1、Designation: C293/C293M 15C293/C293M 16Standard Test Method forFlexural Strength of Concrete (Using Simple Beam WithCenter-Point Loading)1This standard is issued under the fixed designation C293/C293M; the number immediately following the designation indicates the yearof original adoption or, in the
2、 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
3、This test method covers determination of the flexural strength of concrete specimens by the use of a simple beam withcenter-point loading. Test Method C293/C293M is not an alternative to Test Method C78/C78M.1.2 The values stated in either SI units or inch-pound units are to be regarded separately a
4、s standard. The values stated in eachsystem may not be exact equivalents; therefore, 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
5、 any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C31/C31M Practice for Making and Curing Concrete T
6、est Specimens in the FieldC78/C78M Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)C192/C192M Practice for Making and Curing Concrete Test Specimens in the LaboratoryC617C617/C617M Practice for Capping Cylindrical Concrete SpecimensC1077 Practice forAgencies
7、 Testing Concrete and ConcreteAggregates for Use in Construction and Criteria for TestingAgencyEvaluationE4 Practices for Force Verification of Testing Machines2.2 TXDOT Standard:3TEX-420-A Test Method for Flexural Strength of Concrete Using Simple Beam with Center-Point Loading3. Significance and U
8、se3.1 This test method is used to determine the modulus of rupture of specimens prepared and cured in accordance with PracticesC31/C31M or C192/C192M. The strength determined will vary where there are differences in specimen size, preparation, moisturecondition, or curing.3.2 The results of this tes
9、t method may be used to determine compliance with specifications or as a basis for proportioning,mixing and placement operations. This test method produces values of flexural strength significantly higher than Test MethodC78/C78M.4. Apparatus4.1 Testing MachineThe testing machine shall conform to th
10、e requirements of the sections on Basis of Verification,Corrections, and Time Interval Between Verifications of Practices E4. Hand operated testing machines having pumps that do notprovide a continuous loading to failure in one stroke are not permitted. Motorized pumps or hand operated positive disp
11、lacement1 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 edition approved Dec. 1, 2015April 15, 2016. Published February 2016June 2016. Originally approved in
12、1952. Last previous edition approved in 20102015 asC293/C293M 10.15. DOI: 10.1520/C0293_C0293M-15.10.1520/C0293_C0293M-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refe
13、r to the standards Document Summary page on the ASTM website.3 Manual of Testing Procedures, Texas State Department of Highways and Public Transportation, 1986.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
14、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
15、 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 States1pumps having sufficient volume in one continuous stroke to complete a test without requiring replenishment are permitted an
16、d shallbe capable of applying loads at a uniform rate without shock or interruption. The testing machine shall be equipped with a meansof recording or holding the peak value that will indicate the maximum load applied to the specimen during a test, to within 1 %accuracy of the load being applied.4.2
17、 Loading ApparatusThe mechanism by which forces are applied to the specimen shall employ a load-applying block andtwo specimen support blocks. It shall ensure that all forces are applied perpendicular to the face of the specimen withouteccentricity. A diagram of an apparatus that accomplishes this p
18、urpose is shown in Fig. 1.4.2.1 All apparatus for making center-point loading flexure tests shall be similar to Fig. 1 and maintain the span length andcentral position of the load-applying block with respect to the support blocks constant within 61.0 mm 60.05 in.4.2.2 Reactions shall be parallel to
19、the direction of the applied load at all times during the test, and the ratio of the horizontaldistance between the point of load application and nearest reaction to the depth of the beam shall be 1.5 6 2 %.4.2.3 The load-applying and support blocks shall not be more than 65 mm 2.50 in. high, measur
20、ed from the center or the axisof pivot, and shall extend at least across the full width of the specimen. Each hardened bearing surface in contact with the specimenshall 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 coincidentalwith
21、either the axis of the rod or center of the ball, whichever the block is pivoted upon. The angle subtended by the curved surfaceof each block shall be at least 0.80 rad 45. The load-applying and support blocks shall be maintained in a vertical position andin contact with the rod or ball by means of
22、spring-loaded screws that hold them in contact with the pivot rod or ball. The rod inthe center load-applying block in Fig. 1 may be omitted when a spherically seated bearing block is used.5. Testing5.1 The test specimen shall conform to all requirements of Practice C31/C31M or C192/C192M applicable
23、 to beam specimensand shall have a test span within 2 % of being three times its depth as tested. The sides of the specimen shall be at right angleswith the top and bottom. All surfaces shall be smooth and free of scars, indentations, holes, or inscribed identification marks.5.2 The individual who t
24、ests concrete beams for acceptance testing shall meet the concrete laboratory requirements of PracticeC1077 including Test Method C293/C293M as a relevant test.NOTE 1The testing laboratory performing this test method may be evaluated in accordance with Practice C1077.6. Procedure6.1 Flexural tests o
25、f moist-cured specimens shall be made as soon as practical after removal from moist storage. Surface dryingof the specimen results in a reduction in the measured modulus of rupture.6.2 Turn the test specimen on its side with respect to its position as molded and center it on the support blocks. Cent
26、er theloading system in relation to the applied force. Bring the load-applying block in contact with the surface of the specimen at thecenter and apply a load of between 3 and 6 % of the estimated ultimate load. Using 0.10 mm 0.004 in. and 0.40 mm 0.015 in.leaf-type feeler gages, determine whether a
27、ny gap between the specimen and the load-applying or support blocks is greater or lessthan each of the gages over a length of 25 mm 1 in. or more. Grind, cap, or use leather shims on the specimen contact surfaceNOTE 1Apparatus may be used inverted.FIG. 1 Schematic of a Suitable Apparatus for Flexure
28、 Test of Concrete by Center-Point Loading Method.C293/C293M 162to eliminate any gap in excess of 0.10 mm 0.004 in. Leather shims shall be of uniform 6 mm 0.25 in. thickness, 25 to 50 mm1.0 to 2.0 in. in width, and shall extend across the full width of the specimen. Gaps in excess of 0.40 mm 0.015 in
29、. shall beeliminated only by capping or grinding. Grinding of lateral surfaces shall be minimized inasmuch as grinding may change thephysical characteristics of the specimens. Capping shall be in accordance with applicable sections of Practice C617C617/C617M.6.3 Load the specimen continuously and wi
30、thout shock. The load shall be applied at a constant rate to the breaking point.Applythe load so that the maximum stress on the tension face increases at a rate between 0.9 and 1.2 MPa/min 125 and 175 psi/min.The loading rate is computed using the following equation:r 52Sbd23L (1)where:r = loading r
31、ate, N/min lb/min,S = rate of increase in the maximum stress on the tension face, MPa/min psi/min,b = average width of the specimen as oriented for testing, mm in.,d = average depth of the specimen as oriented for testing, mm in., andL = span length, mm in.7. Measurement of Specimens After Test7.1 T
32、o determine the dimensions of the specimen section for use in calculating modulus of rupture, take measurements acrossone of the fractured faces after testing. The width and depth are measured with the specimen as oriented for testing. For eachdimension, take one measurement at each edge and one at
33、the center of the cross section. Use the three measurements for eachdirection to determine the average width and the average depth. Take all measurements to the nearest 1 mm 0.05 in. If thefracture occurs at a capped section, include the cap thickness in the measurement.8. Calculation8.1 Calculate t
34、he modulus of rupture as follows:R 53PL2bd2 (2)where:R = modulus of rupture, MPa psi,P = maximum applied load indicated by the testing machine, N lbf,L = span length, mm in.,b = average width of specimen, at the fracture, mm in., andd = average depth of specimen, at the fracture, mm in.NOTE 2The wei
35、ght of the beam is not included in the above calculation.9. Report9.1 Report the following information:9.1.1 Identification number,9.1.2 Average width to the nearest 1 mm 0.05 in., at the fracture,9.1.3 Average depth to the nearest 1 mm 0.05 in., at the fracture,9.1.4 Span length in mm in.,9.1.5 Max
36、imum applied load in N lbf,9.1.6 Modulus of rupture calculated to the nearest 0.05 MPa 5 psi,9.1.7 Record of curing and apparent moisture condition of the specimens at the time of test,9.1.8 If specimens were capped, ground, or if leather shims were used,9.1.9 Defects in specimens, and9.1.10 Age of
37、specimens.10. Precision and Bias10.1 PrecisionThe single operator coefficient of variation has been found to be 4.4 %. Therefore, results of two properlyconducted tests by the same operator on beams made from the same batch sample are not expected to differ from each other bymore than 12 %. The mult
38、ilaboratory coefficient of variation has been found to be 5.3 %. Therefore, results of two differentlaboratories on beams made from the same batch sample are not expected to differ from each other by more than 15 %.15 %4(Notes 3-5).4 See “Improved Concrete Quality Control Procedures Using Third Poin
39、t Loading” by P. M. Carrasquillo and R. L. Carrasquillo, Research Report 119-1F, Project3-9-87-1119, Center For Transportation Research, The University of Texas at Austin, November 1987, for information as to the relationship of strength and variability undercenter point loading.C293/C293M 163NOTE 3
40、This precision statement was determined using 150 by 150 by 510 mm 6 by 6 by 20 in. specimens.4 The variability of test results changeswith specimen size4 and should not be extrapolated to other sizes.NOTE 4This precision statement was determined using a single brand and model testing machine (Rainh
41、art Series 416, Recording Beam Tester).4NOTE 5This precision statement was obtained by measuring the flexural strength of two concrete mixtures with average modulus of rupture of 5.10and 6.45 MPa 740 and 940 psi. This modulus of rupture was determined in accordance with TEX-420-A.4 The version of TE
42、X-420-Aused in the study(1986) may differ from the current test method.10.2 BiasBecause there is no accepted standard for determining bias in this test method, no statement on bias is made.11. Keywords11.1 beams; concrete; flexural strength testing; modulus of ruptureSUMMARY OF CHANGESCommittee C09
43、has identified the location of selected changes to this test method since the last issue,C293C293/C293M 10,15, that may impact the use of this test method. (Approved Dec. 1, 2015.)April 15,2016.)(1) Added Section 4.12.2 was revised(2) SectionAdded 10.1Notes 3-5 was revised(3) Section 1.1 was revised
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