基于生命周期评价的热再生沥青路面环境效益分析（英文版）

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EnvironmentalBenefitAnalysisofHotCentral

PlantRecyclingAsphaltPavementBasedonLCA

Tocitethisarticle:DLZhuetal2021IOPConf.Ser.:EarthEnviron.Sci.766012101

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IOPConf.Series:EarthandEnvironmentalScience766(2021)012101doi:10.1088/1755-1315/766/1/012101

EnvironmentalBenefitAnalysisofHotCentralPlantRecyclingAsphaltPavementBasedonLCA

DLZhu1,2,JWang1,LXGu1

1SchoolofCivilEngineering,CentralSouthUniversity,HunanProvince,China,410075

2Email:1203170206@Telephone/p>

Abstract.Inordertodeterminetheenergy-savingandemission-reductioneffectsoftheapplicationofhotcentralplantrecyclinginthehighwayasphaltpavementmaintenanceproject,thisstudyselectsaroadsectionofoverhaulprojectinTongrenastheanalysisobject,andadopttheenvironmentalbenefitanalysismethodbasedonlifecycleassessmenttoanalyzetheenergyconsumptionandenvironmentalemissionsofhotcentralplantrecyclingandhotmixasphalt.Thecomparisonshowsthattheapplicationofhotcentralplantrecyclinginhighwayasphaltpavementmaintenanceprojecthasgoodenergysavingandemissionreductionbenefits,andtheaggregateandasphaltproductionstagearethemaincomponents.Moreover,undertheconditionofensuringtheroadperformanceofrecycledpavement,withtheincreasingproportionofreclaimedasphaltpavement,theenvironmentalbenefitofrecycledpavementishigher.Whilewiththeincreaseofreclaimedasphaltpavementtransportationdistance,theenvironmentalbenefitpresentsadownwardtrend.

1.Introduction

Thetransportationsectorgreatlyinfluencethesustainabledevelopmentofasociety,contributingtoairpollutionfromvehicularemissions,globalwarming,consumptionofenergyresources,disturbanceofnaturalspacefrominfrastructureconstruction,andnoisepollution[1].Intherecent40years,highwayconstructionhasmadesignificantprogressinChina.AccordingtothestatisticsofMinistryofTransportofthePeople’sRepublicofChina,bytheendof2019,thetotalmileageofChina’sroadsreached5.0125millionkilometers.Amongthem,themileageofhighwaysis149,600kilometers[2].Astimepassed,thehighwaycompletedearlyhasenteredtherepairstagesuccessively,andtheamountofreclaimedasphaltpavement(RAP)producedinpavementmaintenanceengineeringisalsoincreasing.

RAPisamixture,includingagedasphaltbinderandaggregatesproducedbyrecyclinghotmixasphalt(HMA)knownasthemostcommonrecycledmaterialsusedinflexiblepavements[3].Thehigh-pricedoriginalbindercanbereplacedwithRAPasaless-costlybindertoprepareeco-friendlypavements[4].Forexample,usingRAPaswastematerialinpavementstructuredecreasetheemissionofgreenhousegasintotheatmosphereleadingtoimprovementintheenvironmenthealth[5-6].Inordertoreduceenvironmentalburdenassociatedwithasphaltbinder,anumberofsustainablestrategieshavebeendevelopedandusedinthepavingindustryovertheyears,includingwarm-mixasphalt(WMA)andpartialreplacementofasphaltbinderwithbio-binderorotherindustrybyproduct[7-8].Currently,HMAiswidelyusedassurfacematerialforroadway,airfield,tunnel,andbridgedeck[9].However,thereisalackofaccurateandcomprehensivequantitativeevaluationofhowenergyuseandgreenhousegasemissionareimpactedbytheuseofrecycledmaterials[10].

Lifecycleassessment(LCA)providesacomprehensiveandholisticplatformforenvironmentalassessmentofsustainablepractices.Itcanbeusedtoquantifyenvironmentalimpactofvariousstages

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inthepavement’slifecycle,includingmaterialacquisition,plantproduction,transportation,constructionandmaintenance,usage,andend-of-life.TheLCAmethodhasbeenextensivelyusedindifferentstudiestoassessmentenvironmentalimpactofpavements[9]149-150.MostofthesestudiesfocusonusingLCAmethodtoquantifytheGHG(greenhousegas)emissionofasphaltpavementinusagestage[11];comparetheenergyconsumptionandGHGemissionofdifferentmaintenanceactivitiesthatsignificantlyaffectoptionsbetweenasphaltandconcrete[12];evaluatelife-cycleenvironmentalandeconomicimpactsofflexiblepavementswithvaryingamountsofRAPfrom8%to50%[13];analyzeenvironmentalsustainabilityofthreeasphaltpavementsatallstagesfromrawmaterialstotheendofservicelife[14];quantifyGHGemissionfromasphaltpavementscontainingrecycledasphaltpavementsfromatimeperspective[9].AlthoughanumberofstudieshaveusedLCAtoanalyzeenvironmentalimpactofusingRAPinasphaltmixture,previousstudiesneglectedtheenvironmentalimpactoftheacquisitionprocessofRAP(millingfromoldpavement),transportationofRAPtoprocessingplant,andthereprocessingorpretreatmentofRAPinprocessingplant.

Thus,thestudyisbasedontheexistingresearchresults,fullyconsideringtheenergyconsumptionandGHGemissionimpactsatallstagesinthepavement’slifecycle.Andthen,combinedwiththerealproject,comparethelifecycleenergyconsumptionandenvironmentalemissionsofhotcentralplantrecycling(HCPR)andHMA,showingthepositivesignificanceofHCPRinpracticingtheconceptofecologicalandenvironmentalprotection.

2.Researchmethodology

2.1.GoalandscopeofLCA

HCPRreferstothetechnologyof“crushingandscreeningRAPinthemixingplant,heatingandmixingitwithnewmineralmaterial,newasphaltandasphaltregenerantinacertainproportiontoformasphaltpavement”[15].Thisstudyusesprocess-basedLCAmethodofHCPRistoquantifytheenergyconsumptionandenvironmentalemissionsofRAPmillingrecovery,rawmaterialproduction,asphaltmixtureproductionandpavementconstructionstages,evaluateitsimpactonresourcedestructionandecologicalenvironment.ThesystemboundaryoftheLCAofHCPRisshowninFigure1.

Figure1.BoundaryoflifecycleassessmentsystemforHCPR

2.2.Energyconsumptioninventoryanalysis

Lifecycleenergyconsumptioninventoryanalysismethodsmainlyincludemeasurementmethod,theoreticalmethodandquotamethod,amongwhichquotamethodintegratesthecharacteristicsofmeasurementmethodandtheoreticalmethod,andisthemostcommonlyusedandeffectiveenergyconsumptioncalculationmethod[16].Ittakesthespecificmechanicalequipment,operatingvehicleparametersandusefrequencywithinthequotascopeasthecore,whichcanreflecttheconstructionprocessandenergyconsumptionlevelunderthesocialaveragelevel.Firstly,determinethenumberofmechanicalshiftsperunitoutputaccordingtothetechnologicalprocessspecifiedintheBudgetQuota

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ofHighwayMaintenanceProjectandCostQuotaofMachineShiftforHighwayMaintenanceEngineeringofaprovince;secondly,basingontheenergyconsumptionparametersofmachineshiftandnetcalorificvalue(NCV)(obtainedfromthestatisticalresultsreleasedbyIntergovernmentalPanelonClimateChange),tocalculatetheenergyconsumptionofeachstagebyusingformula(1);finally,thetotalenergyconsumptionoftheproductionunitofrecycledmixtureiscalculatedbysummation.

E=Σ(Qi.Ncvi)（1）

Intheformula:Qiistheunitfuelconsumption(kg)oftypeimechanicalequipment;NCViisthenetcalorificvalue(MJ/kg)ofthefuelusedforthecorrespondingmechanicalequipment.

2.3.Environmentalemissioninventoryanalysis

ThecalculationoftheemissionsofGHGandtheenvironmentalimpactsbytheminthewholelifecycleofHCPRisrelativelycomplicated.ThecalculationgenerallyusestheenvironmentalemissioninventoryanalysismethodbasedonIPCCemissionfactormethodwithstrongapplicabilityandsimpleform:firstofall,onthepremiseofdeterminingthedefaultemissionfactors(asshowninTable1)ofcommonfuelcombustionundertheassumptionof100%oxidationoffuel,tocalculatetheemissionsofvarioussubstances;second,determinethecharacteristicfactorofeachimpactfactor(asshowninTable2);finally,calculatethetotalamountofvariousenvironmentalemissionsofeachstagethroughformula(2).

EP=Σ(Qi.EFi)（2）Intheformula:EPisthetotalcharacteristicemissionoftheenvironmentalimpactofglobalwarming;

Qiistheemissionamountoftypeimaterial;EFiisthecharacteristicfactoroftheiemission.

Table1.Defaultemissionfactoroffuelcombustionbasedonnetcalorificvalue(mg/MJ)

NetCalorific

FuelTypeValue(MJ/Kg)[17]CO2CH4N2O

DieselOil43.074100.003.000.60

HeavyOil40.477400.003.000.60

Table2.Impactfactorandcharacteristicfactor

ImpactFactor

CharacteristicFactorUnit

CharacteristicFactor

CO2CH4N2O

kgequivalentCO2

1.0025.00298.00

Thedatasourcesoflifecycleenergyconsumptionandenvironmentalemissioninventorywereobtainedfromtheonlinedatabaseofbudgetquotaofhighwaymaintenanceengineering,costquotaofmachineshift,peer-reviewedjournal,conferencepapers,andreportspublishedbygovernmentagenciesoracademicinstitutionsthatmetcriteriaforqualityandrelevance.

3.Casestudyofasphaltpavement

OverhaulprojectofaroadsectionofprovincialhighwayS303inTongren,10kilometerslong,isatypicalsectionofmountainoushighwayinGuizhouProvince.Thedesignspeedoftheroadsectionis20km/h,thewidthofthesubgradeis6.5m.Thedistancefromthemaintenancesectiontotheprocessingplantis50kilometers,thedistancetotheasphaltmixingplantis50kilometers,andthedistancetothespoilgroundis75kilometers.Theoriginalpavementstructureis4cmthickAC-13ordinaryasphaltconcretesurfacelayer,15cmthickgradedgravelbaselayer,andthemaindiseasesoftheoriginalpavementarenetworkcracking,longitudinalcracking,transversecracking,anddeformation,etc.Afterpavementmaintenance,thesurfacecourseis4cmthickAC-13plantmixedhotrecycledmixture,andthebasecourseis15cmthickgradedgravel.TheAC-13plantmixedhotrecycledasphaltmixturecontains3.41%asphaltbinder(30%RAP,thecontentofasphaltinRAPis4.5%),67.55%aggregate,and0.09%asphaltregenerant.

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4.Resultsanddiscussion

4.1.Quantitativeanalysisofenergyconsumption

TheLCAofHCPRincludesfourstages:RAPmillingrecovery,rawmaterialsproduction,asphaltmixtureproductionandpavementconstruction.Theenergyconsumptionandenvironmentalemissionofeachstagemainlycomefromthecombustionofdiesel,heavyoilandotherfuelsandpowerconsumptionofrelevantmechanicalequipment.Basedonthis,theconsumptionandemissionateachstageofpaving1tonofAC-13plantmixedhotrecycledasphaltmixtureiscalculatedbysubstitutingtheinventoryanalysisformula(1)and(2).InordertofullyunderstandtheenergyconsumptiondifferencebetweenHCPRandHMA,theenvironmentalemissionsofAC-13asphaltmixtureineachstageofitslifecyclearecalculatedinthesameway,soastoevaluatetheenergysavingandemission

reductioneffectofHCPRreasonablyandobjectively(asshowninFigure2).

Figure2.LifecycleenergyconsumptionbenefitofHCPR(MJ/ton)

Accordingtotheabovequantitativeanalysisresults,thetotalenergyconsumptionofHCPRis643.95MJ/ton.Comparedwiththe741.67MJ/tonconsumedbyHMA,thetotalenergyconsumptionissavedby97.72MJ/ton,andtheenergysavingratiois13.2%.Thisisreflectedin:(1)duetotheshorteningofRAPtransportationdistance,theenergyconsumptionofRAPmillingrecoverystageisreducedby28.02MJ/ton;(2)withtheadditionofRAP,13.53kgofasphaltand276.89kgofnewaggregatecanbesavedforeachtonofHCPRmixture,savingatotalof75.56MJ/tonofenergyconsumption,inwhichtheenergyconsumptionofnewasphaltproductionstageaccountsforthelargestproportion.

4.2.Quantitativeanalysisofenvironmentalemissions

Basedontheenergyconsumptioncalculationresultsofeachstage,combinedwiththedefaultemissionfactorsofdiesel,heavyoil,andelectricpowerandthecharacteristicfactorofeachemissionfactor,substitutingintoequation(2),tocalculatethetotalenvironmentalemissionsateachstageofthelifecycleofAC-13HCPRandHMA(thecalculationresultsareshowninTable3).TheresultsshowthatthetotalenvironmentalemissionsofHCPRare41348.10gequivalentCO2.ComparedwithHMA,theemissionisreducedrespectively4426.39gequivalentCO2,andtheemissionreductionratiois9.97%,whichisduetotheshorteningofRAPtransportationdistanceandthesavingofasphaltandaggregateaswell.

Table3.LifecycleenvironmentalemissionbenefitofHCPR(g/ton)

Type

RAPMillingRecovery

MaterialsProduction

Mixture

Production

Pavement

Construction

InTotal

HCPR

7868.93

6624.92

17480.38

7978.11

39952.34

HMA

9927.25

9276.64

17196.74

7978.11

44378.73

Benefits

2058.32

2651.71

-283.64

0.00

4426.39

4.3.EffectsofRAPcontentandtransportdistance

InordertoclearlyquantifytheenergysavingandemissionreductioneffectofRAPwithdifferent

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proportiononHCPR,thisstudycalculatetheenergyconsumptionandenvironmentalemissionswithdifferentRAPpercentages(variedfrom10%to50%).TheresultsinTable4clearlyshowthatthehighertheRAPcontentis,thelesstheenergyconsumptionandenvironmentalemissionsare,andthebenefitsofenergysavingandemissionreductionaregraduallyincreasing.However,withtheintroductionofRAP,asphaltpavementmighthavethestrongertendencytowarddeterioration,ismoresusceptibletofatigue,longitudinalcracking,andtransversecracking[18],resultingintheshorterservicelifethanasphaltpavementwithvirginmaterials[9]153.Thus,inordertoachievetheeffectofenergysavingandemissionreduction,RAPcannotbeblindlyincreased.

Table4.InfluenceofRAPblendingratioonenvironmentalbenefits

RAPPercentages

Energy

Energy

Environmental

Emission

(%)

Consumption(MJ/ton)

Saving(%)

Emissions(g/ton)

Reduction(%)

10%

690.42

6.91%

41531.86

6.41%

20%

667.19

10.04%

40742.50

8.19%

30%

643.95

13.18%

39952.34

9.97%

40%

620.70

16.31%

39161.38

11.76%

50%

597.44

19.45%

38369.64

13.54%

Tomakeupfortheexistingresearchgaps,understandtheenvironmentalburdenofRAPtransportationstage,thisstudyconsiderstheenvironmentalbenefitsofdifferentdistancesfromtheprocessingplanttotheconstructionsite.ItisworthnotedthatthedatainFigure3showsthatwiththeincreaseoftransportationdistance,theenvironmentalbenefitsbroughtbyRAPwillbecontinuouslyoffset.Whenthetransportationdistanceistoolong(over70kilometers),theenvironmentalbenefitswillbenegative,whichshowstheimportanceofstrictlycontrollingthetransportationdistanceofRAPandrecycledasphaltmixture.

Figure3.Influenceoftransportationdistance

(fromprocessingplanttomaintenancesection)onenvironmentalbenefits

5.Conclusions

ThestudyproposestousequotadatatocalculatetheenvironmentalbenefitsofRAPmillingandtransportation,whichsolvestheresearchgapthatlacksconsiderationofenergyconsumptionandenvironmentalemissionsduringRAPtransportationstage.ThecasestudyhasshownthattheapplicationofHCPRcaneffectivelyimprovetheenergy-savingandemission-reductioneffectsofRAPmillingandrecycling,recycledmixtureproductionandrecycledroadpaving.AndasRAPcontentincreases,theenvironmentalbenefitsincreaseaccordingly.However,withtheincreaseofRAPtransportationdistance,theenvironmentalbenefitsofRAPwillcontinuetodecrease,andmayevenappearnegative.Therefore,itisnecessarytopayattentiontoimprovetheproportionofRAP,shortenthedistancebetweenprocessingplantandmaintenancesection,soastofurtherreducetheenergyconsumptionofHCPR.

Acknowledgments

ThestudyissupportedbytechnicalprojectofGuizhouProvincialDepartmentofTransportation(NO.2020-123-030).

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