毕业作业外文翻译.docx
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毕业作业外文翻译.docx
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毕业作业外文翻译
EffectsofTemperatureandMoistureGradientsonSlabDeformationforJointedPlainConcretePavements
RaniaE.Asbahan1andJulieM.Vandenbossche,P.E.,M.ASCE2
Abstract:
Slabcurvature,whichrepresentstheresponseofconcretepavementslabstoenvironmentalloads,influencesthelocationand
magnitudeofcriticalslabstressesandaffectslong-termpavementperformance.Thepurposeofthisstudywastomeasurethechangesintemperatureandmoistureprofilesinanewlyconstructedconcretepavementandtodetermineboththeoveralldeformedshapesoftheslabsaswellastherelativecontributionsofbuilt-inandtransientenvironmentaleffectsovertime.Datawerecollectedfromaninstrumentedjointedplainconcretepavement(JPCP)overa2-yearperiod.Slabcurvatureswerecomputedorpredictedusingmeasurementsoftemperatureandmoistureconditionsintheslab,staticstrainmeasurements,andpavementsurfaceprofilemeasurements.Itwasfoundthattheadditionalrestraintprovidedbythedowelandtiebarsdoesnotappeartosignificantlyreduceslabcurvatureresultingfromdailytemperaturefluctuationorfromirreversibledryingshrinkage.Itdoeshaveasubstantialeffectonreducingslabcurvatureattributabletolong-termdryingshrinkage.ItwasalsofoundthattheMechanistic-EmpiricalPavementDesignGuidedefaultvalueisclosetothatmeasuredinthisstudyfortherestrainedslabbutdoesnotappeartobeappropriateforunrestrained(i.e.,undoweled)slabs.
CEDatabasesubjectheadings:
Concretepavements;Warpage;Slabs;Curvature;Dewatering;Shrinkage;Temperatureeffects;Moisture.
Authorkeywords:
Concretepavement;CurlingWarping;Slabcurvature;Dryingshrinkage.
Introduction
Itisgenerallyassumedthattransverseslabcrackinginjointedplain
concretepavements(JPCP)initiatesatthebottomoftheslabnearmidpanel.Thereisnowevidencethatthefatiguecrackscan,andtypicallydo,initiateatthetopoftheslabandpropagatedownward
[AppliedResearchAssociates,Inc.(ARA)2004;Gutierrez2008;
McCrackenetal.2008].Thisisbelievedtobeattributabletothe
combinedeffectsofenvironmentalloading(i.e.,temperatureand
moisturegradientsthatcauseslabdeformation)andaxleloading.
Jointedplainconcretepavementsareusuallysubjectedtoawide
rangeoftemperatureandmoistureconditionsthroughouttheirservicelives,resultinginacorrespondinglybroadrangeofdeformedslabshapes.Recognizingthattheshapeoftheslabatthetimeoftrafficloadingsignificantlyaffectsthedevelopmentofslabstresses,
theMechanistic-EmpiricalPavementDesignGuide(MEPDG)considersenvironmentaleffectsinthecomputationofthecritical
stressesfortop-downandbottom-upcrackinganddeterminesaccumulateddamageforeachpossiblefailuremode(i.e.,top-downorbottom-upcracking)individually(ARA2004).Forthisreason,the
shapeoftheslabmustbeaccuratelycharacterizedsothatitcanbeinputintotheMEPDGtoproducethemostaccuratepredictionsof
crackingandJPCPservicelife.
Slabcurvature,whichvarieswithtransientslabtemperatureandmoistureconditions,isalsoinfluencedbyseveraladditionalfactorsincluding
(1)temperatureandmoistureconditionsatthetimeofconstruction(i.e.,“built-ingradients,”whichaffectthelong-termbehavioroftheslab);
(2)concretematerialproperties,suchasthe
coefficientofthermalexpansion,dryingshrinkage,creep,andelasticmodulusoftheconcrete;and(3)restraintstoslabdeformation,
suchasslabself-weigh,frictionattheslab/subbaseinterface,and
restraintstojointmovement(e.g.,dowelbars,tiebars,andaggregateinterlock)(ARA2004).Thefirstofthesefactors,built-ingradients,istheprimaryfocusofthispaper.
Temperatureandmoisturegradientsatthetimeofsetgreatlyaffectslabcurlingandwarping.Theeffectivebuilt-intemperature
gradientisdefinedastheeffectivegradientattributabletocombined
effectsoftemperatureandmoisturegradientsthatarepresentinthe
slabwhenitsetsaswellasthelong-termirreversibledryingshrinkage.Thetimeofsetiswhentheconcretebehaviorchangesfromplastictoelastic,andthisiswhentheconcretecanbegintocarrystructuralstressesandstrains.Theactualvalueoftheeffective
built-intemperaturegradientisdependentonfactorssuchasthe
coefficientofthermalexpansion/contractionoftheportlandcement
concrete(PCC)mix,temperatureconditionsatthetimeofpaving,andcuringpracticesandconditions,Priortothetimetheconcretesets,theslabremainsflatbecausetheconcreteisinaplasticstate.
Aftertheconcretesets,theresponseoftheslabisaffectedbythe
magnitudeanddirectionoftheeffectivebuilt-intemperaturegradient.Forexample,whentheslabtemperatureisuniform(i.e.,no
temperaturegradientexists),itmaybecurledratherthanflatbecauseitcanonlybeflatwhenthetransientgradientequalsthebuilt-ingradient(afteradjustingforanycreeporrelaxationeffectsthathavedevelopedovertime).Thecurlingisupwardifthebuilt-ingradientispositiveanddownwardifitisnegative.Thebuilt-inconstructiongradienthasproventobeanimportantfactorinestimatingstressinconcretepavements,especiallywhenusingtheMEPDG(EisenmannandLeykauf1990;Hansenetal.2006;RaoandRoesler2005;Ruizetal.2001;Wellsetal.2006;Yuetal.1998;YuandKhazanovich2001).
Thispaperexaminesthreedifferentapproachestodetermining
thecurvatureofin-serviceJPCPpanelsinthepresenceofmeasured
temperatureandmoistureconditions:
useofslabtemperatureand
moisturemeasurements,straingaugemeasurements,andsurface
profilemeasurements.ThesethreemethodsareappliedtodatacollectedfromaninstrumentedJPCPandareusedtoevaluatetheeffectsofbuilt-ingradientsonslabcurvature.
ProjectDescription
Thisresearcheffortwasfocusedoncharacterizingthetemperature
andmoistureconditionstowhichanin-servicepavementwassubjectedanddeterminingtheresultingslabbehavior.Aportionof
StateRoute22nearMurrysville,Pennsylvania[approximately32km(20mi)eastofPittsburgh]wasinstrumentedduringconstructioninAugust2004.Theinstrumentedsectionconsistsof
14JPCPslabsmeasuring3.7m(12ft)wideand4.6m(15ft)long.
Twotypesofslabswereconstructed:
unrestrainedandrestrained.
Therestrainedslabsfeatured16mmdiameter(No.5)epoxy-coatedtiebarsplacedevery0.8m(2.5ft)alongthelane/shoulderandcenterlinejoints,and38mm(1.5in.)diameterepoxy-coateddowelbarsplacedevery305mm(12in.)alongthetransversepoint.Theunrestrainedslabsincludednotieordowelbars.
Thepavementstructurecompriseda305mm(12in.)thickPCCslabconstructedona102mm(4in.)asphalttreatedpermeablebase(ATPB)layerand127mm(5in.)ofdenselygradedsubbase.A610mm(24in.)gap-gradedsoilandaggregatemixturewasplacedontopoftheA-6subgrade.Coresobtainedafterconstructionshowedthattheas-builtthicknessoftheconcreteslabvariesbetween305mm(12in.)and355mm(14in.).
Thermocouples,moisturesensors,andvibratingwire(VW)staticstraingaugeswereplacedatvariouslocationsanddepthsinthreerestrainedandthreeunrestrainedslabs,asshowninFig.1.AdditionaldetailsconcerningtheconstructionofthetestsectioncanbefoundinthereportbyWellsetal.(2005).
SlabCurvature
Astheslabissubjectedtoagivensetofmoistureandtemperature
gradients,slabstrainsvarythroughthethicknessoftheconcrete,
causingtheslabtocurl/warpeitherupwardordownward,dependingonwhetherthenetgradientisnegativeorpositive.ThedifferenceinstrainsatthetopandbottomoftheslabcanbeusedtocomputetheslabcurvatureusingEq.
(1):
(1)
where:
=slabcurvature(positivevaluesindicateupwardcurvature),inunitsof1/m;
=strainatthetopoftheslabatthetimeofinterest;
=strainatthebottomoftheslabatthetimeofinterest;andD=distancebetweenthetopandbottomoftheslabwherestrainiscalculatedorstrainmeasurementsaretaken,m.
Thisequationwasderivedusingthefollowingassumptions:
(1)theslabiselastic,homogenous,andisotropic,withtemperatureindependentmaterialproperties;
(2)planesectionsremainplaneafterbending;(3)stressesandstrainsintheverticaldirectionarezero;(4)thedeflectionoftheslabissmallcomparedwiththeslabdimensions;and(5)temperatureandshrinkagestrainsvaryintheverticaldirectiononly(MohamedandHansen1997).
Inthisstudy,thecurvaturesofin-servicepavementslabswereestimatedorcomputedusingcalculatedstrainsattributabletomeasuredtemperatureandmoistureconditions,actualstrainmeasurementsintheconcreteslab,orpavementsurfaceprofilemeasurements.Eachoftheseapproachesisdescribedinthefollowingsections.
CurvatureEstimatesontheBasisofTemperatureand
MoistureMeasurements
TypeTthermocouplewirewasusedtomeasuretemperaturesintheconcreteandunderlyinglayers.SensirionSHT75sensorswereusedtomeasuremoistureandtemperaturevariationsintheconcretewithamanufacturer-reportedaccuracyof1.8%fortherangeofmoisturecontentsmeasured.ProceduresdevelopedbyGrasleyetal.(2003)attheUniversityofIllinoisatUrbana-Champaignfortheuseofthesesensorsinconcreteapplicationswerefollowed.Eqs.
(2)and(3)wereusedtoestimatethethermalandmoisturestrainsattheslabsurfaceasfunctionsofthemeasuredtemperatureandmoisturedistributionsthroughtheslabthickness,thecoefficientofthermalexpansion,andtheultimateshrinkagestrain.Therequiredmaterialpropertieswereobtainedthroughlaboratorytesting(Asbahanetal.2006;McCrackenetal.2008;Wellsetal.2005).ThecoefficientofthermalexpansionoftheconcretewasdeterminedusingAASHTOTP60-00testprocedure,andthed
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