performance of rapid-repair concrete in an aggressive marine environment

1、PerfmanceofRapidRepairConcreteinanAggressiveMarineEnvironmentEdwardG.Moffatt1MichaelD.A.Thomas1HuangYi11.DepartmentofCivilEngineeringUniversityofNewBrunswickFrederictonCanada1.IntroductionThecrosionofreinfcementisoneofth

2、eleadingcausesofprematuredeteriationinconcretestructuresinNthAmerica.Theperationofchlideionsinconcretetypicallyarisesfromconcretelocatedinamarineenvironmentexposedtoroadsalts.Althoughconcreteiscurrentlydesignedtowithstth

3、isingressitisinevitablethatchlideswilleventuallyreachthesurfaceofthereinfcement.Increasedresistancetochlideingresscanbeachievedthroughtheimplementationofalowwatertocementitious(wcm)ratiotheadditionofsupplementarycementit

4、iousmaterials(SCMs)theapplicationofmembranessealersetc.Ettringitebasedconcretesareusedinapplicationswhereconstructiontimeislimitedindertoavoidthedisruptionofthetravellingpublic.Theyarecurrentlyusedtorepairbridgedeckssubs

5、tructureelementsonbridges(i.e.pierscolumns)pavementscomponentsofbuildingspavements.Ettringitebasedconcretesarecapableofachievingaveryhighearlystrength(i.e.20MPain3hours)arealsointendedtolasttheremaininglifeofthestructure

6、.Highearlystrengthisachievedbytherapidfmationofettringite(C3A?3C$?H32)inthefirstfewhoursofhydrationbyusingabindertypicallycomprisedofcalciumsulfoaluminate(C$A)cementcalciumaluminatecement(CAC)pluscalciumsulfate(C$).Marin

7、econcretestructuresareexposedtoveryharshconditions.Theconstantexposuretoseawaterresultsinphysicaldamagestrengthlossasaresultofcrosion(Thomas&Matthews1996).OneoftheharshestmarineenvironmentsinthewldisfoundatTreatIsllocate

8、doffthecoastofEastptMaineinthePassamaquoddyBaywhichispartoftheBayofFundy.Abeachlocatedonthewesternsideoftheislhasbeenusedasamaterialsresearchexposuresitefmethan75years.Approximately100freezethawcyclesoccureveryyearmaking

9、itoneoftheharshestconcreteenvironmentsinthewld.Reinfcedconcretespecimensplacedatthehightidelevelarewherecrosionisatitsmaximumduetothewettingdryingasaresultofthetideswhicharewldrenownasthehighestinthewldreachingelevationc

10、hangesgreaterthan6m.Therepairofconcretestructuresisaneverendingprocess.Approximately$1billionisspenttorepairmarinepilesintheUnitedStatesalone(Fametal.2003).Intidalareasrapidrepairconcretesarerequiredfrepairapplicationswh

11、eretimeisoftheessencetherepairmustbeplacedcuredbetweentides.ThispaperpresentsthecrosionperfmanceofreinfcedbeamsplacedatthehightidelevelofTreatIslfapproximatelytwoyears.Crosionmeasurementschlideperationprofilesxraydiffrac

12、tion(XRD)scanningelectronmicroscopy(SEM)analysiswereconductedonanumberofrepairmaterials.2.Experimental2.1.MaterialsFourrapidrepaircementswerestudiedtogetherwithandinaryPtlcement(PC)asacontrol.Thefirstrepairsystemisaterna

13、rysystemcomposedofdinaryPtlcement(PC)calciumaluminatecement(CAC)asourceofcalciumsulfate(C$)isdesignatedasPCCACC$throughoutthepaper.Aratioof2.2to1partsofCACtoC$wasusedwhereasPtlcementaccountedf70%ofthetotalcementitiouscon

14、tent.Thesecondcementusedwasa1EdwardMoffatt:Tel150644054172.3.TestingLinearpolarization(LPR)resistancemeasurementswerecarriedoutusingaconventionalthreeelectrodecellwithasilversilverchlide(AgAgCl)actingasareferenceelectrod

15、e(RE)atthesurfacea316stainlesssteelrodcastinthesampleasacounterelectrode(CE)theblacksteelbaractedasthewkingelectrode(WE).LPRwasconductedbyinitiallymeasuringthepotential(Ecr)ofthewkingelectrode(i.e.reinfcement)relativetoa

16、referenceelectrodethenscanningarangeof20mVaboutEcratarateofapproximately0.1mVsec.Theshiftinpotentialwithinthisrange(currentvs.potential)islinearwithunitsofresistance–hencethenamelinearpolarizationresistance.Thecrosioncur

17、rentisdeterminedfmthePolarizationResistanceplotwheretherelationshipbetweenRptheTafelcoefficientsthecrosioncurrentisexpressedas:ΔΔi==2.3()()[1]whereRpistheslopeofthelinearregionβaistheanodicTafelconstant(mVdecadeofcurrent

18、)βcisthecathodicTafelconstant(mVdecadeofcurrent)2.3isthenaturallogof10icristhecrosioncurrent(μA).InthisstudyTafelcoefficientsof120mVdecadewereusedwhicharecommonlyusedvaluesinacrosiveenvironment(Millard2000).Concretecesex

19、tractedfromeachofthebeamswereprofilegroundin1mmincrementsresultingpowdersampleswereanalyzedfchlidesrelativetodepth.Thechlidecontentateachlayerwasdeterminedbydigestingpowdersamplesgainedfromprofilegrindinginnitricacidperf

20、mingpotentiometrictitrationwithsilvernitrate.Chlidesweredeterminedfeachlayeruntiltheconcentrationpedbelow0.05%bymassofcement.InadditionXraydiffraction(XRD)wasconductedusingaBrukerD8Advancespectrometer.TheXraysourcewasase

21、aled2.2kWCuXraytubemaintainedatanoperatingcurrentof40kV30mA.Finepowdersampleswerescannedintherangeof580o.Astepsizeof0.02oasteptimeof1.0secwereusedduringtheexperiments.Polishedsectionswerepreparedfromeachofthecesanalyzedw

22、ithaJEOLJSM6400ScanningElectronMicroscopeequippedwithanEDAXGenesis4000EnergyDispersiveXray(EDS)analyzer.SampleswerecarboncoatedusinganEdwards306Acarboncoaterbefeobservationinthemicroscope.EDSanalysiswasperfmedatanacceler

23、atingvoltageof15kVabeamcurrentof1.5nAwithawkingdistanceof14mm.Collectiontimewas50secondsperanalysispoint.3.ResultsDiscussion3.1.ChlidePerationTheaveragechlideprofilesoftwocesfromeachofthefourrapidrepairsystemscontrolarep

24、resentedinFigure1.Profileswereestablishedaftertwoyearsofexposurefallsystems.Thespikeinresultsinthefirstfewmillimetersisattributedtothewashingouteffecttakingplaceinconcreteexposedtoatidalenvironment.C$A1C2Sisfoundtohaveth

25、elowestsurfaceconcentrationofapproximately0.18%althougharelativelyconstantconcentrationwithdepthisobserved.Aconcentrationofapproximately0.10%isfoundatthedepthofreinfcementwhichexceedsthecommonlyusedchlidethresholdof0.05%

26、(bymassofconcrete)ftheinitiationofcrosion.AlthoughtheothersystemscontainsurfaceconcentrationsfargreaterthanC$A1C2S(0.50.7%)thethresholdwasreachedatapproximately2025mm.PCC$A2whichcontains70%PCresultedinasurfaceconcentrati

27、on(0.6%)fargreaterthatofC$A1C2Salthoughthecommonlyusedthresholdwaspassedat20mmcomparedto50mm.TheprofileobservedintheC$A1C2Smaybetheresultofminimalchlidebindingoccurringwhichwillbediscussedinmedetailinsection3.3.AlthoughP