1、Designation: C78/C78M 16C78/C78M 18Standard Test Method forFlexural Strength of Concrete (Using Simple Beam withThird-Point Loading)1This standard is issued under the fixed designation C78/C78M; the number immediately following the designation indicates the year oforiginal adoption or, in the case o
2、f 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 agencies of the U.S. Department of Defense.1. Scope*1.1 This te
3、st method covers the determination of the flexural strength of concrete by the use of a simple beam with third-pointloading.1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in eachsystem may not be exact equivalents; therefore,
4、 each system shall be used independently of the other. Combining values from thetwo systems may result in non-conformance with the standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard
5、to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision
6、 on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2C31/C31M Practice for Making and Curing Concrete Test Specimens in the FieldC42/C42M
7、Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of ConcreteC125 Terminology Relating to Concrete and Concrete AggregatesC192/C192M Practice for Making and Curing Concrete Test Specimens in the LaboratoryC293/C293M Test Method for Flexural Strength of Concrete (Using Simple Beam W
8、ith Center-Point Loading)C617/C617M Practice for Capping Cylindrical Concrete SpecimensC670 Practice for Preparing Precision and Bias Statements for Test Methods for Construction MaterialsC1077 Practice forAgencies Testing Concrete and ConcreteAggregates for Use in Construction and Criteria for Test
9、ingAgencyEvaluationE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Testing3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method, refer to Terminology C125 and Terminology E6.3.2 Definitions of Terms Specific to T
10、his Standard:3.2.1 flexural strengthmaximum resistance of a specimen subjected to bending.3.2.1.1 Discussion1 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 onTesting for Strength.Current ed
11、ition approved July 1, 2016Jan. 1, 2018. Published August 2016February 2018. Originally approved in 1930. Last previous edition approved in 20152016 asC78/C78M 15b.16. DOI: 10.1520/C0078_C0078M-16.10.1520/C0078_C0078M-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contact
12、ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.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 m
13、ade to the previous version. Becauseit 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 versionof the standard as published by ASTM is to be considered the official document.*A
14、 Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1In this test method, flexural strength is reported as the modulus of rupture.3.2.2 flexural testing apparatusfixture used t
15、o apply force to the beam specimen and consists of loading and support blocks.3.2.3 loading blockcomponent of the testing apparatus in the shape of a portion of a cylinder that is used to apply a force tothe beam specimen.3.2.4 modulus of rupturecalculated stress, assuming linear-elastic behavior, i
16、n the tensile face of a beam specimen at themaximum bending moment during a standard test method.3.2.5 span lengthdistance between lines of support, or reaction, for the beam specimen, and it is equal to three times thenominal depth of the beam.3.2.5.1 DiscussionFor example, for a 100 mm 4 in. nomin
17、al depth beam, the span length is 300 mm 12 in. and for a 150 mm 6 in. nominal depthbeam, the span length is 450 mm 18 in. See 3.2.6.1, for discussion of reaction block.3.2.6 support blockcomponent of the testing apparatus in the shape of a portion of a cylinder that is used to provide a reactionto
18、the force applied to the beam specimen.3.2.6.1 DiscussionIf the testing apparatus applies force to the top of the beam, this block supports the beam. If the testing apparatus applies forceto the bottom of the beam, the support block may be considered a reaction block because it provides a line of re
19、action at the topof the beam and does not support the beam.3.2.7 testing machinemechanical device for applying force to a specimen.4. Significance and Use4.1 This test method is used to determine the flexural strength of specimens prepared and cured in accordance withTest MethodsC42/C42M or Practice
20、s C31/C31M or C192/C192M. Results are calculated and reported as the modulus of rupture. For the samespecimen size, the strength determined will vary if there are differences in specimen preparation, curing procedure, moisturecondition at time of testing, and whether the beam was molded or sawed to
21、size.4.2 The measured modulus of rupture generally increases as the specimen size decreasesdecreases.3,4,5 and it has been shownthat the variability of individual test results increases as the specimen size decreases.,4.3 The results of this test method may be used to determine compliance with speci
22、fications or as a basis for mixtureproportioning, evaluating uniformity of mixing, and checking placement operations by using sawed beams. It is used primarily intesting concrete for the construction of slabs and pavements.4.4 For identical test specimens, the modulus of rupture obtained by this tes
23、t method will, on average, be lower than thatobtained by Test Method C293/C293M.5. Apparatus5.1 Testing MachineThe testing machine shall conform to the requirements of the sections on Basis of Verification,Corrections, and Time Interval Between Verifications of Practices E4. Hand operated testing ma
24、chines having pumps that do notprovide a continuous loading in one stroke are not permitted. Motorized pumps or hand operated positive displacement pumpshaving sufficient volume in one continuous stroke to complete a test without requiring replenishment are permitted and shall becapable of applying
25、loads at a uniform rate without shock or interruption. The testing machine shall be equipped with a means ofrecording or holding the peak value that will indicate the maximum load, to within 1 % accuracy, applied to the specimen duringa test.5.1.1 Verification:5.1.1.1 The testing machine shall confo
26、rm to the requirements of the sections on Basis of Verification, Corrections, and TimeInterval Between Verifications of Practice E4.5.1.1.2 Verify the accuracy of the testing machine in accordance with Practice E4, except that the verified loading range shallbe as required for flexural testing. Veri
27、fication is required:(1) Within 13 months of the last verification,3 Tanesi, J; Ardani, A. Leavitt, J. “Reducing the Specimen Size of Concrete Flexural Strength Test (AASHTO T97) for Safety and Ease of Handling,“ TransportationResearch Record: Journal of the Transportation Research Board, No. 2342,
28、Transportation Research Board of National Academies, Washington, D.C., 2013.4 Carrasquillo, P.M. and Carrasquillo, R. L “Improved Concrete Quality Control Procedures Using Third Point Loading”, Research Report 119-1F, Project 3-9-87-1119,Center For Transportation Research, The University of Texas at
29、 Austin, November 1987.5 Bazant, Z. and Novak, D. “Proposal for Standard Test of Modulus of Rupture of Concrete with its Size Dependence,“ ACI Materials Journal, January-February 2001.C78/C78M 182(2) On original installation,(3) After relocation,(4) After making repairs or adjustments that affect th
30、e operation of the force applying system or the values displayed on theload indicator, except for zero adjustments that compensate for the weight of loading or support blocks or specimen, or both, or(5) Whenever there is reason to suspect the accuracy of the indicated forces.5.2 Loading Flexural Tes
31、ting ApparatusTheThe third point loading method shall be used in making flexure tests of concreteemploying bearing blocks that will ensure that to determine the flexural strength of concrete.The loading blocks and support blocksshall be designed so that forces applied to the beam will be along lines
32、 perpendicular to the face side faces of the specimenbeamand applied without eccentricity. A diagram of an apparatus that accomplishes this purpose the flexural testing apparatus is shownin Fig. 1.NOTE 1The flexural testing apparatus shown in Fig. 1 may be used inverted. In this case, the loading bl
33、ocks will be at the bottom of the beam, whilethe reaction blocks will be at the top of the beam.5.2.1 All apparatus for making flexure tests of concrete The flexural testing apparatus shall be capable of maintaining thespecified span length and distances between load-applying blocks and support bloc
34、ks constant distance between the lines of loadingwithin 61.0 mm 60.05 in.in. of the specified values.5.2.2 The ratio of the horizontal distance between the pointline of application of the loadforce and the pointline of applicationof the nearest reaction to the depth of the beam shall be 1.0 6 0.03.5
35、.2.3 If an apparatus similar to that illustrated in The loading blocks Fig. 1 is used: the load-applying and support blocks shallnot be more than 65 mm 2.50 in. high, measured from the center or the axis of pivot, and shouldthe ball or the axis of the rodand shall extend entirely across or beyond th
36、e full width of the specimen. Each case-hardened bearing case, the block surface incontact with the specimen shall not depart from a plane by more than 0.05 mm 0.002 in. and shall be a portion of a cylinder,the axis of which is coincidental with either the axis of the rod or center of the ball, whic
37、hever the block is pivoted upon. The anglesubtended by the curved surface of each block shall be at least 0.80 rad 45. The load-applying and support blocks shall bemaintained in a vertical position and in contact with the rod or ball by means of spring-loaded screws that hold them in contactwith the
38、 pivot rod or ball. The uppermost bearing plate and center point ball in Fig. 1 may be omitted when a spherically seatedbearing block is used, provided one rod and one ball are used as pivots for the upper load-applying blocks.5.2.4 At least every six months or as specified by the manufacturer of th
39、e flexural testing apparatus, clean and lubricatemetal-to-metal contact surfaces, such as internal concave surfaces and steel balls and rods of the loading blocks and support blocks(Fig. 1). The lubricant shall be a petroleum-type oil, such as conventional motor oil, or as specified by the manufactu
40、rer of theapparatus.5.2.5 The support blocks shall be free to rotate.5.2.6 The loading blocks and support blocks shall be maintained in a vertical position and in contact with the rod or ball bymeans of spring-loaded screws that hold them in contact with the rod or ball. The uppermost bearing plate
41、and center point ballin Fig. 1 may be omitted if the testing machine has a spherically seated bearing block, provided one rod and one ball are used aspivots for the upper loading blocks.FIG. 1 Schematic of a SuitableFlexural Testing Apparatus for Flexure Test of Concrete by Third-Point Loading Metho
42、dC78/C78M 1836. Test Specimens6.1 The test specimen shall conform to all requirements of Test Method C42/C42M or Practices C31/C31M or C192/C192Mapplicable to beam specimens and shall have a test span within 2 % of being three times its depth as tested. The sides of thespecimen shall be at right ang
43、les with the top and bottom. All surfaces shall be smooth and free of scars, indentations, holes, orinscribed identification marks.6.2 Provided the smaller cross-sectional dimension of the beam is at least three times the nominal maximum size of the coarseaggregate, the modulus of rupture can be det
44、ermined using different specimen sizes. However, measured modulus of rupturegenerally increases as specimen size decreases.3,4 (Note 12).NOTE 2The strength ratio for beams of different sizes depends primarily on the maximum size of aggregate.5 Experimental data obtained in twodifferent studies have
45、shown that for maximum aggregate size between 19.0 and 25.0 mm 34 and 1 in., the ratio between the modulus of rupturedetermined with a 150 by 150 mm 6 by 6 in. and a 100 by 100 mm 4 by 4 in. may vary from 0.90 to 1.073 and for maximum aggregate size between9.5 and 37.5 mm 38 and 112 in., the ratio b
46、etween the modulus of rupture determined with a 150 by 150 mm 6 by 6 in. and a 115 by 115 mm 4.5by 4.5 in. may vary from 0.86 to 1.00.46.3 The specifier of tests shall specify the specimen size and number of specimens to be tested to obtain an average test result(result. Note 2). The same specimen s
47、ize shall be used for qualification and acceptance testing.NOTE 2It has been shown that the variability of individual test results increases as the specimen size decreases.3,47. Procedure7.1 Moist-cured specimens shall be kept moist during the period between removal from moist storage and testing.NO
48、TE 3Surface drying of the specimen results in a reduction in the measured flexural strength.NOTE 4Methods for keeping the specimen moist include wrapping in moist fabric or matting, ormatting and keeping specimens under lime waterin containers near the flexural testing machine until time of testing.
49、7.2 When using For molded specimens, turn the test specimen on its side with respect to its position as molded and center iton the support blocks. When using sawed specimens, position the specimen so that the tension face corresponds to the top orbottom of the specimen as cut from the parent material. Center the loading systemblocks in relation to the applied force. Bringthe load-applyingloading blocks in contact with the surface of the specimen at the third points and apply a loadforce of between3 and 6 % of the estimated ulti
