Designation: C42/C42M − 16 American Association State

Highway and Transportation Officials Standard

AASHTO No.: T24

Standard Test Method for

Obtaining and Testing Drilled Cores and Sawed Beams of
Concrete1

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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* C78/C78M Test Method for Flexural Strength of Concrete

1.1 This test method covers obtaining, preparing, and test- (Using Simple Beam with Third-Point Loading)
ing cores drilled from concrete for length or compressive C174/C174M Test Method for Measuring Thickness of Con-
strength or splitting tensile strength determinations. This test crete Elements Using Drilled Concrete Cores
method is not applicable to cores from shotcrete. C496/C496M Test Method for Splitting Tensile Strength of
NOTE 1—Test Method C1604/C1604M is applicable for obtaining, Cylindrical Concrete Specimens
preparing, and testing cores from shotcrete. C617/C617M Practice for Capping Cylindrical Concrete
NOTE 2—Appendix X1 provides recommendations for obtaining and
testing sawed beams for flexural performance.
Specimens
C642 Test Method for Density, Absorption, and Voids in
1.2 The values stated in either SI units or inch-pound units
Hardened Concrete
are to be regarded separately as standard. The values stated in
C670 Practice for Preparing Precision and Bias Statements
each system may not be exact equivalents; therefore, each
system shall be used independently of the other. Combining for Test Methods for Construction Materials
values from the two systems may result in non-conformance C823/C823M Practice for Examination and Sampling of
with the standard. Hardened Concrete in Constructions
C1231/C1231M Practice for Use of Unbonded Caps in
1.3 The text of this standard references notes and footnotes Determination of Compressive Strength of Hardened Cy-
that provide explanatory material. These notes and footnotes
lindrical Concrete Specimens
(excluding those in tables and figures) shall not be considered
C1542/C1542M Test Method for Measuring Length of Con-
as requirements of the standard.
crete Cores
1.4 This standard does not purport to address the safety C1604/C1604M Test Method for Obtaining and Testing
concerns, if any, associated with its use. It is the responsibility Drilled Cores of Shotcrete
of the user of this standard to establish appropriate safety and
health practices and determine the applicability of regulatory
3. Significance and Use
limitations prior to use.
3.1 This test method provides standardized procedures for
2. Referenced Documents obtaining and testing specimens to determine the compressive,
2.1 ASTM Standards:2 splitting tensile, and flexural strength of in-place concrete.
C39/C39M Test Method for Compressive Strength of Cylin- 3.2 Generally, test specimens are obtained when doubt
drical Concrete Specimens
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
1
This test method is under the jurisdiction of ASTM Committee C09 on information on older structures.
Concrete and Concrete Aggregates and is the direct responsibility of Subcommittee
C09.61 on Testing for Strength. 3.3 Concrete strength is affected by the location of the
Current edition approved Oct. 1, 2016. Published October 2016. Originally
approved in 1921. Last previous edition approved in 2013 as C42/C42M – 13. DOI: concrete in a structural element, with the concrete at the bottom
10.1520/C0042_C0042M-16. tending to be stronger than the concrete at the top. Core
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or strength is also affected by core orientation relative to the
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on horizontal plane of the concrete as placed, with strength
the ASTM website. tending to be lower when measured parallel to the horizontal

*A Summary of Changes section appears at the end of this standard

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 C42/C42M − 16
plane.3 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 diamond or silicon-carbide cutting edge and shall be capable of
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 have been damaged during removal shall not be used unless the
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
NOTE 3—A procedure is available for estimating the equivalent cylinder at any age depends on the curing history and strength grade of the
strength from a measured core strength.4 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 318,5 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 ded reinforcement, excluding fibers, or other embedded objects
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 “specifier of the tests” referenced in this test method 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. tests is permitted to allow testing of cores with embedded metal
(see Note 8). If a core tested for strength contains embedded
NOTE 5—For investigation of low strength test results, ACI 318 defines metal, the size, shape, and location of the metal within the core
the specifier of the tests as the licensed design professional.
shall be documented in the test report.
3.7 The apparent compressive strength of concrete as mea-
NOTE 8—The presence of steel reinforcement, other than fibers, or other
sured by a core is affected by the length-diameter ratio (L/D) of embedded metal in a core can affect the measured strength.6,7 There are
the core as tested and this must be considered in preparing core insufficient data to derive reliable correction factors that can be applied to
specimens and evaluating test results. the measured strength to account for embedded reinforcement perpendicu-
lar to the core axis. If testing of cores containing embedded reinforcement
is permitted, engineering judgment is required to assess the significance of
4. Apparatus the results. The specifier of the tests should not permit a core to be tested
4.1 Core Drill, for obtaining cylindrical core specimens for strength if bar reinforcement, or other elongated embedded metal
with diamond impregnated bits attached to a core barrel. object, is oriented close to parallel to the core axis.
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5.2 Core Drilling—When a core will be tested to measure

concrete strength, the core shall be drilled perpendicular to the
3
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.

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 C42/C42M − 16
surface and at least 150 mm [6 in.] away from formed joints or diameter. If the ratio of the length to the diameter (L/D) of the
obvious edges of a unit of deposit (see Note 9). This minimum core exceeds 2.1, reduce the length of the core so that the ratio
distance does not apply to the formed boundaries of structural of the capped or ground specimen is between 1.9 and 2.1. Core
members. Record the approximate angle between the longitu- specimens with length-diameter ratios equal to or less than
dinal axis of the drilled core and the horizontal plane of the 1.75 require corrections to the measured compressive strength
concrete as placed. A specimen drilled perpendicular to a (see 7.9.1). A strength correction factor is not required for L/D
vertical surface, or perpendicular to a sloping surface, shall be greater than 1.75. A core having a maximum length of less than
taken from near the middle of a unit of deposit when possible. 95 % of its diameter before capping or a length less than its
If cores are obtained for purposes other than determination of diameter after capping, trimming, or end grinding shall not be
strength, drill cores in accordance with the instructions pro- tested.
vided by the specifier of the tests. Record the date core was 7.2.2 If the compressive strengths of cores are to be com-
drilled. If known, record the date when concrete was placed. pared with specified strengths based on standard concrete
NOTE 9—The intent is to avoid drilling cores in non-representative
cubes, cores shall be tested with L/D, after end preparation, in
concrete that may exist near formed joints or the boundary of a unit of the range of 1.00 to 1.05 unless otherwise directed by the
placement. specifier of the tests. If the strengths of cores with L/D =1 are
5.3 Slab Removal—Remove a slab sufficiently large to to be compared with specified concrete cube strength, do not
secure the desired test specimens without the inclusion of any apply the correction factor in 7.9.1.
concrete that has been cracked, spalled, undercut, or otherwise 7.3 Moisture Conditioning—Test cores after moisture con-
damaged. ditioning as specified in this test method or as directed by the
specifier of the tests. The moisture conditioning procedures
DRILLED CORES specified in this test method are intended to preserve the
6. Measuring the Length of Drilled Cores moisture of the drilled core and to provide a reproducible
moisture condition that minimizes the effects of moisture
6.1 Cores for determining the thickness of pavements, slabs, gradients introduced by wetting during drilling and specimen
walls or other structural elements shall have a diameter of at preparation.
least 94 mm [3.70 in.] when the lengths of such cores are 7.3.1 After cores have been drilled, wipe off surface drill
stipulated to be measured in accordance with Test Method water and allow remaining surface moisture to evaporate.

--``,,,`,,``,``,,,`,,``,,,``-`-`,,`,,`,`,,`---
C174/C174M. When core length for determining the thickness When surfaces appear dry, but not later than 1 h after drilling,
of a member is not required to be measured in accordance with place cores in separate plastic bags or nonabsorbent containers
Test Method C174/C174M, core diameter shall be as directed and seal to prevent moisture loss. Maintain cores at ambient
by specifier of tests. temperature, and protect cores from exposure to direct sunlight.
6.2 For cores that are not intended for determining structural Transport the cores to the testing laboratory as soon as
dimensions, measure the longest and shortest lengths on the cut possible. Keep cores in the sealed plastic bags or nonabsorbent
surface along lines parallel to the core axis. Record the average containers at all times except during end preparation and for a
length to the nearest 5 mm [1⁄4 in.]. maximum time of 2 h to permit capping before testing.
7.3.2 If water is used during sawing or grinding of core
7. Cores for Compressive Strength ends, complete these operations as soon as possible, but no
7.1 Diameter: later than 2 days after drilling of cores unless stipulated
7.1.1 Except as provided in 7.1.2, the diameter of core otherwise by the specifier of tests. After completing end
specimens for the determination of compressive strength shall preparation, wipe off surface moisture, allow the surfaces to
be at least 94 mm [3.70 in.] or at least two times the nominal dry, and place the cores in sealed plastic bags or nonabsorbent
maximum size of the coarse aggregate, whichever is larger. containers. Minimize the duration of exposure to water during
7.1.2 If limited member thickness makes it impossible to end preparation.
obtain cores with length-diameter ratio (L/D) of at least 1.0 or 7.3.3 Allow the cores to remain in the sealed plastic bags or
if clear distance between reinforcement is limited, core diam- nonabsorbent containers for at least 5 days after last being
eters less than 94 mm [3.70 in.] are not prohibited. If a core wetted and before testing, unless stipulated otherwise by the
diameter less than 94 mm [3.70 in.] is used, report the reason. specifier of tests.
NOTE 10—The compressive strengths of nominal 50-mm [2-in.] diam- NOTE 11—The waiting period of at least 5 days is intended to reduce
eter cores are known to be somewhat lower and more variable than those moisture gradients introduced when the core is drilled or wetted during
of nominal 100-mm [4-in.] diameter cores. In addition, smaller diameter sawing or grinding.
cores appear to be more sensitive to the effect of the length-diameter
ratio.8 7.3.4 When direction is given to test cores in a moisture
7.2 Length condition other than achieved by conditioning according to
7.2.1 Except as provided in 7.2.2, the preferred length of the 7.3.1, 7.3.2, and 7.3.3, report the alternative procedure.
capped or ground specimen is between 1.9 and 2.1 times the 7.4 Sawing of Ends—The ends of core specimens to be
tested in compression shall be flat, and perpendicular to the
8
Bartlett, F. M., and MacGregor, J. G., “Effect of Core Diameter on Concrete
longitudinal axis in accordance with Test Method C39/C39M.
Core Strengths,” ACI Materials Journal, Vol 91, No. 5, September–October 1994, If necessary, saw the ends of cores that will be capped so that
pp. 460–470. prior to capping, the following requirements are met:

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 C42/C42M − 16
7.4.1 Projections, if any, shall not extend more than 5 mm report to the nearest 1 mm [0.05 in.]. Do not test a core if the
[0.2 in.] above the end surfaces. difference between the largest and smallest diameter exceeds
7.4.2 The end surfaces shall not depart from perpendicular- 5 % of their average.
ity to the longitudinal axis by a slope of more than 1:8d [or 7.8 Testing—Test the specimens in accordance with Test
1:0.3d] where d is the average core diameter in mm [or inches]. Method C39/C39M. Test the specimens within 7 days after
coring, unless specified otherwise.
7.5 Calculated Density—If the core will be tested for
strength, measure the mass of the core just before capping or 7.9 Calculation—Calculate the compressive strength of
just before testing if bonded caps are not used. Divide the mass each specimen using the computed cross-sectional area based
by the volume of the core calculated from the average diameter on the average diameter of the specimen.
and length determined in 7.7. Record the calculated density to 7.9.1 If the ratio of length to diameter (L/D) of the specimen
is 1.75 or less, correct the result obtained in 7.9 by multiplying

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the nearest 20 kg/m3 [1 lb/ft3].
NOTE 12—The intent of 7.5 is to obtain an approximate density of the by the appropriate correction factor shown in the following
specimen, which can provide additional insight on measured strength. For table (see Note 14):
example, a lower than expected density can be an indication of a batching Ratio of Length Strength
error, that there is too much air in the concrete, or that the concrete was to Diameter (L/D) Correction Factor
not consolidated properly, all of which can affect the compressive
strength. Because the moisture content of the core is not known and 1.75 0.98
1.50 0.96
because the calculated volume is approximate, the calculated density is
1.25 0.93
not intended for evaluating compliance with specified density require- 1.00 0.87
ments. Separate cores should be taken for this purpose, and the specifier
of the tests should indicate the procedure for measuring density; for Use interpolation to determine correction factors for L/D
example, Test Method C642 could be specified for normal weight values not given in the table.
concrete.
NOTE 14—Correction factors depend on various conditions such as
7.6 Capping—If the ends of the cores do not conform to the moisture condition, strength level, and elastic modulus. Average values for
corrections due to length-diameter ratio are given in the table. These
perpendicularity requirements of Test Method C39/C39M, they
correction factors apply to low-density concrete having a density between
shall be sawed or ground to meet those requirements or capped 1600 and 1920 kg/m3 [100 and 120 lb/ft3] and to normal density concrete.
with bonded caps in accordance with Practice C617/C617M. If They are applicable to both dry and wet concrete for strengths between 14
the ends of the cores do not conform to the planeness MPa and 42 MPa [2000 psi and 6000 psi]. For strengths above 70 MPa [10
requirements of Test Method C39/C39M, they shall be sawed 000 psi], test data on cores show that the correction factors may be larger
than the values listed above.9
or ground to meet those requirements or capped with bonded
caps in accordance with Practice C617/C617M or tested with 7.10 Report—Report the results as required by Test Method
unbonded caps in accordance with Practice C1231/C1231M. If C39/C39M with the addition of the following information:
cores are capped in accordance with Practice C617/C617M, the 7.10.1 Length of core as drilled to the nearest 5 mm [1⁄4 in.],
capping device shall accommodate actual core diameters and 7.10.2 If the core diameter is less than 94 mm [3.70 in.],
produce caps that are concentric with the core ends. Measure provide reason for using the smaller diameter.
7.10.3 Length of test specimen before and after capping or
core lengths to the nearest 1 mm [0.05 in.] before capping. If
end preparation to the nearest 1 mm [0.05 in.], and average
unbonded caps are used, the gap between the core and retaining
diameter of core to the nearest 0.2 mm [0.01 in.] or 1 mm [0.05
rings shall conform to the requirements of Practice C1231/
in.],
C1231M.
7.10.4 Compressive strength to the nearest 0.1 MPa [10 psi]
NOTE 13—To satisfy the maximum gap limit in Practice C1231/ when the diameter is measured to the nearest 0.2 mm [0.01 in.]
C1231M the inner diameter of the retaining rings cannot exceed 107 % of and to the nearest 0.5 MPa [50 psi] when the diameter is
the average core diameter. Smaller diameter retaining rings may be needed measured to the nearest 1 mm [0.05 in.], after correction for
for testing cores with diameters smaller than standard cylinders. For length-diameter ratio when required,
example if the core diameter is 95 mm [3.75 in.], the inside diameter of the
retaining rings cannot exceed 102 mm [4.01 in.].
7.10.5 Direction of application of the load on the specimen
with respect to the horizontal plane of the concrete as placed,
7.7 Measurement—If the core will be tested with bonded 7.10.6 The moisture conditioning history:
caps, determine the average length before and after capping, 7.10.6.1 The date and time core was obtained and first
and use the length after capping to compute the length- placed in sealed bag or nonabsorbent container,
diameter ratio (L/D). If the core will be tested with unbonded 7.10.6.2 If water was used during end preparation, the date
caps or with ground ends, determine the average length of the and time end preparation was completed and core placed in
prepared core before testing. Determine the average length of sealed bag or nonabsorbent container,
the core to the nearest 1 mm [0.05 in.] using the jaw caliper 7.10.7 Date concrete was placed, if known,
procedure of Test Method C1542/C1542M or the procedure in 7.10.8 The date and time when tested,
Test Method C174/C174M. Determine the average diameter by 7.10.9 Nominal maximum size of concrete aggregate.
averaging two measurements taken at right angles to each other
at the mid-height of the core. Report the average core diameter 9
Bartlett, F. M., and MacGregor, J. G, “Effect of Core Length-to-Diameter Ratio
to the nearest 0.2 mm [0.01 in.] if the difference in core on Concrete Core Strengths,” ACI Materials Journal, Vol 91, No. 4, July-August
diameters does not exceed 2 % of their average, otherwise 1994, pp. 339–348.

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7.10.10 The calculated density to the nearest 20 kg/m3 [1
lb/ft3].
7.10.11 The location, shape, and size of embedded metal, if
the specifier of the tests permits testing cores with embedded
metal.
7.10.12 If applicable, description of defects in cores that
could not be tested, and
7.10.13 If any deviation from this test method was required,
describe the deviation and explain why it was necessary.
7.11 Precision:10
7.11.1 The single-operator coefficient of variation on cores
has been found to be 3.2 %11 for a range of compressive
strength between 32.0 MPa [4500 psi] and 48.3 MPa [7000
psi]. Therefore, results of two properly conducted tests of
single cores by the same operator on the same sample of
material should not differ from each other by more than 9 %11
of their average.
7.11.2 The multi-laboratory coefficient of variation on cores
has been found to be 4.7 %11 for a range of compressive
strength between 32.0 MPa [4500 psi] and 48.3 MPa [7000
psi]. Therefore, results of two properly conducted tests on
cores sampled from the same hardened concrete (where a
single test is defined as the average of two observations (cores),
each made on separate adjacent drilled 100 mm [4 in.] diameter
cores), and tested by two different laboratories should not differ
from each other by more than 13 %11 of their average.
7.12 Bias—Since there is no accepted reference material
suitable for determining the bias for the procedure in this test
method, no statement on bias is being made.

8. Cores for Splitting Tensile Strength

8.1 Test Specimens—The specimens shall conform to the
dimensional requirements in 7.1, 7.2, 7.4.1, and 7.4.2. Ends are
not to be capped.
8.2 Moisture Conditioning—Condition the specimens as
described in 7.3, or as directed by the specifier of tests.
8.3 Bearing Surfaces—The line of contact between the
specimen and each bearing strip shall be straight and free of FIG. 1 Suitable Capping Device for Splitting Tensile Strength
any projections or depressions higher or deeper than 0.2 mm Test
[0.01 in.]. When the line of contact is not straight or contains
projections or depressions having heights or depths greater
than 0.2 mm [0.01 in.], grind or cap the specimen so as to 8.5 Calculation and Report—Calculate the splitting tensile
produce bearing lines meeting these requirements. Do not test strength and report the results as required in Test Method
specimens with projections or depressions greater than 2.0 mm C496/C496M. When grinding or capping of the bearing
[0.1 in.]. When capping is employed, the caps shall be as thin surfaces is required, measure the diameter between the finished
as practicable and shall be formed of high-strength gypsum surfaces. Indicate that the specimen was a core and provide the
paste. moisture conditioning history as in 7.10.6.
NOTE 15—Fig. 1 illustrates a device suitable for applying caps to the 8.6 Precision:12
--``,,,`,,``,``,,,`,,``,,,``-`-`,,`,,`,`,,`---

bearing surfaces of core specimens.

8.6.1 The within laboratory single-operator coefficient of
8.4 Testing—Test the specimens in accordance with Test variation for splitting tensile strength of cores between 3.6
Method C496/C496M. MPa [520 psi] and 4.1 MPa [590 psi] has been found to be
5.3 %.11 Therefore, results of two properly conducted tests by
10
Bollin, G. E., “Development of Precision and Bias Statements for Testing
Drilled Cores in Accordance with ASTM C42,” ASTM Journal of Cement, Concrete,
12
and Aggregates, Vol 15, No. 1, 1993. Steele, G.W., “Portland Cement Concrete Core Proficiency Sample Program,”
11
These numbers represent, respectively, the (1s %) and (d2s %) limits as Strategic Highway Research Program, SHRP-P-636, National Research Council,
described in Practice C670. Washington, D.C., 1993.

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 C42/C42M − 16
the same operator in the same laboratory on the same sample 8.7 Bias—Since there is no accepted reference material
of material should not differ by more than 14.9 %11 of their suitable for determining the bias for the procedure in this test
average. method, no statement on bias is being made.
8.6.2 The multi-laboratory coefficient of variation for split-
ting tensile strength of cores between 3.6 MPa [520 psi] and 9. Keywords
4.1 MPa [590 psi] has been found to be 15.0 %.11 Therefore,
9.1 compressive strength; concrete coring; concrete sawing;
results of two properly conducted tests on the same sample of
material of hardened concrete and tested by two different concrete strength; flexural strength; splitting tensile strength
laboratories should not differ from each other by more than
42.3 %11 of their average.

APPENDIX

(Nonmandatory Information)

X1. SAWED BEAMS FOR FLEXURAL TESTING

X1.1 General When beams are required for measuring properties other than
X1.1.1 There are insufficient data on the effects of various flexural strength, such as toughness, beam dimensions should
variables that could affect the measured flexural performance conform to the requirements of the applicable test method.
of sawed beams. Considerable resources are necessary to X1.2.2 Sawing and Inspection—Beams should be cut with
provide the data necessary to develop a definitive test method water-cooled masonry saws. Test specimens can be damaged if
and the accompanying precision data. Until that data are sawing is not done carefully. Ensure that an adequate supply of
generated, the following general recommendations are pro- water is used to keep the saw blade cool. The sawed surfaces
vided for obtaining and testing sawed beams. need to be parallel and square within the limits provided by the
X1.1.2 Testing beams sawed from existing concrete is not a specifier of tests. Mark the specimen so that its orientation in
preferred method of assessing the in-place flexural strength the structure can be identified. Check the sawn surface for the
because of the difficulty in obtaining the correct geometry and presence of cracks, which can be seen by surface drying the
because of the risk of damage to the specimens by the sawing specimen and looking for dark lines that indicate water filled
process, subsequent handling, and incorrect moisture condi- cracks. Do not test a beam if there is a crack in the loading span
tioning. If in-place flexural strength needs to be assessed, the or if there is a chip on the face that will be loaded in tension.
splitting tensile strength can be measured on cores in accor- Take care in handling sawed beam specimens to avoid chipping
dance with Section 8 and published relationships between or cracking. Specimens may be rejected by the specifier of tests
flexural strength and splitting tensile strength can be applied.13 if they do not conform to the dimensional tolerances or they do
If it is necessary to test sawed beams, the specifier of tests not conform to contact requirements (at load and support
should provide instructions on the size of the beams, dimen- points) when placed in the loading apparatus.
sional tolerances, and how beams are to be oriented in the X1.3 Moisture Conditioning
testing apparatus.
X1.3.1 The surfaces of sawed specimens need to be pro-
X1.2 Test Specimens tected from drying by covering them with wet burlap and
X1.2.1 Dimensions—A beam specimen for the determina- plastic sheeting during transportation and storage. Relatively
small amounts of drying of the surface of flexural specimens
--``,,,`,,``,``,,,`,,``,,,``-`-`,,`,,`,`,,`---

tion of flexural strength should have a square cross section. The

cross section can be 100 by 100 mm [4 by 4 in.] if the nominal can induce tensile stresses in the extreme fibers that will
maximum aggregate size is 25 mm [1 in.] or less; otherwise the markedly reduce the measured flexural strength. Specimens
cross section should be 150 by 150 mm [6 by 6 in.]. should be tested within 7 days of sawing or as required by the
Cross-sectional dimensions should be within 6 2 % of these specifier of tests. Submerge the test specimens in lime-
nominal dimensions. If the depth of the beam is controlled by saturated water at 23.0 6 2.0 °C [73.5 6 3.5 °F] for at least 40
the depth of the structural element, the specifier of tests needs h immediately before testing. Test the specimens promptly
to specify the beam dimensions. The test specimen should be at after removal from water storage. During the period between
least 50 mm [2 in.] longer than three times the nominal depth. removal from water storage and testing, keep the specimens
moist by covering with a wet blanket of burlap or other suitable
absorbent fabric.
13
See for example Raphael, J., “Tensile Strength of Concrete,” Journal of the
American Concrete Institute, Vol 81, No. 2, March–April 1984, pp. 158–165 and X1.4 Testing
“Referee Testing of Hardened Portland Cement Concrete Pavement—Percent
X1.4.1 Test the specimens in accordance with the applicable
Within Limits Revision,” Engineering Brief No. 34A, Federal Aviation
Administration, http://www.faa.gov/airports/engineering/engineering_briefs/media/ provisions of Test Method C78/C78M except that the orienta-
EB_34a.pdf. tion of the beam in the testing apparatus should be in

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 C42/C42M − 16
accordance with the requirements of the specifier of tests. X1.5 Report
Ideally, the tensile surface during the test should be tensile
X1.5.1 The test results should be reported in accordance
surface as loaded in the structure. This will typically require the
tensile surface to be a cut surface, and the measured flexural with the applicable provisions of Test Method C78/C78M.
strength may be less than the true flexural strength. On the X1.5.2 The test report should include the following infor-
other hand, it may be preferable for the uncut surface to be the mation:
tensile surface if it meets dimensional tolerances. Therefore, X1.5.2.1 The moisture condition at the time of testing.
the specifier of tests needs to state which surface of the beam
will be the tensile surface for testing. The location of the tensile X1.5.2.2 The orientation of the tensile surface face with
surface with respect to the position of that surface in the respect to the position of that surface in the structure.
concrete as placed is to be noted and reported.

SUMMARY OF CHANGES

Committee C09 has identified the location of selected changes to this test method since the last issue,
C42/C42M – 13, that may impact the use of this test method. (Approved October 1, 2016.)

(1) Revised 7.6, 7.7, 7.10.3, and 7.10.4.

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