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

Effectofbiogenicsulfuricacidonbehaviorofalkali-activatedcememtconcreteAbstract：Alkali-activatedcement(AAC)hasshownveryhighresistancetoacidandsalt.Moreover,itisinexpensivethanordinaryPortlandcement(OPC).AACisexpectedtohaveagreatpotentialformarineapplications.Tosimulatemarineenvironmentsinthiswork,AACsampleswereimmersedinbiogenicsulfuricacidinsteadofchemicalsulfuricacid.Threedifferentconcentrationlevelswereused,i.e.pH=l.l,1.6and2.0respectively.Changesinappearance,massloss,compressivestrength,porefluidpHvalue,andthereleasequantityofCa2+weremeasure.ESEM-EDS,XRD,andIRwereusedtocharacterizemicrostructuralandmorphologicalchanges,elementprofile,andcorrosionproductswithinthetop5mmofspecimensection.Theresultsshowthattherewasnocorrosiondamagewhentheacidconcentration(namelypHvalue)waseither1.6or2.0.WhenpHwasreducedto1.1,thechemicalbondsonsurface,suchasCa-O,Si-O,andAl-Ostartedtobreakoff.SO42combinedwithCa2+toformgypsum,leadingtoalooselayeronthesurface.Fortheplace5mmawayfromthesurface,asthepHvalueishigherthan1.1,therewasonlyaslightcorrosion.Theresearchfindingsareusefultoimprovethedurabilityofreinforcedalkali-activatedcementconcreteinmarineapplications.Keywords:Alkali-activatedcementconcrete,Biogenicsulfuricacid,Sulfuricacidconcentrations,Durability1.IntroductionBiogenicsulfuricacidhasadetrimentaleffectonconcrete1.Suchcorrosiondamageoftenoccurinsewagetreatmentfacilities,marineconstruction,oilwells,mining,andanyareaenrichedwithmicroorganisms2.Thecorrosionduetomicroorganismsaccountedfor10%20%ofthedamageofGermanbuildingmaterialsand10.9%ofconcretesewagepipeinAmerica3.$11billionwasspenttorepairthesewagedamageintheUS3.Itwasreportedthat20%ofthedamageofconcretestructureswascausedbymicrobialcorrosioninmarineapplications4.Microbialcorrosionhasbroughthugeeconomiclossestomodernsocieties.TheacidresistanceofordinaryPortlandcement(OPC)ispoorerthanthatofalkali-activatedcement(AAC)6.Inaddition,theimpermeabilityofAACisbetterthanthatofOPC,thepriceofAACischeaperthanOPC5-9.Therefore,AACisexpectedtohaveagreatpotentialinmarineapplications.Paker10foundthatamongallkindsofmicroorganisms,sulfate-reducingbacteria(SRB)andsulphur-oxidisingbacteria(SOB)havecausedthemostseriouscorrosiononconcrete.SulfateandorganicsulfurareturnedintoH2SbySRBinanaerobicenvironments,andthenH-2SisoxidizedintobiogenicsulfuricacidbySOBinaerobicenvironments.ThepHofbiogenicsulfuricacidcanbelowerthan1.0.ThemainhydrationproductsofOPCisC-S-H,Ca(OH)2andsoon,corrodedbyH2SO4,C-S-HandCa(OH)2areresolved,SiO2gelandgypsumisproduced,formingasoftenedlayerll.Monteny12foundthatthesoftenedlayerontheOPCconcretesurfaceactsasabarriertothetransportofchemicalacid,however,asforthebiogenicsulfuricacid,thesoftenedlayerbuildsacomfortableenvironmentforbacteriatogrowandtoproducemorebiogenicsulfuricacid,whichacceleratesthecorrosionrates.Alkali-activatedslagcementconcretewasimmersedinaH2SO4solution(pH=2)for6months,therewaslittlechangeofcompressivestrength13.However,thecompressivestrengthdeclinedrapidlywhenthesamplewasimmersedina5%H2SO4solutionfor1month,andtheconcretewasseriouslydamagedafter3months13.SunandWu14immersedalkali-activatedflyashcementpasteinvariousconcentrationsofH2SO4solutions,andfoundthattherewasslightdamageonthesurfacewhenimmersedin0.05%H2SO4for6months.Whenthesampleswereimmersedina3%H2SO4solution,thesurfacewasdamagedjustafter1week.However,thereisnostudyontheeffectofbiogenicsulfuricacidofdifferentconcentrationsonthebehaviorofAAC.Thispaperstudysthebehaviorofalkali-activatedcementconcreteunderbiogenicsulfuricacidwiththreedifferentconcentrationlevels.BetterunderstandingoftheacidcorrosionresistanceofAACisprerequisitetoawidespreaduseinmarineapplications.!.Experimental2.1MaterialsThefollowingmaterialswereusedinthisstudy.Slag(Tables1&2)wasproducedbyFuzhouTaiyuconcretefactory.Flyash(Tables3&4)wasproducedbyFuzhouShuangtengbuildingmaterialslimitedcompany.Naturalcoarseaggregates(Tables5&6)andriversand(Table7)camefromMinjiangriver.ChemicalgradeNaOH(>96%)wasproducedbyTianjinZhiyuanchemicalreagentcompany.2.2Specimenspreparation2.2.1 MixproportionTheC60concretewasdesignedaccordingtoSpecificationformixproportiondesignofordinaryconcrete15.ThemixcompositionsofalkaliactivatedconcreteisprovidedinTable8.2.2.2 ThepreparationprocessThefollowingprocedureisemployed.1 .Drymixcoarseaggregates,sand,slag,andflyashforoneminute.2 .PremixNaOHwithwater,inablenduntilalltheNaOHisdissolved.3 .AddtheNaOHsolutionintothedrymixandmixforoneminute.4 .Castfreshconcreteintomoldsundervibration5 .Removesamplesfromthemoldsafter24hours,transferintosteampressureequipment,andthenexperiencesanautoclavedcuring(hasavacuumpumpingfor30minutesfirst,andthenincreasedtemperatureto195andpressureto1.2MPafor1hour,thetemperatureandpressureshouldbemaintainfor6hours,andthenreducethepressurein2hours).2.3Testprocedures2.3.1 SimulationdeviceforbiogenicsulfuricacidcorrosionThedesignofsimulationdeviceforbiogenicsulfuricacidcorrosiontakesMontery,sdevice16asareferenceandweimprov