1、Designation: C42/C42M 11American Association StateHighway and Transportation Officials StandardAASHTO No.: T24Standard Test Method forObtaining and Testing Drilled Cores and Sawed Beams ofConcrete1This standard is issued under the fixed designation C42/C42M; the number immediately following the desi
2、gnation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by
3、 agencies of the Department of Defense.1. Scope*1.1 This test method covers obtaining, preparing, and test-ing cores drilled from concrete for length or compressivestrength or splitting tensile strength determinations.NOTE 1Appendix X1 provides recommendations for obtaining andtesting sawed beams fo
4、r flexural performance.1.2 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result
5、in non-conformancewith the standard.1.3 The text of this standard references notes and footnotesthat provide explanatory material. These notes and footnotes(excluding those in tables and figures) shall not be consideredas requirements of the standard.1.4 This standard does not purport to address the
6、 safetyconcerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety andhealth practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C39/C39M Test Method for Compres
7、sive Strength of Cy-lindrical Concrete SpecimensC78 Test Method for Flexural Strength of Concrete (UsingSimple Beam with Third-Point Loading)C174/C174M Test Method for Measuring Thickness ofConcrete Elements Using Drilled Concrete CoresC496/C496M Test Method for Splitting Tensile Strength ofCylindri
8、cal Concrete SpecimensC617 Practice for Capping Cylindrical Concrete SpecimensC642 Test Method for Density, Absorption, and Voids inHardened ConcreteC670 Practice for Preparing Precision and Bias Statementsfor Test Methods for Construction MaterialsC823 Practice for Examination and Sampling of Harde
9、nedConcrete in ConstructionsC1231/C1231M Practice for Use of Unbonded Caps inDetermination of Compressive Strength of Hardened Con-crete CylindersC1542/C1542M Test Method for Measuring Length of Con-crete Cores2.2 ACI Standards:3318 Building Code Requirements for Structural Concrete3. Significance a
10、nd Use3.1 This test method provides standardized procedures forobtaining and testing specimens to determine the compressive,splitting tensile, and flexural strength of in-place concrete.3.2 Generally, test specimens are obtained when doubtexists about the in-place concrete quality due either to lows
11、trength test results during construction or signs of distress inthe structure. Another use of this method is to provide strengthinformation on older structures.3.3 Concrete strength is affected by the location of theconcrete in a structural element, with the concrete at the bottomtending to be stron
12、ger than the concrete at the top. Corestrength is also affected by core orientation relative to thehorizontal plane of the concrete as placed, with strengthtending to be lower when measured parallel to the horizontalplane.4These factors shall be considered in planning thelocations for obtaining conc
13、rete samples and in comparingstrength test results.3.4 The strength of concrete measured by tests of cores isaffected by the amount and distribution of moisture in thespecimen at the time of test. There is no standard procedure to1This test method is under the jurisdiction of ASTM Committee C09 onCo
14、ncrete and Concrete Aggregates and is the direct responsibility of SubcommitteeC09.61 on Testing for Strength.Current edition approved Aug. 15, 2011. Published September 2011. Originallyapproved in 1921. Last previous edition approved in 2010 as C42/C42M10a. DOI:10.1520/C0042_C0042M-11.2For referenc
15、ed ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American Concrete Institute (ACI), P.O. Box 9094, Farmingt
16、onHills, MI 48333-9094, http:/www.concrete.org.4Neville, A., “Core Tests: Easy to Perform, Not Easy to Interpret,” ConcreteInternational, Vol. 23, No. 11, November 2001, pp. 59-68.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive,
17、PO Box C700, West Conshohocken, PA 19428-2959, United States.condition a specimen that will ensure that, at the time of test,it will be in the identical moisture condition as concrete in thestructure. The moisture conditioning procedures in this testmethod are intended to provide reproducible moistu
18、re condi-tions that minimize within-laboratory and between-laboratoryvariations and to reduce the effects of moisture introducedduring specimen preparation.3.5 There is no universal relationship between the compres-sive strength of a core and the corresponding compressivestrength of standard-cured m
19、olded cylinders. The relationshipis affected by many factors such as the strength level of theconcrete, the in-place temperature and moisture history, and thestrength gain characteristics of the concrete. Historically, it hasbeen assumed that core strengths are generally 85 % of thecorresponding sta
20、ndard-cured cylinder strengths, but this is notapplicable to all situations. The acceptance criteria for corestrength are to be established by the specifier of the tests. ACI318 provides core strength acceptance criteria for new con-struction.3.6 The apparent compressive strength of concrete as mea-
21、sured by a core is affected by the length-diameter ratio (L/D) ofthe core as tested and this must be considered in preparing corespecimens and evaluating test results.4. Apparatus4.1 Core Drill, for obtaining cylindrical core specimenswith diamond impregnated bits attached to a core barrel.4.2 Saw,
22、for trimming ends of cores. The saw shall have adiamond or silicon-carbide cutting edge and shall be capable ofcutting cores without introducing cracks or dislodging aggre-gate particles.4.3 Balance, accurate to at least 5 g 0.01 lb.5. Sampling5.1 General:5.1.1 Samples of hardened concrete for use i
23、n the prepara-tion of strength test specimens shall not be taken until theconcrete is strong enough to permit sample removal withoutdisturbing the bond between the mortar and the coarse aggre-gate (see Note 2 and Note 3). When preparing strength testspecimens from samples of hardened concrete, sampl
24、es thathave been damaged during removal shall not be used unless thedamaged portion(s) are removed and the lengths of resultingtest specimens satisfy the minimum length-diameter ratiorequirement in 7.2. Samples of defective or damaged concretethat cannot be tested shall be reported along with the re
25、asonthat prohibits use of the sample for preparing strength testspecimens.NOTE 2Practice C823 provides guidance on the development of asampling plan for concrete in constructions.NOTE 3It is not possible to specify a minimum age when concrete isstrong enough to withstand damage during removal, becau
26、se the strengthat any age depends on the curing history and strength grade of theconcrete. If time permits, the concrete should not be removed before it is14 days old. If this is not practical, removal of concrete can proceed if thecut surfaces do not display erosion of the mortar and the exposed co
27、arseaggregate particles are embedded firmly in the mortar. In-place testmethods may be used to estimate the level of strength development priorto attempting removal of concrete samples.5.1.2 Except as provided in 5.1.3, cores containing embed-ded reinforcement, excluding fibers, or other embedded ob
28、jectsshall not be used for determining strength of concrete.5.1.3 If it is not possible to prepare a test specimen thatmeets the requirements of 7.1 and 7.2 and that is free ofembedded reinforcement or other metal, the specifier of thetests is permitted to allow testing of cores with embedded metal(
29、see Note 4). If a core tested for strength contains embeddedmetal, the size, shape, and location of the metal within the coreshall be documented in the test report.NOTE 4The presence of steel reinforcement, other than fibers, orother embedded metal in a core can affect the measured strength.5,6There
30、are insufficient data to derive reliable correction factors that can be appliedto the measured strength to account for embedded reinforcement perpen-dicular to the core axis. If testing of cores containing embedded reinforce-ment is permitted, engineering judgment is required to assess thesignifican
31、ce of the results. The specifier of the tests should not permit acore to be tested for strength if bar reinforcement, or other elongatedembedded metal object, is oriented close to parallel to the core axis.5.2 Core DrillingWhen a core will be tested to measureconcrete strength, the core shall be dri
32、lled perpendicular to thesurface and at least 150 mm 6 in. away from formed joints orobvious edges of a unit of deposit (see Note 5). This minimumdistance does not apply to the formed boundaries of structuralmembers. Record the approximate angle between the longitu-dinal axis of the drilled core and
33、 the horizontal plane of theconcrete as placed. A specimen drilled perpendicular to avertical surface, or perpendicular to a sloping surface, shall betaken from near the middle of a unit of deposit when possible.If cores are obtained for purposes other than determination ofstrength, drill cores in a
34、ccordance with the instructions pro-vided by the specifier of the tests. Record the date core wasdrilled. If known, record the date when concrete was placed.NOTE 5The intent is to avoid drilling cores in non-representativeconcrete that may exist near formed joints or the boundary of a unit ofplaceme
35、nt.5.3 Slab RemovalRemove a slab sufficiently large tosecure the desired test specimens without the inclusion of anyconcrete that has been cracked, spalled, undercut, or otherwisedamaged.DRILLED CORES6. Measuring the Length of Drilled Cores6.1 Cores for determining the thickness of pavements, slabs,
36、walls or other structural elements shall have a diameter of atleast 94 mm 3.70 in. when the lengths of such cores arestipulated to be measured in accordance with Test MethodC174/C174M. When core length for determining the thicknessof a member is not required to be measured in accordance withTest Met
37、hod C174/C174M, core diameter shall be as directedby specifier of tests.5Gaynor, R.D., “Effect of Horizontal Reinforcing Steel on the Strength ofMolded Cylinders,” Problems and Practices in Journal of the American ConcreteInstitute, Proceedings, Vol. 62, No. 7, July 1965, pp. 837-8406Concrete Societ
38、y Working Party, “Concrete Core Testing for Strength,”Concrete Society Technical Report No. 11, The Concrete Society, England, May1976.C42/C42M 1126.2 For cores that are not intended for determining structuraldimensions, measure the longest and shortest lengths on the cutsurface along lines parallel
39、 to the core axis. Record the averagelength to the nearest 5 mm 14 in.7. Cores for Compressive Strength7.1 Diameter7.1.1 Except as provided in 7.1.2, the diameter of corespecimens for the determination of compressive strength shallbe at least 94 mm 3.70 in. or at least two times the nominalmaximum s
40、ize of the coarse aggregate, whichever is larger.7.1.2 If limited member thickness makes it impossible toobtain cores with length-diameter ratio (L/D) of at least 1.0 orif clear distance between reinforcement is limited, core diam-eters less than 94 mm 3.70 in. are not prohibited. If a corediameter
41、less than 94 mm 3.70 in. is used, report the reason.NOTE 6The compressive strengths of nominal 50-mm 2-in. diam-eter cores are known to be somewhat lower and more variable than thoseof nominal 100-mm 4-in. diameter cores. In addition, smaller diametercores appear to be more sensitive to the effect o
42、f the length-diameterratio.77.2 Length7.2.1 Except as provided in 7.2.2, the preferred length of thecapped or ground specimen is between 1.9 and 2.1 times thediameter. If the ratio of the length to the diameter (L/D) of thecore exceeds 2.1, reduce the length of the core so that the ratioof the cappe
43、d or ground specimen is between 1.9 and 2.1. Corespecimens with length-diameter ratios equal to or less than1.75 require corrections to the measured compressive strength(see 7.9.1). A strength correction factor is not required for L/Dgreater than 1.75.Acore having a maximum length of less than95 % o
44、f its diameter before capping or a length less than itsdiameter after capping, trimming, or end grinding shall not betested.7.2.2 If the compressive strengths of cores are to be com-pared with specified strengths based on standard concretecubes, cores shall be tested with L/D, after end preparation,
45、 inthe range of 1.00 to 1.05 unless otherwise directed by thespecifier of the tests. If the strengths of cores with L/D =1 areto be compared with specified concrete cube strength, do notapply the correction factor in 7.9.1.7.3 Moisture ConditioningTest cores after moisture con-ditioning as specified
46、 in this test method or as directed by thespecifier of the tests. The moisture conditioning proceduresspecified in this test method are intended to preserve themoisture of the drilled core and to provide a reproduciblemoisture condition that minimizes the effects of moisturegradients introduced by w
47、etting during drilling and specimenpreparation.7.3.1 After cores have been drilled, wipe off surface drillwater 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 containersand seal to
48、 prevent moisture loss. Maintain cores at ambienttemperature, and protect cores from exposure to direct sunlight.Transport the cores to the testing laboratory as soon aspossible. Keep cores in the sealed plastic bags or nonabsorbentcontainers at all times except during end preparation and for amaxim
49、um time of2htopermit capping before testing.7.3.2 If water is used during sawing or grinding of coreends, complete these operations as soon as possible, but nolater than 2 days after drilling of cores unless stipulatedotherwise by the specifier of tests. After completing endpreparation, wipe off surface moisture, allow the surfaces todry, and place the cores in sealed plastic bags or nonabsorbentcontainers. Minimize the duration of exposure to water duringend preparation.7.3.3 Allow the cores to remain in the sealed plastic bags ornonabsorbent containers
