

Ca

jO

19

Figure 1 . Typical Concrete Slab Used for the Tensile Tests

of Drilled Cores.

20

1.6

mm

(1/16

in.)

dia.

9.5

mm

(3/8

in.)

dia.

x

air

pressurization

31

.8

mm

(1

-1/4

in.)

long,

channels

—i

all-thread

(threads

shown)

EE

EE

CO CO

Ti

21

Figure

2.

Sketch

of

Cross-Section

of

Pneumatic

Apparatus

Attached

to

an

Isolated

Core.

Figure 3a. Pneumatic Apparatus Positioned for Testing

Pneumatic Apparatus with Attached Rubber Sheet toReduce Movement at Failure and Prevent Damage toPiston.

Figure 3b

Figure 4. Heise Air Pressure Gauge with Pacing Dial used toPressurize Piston Air Chamber at a Uniform Rate.

t23

S oO 0-0 Tl « 8O rt^’D.O (0^.Q CO-E-tio tr 0) ^

Z Q-:B Q.CO o2? ®

EECO

24

Figure

5.

Sketch

of

Cross-Section

of

Calibration

Setup

for

Pneumatic

Apparatus

slO

slO

(isd) gi6uaj)s 9J00 ansuaj.

o o o o o oin o to o in o

CO CO CM CM

0) n OU) CJ • as

a u CD o nA CU cn ^

n>

M ^ o«> o CO • ^> u 1 ^ in

O ou mo

0) CO om u • fM« u oi rH \0ja cu lO ri ^

CM>1to

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rH >1«

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sCM

o fH ro ^

x:• •po O'

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i3 a pto o prH *> <0 0)

(0 V •ok w»u « a «-Hc 0) B & a

o £ 0.o O'o < O ww

CS © OX K—>0< X

n

CQ

X

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otz;

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rHW

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o

md

o eoxx-x-x

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#

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e

oo §,

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w

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o«>

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a>

(/)

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—

-X

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E3Vc0.

II

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O

o

Si(0

rHw

X-X-

©-© ©-0X >0<r X

— CD

— O

CD

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lO

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CO tn

cvj

CM in

0)

(0

to

0) pain

'0

c(0

(0

PQ

U0)

>o>1to >1iH I—

I

u c0) o>o 0)

4->

0)

u(M O

c(0 o4-> O(0

Q >1to

s: -H4-> UCJ' 0)

c > •

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CQ >1Q) rHIH O COu

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0) 4J 4J

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U 0c: c:

o o

in

c:

0)

E-* O O

0)

u3D>•HPk

(BdV\|) ij;6uaj;s 9J00 ajisuai

26

Figure

8.

Failed

Cores

from

Slab

No

28

Figure

9.

Failed

Cores

from

Slab

No

I

i

29

Figure

10.

Failed

Cores

from

Slab

No.

uniaxial tensile tests to measure the bond of in situ

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