毕业设计中英文翻译混凝土受持续高温影响的强度的研究.docx
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毕业设计中英文翻译混凝土受持续高温影响的强度的研究.docx
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毕业设计中英文翻译混凝土受持续高温影响的强度的研究
外文资料
STUDIESONIMPACTSTRENGTHOFCONCRETESUBJECTEDTOSUSTAINED
ELEVATEDTEMPERATURE
SureshNARAYAN
Concretehasaremarkablefireresistingproperties.Damageinconcreteduetofiredependsonagreatextentontheintensityanddurationoffire.Spallingcrackingduringheatingarecommonconcretebehaviourobservedintheinvestigationofthefireaffectedstructures.Plentyofliteratureisavailableonthestudiesofconcretebasedontimetemperaturecures.Inpower,oilsectorsandnuclearreactorsconcreteisexposedtohightemperatureforconsiderableperiodoftime.Theseeffectscanbereckonedasexposuretosustainedelevatedtemperature.Thesustainedelevatedtemperaturemaybevaryingfromafewhourstoanumberofyearsdependinguponpracticalconditionofexposures.Theknowledgeonpropertiesundersuchconditionsisalsoofprimeimportanceapartfromthestructuressubjectedtohighintensityfire.Impactstudiesofstructuresubjectedtosustainedelevatedtemperaturebecomesmoreimportantasitinvolvessensitivestructureswhichismorepronetoattacksandaccidents.Inthispaperimpactstudiesonconcretesubjectedtosustainedelevatedtemperaturehasbeendiscussed.Experimentshavebeenconductedon180specimensalongwith180companioncubespecimens.Thetemperaturesof100°C,200°Cand300°Cforadurationofexposureof2hours4hoursand6hourshasbeenconsideredintheexperiments.Theresultsarelogicallyanalyzedandconcluded.
1.INTRODUCTION
Theremarkablepropertyofconcretetoresistthefirereducesthedamageinaconcretestructurewheneverthereisanaccidentalfire.Inmostofthecasestheconcreteremainsintactwithminordamagesonly.Thereasonbeinglowthermalconductivityofconcreteathighertemperaturesandhencelimitingthedepthofpenetrationoffiredamage.Butwhentheconcreteissubjectedtohightemperatureforlongdurationthedeteriorationofconcretetakesplace.Henceitisessentialtounderstandthestrengthanddeformationcharacteristicsofconcretesubjectedtotemperatureforlongduration.InthispaperanattempthasbeenmadetostudythevariationinImpactStrengthofconcretewhensubjectedtoatemperaturerange100oC,200oCand300oCsustainedforaperiodof2hrs,4hrsand6hrs.
Thereviewoftheliteratureshowsthatalotofresearchwork[1–3]hastakenplaceontheeffectofelevatedtemperatureonconcrete.Allthesestudiesarebasedontime–temperaturecurves.Henceanattempthasbeenmadetostudytheeffectofsustainedelevatedtemperatureonimpactstrengthofconcreteandtheresultsarecomparedwiththecompressivestrength.Theexperimentalprogrammehasbeenplannedforunstressedresidualstrengthtestbasedontheavailablefacilities.Residualstrengthisthestrengthofheatedandsubsequentlycooledconcretespecimensexpressedaspercentageofthestrengthofunheatedspecimens.
2.EXPERIMENTALINVESTIGATION
2.1.TESTSPECIMENANDMATERIALS
Atotalof180specimensweretestedinthepresentstudyalongwith180companioncubes.Anelectricovencapableofreachingamaximumtemperatureof300oChasbeenusedforinvestigation.FineandcoarseaggregatesconformingtoIS383hasbeenusedtopreparethespecimenwithmixproportionsM1=1:
2.1:
3.95w/c=0.58,M2=1:
1.15:
3.56w/c=0.53,M3=1:
0.8:
2.4w/c=0.4.
2.2TESTVARIABLES
Theeffectsofthefollowingvariableswerestudied.
2.2.1Sizes
SizeofImpactStrengthTestSpecimenwas150mmdialand64mmthicknessandsizeofcompanioncube150x150x150mm.
2.2.2MaximumTemperature
Inadditiontoroomtemperature,theeffectofthreedifferenttemperatures(100oC,200oCand300oC)onthecompressivestrengthwasinvestigated.
2.2.3ExposureTimeatMaximumTemperature
Threedifferentexposuretimeswereusedtoinvestigatetheinfluenceofheatoncompressivestrength;theyare2hrs,4hrsand6hrs.
2.2.4CoolingMethod
Specimenswerecooledinairtoroomtemperature.
3.TESTPROCEDURE
AllthespecimenswerecastinsteelmouldsasperIS516andeachlayerwascompacted.Specimenswerethenkeptintheirmouldsfor24hoursafterwhichtheyweredecoupledandplacedintoacuringtankuntil28days.Afterwhichthespecimenswereremovedandwereallowedtodryinroomtemperature.Thesespecimenswerekeptintheovenandtherequiredtargettemperaturewasset.Dependingonthenumberofspecimenkeptinsidetheoventhetimetakentoreachthesteadystatewasfoundtovary.Afterthesteadystatewasreachedthespecimensweresubjectedtopredeterminedsteadydurationattheendofwhichthespecimensarecooledtoroomtemperatureandtested.
ACIdropweightimpactstrengthtestwasadopted.Thisisthesimplestmethodforevaluatingimpactresistanceofconcrete.Thesizeofthespecimenis150mmdialand64mmthickness.Thediscspecimenswerepreparedusingsteelmouldscuredandheatedandcooledas.Thisconsistsofastandardmanuallyoperated4.54kghammerwith457mmdrop.A64mmhardenedsteelballandaflatbaseplatewithpositioningbracketandlugs.Thespecimenisplacedbetweenthefourguidespieces(lugs)located4.8mmawayfromthesample.Aframe(positioningbracket)isthenbuiltinordertotargetthesteelballatthecentreofconcretedisc.Thedisciscoatedatthebottomwithathinlayerofpetroleumjellyorheavygreasetoreducethefrictionbetweenthespecimenandbaseplate.Thebottompartofthehammerunitwasplacedwithitsbaseuponthesteelballandtheloadwasappliedbydroppingweightrepeatedly.Theloadingwascontinueduntilthediscfailedandopenedupsuchthatittouchedthreeofthefourpositioninglugs.Thenumberofblowsthatcausedthisconditionisrecordedasthefailurestrength.Thecompanioncubesweretestedforcubecompressionstrength(fake).
4.ANALYSISANDRESULTS
4.1RESIDUALCOMPRESSIVESTRENGTHVS.TEMPERATURE
FromTable1,at100°CsustainedelevatedtemperatureitisseenthattheresidualstrengthofaircooledspecimensofmixesM1,M2andM3hasincreasedinstrength114%forM1mix,109%forM2mixand111%forM3mixfor6hoursdurationofexposure.Whenthesustainedelevatedtemperatureisto200°Cforaircooledspecimensthereisadecreaseinstrengthupto910%approximatelyforM1mixforadurationof6hours,butincaseofM2mixitis82%andforM3mixitis63%maximumfor6hoursdurationofexposure.WhentheconcretemixesM1,M2andM3areexposedto300°Csustainedtemperaturethereisareductioninstrengthupto78%forM1mixfor6hourdurationofexposure.
4.2RESIDUALCOMPRESSIVESTRENGTHVSDURATIONOFEXPOSURE
FromTable1,resultshowsthatheatingupto100°Cfor2hoursand4hours,theresidualstrengthofmixM1hasdecreasedwhereastheresidualstrengthofmixM2andM3hasincreased.Theresidualstrengthisfurtherincreasedfor6hoursdurationofexposureinallthethreemixesM1,M2andM3evenbeyondthestrengthatroomtemperature.WhenthespecimensofmixesM1,M2andM3areexposedto200°Cfor2,4and6hoursofduration,itisobservedthattheresidualstrengthhasdecreasedbelowtheroomtemperatureandhasreached92%forM1mix,82and73%forM2andM3mixrespectively.ConcretecubesofmixesM1,M2andM3whensubjectedto300°Ctemperaturefor2,4and6hourstheresidualstrengthformixM1reducesto92%for2hoursupto78%forsixhoursdurationofexposure,forM2mix90%for2hoursdurationofexposureupto76%forsixhourdurationofexposure,forM3mix88%upto68%between2and6hoursofdurationofexposure.
5.IMPACTSTRENGTHOFCONCRETE
5.1RESIDUALIMPACTSTRENGTHVSTEMPERATURE
Fromthetable1,itcanbeobservedthatforthesustainedelevatedtemperatureof100°Ctheresidualimpactstrengthofallthespecimensreducesandvarybetween20and50%formixM1,15to40%formixM2andM3.Whenthesustainedelevatedtemperatureis200°Ctheresidualimpactstrengthofallthemixesfurtherdecreases.Thereductionisaround60-70%formixM1,55to65%forM2andM3mix.Whenthesustainedelevatedtemperatureis300°Citisobservedthattheresidualimpactstrengthreducesfurtherandvarybetween85and70%formixM1and85to90%formixM2andmixM3.
5.2RESIDUALIMPACTSTRENGTHVSDURATIONOFEXPOSURE
FromtheTable1andFigures1to3,itcanbeobservedthatthereisareductioninimpactstrengthwhenthesustainedelevatedtemperatureis100°Cfor2hrs,4hrsand6hrs,anditsrangeis15to50%forallthemixesM1,M2andM3.TheinfluenceofdurationofexposureishigherformixM1whichdecreasesmorerapidlyascomparedtomixM2andmixM3forthesamedurationofexposure.Whenthespecimensaresubjectedtosustainedelevatedtemperatureof200°Cfor2,4and6hourofduration,furtherreductioninresidualimpactstrengthisobservedascomparedtoat100°C.Thereductionisintherangeof55-70%forallthemixes.Thesixhourdurationofexposurehasagreaterinfluenceontheresidualimpactstrengthofconcrete.Whenthesustainedelevatedtemperatureis300°Cfor2,4and6hoursdurationofexposuretheresidualimpactstrengthreduces.Itcanbeseenthatbothtemperatureanddurationofexposurehaveaveryhighinfluenceontheresidualimpactstrengthofconcretewhichshowsareductionupto90%approximatelyforallthemixes.
Table1.Residualimpactstrengthandresidualcompressivestrength
Temperature
Durationofexposue
Residualimpact
Strengthatfailure
ResidualcompressivestrengthinN/mm2
%variationinresidualimpactstrength
%variationinresidualcompressivestrengt
°C
Hours
I1
I2
I3
M1
M2
M3
ri1
ri2
ri3
M1
M2
M3
0
41.3
49
66
33
44
60
100
100
100
100
100
100
100°C
2
4
6
33.6
24
19.3
43
36
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