effect of aggregate gradation on measured asphalt content
TRANSCRIPT
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EFFECTOFAGGREGATEGRADATIONONMEASUREDASPHALT CONTENT
By
PrithviS.Kandhal
AssistantDirectorNationalCenterforAsphaltTechnology
AuburnUniversity,Alabama
StephenA.Cross
AssistantProfessorUniversityofKansas
PaperpublishedinTransportationResearchBoard,TransportationResearchRecord1417,1993
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DISCLAIMER
Thecontentsofthisreportreflecttheviewsoftheauthorswhoaresolelyresponsibleforthefactsandtheaccuracyofthedatapresentedherein.ThecontentsdonotnecessarilyreflecttheofficialviewsandpoliciesoftheNationalCenterforAsphaltTechnologyofAuburnUniversity.Thisreportdoesnotconstituteastandard,specification,orregulation.
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ABSTRACT
Itisnecessarytocontroltheasphaltcontentcloselyinhotmixasphalt(HMA)mixestoobtainoptimumserviceabilityanddurability.However,coarsermixes(binderandbasecourses)madewithlargermaximumparticle-sizedaggregatetendtosegregate,TheresultingvariationintheaggregategradationofthesampledHMAmixcansignificantlyaffectthemeasuredasphaltcontent.Theobjectiveofthisresearchwastoevaluatetheeffectofaggregategradationonthemeasuredasphaltcontent.
Actualmixcomposition(asphaltcontentandgradation)datafromamajorinterstatepaving
projectwasobtainedandanalyzed.Atotalof547bindercourseand147wearingcoursemixsampleswereobtainedbehindthepaverandsubjectedtoextractionanalysis,Asubstantialamountofsegregationwasobservedinthebindercoursemixwhichprovidedtheopportunitytocorrelatetheaggregategradationwiththemeasuredasphaltcontent.
Someofthedeviationinthemeasuredasphaltcontentofthebindercoursemixesfromthejobmixformula(JMF)wasdeterminedtobetheresultofthechangeingradationofthemixfromtheJMF.Thepercentagesofmaterialpassingthe4.75mm(No.4)and2.36mm(No.8)sievesarecorrelatedwithmeasuredasphaltcontents.Forsegregatedbindercoursemixesevaluatedinthisstudy,equationsweredevelopedtoadjustthemeasuredasphaltcontenttoaccountforthechangeingradationfromtheJMFasmeasuredonthe12.5mm(1/2inch)andeither4.75mm(No.4)or2.36mm(No.8)sieves.
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EFFECTOFAGGREGATEGRADATIONONMEASUREDASPHALTCONTENT
PrithviS.KandhalandStephenA.Cross
INTRODUCTIONAsphaltcontentmustbecloselycontrolledinhotmixasphalt(HMA)mixestoobtainoptimumserviceabilityanddurability.AHMApavementcanraveland/orcrackifitisdeficientinasphaltcontentbyaslittleas1/2percent,whereas1/2percentexcessiveasphaltcontentcancauseflushingandrutting.Qualitycontrol(QC)andqualityassurance(QA)ofHMApavementsgenerallyrequirethemeasurementofasphaltcontentinHMAmixesduringproductionusingeitherastandardextractiontestoranuclearasphaltcontentgauge.However,themeasuredvaluecanvaryfromtesttotestbecauseofmaterial,sampling,andtestingvariability.Inrecentyears,thematerialvariabilityhasbeenreducedsubstantiallybytheuseofautomatedHMAfacilities.Testingproficiencycanbeimprovedthroughtraining.ObtainingarepresentativeHMAsamplefortestingstillremainsaproblemeitherbecauseofsegregationorineffectivesampling/splittingtechniques.Whencoarsermixes(binderandbasecourses)madewithlargermaximumparticle-sizedaggregatesareinvolved,thesamplingvariationcanovershadowthematerialvariationandtestingvariation.CoarseHMAmixestendtosegregate.ThecoarseaggregatefractionintheHMAmixholdslessasphaltcementbyweightcomparedtothefineaggregatefraction,Segregationcausestheproportionsofcoarseandfineaggregateparticles(therefore,thegradation)tovaryinHMAsamplesandthusaffectthemeasuredasphaltcontents.ThereisaneedtoevaluatetheeffectofaggregategradationonmeasuredasphaltcontentsothatanadjustedasphaltcontentwhichisclosertotheasphaltcontentactuallyincorporatedintheHMAmix,canbeascertained.
PROJECTDETAILSThetestdataforthisstudywasobtainedfromamajor4-laneinterstatepavingprojectinPennsylvania.Thisrehabilitationprojectinvolved50.8mm(2inches)ofPennsylvaniaID-2bindercourse(adensegradedbindermixwith38,1mmor11/2inchmaximumaggregatesize)and38.1mm(11/2inches)ofPennsylvaniaID-2wearingcourse(adensegradedwearingmixwith12.5mmor1/2inchmaximumaggregatesize).Thejob-mixformulas(JMF)forthebinderandwearingcoursemixturesaregiveninTables1and2,respectively.Northbound(NB)andsouthbound(SB)laneswerepavedwithseparatepavers.SincethemixacceptanceorQAsampleswereobtainedbehindeachpaverseparately,thetestdatahasbeenreportedandanalyzedseparatelyforNBandSBlanes.PennsylvaniaDepartmentofTransportation(PennDOT)hasastatisticallybasedendresultspecificationforHMApavements
whichrequiresobtainingloosemixsamplesbehindthepaveratrandomlocations.Theentireloosemixisscrapedoutofawelldefinedarea(usually229mmx229mmor9inchesx9inches)attheselectedrandomlocationtominimizesegregationduetosamplingoperation.Fiveloosemixsubletsamplesareobtainedforeachlotconsistingofabout500Mg(550tons).ThesesamplesaresenttoPennDOTcentrallaboratoryforextractiontodeterminethemixcomposition.Roadwaycoresarealsoobtainedaftercompactionandsenttothecentrallaboratoryfordeterminingthepavementdensity.Priceadjustmentsforeachlotarecalculatedbythecentrallaboratorythepercentageofmaterialpassing75:mbasedonthreepayitems:asphaltcontent,(No.200)sieve,andtheroadwaydensity.
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Table1.SummaryStatisticsforBinderMixes
TestParameter
JMF NBLanes
n=271
SBLanes
n=276
All
n=547
Mean Std.Dev. Mean Std.Dev. Mean Std.Dev.
Asphalt 4.8 4.70 0.429 4.66 0.416 4.68 0.422Content(%)
Density(pcf) N/A 153.6 1.69 153.5 1.96 153.6 1.83
1-1/2inch 100 99.9 0.77 100.0 0.00 100.0 0.54(%)
1inch(%) 92 92.2 6.74 91.9 5.16 92.0 5.99
1/2inch(%) 56 63.0 8.32 62.2 7.78 62.6 8.05
No.4(%) 39 40.4 5.19 42.7 5.81 41.5 5.63
No.8(%) 30 30.8 3.77 32.3 4.07 31.6 4.00No.16(%) 19 22.1 2.70 22.2 2.81 22.2 2.75
No.30(%) 12 16.3 2.27 15.7 2.16 16.0 2.23
No.50(%) 8 11.2 1.67 10.5 1.69 10.8 1.71
No.100(%) 6 7.59 0.984 7.42 1.094 7.51 1.044
No.200(%) 4.8 5.34 0.693 5.37 0.807 5.36 0.752
Table2.SummaryStatisticsforWearingMixes
Test
Parameter
JMF NBLanes
n=67
SBLanes
n=80
All
n=147Mean Std.Dev. Mean Std.Dev. Mean Std.Dev.
Asphalt 6.6 6.37 0.270 6.45 0.342 6.41 0.313Content(%)
Density(pcf) N/A 143.6 2.38 142.5 2.70 143.0 2.61
1/2Inch(%) 100 100.0 0.00 100.0 0.00 100.0 0.00
3/8Inch(%) 96 96.6 1.43 96.8 1.48 96.7 1.46
No.4(%) 72 70.8 4.35 71.8 3.36 71.3 3.86
No.8(%) 48 49.4 3.82 49.8 2.35 49.6 3.10
No.16(%) 34 35.0 2.49 34.9 1.49 34.9 2.00No.30(%) 24 25.7 1.88 25.5 1.17 25.6 1.53
No.50(%) 16 16.4 1.83 16.6 1.36 16.5 1.59
No.100(%) 10 9.28 1.253 9.54 0.913 9.42 1.085
No.200(%) 4.5 5.54 0.779 5.57 0.654 5.56 0.711
Atotalof547bindermixsamples(271inNBlanesand276147wearingmixsamples(67inNBlanesand80inSBlanes)wereinSBlanes)andobtainedbehindthepaverandtestedbythecentrallaboratory.
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Asubstantialamountofsegregationwasobservedinthecompactedbindercoursemixofthis
projectapparentlyduetomixhandlingandplacingoperations.Obviously,themixgradationofsubletsamplesobtainedbehindthepavervariedconsiderablyanditaffectedtheextractedasphaltcontent.Sincealargenumberofbindermixsampleswereobtainedatrandomlocations
behindthepaveronthisprojectandwereanalyzedformixcomposition(asphaltcontentandgradation),auniqueopportunitywasavailableforevaluatingtheeffectofaggregategradationonthemeasuredasphaltcontents.MaterialproductionvariabilitywasconsideredtobeminimalonthisprojectbecauseanautomatedHMAfacilitywasused,andthemixsamplesobtainedatthefacilitywerereasonablyuniformincomposition.ThetestingvariabilityisalsoconsideredtobeminimalbecauseallextractiontestingwasdoneintheDOTcentrallaboratorybyessentiallythesametestingcrew.ASTMD2172(MethodD)wasusedforextractingtheasphaltcementfromHMAmixsamples.
Itispossibletoconductasimilarstudyinalaboratory.Amixcanbepreparedwithaknown
asphaltcontent,intentionallysegregated,andthenextracted.Thiswouldeliminatetheinherentmaterialvariation.However,itisnotpossibletosimulatethesegregationwhichoccursinthe
field.Also,itisnotpracticaltotestaverylargenumberofsamplesaswasdoneinthisstudy.TESTRESULTS
Duetospacerestrictionsitisnotpossibletoincludethemixcompositiontestdatafor547bindermixsamplesand147wearingmixsamplesinthispaper.However,Tables1and2givethesummarystatisticsforbindermixesandwearingmixes,respectively.Figures1,2,3and4givethecontrolchartsofthetestdataforasphaltcontent,thepercentpassingthe12.5mm(1/2inch),4.75mm(No.4),and2.36mm(No.8)sievesfor271bindermixsamplesobtainedfromtheNBlanesofthepavingproject.ThecontrolchartsofthetestdatafromtheSBlanesaresimilartothoseoftheNBlanesand,therefore,arenotincludedduetospacelimitationsinthepaper.
ANALYSISOFTESTRESULTS
Thepurposeofthisstudywastodeterminetheeffectofachangeingradationonthecorrespondingmeasuredasphaltcontent.Ifastrongcorrelationexistsbetweengradationandasphaltcontent,thenapartofthedeviationfromtheJMFinthemeasuredasphaltcontentcouldbeexplainedbythemeasureddeviationingradation.
Asmentionedearlier,thesummarystatisticsofmeanandstandarddeviationforthequality
assurancedataisshowninTable1forthebindermixesandTable2forthewearingmixes.Forthebindermixes,thestandarddeviationisover5percentforpercentpassingthe25.4mm(1inch),12.5mm(1/2inch)and4.75mm(No.4)sieves,and0.42percentforasphaltcontent.
Table2showslowerstandarddeviationsforthewearingmixesformostsievesizes,andnoneof
thesievesizeshadastandarddeviationover3.9percent.Thestandarddeviationforasphalt
contentwas0.31YOforthewearingmixes.However,areviewofthecontrolchartsshowedthestandarddeviationforasphaltcontentmightbeartificiallyhighduetoanapparentchangeintheJMFasphaltcontentbythecontractorwhichdidnotappearinthetestrecords.
Controlchartsofthetestdataforasphaltcontentandthepercentpassingthe12.5mm(1/2inch),
4.75mm(No.4),and2.36mm(No.8)sievesforthebindermixes(NBlanes)areshowninFigures1-4.Thepermissibletolerancelimitsforthesefourtestparameterswere0.5,8,and6percent,respectively.Tables3and4showthefrequencythattheabovetestparameterswerewithinandoutsidethespecificationtolerancelimitsforthebinderandwearingmixes,respectively.Forthebindermix,asphaltcontentwasoutsidethespecificationlimits23.4percentofthetimeandthepercentpassingthe12.5mm(1/2inch),4.75mm(No.4),and2.36mm(No.8)sieves28.9,20.3,and17.5percentofthetime,respectively.Fromthecontrolchartsandthedata
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Figure1.ControlChartforAsphaltContentinBinderMixes(NBLanes)
Figure2.ControlChartforPassing1/2InchSieveinBinderMixes (NBLanes)
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Figure3.ControlChartforPassingNo.4SieveinBinderMixes(NB Lanes)
Figure4.ControlChartforPassingNo.8SieveinBinderMixes (NBLanes)
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inTable3,itisobviousthatthebindermixsampledfromtheroadwaywasnotuniform.Review
ofthetestdataandvisualobservationsshowedsegregationofthemixtobeamajorproblemonboththeNBandSBlanes.
Table3.FrequencyDistributionofTestDataforBinderMixes
AsphaltContent
PercentPassing1/2InchSieve
PercentPassingNo.4Sieve
PercentPassingNo.8Sieve
InSpec.
Out-Low
Out-High
InSpec.
Out-Low
Out-High
InSpec.
Out-Low
Out-High
InSpec.
Out-Low
Out-High
NBLanes
74.2
15.9
9.9
67.5
9.2
23.3
84.9
1.5
13.6
87.8
2.2
10.0
SBLanes
79.0
16.7
4.3
74.6
9.8
15.6
74.6
1.5
23.9
77.2
1.8
21.0
All
76.6
16.3
7.1
71.1
9.5
19.4
79.7
1.5
18.8
82.5
2.0
15.5
Table4.FrequencyDistributionofTestDataforWearingMixes
AsphaltContent
PercentPassingNo.4Sieve
PercentPassingNo.8Sieve
InSpec.
Out-Low
Out-High
InSpec.
Out-Low
Out-High
InSpec.
Out-Low
Out-High
NBLanes
76.1
23.9
0.00
95.5
3.0
1.5
89.5
1.5
9.0
SBLanes
80.0
12.5
7.5
100.0
0.0
0.0
98.8
0.0
1.2
All
78.2
17.7
4.1
97.9
1.4
0.7
94.5
0.7
4.8
Table4showsthefrequencythatthewearingmixtestparametersofasphaltcontentandthepercentpassingthe4.75mm(No.4)and2.36mm(No.8)sieveswerewithinspecificationtolerancelimits.Thepermissibletolerancelimitsforthesethreetestparameterswere0.4,8,and6percent,respectively.Asphaltcontentwasoutsidethespecificationlimits21.8percentofthetime,andthepercentpassingthe4.75mm(No.4)and2.36mm(No.8)sieves2.1and5.5percentofthetime,respectively.Reviewofthecontrolchartsandtestdatashowedthatthegradationofthemixwaswithinprojectlimits95percentofthetime.SomeofthescatterinasphaltcontentoccurredwhenthecontractorloweredtheasphaltcontentontheNBlanesfrom6.6percenttoapproximately6.2percentafter35tests.However,theavailabletestdatadidnotshowacorrespondingchangeintheJMFasphaltcontent.IftheJMFhadbeenchangedto6.2percent,asthedataindicates,andtheapplicabletoleranceof0.4percentapplied,thepercentof
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theasphaltcontenttestswithinspecificationlimitswouldchangefrom76.1percentto97.0
percentfortheNBlanesandfrom78.2percentto87.8percentforallofthedata.
Correlationanalysiswasperformedtodetermineifthematdensityorthepercentagespassing
varioussievesizescorrelatewithasphaltcontent.Table5showstheresultsofthecorrelationanalysisforthebindermixes,bylane,andwithallofthedata.Theresultsshowalloftheparametersexceptunitweight(densityofthecoresamples)andpercentpassingthe38.1mm(11/2inch)sievehaveahighprobabilityofatruecorrelation(alpha=0.0001)withasphaltcontent.Thebestcorrelationswithasphaltcontentforthebindermixeswerewiththepercentpassingthe4.75mm(No.4)and2.36mm(No.8)sieves.
Table5.SummaryofCorrelationCoefficients(R)withAsphaltContentforBinderMixes
Parameter
R
NBLanes
n=271
Alpha*
R
SBLanes
n=276
Alpha*
R
All
n=547
Alpha*
Density 0.121 0.0474 -0.033 0.589 0.040 0.354611/2Inch 0.056 0.3577 N/A N/A N/A N/A1
Inch 0.413 0.0001 0.517 0.0001 0.455 0.0001
1/2Inch 0.649 0.0001 0.790 0.0001 0.716 0.0001
No.4 0.822 0.0001 0.842 0.0001 0.800 0.0001
No.8 0.819 0.0001 0.825 0.0001 0.795 0.0001
No.16 0.738 0.0001 0.682 0.0001 0.707 0.0001
No.30 0.635 0.0001 0.556 0.0001 0.597 0.0001
No.50 0.586 0.0001 0.457 0.0001 0.521 0.0001
No.100 0.640 0.0001 0.474 0.0001 0.554 0.0001
No.200 0.611 0.0001 0.476 0.0001 0.535 0.0001*1-Alpha=Probabilitycorrelationcoefficient(R)notequalto0. TheresultsofthecorrelationanalysisforthewearingmixesareshowninTable6.Theanalysisshowsthehighestprobabilityofatruecorrelation(alpha=0.0001)withasphaltcontentforthe
percentpassingthe300 :m2(No.50),150:m(No.100)and75:m(No.200)sieves.However,the
correlationcoefficients(R)arenotonlytoolowtobeuseful,theyindicateanunexpectedtrend,thatis,theasphaltcontentdecreaseswithincreaseinthematerialpassingthesesieves.
Tofurtherinvestigatetherelationshipbetweenasphaltcontentandgradation,regressionanalysiswasperformed.Thepurposeofthisstudyistodetermineifasphaltcontentcouldbepredictedfrommeasuredgradation;therefore,asphaltcontentwasselectedasthedependentvariableandgradationtheindependentvariable,Table7isasummaryofthebestcoefficientsofdetermination(R2),bylaneandbymixtype,forthebinderandwearingmixes.
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Table6.SummaryofCorrelationCoefficients(R)withAsphaltContentforWearingMixes
Parameter
R
NBLanes
n=67
Alpha*
R
SBLanes
n=80
Alpha*
R
ALL
n=147
Alpha*
Density -0.022 0.8577 -0.003 0.9807 -0.038 0.6489
1/2Inch N/A N/A N/A N/A N/A N/A
3/8Inch 0.443 0.0002 0.114 0.3135 0.247 0.0025
No.4 -0.106 0.3942 0.073 0.5174 0.009 0.9144
No.8 -0.165 0.1824 0.124 0.2716 -0.014 0.8653
No.16 -0.113 0.3637 0.242 0.0307 0.050 0.5495
No.30 -0.264 0.0308 0.078 0.4940 -0.101 0.2229
No.50 -0.418 0.0004 -0.330 0.0028 -0.345 0.0001
No.100 -0.326 0.0071 -0.490 0.0001 -0.375 0.0001
No.200 -0.257 0.0356 -0.522 0.0001 391 0.0001*1-Alpha=Probabilitycorrelationcoefficient(R)notequalto0. ThedatainTable7indicatesthatnocorrelationexistsbetweenasphaltcontentandthepercentpassingthe4.75mm(No.4)and2.36mm(No.8)sievesforthewearingmix.Thereisverylittlespreadinthegradationdata,andnosegregationwasobservedinthefield.Therefore,allofthescatterappearstobeduetothenormalvariationinthematerial,samplingandtestingoperations.
Table7.SummaryofCoefficientsofDetermination(R2)withAsphaltContentfor
Id2Mixes
NumberofObservations
IndependentVariable
1/2InchSieve
No.4Sieve
No.8Sieve
1/2Inch&No.4Sieves
1/2Inch&No.8Sieves
No.4Sieve
No.8Sieve
N13Lanes
n=271
R2
0.422
0.676
0.671
0.686
0.685
0.011
0.027
SBLanes
n=276
R2
ID2BinderMixes
0.625
0.708
0.680
0.722
0.729
ID2WearingMixes
0.005
0.016
All
n=547
R2
0.515
0.640
0.632
0.669
0.676
0.000
0.000
Figures5and6showtherelationshipbetweenasphaltcontentandthepercentpassingthe4.75mm(No.4)and2.36mm(No.8)sievesforthebindermixinbothlanes,respectively.Theresultsshowthatthereisarelationshipbetweenchangeingradationandmeasuredasphaltcontent.Therelationshipsshowthatasthemixbecomesfinerforthegivensievesize,theasphaltcontentincreases.Therelationshipshavethefollowingform:
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Figure5.PercentagePassingNo.4Sievevs.AsphaltContent(BinderMixesfromBothLanes)
Figure6.PercentagePassingNo.8Sievevs.AsphaltContent(BinderMixesfromBothLanes)
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AC=2.186+0.060(P4) (1)
R-square=0.64
AC=2.025+0.084(P8) (2)
R-square=0.63
where,AC=AsphaltcontentP4=Percentpassingthe4.75mm(No.4)sieveP8=Percentpassingthe2.36mm(No.8)sieve
Equations1and2indicatethatthemeasuredasphaltcontentsofthebindercoursemixinthis
studyincreaseby0.06and0.08percent(basedonslopesoftheregressionlines)witheachonepercentincreaseinthematerialpassing4.75mm(No.4)and2.36mm(No.8)sieves,respectively,fromtheJMF.Conversely,therewillbeasimilardecreaseinthemeasuredasphaltcontentsifthesampledmixiscoarserthantheJMF.Theseso-called"correctionfactors"canbe
usedtocorrectthemeasuredasphaltcontentforeachonepercentdeviationfromtheJMF.Someresearchers(1,2,and3)havedevelopedthefollowing"correctionfactors"forbindercoursemixes(maximumaggregatesizegreaterthan25.4mmor1inch)basedonthematerialpassing2.36mm(No.8)sieveafteranalyzinglimitedfielddata.
CorrectionFactor,%
CustomaryinUKforrolled-asphaltmixpriorto1970(1)
GoodsallandMathews(l)
Warden(2)
Brownetal(3)
KandhalandCross(Thispaper)
0.08
0.14
0.16
0.10
0.08The"correctionfactor"isexpectedtobegenerallydependentonthefineaggregategradation,theparticleshapeandsurfacetextureoftheaggregates,andtheactualasphaltcontentofthebindercoursemix.Furtheranalysiswasperformedtodetermineifamulti-variablemodelwouldgiveastatisticallystrongermodel.Thebestmulti-variablemodelwasfoundbyincludingthe12.5mm(1/2inch)sievewitheitherthe4.75mm(No.4)or2.36mm(No.8)sieve.Therelationshipbetweenasphaltcontentandthepercentpassingthe12.5mm(1/2inch)sieveisshowninFigure7.TherelationshiphasanR2of0.52.Bycombiningthe12.5mm(1/2inch)sievewiththe4.75mm(No.
4)sievethemodelhasanR2
of0.67.Therelationshiphasthefollowingform:AC=1.947+0.014(P1/2)+0.045(P4) (3)
R-square=0.67
Where,
AC=AsphaltcontentP1/2=Percentpassing12.5mm(1/2inch)sieveP4=Percentpassing4.75mm(No.4)sieve
Aslightlystrongermodelwasfoundutilizingthe12.5mm(1/2inch)and2.36mm(No.8)sieves.
TherelationshipisshowninFigure8andhasthefollowingform:
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Figure7.PercentagePassing1/2InchSievevs.AsphaltContent(BinderMixesfromBothLanes)
Figure8.Actualvs.PredictedAsphaltContent(BinderMixesfromBothLanes)
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AC=1.757+0.016(P1/2)+0.061(P8) (4)
R-square=0.68where,
AC=Asphaltcontent
P1/2=Percentpassing12.5mm(1/2inch)sieveP8=Percentpassing2.36mm(No.8)sieve
ThedatashowninFigures6-8showthatthemeasuredasphaltcontentisaffectedbyachangein
gradation.Achangeingradationwillcauseacorrespondingchangeinthemeasuredasphaltcontent.Byutilizingeitheroftheabovefourmodels,themeasuredasphaltcontentcanbeadjustedfortheamountcausedbythechangeingradation.TheadjustedasphaltcontentcanthenbecheckedagainstthetolerancelimitsfortheJMFasphaltcontenttodetermineifthevariationinasphaltcontentisduetothechangeingradation,segregation,oratruechangeintheasphaltcontent.
Tocheckthemodelsdeveloped,themeasuredasphaltcontentswereadjustedforthemeasured
changeingradationusingequations1,2and4.Theadjustedasphaltcontent(AAC)isdeterminedbyaddingthedifferencebetweenthemeasuredasphaltcontent(MAC)andthepredictedasphaltcontent(PAC),totheJMF.TheadjustedasphaltcontentisthencheckedagainsttheupperandlowertolerancelimitsoftheJMFasphaltcontent.
where,
AAC=JMFAC+(MAC-PAC)
AAC=AsphaltcontentadjustedforgradationJMFAC=JobmixformulaasphaltcontentMAC=MeasuredasphaltcontentPAC=PredictedasphaltcontentfromEq.1,2,3or4
(5)
Figure9showsthecontrolchartsfortheasphaltcontentadjustedutilizingequation5forbindermixsamplesfromNBlanes.Table8showsthefrequencythattheadjustedasphaltcontent,adjustedutilizingequations1,2and4,arewithinspecificationlimits.Theresultsshow95percentoftheadjustedasphaltcontentswithinspecificationlimitsregardlessoftheequationsutilized.Theadjustedasphaltcontentsforthebindermixshowacompliancepercentageverysimilartothatobtainedforthewearingmixeswheresegregationwasnotaproblem.
Table8.FrequencyDistributionofAdjustedAsphaltContentforBinderMixes
AsphaltContent NBLanes SBLanes All
InSpec. 93.7 96.7 95.2
AdjustedonNo.Out-Low 0.4 0.8 0.5
4Sieve(Eq.1)Out-High 5.9 2.5 4.2
InSpec. 94.1 96.0 95.1
AdjustedonNo.Out-Low
8Sieve(Eq.2)Out-High
0.4
5.5
2.9
1.1
1.6
3.3
Adjustedon
1/2"&No.8Sieve(Eq.4)
InSpec.
Out-Low
Out-High
94.8
1.5
3.7
96.4
0.7
2.9
95.6
1.1
3.3
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Figure9.ControlChartforAsphaltContentAdjustedfor1/2InchandNo.8Sieves(BinderMixesfromNBLanes)
CONCLUSIONSANDRECOMMENDATIONS
Basedonthedataobtainedinthisstudythefollowingconclusionsarewarranted.1.InsegregatedHMApavements,someofthedeviationinasphaltcontentfromthejobmixformula(JMF)iscontrolledbythechangeingradationofthemixfromtheJMF.
2.Whensegregatedbindercoursemixesweresampledbehindthepaver,thepercentpassingthe4.75mm(No.4)and2.36mm(No.8)sievescorrelatedwithmeasuredasphaltcontent.
3.Forsegregatedbindercoursemixes,theasphaltcontentcanbeadjustedtoaccountforthechangeingradationfromtheJMFasmeasuredonthe12.5mm(1/2inch)andeitherthe4.75mm(No.4)or2.36mm(No.8)sievesasshowninequations3and4.However,theseequationsarevalidfortheaggregatesandtheJMFusedinthisstudy.Careshouldbetakeninapplyingtheseformulastoothermixes.
4.Sincenosignificantsegregationoccurredduringthelaydownofthewearingcoursemix,gradationcouldnotberelatedtothemeasuredasphaltcontent.
DISCLAIMER
Theopinions,findings,andconclusionsexpressedherearethoseoftheauthorsandnotnecessarilythoseoftheNationalCenterforAsphaltTechnologyorAuburnUniversityortheUniversityofKansas.
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REFERENCES
1.
2.3.
G.D.GoodsallandD.H.Mathews.SamplingofJournalofAppliedChemistry, Vol.20,DecemberRoadSurfacingMaterials.1970.
WarrenB.Warden,BitumenExtractionTesting.PaperpresentedattheSixthWorldMeetingoftheInternationalRoadFederation,Montreal,Canada,October1970.E.R.Brown,RonaldCollins,andJ.R.Brownfield.InvestigationofSegregationofAsphaltMixturesinStateofGeorgia.TransportationResearchRecord1217, TRB,NationalResearchCouncil,Washington,DC,1989.
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