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Time-dependent

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Time-dependenttime,Time

    Time-dependent

;:8,Volume2,No.12(SerialNo.13)

    ;Journalof

    ;MaterialsScienceandEngineering,ISSN1934.8959,USA ;Timedependentpermeatingbehaviorofhydraulicconcrete ;FANGYong-hao,DENGHong-feng,ZHOUYue

    ;(CollegeofMaterialsScienceandEngineering,HohaiUniversi~,Nanjing210098,China)

    ;Abstract:Inthepresentpaper,thepermeatingbehaviorof ;hydraulicconcretesubjectedtohydraulicpressurewasstudied

    ;usingaself-designedconcretepermeabilitytestingsetup.The ;resultsshowthatwhensubjectedtohydraulicpressure,the

    ;permeatingrateoftheconcretewilldecrease

    ;negative-exponentiallywiththeelapsedtimeandeventually ;towardsastablevalue.Atime-dependentmodelforconcrete ;subjectedtohydraulicpressureisproposed.

    ;Keywords:concrete;permeability;permeabilitytestingsetup; ;time-dependentmodel

    ;1.IntrOducti0n

    ;Permeatingandwatercorrosionisoneofthemain ;causesforthedamageofhydraulicconcretestructure. ;Underhydraulicpressure,concretewillbepermeated ;bywateranditsconstituentswillbecorroded,which ;willresultinthedamageofthehardenedcementpaste ;intheconcrete.Permeabilityofconcreteisthusoneof ;themostinterestedpropertiesforhydraulicconcrete ;structures.Thepermeabilityofconcreteisusually ;expressedasthehighestwaterpressurethatthe ;concretecansubjectedwithoutseepageundera ;specifiedtestprocedure,orthepermeatedheightof ;waterintheconcretespecimenunderagivenwater ;pressureforaspecifiedtimeJJ|Gaspermeabilityhas

    ;alsobeenstudiedtocharacterizethepermeabilityof ;concrete2_3J.butonlyveryfewworkshavebeendone ;onthepermeatingbehaviorofconcreteafterbeen ;penetratedthrough.Yuanetal[]studiedtheseepage ;andwatercorrosionofconcretepanelunderdifferent ;waterpressuresandfoundthatthepermeabilityofthe ;Acknowledgement:Theauthorswould1iketothankthe ;NationalNaturalScienceFoundationofChinaforthefinancial

;supportforthisworkfNo.5Ol39030).

    ;COrrespondingauthor:FANGYonghao,PhD.professor;

    ;researchfield:cementbasedmaterials.Email:

    ;fangyonghaol95609@163.com.

    ;54

    ;concretedecreasedwithtime,eventuallytoastable ;value.However,nomoreinformationconcerningthe ;time-dependentpermeatingbehaviorofconcretewas ;reported.

    ;Inthepresentpaper,thetimedependent

    ;permeatingbehaviorofhydraulicconcretewasstudied ;usingcylindricalspecimensandaself-designed ;permeabilitytestingsetup.

    ;2.Experiment

    ;2?lMaterialsandspecimens

    ;CfiineseP?O32.5cement,GradeIIflayash,river ;sandwiththefinemodulusof2.5,crushedlimestone ;withDmax10mmandtapwaterwereusedtoprepare ;theconcretespecimenswiththemixproportions ;showninTable1.Sixcylindricalspecimenswiththe ;innerandouterdiametersof60milland1601Tlnaand ;theheightof160rnlTl,respectively,werepreparedfor ;eachsetoftheconcrete,twoforwaterpermeatingtest, ;threeforcompressivestrengthtestandoneasthespare. ;Thespecimenswerecuredat202?withtherelative

    ;humidity(RH)higherthan90%for28days,andthe ;compressivestrengthsweretested.Theresultsare ;showninTable1.

    ;2.2Testingmethodanddataprocessing

    ;Aself-designedpermeabilitytestingsetupshown ;inFig.1wasusedforwaterpermeatingtestofthe ;concretespecimens.Thetwoopenedendsofthe ;cylindricalspecimenwerecoveredwithtwosteel ;plates.Thereisan”L’’typeholewiththediameterof

    ;5mmintheupperplateasshowninthefigure, ;throughwhichthehighpressurewaterfromamortar ;permeabilitytestinginstrumentcanbedriveintothe ;Timedependentpermeatingbehaviorofhydraulicconcrete ;innerroomofthecylindricalspecimen,exertinga ;hydraulicpressontheinnerwallface.Thehydraulic

    ;pressureisadjustedbythemeteronthemortar ;permeabilitytestinginstrument.Thespecimenis ;immergedinaPVCsleevefilledwithwaterand ;coveredwitharubberringtopreventthewaterfrom

    ;evaporation.Thereisanoverflowtokeeptheheight ;ofthewaterinthesleevestable.Assoonasthewater ;haspermeatedthroughthecylindricalspecimentothe ;sleeve.itwil1makethewaterinthesleeveoverflow. ;Theoverflowedwaterisconductedbyarubbertubeto ;aflask,sothatallthequantityofthewaterpermeated ;throughthecylindricalspecimencanbecollected, ;whichismeasuredusinganelectronicbalance. ;Table1Mixproportionandcompressivestrengthofthespecimens

    ;SreelplateIn_letforhi

    ;pres5Ll~-ewater

    ;Fig.1Setupforwaterpermeating

    ;testofconcretespecimen

    ;Beforethetest,thetwoplateswereboundtothe ;specimenusingepoxyresinmortarasthebinder,and ;setthespecimenindryplacefor24hrstomakethe ;bindingbestrongenoughtowithstandthetesting ;hydraulicpressure.Thenthespecimenwasvacuum ;saturatedwithwater,sothatthepermeatingcould ;reachstableinshorttime.Inthepresentwork, ;steady

    ;hydraulicpressuresof1.0MPaand1.5MPa, ;equivalentto20MP’a/mand30MPa/mhydraulic

    ;gradients,wereexertedoffC1andC2specimens ;respectivelyduringthetests.Thewaterpermeatedwas ;collectedasmentionedaboveandthemassofthe ;waterisweighedevery12hrs,whichisconvertedto ;averagevolumetricflowratetakingthedensityofthe ;waterbeing1.0g/cm.

    ;Thepermeabilitycoefficientsoftheconcrete ;specimensatdifferentpermeatingtimewascalculated ;basedontheaveragevolumetricflowratesbya ;modifiedDarcy’sequation,whichisworkedoutas

    ;follows.

    ;AccordingtoDarcy’slaw[.

    ;Q:K(1)

    ;“?

    ;whereQisthevolumetricpermeatingrateinunitsof ;cmpersec,Kthewaterpermeabilitycoefficientin ;unitsofcm,Athepermeatingareainunitsofcm,AP ;thewaterpressureinunitsofPa,Lthepermeating ;distanceinunitsofcm,and/./viscositycoefficient ;ofwaterinunitofPasfbeing1.005~10Pa?sat

    ;20~C).

;ExpressingEq.(1)indifferentialformasEq.(2)

    ;forcylindricalspecimens,

    ;Q=x(2)

    ;wherehistheheightofthespecimenand,.the ;distanceofthepermeatingfrontfacetotheaxisofthe

    ;cylindricalspecimen.Thatis, ;u.Q:K.2h.

    ;Calculustheequation,

    ;?.Q.[=K.2.r

    ;Theequationforcalculatethepermeabilitycoefficient

    ;forcylindricalspecimensisobtained. ;55

    ;.

    ;T

    ;........

    ;i

    ;...

    ;m

    ;...........

    ;e

    ;.....

    ;-

    ;.....

    ;d

    ;.......

    ;e

    ;.....

    ;p.......

    ;e.

    ;ndent——

    ;pe———

    ;r———

    ;meatingbehaviorofhydraulicconcrete ;K=——

    ;?

    ;Q1n

    ;,2

    ;2X?h??

    ;whereFIandr2aretheinnerradius(30ITUTI)andouter

    ;radius(80nun),andhtheheightofthespecimenf160

    ;mm),respectively.

    ;3.Resultsanddiscussion

    ;3.1Permeatingandpermeability ;Fig.2illustratesthechangeofpermeability

    ;coefficients(dotsinthefigure)ofthetwosetsofthe ;cylindricalconcretespecimens(twopiecesforeach ;set)withtheelapsedtime.Itisobserved,thoughnot ;exact,thatattheinitial3to4hrs,thereisafluctuant ;increaseinthepermeatingrate.Oneofthepossible ;reasonsfortheincreaseofthepermeatingrateisthe ;inhomogeneityofthespecimenwhichmadethe ;differentpartshavedifferentpermeatingthroughtime, ;andtheotherreasonisthatthehydraulicpressure ;graduallybroketheoriginallyclosedporesinthe ;specimens,changedtheporestructure.Afterthe ;permeatingratehasreachedthehighestvalue,it ;beginstodecrease.Thetime(f)inFig.2isthetime ;elapsedafter4hrs.Itcanbeseenfromthefigurethat ;thepermeabilitycoefficientsofthespecimens ;decreasewiththeelapsedtimeafter4hrs. ;Therearetwopossiblereasonsforthedecrease ;ofpermeabilitycoefficients.Oneisthatthehardened ;cementpasteandsand

    ;hydraulicpressuredeposit

    ;particlesscouredoffby

    ;inandblockthecapillary

    ;poresintheconcrete,andtheotheristhatthenewly ;formedhydrationproductsoftheresidualcement ;clinkerparticlesblockthecapillarypores. ;Inthepresentwork,thepermeabilitycoefficients ;ofthespecimensdecreaseremarkablyin40to60hrs ;afterthehighestpermeatingrateisreached,then ;decreasegraduallyasthetimeelapsed.

    ;56

    ;Elaspedtime/h

    ;Elaspedtime/h

    ;Fig.2Permeabilitycoefficientvstimeforconcrete ;ComparedwiththeC2specimens,theC1

    ;specimenswithlowerstrengths,notonlywithhigher ;permeatingrate,butalsoreachedtherelativelystable ;permeatingstageearlier,beingearlierthan1O0hrsfor ;C1andlongerthan140hrsforC2,thoughtested ;underlowerhydraulicpressure.Thereasonforthe ;factisthattheC1specimenspreparedwithhigher ;water/cementratiohascontinuousporosity,which ;madethepermeatingtoreachstablefaster. ;ItcanalsobeseenfromFig.2thatforeitherthe ;C1orC2setofthespecimens,theexperimentaldata

    ;formthetwopiecesspecimensofthesamesetare ;ratherdifferent.Theresultindicatesthatinthesense ;ofpermeability,concreteisakindsofrather ;inhomogeneousmaterials.

    ;3,2Timedependencemodelandstability ;analysisofpermeating

    ;ItcanbeseenfromFig2thatthepermeability ;coefficientsforalltheconcretespecimenschangedin ;thesimilarway,decreasingwiththeelapsedtimewith ;asimilarprofile.DatafittingisperformedforFig2 ;accordingtoEq.(4):

    ;gu\_0Ixluul.0uIlgJj(王童0cuQ0兰善08go’

    ;Timedependentpermeatingbehavioro

    ;f

    ;h

    ;

    ;y

    ;d

    ;

    ;r

    ;

    ;a

    ;

    ;u

    ;

    ;li

    ;c

    ;

    ;c

    ;

    ;o

    ;

    ;n

    ;

    ;cr

    ;

    ;e

    ;

    ;te

    ;K=K+ae

    ;whereistheelapsedtimeinhr,Kthepermeability ;coefficientincm2,,a,and6thefittingconstants. ;TheresultsareshowninTable2,andthefitting ;curvesareshowninFig.2.

;Table2Fittingcoefficientsforwater

    ;permeatingcoefficientvstime

    ;ItcanbeseenformFig.2thattheexperimental ;resultsfitEq.(4)verywell,thesquaresofthe ;compoundcorrelationcoefficientsbeingallgreater ;than0.95.TheresultsindicatethatEq.(4)reflects

    dependentbehaviorof ;reasonablythetime

    ;permeabilityofhydraulicconcrete,thepermeability ;coefficientsdecreasingnegativeexponentiallywith

    ;theelapsedtime.Asthetimeprolonged,thedecrease ;ofthepermeabilitycoefficientsbecomeslowand ;eventuallybecomestable.RefertoEq.(4),whenthe ;timetislongenough,thesecondpartontherightof ;Eq.(4)tendstobezero,sothatmayberegardas ;thepossiblestablepermeabilitycoefficient. ;Itshouldbenotedthatinthepresentwork,the ;hydraulicpressuresappliedwerenothighenoughto ;breakdownthespecimens.Itisonlyonthiscondition ;thatafterreachingtheirmaximums,thepermeating ;flowratesdecreasewiththetime.Inrealhydraulic ;concreteengineering,however,whenthereismacro ;defectinconcrete,orwhensomecriticalhydraulic ;gradientisexceeded,theblockeffectoftheparticles ;mentionedabovewillbecomeveryweakandthe ;permeabilitycoefficientoftheconcretewillbecome ;higherandhigher,andtheconcretewilleventuallybe ;broken.

    ;4.Conclusion

    ;(1)Theself-designedpermeabilitytestingsetup ;usedinthepresentworkisapplicableforstudyingthe ;permeatingbehaviorofhydraulicconcreteafterbeing ;permeatedthrough.

    ;(2)Whenthehydraulicgradientislowerthan ;somecriticalvalue,thepermeabilityofhydraulic ;concretewilldecreasenegativeexponentiallywiththe

    ;elapsedtimeandeventuallytowardsastablevalue. ;References:

    ;lTheEconomyandTradeCommitteeofThePeople’s

    ;RepublicofChinaDL/T51502001testcodefor

    ;hydraulicconcrete.Beijing:ChinaElectricalPowerPress, ;2002.

    ;2]PicandetV.,Khelidj,A.andBastian,G..Effectofaxial ;compressivedamageongaspermeabilityofordinaryand ;highperformanceconcrete.CemConcrRes,2001,31(11)

;l525.

    ;3]Takafumi,S.,Theodore,W.B.andThomas,A.H..Effect ;ofstressongaspermeabilityinconcrete.AC/Mater’,’

    ;1996,9(5):443.

    RUANY.,FANGK.andWUL..Studyonthepermeating ;[4

    ;andcorrosionofconcrete.Yang~eRiver,2000,3,(9):33. ;(inChinese1

    ;51GUWprinc|pleandApplicationofSeepageCalculation ;Beijing:ChineseBuildingMaterialsIndustryPress,2000. ;(EditedbyMalikandDonna)

    ;57

    ;

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