ASTM D7522/D7522M-09
(Test Method)Standard Test Method for Pull-Off Strength for FRP Bonded to Concrete Substrate
Standard Test Method for Pull-Off Strength for FRP Bonded to Concrete Substrate
SIGNIFICANCE AND USE
The pull-off strength of a bonded FRP system is an important performance property that has been used in specifications, particularly those for assessing the quality of an application. This test method serves as a means for uniformly preparing and testing bonded FRP systems, and evaluating and reporting the results.
Variations in results obtained using different devices are possible. Therefore, it is recommended that the type of adhesion test device (including manufacturer and model) be mutually agreed upon between the interested parties.
This test method is intended for use in both the field and the laboratory.
The basic material properties obtained from this test method can be used in the control of the quality of adhesives and in the theoretical equations for designing FRP systems for external reinforcement to strengthen existing structures.
SCOPE
1.1 This test method describes the apparatus and procedure for evaluating the pull-off strength of wet lay-up or pultruded (shop-fabricated) Fiber Reinforced Polymer (FRP) laminate systems adhesively bonded to a flat concrete substrate. The test determines the greatest perpendicular force (in tension) that an FRP system can bear before a plug of material is detached. Failure will occur along the weakest plane within the system comprised of the test fixture, FRP laminate, adhesive and substrate.
1.2 This test method is primarily used for quality control and assessment of field repairs of structures using adhesive-applied composite materials.
1.3 This test method is appropriate for use with FRP systems having any fiber orientation or combination of ply orientations comprising the FRP laminate.
1.4 This test method is not appropriate for use as an “acceptance” or “proof” wherein the FRP system remaining intact at a prescribed force is an acceptable result.
1.5 Pull-off strength measurements depend upon both material and instrumental parameters. Different adhesion test devices and procedures will give different results and cannot be directly compared.
1.6 This test method can be destructive. Spot repairs may be necessary. The test method will result in an exposed cut FRP section; repair methods must consider the potential for moisture uptake through this cut section.
1.7 Prior to the installation of some adhesively bonded FRP systems, the substrate concrete must be patched (often to replace lost concrete volume). This test method is not appropriate for determining the pull-off strength of the FRP from the patch material. An additional test method is required to determine the pull-off strength of the patch from the substrate concrete. Throughout this standard, “substrate” is understood to mean the concrete or concrete patch material to which the FRP is adhered.
1.8 The values stated in either SI units or inch-pound units are to be regarded as standard. Within the text, the inch-pound units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D7522/D7522M − 09
StandardTest Method for
Pull-Off Strength for FRP Bonded to Concrete Substrate
This standard is issued under the fixed designation D7522/D7522M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.8 The values stated in either SI units or inch-pound units
are to be regarded as standard. Within the text, the inch-pound
1.1 This test method describes the apparatus and procedure
units are shown in brackets. The values stated in each system
for evaluating the pull-off strength of wet lay-up or pultruded
are not exact equivalents; therefore, each system must be used
(shop-fabricated) Fiber Reinforced Polymer (FRP) laminate
independently of the other. Combining values from the two
systems adhesively bonded to a flat concrete substrate.The test
systems may result in nonconformance with the standard.
determines the greatest perpendicular force (in tension) that an
1.9 This standard does not purport to address all of the
FRP system can bear before a plug of material is detached.
safety concerns, if any, associated with its use. It is the
Failure will occur along the weakest plane within the system
responsibility of the user of this standard to establish appro-
comprised of the test fixture, FRP laminate, adhesive and
priate safety and health practices and determine the applica-
substrate.
bility of regulatory limitations prior to use.
1.2 This test method is primarily used for quality control
and assessment of field repairs of structures using adhesive-
2. Referenced Documents
applied composite materials.
2.1 ASTM Standards:
1.3 This test method is appropriate for use with FRP
C125 Terminology Relating to Concrete and Concrete Ag-
systems having any fiber orientation or combination of ply
gregates
orientations comprising the FRP laminate.
D883 Terminology Relating to Plastics
1.4 This test method is not appropriate for use as an
D3878 Terminology for Composite Materials
“acceptance” or “proof” wherein the FRP system remaining
D5229/D5229M Test Method for MoistureAbsorption Prop-
intact at a prescribed force is an acceptable result.
erties and Equilibrium Conditioning of Polymer Matrix
Composite Materials
1.5 Pull-off strength measurements depend upon both ma-
E6 Terminology Relating to Methods of Mechanical Testing
terial and instrumental parameters. Different adhesion test
E122 Practice for Calculating Sample Size to Estimate,With
devicesandprocedureswillgivedifferentresultsandcannotbe
Specified Precision, the Average for a Characteristic of a
directly compared.
Lot or Process
1.6 This test method can be destructive. Spot repairs may be
necessary. The test method will result in an exposed cut FRP
3. Terminology
section; repair methods must consider the potential for mois-
3.1 Definitions—Terminology D3878 defines terms relating
ture uptake through this cut section.
to high-modulus fibers and their composites. Terminology
1.7 Prior to the installation of some adhesively bonded FRP
D883definestermsrelatingtoplastics.TerminologyE6defines
systems, the substrate concrete must be patched (often to
termsrelatingtomechanicaltesting.TerminologyC125defines
replace lost concrete volume). This test method is not appro-
terms relating to concrete. In the event of a conflict between
priate for determining the pull-off strength of the FRPfrom the
terms, Terminology D3878 shall have precedence over the
patch material. An additional test method is required to
other standards.
determine the pull-off strength of the patch from the substrate
3.2 Symbols:
concrete. Throughout this standard, “substrate” is understood
3.2.1 D—diameter of the loading fixture.
to mean the concrete or concrete patch material to which the
3.2.2 F —pull-off force.
p
FRP is adhered.
3.2.3 σ —pull-off bond stress.
p
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.10 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Composites for Civil Structures. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved June 1, 2009. Published July 2009. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D7522_D7522M-09. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7522/D7522M − 09
4. Summary of Test Method Variation in the rate of loading between specimens can cause
biased or scattered test results.
4.1 The pull-off test is performed by securing a circular
6.3 Environmental Conditions at Time of Testing—Testing
loading fixture (dolly) normal (perpendicular) to the flat
surface of the FRP laminate with an affixing adhesive. An at non-standard temperatures or relative humidities may affect
the test results. Specimens tested in field conditions should be
adhesion testing device is attached to the loading fixture and
aligned to apply tension normal to the test surface. The force noted as such.
applied to the loading fixture is gradually increased and
7. Apparatus
monitored until a plug of material is detached exposing the
7.1 Fixed Alignment Adhesion Test Device, commercially
plane of limiting strength within the system. The nature of the
available, or comparable apparatus conforming to the follow-
failure is qualified in accordance with the percent of adhesive
ing specifications. A specific example of an appropriate com-
and cohesive failures, and the actual interfaces and layers
mercially available tester is provided in Annex A1.
involved. The pull-off strength is computed based on the
7.1.1 The tester is comprised of detachable circular loading
maximum indicated force, the instrument calibration data, and
fixtures, screws with spherical heads that are screwed into the
theoriginalsurfaceareastressed.Pull-offstrengthresultsusing
center of a fixture, a socket in the testing assembly that holds
differentdevicesmayvary,asresultsaresensitivetotestdevice
the head of the screw, pressure gage or dynamometer, and a
parameters.
mechanical or hydraulic means of applying the force in a
controlled manner.
5. Significance and Use
7.1.2 Loading Fixtures, having a minimum diameter of 50
5.1 The pull-off strength of a bonded FRP system is an
mm [2.0 in.], a flat surface on one end that can be adhered to
important performance property that has been used in
the FRP surface and a means of attachment to the tester on the
specifications, particularly those for assessing the quality of an
other end.
application. This test method serves as a means for uniformly
7.1.3 Adhesion Tester Grip, having a central grip for engag-
preparing and testing bonded FRPsystems, and evaluating and
ing the loading fixture in a manner such that the resultant force
reporting the results.
is normal to the FRP surface (typically achieved with a
5.2 Variations in results obtained using different devices are spherical head bearing).
possible. Therefore, it is recommended that the type of adhe-
7.1.4 Adhesion Tester Base, permitting a uniform bearing
sion test device (including manufacturer and model) be mutu- against the FRP surface to react the test force.
ally agreed upon between the interested parties.
7.1.5 Means of moving the grip away from the base in as
smooth and continuous a manner as possible so that a torsion-
5.3 This test method is intended for use in both the field and
free, co-axial (opposing pull of the grip and push of the base
the laboratory.
along the same axis) force results between them.
5.4 The basic material properties obtained from this test
7.1.6 Timer, or means of limiting the rate of stress applied to
method can be used in the control of the quality of adhesives
the FRP-concrete interface being tested to less than 1 MPa/
and in the theoretical equations for designing FRP systems for
min. [150 psi/min.]. A timer is the minimum equipment when
external reinforcement to strengthen existing structures.
used by the operator along with the force indicator in 7.1.7.
7.1.7 Force Indicator and Calibration Information, for
6. Interferences
determining the actual force delivered to the loading fixture.
6.1 Material and Specimen Preparation—Improper prepa-
7.2 Loading Fixture Bonding Adhesive, for securing the
ration of the surface of the composite material before bonding
fixture to the FRP laminate such that laminate properties are
the circular loading fixture is known to cause premature
notaffected.Thebondingadhesivemusthaveatensilecapacity
failures at this interface. Improper curing of the bonding
greater than the expected tensile capacity of the FRP system
adhesive can also cause failure at this interface. Non-uniform
andtheconcretesubstrateandbesufficienttomitigateaFailure
FRP or FRP-to-substrate adhesive thickness in one specimen
ModeA(see 12.2.1).Two component epoxies have been found
canaffectanindividualtestresultandleadtonon-symmetricor
to be appropriate.
mixed-mode failure pattern. Variation in FRP or adhesive
7.3 CircularHoleCutter, having an inside diameter equal to
thickness between specimens can cause biased or scattered test
that of the loading fixture to score through the FRP laminate
results. Improper fixturing of the hole cutter relative to the
into the substrate around the loading fixture. The hole cutter
specimen can lead to a non-circular hole or damage to the FRP
must not damage the FRP laminate while scoring through it;
composite/substrate interface around the perimeter of the hole.
therefore a thin-walled diamondgrit hole sawis appropriate. In
This can cause biased or scattered test results and non-
most cases a center drill arbor may be used to facilitate the
symmetric or mixed-mode failure patterns. Misalignment be-
scoring operation without affecting test results.
tween the circular test fixture and the drilled circle can also
lead to biased or scattered test results and noo-symmetric or 8. Test Specimen Preparation and Sampling
mixed-mode failure patterns.
8.1 The FRP system is applied to the concrete surface in
6.2 Adhesion Testing Device—Improper alignment of the accordance with the manufacturer’s recommended procedure.
adhesion tester grip (see 7.1.3) can lead to biased or scattered The manufacturer’s instructions should be followed as to the
test results and non-symmetric or mixed-mode failure patterns. elapsed time between FRP application and pull-off testing.
D7522/D7522M − 09
8.2 Sampling—Test at least five specimens per test condi- solvent, sanded with medium-grit sandpaper, rinsed with
tion unless valid results can be gained through the use of fewer solvent, and allowed to dry.
NOTE 3—Generally, any surface preparation of the FRP that results in
specimens, such as in the case of a designed experiment. For
test fixture adhesion sufficient to avoid occurrence of Failure ModeA(see
statistically significant data, the procedures outlined in Practice
12.2.1) is adequate.
E122 should be consulted. The method of sampling shall be
11.5 Attach the loading fixture with the designated bonding
reported.
adhesive following the manufacturer’s instructions. The bond-
9. Calibration
ing adhesive must be permitted to cure sufficiently so that
Failure Mode A (see 12.2.1) does not occur.
9.1 The accuracy of all measuring equipment shall have
certified calibrations that are current at the time of use of the
11.6 Carefullyconnectthecentralgripoftheadhesiontester
equipment.
to the loading fixture without bumping, bending, or otherwise
stressing the sample and connect the assembly to its control
10. Conditioning
mechanism. For non-horizontal surfaces, support the adhesion
10.1 This testing may be completed to assess a variety of
tester assembly so that its weight does not contribute to the
effects including concrete surface preparation, adhesive curing
force exerted in the test.
conditions, hygrothermal exposure, environmental exposure
11.7 Align the device according to the manufacturer’s
(for example, alkaline solution, etc.). In such cases, test
instructions and set the force indicator to zero.
specimens should be conditioned as specified in the experi-
11.8 Apply manual or mechanized loading so that the
mental protocol.
continuous grip assembly motion results in a rate of applied
10.2 If not otherwise specified, the recommended pre-test
normal stress at the FRP-concrete interface of less than 1
condition is effective moisture equilibrium at a specific relative
MPa/min. [150 psi/min.] until rupture occurs.
humidity as established by Test Method D5229/D5229M;
11.9 Record pull-off force measurement and nature of fail-
however, if the test requestor does not explicitly specify a
ure plane.
pre-test conditioning environment, no conditioning is required
and the specimens may be tested as prepared.
11.10 If a plug of material is detached, label and store the
test specimen including the attached loading fixture for quali-
10.3 If pre-conditioning is completed, the pre-test specimen
fication of the failed surface in accordance with the experiment
conditioning process, to include specified environmental expo-
protocol.
sure levels shall be reported with the test data.
11.11 Report any departures from the procedure such as
10.4 If no explicit conditioning process is performed the
possible misalignment, hesitations in the force application, etc.
specimen conditioning process shall be reported as uncondi-
tioned and the moisture content as unknown.
12. Calculation and Interpretation of Results
NOTE 1—The term moisture, as used in Test Method D5229/D5229M,
includes not only the vapor of a liquid and its condensate, but the liquid
12.1 Calculations—Compute and record the pull-off bond
itself in large quantities, as for immersion.
strength or concrete strength as follows:
11. Procedure 4F
p
σ 5 (1)
p
πD
11.1 Select a flat measurement site in accordance with the
sampling schedule.
where:
11.2 Select a circular loading fixture having a diameter not σ = the pull-off bond strength, MPa [psi],
p
F = the pull-off force N [lb], and
less than 50 mm [2.0 in.]. For FRP bonded to concrete
p
D = the diameter of the loading fixture, mm [in.].
substrates which are known to contain large aggregate sizes, a
NOTE 4—In some cases, this calculation may be automatically com-
larger fixture may be used
pleted with the adhesion tester force indicator; ensure that calibration
NOTE 2—The loading fixture diameter is limited by the test device
parameters are correct.
dimensions and capacity. Little data is available for diameters gr
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