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sialate-disiloxo type of geopolymeric cement

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sialate-disiloxo type of geopolymeric cementof,type

    sialate-disiloxo type of geopolymeric cement J.Cent.SouthUniv.Techno1.(2009)16:0906-0913

    DOI:10.1007/sl17710090151-y

    Preparationandmicrostructurecharacterizationof

    poly?-sialate--disiloxotypeofgeopolymericcement

    ZHANGYun-sheng(张云升),SUNWei(~b),LIzonin(李宗津)

    Springer

    (1.JiangsuKeylaboratoryforConstructionMaterials,SoutheastUniversity,Nanjing211189,China;

    2.DepartmentofCivilEngineering,TheHongKongUniversityofScienceandTechnology,Kowloon,China)

    Abstract:Inordertoinvestigatetheinfluenceofthreekeymolarratios(n(SiO2)/n(A1203),(K2O)/n(A12O3)andn(H2O)/n(K2O)),a

    totalofninepotassiumpolysialate

    disiloxo(K-PSDS)geopolymericcementmatricesweredesignedaccordingtoo~hogonaldesign

    principle.Subsequentl~XRD.ESEMEDXAandMAS

    NMRtechniqueswereemployedtofurthercharacterizethemicrostructure ofthemostfullyreactedgeopolymericcementmatrix.Theexperimentalresultsshowthatn(K20)in(Al,O)hasthemostsignificant

    effectoncompressives~engthamongstthethreeratios.Thehighestcompressivestrength(20.1MPa)canbeachievedwhen

    n(Si02(A1203)=6.5,n(K20(A1203)=0.8andn(H2O)/n(K2o)=10.0.TheFTIRspectraofninePSDSgeopolymericcement

    matricesalsoindicate

    atgeopolymericcementmatrixwiththehighests~engthisthemostfullyreactedoneandpossessesthe

largestamountofgeopolymericcementproducts.ThemicroscopicanalysisrevealsthatPSD

    Sgeopolymericcementmatrixpossesses

    structuralcharacteristicssimilartogelsubstancesinhavingawiderangeofSiendowments.b

    utpredominantlytheframework

    molecularchainsofSipartiallyreplacedby4-coordinatedAltetrahedra1.

    Keywords:geopolymericcement;poly-sialate--disiloxo;preparation;microstructure 1Introduction

    Agreatdevelopmenthasbeenmadeinanewtype

    ofinorganiccementitiousmaterialsinrcccnt

    years--geopolymericcementaroundtheworld.

    Geopolymericcementisonetypeofthreedimensional CaOfleealuminosilicategelbinders,whichwas introducedintotheinorganiccementitiousworidby DAVIDOVITSinthelate1970s11.Geopolymercanbe

    synthesizedbymixingaluminosilicatereactivematerials withlessornoCaOcomponent(suchasmetakaolin)and s~onglyalkalinesolutions(suchasNa0HorKOH).and thencuringatroomtemperature.Inas~onglyalkaline solution,aluminosilicatereactivematerialsarerapidly dissolvedintosolutiontoformfreeSiO4andAl04 tetrahedralunits.Withthedevelopmentofreaction. mixingwaterisgraduallysplitoutandtheseSiO4and A104tetrahedralunitsarelinkedalternativelytoyield threetypesofmonolithiclikegeopolymerproducts:

    SiO4AIO4(PS),SiO4AIO4SiO4(PSS),and

    

    Sio4-A1o4Si04Si04(PSDS)bysharingalloxygen

    atomsbetweentwotetrahedralunits[2].Comparedto Portlandcement,geopolymerpossesseslowenergy

consumption[14],lessCO2emission[57],highearly

    strength[89,lessshrinkage[10l1],lowpermeability

    [12],goodfireandacidresistanceandgood

    durability[1315].Thesemeritsmakegeopolymer

    exhibitpromisingpotentialsinthefieldsofcivil,bridge, pavement,hydraulic,undergroundandmilitia

    engineering[1622].

    ComparedtothePSandPSStypes,PSDS

    geopolymericcementshowssomeadvantagesoverthe othertwotypessuchaseasyoperation,highstrength, sffongbondtoaconcreteorsteelsubstrate,goodfireand hightemperatureresistance.ThemeritsmakePSDS geopolymericcementhavepotentialsforapplications whentemperatureishighorfireisconcerned,suchas bridge,underground,tunnelandmilitaryengineering. Theprocessing.intrinsicmicrostructureandpropertiesof PSSgeopolymericcementhavebeeninvestigated

    [23(25].However,PSDSgeopolymericcementwasnot investigatedsystematicallybefore.Themicrostructureof PSDSgeopolymericcementmatrixisalsonot

    quantitativelycharacterized.Alltheseseriouslyinfluence thecommercialapplicationofPSDSgeopolyemric cement.

    Inthiswork,analmostfullyreactedpotassium

    polysialatedisiloxo(K-PSDS)geopolymericcement

    matrixwaspreparedatroomtemperaturebyoptimizing Foundationitem:Pr0jec2o09CB623200)supportedbytheNationalBasicResearchProgra

    mofChina;arojects(50702014,50878043)supposedbythe NationalNaturalScienceFoundationofChina;Project(NCET

    08-0116)supportedbytheProgramforNewCenturyExcellentTalentsin

UniversityofMinistryofEducation,China

    Receiveddate:2008——12——26;Accepteddate:2009--04——21

    Correspondingauthor:ZHANGYunsheng,Professor,PhD;Tel:+8613770936908;Email:zhangys279@163.com

    J.Cent.SouthUniv.Techno1.(2009)16:0906-0913907 thethreekeymolarratios:n(SiO2)/n(A1203),"(K2O)/ n(A1203)andn(H20)/n(K20).Thecompressivestrength andmicrostructureasafunctionofthethreeratiosofthe hardenedgeopolymericcementmatriceswereevaluated. Theinfluencingextentofeachratioonthecompressive strengthwasquantitativelydeterminedonbasisofthe varianceanalysis.Themicrostructuralchangesasa functionofratioswerealsoinvestigatedbyusingXray

    powderdiffractometryrXRD1andFouriertransforill infraredspectroscopy(FTIR)techniques.Basedonthe macroscopicandmicroscopicexperiments,analmost fullyreactedK.PSDSgeopolymericcementmatrixwith thehigheststrengthandoptimummicrostructurecanbe obtainedbyproperlyadjustingthethreemolarratios. Subsequently.thecoordinationstatusoftwomain constructionelements(Alandsi),micrographicsand chemicalcompositionsofK.PSDSgeopolymericcement matrixwerefurthercharacterizedandexaminedbyusing environmentscanningelectronmicroscopeequipped withenergydispersionXrayanalysis(ESEM-EDXA),

    hilysensitivemagicanglespinningnuclearmagnetic

    resonancespectroscopy(MASNMR1techniques.

    2Experimental

    2.1Materials

    Metakaolinusedasthemostmainlyaluminosilicate

    reactiverawmaterialsinthisworkwasobtainedby calciningpurekaolinfromChinaKaolinClayCompany, Suzhou,China.at700?for12h.TheMASNMR

    resonancespectrumofcalcinedkaolin.i.e.metakaolin showsthatabout95%of6foldcoordinatedAlinthe originkaolinistransformedinto4.foldCO0rdinatedone. Thechemicalcompositionsandphysicalpropertiesof metakaolinare1istedinTable1.AnalyticalreagentK0H pelletandpotassiumsilicatesolutionwithn(SiO2)/ "fK201of3.3andthesolidcontentof40%wereusedas alkalinereagents.Silicafumewithabout95%ofSiO, contentwasusedassiliconadditivetocompensatelhe shortageofsiliconinmetakaolin.Distilledwaterwas usedthroughouttheexperiment.

    2.2Methods

    2.2.1Specimenpreparationformechanicaltest Inthiswork,KOH,potassiumsilicatesolutionand waterwerefirstlymixedinabeakerandcooleddownto roomtemperature,andthenmetakaolinandsilicafume powderswereslowlyaddedintotheabovepre.mixed alkalinesolutionandmixedfor3min.Afterthat,the fleshgeopolymericcementmatrixwasrapidlypoured intocubicstee1mouldof40mlTl×401TInq×40mlT1.Al1

    sampleswerevibratedfor2minonthevibrationtable andsetatroomtemperature.Inordertopreventthe evaporationofmixingwater,thespecimenswere coveredbyplasticfilmduringthesettingandhardening process.Themouldwasremovedafter24h.The demouldedspecimenswerecuredat20?and95%

    relativehumidityfR.Hfor28d.At1eastsixspecimens

weremadeforeachformula.

    2.2.2Compressivetest

    Compressivestrengthtestwasperformedaccording ASTMC39-96.Atleastsixsamplesofeachformula weretested.Theaveragevaluewasservedasthe ultimatecompressivestrength.Aclosed.1oopservo. hydraulicallycontrolledmaterialstestingmachine (Sintech10/DMTS8l01wasusedtoconduct

    compressivetest.Theloadingwasdisplacement- controlledataconstantrateof1.3mm]minforallthe compressiontests.

    2.2.3Samplepreparationformicroanalysis Thefragmentsfromdifferentformulaewere collectedaftercompressivetest.Someofthemwereused toconductESEMEDXAanalysis.Theotherswere

    furtherfinelycrushed.andthenimmersedinethano1for 3dtostopthefurthergeopolymerizationreactionof geopolymericcement.subsequentlyovendriedat60?

    for6htoremovethephysicallyabsorbedwater.After that,thesehardenedgeopolymericcementpastefractions werefurthergroundintoveryfineparticleswithagate mortar,andremovethecoarseparticleswiththesieveof 80panindiameter.Thefinepowderswereplacedin desiccatorsfor24h.

    2.2.4FTIRanalysis

    Fouriertransforminfraredspectroscopy(FTIR) analysiswasperformedonABio.RadFTS6000FTIR byusingKBrpellettechniquesr3mgoffinepowders preparedpreviouslywerehomogenouslygroundwith 300mgofKBrpowdertogetheruntilthemixturehasthe

    consistencyoffmeflour,andthenpressedintoadisk1. 2.2.5XRDanalysis

    XraypowderdiffractionwasrecordedonaPhilips PW1830spectrometerwiththefollowingtesting parameters:40kV,30mA,CuIradiation.TheXRD pa~eruswereobtainedatascanningrateofl(.)/min from10.to80.(2andstepsof0.05.(2.The

    wavelengthwasselectedas0.1542nn1.

    Table1Chemicalcompositionsand1ohysicalorooertiesofmetakaolin

    J.Cent.SouthUniv.Techno1.(2009)16:09060913

    2.2.6ESEM.EDXAanalysis

    XL30-ESEMequippedwithEDXAwasusedto

    charaeterizethemicrostructureandchemical compositionsofthefullyreactedPSDSgeopolymeric cementmatrix.Thefollowingtestparameterswere employedinthiswork:acceleratingvoltageof20keV, pressureandrelativehumidityinsamplechamberof 559.952Paand80%.respectively.

    2.2.7M_AS.NMRanalysis

    AJEOLNM-ESH40MUnuclearmagnetic

    resonancespectroscopy(NMR)wichthemagicangle spinnhagtechniquewasadopted.Inthiswork,the spinningspeedofthecapsulewas4.8kHz.SiandAl spectraweremeasuredandrecordedatNMRfrequency Of793and72.18MHz.respectively.Thespectrometer wasinterfacedwithacomputerandequippedwitha MASbroad-bandprobeforthesolidstateexperiments. TheoeakswerefiredbyGaussianlines.

    2.3Experimentalprogram

    Afully..reactedpotassiumpoly..sialate..disiloxo

    rKPSDS)geopolymericcementwassynthesized.The mainobjectiveofthestudywastoinvestigatetheeffects ofthreefactors:n(SiO2)/n(Alz03)(factorA),n(K20)/ n(A1203)(factorB)andn(H20)/n(KzO)(factorC)on mechanicalstrengthandmicrostructure.Thethreemolar ratioswerevariedinthefollowingrangesrespectively:

    n(Si02)/n(A1203)?6.5,0.8?(K2O)/n(A1203)? 5.5?

    1.2,and7.O~n(H20)/n(K2O)?10.0.The1evelsforeach

    ofthefactorsweresetatthreegrades(1ow,intermediate, andhi).Thustheexperimentalprogramherewasthree factorsexperimentwiththreelevelsforeachfactor. Basedonthefactor-leveltable.atota1ofnine experimentalformulaeweredesignedaccordingtoa L9(3)orthogonaldesignprinciple,asshowninTable2. Theinteractioneffc:ctbetweendifferentfactorswasnot takenintoaccountintheexperimentalarrangement. 3Resultsanddiscussion

    3.1Preparationoffully-reactedPSDSgeopolymeric cementmatrix

    ThecompressivestrengthsofninedifferentPSDS geopomymericcementmatricesaregiveninTable2. Theeffectsofthethreemolarratios(n(SiO2)/n(A1203), n(K20)/n(Al203)andn(H20)/n(K20))werequantita- tivelydeterminedbyusingthegradationanalysisand varianceanalysis.Subsequently.XRDandFTIRanalysis ofeachgeopolymericcementformulawasalso

    conducted.Onbasisofthemacroscaleandmicroscale results.analmostfully-reactedPSDSgeopolymeric cementmatrixwiththehighestcompressivestrengthand optimummicrostructurecanbeobtainedbyproperly

selectingthethreemolarratios.

    3.1.1Compressivetest

    Inordertodeterminetheinfluencingextentofthe threemolarratios(n(SiOE)/n(A1203),n(K20)/n(A1203) andn(H20)/n(K20))andtheoptimummixture

    proportionofPSDSgeopolymericcementmatrix,the gradationanalysiswasfirstemployed.Theanalysiswas illustratedintabularforlTlinorderthatitcanbeclearly anderstood.asshowninTable2.Itcanbeseenfrom Table2t}Iat(K2O)/n(A1203)exhibitsthemost significantinfluencingextentonthecompressive strengthofthehardengeopolymericcementmatrices amongthethreemolarratios.Thecorresponding gradationrangeis8.6.Comparatively,n(SiO2)/n(Al203) andn(H2O)/n(K2O,haverelativelylittleinfluenceonthe compressivestrength,whosegradationrangesare2.4 and4.1.respectively.Carefullycomparingthedifference Table2Exoerimentaloro~ramandcompressivestrengthofPSDSgeopolymericcementmat

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    J.Cent.SouthUniv.Techno1.(2009)16:0906-0913 amongKl,K,andK1showsthatthehardened

    geopolymericcementmatrixhasthehighestcompressive strengthat(Si02)(Al203):6.5,n(K20)/n(A1203):0.8 andn(H,01/n(K2O)=l0.0.

    Thesignificanceandinfluencingextentofthethree molarratiosoncompressivestrengthcanbeeasily observedthroughtheabovesimplegradationanalysis. However.itiswellknownthatthegradationanalysis cannotquantitativelydistinguishwhetherthe compressivestrengthdifferenceamongdifferentlevelsis causedbytestingerrorsorbydifferentlevelsinthecase Ofthesamefactor.Inordertosolvethepr0blem. varianceanalysiswasemployedinthefollowingstudies. Table3liststhevariancesanalysisresultsofdifferent

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