1995 Riley Pavement Ages

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SPECIFICATIONFORTHEHDM-4ROADDETERIORATIONMODELNOTESONPAVEMENTAGESIntroductionHDM-IIIused3pavementages,resetsdependingontreatmenttypeanddifferentageswereusedindifferentdistressmodels.Withtheenlargementofthemodellingbasein

HDM-4,itisthoughtthatthedefinitionsandapplicationsofpavementagesmayneedreview.PavementAgesinHDM-IIIThethreepavementagesinHDM-IIIweredefinedinWatanatadaetal.(1987)as:AGE1 preventivetreatmentage,definedasthenumberofyearselapsedsincethe

latestpreventivetreatment,reseal,overlay,pavementreconstructionornewreconstruction

AGE2 surfacing age, defined as the number of years elapsed since the latest

reseal,overlay,pavementreconstructionornewconstructionAGE3 construction age, definedas thenumber of yearselapsedsince the latest

overlay,pavementreconstructionornewconstructionPavementagesareusedinthefollowingdeteriorationmodels,basedonWatanatadaetal.(1987)andchecksonthesourcecode(RDMPV88.FOR).CrackingAGE2isusedtodeterminewhetherthecrackprogressionmodelsshouldbeapplied.RavellingAGE2isusedtodeterminewhethertheravellingprogressionmodelshouldbeapplied.PotholingAGE2isusedtodeterminewhetherthepotholingprogressionmodelshouldbeapplied.RuttingItwastheintentionthat,whenAGE3=0,thefirstyearrutdepthincrementwouldusetheabsolutemodelgiven inPaterson,1987. Thereafter,an incremental form of the

modelisappliedwhichdirectlyincorporatesAGE3asavariable.Inmy version of the code, the absolute expression is applied whenRDMA=0,notwhenAGE3=0.Thisimpliesthat,ifanoldpavementisspecifiedintheinputdatawithzerorutdepth,HDM-IIIwill,inthefirstanalysisyear,calculatetherutdepthusingtheabsolutemodelformintendedforanewpavement.HaveanyHDM-IIIusersnoticedthisoccurring?It is also noted that, in this version of the code, the rehabilitation factor RH is hardcodedaszeroanddoesnotappearinthetreatmentresets.i.e.RHisnotused.



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ThesamecommentsapplytobothmeanandSTDofrutdepth.RoughnessAGE3 is a variable in the structural component of the incremental roughnessprogressionmodel.

TreatmentInterventionsandResetsAll three ages can, potentially, be applied in treatment interventions if minimumintervalsorscheduledpoliciesarespecified.Forexample,ifapreventivetreatmentisspecified witha minimum interval of 5 years, reconstructionwould not beapplied ifAGE1 < 5 years even though condition responsive conditions for reconstruciton aremet.AGE1issettozeroafterpreventivetreatment,seal,overlayorreconstruction.AGE2issettozeroafterseal,overlayorreconstruction.AGE3issettozeroafteroverlayorreconstruction.

PavementAgesinHDM-4It is thought that the use of the three pavement ages in HDM-III is generallysatisfactory.TheonlyareaofdoubtconcernstheresetofAGE3afteroverlays.Wherea thin overlay is used, this may lead to inaccurate predictions of rut depth androughness.Theseaspectsarediscussedbelow.Rutting-DensificationComponentIn thecaseof thin surfacings, thedensificationcomponentof therut depthmodel ismainly derived from the base and lower layers. It therefore seems incorrect touseAGE3 =0after applyinganoverlay;AGE3, forthispurpose,shouldonlybereset tozeroafterareconstructionthatinvolvesreplacementofthebaseand/orsubbase.This only becomes of significance if the HDM-III incremental model is used, whereAGE3isavariableintheexpression.Forthefirstyearafteroverlay,followingthelogicoftheHDM-IIIcode, theabsolutemodelwillmostlynotbeapplied;assumingthatrutdepthwasgreaterthanzerobeforeoverlay,itisresetto0.15xtheoldvalueandisthusgreaterthanzero(seeabove).Thenewrutdepthwill,however,bequitesmallandassubsequent incremental increase isa functionofRDMa itwillbeless than that for anewpavement. ItthusappearsthatHDM-IIIisgivingtherightansweralthoughmaybeforthewrongreasons.TheonlycasewheretheHDM-IIIlogicmaygiveanincorrect

resultiswheretheexistingpavementhasarutdepthofzeroasalreadymentioned.Ifalinearincrementalmodelisused(seemynotesonthissubject)ageisnotavariableintheexpressionsothechoiceofageresethasnosignificance.Rutting-PlasticFlowComponent



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The plastic flowmodel, as proposed in the HTRSreport, is incremental in formanddoesnotuseagedirectlyasavariable.Themodelis,however,non-linearwithtimeandif,ashasbeenproposed,asimplifiedformofthemodelisderivedthenagewillundoubtedly become a variable in the expression. In this case the choice of agebecomesproblematiciftherearemultipleasphaltlayersofdifferentages.Itmightbeexpected that the surfacing age will predominate where the latest surfacing has athickness greater than, say, 50 mm but not for seals or thin overlays over existing

thicker bituminous layers. It is suggested that the definition of age is carefullyconsideredifasimplifiedplasticflowmodelisdeveloped.RoughnessTheroughnessprogressionmodel,originallyestimatedfromBraziliandata,containsanagetermthatwasdefinedinPaterson,1987as“ageofpavementoroverlay”.InHDM-III,AGE3 isusedintheexpressionwhichiscompatiblewiththedefinitionofAGE3inthemodel.ThedefinitionofAGE3herecreatesabiaswhencomparingthinoverlaysandseals,especially if the pavement age is high prior to treatment. This may be one of the

reasonswhy HDM-III tendsnot to favourseals asmaintenance treatments; notonlydoes a thin overlay give a greater reduction in roughness than a seal, but thesubsequentprogressionisalsolowerduetoAGE3beingresettozero.Thereisthusan argument for changing the definition of AGE3 by resetting only after an overlaygreaterthanacertainthickness,say,50mm.ConclusionsIt is proposed that, inHDM-4, the following changes are made to the definition andapplicationofpavementageswithrespecttoHDM-III:1.Forthinoverlays(<50mm)AGE2isresettozerobutnotAGE3.2.IfananalysissectionisspecifiedwithAGE3>0andRDM=0,RDMisresettoa

nominalvalue(e.g.1mm)attheendofthefirstanalysisyear.3.If,afteratreatment,AGE3>0andRDM=0,RDMisresettoanominalvalue(e.g.1

mm).4.If a simplified plastic flow model is developed, the age term should be a value

betweenAGE2andAGE3dependingontherelativethicknessesoftheoldandnewasphaltlayers.

MikeRiley12/4/96

1995 Riley Pavement Ages

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