Astm C42 C42M 20
Astm C42 C42M 20
Astm C42 C42M 20
for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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1.2 The values stated in either SI units or inch-pound units
are to be regarded separately as standard. The values stated in
Cylindrical Concrete Specimens
C617/C617M Practice for Capping Cylindrical Concrete
Specimens
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each system may not be exact equivalents; therefore, each
system shall be used independently of the other. Combining
C642 Test Method for Density, Absorption, and Voids in
Hardened Concrete
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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
concrete in a structural element, with the concrete at the bottom specimens and evaluating test results.
tending to be stronger than the concrete at the top. Core
strength is also affected by core orientation relative to the 4. Apparatus
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.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
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relationship is affected by many factors such as the strength
level of the concrete, the in-place temperature and moisture
that cannot be tested shall be reported along with the reason
that prohibits use of the sample for preparing strength test
histories, the degree of consolidation, batch-to-batch
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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.
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NOTE 3—A procedure is available for estimating the equivalent cylinder
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
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
building code or of other contractual or legal documents ASTM C42/C42M-20
14 days old. If this is not practicable, removal of concrete can proceed if
that may govern the cut surfaces do not display erosion of the mortar and the exposed
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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
NOTE 5—For investigation of low strength test results, ACI 318-14 (see Note 8). If a core tested for strength contains embedded
defines the specifier of the tests as the licensed design professional or metal, the size, shape, and location of the metal within the core
building official. 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
insufficient data to derive reliable correction factors that can be applied to
the measured strength to account for embedded reinforcement perpendicu-
lar to the core axis. If testing of cores containing embedded reinforcement
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 − 20
is permitted, engineering judgment is required to assess the significance of 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.8
for strength if bar reinforcement, or other elongated embedded metal
object, is oriented close to parallel to the core axis.
7.2 Length:
7.2.1 Except as provided in 7.2.2, the preferred length of the
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). A strength correction factor is not required for L/D
concrete as placed. A specimen drilled perpendicular to a greater than 1.75. A core having a maximum length of less than
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
If cores are obtained for purposes other than determination of tested.
strength, drill cores in accordance with the instructions pro- 7.2.2 If the compressive strengths of cores are to be com-
vided by the specifier of the tests. Record the date core was pared with specified strengths based on standard concrete
drilled. If known, record the date when concrete was placed. 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
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
placement.
to be compared with specified concrete cube strength, do not
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
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specifier of the tests. The moisture conditioning procedures
damaged.
specified in this test method are intended to preserve the
DRILLED CORES moisture of the drilled core and to provide a reproducible
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6. Measuring the Length of Drilled Cores
moisture condition that minimizes the effects of moisture
gradients introduced by wetting during drilling and specimen
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preparation.
6.1 Cores for determining the thickness of pavements, 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 withASTM C42/C42M-20
Test Method place cores in separate plastic bags or nonabsorbent containers
C174/C174M. When core length for determining the thickness
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and seal to prevent moisture loss. Maintain cores at ambient
of a member is not required to be measured in accordance with temperature, and protect cores from exposure to direct sunlight.
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 For cores that are not intended for determining structural
maximum time of 2 h to permit capping before testing.
dimensions, measure the longest and shortest lengths on the cut
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.].
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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
7.1 Diameter: dry, and place the cores in sealed plastic bags or nonabsorbent
7.1.1 Except as provided in 7.1.2, the diameter of core containers. Minimize the duration of exposure to water during
specimens for the determination of compressive strength shall end preparation.
be at least 94 mm [3.70 in.] or at least two times the nominal 7.3.3 Allow the cores to remain in the sealed plastic bags or
maximum size of the coarse aggregate, whichever is larger. nonabsorbent containers for at least 5 days after last being
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
if clear distance between reinforcement is limited, core diam- NOTE 11—The waiting period of at least 5 days is intended to reduce
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- 8
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.