1、Designation: C348 14Standard Test Method forFlexural Strength of Hydraulic-Cement Mortars1This standard is issued under the fixed designation C348; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、 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 re
3、garded 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 sta
4、ndard 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 cem
5、entitious mixtures are caustic and may causechemical burns to skin and tissue upon prolonged exposure.2)2. Referenced Documents2.1 ASTM Standards:3C109/C109M Test Method for Compressive Strength ofHydraulic Cement Mortars (Using 2-in. or 50-mm CubeSpecimens)C230/C230M Specification for Flow Table fo
6、r Use in Testsof Hydraulic CementC305 Practice for Mechanical Mixing of Hydraulic CementPastes and Mortars of Plastic ConsistencyC349 Test Method for Compressive Strength of Hydraulic-Cement Mortars (Using Portions of Prisms Broken inFlexure)C670 Practice for Preparing Precision and Bias Statementsf
7、or Test Methods for Construction MaterialsC778 Specification for SandC1005 Specification for Reference Masses and Devices forDetermining Mass and Volume for Use in the PhysicalTesting of Hydraulic CementsC1437 Test Method for Flow of Hydraulic Cement MortarIEEE/ASTM SI 10 Standard for Use of the Int
8、ernationalSystem 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 other cements is that s
9、ufficient 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 means for determin
10、ing 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 C349.4.2 The values are determined from this test method forresearch or reference
11、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 C1005. Thebalance shall be evaluated for precision and accuracy at2000 g.5.2 Mixer, Bowl and Paddl
12、e, an electrically driven mechani-cal mixer of the type equipped with paddle and mixing bowl,as specified in the Apparatus Section of Practice C305.5.3 Flow Table and Flow Mold, shall conform to Specifica-tion C230/C230M.5.4 Specimen MoldsMolds for the 40 by 40 by 160-mmprism specimens shall be trip
13、le-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 made1This test method is under the jurisdiction ofASTM Committee C01 on Cementand is the direct responsibility of Subcommittee C01.27 on Strength.Current
14、 edition approved Dec. 1, 2014. Published December 2014. Originallyapproved in 1954. Last previous edition approved in 2008 as C348 08. DOI:10.1520/C0348-14.2See the section on Safety, Manual of Cement Testing, Annual Book of ASTMStandards, Vol 04.01.3For referenced ASTM standards, visit the ASTM we
15、bsite, 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor
16、 Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1of a hard metal, not attacked by cement mortar, and with aRockwell hardness of not less than HRB 55. The parts of themolds shall be matchmarked and, when assembled, shall betight-fitting and positively held together.The sides of th
17、e 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, of0.03 mm for new molds and 0.05 mm for molds in use. Thedistance between opposite sides shall be 40 6 0.13 mm forne
18、w molds and 40 6 0.3 mm for molds in use. The height ofthe molds shall be 40 mm with permissible variations of +0.25and 0.15 mm for new molds, and +0.25 and 0.40 mm formolds in use. The inside length of the molds shall be 160 62.5 mm. The angle between adjacent interior faces and top andbottom plane
19、s of the mold shall be 90 6 0.5, measured atpoints slightly removed from the intersections of the faces. Thebase plate shall be approximately 10 mm in thickness and shallhave a plane surface 200 by 180 mm with a permissiblevariation in any 50-mm line on the surface of 0.03 mm.5.5 TamperThe tamper (s
20、ee 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 200C. The face of thetamper shall be 22 by 85 mm.5.6 Tamper GuideT
21、he 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 be25 mm.5.7 TrowelThe
22、 trowel shall have a steel blade 115 by250 mm 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 and ap
23、pliedwithout 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 loadapplic
24、ation 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 load
25、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 C109/C109M.NOTE 1Most hyd
26、raulic 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 cylind
27、ers. 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 the u
28、pper 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 and para
29、llel 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 C778.7. Number of Specimens7.1 Three or more specimens shall be made
30、for each periodof test specified.8. Preparing Specimen Molds8.1 Prepare the specimen molds as prescribed in TestMethod C109/C109M.FIG. 1 TamperC348 1429. Procedure9.1 Proportioning, Consistency, and Mixing of MortarsThe proportioning, consistency, and mixing of the standardmortar shall be in accorda
31、nce with the Procedure Section ofTest Method C109/C109M.9.2 Determination of FlowThe flow shall be determinedin accordance with Test Method C1437.9.3 Molding Test Specimens:9.3.1 Immediately following completion of the flow test,return the mortar from the flow table to the mixing bowl.Quickly scrape
32、 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 immediately foradditi
33、onal 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.9.3.3 Star
34、t 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 in each mo
35、ld 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 aboutFIG. 2 Tamper Guide AttachmentC348 143FIG. 3C348 14425 mm above the mortar level and then thr
36、ust directly down-ward with sufficient force to squeeze out a small amount ofmortar from under the tamping surface. Fill the molds withmortar which shall be uniformly distributed and tamped in thesame manner as the bottom layer. Then remove the tamperguide and smooth off the specimens by drawing the
37、 flat side ofthe trowel (with the leading edge slightly raised) once along thelength of the molds. Cut the mortar off flush with the top of themolds by the straight edge of the trowel (held nearly perpen-dicular to the molds) with a sawing motion over the length ofthe molds. Following the cutting op
38、eration repair tears orcracks in the top surfaces and then make the surfaces of thespecimens plane by two or three light longitudinal strokes ofthe trowel held with the leading edge slightly raised.9.4 Storage of Test SpecimensStore the test specimens inaccordance with Test Method C109/C109M.9.5 Det
39、ermination 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 prescr
40、ibed below:Test Age Permissible Tolerance, h24 h 123 days 17 days 328 days 12When the portions of prisms are tested as modified cubes inaccordance with Test Method C349, test the prisms earlyenough so that the modified cubes are also broken within theabove tolerances. If more than one specimen at a
41、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 2.0C and ofsuffici
42、ent 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 and teste
43、d 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 loose sand
44、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 forwipin
45、g 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. Turn thes
46、pecimen 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 right angle
47、s 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. Apply t
48、he 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 than44 N. 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 flexur
49、al 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
