ASTM D7522/D7522M-21

Standard Test Method for Pull-Off Strength for FRP Laminate Systems Bonded to Concrete or Masonry Substrates

SIGNIFICANCE AND USE
5.1 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.  
5.2 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.  
5.3 This test method is intended for use in both the field and the laboratory.  
5.4 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 appropriate for use with flat concrete, concrete masonry, clay masonry, and stone masonry substrates.  
1.5 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.  
1.6 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.  
1.7 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.  
1.8 Prior to the installation of some adhesively bonded FRP systems, the substrate must be patched. 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.  
1.9 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.  
1.10 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.11 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Dec-2020
• ICS: 91.100.40 - Products in fibre-reinforced cement
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.10 - Composites for Civil Structures

Relations

• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM C1232-23 - Standard Terminology for Masonry
• Effective Date: 15-Dec-2023
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM D5229/D5229M-20 - Standard Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite Materials
• Effective Date: 01-Mar-2020
• Refers: ASTM D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM C125-19a - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 15-Dec-2019
• Refers: ASTM D3878-19a - Standard Terminology for Composite Materials
• Effective Date: 15-Oct-2019
• Refers: ASTM D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM D3878-19 - Standard Terminology for Composite Materials
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019
• Refers: ASTM C125-19 - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 01-Jan-2019
• Refers: ASTM D883-18a - Standard Terminology Relating to Plastics
• Effective Date: 01-Dec-2018
• Refers: ASTM D883-18 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2018
• Refers: ASTM C125-18b - Standard Terminology Relating to Concrete and Concrete Aggregates
• Effective Date: 01-Oct-2018

Overview

ASTM D7522/D7522M-21 is the Standard Test Method for Pull-Off Strength for FRP Laminate Systems Bonded to Concrete or Masonry Substrates. Published by ASTM International, this method provides a reliable procedure for evaluating the pull-off (tensile) strength of fiber reinforced polymer (FRP) laminate systems that are adhesively bonded to flat concrete, concrete masonry, clay masonry, or stone masonry substrates. The pull-off strength is a critical metric for assessing the quality of an FRP application, especially in repair and reinforcement projects for civil structures.

By standardizing the test procedure, ASTM D7522/D7522M-21 ensures consistent preparation, testing, and reporting of the pull-off strength for wet lay-up or pultruded FRP systems. This allows for meaningful evaluation and comparison of bond strength where FRP materials are used for structural strengthening and rehabilitation.

Key Topics

• Purpose of Testing: The primary objective is to determine the greatest perpendicular force a bonded FRP system can withstand before detachment occurs, typically along the weakest interface in the system.

• Applicability: Suitable for field and laboratory use; can be used on FRP systems with any fiber orientation or ply combination.

• Sample Preparation and Equipment:

  • Test requires the use of a circular loading fixture (minimum 50 mm diameter) adhered to the FRP surface, a compatible bonding adhesive, and an adhesion tester capable of recording and applying controlled tension.
  • The FRP must be properly prepared per manufacturer’s instructions before testing.
  • Five specimens per test condition are recommended for statistical reliability.

• Accepted Substrates:

  • Flat concrete
  • Concrete masonry
  • Clay masonry
  • Stone masonry

• Result Interpretation:

  • Multiple failure modes considered, such as cohesive failure in the FRP or substrate, or adhesive failures at various interfaces.
  • The desired failure mode is cohesive failure in the substrate, indicating a strong system.
  • Not suitable as an “acceptance” or “proof” test for in-service FRP, but valuable for quality control and repair assessment.

• Limitations:

  • Results depend on material properties and the specific test equipment used.
  • This is a destructive test; localized repairs may be required after testing.
  • Not intended for determining FRP-to-patch bond strength when patching is used prior to FRP installation.

Applications

ASTM D7522/D7522M-21 is especially valuable in the following contexts:

• Quality Assurance in Construction: Ensures installation quality of FRP systems in new builds or rehabilitation projects.
• Assessment of Field Repairs: Evaluates the effectiveness of adhesive-applied FRP repairs during maintenance or retrofit of concrete or masonry structures.
• Material Development and Selection: Useful for comparing the performance of different FRP systems, adhesives, and installation procedures.
• Design Verification: Supports theoretical design and calculations for external reinforcement by providing essential bond strength data.
• Research: Serves as a basis for academic and industry research into FRP composite behaviors and construction materials performance.

Related Standards

Several ASTM standards and terminology documents are closely related, supporting the correct application and interpretation of ASTM D7522/D7522M-21:

• ASTM C125 – Terminology Relating to Concrete and Concrete Aggregates
• ASTM C1232 – Terminology for Masonry
• ASTM D883 – Terminology Relating to Plastics
• ASTM D3878 – Terminology for Composite Materials
• ASTM D5229/D5229M – Test Method for Moisture Absorption of Polymer Matrix Composite Materials
• ASTM E6 – Terminology Relating to Mechanical Testing
• ASTM E122 – Practice for Calculating Sample Size for Estimating a Characteristic of a Lot or Process

Practical Value

Using ASTM D7522/D7522M-21 enhances the reliability and safety of FRP retrofit and repair systems for concrete and masonry. By providing a standardized approach to pull-off testing, it helps engineers, material suppliers, contractors, and inspectors ensure that bonded systems meet necessary quality thresholds. This method supports effective decision making in both the design and maintenance of civil infrastructure, improving project outcomes and structural life cycles.

Keywords: bond strength, pull-off testing, FRP laminate, concrete repair, composite systems, masonry, quality control, ASTM standards.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D7522/D7522M − 21
Standard Test Method for
Pull-Off Strength for FRP Laminate Systems Bonded to
Concrete or Masonry Substrates
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 from the patch material. An additional test method is required
to determine the pull-off strength of the patch from the
1.1 This test method describes the apparatus and procedure
substrate.
for evaluating the pull-off strength of wet lay-up or pultruded
(shop-fabricated) Fiber Reinforced Polymer (FRP) laminate
1.9 Units—The values stated in either SI units or inch-
systems adhesively bonded to a flat concrete substrate.The test
pound units are to be regarded separately as standard. The
determines the greatest perpendicular force (in tension) that an
values stated in each system are not necessarily exact equiva-
FRP system can bear before a plug of material is detached.
lents; therefore, to ensure conformance with the standard, each
Failure will occur along the weakest plane within the system
system shall be used independently of the other, and values
comprised of the test fixture, FRP laminate, adhesive, and
from the two systems shall not be combined.
substrate.
1.10 This standard does not purport to address all of the
1.2 This test method is primarily used for quality control
safety concerns, if any, associated with its use. It is the
and assessment of field repairs of structures using adhesive-
responsibility of the user of this standard to establish appro-
applied composite materials.
priate safety, health, and environmental practices and deter-
1.3 This test method is appropriate for use with FRP
mine the applicability of regulatory limitations prior to use.
systems having any fiber orientation or combination of ply
1.11 This international standard was developed in accor-
orientations comprising the FRP laminate.
dance with internationally recognized principles on standard-
1.4 This test method is appropriate for use with flat ization established in the Decision on Principles for the
concrete, concrete masonry, clay masonry, and stone masonry Development of International Standards, Guides and Recom-
substrates. mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.5 This test method is not appropriate for use as an
“acceptance” or “proof” wherein the FRP system remaining
2. Referenced Documents
intact at a prescribed force is an acceptable result.
1.6 Pull-off strength measurements depend upon both ma- 2.1 ASTM Standards:
terial and instrumental parameters. Different adhesion test C125 Terminology Relating to Concrete and Concrete Ag-
devicesandprocedureswillgivedifferentresultsandcannotbe gregates
directly compared. C1232 Terminology for Masonry
D883 Terminology Relating to Plastics
1.7 This test method can be destructive. Spot repairs may be
D3878 Terminology for Composite Materials
necessary. The test method will result in an exposed cut FRP
D5229/D5229M Test Method for MoistureAbsorption Prop-
section; repair methods must consider the potential for mois-
erties and Equilibrium Conditioning of Polymer Matrix
ture uptake through this cut section.
Composite Materials
1.8 Prior to the installation of some adhesively bonded FRP
E6 Terminology Relating to Methods of Mechanical Testing
systems, the substrate must be patched. This test method is not
E122 Practice for Calculating Sample Size to Estimate,With
appropriate for determining the pull-off strength of the FRP
Specified Precision, the Average for a Characteristic of a
Lot or Process
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.10 on
Composites for Civil Structures. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Jan. 1, 2021. Published February 2021. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2009. Last previous edition approved in 2015 as D7522/D7522M – 15. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D7522_D7522M-21. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7522/D7522M − 21
3. Terminology canaffectanindividualtestresultandleadtonon-symmetricor
mixed-mode failure pattern. Variation in FRP or adhesive
3.1 Definitions—Terminology D3878 defines terms relating
thickness between specimens can cause biased or scattered test
to high-modulus fibers and their composites. Terminology
results. Improper fixturing of the hole cutter relative to the
D883definestermsrelatingtoplastics.TerminologyE6defines
specimen can lead to a non-circular hole or damage to the FRP
termsrelatingtomechanicaltesting.TerminologyC125defines
composite/substrate interface around the perimeter of the hole.
terms relating to concrete. Terminology C1232 defines terms
This can cause biased or scattered test results and non-
related to masonry. In the event of a conflict between terms,
symmetric or mixed-mode failure patterns. Misalignment be-
Terminology D3878 shall have precedence over the other
tween the circular test fixture and the drilled circle can also
standards.
lead to biased or scattered test results and non-symmetric or
3.2 Symbols:
mixed-mode failure patterns.
D—diameter of the loading fixture.
6.2 Adhesion Testing Device—Improper alignment of the
F —pull-off force.
p
adhesion tester grip (see 7.1.3) can lead to biased or scattered
σ —pull-off bond stress.
p
test results and non-symmetric or mixed-mode failure patterns.
Variation in the rate of loading between specimens can cause
4. Summary of Test Method
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
atnon-standardtemperatureorrelativehumiditymayaffectthe
surface of the FRP laminate with an affixing adhesive. An
test results. Specimens tested in field conditions should be
adhesion testing device is attached to the loading fixture and
noted as such.
aligned to apply tension normal to the test surface. The force
applied to the loading fixture is gradually increased and
6.4 Location of Test on Masonry Substrate—Inclusion of a
monitored until a plug of material is detached exposing the
masonry joint within the cut specimen may affect the test
plane of limiting strength within the system. The nature of the
results. Tests including a joint should not be used.
failure is qualified in accordance with the percent of adhesive
and cohesive failures, and the actual interfaces and layers
7. Apparatus
involved. The pull-off strength is computed based on the
7.1 Adhesion Test Device, commercially available, or com-
maximum indicated force, the instrument calibration data, and
parable apparatus conforming to the following specifications.
theoriginalsurfaceareastressed.Pull-offstrengthresultsusing
A specific example of an appropriate commercially available
differentdevicesmayvary,asresultsaresensitivetotestdevice
tester is provided in Annex A1.
parameters.
7.1.1 The tester is comprised of detachable circular loading
5. Significance and Use fixtures, screws with spherical heads that are screwed into the
center of a fixture, a socket in the testing assembly that holds
5.1 The pull-off strength of a bonded FRP system is an
the head of the screw, pressure gage or dynamometer, and a
important performance property that has been used in
mechanical or hydraulic means of applying the force in a
specifications, particularly those for assessing the quality of an
controlled manner.
application. This test method serves as a means for uniformly
7.1.2 Loading Fixtures, having a minimum diameter of
preparing and testing bonded FRPsystems, and evaluating and
50 mm [2.0 in.], a flat surface on one end that can be adhered
reporting the results.
to the FRP surface and a means of attachment to the tester on
5.2 Variations in results obtained using different devices are
the other end.
possible. Therefore, it is recommended that the type of adhe-
7.1.3 Adhesion Tester Grip, having a central grip for engag-
sion test device (including manufacturer and model) be mutu-
ing the loading fixture in a manner such that the resultant force
ally agreed upon between the interested parties.
is normal to the FRP surface (typically achieved with a
5.3 This test method is intended for use in both the field and
spherical head bearing).
the laboratory.
7.1.4 Adhesion Tester Base, permitting a uniform bearing
against the FRP surface to react the test force.
5.4 The basic material properties obtained from this test
method can be used in the control of the quality of adhesives
7.1.5 Means of moving the grip away from the base in as
and in the theoretical equations for designing FRP systems for
smooth and continuous a manner as possible so that a torsion-
external reinforcement to strengthen existing structures.
free, co-axial (opposing pull of the grip and push of the base
along the same axis) force results between them.
6. Interferences
7.1.6 Timer, or means of limiting the rate of stress applied to
the FRP-substrate interface being tested to less than or equal to
6.1 Material and Specimen Preparation—Improper prepa-
1 MPa/min [150 psi/min]. A timer is the minimum equipment
ration of the surface of the composite material before bonding
when used by the operator along with the force indicator in
the circular loading fixture is known to cause premature
7.1.7.
failures at this interface. Improper curing of the bonding
adhesive can also cause failure at this interface. Non-uniform 7.1.7 Force Indicator and Calibration Information, for
FRP or FRP-to-substrate adhesive thickness in one specimen determining the actual force delivered to the loading fixture.
D7522/D7522M − 21
7.2 Loading Fixture Bonding Adhesive, for securing the 11. Procedure
fixture to the FRP laminate such that laminate properties are
11.1 Select a flat measurement site in accordance with the
notaffected.Thebondingadhesivemusthaveatensilecapacity
sampling schedule.
greater than the expected tensile capacity of the FRP system
andtheconcretesubstrateandbesufficienttomitigateaFailure 11.2 Select a circular loading fixture having a diameter not
Mode A (see 11.12.1). Two component epoxies have been less than 50 mm [2.0 in.]. For FRP bonded to concrete
found to be appropriate. substrates which are known to contain large aggregate sizes, a
larger fixture may be used.
7.3 Circular Hole Cutter, having an inside diameter equal to
NOTE 2—The loading fixture diameter is limited by the test device
that of the loading fixture to score through the FRP laminate
dimensions and capacity. Little data is available for diameters greater than
into the substrate around the loading fixture. The hole cutter
50 mm regardless of aggregate size; generally a 50 mm diameter test
must not damage the FRP laminate while scoring through it;
fixture will be adequate.
therefore, a thin-walled diamond grit hole saw is appropriate.
11.3 Score through the FRP laminate into the substrate
In most cases, a center drill arbor may be used to facilitate the
using a core drill apparatus. The remaining scribed circle (that
scoring operation without affecting test results.
is, the inside diameter of the core drill) should be the same
diameter as the loading fixture used. The core shall be drilled
8. Test Specimen Preparation and Sampling
through the bonded FRP and adhesive layers and into the
8.1 The FRP system is applied to the substrate surface in
substrate a depth of between 6 mm [0.25 in.] and 12 mm
accordance with the manufacturer’s recommended procedure.
[0.50 in.].
The manufacturer’s instructions should be followed as to the
11.3.1 The operator must be aware of existing internal
elapsed time between FRP application and pull-off testing.
reinforcement (“rebar”). Under no circumstances should the
8.2 Sampling—Test at least five specimens per test drilled core cut through existing reinforcement.
condition, unless valid results can be gained through the use of
11.3.2 Joints in masonry substrates should not be included
fewer specimens, such as in the case of a designed experiment.
in the specimen.
For statistically significant data, the procedures outlined in
11.4 Prepare the FRP surface for bonding the loading
Practice E122 should be consulted. The method of sampling
fixture. Generally, the FRP surface should be cleaned with
shall be reported.
solvent, sanded with medium-grit sandpaper, rinsed with
8.3 Sampling on Masonry Substrates—Specimens should
solvent, and allowed to dry.
not include joints in masonry substrates.
NOTE 3—Generally, any
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7522/D7522M − 15 D7522/D7522M − 21
Standard Test Method for
Pull-Off Strength for FRP Laminate Systems Bonded to
Concrete Substrateor Masonry Substrates
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
1.1 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 appropriate for use with flat concrete, concrete masonry, clay masonry, and stone masonry substrates.
1.5 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.
1.6 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.
1.7 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.
1.8 Prior to the installation of some adhesively bonded FRP systems, the substrate concrete must be patched (often to replace lost
concrete volume). must be patched. 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.substrate.
1.9 Units—The values stated in either SI units or inch-pound units are to be regarded as standard. Within the text, the inch-pound
This test method is under the jurisdiction of ASTM Committee D30 on Composite Materials and is the direct responsibility of Subcommittee D30.10 on Composites
for Civil Structures.
Current edition approved April 15, 2015Jan. 1, 2021. Published May 2015February 2021. Originally approved in 2009. Last previous edition approved in 20092015 as
D7522/D7522MD7522/D7522M – 15.-09. DOI: 10.1520/D7522_D7522M-15.10.1520/D7522_D7522M-21.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7522/D7522M − 21
units are shown in brackets. separately as standard. The values stated in each system are not necessarily exact equivalents;
therefore, to ensure conformance with the standard, each system mustshall be used independently of the other. Combiningother,
and values from the two systems may result in nonconformance with the standard.shall not be combined.
1.10 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.11 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C125 Terminology Relating to Concrete and Concrete Aggregates
C1232 Terminology for Masonry
D883 Terminology Relating to Plastics
D3878 Terminology for Composite Materials
D5229/D5229M Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite
Materials
E6 Terminology Relating to Methods of Mechanical Testing
E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or
Process
3. Terminology
3.1 Definitions—Terminology D3878 defines terms relating to high-modulus fibers and their composites. Terminology D883
defines terms relating to plastics. Terminology E6 defines terms relating to mechanical testing. Terminology C125 defines terms
relating to concrete. Terminology C1232 defines terms related to masonry. In the event of a conflict between terms, Terminology
D3878 shall have precedence over the other standards.
3.2 Symbols:
3.2.1 D—diameter of the loading fixture.
3.2.2 F —pull-off force. D—diameter of the loading fixture.
p
3.2.3 σ —pull-off bond stress.
p
F —pull-off force.
p
σ —pull-off bond stress.
p
4. Summary of Test Method
4.1 The pull-off test is performed by securing a circular loading fixture (dolly) normal (perpendicular) to the flat surface of the
FRP laminate with an affixing adhesive. An adhesion testing device is attached to the loading fixture and aligned to apply tension
normal to the test surface. The force applied to the loading fixture is gradually increased and monitored until a plug of material
is detached exposing the plane of limiting strength within the system. The nature of the failure is qualified in accordance with the
percent of adhesive and cohesive failures, and the actual interfaces and layers involved. The pull-off strength is computed based
on the maximum indicated force, the instrument calibration data, and the original surface area stressed. Pull-off strength results
using different devices may vary, as results are sensitive to test device parameters.
5. Significance and Use
5.1 The pull-off strength of a bonded FRP system is an important performance property that has been used in specifications,
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
D7522/D7522M − 21
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.
5.2 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.
5.3 This test method is intended for use in both the field and the laboratory.
5.4 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.
6. Interferences
6.1 Material and Specimen Preparation—Improper preparation of the surface of the composite material before bonding the
circular loading fixture is known to cause premature failures at this interface. Improper curing of the bonding adhesive can also
cause failure at this interface. Non-uniform FRP or FRP-to-substrate adhesive thickness in one specimen can affect an individual
test result and lead to non-symmetric or mixed-mode failure pattern. Variation in FRP or adhesive thickness between specimens
can cause biased or scattered test results. Improper fixturing of the hole cutter relative to the specimen can lead to a non-circular
hole or damage to the FRP composite/substrate interface around the perimeter of the hole. This can cause biased or scattered test
results and non-symmetric or mixed-mode failure patterns. Misalignment between the circular test fixture and the drilled circle can
also lead to biased or scattered test results and non-symmetric or mixed-mode failure patterns.
6.2 Adhesion Testing Device—Improper alignment of the adhesion tester grip (see 7.1.3) can lead to biased or scattered test results
and non-symmetric or mixed-mode failure patterns. Variation in the rate of loading between specimens can cause biased or
scattered test results.
6.3 Environmental Conditions at Time of Testing—Testing at non-standard temperature or relative humidity may affect the test
results. Specimens tested in field conditions should be noted as such.
6.4 Location of Test on Masonry Substrate—Inclusion of a masonry joint within the cut specimen may affect the test results. Tests
including a joint should not be used.
7. Apparatus
7.1 Adhesion Test Device, commercially available, or comparable apparatus conforming to the following specifications. A specific
example of an appropriate commercially available tester is provided in Annex A1.
7.1.1 The tester is comprised of detachable circular loading fixtures, screws with spherical heads that are screwed into the center
of a fixture, a socket in the testing assembly that holds the head of the screw, pressure gage or dynamometer, and a mechanical
or hydraulic means of applying the force in a controlled manner.
7.1.2 Loading Fixtures, having a minimum diameter of 50 mm 50 mm [2.0 in.], a flat surface on one end that can be adhered to
the FRP surface and a means of attachment to the tester on the other end.
7.1.3 Adhesion Tester Grip, having a central grip for engaging the loading fixture in a manner such that the resultant force is
normal to the FRP surface (typically achieved with a spherical head bearing).
7.1.4 Adhesion Tester Base, permitting a uniform bearing against the FRP surface to react the test force.
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-free,
co-axial (opposing pull of the grip and push of the base along the same axis) force results between them.
7.1.6 Timer, or means of limiting the rate of stress applied to the FRP-concreteFRP-substrate interface being tested to less than
or equal to 1 MPa/min.MPa/min [150 psi/min.].psi/min]. A timer is the minimum equipment when used by the operator along with
the force indicator in 7.1.7.
7.1.7 Force Indicator and Calibration Information, for determining the actual force delivered to the loading fixture.
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7.2 Loading Fixture Bonding Adhesive, for securing the fixture to the FRP laminate such that laminate properties are not affected.
The bonding adhesive must have a tensile capacity greater than the expected tensile capacity of the FRP system and the concrete
substrate and be sufficient to mitigate a Failure Mode A (see 12.2.111.12.1). Two component epoxies have been found to be
appropriate.
7.3 Circular Hole Cutter, having an inside diameter equal to that of the loading fixture to score through the FRP laminate into the
substrate around the loading fixture. The hole cutter must not damage the FRP laminate while scoring through it; therefore, a
thin-walled diamond grit hole saw is appropriate. In most cases, a center drill arbor may be used to facilitate the scoring operation
without affecting test results.
8. Test Specimen Preparation and Sampling
8.1 The FRP system is applied to the concretesubstrate surface in accordance with the manufacturer’s recommended procedure.
The manufacturer’s instructions should be followed as to the elapsed time between FRP application and pull-off testing.
8.2 Sampling—Test at least five specimens per test condition, unless valid results can be gained through the use of fewer
specimens, such as in the case of a designed experiment. For statistically significant data, the procedures outlined in Practice E122
should be consulted. The method of sampling shall be reported.
8.3 Sampling on Masonry Substrates—Specimens should not include joints in masonry substrates.
9. Calibration
9.1 The accuracy of all measuring equipment shall have certified calibrations that are current at the time of use of the equipment.
10. Conditioning
10.1 This testing may be completed to assess a variety of effects, including concrete surface preparation, adhesive curing
conditions, hygrothermal exposure, and environmental exposure (for example, alkaline solution, etc.). In such cases, test specimens
should be conditioned as specified in the experimental protocol.
10.2 If not otherwise specified, the recommended pre-test condition is effective moisture equilibrium at a specific relative humidity
as established by Test Method D5229/D5229M; however, if the test requestor does not explicitly specify a pre-test conditioning
environment, no conditioning is required and the specimens may be tested as prepared.
10.3 If pre-conditioning is completed, the pre-test specimen conditioning process, to include specified environmental exposure
levels, shall be reported with the test data.
10.4 If no explicit conditioning process is performed, the specimen conditioning process shall be reported as unconditioned and
the moisture content as unknown.
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 itself in
large quantities, as for immersion.
11. Procedure
11.1 Select a flat measurement site in accordance with the sampling schedule.
11.2 Select a circular loading fixture having a diameter not less than 50 mm [2.0 in.]. For FRP bonded to concrete substrates which
are known to contain large aggregate sizes, a larger fixture may be used.
NOTE 2—The loading fixture diameter is limited by the test device dimensions and capacity. Little data is available for diameters greater than 50 mm
regardless of aggregate size; generally a 50 mm diameter test fixture will be adequate.
11.3 Score through the FRP laminate into the substrate concrete using a core drill apparatus. The remaining scribed circle (that
D7522/D7522M − 21
is, the inside diameter of the core drill) should be the same diameter as the loading fixture used. The core shall be drilled through
the bonded FRP and adhesive layers and into the concrete substrate a depth of between 6 mm [0.25 in.] and 12 mm [0.50
in.].[0.50 in.].
11.3.1 The operator must be aware of existing internal reinforcement (“rebar”). Under no circumstances should the drilled core
cut through existing reinforcement.
11.3.2 Joints in masonry substrates should not be included in the specimen.
11.4 Prepare the FRP surface for bonding the loading fixture. Generally, the FRP surface should be cleaned with solvent, sanded
with medium-grit sandpaper, rinsed with solvent, and allowed to dry.
NOTE 3—Generally, any surface preparation of the FRP that results in test fixture adhesion sufficient to avoid occurrence of Failure Mode A (see
12.2.111.12.1) is adequate.
11.5 Attach the loading fixture with the designated bonding adhesive following the manufacturer’s instructions. The bonding
adhesive must be permitted to cure sufficiently so that Failure Mode A (see 12.
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