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TESTSFORPLASTICFINESINAGGREGATESRELATEDTOSTRIPPINGINASPHALTPAVINGMIXTURES
By
PrithviS.Kandal
CynthiaY.LynnFrazierParker
PublishedintheJournaloftheAssociationofAsphaltPavingTechnologists,AsphaltPavingTechnology,Volume67,1998
277TechnologyParkway Auburn,AL36830
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TESTSFORPLASTICFINESINAGGREGATESRELATEDTOSTRIPPINGINASPHALTPAVINGMIXTURES
By
PrithviS.Kandhal
AssociateDirectorNationalCenterforAsphaltTechnology
AuburnUniversity,Alabama
CynthiaY.Lynn
GraduateStudentNationalCenterforAsphaltTechnology
AuburnUniversity,Alabama
FrazierParkerDirector
HighwayResearchCenterAuburnUniversity,Alabama
PublishedintheJournaloftheAssociationofAsphaltPavingTechnologists,AsphaltPavingTechnology,
Volume67,1998
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DISCLAIMER
Thecontentsofthisreportreflecttheviewsoftheauthorswhoaresolelyresponsibleforthefactsandtheaccuracyofthedatapresentedherein.ThecontentsdonotnecessarilyreflecttheofficialviewsandpoliciesoftheNationalCenterforAsphaltTechnologyofAuburnUniversity.Thisreportdoesnotconstituteastandard,specification,orregulation.
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ABSTRACT
Thisstudywasundertakenfordeterminingthebestaggregatetestmethodthatindicatesthe
presenceofdetrimentalplasticfinesinthefineaggregate,whichmayinducestrippinginhotmixasphalt(HMA)mixtures.
Tenfineaggregatesrepresentingawiderangeofmineralogicalcompositionsandplasticity
characteristicswereused.Theirplasticitycharacteristicswereevaluatedbythreetestmethods:(a)sandequivalentvalue,(b)plasticityindex,and(c)methylenebluevalue.TenHMAmixturesweremadeusingacommonlimestonecoarseaggregatebutthesedifferentfineaggregates.Superpavevolumetricmixdesignwasusedtoestablishtheoptimumasphaltcontents.Twomixvalidationtests:(a)AASHTOT283and(b)theHamburgwheel-trackingdevicewereusedtoevaluatethestrippingpotentialofthetenHMAmixtures.
Statisticalanalysisoftheaggregatetestdataandthemixvalidationtestdatashowsthatthe
methylenebluetestisbestrelatedtostrippinginasphaltpavingmixtures.
KEYWORDS:Hotmixasphalt,stripping,moisturedamage,plasticfines,fineaggregate,sandequivalent,plasticityindex,methyleneblue
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SampleNumber
PF-1
PF-2
PF-3
PF-4
PF-5
PF-6
PF-7
PF-8
PF-9
PF-10
Table1.FineAggregateTypesandLocation
Description
PitRunNaturalSand
HighCalciumLimestone
Dolomite
Granite
BlastFurnaceSlag
Limerock
Granitewith4%HighPlasticityClay
Limerockwith3.4%HighPlasticityClay
Granitewith2.6%HighPlasticityClay
Limerockwith1%HighPlasticityClay
Location
Alabama
Alabama
Alabama
Georgia
Alabama
Florida
Georgia
Florida
Georgia
Florida
AggregateTestsandResults Thefollowingtestprocedureswereusedtotestthefineaggregates: AASHTOT176 PlasticFinesinGradedAggregatesandSoilsbyuseoftheSand
(ASTM2419) EquivalentTest AASHTOT90 DeterminingthePlasticLimitandPlasticityIndexofSoils
(ASTMD4318) OhioDOT MethyleneBlueValueofClays,MineralFillers,andFines
SandEquivalentTest
Thesandequivalenttestisusedtodeterminetherelativeproportionsofplasticfinesorclay-like
materialinfineaggregates.Fineaggregatepassingthe4.75mm(No.4)sieveisplacedinagraduated,transparentcylinderwhichisfilledwithamixtureofwaterandaflocculatingagent.Afteragitationand20minutesofsettling,thesandseparatesfromtheclay-likefines,andtheheightsofsandandsandplusclayaremeasured.Thesandequivalentistheratiooftheheightofthesandtotheheightofsandplusclaytimes100.Highersandequivalentwillbeobtainedincaseofacleanerfineaggregate.MinimumspecifiedsandequivalentvaluesforfineaggregateinHMArangefrom26to60(5).Theminimumrequirementof45ismostcommon.TherequirementisalsobasedonthetypeofHMAcoursesuchasbaseandsurfacecourse.Thistesthastheadvantagesthatitisquicktoperform,requiresverysimpleequipmentwhichcanbeusedwithminimaltrainingorexperience,andhasgivenreasonablygoodresults.
PlasticityIndex
PlasticityIndexisbeingusedbyseveralagenciestomeasurethedegreeofplasticityoffines.
PlasticityIndex(PI)isthedifferencebetweentheliquidlimitandtheplasticlimitofthematerialpassing425:m(No.40)sieve.ASTMD1073(StandardspecificationforFineAggregateinBituminousPavingMixtures)andD242(StandardSpecificationforMineralFillerforBituminousPavingMixtures)limitthePIofthisfractionpassingthe425 :m(No.40)sieve(includingthemineralfiller)toavalueof4orless.SomestatesspecifyamaximumPIfortheP200material.AreviewofliteratureindicatesnoreportedcorrelationbetweenthePIandthefieldperformanceofHMA.Precisiondatahavenotbeenestablishedforliquidlimitandplasticlimittestswhicharebasedonsubjectivejudgementandexperienceofthetester.
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MethyleneBlueTest
ThisFrenchtestmethodisrecommendedbytheInternationalSlurrySealAssociation(ISSA)to
quantifytheamountofharmfulclaysofthesmectite(montmorillinite)group,organicmatterand
ironhydroxidespresentinfineaggregate.Thetestmethodtitled"DeterminationofMethyleneBlueAdsorptionValue(MBV)ofMineralAggregateFillersandFines,"iscontainedinTechnicalBulletin145ofISSA(9).Theprincipleofthetestistoaddquantitiesofastandardaqueoussolutionofthedye(methyleneblue)toasampleuntiladsorptionofthedyeceases.
ArepresentativesampleofdryfineaggregateisscreenedthroughtheNo.200sieve.Theportion
ofthesamplepassingtheNo.200sieveistestedformethylenebluevalue(MBV).Tengramsofthesamplearedispersedin30gramsofdistilledwaterinabeaker.Onegramofmethyleneblue(MB)isdissolvedinenoughdistilledwater,toproduce200mlofsolution,sothat1mlofsolutioncontains5mgofmethyleneblue.ThisMBsolutionistitratedstepwisein0.5mlaliquotesfromtheburretteintothecontinuallystirredfineaggregatesuspension.AftereachadditionofMBsolutionandstirringforoneminute,asmalldropoftheaggregatesuspensionis
removedwithaglassrodandplacedonafilterpaper.SuccessiveadditionsofMBsolutionarerepeateduntiltheendpointisreached.Initially,awell-definedcircleofMB-staineddustisformedandissurroundedwithanouterringorcoronaofclearwater.Theendpointisreachedwhenapermanentlightbluecolorationor"halo"isobservedinthisringofclearwater.TheMBvalueofaspecificfineaggregatefractionisreportedasmilligramsofmethylenebluepergramofspecificfineaggregatefractionsuchas:MBV=5.3mg/g,0/#200.TheMBVexpressesthequantityofMBrequiredtocoverthetotalsurfaceoftheclayfractionofthesamplewithamono-molecularlayeroftheMB.Therefore,theMBVisproportionaltotheproductoftheclaycontenttimesthespecificsurfaceoftheclay(10).Themethylenebluetestissimpleandpractical,anditscostisreasonable.AnOhioDOTversionofthetest(givenintheAppendix)wasusedinthisstudy.
Table2summarizesmeasuredaggregateproperties.Eachtestwasrunintriplicateandaverage
valuesarereported.Specificgravityandwaterabsorptionoffineaggregate(AASHTOT84)weredeterminedformixdesignpurposesonly.
Table2.FineAggregateTestResults
Mix# PF-1 PF-2 PF-3 PF-4 PF-5 PF-6 PF-7 PF-8 PF-9 PF-10Test Natural Lime- Dolo- Granite Blast Lime- Granite Limerock Granite Limerock
Sand stone mite Furnace rock +4% +3.4% +2.6% +1%Slag Clay Clay Clay Clay
SandEquivalent 24 90 91 58 87 84 39 63 51 74PlasticityIndex NP NP NP NP NP NP NP NP NP NP(Passing#40)PlasticityIndex 29 NP NP NP NP NP 40 40 40 40(Passing#200)
MethyleneBlue 18.4 1.3 0.3 2.1 2 9.5 80.0 66.0 47.5 26.9ApparentSG. 2.667 2.744 2.869 2.750 2.711 2.678 2.730 2.672 2.823 2.676BulkSG. 2.558 2.665 2.786 2.657 1.623 2.358 2.651 2.363 2.743 2.360Water 2.0 1.1 1.1 1.3 1.2 5.1 - - - -Absorption
AsshowninTable2,theplasticityindexforalloftheseaggregates,especiallythefractionpassing425:m(No.40)sieve,waszero(nonplastic),therefore,thetwomainaggregateteststhatwereusedforcomparativepurposeswerethesandequivalenttestandthemethylenebluetest.Asmentionedearlier,thesandequivalencemeasurestherelativeamountofclay-sizedparticlesinafineaggregate.Themethylenebluetestdeterminestheamountandnatureof
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potentiallydetrimentalmaterial,suchasclayandorganicmaterial,thatmaybepresentina
aggregate.
MixtureTestsandResults
ThegradationwasheldconstantforallmixesandisshowninFigure1.Allmixescontainedacommonlimestonecoarseaggregate(33%)butdifferentfineaggregates.Superpavevolumetricmixdesignwasusedtodeterminetheoptimumasphaltcontenttogive4%airvoidsformixwitheachfineaggregate.Themixdesigndatasuchasoptimumasphaltcontent,voidsinthetotalmix(VTM),andvoidsinthemineralaggregate(VMA)aregiveninTable3.
Figure1.MixGradation
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Table3.SuperpaveVolumetricMixDesignData
OptimumAsphaltMixDesignation Content VTM VMA
PF-1 5.5 4.0 14.2
PF-2 5.3 4.0 15.8
PF-3 3.9 4.0 11.9
PF-4 5.2 4.0 14.4
PF-5 6.8 4.0 15.2
PF-6 8.0 4.0 20.6
PF-7 5.2 4.0 14.4
PF-8 8.0 4.0 20.6
PF-9 5.2 4.0 14.4
PF-10 8.0 4.0 20.6
ThefollowingtwomixturevalidationtestswereusedtoevaluatethestrippingpotentialofHMAmixtures:
AASHTOT283ResistanceofcompactedBituminousMixturetoMoistureInducedDamage
HamburgWheel-TrackingDevice
Ofallthetestmethodsavailableforevaluatingmoisturesusceptibility,AASHTOT283
(modifiedLottmantest)ismorewidelyusedanditsreliabilityisconsideredrelativelybetterthannumerousothertestmethods(2).RecentfieldstudiesbyAschenbrener(8)indicatedthat
AASHTOT283couldreasonablepredictthestrippingpotentialofColoradoaggregates.ThemoisturesusceptibilityoftheHMAmixturesisquantifiedintermsofretainedtensilestrengthafterwaterconditioning.
TheHamburgwheel-trackingdevice(HWTD)wasusedforadditionalvalidation.Thisdevice
hasbeenusedsuccesfullybytheCityofHamburg,Germany,theColoradoDepartmentofTransportation(8),andKochMaterialsCompany'slaboratoryinTerreHaute,Indianaforidentifyingaggregateswhicharesusceptibletomoisture-induceddamage.TheHWTDmeasuresthecombinedeffectsofruttingandmoisturedamagebyrollingasteelwheelbackandforthacrossthesurfaceofaHMAslabthatissubmergedinhotwater.TheHMAslabiscompactedinthelaboratorybyamechanicallyoperatedcompactorcalledalinearkneadingcompactor.Theslabmeasures320mminlength,260mminwidth,and80mmin
thickness.Theslabweighsabout15kgandiscompactedtoavoidcontentof71percent.TheslabissecuredinareusablesteelcontainerwithplasterofParis.Theslabissubmergedinwaterwhichcanbeheatedfrom250C(770F)to700C(1580F),thestandardtestingtemperaturebeing50(122).
Twoslabscanbetestedsimultaneouslywithtworeciprocatingsolidsteelwheels(diameter
203.5mmandwidth47.0mm)loadedto710N.Thelengthoftravelis230mmandtheaveragespeedis1.1km/hourresultingin532passes/minute.
Thetestingdurationis20,000cyclesanddeformationisrecordedandplottedaftereachcycle.
Onthecyclesversusdeformationplottwodistinctlinesaregenerallyobserved.Thefirstline(ruttingline)indicatesruttingintheHMAunaffectedbystripping.Thefollowingsecondline
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(strippingline)withasteeperslopeindicatesruttingduetostripping.Thepoint(numberof
cycles)wheretheslopeoftheruttinglineandtheslopeofthestrippinglineintersectiscalledtheinflectionpoint.Thisisthepointwherestrippingisassumedtohavebeeninitiated.Inflectionpoint(expressedintermsofnumberofcycles)isthetestparameterofinterestforthisstudy.
Table4containstheaveragespecimenvoidsinthetotalmix(VTM)andvoidsinthemineralaggregate(VMA)informationfortheslabsusedintheHamburgwheeltrackingtests.
Table4.VTMandVMAforHamburgWheelTrackingSpecimens
OptimumAsphaltMixDesignation
PF-1
PF-2
PF-3
PF-4
PF-5PF-6
PF-7
PF-8
PF-9
PF-10
Content
5.5
5.3
3.9
5.2
6.88.0
5.2
8.0
5.2
8.0
VTM
6.0
5.0
7.1
4.6
5.45.0
5.0
5.8
4.2
5.0
VMA
16.0
15.7
14.9
15.0
15.621.6
15.5
22.2
14.9
21.5
Table5containstheaveragespecimenVTMandVMAinformationforthespecimensusedintheAASHTOT283tests.MixesPF-6,PF-8,andPF-10usedFloridalimerockasthemainfineaggregate.MixesPF-8andPF-10onlydifferfromPF-6inthattheycontainadditionalamountsofclay.ThesethreemixeshaveveryhighVMAandhighoptimumasphaltcontent(Table3).
Theonlycriteriausedtodeterminetheoptimumasphaltcontentofthesemixeswas4%VTM.Itisverylikelythatthislimerockdegradedexcessivelyinthegyratorycompactor.TheresultingdegradationwillincreasetheVMAofthemixthusrequiringanincreasedasphaltcontentinordertoachievetheproperVTM.Moreover,thelimerockishighlyabsorptiveand,therefore,requiredadditionalasphaltbinder.
Table5.VTMandVMAforAASHTOT283Specimens
MixDesignation ConditionedSpecimens UnconditionedSpecimens
VTM VMA VTM VMA
PF-1 6.9 16.8 6.9 16.8
PF-2 7.2 17.7 7.4 17.9
PF-3 7.0 14.7 7.0 14.8PF-4 7.0 17.1 7.0 17.1
PF-5 7.3 17.3 7.2 17.2
PF-6 7.4 23.6 7.3 23.5
PF-7 7.4 17.6 7.3 17.6
PF-8 7.1 23.3 7.1 23.2
PF-9 8.0 18.3 8.4 18.6
PF-10 6.5 23.0 6.5 22.8
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Table6containsthemixturevalidationtestresults.
Table6.MixtureValidationTestResults
MixDesignation
PF-1
PF-2
PF-3
PF-4
PF-5
PF-6
PF-7
PF-8
PF-9
PF-10
AsphaltContentat4%Voids
5.5
5.3
3.9
5.2
6.8
8.0
5.2
8.0
5.2
8.0
TSRResults,%
49.3
85.0
79.1
61.3
47.5
62.0
44.2
48.4
30.8
49.0
HamburgWheelTest(InflectionPoint)
5000
17000
17500
6800
17000
3800
5500
5200
4300
2400
STATISTICALANALYSISOFTESTDATASinglevariablecorrelationanalysisandmultipleregressionanalysesweremadeusingaggregatetestvaluesasindependentvariablesandmixvalidationtestvaluesasdependentvariables.CorrelationmatricesweredevelopedusingtheSAScomputerprogramsothattherelationshipsbetweenaggregatetestsandHMAperformanceparameter(strippinginthiscase)couldbeexaminedinatabularform.Correlationcoefficients,thatis,Rvalueswereusedinthe
correlationmatricestablesbecausetheirsign(+or-_indicatesthenatureoftherelationshipbetweenthevariables.Whenlinearequations(y=a+bx)areshown,coefficientsofdetermination,thatis,R2valueswereusedsincethesignofthe"b"coefficientwillindicatethenatureoftherelationshipbetweentheindependent(x)andthedependent(y)variables.
TheforwardselectionmultiplevariablesproceduregivenintheSASprogramwasusedtoselect
theaggregatetest(s)whichis(are)relatedtoHMAstripping.Theforwardselectionprocedurebeginsbyfindingthevariablethatproducestheoptimumone-variablesubset,thatis,thevariablewiththelargestcoefficientofdeterminationorR2.Inthesecondstep,theprocedurefindsthatvariablewhich,whenaddedtothealreadychosenvariable,resultsinthelargestincreaseinR2andsoon.TheprocesscontinuesuntilnovariableconsideredforadditiontothemodelprovidesanincreaseinR2consideredstatisticallysignificantatthespecificlevel(P=0.05forthisstudy).
Table7containsacorrelationbetweentheaggregatetestsandmixvalidationtests.Inadditionto
thecomparisontosandequivalent(SE)andmethyleneblue(MB),themixvalidationtestswerealsocomparedtovariationsoftheresultsofthesetwoaggregatetests,intheeventthattherelationshipsmaynotbelinear.Thevariationsusedinthecomparisonwerethelogofeachtestresult,thesquareofeachresult,andtheinverseofthesquareoftheresults.
TheTSRisbestrelatedtologmethyleneblue(R=-0.79,P=0.006).Itscorrelationwiththesquare
ofsandequivalenthasaR=0.67,.P=0.03.Inflectionpointisalsobestrelatedtologmethyleneblue(R=-0.82,P=0.03).ItscorrelationwiththesquareofsandequivalenthasR=0.69,P=0.03.
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Table7.CorrelationBetweenAggregatePropertiesandMixPropertiesa
AggregateTest
SandEquivalentMethyleneBlue
(SandEquivalent)2
(MethyleneBlue)2
Log(SandEquivalent)
Log(MethyleneBlue)1/(SandEquivalent)2
1/(MethyleneBlue)2
TSR
0.6150.06
-0.6390.05
0.6730.03
-0.5020.14
0.5250.12
-0.7940.006
-0.3160.37
0.5380.11
InflectionPoint
0.6180.06
-0.5520.098
0.6860.03
-0.3900.27
0.5280.12
-0.8250.003
-0.3400.34
0.5590.09
aTopvaluesarecorrelationcoefficientsRandbottomvaluesaresignificancelevelsPineachcell.
TheforwardselectionprocedureinSAScomputerprogramwasusedtodetermineifcombinationsofvariablescontainingmethyleneblueandsandequivalentvaluescouldimprovepredictionofTSRandinflectionpoint.Nocombinationwasfoundthatimprovedthe
predictabilityoftherelationshipswithlogMBshowninTable8.TheforwardselectionproceduredidnotproceedbeyondSteponeafterselectingthemethylenebluetest.
Figures2and3showtheplotsoflogmethyleneblueversusTSRandinflectionpoint,
respectively.
Table8.ResultsofForwardSelectionProcedure
StepDependent Independent Model R2 PVariable Variable
1 TSR Log TSR=70.277-6.84(LogMethylene 0.63 0.006
Methylene Blue)Blue
1 Inflection Log InflectionPoint=14104.2-2644.4(Log 0.68 0.003Point Methylene MethyleneBlue)
Blue
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Figure2.MethyleneBluevs.TSR
Figure3.MethyleneBluevs.InflectionPoint
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CONCLUSIONS
BothTSRandinflectionpointtestdataindicatethatmethyleneblueisthefineaggregatetestwhichisbestrelatedtostrippingofHMA.Therefore,themethylenebluetestisrecommendedto
indicatethepresenceofdetrimentalplasticfineswhichmayinducestrippinginHMAmixtures.REFERENCES1.
2.
3.4.5.
6.
7.
8.
9.
10.
Stuart,KD,"EvaluationofProceduresUsedtoPredictMoistureDamageinAsphaltMixtures,"FHWA,ReportFHWA/RD-86/091,1986.Kandhal,P.S.,"MoistureSusceptibilityofHMAMixes:IdentificationofProblemandRecommendedSolutions,"NationalAsphaltPavementAssociation,QualityImprovementPublication119,December1992.Balghunaim,F.,"ImprovingtheAdhesionCharacteristicsofBituminousMixesbyWashingDustContaminatedCoarseAggregates,"paperpresentedtotheTransportationResearchBoard,1990.Hveem,F.N.,:"SandEquivalentTestforControlofMaterialsDuringConstruction,"Proceedings,HighwayResearchBoard,Vol.32,1953.O'Hara,W.G.,"EvaluationoftheCaliforniaSand-EquivalentTest,"Proceedings,.HighwayResearchBoard,Vol.34,1955.Clough,R.H.,andMartinez,J.E.,"ResearchonBituminousPavementsUsingtheSandEquivalentTest,"HighwayResearchBoard,Bulleting300,1961.Kandhal,P.S.,"EvaluationofBaghouseFinesinBituminousPavingMixtures,"JournaloftheAssociationofAsphaltPavingTechnologists,Vol.50,1981.Aschenbrener,T.,"ComparisonofColoradoComponentHotMixAsphaltMaterialswithSomeEuropeanSpecifications,"ColoradoDepartmentofTransportation,ReportNo.CDOT-DTD-R-92-14,December1992.InternationalSlurrySealAssociation,"TestMethodforDeterminationofMethylene
BlueAbsorptionValue(MBV)ofMineralAggregateFillersandFines,"ISSABulleting145,1989.Hosking,R.,"RoadAggregatesandSkidding,"TransportationResearchLaboratory,State-of-the-ArtReview4,HMSO,London,1992.
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AppendixA
StandardMethodofTestforMethyleneBlueValueofClays,MineralFillers,andFines
1.Scope
1.1Thisstandardprovidesproceduresfordeterminingtheamountofpotentiallyharmfulfinematerial(includingclayandorganicmaterial)presentinanaggregate.
1.2ThevaluesstatedinS1unitsaretoberegardedasthestandard.
1.3Thisstandardmayinvolvehazardousmaterials,operations,andequipment.This
standarddoesnotpurporttoaddressallofthesafetyproblemsassociatedwithitsuse.Itistheresponsibilityoftheuserofthisproceduretoestablishappropriatesafetyand
healthpracticesandtodeterminetheapplicabilityofregulatorylimitationspriortouse.
2.SummaryofTest
2.1MethyleneBluesolutionistitratedintodistilledwatercontainingthesamplematerial
(passing75mmsieve)inincrements.AsmallamountofwatercontainingthesamplematerialandtitratedMethyleneBlueisremovedviaaglassrodanddroppedontofilterpaper.WhenthesampleaggregatecannolongerabsorbmoreMethyleneBlue,ablueringisformedonthefilterpaper.
3.SignificanceandUse
3.1TheMethyleneBlueValuedeterminedbythisstandardcanbeusedtoestimatetheamountofharmfulclaysandorganicmatterpresentinanaggregate.AlargevalueforMethyleneBlueValueindicatesalargeamountofclayororganicmaterialpresentinthesample.
4.Apparatus
4.1Ambercoloredburetteofatleast50mlcapacity4.2MagneticMixerwithstirbar
4.3Balancesensitiveto0.01g
4.4Glassrodofapproximately250mmlengthandapproximately8mmdiameter
4.5Timerorstopwatch
4.6Sieve(75mm)andpan
4.7VolumetricFlaskof1000mlcapacity
4.8WhatmanNo.2filterpaper
4.9Glassbeakers
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4.10 MethyleneBlue,reagentgrade-datedandstoredfornomorethanfourmonthsin
abrownbottlewrappedwithfoilinadarkcabinetatlabtemperature.
4.11 Distilledwateratlabtemperature
5.Sampling
5.1Arepresentativesampleofthefineaggregatetobetestedisdriedtoconstantweightandscreenedthroughthe75mm(No.200)sieve.Theportionpassingthroughthesieve(P200material)isretainedfortesting;therestisdiscarded.
6.Procedure
6.1Weightout10.0g(+/-0.05g)oftheP200materialthathasbeendriedtoconstant
weightandplaceinbeaker.
6.2Add30gofdistilledwaterandstirwiththemixeruntiltheP200materialisuniformly
dispersed.
6.3OnegramofMethyleneBlueisdissolvedinenoughdistilledwatertoproduce200ml
ofsolution,witheach1mlofsolutioncontain5mgofMethyleneBlue.
6.4Withtheslurrystillmixing,filltheburettewiththeMethyleneBluesolution,add0.5
mlofthesolutiontotheslurry,andstirforoneminute.
6.5Removeadropoftheslurry,usingtheglassstirringrod,andplaceonthefilerpaper.
6.6Observetheappearanceofthedroponthefilterpaper.Theendpointisindicatedby
theformationofalightbluehaloaroundthedrop.ContinueaddingtheMethylene
Bluesolutiontotheslurryin0.5mlincrementswith1minutestirringaftereachaddition,thentesting,untiltheendpointisreached.
6.7Aftertheendpointisreached,continuestirringfor5minutesandretest.
Note:Withexperience,thepersonperformingthetestcanreachtheendpointmorequicklybyskippingearlyincrements.
7.Calculation
7.1MBV=CV/W
where:
MBV=MethyleneBlueValueinmgofsolutionpergoftheP200material
C=mgofMethyleneBlue/mlofsolutionV=mlofMethyleneBluesolutionrequiredfortitrationW=gramsofdrymaterial
7.2ThecalculationsmaybesimplifiedbyinsertingthemgofMethyleneBluepermlof
solutionandthegramsofdrymaterial.
MBV=(5xV)/10
MBV=0.5V
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8.PrecisionandBias
8.1Precision-Noprecisionhasbeenestablishedforthistest.
8.2Bias-Nobiascanbeestablishedbecausenoreferencematerialisavailableforthistest.
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