道路工程施工概况(英文).doc

道路工程施工概况(英文).doc

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Overview

Constructionqualityiscrucialtothelong-termpavementperformance.Constructionfactorssuchassurfacepreparation,placement,jointconstructionandcompaction/consolidationhaveanoverwhelmingeffectonpavementperformance,whichcannotbeignoredorcompensatedforinmixorstructuraldesign.

Compaction

CompactionistheprocessbywhichthevolumeofairinanHMAmixtureisreducedbyusingexternalforcestoreorienttheconstituentaggregateparticlesintoamorecloselyspacedarrangement.ThisreductionofairvolumeproducesacorrespondingincreaseinHMAdensity（Robertsetal.,1996[1]）.

Figure1:

ASteelWheelandaPneumaticTireRollerWorkingSide-by-Side.

Compactionisthegreatestdeterminingfactorindensegradedpavementperformance（ScherocmanandMartenson,1984[2];Scherocman,1984[3];Geller,1984[4];Brown,1984[5];Bellet.al.,1984[6];Hughes,1984[7];Hughes,1989[8]）.Inadequatecompactionresultsinapavementwithdecreasedstiffness,reducedfatiguelife,acceleratedaging/decreaseddurability,rutting,raveling,andmoisturesusceptibility（Hughes,1984[7];Hughes,1989[8]）.

CompactionMeasurementandReporting

CompactionreducesthevolumeofairinHMA.Therefore,thecharacteristicofconcernisthevolumeofairwithinthecompactedpavement,whichistypicallyquantifiedasapercentageofairvoidsinrelationtototalvolumeandexpressedas“percentairvoids”.Percentairvoidsiscalculatedbycomparingatestspecimen’sdensitywiththedensityitwouldtheoreticallyhaveifalltheairvoidswereremoved,knownas“theoreticalmaximumdensity”（TMD）or“Ricedensity”afterthetestprocedureinventor.

AlthoughpercentairvoidsistheHMAcharacteristicofinterest,measurementsareusuallyreportedasameasureddensityinrelationtoareferencedensity.Thisisdonebyreportingdensityas:

·PercentageofTMD（or“percentRice”）.Thisexpressionofdensityiseasytoconverttoairvoidsbecauseanyvolumethatisnotasphaltbinderoraggregateisassumedtobeair.Forexample,adensityreportedas93percentRicemeansthatthereare7percentairvoids（100%–93%=7%）.

·Percentageofalaboratory-determineddensity.Thelaboratorydensityisusuallyadensityobtainedduringmixdesign.

·Percentageofacontrolstripdensity.Acontrolstripisashortpavementsectionthatiscompactedtothedesiredvalueunderclosescrutinythenusedasthecompactionstandardforaparticularjob.

Pavementairvoidsaremeasuredinthefieldbyoneoftwoprincipalmethods:

·Cores（Figures2and3）.AsmallpavementcoreisextractedfromthecompactedHMAandsenttoalaboratorytodetermineitsdensity.Usually,coredensityresultsareavailablethenextdayattheearliest.Thistypeofairvoidstestingisgenerallyconsideredthemostaccuratebutisalsothemosttimeconsumingandexpensive.

·Nucleargauges（Figures4and5）.Anucleardensitygaugemeasuresin-placeHMAdensityusinggammaradiation.Gaugesusuallycontainasmallgammasource（about10mCi）suchasCesium-137locatedinthetipofasmallprobe,whichiseitherplacedonthesurfaceofthepavementorinsertedintothepavement.Readingsareobtainedinabout2–3minutes.Nucleargaugesrequirecalibrationtothespecificmixturebeingtested.Usuallynucleargaugesarecalibratedtocoredensitiesatthebeginningofaprojectandatregularintervalsduringtheprojecttoensureaccuracy.

Eachcontractingagencyorownerusuallyspecifiesthecompactionmeasurementmethodsandequipmenttobeusedoncontractsundertheirjurisdiction.

Figure2:

CoreExtraction

Figure3:

PavementCore

Figure4:

ThinLiftNuclearDensityGauge

Figure5:

TakingaNuclearDensityReading

FactorsAffectingCompaction

HMAcompactionisinfluencedbyamyriadoffactors;somerelatedtotheenvironment,somedeterminedbymixandstructuraldesignandsomeundercontractorandagencycontrolduringconstruction（seeTable1）.

Table1:

FactorsAffectingCompaction

EnvironmentalFactors

MixPropertyFactors

ConstructionFactors

Temperature

Aggregate

Rollers

*Groundtemperature

*Gradation

*Type

*Airtemperature

*Size

*Number

*Windspeed

*Shape

*Speedandtiming

*Solarflux

*Fracturedfaces

*Numberofpasses

*Volume

*Liftthickness

AsphaltBinder

Other

*Chemicalproperties

*HMAproductiontemperature

*Physicalproperties

*Hauldistance

*Amount

*Haultime

Foundationsupport

ANoteontheTimeAvailableforCompaction

HMAtemperaturedirectlyaffectsasphaltbinderviscosityandthuscompaction.AsHMAtemperaturedecreases,theconstituentasphaltbinderbecomesmoreviscousandresistanttodeformationresultinginasmallerreductioninairvoidsforagivencompactiveeffort.Asthemixcools,theasphaltbindereventuallybecomesstiffenoughtoeffectivelypreventanyfurtherreductioninairvoidsrega