Effect of biogenic sulfuric acid on behavior of alkali-activated cememt concrete.docx

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1、Effectofbiogenicsulfuricacidonbehaviorofalkali-activatedcememtconcreteAbstract：Alkali-activatedcement(AAC)hasshownveryhighresistancetoacidandsalt.Moreover,itisinexpensivethanordinaryPortlandcement(OPC).AACisexpectedtohaveagreatpotentialformarineapplications.Tosimulatemarineenvironmentsinthiswork,AAC

2、sampleswereimmersedinbiogenicsulfuricacidinsteadofchemicalsulfuricacid.Threedifferentconcentrationlevelswereused,i.e.pH=l.l,1.6and2.0respectively.Changesinappearance,massloss,compressivestrength,porefluidpHvalue,andthereleasequantityofCa2+weremeasure.ESEM-EDS,XRD,andIRwereusedtocharacterizemicrostru

3、cturalandmorphologicalchanges,elementprofile,andcorrosionproductswithinthetop5mmofspecimensection.Theresultsshowthattherewasnocorrosiondamagewhentheacidconcentration(namelypHvalue)waseither1.6or2.0.WhenpHwasreducedto1.1,thechemicalbondsonsurface,suchasCa-O,Si-O,andAl-Ostartedtobreakoff.SO42combinedw

4、ithCa2+toformgypsum,leadingtoalooselayeronthesurface.Fortheplace5mmawayfromthesurface,asthepHvalueishigherthan1.1,therewasonlyaslightcorrosion.Theresearchfindingsareusefultoimprovethedurabilityofreinforcedalkali-activatedcementconcreteinmarineapplications.Keywords:Alkali-activatedcementconcrete,Biog

5、enicsulfuricacid,Sulfuricacidconcentrations,Durability1.IntroductionBiogenicsulfuricacidhasadetrimentaleffectonconcrete1.Suchcorrosiondamageoftenoccurinsewagetreatmentfacilities,marineconstruction,oilwells,mining,andanyareaenrichedwithmicroorganisms2.Thecorrosionduetomicroorganismsaccountedfor10%20%

6、ofthedamageofGermanbuildingmaterialsand10.9%ofconcretesewagepipeinAmerica3.$11billionwasspenttorepairthesewagedamageintheUS3.Itwasreportedthat20%ofthedamageofconcretestructureswascausedbymicrobialcorrosioninmarineapplications4.Microbialcorrosionhasbroughthugeeconomiclossestomodernsocieties.Theacidre

7、sistanceofordinaryPortlandcement(OPC)ispoorerthanthatofalkali-activatedcement(AAC)6.Inaddition,theimpermeabilityofAACisbetterthanthatofOPC,thepriceofAACischeaperthanOPC5-9.Therefore,AACisexpectedtohaveagreatpotentialinmarineapplications.Paker10foundthatamongallkindsofmicroorganisms,sulfate-reducingb

8、acteria(SRB)andsulphur-oxidisingbacteria(SOB)havecausedthemostseriouscorrosiononconcrete.SulfateandorganicsulfurareturnedintoH2SbySRBinanaerobicenvironments,andthenH-2SisoxidizedintobiogenicsulfuricacidbySOBinaerobicenvironments.ThepHofbiogenicsulfuricacidcanbelowerthan1.0.Themainhydrationproductsof

9、OPCisC-S-H,Ca(OH)2andsoon,corrodedbyH2SO4,C-S-HandCa(OH)2areresolved,SiO2gelandgypsumisproduced,formingasoftenedlayerll.Monteny12foundthatthesoftenedlayerontheOPCconcretesurfaceactsasabarriertothetransportofchemicalacid,however,asforthebiogenicsulfuricacid,thesoftenedlayerbuildsacomfortableenvironme

10、ntforbacteriatogrowandtoproducemorebiogenicsulfuricacid,whichacceleratesthecorrosionrates.Alkali-activatedslagcementconcretewasimmersedinaH2SO4solution(pH=2)for6months,therewaslittlechangeofcompressivestrength13.However,thecompressivestrengthdeclinedrapidlywhenthesamplewasimmersedina5%H2SO4solutionf

11、or1month,andtheconcretewasseriouslydamagedafter3months13.SunandWu14immersedalkali-activatedflyashcementpasteinvariousconcentrationsofH2SO4solutions,andfoundthattherewasslightdamageonthesurfacewhenimmersedin0.05%H2SO4for6months.Whenthesampleswereimmersedina3%H2SO4solution,thesurfacewasdamagedjustafte

12、r1week.However,thereisnostudyontheeffectofbiogenicsulfuricacidofdifferentconcentrationsonthebehaviorofAAC.Thispaperstudysthebehaviorofalkali-activatedcementconcreteunderbiogenicsulfuricacidwiththreedifferentconcentrationlevels.BetterunderstandingoftheacidcorrosionresistanceofAACisprerequisitetoawide

13、spreaduseinmarineapplications.!.Experimental2.1MaterialsThefollowingmaterialswereusedinthisstudy.Slag(Tables1&2)wasproducedbyFuzhouTaiyuconcretefactory.Flyash(Tables3&4)wasproducedbyFuzhouShuangtengbuildingmaterialslimitedcompany.Naturalcoarseaggregates(Tables5&6)andriversand(Table7)camefromMinjiang

14、river.ChemicalgradeNaOH(96%)wasproducedbyTianjinZhiyuanchemicalreagentcompany.2.2Specimenspreparation2.2.1 MixproportionTheC60concretewasdesignedaccordingtoSpecificationformixproportiondesignofordinaryconcrete15.ThemixcompositionsofalkaliactivatedconcreteisprovidedinTable8.2.2.2 Thepreparationproces

15、sThefollowingprocedureisemployed.1 .Drymixcoarseaggregates,sand,slag,andflyashforoneminute.2 .PremixNaOHwithwater,inablenduntilalltheNaOHisdissolved.3 .AddtheNaOHsolutionintothedrymixandmixforoneminute.4 .Castfreshconcreteintomoldsundervibration5 .Removesamplesfromthemoldsafter24hours,transferintost

16、eampressureequipment,andthenexperiencesanautoclavedcuring(hasavacuumpumpingfor30minutesfirst,andthenincreasedtemperatureto195andpressureto1.2MPafor1hour,thetemperatureandpressureshouldbemaintainfor6hours,andthenreducethepressurein2hours).2.3Testprocedures2.3.1 SimulationdeviceforbiogenicsulfuricacidcorrosionThedesignofsimulationdeviceforbiogenicsulfuricacidcorrosiontakesMontery,sdevice16asareferenceandweimprov