1、Designation: C 293 08Standard Test Method forFlexural Strength of Concrete (Using Simple Beam WithCenter-Point Loading)1This standard is issued under the fixed designation C 293; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 This test method covers det
3、ermination of the flexuralstrength of concrete specimens by the use of a simple beamwith center-point loading. It is not an alternative to TestMethod C 78.1.2 The values stated in inch-pound units are to be regardedas standard. The SI equivalent of inch-pound units has beenrounded where necessary fo
4、r practical application.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prio
5、r to use.2. Referenced Documents2.1 ASTM Standards:2C 31/C 31M Practice for Making and Curing Concrete TestSpecimens in the FieldC78 Test Method for Flexural Strength of Concrete (UsingSimple Beam with Third-Point Loading)C 192/C 192M Practice for Making and Curing ConcreteTest Specimens in the Labo
6、ratoryC 617 Practice for Capping Cylindrical Concrete Speci-mensC 1077 Practice for Laboratories Testing Concrete and Con-crete Aggregates for Use in Construction and Criteria forLaboratory EvaluationE4 Practices for Force Verification of Testing Machines3. Significance and Use3.1 This test method i
7、s used to determine the modulus ofrupture of specimens prepared and cured in accordance withPractices C 31 or C 192. The strength determined will varywhere there are differences in specimen size, preparation,moisture condition, or curing.3.2 The results of this test method may be used to determineco
8、mpliance with specifications or as a basis for proportioning,mixing and placement operations. This test method producesvalues of flexural strength significantly higher than TestMethod C 78 (Note 1).NOTE 1The testing laboratory performing this test method may beevaluated in accordance with Practice C
9、 1077.4. Apparatus4.1 The testing machine shall conform to the requirementsof the sections on Basis of Verification, Corrections, and TimeInterval Between Verifications of Practices E 4. Hand operatedtesting machines having pumps that do not provide a continu-ous loading to failure in one stroke are
10、 not permitted. Motor-ized pumps or hand operated positive displacement pumpshaving sufficient volume in one continuous stroke to completea test without requiring replenishment are permitted and shallbe capable of applying loads at a uniform rate without shock orinterruption.4.2 Loading ApparatusThe
11、 mechanism by which forcesare applied to the specimen shall employ a load-applying blockand two specimen support blocks. It shall ensure that all forcesare applied perpendicular to the face of the specimen withouteccentricity. A diagram of an apparatus that accomplishes thispurpose is shown in Fig.
12、1.4.2.1 All apparatus for making center-point loading flexuretests shall be similar to Fig. 1 and maintain the span length andcentral position of the load-applying block with respect to thesupport blocks constant within 60.05 in. (61.3 mm).4.2.2 Reactions shall be parallel to the direction of theapp
13、lied load at all times during the test, and the ratio of thehorizontal distance between the point of load application andnearest reaction to the depth of the beam shall be 1.5 6 2%.4.2.3 The load-applying and support blocks shall not bemore than 212 in. (64 mm) high, measured from the center orthe a
14、xis of pivot, and shall extend at least across the full widthof the specimen. Each hardened bearing surface in contact withthe specimen shall not depart from a plane by more than 0.002in. (0.05 mm) and shall be a portion of a cylinder, the axis of1This test method is under the jurisdiction of ASTM C
15、ommittee C09 onConcrete and Concrete Aggregates and is the direct responsibility of SubcommitteeC09.61 on Testing for Strength.Current edition approved Feb. 1, 2008. Published February 2008. Originallyapproved in 1952. Last previous edition approved in 2007 as C 293 07.2For referenced ASTM standards
16、, 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.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM Internati
17、onal, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.which is coincidental with either the axis of the rod or centerof the ball, whichever the block is pivoted upon. The anglesubtended by the curved surface of each block shall be at least45 (0.79 rad). The load-a
18、pplying and support blocks shall bemaintained in a vertical position and in contact with the rod orball by means of spring-loaded screws that hold them incontact with the pivot rod or ball. The rod in the centerload-applying block in Fig. 1 may be omitted when a spheri-cally seated bearing block is
19、used.5. Testing5.1 The test specimen shall conform to all requirements ofPractice C 31 or C 192 applicable to beam specimens and shallhave a test span within 2 % of being three times its depth astested. The sides of the specimen shall be at right angles withthe top and bottom. All surfaces shall be
20、smooth and free ofscars, indentations, holes, or inscribed identification marks.5.2 The individual who tests concrete beams for acceptancetesting shall meet the concrete laboratory requirements ofPractice C 1077 including Test Method C 293 as a relevant test.6. Procedure6.1 Flexural tests of moist-c
21、ured specimens shall be made assoon as practical after removal from moist storage. Surfacedrying of the specimen results in a reduction in the measuredmodulus of rupture.6.2 Turn the test specimen on its side with respect to itsposition as molded and center it on the support blocks. Centerthe loadin
22、g system in relation to the applied force. Bring theload-applying block in contact with the surface of the specimenat the center and apply a load of between 3 and 6 % of theestimated ultimate load. Using 0.004 in. (0.10 mm) and 0.015in. (0.38 mm) leaf-type feeler gages, determine whether anygap betw
23、een the specimen and the load-applying or supportblocks is greater or less than each of the gages over a length of1 in. (25 mm) or more. Grind, cap, or use leather shims on thespecimen contact surface to eliminate any gap in excess of0.004 in. (0.10 mm). Leather shims shall be of uniform14 in.(6.4 m
24、m) thickness, 1 to 2 in. (25 to 50 mm) in width, and shallextend across the full width of the specimen. Gaps in excess of0.015 in. (0.38 mm) shall be eliminated only by capping orgrinding. Grinding of lateral surfaces shall be minimizedinasmuch as grinding may change the physical characteristicsof t
25、he specimens. Capping shall be in accordance with PracticeC 617.6.3 Load the specimen continuously and without shock. Theload shall be applied at a constant rate to the breaking point.Apply the load so that the maximum stress on the tension faceincreases at a rate between 125 and 175 psi/min (0.9 an
26、d 1.2MPa/min). The loading rate is computed using:r 5 2Sbd2/3L (1)where:r = loading rate, lb/min (N/min),S = rate of increase in the maximum stress on the tensionface, psi/min (MPa/min),b = average width of the specimen as oriented for testing,in. (mm),d = average depth of the specimen as oriented f
27、or testing,in. (mm), andL = span length, in. (mm).7. Measurement of Specimens After Test7.1 To determine the dimensions of the specimen sectionfor use in calculating modulus of rupture, take measurementsacross one of the fractured faces after testing. The width anddepth are measured with the specime
28、n as oriented for testing.For each dimension, take one measurement at each edge andone at the center of the cross section. Use the three measure-ments for each direction to determine the average width and theaverage depth. Take all measurements to the nearest 0.05 in. (1mm). If the fracture occurs a
29、t a capped section, include the capthickness in the measurement.8. Calculation8.1 Calculate the modulus of rupture as follows:R 5 3 PL/2bd2(2)where:NOTE 1Apparatus may be used inverted.FIG. 1 Diagrammatic View of a Suitable Apparatus for Flexure Test of Concrete by Center-Point Loading Method.C29308
30、2R = modulus of rupture, psi, or MPa,P = maximum applied load indicated by the testing ma-chine, lbf, or N,L = span length, in., or mm,b = average width of specimen, at the fracture, in., or mm,andd = average depth of specimen, at the fracture, in., or mm.NOTE 2The weight of the beam is not included
31、 in the abovecalculation.9. Report9.1 Report the following information:9.1.1 Identification number,9.1.2 Average width to the nearest 0.05 in. (1 mm), at thefracture,9.1.3 Average depth to the nearest 0.05 in. (1 mm), at thefracture,9.1.4 Span length in inches (or millimetres),9.1.5 Maximum applied
32、load in pounds-force (or newtons),9.1.6 Modulus of rupture calculated to the nearest 5 psi(0.05 MPa),9.1.7 Record of curing and apparent moisture condition ofthe specimens at the time of test,9.1.8 If specimens were capped, ground, or if leather shimswere used,9.1.9 Defects in specimens, and9.1.10 A
33、ge of specimens.10. Precision and Bias10.1 PrecisionThe coefficient of variation of test resultshas been observed to be dependent on the strength level of thebeams.3The single operator coefficient of variation has beenfound to be 4.4 %. Therefore, results of two properly con-ducted tests by the same
34、 operator on beams made from thesame batch sample should not differ from each other by morethan 12 %. The multilaboratory coefficient of variation hasbeen found to be 5.3 %. Therefore, results of two differentlaboratories on beams made from the same batch sampleshould not differ from each other by m
35、ore than 15 %.10.2 BiasSince there is no accepted standard for deter-mining bias in this test method, no statement on bias is made.11. Keywords11.1 beams; concrete; flexural strength testing; modulus ofruptureSUMMARY OF CHANGESCommittee C09 has identified the location of selected changes to this tes
36、t method since the last issue,C 293 07, that may impact the use of this test method. (Approved February 1, 2008)(1) Revised the title of Section 5 and added new 5.2.Committee C09 has identified the location of selected changes to this test method since the last issue,C 293 02, that may impact the us
37、e of this test method. (Approved July 15, 2008)(1) Revised 5.1.(2) Revised 6.3.(3) Revised 7.1.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determina
38、tion of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or with
39、drawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that you
40、r comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (sing
41、le or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).3See “Improved Concrete Quality Control Procedures Using Third PointLoading” by P. M. Carrasquillo and R. L. Carrasquillo, Research Report 119-1F,Project 3-9-87-1119, Center For Transportation Research, The University of Texasat Austin, November 1987, for information as to the relationship of strength andvariability under center point loading.C293083
