ASTM C42/C42M-20

Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete

SIGNIFICANCE AND USE
3.1 This test method provides standardized procedures for obtaining and testing specimens to determine the compressive, splitting tensile, and flexural strength of in-place concrete.  
3.2 Generally, test specimens are obtained when doubt exists about the in-place concrete quality due either to low strength test results during construction or signs of distress in the structure. Another use of this method is to provide strength information on older structures.  
3.3 Concrete strength is affected by the location of the concrete in a structural element, with the concrete at the bottom tending to be stronger than the concrete at the top. Core strength is also affected by core orientation relative to the horizontal plane of the concrete as placed, with strength tending to be lower when measured parallel to the horizontal plane.3 These factors shall be considered in planning the locations for obtaining concrete samples and in comparing strength test results.  
3.4 The strength of concrete measured by tests of cores is affected by the amount and distribution of moisture in the specimen at the time of test. There is no standard procedure to condition a specimen that will ensure that, at the time of test, it will be in the identical moisture condition as concrete in the structure. The moisture conditioning procedures in this test method are intended to provide reproducible moisture conditions that minimize within-laboratory and between-laboratory variations and to reduce the effects of moisture introduced during specimen preparation.  
3.5 The measured compressive strength of a core will generally be less than that of a corresponding properly molded and cured standard cylinder tested at the same age. For a given concrete, however, there is no unique relationship between the strengths of these two types of specimens (see Note 3). The relationship is affected by many factors such as the strength level of the concrete, the in-place temperature and moisture histories, the de...
SCOPE
1.1 This test method covers obtaining, preparing, and testing cores drilled from concrete for length or compressive strength or splitting tensile strength determinations. This test method is not applicable to cores from shotcrete.
Note 1: Test Method C1604/C1604M is applicable for obtaining, preparing, and testing cores from shotcrete.
Note 2: Appendix X1 provides recommendations for obtaining and testing sawed beams for flexural performance.  
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.  
1.3 The text of this standard references notes and footnotes that provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.  
1.4 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.  
1.5 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-Mar-2020
• ICS: 91.100.30 - Concrete and concrete products
• Technical Committee: C09 - Concrete and Concrete Aggregates
• Drafting Committee: C09.61 - Testing for Strength

Relations

• Refers: ASTM C670-24a - Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
• Effective Date: 01-Feb-2024
• Refers: ASTM C670-24 - Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
• Effective Date: 01-Jan-2024
• Refers: ASTM C39/C39M-23 - Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens
• Effective Date: 01-Dec-2023
• Refers: ASTM C617/C617M-23 - Standard Practice for Capping Cylindrical Concrete Specimens
• Effective Date: 01-Oct-2023
• Refers: ASTM C1231/C1231M-23 - Standard Practice for Use of Unbonded Caps in Determination of Compressive Strength of Hardened Cylindrical Concrete Specimens
• Effective Date: 01-Oct-2023
• Refers: ASTM C1604/C1604M-05(2019) - Standard Test Method for Obtaining and Testing Drilled Cores of Shotcrete
• Effective Date: 15-Dec-2019
• Refers: ASTM C1542/C1542M-19 - Standard Test Method for Measuring Length of Concrete Cores
• Effective Date: 01-Dec-2019
• Refers: ASTM C39/C39M-17b - Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens
• Effective Date: 01-Aug-2017
• Refers: ASTM C823/C823M-12(2017) - Standard Practice for Examination and Sampling of Hardened<brk/> Concrete in Constructions
• Effective Date: 01-May-2017
• Refers: ASTM C174/C174M-17 - Standard Test Method for Measuring Thickness of Concrete Elements Using Drilled Concrete Cores
• Effective Date: 01-May-2017
• Refers: ASTM C78/C78M-15b - Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)
• Effective Date: 01-Dec-2016
• Refers: ASTM C39/C39M-16b - Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens
• Effective Date: 01-Aug-2016
• Refers: ASTM C39/C39M-16a - Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens
• Effective Date: 01-Jul-2016
• Refers: ASTM C174/C174M-16 - Standard Test Method for Measuring Thickness of Concrete Elements Using Drilled Concrete Cores
• Effective Date: 01-Jun-2016
• Refers: ASTM C1542/C1542M-16a - Standard Test Method for Measuring Length of Concrete Cores
• Effective Date: 01-Jun-2016

Overview

ASTM C42/C42M-20 is the internationally recognized standard test method for obtaining and testing drilled cores and sawed beams of concrete. Developed and published by ASTM International, this standard provides detailed procedures for extracting, preparing, and testing concrete samples from structures to determine properties such as compressive strength, splitting tensile strength, and flexural strength. The test method is essential for assessing the in-place quality and integrity of concrete in buildings, bridges, pavements, and other civil infrastructure.

This standard is particularly valuable in situations where questions arise about the in-situ concrete strength, such as after suspect strength test results during construction or when visible distress occurs in a structure. It is also widely used to evaluate the condition of concrete in older structures for maintenance or renovation projects.

Key Topics

• Specimen Extraction: Procedures for drilling cylindrical cores from hardened concrete and recommendations for obtaining sawed beams.
• Test Preparation: Guidelines for the handling, capping, grinding, and dimension measurement of specimens to ensure accurate and reproducible results.
• Strength Testing: Methods for determining compressive strength, splitting tensile strength, and flexural strength from the extracted specimens.
• Moisture Conditioning: Instructions to manage and report the moisture condition of specimens, a crucial factor impacting the measured strength.
• Reporting Requirements: Detailed documentation needed for each test, including sample dimensions, preparation history, testing dates, moisture conditioning, and any deviations from the standard procedures.
• Specimen Rejection Criteria: Recommendations for rejecting samples that do not meet dimensional tolerances or show signs of damage, cracks, or embedded objects.
• Limitations: Exclusion of shotcrete cores (covered by ASTM C1604/C1604M) and safety/environmental considerations which are the user’s responsibility.

Applications

The ASTM C42/C42M-20 standard is applied in a wide range of practical scenarios, including:

• Forensic Investigations: Assessing the structural adequacy of concrete where low strength test results or structural distress have been observed.
• Quality Control: Confirming the in-place compressive strength of concrete when compliance with project specifications is uncertain.
• Condition Assessment: Providing data for structural evaluation, retrofit, or renovation of existing concrete structures, especially for regulatory or code compliance.
• Research and Development: Supporting the development of new materials or construction techniques by enabling direct measurement of concrete strength after placement.
• Regulatory Compliance: Used by building officials, inspectorial agencies, and engineers as a basis for compliance with codes such as ACI 318, which specifies acceptance criteria for in-place concrete strength.

Related Standards

The ASTM C42/C42M-20 standard references and is closely connected to several key ASTM standards:

• ASTM C39/C39M: Test Method for Compressive Strength of Cylindrical Concrete Specimens
• ASTM C78/C78M: Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)
• ASTM C496/C496M: Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens
• ASTM C617/C617M: Practice for Capping Cylindrical Concrete Specimens
• ASTM C642: Test Method for Density, Absorption, and Voids in Hardened Concrete
• ASTM C823/C823M: Practice for Examination and Sampling of Hardened Concrete in Constructions
• ASTM C1604/C1604M: Test Method for Obtaining and Testing Drilled Cores of Shotcrete (for shotcrete applications)
• ASTM C174/C174M: Test Method for Measuring Thickness of Concrete Elements Using Drilled Concrete Cores

By following the guidance in ASTM C42/C42M-20, professionals achieve reliable, standardized, and reproducible results when testing in-place concrete, supporting safe, resilient, and high-quality concrete infrastructure.

Keywords: ASTM C42, core testing, concrete coring, compressive strength, splitting tensile strength, flexural strength, in-place concrete, standardized test methods, concrete quality assessment, civil infrastructure.

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: C42/C42M − 20 American Association State
Highway and Transportation Officials Standard
AASHTO No.: T24
Standard Test Method for
Obtaining and Testing Drilled Cores and Sawed Beams of
Concrete
This standard is issued under the fixed designation C42/C42M; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers obtaining, preparing, and test-
C39/C39M Test Method for Compressive Strength of Cylin-
ing cores drilled from concrete for length or compressive
drical Concrete Specimens
strength or splitting tensile strength determinations. This test
C78/C78M Test Method for Flexural Strength of Concrete
method is not applicable to cores from shotcrete.
(Using Simple Beam with Third-Point Loading)
NOTE 1—Test Method C1604/C1604M is applicable for obtaining,
C174/C174M Test Method for MeasuringThickness of Con-
preparing, and testing cores from shotcrete.
crete Elements Using Drilled Concrete Cores
NOTE 2—Appendix X1 provides recommendations for obtaining and
C496/C496M Test Method for Splitting Tensile Strength of
testing sawed beams for flexural performance.
Cylindrical Concrete Specimens
1.2 The values stated in either SI units or inch-pound units
C617/C617M Practice for Capping Cylindrical Concrete
are to be regarded separately as standard. The values stated in
Specimens
each system may not be exact equivalents; therefore, each
C642 Test Method for Density, Absorption, and Voids in
system shall be used independently of the other. Combining
Hardened Concrete
values from the two systems may result in non-conformance
C670 Practice for Preparing Precision and Bias Statements
with the standard.
for Test Methods for Construction Materials
C823/C823M Practice for Examination and Sampling of
1.3 The text of this standard references notes and footnotes
Hardened Concrete in Constructions
that provide explanatory material. These notes and footnotes
C1231/C1231M Practice for Use of Unbonded Caps in
(excluding those in tables and figures) shall not be considered
Determination of Compressive Strength of Hardened Cy-
as requirements of the standard.
lindrical Concrete Specimens
C1542/C1542M Test Method for Measuring Length of Con-
1.4 This standard does not purport to address all of the
crete Cores
safety concerns, if any, associated with its use. It is the
C1604/C1604M Test Method for Obtaining and Testing
responsibility of the user of this standard to establish appro-
Drilled Cores of Shotcrete
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
3. Significance and Use
1.5 This international standard was developed in accor-
3.1 This test method provides standardized procedures for
dance with internationally recognized principles on standard-
obtaining and testing specimens to determine the compressive,
ization established in the Decision on Principles for the
splitting tensile, and flexural strength of in-place concrete.
Development of International Standards, Guides and Recom-
3.2 Generally, test specimens are obtained when doubt
mendations issued by the World Trade Organization Technical
exists about the in-place concrete quality due either to low
Barriers to Trade (TBT) Committee.
strength test results during construction or signs of distress in
the structure.Another use of this method is to provide strength
information on older structures.
This test method is under the jurisdiction of ASTM Committee C09 on
Concrete and ConcreteAggregates and is the direct responsibility of Subcommittee
C09.61 on Testing for Strength. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2020. Published May 2020. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1921. Last previous edition approved in 2018 as C42/C42M – 18a. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/C0042_C0042M-20. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C42/C42M − 20
3.3 Concrete strength is affected by the location of the the core as tested and this must be considered in preparing core
concreteinastructuralelement,withtheconcreteatthebottom specimens and evaluating test results.
tending to be stronger than the concrete at the top. Core
4. Apparatus
strength is also affected by core orientation relative to the
horizontal plane of the concrete as placed, with strength
4.1 Core Drill, for obtaining cylindrical core specimens
tending to be lower when measured parallel to the horizontal with diamond-impregnated bits attached to a core barrel.
plane. These factors shall be considered in planning the
4.2 Saw, for trimming ends of cores. The saw shall have a
locations for obtaining concrete samples and in comparing
diamondorsilicon-carbidecuttingedgeandshallbecapableof
strength test results.
cutting cores without introducing cracks or dislodging aggre-
3.4 The strength of concrete measured by tests of cores is gate particles.
affected by the amount and distribution of moisture in the
4.3 Balance, accurate to at least 5 g [0.01 lb].
specimen at the time of test. There is no standard procedure to
condition a specimen that will ensure that, at the time of test,
5. Sampling
it will be in the identical moisture condition as concrete in the
5.1 General:
structure. The moisture conditioning procedures in this test
5.1.1 Samples of hardened concrete for use in the prepara-
method are intended to provide reproducible moisture condi-
tion of strength test specimens shall not be taken until the
tions that minimize within-laboratory and between-laboratory
concrete is strong enough to permit sample removal without
variations and to reduce the effects of moisture introduced
disturbing the bond between the mortar and the coarse aggre-
during specimen preparation.
gate (see Note 6 and Note 7). When preparing strength test
3.5 The measured compressive strength of a core will
specimens from samples of hardened concrete, samples that
generally be less than that of a corresponding properly molded
havebeendamagedduringremovalshallnotbeusedunlessthe
and cured standard cylinder tested at the same age. For a given
damaged portion(s) are removed and the lengths of resulting
concrete, however, there is no unique relationship between the
test specimens satisfy the minimum length-diameter ratio
strengths of these two types of specimens (see Note 3). The
requirement in 7.2. Samples of defective or damaged concrete
relationship is affected by many factors such as the strength
that cannot be tested shall be reported along with the reason
level of the concrete, the in-place temperature and moisture
that prohibits use of the sample for preparing strength test
histories, the degree of consolidation, batch-to-batch
specimens.
variability, the strength-gain characteristics of the concrete, the
NOTE 6—Practice C823/C823M provides guidance on the development
condition of the coring apparatus, and the care used in
of a sampling plan for concrete in constructions.
removing cores.
NOTE 7—It is not possible to specify a minimum age when concrete is
strong enough to withstand damage during removal, because the strength
NOTE3—Aprocedureisavailableforestimatingtheequivalentcylinder
at any age depends on the curing history and strength grade of the
strength from a measured core strength.
concrete. If time permits, the concrete should not be removed before it is
NOTE 4—In the absence of core strength requirements of an applicable
14 days old. If this is not practicable, removal of concrete can proceed if
building code or of other contractual or legal documents that may govern
the cut surfaces do not display erosion of the mortar and the exposed
the project, the specifier of tests should establish in the project specifica-
coarse aggregate particles are embedded firmly in the mortar. In-place test
tions the acceptance criteria for core strengths.An example of acceptance
methods may be used to estimate the level of strength development prior
criteria for core strength is provided in ACI 318, which are used to
to attempting removal of concrete samples.
evaluate cores taken to investigate low strength test results of standard-
cured cylinder during construction. According to ACI 318, the concrete 5.1.2 Except as provided in 5.1.3, cores containing embed-
represented by the cores is considered structurally adequate if the average
dedreinforcement,excludingfibers,orotherembeddedobjects
strength of three cores is at least 85 % of the specified strength and no
shall not be used for determining strength of concrete.
single core strength is less than 75 % of the specified strength.
5.1.3 If it is not possible to prepare a test specimen that
3.6 The“specifierofthetests”referencedinthistestmethod
meets the requirements of 7.1 and 7.2 and that is free of
is the individual responsible for analysis or review and
embedded reinforcement or other metal, the specifier of the
acceptance of core test results.
testsispermittedtoallowtestingofcoreswithembeddedmetal
(see Note 8). If a core tested for strength contains embedded
NOTE 5—For investigation of low strength test results, ACI 318-14
metal, the size, shape, and location of the metal within the core
defines the specifier of the tests as the licensed design professional or
building official.
shall be documented in the test report.
3.7 The apparent compressive strength of concrete as mea-
NOTE8—Thepresenceofsteelreinforcement,otherthanfibers,orother
6,7
suredbyacoreisaffectedbythelength-diameterratio(L/D)of
embedded metal in a core can affect the measured strength. There are
insufficient data to derive reliable correction factors that can be applied to
themeasuredstrengthtoaccountforembeddedreinforcementperpendicu-
lar to the core axis. If testing of cores containing embedded reinforcement
Neville, A., “Core Tests: Easy to Perform, Not Easy to Interpret,” Concrete
International, Vol 23, No. 11, November 2001, pp. 59–68.
4 6
“Guide for Obtaining Cores and Interpreting Compressive Strength Results,” Gaynor, R. D., “Effect of Horizontal Reinforcing Steel on the Strength of
ACI 214.4R, American Concrete Institute, P.O. Box 9094, Farmington Hills, MI Molded Cylinders,” Problems and Practices in Journal of the American Concrete
48333, www.concrete.org. Institute, Proceedings, Vol 62, No. 7, July 1965, pp. 837–840.
5 7
“Building Code Requirements for Structural Concrete and Commentary,” ACI Concrete Society Working Party, “Concrete Core Testing for Strength,”
318, American Concrete Institute, P.O. Box 9094, Farmington Hills, MI 48333, Concrete Society Technical Report No. 11, The Concrete Society, England, May
www.concrete.org. 1976.
C42/C42M − 20
ispermitted,engineeringjudgmentisrequiredtoassessthesignificanceof cores appear to be more sensitive to the effect of the length-diameter
the results. The specifier of the tests should not permit a core to be tested ratio.
for strength if bar reinforcement, or other elongated embedded metal
7.2 Length:
object, is oriented close to parallel to the core axis.
7.2.1 Exceptasprovidedin7.2.2,thepreferredlengthofthe
5.2 Core Drilling—When a core will be tested to measure
capped or ground specimen is between 1.9 and 2.1 times the
concrete strength, the core shall be drilled perpendicular to the
diameter. If the ratio of the length to the diameter (L/D) of the
surface and at least 150 mm [6 in.] away from formed joints or
core exceeds 2.1, reduce the length of the core so that the ratio
obvious edges of a unit of deposit (see Note 9). This minimum
of the capped or ground specimen is between 1.9 and 2.1. Core
distance does not apply to the formed boundaries of structural specimens with length-diameter ratios equal to or less than
members. Record the approximate angle between the longitu-
1.75 require corrections to the measured compressive strength
dinal axis of the drilled core and the horizontal plane of the (see 7.9.1).Astrength correction factor is not required for L/D
concrete as placed. A specimen drilled perpendicular to a greaterthan1.75.Acorehavingamaximumlengthoflessthan
vertical surface, or perpendicular to a sloping surface, shall be 95 % of its diameter before capping or a length less than its
taken from near the middle of a unit of deposit when possible. diameter after capping, trimming, or end grinding shall not be
tested.
If cores are obtained for purposes other than determination of
strength, drill cores in accordance with the instructions pro- 7.2.2 If the compressive strengths of cores are to be com-
pared with specified strengths based on standard concrete
vided by the specifier of the tests. Record the date core was
cubes, cores shall be tested with L/D, after end preparation, in
drilled. If known, record the date when concrete was placed.
the range of 1.00 to 1.05 unless otherwise directed by the
NOTE 9—The intent is to avoid drilling cores in non-representative
specifier of the tests. If the strengths of cores with L/D =1 are
concrete that may exist near formed joints or the boundary of a unit of
to be compared with specified concrete cube strength, do not
placement.
apply the correction factor in 7.9.1.
5.3 Slab Removal—Remove a slab sufficiently large to
7.3 Moisture Conditioning—Test cores after moisture con-
secure the desired test specimens without the inclusion of any
ditioning as specified in this test method or as directed by the
concrete that has been cracked, spalled, undercut, or otherwise
specifier of the tests. The moisture conditioning procedures
damaged.
specified in this test method are intended to preserve the
moisture of the drilled core and to provide a reproducible
DRILLED CORES
moisture condition that minimizes the effects of moisture
gradients introduced by wetting during drilling and specimen
6. Measuring the Length of Drilled Cores
preparation.
6.1 Coresfordeterminingthethicknessofpavements,slabs,
7.3.1 After cores have been drilled, wipe off surface drill
walls or other structural elements shall have a diameter of at
water and allow remaining surface moisture to evaporate.
least 94 mm [3.70 in.] when the lengths of such cores are
When surfaces appear dry, but not later than 1 h after drilling,
stipulated to be measured in accordance with Test Method
place cores in separate plastic bags or nonabsorbent containers
C174/C174M. When core length for determining the thickness
and seal to prevent moisture loss. Maintain cores at ambient
of a member is not required to be measured in accordance with
temperature,andprotectcoresfromexposuretodirectsunlight.
Test Method C174/C174M, core diameter shall be as directed
Transport the cores to the testing laboratory as soon as
by specifier of tests.
possible. Keep cores in the sealed plastic bags or nonabsorbent
containers at all times except during end preparation and for a
6.2 Forcoresthatarenotintendedfordeterminingstructural
maximum time of2hto permit capping before testing.
dimensions,measurethelongestandshortestlengthsonthecut
7.3.2 If water is used during sawing or grinding of core
surface along lines parallel to the core axis. Record the average
ends, complete these operations as soon as possible, but no
length to the nearest 5 mm [ ⁄4 in.].
later than 2 days after drilling of cores unless stipulated
otherwise by the specifier of tests. After completing end
7. Cores for Compressive Strength
preparation, wipe off surface moisture, allow the surfaces to
dry, and place the cores in sealed plastic bags or nonabsorbent
7.1 Diameter:
containers. Minimize the duration of exposure to water during
7.1.1 Except as provided in 7.1.2, the diameter of core
end preparation.
specimens for the determination of compressive strength shall
7.3.3 Allow the cores to remain in the sealed plastic bags or
be at least 94 mm [3.70 in.] or at least two times the nominal
nonabsorbent containers for at least 5 days after last being
maximum size of the coarse aggregate, whichever is larger.
wetted and before testing, unless stipulated otherwise by the
7.1.2 If limited member thickness makes it impossible to
specifier of tests.
obtain cores with length-diameter ratio (L/D) of at least 1.0 or
NOTE 11—The waiting period of at least 5 days is intended to reduce
if clear distance between reinforcement is limited, core diam-
eters less than 94 mm [3.70 in.] are not prohibited. If a core
diameter less than 94 mm [3.70 in.] is used, report the reason.
NOTE 10—The compressive strengths of nominal 50-mm [2-in.] diam-
Bartlett, F. M., and MacGregor, J. G., “Effect of Core Diameter on Concrete
eter cores are known to be somewhat lower and more variable than those
Core Strengths,” ACI Materials Journal, Vol 91, No. 5, September–October 1994,
of nominal 100-mm [4-in.] diameter cores. In addition, smaller diameter pp. 460–470.
C42/C42M − 20
moisture gradients introduced when the core is drilled or wetted during
ground ends, determine the average length of the prepared core
sawing or grinding.
before testing. Determine the average length of the core to the
7.3.4 When direction is given to test cores in a moisture nearest 1 mm [0.05 in.] using the jaw caliper procedure of Test
condition other than achieved by conditioning according to Method C1542/C1542M or the procedure in Test Method
7.3.1, 7.3.2, and 7.3.3, report the alternative p
...

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: C42/C42M − 18a C42/C42M − 20 American Association State
Highway and Transportation Officials Standard
AASHTO No.: T24
Standard Test Method for
Obtaining and Testing Drilled Cores and Sawed Beams of
Concrete
This standard is issued under the fixed designation C42/C42M; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This test method covers obtaining, preparing, and testing cores drilled from concrete for length or compressive strength or
splitting tensile strength determinations. This test method is not applicable to cores from shotcrete.
NOTE 1—Test Method C1604/C1604M is applicable for obtaining, preparing, and testing cores from shotcrete.
NOTE 2—Appendix X1 provides recommendations for obtaining and testing sawed beams for flexural performance.
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.3 The text of this standard references notes and footnotes that provide explanatory material. These notes and footnotes
(excluding those in tables and figures) shall not be considered as requirements of the standard.
1.4 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.
1.5 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:
C39/C39M Test Method for Compressive Strength of Cylindrical Concrete Specimens
C78/C78M Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)
C174/C174M Test Method for Measuring Thickness of Concrete Elements Using Drilled Concrete Cores
C496/C496M Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens
C617/C617M Practice for Capping Cylindrical Concrete Specimens
C642 Test Method for Density, Absorption, and Voids in Hardened Concrete
C670 Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
C823/C823M Practice for Examination and Sampling of Hardened Concrete in Constructions
C1231/C1231M Practice for Use of Unbonded Caps in Determination of Compressive Strength of Hardened Cylindrical
Concrete Specimens
C1542/C1542M Test Method for Measuring Length of Concrete Cores
C1604/C1604M Test Method for Obtaining and Testing Drilled Cores of Shotcrete
3. Significance and Use
3.1 This test method provides standardized procedures for obtaining and testing specimens to determine the compressive,
splitting tensile, and flexural strength of in-place concrete.
This test method is under the jurisdiction of ASTM Committee C09 on Concrete and Concrete Aggregates and is the direct responsibility of Subcommittee C09.61 on
Testing for Strength.
Current edition approved Dec. 15, 2018April 1, 2020. Published February 2019May 2020. Originally approved in 1921. Last previous edition approved in 2018 as
C42/C42M – 18.18a. DOI: 10.1520/C0042_C0042M-18A.10.1520/C0042_C0042M-20.
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.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C42/C42M − 20
3.2 Generally, test specimens are obtained when doubt exists about the in-place concrete quality due either to low strength test
results during construction or signs of distress in the structure. Another use of this method is to provide strength information on
older structures.
3.3 Concrete strength is affected by the location of the concrete in a structural element, with the concrete at the bottom tending
to be stronger than the concrete at the top. Core strength is also affected by core orientation relative to the horizontal plane of the
concrete as placed, with strength tending to be lower when measured parallel to the horizontal plane. These factors shall be
considered in planning the locations for obtaining concrete samples and in comparing strength test results.
3.4 The strength of concrete measured by tests of cores is affected by the amount and distribution of moisture in the specimen
at the time of test. There is no standard procedure to condition a specimen that will ensure that, at the time of test, it will be in
the identical moisture condition as concrete in the structure. The moisture conditioning procedures in this test method are intended
to provide reproducible moisture conditions that minimize within-laboratory and between-laboratory variations and to reduce the
effects of moisture introduced during specimen preparation.
3.5 The measured compressive strength of a core will generally be less than that of a corresponding properly molded and cured
standard cylinder tested at the same age. For a given concrete, however, there is no unique relationship between the strengths of
these two types of specimens (see Note 3). The relationship is affected by many factors such as the strength level of the concrete,
the in-place temperature and moisture histories, the degree of consolidation, batch-to-batch variability, the strength-gain
characteristics of the concrete, the condition of the coring apparatus, and the care used in removing cores.
NOTE 3—A procedure is available for estimating the equivalent cylinder strength from a measured core strength.
NOTE 4—In the absence of core strength requirements of an applicable building code or of other contractual or legal documents that may govern the
project, the specifier of tests should establish in the project specifications the acceptance criteria for core strengths. An example of acceptance criteria for
core strength is provided in ACI 318, which are used to evaluate cores taken to investigate low strength test results of standard-cured cylinder during
construction. According to ACI 318, the concrete represented by the cores is considered structurally adequate if the average strength of three cores is at
least 85 % of the specified strength and no single core strength is less than 75 % of the specified strength.
3.6 The “specifier of the tests” referenced in this test method is the individual responsible for analysis or review and acceptance
of core test results.
NOTE 5—For investigation of low strength test results, ACI 318-14 defines the specifier of the tests as the licensed design professional or building
official.
3.7 The apparent compressive strength of concrete as measured by a core is affected by the length-diameter ratio (L/D) of the
core as tested and this must be considered in preparing core specimens and evaluating test results.
4. Apparatus
4.1 Core Drill, for obtaining cylindrical core specimens with diamond-impregnated bits attached to a core barrel.
4.2 Saw, for trimming ends of cores. The saw shall have a diamond or silicon-carbide cutting edge and shall be capable of
cutting cores without introducing cracks or dislodging aggregate particles.
4.3 Balance, accurate to at least 5 g [0.01 lb].
5. Sampling
5.1 General:
5.1.1 Samples of hardened concrete for use in the preparation of strength test specimens shall not be taken until the concrete
is strong enough to permit sample removal without disturbing the bond between the mortar and the coarse aggregate (see Note 6
and Note 7). When preparing strength test specimens from samples of hardened concrete, samples that have been damaged during
removal shall not be used unless the damaged portion(s) are removed and the lengths of resulting test specimens satisfy the
minimum length-diameter ratio requirement in 7.2. Samples of defective or damaged concrete that cannot be tested shall be
reported along with the reason that prohibits use of the sample for preparing strength test specimens.
NOTE 6—Practice C823/C823M provides guidance on the development of a sampling plan for concrete in constructions.
NOTE 7—It is not possible to specify a minimum age when concrete is strong enough to withstand damage during removal, because the strength at
any age depends on the curing history and strength grade of the concrete. If time permits, the concrete should not be removed before it is 14 days old.
If this is not practicable, removal of concrete can proceed if the cut surfaces do not display erosion of the mortar and the exposed coarse aggregate particles
are embedded firmly in the mortar. In-place test methods may be used to estimate the level of strength development prior to attempting removal of
concrete samples.
Neville, A., “Core Tests: Easy to Perform, Not Easy to Interpret,” Concrete International, Vol 23, No. 11, November 2001, pp. 59–68.
“Guide for Obtaining Cores and Interpreting Compressive Strength Results,” ACI 214.4R, American Concrete Institute, P.O. Box 9094, Farmington Hills, MI 48333,
www.concrete.org.
“Building Code Requirements for Structural Concrete and Commentary,” ACI 318, American Concrete Institute, P.O. Box 9094, Farmington Hills, MI 48333,
www.concrete.org.
C42/C42M − 20
5.1.2 Except as provided in 5.1.3, cores containing embedded reinforcement, excluding fibers, or other embedded objects shall
not be used for determining strength of concrete.
5.1.3 If it is not possible to prepare a test specimen that meets the requirements of 7.1 and 7.2 and that is free of embedded
reinforcement or other metal, the specifier of the tests is permitted to allow testing of cores with embedded metal (see Note 8).
If a core tested for strength contains embedded metal, the size, shape, and location of the metal within the core shall be documented
in the test report.
6,7
NOTE 8—The presence of steel reinforcement, other than fibers, or other embedded metal in a core can affect the measured strength. There are
insufficient data to derive reliable correction factors that can be applied to the measured strength to account for embedded reinforcement perpendicular
to the core axis. If testing of cores containing embedded reinforcement is permitted, engineering judgment is required to assess the significance of the
results. The specifier of the tests should not permit a core to be tested for strength if bar reinforcement, or other elongated embedded metal object, is
oriented close to parallel to the core axis.
5.2 Core Drilling—When a core will be tested to measure concrete strength, the core shall be drilled perpendicular to the surface
and at least 150 mm [6 in.] away from formed joints or obvious edges of a unit of deposit (see Note 9). This minimum distance
does not apply to the formed boundaries of structural members. Record the approximate angle between the longitudinal axis of
the drilled core and the horizontal plane of the concrete as placed. A specimen drilled perpendicular to a vertical surface, or
perpendicular to a sloping surface, shall be taken from near the middle of a unit of deposit when possible. If cores are obtained
for purposes other than determination of strength, drill cores in accordance with the instructions provided by the specifier of the
tests. Record the date core was drilled. If known, record the date when concrete was placed.
NOTE 9—The intent is to avoid drilling cores in non-representative concrete that may exist near formed joints or the boundary of a unit of placement.
5.3 Slab Removal—Remove a slab sufficiently large to secure the desired test specimens without the inclusion of any concrete
that has been cracked, spalled, undercut, or otherwise damaged.
DRILLED CORES
6. Measuring the Length of Drilled Cores
6.1 Cores for determining the thickness of pavements, slabs, walls or other structural elements shall have a diameter of at least
94 mm [3.70 in.] when the lengths of such cores are stipulated to be measured in accordance with Test Method C174/C174M.
When core length for determining the thickness of a member is not required to be measured in accordance with Test Method
C174/C174M, core diameter shall be as directed by specifier of tests.
6.2 For cores that are not intended for determining structural dimensions, measure the longest and shortest lengths on the cut
surface along lines parallel to the core axis. Record the average length to the nearest 5 mm [ ⁄4 in.].
7. Cores for Compressive Strength
7.1 Diameter:
7.1.1 Except as provided in 7.1.2, the diameter of core specimens for the determination of compressive strength shall be at least
94 mm [3.70 in.] or at least two times the nominal maximum size of the coarse aggregate, whichever is larger.
7.1.2 If limited member thickness makes it impossible to obtain cores with length-diameter ratio (L/D) of at least 1.0 or if clear
distance between reinforcement is limited, core diameters less than 94 mm [3.70 in.] are not prohibited. If a core diameter less than
94 mm [3.70 in.] is used, report the reason.
NOTE 10—The compressive strengths of nominal 50-mm [2-in.] diameter cores are known to be somewhat lower and more variable than those of
nominal 100-mm [4-in.] diameter cores. In addition, smaller diameter cores appear to be more sensitive to the effect of the length-diameter ratio.
7.2 Length:
7.2.1 Except as provided in 7.2.2, the preferred length of the capped or ground specimen is between 1.9 and 2.1 times the
diameter. If the ratio of the length to the diameter (L/D) of the core exceeds 2.1, reduce the length of the core so that the ratio of
the capped or ground specimen is between 1.9 and 2.1. Core specimens with length-diameter ratios equal to or less than 1.75
require corrections to the measured compressive strength (see 7.9.1). A strength correction factor is not required for L/D greater
than 1.75. A core having a maximum length of less than 95 % of its diameter before capping or a length less than its diameter after
capping, trimming, or end grinding shall not be tested.
7.2.2 If the compressive strengths of cores are to be compared with specified strengths based on standard concrete cubes, cores
shall be tested with L/D, after end preparation, in the range of 1.00 to 1.05 unless otherwise directed by the specifier of the tests.
If the strengths of cores with L/D =1 are to be compared with specified concrete cube strength, do not apply the correction factor
in 7.9.1.
Gaynor, R. D., “Effect of Horizontal Reinforcing Steel on the Strength of Molded Cylinders,” Problems and Practices in Journal of the American Concrete Institute,
Proceedings, Vol 62, No. 7, July 1965, pp. 837–840.
Concrete Society Working Party, “Concrete Core Testing for Strength,” Concrete Society Technical Report No. 11, The Concrete Society, England, May 1976.
Bartlett, F. M., and MacGregor, J. G., “Effect of Core Diameter on Concrete Core Strengths,” ACI Materials Journal, Vol 91, No. 5, September–October 1994, pp.
460–470.
C42/C42M − 20
7.3 Moisture Conditioning—Test cores after moisture conditioning as specified in this test method or as directed by the specifier
of the tests. The moisture conditioning procedures specified in this test method are intended to preserve the moisture of the drilled
core and to provide a reproducible moisture condition that minimizes the effects of moisture gradients introduced by wetting during
drilling and specimen preparation.
7.3.1 After cores have been drilled, wipe off surface drill water and allow remaining surface moisture to evaporate. When
surfaces appear dry, but not later than 1 h after drilling, place cores in separate plastic bags or nonabsorbent containers and seal
to prevent moisture loss. Maintain cores at ambient temperature, and protect cores from exposure to direct sunlight. Transport the
cores to the testing laboratory as soon as possible. Keep cores in the sealed plastic bags or nonabsorbent containers at all times
except during end preparation and for a maximum time of 2 h to permit capping before testing.
7.3.2 If water is used during sawing or grinding of core ends, complete these operations as soon as possible, but no later than
2 days after drilling of cores unless stipulated otherwise by the specifier of tests. After completing end preparation, wipe off surface
moisture, allow the surfaces to dry, and place the cores in sealed plastic bags or nonabsorbent containers. Minimize the duration
of exposure to water during end preparation.
7.3.3 Allow the cores to remain in the sealed plastic bags or nonabsorbent containers for at least 5 days after last being wetted
and before testing, unless stipulated otherwise by the specifier of tests.
NOTE 11—The waiting period of at least 5 days is intended to reduce moisture gradients introduced when the core is drilled or wetted during sawing
or grinding.
7.3.4 When direction is given to test cores in a moisture condition other than achieved by conditioning according to 7.3.1, 7.3.2,
and 7.3.3, report the alternative procedure.
7.4 Sawing of Ends—The ends of core specimens to be tested in compression shall be flat, and perpendicular to the longitudinal
axis in accordance with Test Method C39/C39M. If necessary, saw the ends of cores that will be capped so that prior to capping,
the following requirements are met:
7.4.1 Projections, if any, shall not extend more than 5 mm [0.2 in.] above the end surfaces.
7.4.2 The end surfaces shall not depart from perpendicularity to the longitudinal axis by a slope of more than 1:0.3d [1:8d]
where d is the average core diameter in mm [in.].
7.5 Calculated Density—If the core will be tested for strength, measure the mass of the core just before capping or just before
testing if bonded caps are not used. Divide the mass by the volume of the core calculated from the average diameter and length
3 3
determined in 7.7. Record t
...