1、Designation: C78/C78M 15C78/C78M 15aStandard 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
2、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 agencies of the U.S. Department of Defense.1. Scope*1.1 This t
3、est 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 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 Test Specimens in the FieldC42/C42M Test Method for Obtaining and Testing Drilled Co
6、res and Sawed Beams of ConcreteC192/C192M Practice for Making and Curing Concrete Test Specimens in the LaboratoryC617 Practice for Capping Cylindrical Concrete SpecimensC1077 Practice forAgencies Testing Concrete and ConcreteAggregates for Use in Construction and Criteria for TestingAgencyEvaluatio
7、nE4 Practices for Force Verification of Testing Machines3. Significance and Use3.1 This test method is used to determine the flexural strength of specimens prepared and cured in accordance withTest MethodsC42/C42M or Practices C31/C31M or C192/C192M. Results are calculated and reported as the modulu
8、s of rupture. The strengthdetermined will vary where there are differences in specimen size, preparation, moisture condition, curing, or where the beam hasbeen molded or sawed to size.3.2 The results of this test method may be used to determine compliance with specifications or as a basis for propor
9、tioning,mixing and placement operations. It is used in testing concrete for the construction of slabs and pavements.4. Apparatus4.1 Testing MachineThe testing machine shall conform to the requirements of the sections on Basis of Verification,Corrections, and Time Interval Between Verifications of Pr
10、actices E4. Hand operated testing machines 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 permit
11、ted and shall be1 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 April 1, 2015May 1, 2015. Published May 2015June 2015. Originally approved in
12、 1930. Last previous edition approved in 20102015 asC78C78/C78M 1015.1. DOI: 10.1520/C0078_C0078M-15.10.1520/C0078_C0078M-15A.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information,
13、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 made to the previous version. Becauseit may not be technically possible to adequately depict all
14、 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 Summary of Changes section appears at the end of this standardCopyright ASTM International, 10
15、0 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1capable of applying 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 % acc
16、uracy, applied to the specimen duringa test.4.2 Loading ApparatusThe third point loading method shall be used in making flexure tests of concrete employing bearingblocks that will ensure that forces applied to the beam will be perpendicular to the face of the specimen and applied withouteccentricity
17、. A diagram of an apparatus that accomplishes this purpose is shown in Fig. 1.4.2.1 All apparatus for making flexure tests of concrete shall be capable of maintaining the specified span length and distancesbetween load-applying blocks and support blocks constant within 61.0 mm 60.05 in.4.2.2 The rat
18、io of the horizontal distance between the point of application of the load and the point of application of the nearestreaction to the depth of the beam shall be 1.0 6 0.03.4.2.3 If an apparatus similar to that illustrated in Fig. 1 is used: the load-applying and support blocks shall not be more than
19、65 mm 2.50 in. high, measured from the center or the axis of pivot, and should extend entirely across or beyond the full widthof the specimen. Each case-hardened bearing surface in contact with the specimen shall not depart from a plane by more than 0.05mm 0.002 in. and shall be a portion of a cylin
20、der, the axis of which is coincidental with either the axis of the rod or center ofthe ball, whichever the block is pivoted upon. The angle subtended by the curved surface of each block shall be at least 0.80 rad45. The load-applying and support blocks shall be maintained in a vertical position and
21、in contact with the rod or ball by meansof spring-loaded screws that hold them in contact with the pivot rod or ball. The uppermost bearing plate and center point ball inFig. 1 may be omitted when a spherically seated bearing block is used, provided one rod and one ball are used as pivots for theupp
22、er load-applying blocks.5. Testing5.1 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
23、 angles with the top and bottom. All surfaces shall be smooth and free of scars, indentations, holes, orinscribed identification marks.5.2 The individual who tests concrete beams for acceptance testing shall meet the concrete laboratory technician requirementsof Practice C1077 including Test Method
24、C78/C78M 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 of moist-cured specimens shall be made as soon as practical after removal from moist storage. Surface dryingof the specimen results i
25、n a reduction in the measured flexural strength.NOTE 1This apparatus may be used inverted. If the testing machine applies force through a spherically seated head, the center pivot may be omitted,provided one load-applying block pivots on a rod and the other on a ball.FIG. 1 Schematic of a Suitable A
26、pparatus for Flexure Test of Concrete by Third-Point Loading MethodC78/C78M 15a26.2 When using molded specimens, turn the test specimen on its side with respect to its position as molded and center it on thesupport blocks. When using sawed specimens, position the specimen so that the tension face co
27、rresponds to the top or bottom ofthe specimen as cut from the parent material. Center the loading system in relation to the applied force. Bring the load-applyingblocks in contact with the surface of the specimen at the third points and apply a load of between 3 and 6 % of the estimatedultimate load
28、. Using 0.10 mm 0.004 in. and 0.40 mm 0.015 in. leaf-type feeler gages, determine whether any gap between thespecimen and the load-applying or support blocks is greater or less than each of the gages over a length of 25 mm 1 in. or more.Grind, cap, or use leather shims on the specimen contact surfac
29、e to eliminate any gap in excess of 0.10 mm 0.004 in. in width.Leather shims shall be of uniform 6 mm 0.25 in. thickness, 25 to 50 mm 1.0 to 2.0 in. width, and shall extend across the fullwidth of the specimen. Gaps in excess of 0.40 mm 0.015 in. shall be eliminated only by capping or grinding. Grin
30、ding of lateralsurfaces shall be minimized inasmuch as grinding may change the physical characteristics of the specimens. Capping shall be inaccordance with the applicable sections of Practice C617.6.3 Load the specimen continuously and without shock. The load shall be applied at a constant rate to
31、the breaking point.Applythe load at a rate that constantly increases the maximum stress on the tension face between 0.9 and 1.2 MPa/min 125 and 175psi/min until rupture occurs. The loading rate is calculated using the following equation:r 5Sbd2L (1)where:r = loading rate, N/min lb/min,S = rate of in
32、crease in 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 To determine the dimensions of the sp
33、ecimen cross section for use in calculating modulus of rupture, take measurementsacross one of the fractured faces after testing. The width and depth are measured with the specimen as oriented for testing. Foreach dimension, take one measurement at each edge and one at the center of the cross sectio
34、n. Use the three measurements foreach direction 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 If the fracture initiates in the tension
35、surface within the middle third of the span length, calculate the modulus of ruptureas follows:R 5 PLbd2 (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, mm in., at the fracture, andd = av
36、erage depth of specimen, mm in., at the fracture.NOTE 2The weight of the beam is not included in the above calculation.8.2 If the fracture occurs in the tension surface outside of the middle third of the span length by not more than 5 % of the spanlength, calculate the modulus of rupture as follows:
37、R 53Pabd 2 (3)where:a = average distance between line of fracture and the nearest support measured on the tension surface of the beam, mm in.NOTE 3The weight of the beam is not included in the above calculation.8.3 If the fracture occurs in the tension surface outside of the middle third of the span
38、 length by more than 5 % of the spanlength, discard the results of the test.9. Report9.1 Report the following information:9.1.1 Identification number,C78/C78M 15a39.1.2 Average width to the nearest 1 mm 0.05 in.,9.1.3 Average depth to the nearest 1 mm 0.05 in.,9.1.4 Span length in mm in.,9.1.5 Maxim
39、um applied load in N lbf,9.1.6 Modulus of rupture calculated to the nearest 0.05 MPa 5 psi,9.1.7 Curing history 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 Whether sawed or molded and defects in spec
40、imens, and9.1.10 Age of specimens.10. Precision and Bias10.1 PrecisionThe coefficient of variation of test results has been observed to be dependent on the strength level of the beams.The single operator coefficient of variation has been found to be 5.7 %. Therefore, results of two properly conducte
41、d tests by thesame operator on beams made from the same batch sample are not expected to differ from each other by more than 16 %. Themultilaboratory coefficient of variation has been found to be 7.0 %. Therefore, results of two different laboratories on beams madefrom the same batch sample are not
42、expected to differ from each other by more than 19 %.310.2 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 has identified th
43、e location of selected changes to this test method since the last issue,C78/C78M 1015,1, that may impact the use of this test method. (Approved May 1, 2015April 1, 2015.).)(1) Revised Fig. 14.1.ASTM International takes no position respecting the validity of any patent rights asserted in connection w
44、ith any item mentionedin this standard. Users of this standard are expressly advised that determination 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 tec
45、hnical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn.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 considerat
46、ion at a meeting of theresponsible technical committee, which you may attend. If you feel that your 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 Ha
47、rbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single 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(ww
48、w.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ See “Improved Concrete Quality Control Procedures Using Third Point 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 possible guidance as to the relationship of strength and variability.C78/C78M 15a4
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