1、Designation: C 348 02Standard 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 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 as thestandard. The values shown in parentheses are for informationonly.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
4、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 prior to use. (WarningFreshhydraulic
5、cementitious mixtures are caustic and may causechemical burns to skin and tissue upon prolonged exposure.2)2. Referenced Documents2.1 ASTM Standards:C 109/C 109M Test Method for Compressive Strength ofHydraulic Cement Mortars (Using 2-in. or 50-mm CubeSpecimens)3C 230 Specification for Flow Table fo
6、r Use in Tests ofHydraulic Cement3C 305 Practice for Mechanical Mixing of Hydraulic CementPastes and Mortars of Plastic Consistency3C 349 Test Method for Compressive Strength of HydraulicCement Mortars (Using Portions of Prisms Broken inFlexure)3C 670 Practice for Preparing Precision and Bias Statem
7、entsfor Test Methods for Construction Materials4C 778 Specification for Standard Sand3IEEE/ASTM SI 10 Standard for Use of the InternationalSystem of Units (SI): The Modern Metric System53. Summary of Test Method3.1 The test mortar used consists of 1 part cement and 2.75parts of sand proportion by ma
8、ss. Portland or air-entrainingportland cements are mixed at specified water-cement ratios.Water content of other 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
9、 molds and stripped until testedby center point loading.4. Significance and Use4.1 This test method provides a 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 comp
10、ressive strength inaccordance with Test Method C 349.4.2 The values are determined from this test method forresearch or reference purposes only and are not used fordetermining compliance with specification requirements.5. Apparatus5.1 Weights, Weighing Devices and Glass Graduates, shallconform to th
11、e Apparatus Section of Test Method C 109/C 109M.5.2 Mixer, 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 230.5.4 Specim
12、en MoldsMolds for the 40 by 40 by 160-mmprism 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 n
13、ot less than HRB 55. The parts of themolds shall be matchmarked and, when assembled, shall betight-fitting and positively held together. The sides of the moldsshall be sufficiently rigid to prevent spreading or warping. Theinterior faces of the molds shall be plane surfaces with apermissible variati
14、on, in any 50-mm line on a surface, of 0.031This test method is under the jurisdiction of ASTM Committee C01 on Cementand is the direct responsibility of Subcommittee C01.27 on Strength.Current edition approved June 10, 2002. Published August 2002. Originallypublished as C 348 54 T. Last previous ed
15、ition C 348 97.2See the section on Safety, Manual of Cement Testing, Annual Book of ASTMStandards, Vol 04.01.3Annual Book of ASTM Standards, Vol 04.01.4Annual Book of ASTM Standards, Vol 04.02.5Annual Book of ASTM Standards, Vol 14.04.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700
16、, West Conshohocken, PA 19428-2959, United States.mm for new molds and 0.05 mm for molds in use. The distancebetween opposite sides shall be 40 6 0.13 mm for 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
17、, 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 bottomplanes of the mold shall be 90 6 0.5, measured at pointsslightly removed from the intersections of the faces. The baseplate shall be approximately
18、 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 tamper (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 ors
19、easoned oak wood rendered nonabsorptive by immersion for15 min in paraffin at approximately 200C (392F). The face ofthe tamper shall be 22 by 85 mm.5.6 Tamper GuideThe tamper guide (see Fig. 2), shall bemade of metal (such as brass of Rockwell hardness not lessthan HRB 55) not attacked by the cement
20、 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 TrowelThe trowel shall have a steel blade 115 by 250mm (4.5 by 10 in.) in length, with straight edges.5.8 Flexure Testing DeviceThe centerpoint
21、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 appliedwithout eccentricity. A device that accomplishes this purpose,for use in a compression testing machine, is shown i
22、n 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 loadapplication shall remain constant.5.8.2 The load shall be applied normal to the loaded surfaceof the specimen and in such a m
23、anner 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 should be applied at a uniform rate and in amanner to avoid shock.5.9 Compression Testing MachineThe compression test-i
24、ng 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 1Most hydraulic compression machines designed for breaking50-mm (2-in.) cubes have a relatively small diameter lower bearingsu
25、rface directly centered below the upper spherically seated head, onwhich close-fitting pedestals of appropriate heights are set for breaking50-mm cubes and 50-mm (2-in.) and 50 by 100-mm (2 by 4-in.) or 75 by150-mm (3 by 6-in.) cylinders. The base plate of the flexure testingapparatus shown in Fig.
26、3 is designed to rest on the low pedestal intendedfor tests on 75 by 150-mm (3 by 6-in.).NOTE 2In the absence of self-centering arrangements on machineswith large lower bearing surfaces, the center of this surface directly belowthe center of the upper spherically seated head shall be accurately loca
27、ted.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 parallel and at 90 to the axis of the cylinder.The upper
28、face shall have a diameter of 77.5 mm (3.05 in.).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 be made for each periodof test specified.8. Prepa
29、ring 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 standardmortar shall be in accordance with the Procedure Section ofTest Method C 109/C 109M.9.
30、2 Determination of FlowThe flow shall be determinedin accordance with Test Method C 109/C 109M.9.3 Molding Test Specimens:9.3.1 Immediately following completion of the flow test,FIG. 1 TamperC 3482return the mortar from the flow table to the mixing bowl.Quickly scrape down into the batch the mortar
31、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 foradditional specimens, the flow test ma
32、y 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 Start molding the specimens within a
33、 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 mold by twelve strokesof the tampe
34、r, 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 force to squeeze out a small amount of mortarfr
35、om 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 andsmooth off the specimens by drawing the flat side of the trowel(with the leading edge slightly raised) once along the length
36、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 repair tears or cracks in the topsurfaces and then make the surfaces of the spec
37、imens plane bytwo or three light longitudinal strokes of the trowel held withFIG. 2 Tamper Guide AttachmentC 3483the leading edge slightly raised.9.4 Storage of Test SpecimensStore the test specimens inaccordance with Test Method C 109/C 109M.9.5 Determination of Flexural Strength:9.5.1 Test the spe
38、cimens 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 theC 3484permissible tolerance prescribed below:Test Age Permissible Tolerance, h
39、24 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 at a time isremoved from the moist closet fo
40、r 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 (73 6 3F)and of sufficient depth to completely immer
41、se each specimenuntil time 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 tested immediately. If there is a
42、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 grains or incrustations from
43、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 forwiping 24-h specimens shall be not
44、 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 thespecimen on its side with resp
45、ect 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 angles to thelength of the prism a
46、nd 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 the load at the rateof 2640 6
47、110 N (600 6 25 lbf/min) which shall be indicatedwithin an accuracy of 61 % on a dial graduated in incrementsof not more than 44 N (10 lbf). Estimate the total maximumload to the closest 22 N (5 lbf).10. Calculation10.1 Record the total maximum load indicated by the testingmachine and calculate the
48、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 dif
49、fering 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 are left for determiningthe flexural strength at any given period a retest shall be made.12. Precision and Bias12.1 Precision:12.1.1 The following precision statements are applicablewhen a test result is the average of flexural strength tests ofthree prisms molded from a single batch of mortar and teste
