Designation:D6572−21StandardTestMethodsforDeterminingDispersiveCharacteristicsofClayeySoilsbytheCrumbTest1ThisstandardisissuedunderthefixeddesignationD6572;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope*1.1Twotestmethodsareprovidedtogiveaqualitativeindicationofthenaturaldispersivecharacteristicsofclayeysoils:MethodAandMethodB.1.1.1MethodA—ProcedureforNaturalSoilCrumbsde-scribedin10.1.1.1.2MethodB—ProcedureforRemoldedSoilCrumbsdescribedin10.2.1.2Thecrumbtest,whileagood,quickindicationofdispersivesoil,shouldusuallyberuninconjunctionwithapinholetestandadoublehydrometertest,TestMethodsD4647/D4647MandD4221,respectively.Sincethistestmethodmaynotidentifyalldispersiveclaysoils,othertestssuchas,pinholedispersion(TestMethodsD4647/D4647M),doublehydrometer(TestMethodD4221)andtheanalysisofporewaterextraction(TestMethodsD4542)maybeperformedindividuallyorusedtogethertohelpverifydispersion.1.3Thecrumbtesthassomelimitationsinitsusefulnessasanindicatorofdispersivesoil.Adispersivesoilmaysometimesgiveanon-dispersivereactioninthecrumbtest.Soilscontain-ingkaolinitewithknownfielddispersionproblems,haveshownnon-dispersivereactionsinthecrumbtest(1).2However,ifthecrumbtestindicatesdispersion,thesoilisprobablydispersive.1.4Thesetestmethodsareapplicableonlytosoilswherethepositionoftheplasticityindexversusliquidlimitplots(TestMethodsD4318)fallsonorabovethe“A”line(PracticeD2487)andmorethan12%ofthesoilfractionisfinerthan2-µmasdeterminedinaccordancewithTestMethodD7928.1.5Oven-driedsoilshouldnotbeusedtopreparecrumbtestspecimens,asirreversiblechangescouldoccurtothesoilpore-waterphysicochemicalpropertiesresponsiblefordisper-sion(2).NOTE1—Insomecases,theresultsofthepinhole,crumb,anddouble-hydrometertestmethodsmaydisagree.Thecrumbtestisabetterindicatorofdispersivesoilsthanofnon-...
