1、Designation:C68909(Reapproved 2014)Standard Test Method forModulus of Rupture of Unfired Clays1This standard is issued under the fixed designation C689;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A numbe
2、r 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 modu-lus of rupture of ceramic whiteware clays both dry and afterconditioning at 50 or 80%rela
3、tive humidity,or both.1.2 The values stated in inch-pound units are to be regardedas standard.The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 This standard does not purport to address all of thesafety c
4、oncerns,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.2.Referenced Documents2.1 ASTM Standards:2C322 Practice for Sampling Ceramic White
5、ware Clays3.Significance and Use3.1 The purpose of this test method is to obtain values ofrupture modulus of clays before firing,under various process-ing conditions(relative humidity).4.Apparatus4.1 Conditioning CabinetAny suitable airtight cabinetwith means for circulating air,or vacuum desiccator
6、,whereinprescribed specimens can be conditioned as desired beforetesting.Specimens for dry strength shall be stored with silicagel desiccant.Specimens for 50%relative humidity shall bestored over a saturated solution of sodium dichromate(Na2CR2O72H2O),and specimens for 80%relative humidityshall be s
7、tored over a saturated solution of ammonium chloride(NH4Cl).4.2 Testing MachineAny suitable testing machine may beused,provided a uniform rate of direct loading can bemaintained at no more than 1 lb/min(4.4 N/min)using theprescribed specimens.For the support of the test specimen,twosteel bars having
8、 a diameter of 0.5-in.(12.7-mm)shall beprovided.The load shall be applied by means of a third steelbar having a diameter of 0.5-in.(12.7-mm).All three bars areto be smooth polished steel without surface defects such asscratches or gouges.5.Test Specimen Preparation5.1 Preparation of Extruded Specime
9、ns 100%clay speci-men preparation:The test sample shall be blunged withsufficient distilled water to give complete dispersion andproduce a slip of sufficient viscosity to avoid noticeable settlingof particles(usually in the range of 25 to 50 percent solids).Slip shall be sieved through a No.120(125
10、m)sieve orequivalent.After aging 24 h the slip shall be dewatered to aplastic condition preferably by filter pressing.At this point themoisture content must be adjusted to optimum conditions forforming by some measure of plasticity such as Pfefferkornapparatus,plumb bob penetration,or other acceptab
11、le means.After the water of plasticity has been adjusted(usually willrange from 20 to 50%),test specimens shall be formed byextrusion.Where hand-operated extruder is used withoutvacuum,the plastic clay shall be thoroughly hand-wedged toeliminate entrapped air as a preliminary to forming test pieces.
12、Where a vacuum extruder is used,a vacuum of not less than 25in.(635 mm)Hg shall be maintained during forming operation.5.1.1 Clay-Flint Specimensto be used in the case of strongclays that are considered bonding materials.Prepare specimensas in 5.1 using a mixture of clay and 200 mesh potters flint i
13、na 1/1 ratio blend that has been thoroughly dry mixed.5.1.2 Solid Cast Specimens100%clay and clay-flintspecimens should be prepared by making a high solids slurrydeflocculated to minimum viscosity.Adjust the solids contentof the slurry to obtain a viscosity between 100-500 cps.Theslurry should be ca
14、st in plaster molds until solid,and the barsthen dried in accordance to the procedure outlined in 5.3 and5.4.5.2 DimensionThe test specimens shall be round bars of0.50(12.8 mm)diameter,and at least 4.5 in.(114 mm)inlength to permit an overhang of at least 0.25 in.at each endwhen mounted on the suppo
15、rts.1This test method is under the jurisdiction ofASTM Committee C21 on CeramicWhitewares and Related Productsand is the direct responsibility of SubcommitteeC21.04 on Raw Materials.Current edition approved Dec.1,2014.Published December 2014.Originallyapproved in 1971.Last previous edition approved
16、in 2009 as C689 09.DOI:10.1520/C0689-09R14.2For 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 website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 5.3 Handling and WarpageAll due precaution shall
