1、Designation: C 348 08Standard Test Method forFlexural Strength of Hydraulic-Cement Mortars1This standard is issued under the fixed designation C 348; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A numb
2、er in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of the flexuralstrength of hydraulic-cement mortars.1.2 The values stated in SI units are to be
3、regarded asstandard. No other units of measurement are included in thisstandard.1.3 Values in SI units shall be obtained by measurement inSI units or by appropriate conversion, using the Rules forConversion and rounding given in Standard IEEE/ASTM SI10, of measurements made in other units.1.4 This s
4、tandard 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 prior to use. (WarningFreshhydraulic c
5、ementitious mixtures are caustic and may causechemical burns to skin and tissue upon prolonged exposure.2)2. Referenced Documents2.1 ASTM Standards:3C 109/C 109M Test Method for Compressive Strength ofHydraulic Cement Mortars (Using 2-in. or 50-mm CubeSpecimens)C 230/C 230M Specification for FlowTab
6、le for Use inTestsof Hydraulic CementC 305 Practice for Mechanical Mixing of Hydraulic CementPastes and Mortars of Plastic ConsistencyC 349 Test Method for Compressive Strength of Hydraulic-Cement Mortars (Using Portions of Prisms Broken inFlexure)C 670 Practice for Preparing Precision and Bias Stat
7、ementsfor Test Methods for Construction MaterialsC 778 Specification for Standard SandC 1005 Specification for Reference Masses and Devices forDetermining Mass and Volume for Use in the PhysicalTesting of Hydraulic CementsC 1437 Test Method for Flow of Hydraulic Cement MortarIEEE/ASTM SI 10 Standard
8、 for Use of the InternationalSystem of Units (SI): The Modern Metric System3. Summary of Test Method3.1 The test mortar used consists of 1 part cement and 2.75parts of sand proportion by mass. Portland or air-entrainingportland cements are mixed at specified water-cement ratios.Water content of othe
9、r cements is that sufficient to obtain aflow of 110 6 5 % with 25 drops of the flow table. Test prisms,40 by 40 by 160-mm are molded by tamping in two layers.Prisms are cured one day in the molds and stripped until testedby center point loading.4. Significance and Use4.1 This test method provides a
10、means for determining theflexural strength of hydraulic cement mortars. Portions of themortar prisms tested in flexure according to this test methodmay be used for the determination of compressive strength inaccordance with Test Method C 349.4.2 The values are determined from this test method forres
11、earch or reference purposes only and are not used fordetermining compliance with specification requirements.5. Apparatus5.1 Weights, Weighing Devices and Glass Graduates, shallconform to the requirements of Specification C 1005. Thebalance shall be evaluated for precision and accuracy at 2000g.5.2 M
12、ixer, Bowl and Paddle, an electrically driven mechani-cal mixer of the type equipped with paddle and mixing bowl,as specified in the Apparatus Section of Practice C 305.5.3 Flow Table and Flow Mold, shall conform to Specifica-tion C 230/C 230M.5.4 Specimen MoldsMolds for the 40 by 40 by 160-mmprism
13、specimens shall be triple-gang molds and shall be sodesigned that the specimens will be molded with their longi-tudinal axes in a horizontal position. The molds shall be madeof a hard metal, not attacked by cement mortar, and with aRockwell hardness of not less than HRB 55. The parts of the1This tes
14、t method is under the jurisdiction ofASTM Committee C01 on Cementand is the direct responsibility of Subcommittee C01.27 on Strength.Current edition approved Dec. 1, 2008. Published January 2009. Originallyapproved in 1954. Last previous edition approved in 2002 as C 348 02.2See the section on Safet
15、y, Manual of Cement Testing, Annual Book of ASTMStandards, Vol 04.01.3For referenced 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
16、website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.molds shall be matchmarked and, when assembled, shall betight-fitting and positively held together. The sides o
17、f the moldsshall be sufficiently rigid to prevent spreading or warping. Theinterior faces of the molds shall be plane surfaces with apermissible variation, in any 50-mm line on a surface, of 0.03mm for new molds and 0.05 mm for molds in use. The distancebetween opposite sides shall be 40 6 0.13 mm f
18、or new moldsand 40 6 0.3 mm for molds in use. The height of the moldsshall be 40 mm with permissible variations of +0.25 and 0.15mm for new molds, and +0.25 and 0.40 mm for molds in use.The inside length of the molds shall be 160 6 2.5 mm. Theangle between adjacent interior faces and top and bottomp
19、lanes of the mold shall be 90 6 0.5, measured at pointsslightly removed from the intersections of the faces. The baseplate shall be approximately 10 mm in thickness and shall havea plane surface 200 by 180 mm with a permissible variation inany 50-mm line on the surface of 0.03 mm.5.5 TamperThe tampe
20、r (see Fig. 1) shall be made ofnonabsorptive, nonabrasive material, such as a rubber com-pound having a Shore A durometer hardness of 80 6 10 orseasoned oak wood rendered nonabsorptive by immersion for15 min in paraffin at approximately 200 C. The face of thetamper shall be 22 by 85 mm.5.6 Tamper Gu
21、ideThe tamper guide (see Fig. 2), shall bemade of metal (such as brass of Rockwell hardness not lessthan HRB 55) not attacked by the cement mortar. It shall lie flaton the mold and shall not protrude over any interior edge of theform more than 0.40 mm. The height of the guide shall be 25mm.5.7 Trowe
22、lThe trowel shall have a steel blade 115 by 250mm in length, with straight edges.5.8 Flexure Testing DeviceThe centerpoint loadingmethod shall be used in making flexure tests on the prismspecimens. The device used shall be designed such that theforces applied to the specimen will be vertical only an
23、d appliedwithout eccentricity. A device that accomplishes this purpose,for use in a compression testing machine, is shown in Fig. 3.Apparatus for making flexure tests of mortar specimens shallbe designed to incorporate the following principles:5.8.1 The distance between supports and points of loadap
24、plication shall remain constant.5.8.2 The load shall be applied normal to the loaded surfaceof the specimen and in such a manner as to avoid alleccentricity of loading.5.8.3 The direction of the reactions should be parallel to thedirection of the applied load at all times during the test.5.8.4 The l
25、oad should be applied at a uniform rate and in amanner to avoid shock.5.9 Compression Testing MachineThe compression test-ing machine used with the flexure testing device, as shown inFig. 3, shall be of the hydraulic type and conform to therequirements prescribed in Test Method C 109/C 109M.NOTE 1Mo
26、st hydraulic compression machines designed for breaking50-mm cubes have a relatively small diameter lower bearing surfacedirectly centered below the upper spherically seated head, on whichclose-fitting pedestals of appropriate heights are set for breaking 50-mmcubes and 50 by 100-mm or 75 by 150-mm
27、cylinders. The base plate ofthe flexure testing apparatus shown in Fig. 3 is designed to rest on the lowpedestal intended for tests on 75 by 150-mm.NOTE 2In the absence of self-centering arrangements on machineswith large lower bearing surfaces, the center of this surface directly belowthe center of
28、 the upper spherically seated head shall be accurately located.A circle or concentric circles of appropriate diameters shall be scribed onthe lower bearing surface around this point. A cylindrical pedestal ofappropriate diameter and height shall be obtained. End faces of thepedestal must be plane an
29、d parallel and at 90 to the axis of the cylinder.The upper face shall have a diameter of 77.5 mm.6. Materials6.1 Graded Standard Sand:6.1.1 The sand used for making test specimens shall benatural silica sand and conform to Specification C 778.7. Number of Specimens7.1 Three or more specimens shall b
30、e made for each periodof test specified.8. Preparing Specimen Molds8.1 Prepare the specimen molds as prescribed in TestMethod C 109/C 109M.9. Procedure9.1 Proportioning, Consistency, and Mixing of MortarsThe proportioning, consistency, and mixing of the standardFIG. 1 TamperC348082mortar shall be in
31、 accordance with the Procedure Section ofTest Method C 109/C 109M.9.2 Determination of FlowThe flow shall be determinedin accordance with Test Method C 1437.9.3 Molding Test Specimens:9.3.1 Immediately following completion of the flow test,return the mortar from the flow table to the mixing bowl.Qui
32、ckly scrape down into the batch the mortar that may havecollected on the side of the bowl and then remix the entirebatch 15 s at medium speed. Upon completion of mixing, themixing paddle shall be shaken to remove excess mortar into themixing bowl.9.3.2 When a duplicate batch is to be made immediatel
33、y foradditional specimens, the flow test may be omitted and themortar allowed to remain in the mixing bowl for 90 s withoutcovering. During the last 15 s of this interval, quickly scrapedown into the batch the mortar that may have collected on theside of the bowl. Then remix for 15 s at medium speed
34、.9.3.3 Start molding the specimens within a total elapsedtime of not more than 2 min and 30 s after completion of theoriginal mixing of the mortar batch.9.3.4 Evenly distribute a layer of mortar about 20 mm inthickness in each of the three molds with the tamper guide inplace. Then compact the mortar
35、 in each mold by twelve strokesof the tamper, applied in three rounds of four strokes each, asshown in Fig. 4. Complete the twelve strokes in about 15 s. Foreach stroke hold the tamper face in horizontal position about 25mm above the mortar level and then thrust directly downwardwith sufficient forc
36、e to squeeze out a small amount of mortarfrom under the tamping surface. Fill the molds with mortarwhich shall be uniformly distributed and tamped in the samemanner as the bottom layer. Then remove the tamper guide andFIG. 2 Tamper Guide AttachmentC348083smooth off the specimens by drawing the flat
37、side of the trowel(with the leading edge slightly raised) once along the length ofthe molds. Cut the mortar off flush with the top of the molds bythe straight edge of the trowel (held nearly perpendicular to themolds) with a sawing motion over the length of the molds.Following the cutting operation
38、repair tears or cracks in the topC348084surfaces and then make the surfaces of the specimens plane bytwo or three light longitudinal strokes of the trowel held withthe leading edge slightly raised.9.4 Storage of Test SpecimensStore the test specimens inaccordance with Test Method C 109/C 109M.9.5 De
39、termination of Flexural Strength:9.5.1 Test the specimens immediately after their removalfrom the moist closet in the case of 24-h specimens and fromthe storage water in the case of all other specimens. All testspecimens for a designated test age shall be broken within thepermissible tolerance presc
40、ribed below:Test Age Permissible Tolerance, h24 h 6123 days 617 days 6328 days 612When the portions of prisms are tested as modified cubes inaccordance with Test Method C 349, test the prisms earlyenough so that the modified cubes are also broken within theabove tolerances. If more than one specimen
41、 at a time isremoved from the moist closet for the 24-h test, cover thesespecimens with waterproof plastic until the time of test. Forolder specimens, if more than one specimen at a time isremoved from the storage water for testing, place thesespecimens in water at a temperature of 23 6 2.0 C and of
42、sufficient depth to completely immerse each specimen untiltime of test.NOTE 3The flexural strength of prisms is quickly affected by dryingwhich produces skin tension in the specimens and yields low strengths.Specimens for test at 24 h should, therefore, be removed from moldspreferably at that age an
43、d tested immediately. If there is a delay in testing,specimens shall be wrapped in waterproof plastic and placed in the moistcloset until immediately before testing. After breaking, rewrap in plasticuntil compressive tests are made.9.5.2 Wipe each prism to a surface-dry condition, andremove any loos
44、e sand grains or incrustations from the facesthat will be in contact with the bearing surfaces of the points ofsupport and load application. Check these faces by applying astraightedge. If there is appreciable curvature, grind the face orfaces to plane surfaces or discard the specimen. Cloths used f
45、orwiping 24-h specimens shall be not more than faintly damp.9.5.3 Center the pedestal on the base plate of the machinedirectly below the center of the upper spherical head, and placethe bearing plate and support edge assembly on the pedestal.Attach the center-loading device to the spherical head. Tu
46、rn thespecimen on its side with respect to its position as molded andplace it on the supports of the testing device. The longitudinalcenter line of the specimen shall be set directly above themidpoint of both supports. Adjust the center-point loadingdevice so that its bearing edge is at exactly righ
47、t angles to thelength of the prism and parallel to its top face as placed, withthe center of the bearing edge directly above the center line ofthe prism and at the center of the span length. Take care toensure that contact between the specimen and loading edge iscontinuous when the load is applied.
48、Apply the load at the rateof 2640 6 110 N which shall be indicated within an accuracyof 61 % on a dial graduated in increments of not more than 44N. Estimate the total maximum load to the closest 22 N.10. Calculation10.1 Record the total maximum load indicated by the testingmachine and calculate the
49、 flexural strength (for the particularsize of specimen and conditions of test herein described) inMPa as follows:Sf5 0.0028 P (1)where:Sf= flexural strength, MPa, andP = total maximum load, N.11. Faulty Specimens and Retests11.1 Test specimens that are manifestly faulty or that resultin strengths differing by more than 10 % from the averagevalue of all test specimens made from the same sample andtested at the same period shall not be considered in determiningthe flexural strength. After discarding specimens or strengthvalues, if less than two strength values a
