Development of a New Test Method for Measuring Bulk Specific Gravity of Fine Aggregate

8/9/2019 Development of a New Test Method for Measuring Bulk Specific Gravity of Fine Aggregate

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DEVELOPMENTOFANEWTESTMETHODFORMEASURINGBULKSPECIFICGRAVITYOFFINE AGGREGATES

By

PrithviS.Kandhal

RajibB.MallickMikeHuner

PaperpublishedinTransportationResearchBoard,TransportationResearchRecord1721,2000

277TechnologyParkway Auburn,AL36830


2/23

DEVELOPMENTOFANEWTESTMETHODFORMEASURINGBULK SPECIFICGRAVITYOFFINEAGGREGATES

By

PrithviS.Kandhal

AssociateDirectorNationalCenterforAsphaltTechnology

AuburnUniversity,Alabama

RajibB.Mallick

AssistantProfessorWorcesterPolytechnicInstituteWorcester,Massachusetts

MikeHunerResearchEngineer

NationalCenterforAsphaltTechnologyAuburnUniversity,Alabama

PaperpublishedinTransportationResearchBoard,TransportationResearchRecord1721,2000


3/23

DISCLAIMER

Thecontentsofthisreportreflecttheviewsoftheauthorswhoaresolelyresponsibleforthefactsandtheaccuracyofthedatapresentedherein.ThecontentsdonotnecessarilyreflecttheofficialviewsandpoliciesoftheNationalCenterforAsphaltTechnologyofAuburnUniversity.Thisreportdoesnotconstituteastandard,specification,orregulation.

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ABSTRACT

Bulkspecificgravityofthefineaggregateisusedinhotmixasphalt(HMA)volumetricmix

design(includingSuperpave)todeterminetheamountofasphaltbinderabsorbedbytheaggregateandthepercentageofthevoidsinthemineralaggregate(VMA).Thecurrenttestmethod(AASHTOT84)usesaconemethodtoestablishthesaturatedsurfacedry(SSD)conditionofthesample,whichisnecessarytoconductthetest.Thismethoddoesnotworksatisfactorilyforfineaggregateswhichareveryangularandhaveroughsurfacetexture,and,therefore,donotslumpreadilywheninSSDcondition.

Thisresearchprojectwasundertakentodevelopanautomatedequipmentandmethodof

establishingtheSSDconditionofthefineaggregate.Thewetsampleofthefineaggregateisplacedinarotatingdrumandissubjectedtoasteadyflowofwarmair.ThetemperaturegradientoftheincomingandoutgoingairandtherelativehumidityoftheoutgoingairaremonitoredtoestablishtheSSDcondition.

Twoprototypesdeviceswereconstructed.Thetestresultsobtainedwiththesecondprototypedeviceareencouragingandhavebeenreportedinthepaper.Furtherimprovementstobemadetothesecondprototypedevicetoimprovetherepeatabilityandreproducibilityofthetest,havebeenidentified.

KEYWORDS:bulkspecificgravity,fineaggregate,saturatedsurfacedry,Superpave,hotmix

asphalt,mixdesign

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Kandhal,Mallick,&Huner

DEVELOPMENTOFANEWTESTMETHODFORMEASURINGBULKSPECIFIC

GRAVITYOFFINEAGGREGATES

PrithviS.Kandhal,RajibB.Mallick,andMikeHuner

INTRODUCTIONANDOBJECTIVEBulkspecificgravityofthefineaggregateisusedinSuperpavevolumetricmixdesigncalculationstodeterminetheamountofasphaltbinderabsorbedbytheaggregateandthepercentageofthevoidsinthemineralaggregate(VMA).Thecurrenttestmethodofmeasuringthebulkspecificgravityoffineaggregate(AASHTOT84orASTMC128)doesnothavesatisfactoryreproducibility.Thismethoddoesnotworksatisfactorilyforcertainfineaggregateswhichareveryangularandhaveroughsurfacetexture.Thesematerialsdonotslumpreadilywhentestedbytheconemethodspecifiedinthesestandardteststodeterminethesaturatedsurfacedrycondition(SSD).Thislackofprecisioninobtainingthebulkspecificgravityoffine

aggregateaffectstheSuperpavevolumetricmixdesign.Theoptimumasphaltcontentcanbeunderestimatedresultinginleanandbrittlemixture(ravelingandcracking)orcanbeoverestimatedresultinginrichandplasticmixture(flushingorrutting).Thereisanurgentneedtodevelopanaccurateandmorereproducibletestmethodfordeterminingthebulkspecificgravityofthefineaggregates.

Thisstudywasundertakentodevelopanautomatedequipmentandmethodofdeterminingthe

saturatedsurfacedryconditionofthefineaggregatesothatitsbulkspecificgravitycanbemeasuredwithsatisfactoryprecisionandaccuracy.

REVIEWOFLITERATURE

Bulkspecificgravityistheratioofweightinairofagivenvolumeofapermeablematerial

(includingbothpermeableandimpermeablevoidsnormaltothematerial)atastatedtemperaturetotheweightinairofanequalvolumeofdistilledwateratastatedtemperature.Thebulkspecificgravityofanaggregate,asdefinedbytheASTM,equalstheoven-dryweightoftheaggregate(A)dividedbythesumoftheaggregatesolidvolume(Vs),thevolumeofthepermeablevoids(Vp),andthevolumeoftheimpermeablevoids(Vi)timestheunitweightofwater((w).Thosevoidsthatcannotbefilledwithwateraftera24-hoursoakingarereferredtoasimpermeable.Thebulkspecificgravityofanaggregateisdeterminedinthelaboratoryusingthefollowingformula:

whereAistheoven-dryweightoftheaggregate,Bisthesaturatedsurface-dryweight(ingrams)ofthematerialinair,andCistheweight(ingrams)ofsaturatedmaterialinwater.

Bulkspecificgravityofbothcoarseandfineaggregateareusedinhotmixasphalt(HMA)mix

designtocalculatetheamountofasphaltbinderabsorbedbytheaggregateandthepercentageofvoidsinthemineralaggregate(VMA).Accuratedeterminationofbulkspecificgravityoftheaggregatesis,therefore,necessarytocalculatetherealisticvolumetricpropertiesofthecompactedHMAmixtures.

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Experiencehasshownthat,forsomematerials,theresultsofbulkspecificgravityarevery

difficulttoreproduce.Thisismainlycausedbythepersonalelementinvolvedinjudgingthepointatwhichthewetaggregatehasdriedoutsufficientlytoreachthe"saturatedsurface-dry(SSD)condition"whichistheoreticallythepointatwhichallthesurfacemoisturehasgonefrom

theparticlesbutwiththepermeableporesremainingcompletelyfilled.ASTMStandardMethodsC127andC128outlinemeansfordeterminingabsorptionandbulkspecificgravityofcoarseandfineaggregates,respectively.Thesestandardscallforimmersionofmaterialinwater,followedbydryinguntilthesurface-drystateisattained.Coarseaggregatesarerolledinanabsorbentclothuntilallvisiblefilmsofwateraregone.TheestablishmentoftheSSDconditionofcoarseaggregatesissimpleandreasonablyreproducible.However,thesameisnottrueforfineaggregates.

Fineaggregatesarespreadonapanandexposedtoagentlecurrentofwarmairuntilafree-

flowingconditionisreached.Theaggregateisthenlightlytampedintoaspecifiedconicalmold.Iftheconestandswhenthemoldisremoved,thefineaggregateisassumedtohavemoistureonits

surface,anditisdriedfurther.Whentheconejustbeginstoslumpafterremovalofthecone,itisassumedtobeinasaturatedsurface-drystate.Inadditiontovariationcausedbyindividualjudgement,thefactthatlargeparticlestendtodrymorequicklythansmallparticlesmayleadtooverdryingofthelargerparticles,unlesstheprecautionistakenofrecognizingandhandlingtheseparticlesseparately.Thesevariationsbecomesignificantinthecaseofaggregateshavingaroughandporoussurface.

Fornatural,well-gradedfineaggregates,thesaturatedsurface-dryconditionisusually

reproducible.Theendpointismoreerraticforcrushedfineaggregatesbecausetheangularityoftheparticlesdoesnotpermitadefiniteslumpconditionasdotheroundedsurfacesofnaturalsands.Besides,thehigherpercentageofmaterialpassingthe0.15mm(No.100)sievealsoposesaprobleminachievingtheslumpcondition.

Variousattemptshavebeenmadeinthepasttopinpointthesaturatedsurface-dryconditionoftheaggregatestoimprovethereproducibilityofthebulkspecificgravitytestresults.TheseincludeHoward'sglassjarmethod(1,2),Martin'swetanddrybulbtemperaturemethod(3),Saxer'sabsorptiontimecurveprocedure(4),andHughesandBahramian'ssaturatedair-dryingmethod(5).However,thevariousmodificationseitherofferlittleimprovementoraretooelaboratetobeofpracticalvalueinthefieldoraveragelaboratory.

KandhalandLee(6)developedacolorimetricprocedure,alsomentionedinASTMC128,to

establishtheSSDconditionofbothcoarseandfineaggregates.Thismethodinvolvessoakingtheaggregateinwatercontainingaspecialchemicaldye.Onremovalfromwater,theaggregateacquiresthecolorofthewetdye.However,thisdyechangescolorwhendry(forexample,cobaltchloridechangescolorfromredtoblue).Assoonasthefineaggregateparticleschangecolor(whensubjectedtodryingwithafan),thesaturatedsurfacedrycondition(SSD)hasbeen

reached.However,thefollowingproblemsareassociatedwiththismethod:a.Thedyesdonotshowwellondarkcoloredaggregates;b.Anefficientmethodofmixingthefineaggregateduringthedryingoperationis

neededsothatlargerparticlesdonotdryoutsoonerthanfinerparticles;andc.Detectionofthecolorchangeneedstobeautomatedsothatthesubjectivejudgement

oftheoperatoriseliminated.

DanaandPeters(7)ofArizonaDepartmentofTransportationdirectlymeasuredthesurface

moistureconditionsofmineralaggregateusingbasicprinciplesofthermodynamics.Thewetfineaggregatesamplewasplacedinasmallrotatingdrum.Hotairwasblownintooneendofthedrumtodrythetumblingaggregateuniformly.Thermocouplesmountedintheinletandoutlettubesoftheprototyperotatingdryingdrummonitoredthetemperaturesoftheincomingand

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outgoinghotair.Amillivoltstripchartrecorderdisplayedthedifferenceintemperature(thermal

gradient)ofthethermocouples.Aslongastherewasfreesurfacemoistureontheaggregateasteadyvalueofthethermalgradientwasobserved.Assoonasthesaturatedsurfacedry(SSD)conditionwasachieved,thethermalgradientreducedsuddenly.Atthattime,thesampleistaken

outofthedrumandtested.Thepreliminaryprototypeequipmentgaveencouragingresults,however,thedevelopmentoftheequipmentwasnotfinalizedanditwasrecommendedtotestawidevarietyoffineaggregates.

Krugler,TahmoressiandRand(8)havereportedfourprocedurestoestablishthesaturated-

surface-dry(SSD)conditionoffineaggregates:1.Anoven-dryaggregatesampleisplacedside-by-sidewiththetestsamplewhichis

beingdried.TheSSDconditionisdefinedasthepointwhenthetestsamplehasthesamecolorastheoven-drycomparisonsample.ItispreferredtoerronthedrysideoftheSSDconditionbecausethebulkspecificgravitydoesnotchangesignificantlywithadditionaldrying.

2.Observehowthetestsampleslidesdownthebottomofatiltedpan.Whenthetest

samplenolongeradherestothebottomandflowsfreely,itisjudgedtobesurfacedry.3.Observehowthetestsampleflowsoffatiltedmasonrytrowel.Whenthetestsample

nolongeradherestothetrowelandflowsofffreelyasindividualparticles,itisconsideredsurfacedry.

4.Useastripofpackagingtape(SupremeSuperstandardGummedPaperTape,two-inchmediumduty)attachedtoasmallblockofwood.Thetapeisplacedonthetestsampleforfivesecondsandlifted.TheSSDconditionisreachedifnotmorethanonetestsampleparticleadherestothetapeontwoconsecutivechecks.(Thewater-solubleglueofthetapeisactivatedbymoistureinthetestsample.)

TheSSDconditionmustbeestablishedbyusingatleasttwocriteriaofthefourTexasDOT

proceduresdescribedabove.Obviously,somesubjectivityisinvolvedinallprocedures.

ThereviewofliteratureonestablishingtheSSDconditionofthefineaggregateindicatesthatthe

conceptusedbytheArizonaDepartmentofTransportation(7)hadthemostpotentialofdevelopinganautomatedequipmenttoaccomplishthis.ThedifficultiesencounteredintheArizonaexperimentsarelikelytobesurmountedwiththemoderndayelectronictechnology.Itwasalsodecidedtomeasurethehumidityoftheoutgoingwarmairinadditiontothetemperaturegradientusedinthoseexperiments.Thiswasattemptedinthisstudy.

EXPLANATIONOFTEMPERATUREANDHUMIDITYGRADIENTAPPROACH

Ifawetsampleoffineaggregateissubjectedtodryingwithhotair,thenthefreemoistureonthesurfaceoftheaggregateevaporatesfirst,followedbytheabsorbedwater.Iftheaggregatesaredrieduniformly,paststudieshaveindicatedthatasharpbreakpointcanbeobtainedinaplotof

timeversustemperaturedifference(gradient)ofincomingandoutgoingairatthesaturatedsurfacedrycondition(Figure1)(7).Thedifferentphasescanbeexplainedasfollows.Atthebeginningofthetestthereisasharpdifferencebetweentheincomingandoutgoingairtemperature,sincethetemperatureoftheincomingairisextremelyhigh.Inthesecondphase,theentirechamberordrumisataconstanthightemperature,andthefreewaterfromthesurfaceoftheaggregatesisdrivenoffatarelativelyconstantrate.Thisisindicatedbytherelativelyconstanttemperaturegradient.Inthethirdphasethereisanincreaseinthetemperaturegradient.Thishappensbecauseatthispointthereisaverythinlayerofsurfacewatersurroundingtheaggregateparticles,andtherateofevaporationisveryhigh,higherthanthatinPhase2.Inthefourthphase,thereisasuddenbreakinthecurve,indicatingthatthereisnomorefreesurfacewaterontheaggregate,andhencenomorehighevaporationrateandcoolingrate.Therefore,thesuddenbreakpointindicatesthepointofsaturatedsurfacedry(SSD)condition.Afterthispoint,

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30

25

20

15

10

5

0

0 5 10 15 20 25Time(minutes)

Figure1.TypicalTimeVersusTemperatureGradientPlot

theaggregatesabsorbmoreheat,todriveofftheabsorbedwater,causinganincreaseinthetemperatureoftheoutgoingair.Theincreaseinthetemperatureoftheoutgoingairthereforedecreasesthetemperaturegradient.Hence,thekeythingistostopthetestwhentheaggregate

reachesthesaturatedsurfacedrycondition,bylookingatthetemperaturegradientplotandcapturingthepeak.However,oneimportantthingisthatifthetestisstoppedatthepeak,theaggregateundergoessomeadditionaldryingwhileitisbeingtakenoutandtested.Hence,abettermethodwillbetostopthetestsufficientlyaheadofthepeak,sothattheaggregate,whentestedforweightandvolume,isatthesamestateasitwouldhavebeenatthepeakofthetemperaturegradientplot.

AnotherpossibleapproachthatwastriedbytheresearchersoftheNationalCenterforAsphalt

Technology(NCAT)studyistheanalysisofhumidityofoutgoingair.AnexampleofhumidityofoutgoingairversustimeplotisshowninFigure2.Itisseenthatingeneralthehumidityoftheoutgoingairishighatthebeginningofthetest,thenitdropsoffrapidlyastheaggregatelosesmoisture.Inthenextphasethehumidityincreasesslightly,andultimatelyreachesapeakandthendropsoff.Thispointwhereitdropsoffisconsideredtobethesaturatedsurfacedry

condition.Thedifferentphasescanbeexplainedasfollows.Atthebeginningofthetest,alargeamountofmoistureisdrivenoffbecauseofthehighinletairtemperature.Thehumidityoftheoutgoingairfallsandbecomesconstantastheentirechamberheatsup,andthereisaconstantrateofevaporationfromtheentireaggregatemass.Inthenextphase,becauseofthepresenceofarelativelythinlayerofmoisturearoundaggregateparticles,therateofevaporationincreases,andtheresultanthumidityoftheoutgoingairalsoincreasesandreachesapeak,andthendropsoff.ThepeakindicatesthepointofSSD,beyondwhichthereisnofreemoistureonthesurface.

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Tem

eraturedifference

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70

60

50

40

30

20

10

0

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0Time(minutes)

Figure2.TypicalTimeVersusHumidityPlot

DEVELOPMENTOFTHEFIRSTPROTOTYPETESTEQUIPMENT

ThefirstequipmentwasdevelopedessentiallyonthebasisoftheequipmentthatwasusedbytheresearchersatArizonaDOT(7).Figure3andFigure4showaschematicandaphotooftheequipment.Basically,thedeviceconsistedofarotatingPlexiglasdrum,mountedoncasterwheels,anddrivenbyabeltthroughamotor.Airwasblownwithadryerfan(ahairdryerwasused)atoneendofthedrum,andsensorsfortemperaturewereinstalledateitherendofthedrumformeasuringtemperatureofincomingandoutgoingair.ThedrumwasmadeoutofPlexiglasforconvenienceofviewingtheaggregateinsidethedrumduringtesting.Twoflightsintherotatingdrumprovidedreasonablyconsistentdryingofthetestsample.Thisdrumalsoutilizeda"bumping"deviceinitsrollerstoreducetheamountoffinesstickingtothewallsofthedrum.Thesampleoffineaggregatewasconfinedinthedryerdrumbyutilizingscreensonboththeinletandoutletsidesofthedrum.Asampleofabout1300gramswasusedin

allexperiments.Thisgivesatleast500gramsfordeterminingtheweightandvolumeoftheSSDsample,andatleast500gramsforobtainingtheoven-dryweightoftheSSDsample.Thetemperaturesensorsweremonitoredandrecordedona30-secondcycleduringtestingforestablishingtheSSDcondition.

Initially,naturalsandwassubjectedtothedryingprocessinthefirstprototypeequipment.

TemperaturegradientversustimeplotsfromtestswitheightsamplesofnaturalsandareshowninFigure5.Theplotsshowexpectedtrendsasdiscussedearlier.However,thedatawasnotveryconsistent,andthepeaksindicatingSSDconditionarenotwithinasmallrangeoftimeforthedifferentsamples.Thesamplesweretakenoutattheobservedpeakandtestedforspecificgravity.Comparisonsamplesofthesamenaturalsandweretestedwiththesandconemethod(ASTMC128)forspecificgravity.TheresultsfrombothtestsareshowninTable1(firstset).

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Humidito

foutoin

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6

Fiure3.

Schematicoft

heFirstProtot

eTestE

ui

ment


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Figure4.PhotographoftheFirstPrototypeTestEquipment

Figure5.TimeVersusTemperatureGradientPlotsforEightSamplesofNaturalSand (FirstPrototypeTestEquipment)

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Kandhal,Mallick,&HunerTheobservationswerethatthesamplesweremostlytoowetwhentakenout,indicatingthattheSSDconditionhadnotbeenreachedyet,orthesamplesweretoodry,indicatingthatthesampleswerepastthepointofSSD.ItseemedthattheSSDconditionwasbeingaffectedbytheinletair

temperature,andtheamountofsandthatwasstickingtothesidesoftheinsidewalloftherotatingchamber.Itwasdecidedtostopthetestatthebaseofthepeakofthetemperaturegradientplotandtakeoutthesampleandtestthem.Thecriterionfordeterminingthebaseofthepeakwasatleasta1-degreeincreaseintemperature.However,specificgravitiesandabsorptionofsamplesrunthiswaydidnotmatchwithspecificgravitiesandabsorptionrunbythesandconemethod(Table1,secondset)andinbothcasesthesampleswerefoundtobeoverdried.Theconclusionwasthattousethismethodsuccessfully,theresultsshouldbemoreconsistent,andthereshouldbearationalandpracticalmethodofidentifyingtheapproachingSSDconditionandstoppingthetestattherighttimeforspecificgravitydetermination.Fromtheresultsofthisphaseofthestudy,thefollowingconclusionsweremade:

1.Thetemperaturegradientversustimeplot,althoughconsistentwiththeory,didnotseemtobeareliablemethodofpredictingtheSSDcondition.

2.Therewastoomuchstickingoffineparticlesontheinsideofthedrum,whichcouldaffecttheresultssignificantlybyresultinginnon-uniformdryingofthesand.3.SomeofthesandwasbeingblownoutneartheSSDcondition,resultinginlossof

materials.4.Thedrumhastobere-designedinsuchawaythatthesamplecanbetakenout

immediatelyafterachievingtheSSDconditionformeasuringitsweightandvolume.Withthefirstprototype,ittook3-5minutestodisassemblethedrumandgetthesampleout.

Table1.ComparisonofSpecificGravityandAbsorptionData(FirstPrototypeTest

Equipment)

Sample NewMethod(Drum) SandConeMethod Observation

AbsorptionSpecific Absorption SpecificGravity Gravity

FirstSet

1 0.482 2.472 0.583 2.616 Toowet2

3.219 2.443 0.624 2.618 Toowet3

2.311 2.501 Toowet4 0.040 2.650Too

dry

5 0.664 2.605 Slightlywet

SecondSet

1 0.09 2.649 0.583 2.616 Toodry2

0.10 2.649 0.624 2.618 Toodry

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SECONDPROTOTYPETESTEQUIPMENT

Torectifytheproblemsencounteredwiththefirstprototypeequipment,thesecondprototype(Figures6and7)wasmadewiththefollowingchangesandmodifications:

1.Thedryerdrumwasmadeoutofpolishedaluminumratherthanplexiglass.Gearsandrollersimprovedtherotationsystem.Thismadetheoveralldevicesturdier,moredurable,andeasiertoworkwith.

2.Thedrumconsistedofthreesegmentswith"quick-snap"clampstoholdittogether.Also,theconfigurationofthesecondprototypedeviceallowsthedrumitselftobequicklymountedorremovedfromtheroller/dryersystem.Thesetwochangesenabletheoperatortobreakdownthesystemanddruminapproximately20-30seconds,minimizingthetimebetweenachievingSSDconditionandphysicallyobtainingtheSSDsamplefortesting.

3.Thefirstprototypehadscreensgluedintothedrumandthesescreenscouldnotbechangedeasily.Thesecondprototypeutilizesscreeninsertsthatcanbechangedquickly.Sincethisdeviceisstillunderdevelopment,theabilitytochangescreen

sizesisnecessary.4.A"tapping"devicecontactingtheoutsidewallofthealuminumdrumwasinstalledinthesecondprototypetoshakeofffinesstickingtotheinteriorofthedrum.Thefirstprotoypeuseda"bumping"device.Thealuminumdrumwasalsocoatedwithteflontoreducethestickingoffinestothewallofthedrum.

5.Avariablespeedmechanismwasprovidedtovarytherotationalspeedofthedrumduringthedevelopmentalstage.

Preliminarytestsindicatedthattherewasnosignificantstickingofsandontheinsidesurfaceof

thenewdrum.However,therewassomesignificantblowingoffineswhichblindedthescreenresultinginariseintheairtemperatureinsidethedrum.ItwasinterestingtonotethatthescreenblindingproblemwasoccurringataboutthesametimethesamplewasachievingtheSSDcondition.Becauseoftheblindingproblem,thetestswerecompletedonplus0.6mmmaterial

onlytoprovethattheconceptworks.

Sincetheplotsoftemperaturegradientversustimedidnotprovideadistinctwayofidentifying

theSSDconditioninthefirstsetoftests,itwasdecidedtoobservebothtemperaturegradientandrelativehumidityoftheoutgoingair.TypicalplotsoftimeversusrelativehumidityforfivedifferentfineaggregatesareshowninFigure8.Thedatawasanalyzed,anditwasobservedthatthetrendofthehumidityplotismoreconsistentforaparticularaggregatethanthetrendofthetemperaturegradientplot.AsTable2shows,thepointatwhichthepeakhumiditywasreachedissignificantlymoreconsistentthanthepointatwhichthepeakofthetemperaturegradientwasobserved.ASSDcriteriawasestablishedtotaketheaggregateoutwhenthereweretwosuccessivedecreasesinrelativehumidity.Themagnitudeofthesetwosuccessivedecreasesgenerallyrangedfrom1to2percentasshowninthefifthcolumnofTable2.Specificgravitieswererunwiththisaggregate,andthevalueswerecomparedtothevaluesobtainedbythesand

conetestmethod.Tables3and4showthedataofwaterabsorptionandbulkspecificgravityofsamples,respectively,testedbythenew(drum)methodandbythesandconemethod.ComparisonsofaveragevaluesandstandarddeviationofwaterabsorptionvaluesareshowninFigures9and10,respectively.ComparisonofaveragevaluesandstandarddeviationofbulkspecificgravityvaluesfrombothtestsareshowninFigures11and12.

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Fiure6.

SchematicoftheSecondProtot

eTestEu

iment


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Figure7(a).PhotooftheSecondPrototypeEquipment

Figure7(b).PhotooftheSecondPrototypeEquipmentwiththeData AcquisitionSystem

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80

70

60

50

40

30

20

10

SS M10 LMS FA2 FA4 FA5 FA900.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Time(minutes)

Figure8.TypicalTimeVersusHumidityPlotforSevenDifferentAggregates(Second PrototypeEquipment)

Table2.TimeVersusPeakHumidityandPeakTemperatureGradientData(Second

PrototypeTestEquipment)FineAggregate

Granite

ShorterSand(Natural)

Sample1

2

3

4

5

6

7

8

9101

2

3

4

5

6

7

8

910

PeakTimeVersusHumidity(minutes)

10.08.5

9.5

9.0

9.5

8.5

9.0

9.5

8.5

9.511.5

13.01112.5

12.0

12.5

11.0

13.0

11.0

12.0

PeakHumidity(percent)

54

57

52

54

54

52

53

53

53

54

52

50

50

52

51

51

49

53

52

52

)BetweenTwoSuccessiveHumidityReadingsAfterPeak(-veindicatesdrop),%-1,-2-

1,-1-

1,-2-

1,-1-

2,-2-

1,-1-

2,-2-

1,-2-

1,-1-

1,-2-

1,-2-

1,-3-

1,-2-

1,-1-

1,-1-

1,-1-1,-1-

1,-1-

1,-1-

1,-1

PeakTimeVersusTemperatureDifference(minutes)

11.0

8.0

9.510.0

9.5

7.0

9.0

9.5

8.5

9.011.5

14.01113.5

13.0

12.0

12.0

14.0

11.5

13.0

PeakTemperatureDifference(C)

20.7

19.3

20.1

20.2

20.9

20.8

20.2

21.8

20.7

20.3

20.1

20.4

20.1

20.1

20.3

20.2

18.8

20.3

20.0

20.8

)BetweenTwoSuccessiveTemperatureReadingsAfterPeak(C)TestStopped-0.3,0.1-0.1,-0.55TestStopped-0.2,-0.2-

0.3,0.1-

0.2,-0.1-

0.55,-0.9-0.2,0.1-

0.1,0.1-

0.4,-0.1TestStopped-0.3,0TestStopped

TestStopped-0.4,0TestStopped

TestStopped-0.2TestStopped

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Relativehumidity(%)


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Kandhal,Mallick,&HunerTable2.TimeVersusPeakHumidityandPeakTemperatureGradientData(Second

PrototypeTestEquipment)Fine Sample Peak Peak )BetweenTwo PeakTime Peak )BetweenAggregate Time Humidity Successive Versus Temperature Two

Versus (percent) Humidity Temperature Difference SuccessiveHumidity ReadingsAfter Difference (C) Temperature(minutes) Peak(-ve (minutes) Readings

indicatesdrop), AfterPeak% (C)

Sandstone 1 10.0 49 -3 10.5 19.5 TestStopped2 8.5 49 -1,-2 7.5 18.2 -0.4,-0.13 6.0 47 -1,0 6.0 18.5 -0.5,0.14 8.0 48 -1,-1 8.0 17.9 -0.7,-0.15 7.5 51 -1,-2 8.0 19.1 -0.6,0.36 7.0 50 -1,0 6.5 18.8 -0.2,-0.17 7.0 54 -1,0 6.5 18.6 -0.3,-0.18 8.0 51 -1,-1 8.5 16.9 -0.69 7.5 51 -1,-1 8.5 17.6 TestStopped10

7.5

53

-1,-2

6.5

18.4

-0.5,0.2Diabase 1 8.5 49 -2,-2 7.5 20.8 -0.55,-0.6

2 7.5 47 -2,-3 7.5 19.2 -0.3,-0.13 7.5 49 -1,-2 7.5 20.1 -0.5,0.14 7.0 50 -1,-2 6.0 20.3 -0.1,-1.45 7.0 51 -2,-4 5.5 20.7 -0.3,-0.1

Dolomite 1 10.0 54 -1,-1 10.5 20.5 -0.62 9.5 53 -1,-1 10.5 20.2 TestStopped3 9.0 53 -1,-2 10.0 21.1 TestStopped4 8.5 52 -1,-1 8.0 20.4 -0.5,0.45 8.5 52 -1,-1 7.5 20.2 -0.1,-0.5

Limestone 1 9.5 57 -1,-1 7.5 20.3 0.2,-0.12 9.0 56 -1,-1 7.5 19.5 -0.7,03 10.5 56 -1,-3 9.0 19.6 -0.1,-0.14

11.0

55

-1,-2

8.5

18.5

-0.3,-0.25 7.5 53 -1,-1 7.5 20.7 -0.8,0.5

Quartz 1 8.0 54 -1,-1 8.5 20.9 -0.55Sand 2 7.0 56 -1,-1 8.0 20.4 TestStopped

3 7.0 53 -1,-1 7.5 19.7 -0.24 6.0 53 -1,-1 5.5 19.6 -0.1,-0.55 7.5 53 -1,-2 8.0 21.3 -0.6

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Table3.ComparisonofAbsorptionData(SecondPrototypeTestEquipment)

Shorter Granite Limestone FineAgg#2 FineAgg#4 FineAgg#5 FineAgg#9SampleSand Screenings Screenings QuartzSand Sandstone Dolomite DiabaseNumber(46.0)* (49.3)* (45.8)* (42.6)* (49.7)* (50.3)* (50.1)*

ConeDrumConeDrumConeDrumConeDrum ConeDrumConeDrum ConeDrum

1 0.46 0.60 0.58 0.76 0.77 0.80 3.20 2.20 1.33 1.81 0.62 1.10 1.21 1.55

2 0.52 0.32 0.42 1.00 0.68 0.74 2.73 2.69 1.44 1.72 0.68 1.05 1.27 1.56

3 0.48 0.40 0.52 1.15 0.70 0.75 3.02 2.60 1.38 1.84 0.64 0.95 1.15 1.59

4 0.38 0.54 0.64 0.93 0.70 0.62 2.86 3.27 1.36 1.62 0.72 1.12 1.40 1.64

5 0.36 0.48 0.40 1.18 0.83 0.83 2.79 2.49 1.45 1.24 0.68 1.32 1.15 1.47

6 0.38 0.50 0.62 0.99 1.56 1.70

7 0.40 0.42 0.56 0.84 1.48 1.49

8 0.38 0.46 0.58 1.15 1.58 1.71

9 0.42 0.36 0.56 0.88 1.23 1.92

10 0.26 0.56 0.64 0.96 1.56 1.70

Average0.400.46 0.55 0.98 0.74 0.75 2.92 2.65 1.44 1.68 0.67 1.11 1.24 1.56

Std. 0.070.09 0.08 0.14 0.06 0.08 0.19 0.39 0.11 0.19 0.04 0.14 0.10 0.06Dev.

*Thevaluesinparenthesesarefineaggregateangularity(FAA)valuesinaccordancewithAASHTOT304,MethodA.

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3.50

Cone Drum

3.00 2.92

2.502.001.501.000.50

0.00

0.400.46

0.55

0.98

0.740.75

2.65 1.44

1.68

0.67

1.11

1.24

1.56

ShorterSand Granite Limestone FineAgg#2 FineAgg#4 FineAgg#5 FineAgg#9Screenings Screenings

Aggregate

Figure9.ComparisonofAverageWaterAbsorptionData(SecondPrototypeTest Equipment)

0.45

Cone Drum

0.40 0.39

0.35

0.30

0.25

0.20 0.19 0.19

0.15 0.14 0.14

0.110.1

0.10 0.09

0.05

0.00

0.07 0.08 0.06

0.08

0.04

0.06


Aggregate

Figure10.ComparisonofStandardDeviationofWaterAbsorptionData(Second

PrototypeTestEquipment)

16

Avera

ewaterabsortion(%)

StandardDeviation(%)


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3

Cone2.9

2.8

2.7

Drum

2.6942.694

2.6852.674

2.795

2.691

2.891

2.86

2.659

2.632.6132.608

2.6

2.5

2.4462.458

2.4

2.3

2.2


Aggregate

Figure11.ComparisonofAverageBulkSpecificGravity(SecondPrototypeTest Equipment)

0.0350.03

0.0250.02

0.015

Cone

Drum

0.0136

0.023

0.032

0.011

0.010.01 0.009

0.008

0.0070.007 0.006 0.006 0.006

0.005 0.0040.003

0


Aggregate

Figure12.ComparisonofStandardDeviationofBulkSpecificGravity(Second PrototypeTestEquipment)

17

Avera

ebulks

ecific

ravit(

%

StandardDeviation(%)


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Theaveragebulkspecificgravityvalueofthenatural(Shorter)sandobtainedfromthedrumtest

method(proposednewmethod)isnotsignificantlydifferentfromthevalueobtainedfromtestswiththecone(currentlyused)method.Thesandconemethodisbelievedtoworkbestwithnaturalsandsand,therefore,itisencouragingtoseethatbothmethodsgivesimilartestresults

(Table4,Figure11).Thewaterabsorptionvaluesofcrushedfineaggregates(Table3,Figure9)aregenerallylowerincaseofsandconemethodcomparedtodrummethod.Thisobviouslyresultsfromoverdryingofthecrushed,angularfineaggregatestocausetheslump.Theresultingbulkspecificgravityvaluesare,therefore,higherincaseofsandconemethodcomparedtodrummethod(Table4,Figure11).

Tables3and4alsogivethefineaggregateangularity(FAA)valuesforthesevenfineaggregates

used.Itisinterestingtonotethattheaveragewaterabsorptionandbulkspecificgravityvaluesobtainedfrombothmethodsarenotsignificantlydifferentforthreefineaggregates(shortersand,limestone,andquartzsand)withFAAvaluesof46.0orless.ThedifferencesaresignificantfortheremainingfourfineaggregateswithFAAvaluesofmorethan49.HigherFAAvaluesindicatemoreangularandroughtexturedaggregate.Therefore,theapparentbulkspecific

gravityvaluesobtainedbythesandconemethodforaggregateswithhighFAAvaluesmaynotbethetrueoractualbulkspecificgravityvalues.

However,thestandarddeviationvaluesfromthedrummethodareslightlygreaterthanthe

standarddeviationvaluesfromtheconetestmethodincaseoffouroutofsevenaggregates(Table4,Figure11).ThiscanprobablybeattributedtothefactthatthestoppingofthetestattheSSDconditionisdonemanually,andthetimetakentoobservethehumiditydata,stopthetest,andtransportthematerialfortestingcancausesignificantvariationinthesubsequenttesting.Anidealapproachwouldtobetoautomatethetestcompletely,sothatthedrumstopsautomaticallyoncetheSSDconditionisreached.

Itisproposedtobuildathirdprototypeequipmenttoaccomplishthefollowing:

1.Preventthescreenfromblindingsothattheentirefineaggregate(retainedon75:m

sieve)canbetested.Onesuggestionistoincreasethesurfaceareaofthescreenbyusingasphericalscreen.2.AutomatetheequipmentsothatitshutsdownwhentheSSDconditionisreached.3.Enhancethecapabilityofthepersonalcomputeralreadyinusetoautomatethedata

acquisitionsystem.

EquipmentmanufacturerswereinvitedtobuildthecommercialversionoftheNCAT'sSSD

devicereportedinthispaper,whichwillbeevaluatedbyNCAT.Ifthecommercialversionhasthecapacityofcontinuouslymonitoringthemassofthefineaggregatewhileitisdryinginthedrum,thesampledoesnothavetobetakenoutofthedrumforweighingwhenitreachestheSSDcondition.Thedryingcanthencontinueuntilthesampleiscompletelydrytoobtainitsdrymasswhileinthedrum.ThedifferencebetweentheSSDmassandthedrymassisthewaterabsorptionofthefineaggregate.Theapparentspecificgravityoftheaggregate,whichdoesnot

involvetheSSDconditionandisreasonablyreproducible,canbemeasuredinaseparatetest.Thebulkspecificgravityofthefineaggregatecanbecalculatedbyaformulausingitspercentwaterabsorption,obtainedintheNCATSSDdeviceanditsapparentspecificgravity.

CONCLUSIONSANDRECOMMENDATIONS

Ithasbeendemonstratedthattheconceptofmonitoringthetemperaturegradientofincomingandoutgoingairorrelativehumidityoftheoutgoingair,whileasampleofwetfineaggregateisdriedinarotatingdrum,canbeusedtoestablishthesaturatedsurfacedry(SSD)conditionofthefineaggregate.ThehumidityoftheoutgoingairappearstoestablishtheSSDconditionmoredistinctlythanthetemperaturegradient.

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ThesecondprototypedevicebuiltbytheNationalCenterforAsphaltTechnology(NCAT)

surmountedmanyproblemsencounteredinthefirstprototypedevice.However,blindingofthescreenassoonastheSSDconditionisachievedstillremainstobeaproblem.Also,thedeviceneedstobeautomatedfurthersothatitshutsdownassoonasthecriteriafortheSSDcondition

ismet.Thiswillenhancetherepeatabilityandreproducibilityofthetest.Athirdprototypedevice,therefore,needstobeconstructedandevaluatedassoonaspossible.Ifthedevicehasthecapacityofcontinuouslymonitoringthemassoffineaggregatewhileitisdryinginthedrum,thesampledoesnothavetobetakenoutofthedrumforweighingwhenitreachestheSSDcondition.

ThisresearchprojectwasfundedbytheFederalHighwayAdministrationunderthecooperative

agreementwithAuburnUniversity.REFERENCES

1.2.

3.

4.

5.

6.

7.

8.

Howard,E.L.Discussion,Proc.Am.ConcreteInst.,Vol.54,1958,p.1215.Pearson,J.C.ASimpleTitrationMethodforDeterminingtheAbsorptionofFineAggregate.RockProducts,Vol.32,1929,p.64.Martin,J.R.TwoYearsofHighwayResearchatOklahomaA.andM.Proc.AAPT,Vol.19,1950,pp.41-54.Saxer,E.L.ADirectMethodofDeterminingAbsorptionandSpecificGravityofAggregates.RockProducts,Vol.87,1956,pp.77-79.Hughes,B.P.,andBahramian,B.AnAccurateLaboratoryTestforDeterminingtheAbsorptionofAggregates.MaterialsResearchandStandards,1967,pp.18-23.Kandhal,P.S.andD.Y.Lee.AnEvaluationoftheBulkSpecificGravityforGranularMaterials.HighwayResearchRecord307,1970,pp.44-55.Dana,J.S.andR.J.Peters.ExperimentalMoistureDeterminationforDefiningSaturatedSurfaceDryStateofHighwayAggregates.ArizonaHighwayDepartment,ReportNo.6,

HPR1-11(153),June1974.Krugler,P.E.,M.Tahmoressi,andD.A.Rand.ImprovingthePrecisionofTestMethodsUsedinVMADetermination.AsphaltPavingTechnology,Volume61,1992,pp.272-303.

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Development of a New Test Method for Measuring Bulk Specific Gravity of Fine Aggregate

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