硅灰粉煤灰对水泥石膏微观结构的影响的AFMSEM研究毕业论文外文翻译Word文档格式.docx

硅灰粉煤灰对水泥石膏微观结构的影响的AFMSEM研究毕业论文外文翻译Word文档格式.docx

《硅灰粉煤灰对水泥石膏微观结构的影响的AFMSEM研究毕业论文外文翻译Word文档格式.docx》由会员分享，可在线阅读，更多相关《硅灰粉煤灰对水泥石膏微观结构的影响的AFMSEM研究毕业论文外文翻译Word文档格式.docx（14页珍藏版）》请在冰豆网上搜索。

Atomicforcemicroscopy（AFM）wasusedtoobserveparticleshapeandsurfacetexturedetailsofnormalportlandcementandsupplementarycementingmaterials（silicafume,low-calciumflyash,andhigh-calciumflyash）.Thelattermaerialsmixedwithcementwereexaminedafterprolongedhydration.Significantinnovativeinformationonparticleshapeandhydratedpastemicrostucturewasobtained.Conventionalmicroscopytechniques,suchasscanningelectronmicroscopy（SEM）,cannotprovidesuchdetailedimagesandsurfacetexturecharacteristicsofthefinematerials（especiallysilicafume）andoftheproductmicrostructure.AFMshowed,forthefirsttime,thatsilicafumeparticlesareprimarilycomposedoftwocomplimentaryparts（hemispheresorsemicylinders）.Nano-sizeparticleswerefoundinallmaterials.Arelativelysmoothproductsurfacewasobservedinthehydratedcementpaste.Thehydratedsurfaceoftheaddition-cementpastespresentedsmallspheroidbulges,givinganadditionalroughnessaswasmeasuredbyAFM.Asufficientcorrelationofthismicroscopicalquantitativeinformationwithmacroscopicalengineeringanddurabilitypropertiesofcementproductsisalsopresented.

1.Introduction

Fortechnicalandeconomicreasons,newmaterialswithpozzolanicandcementitiouspropertieshavebeenmixedwithcementduringthelastyears.Amongthesematerialsareindustrialby-productssuchasflyashfromcoal-burningelectricpowerplants,slagsfrommetallurgicalfurnaces,silicafume（ormicrosilica）fromelectricarcfurnacesproducingsiliconandferrosiliconalloys,andsomenaturallyactivematerialssuchasvolcanictuffs.TheiractivityismainlyduetotereactionoftheiractiveconstituentswithCa（OH）2producedfromcementhydration（pozzolanicactivity）andtheformationofhydratedproductswithbindingproperties.Theexactstuctureandchemicalformulaoftheseproductsarestillunknown.

Thedetailedknowledgeofcementpastemicrostructureisofgreatimportancefortheunderstandingandpredictionofcementapplications’performance.Visualexamination,opticalmicroscopy,andscanningelectronmicroscopy（SEM）havebeenextensivelyusedinmicrostuctureresearchofhardenedcementpasteandconcrete,providingadditionalunderstandingofmacroscopicalproperties.Electronmicroprobeanalysisstudiesofhardenedcementpasteshavecontributedtothecompositionalcharacterizationofhydrationproductsandspatialinformation.Transmissionenergymicroscopy（TEM）enablestheidentificationandanalysisoffeaturesonasignificantlysubmicrometrescale.However,thesetechniquesmostcommonlyinvestiatespecimensunderhighvacuum,andthusalterationofdamageonmicrostructuremorpologymayoccur.Furthermore,someofthesematerials,suchassilicafume,withagrainsizedistributioninthe0.02to0.3umrange,aretoosmalltobeobservedindetailbySEM.Techniqueswithstrongermagnificationcapabilitieswouldbeveryusefulinthesecases,aswellinthebetterconceptionofthepurecementpastemicrostructure.

Byatomicforcemicroscopy（AFM）,asharptipisscanningoverasamplesurfaceandthreedimensionalimageshaveingresolutionatnanometerlevelareobtainedatatmosphericconditions（roomtemperature,humidity,andambientpressure）.AFMhasbeenusedtoproduceatomicresolutionimagesofbothconductorsandnonconductors.Inthepresentdecade,AFMhasalsobeenusedinthestudyofcementsurfacemicrostucture,especiallybecausesurfacescanbeimagedunderaqueoussolutionsatnormalconditions.AFMhasbeenappliedtoinvestigatethesurfaceofalitealoneandofalitecoveredwithanorganicadmixtureandhasshownthatthesurfaceroughnessofthealitedecreasedmarkedlyafterreactionwiththeorganicadmixture.AFMwasalsousedtoinvestigatetheearlyperiodofportlandcementhydration,andamembrane/osmosismodelwasproposed.Acombinationofnuclearmagneticresonance（NMR）andAFMshowedthatthehydrationrateishighlycorrelatedwiththeroughnessofthegelsurface.Forflyashparticles,AFMshowedtwotypesofspheres,dark,largeones（approximately100um）withnumerouscratersontheirsurfaceandclear,smallones（approximately10um）withsmoothsurface.

Inthepresentwork,AFMwasusedtoobserveparticleshapeandsurfacetexturedetailsofcementsilicafume,flyashes,andhydratedmixtures.Distinctmicrographsof1um×

1umweretaken,providinginformationontheparticleshapeoftheadditionsandmicrostructureofthehydratedmixtures.ThesamematerialswereexaminedunderSEMtoobtainageneraloverview,andthecomparativeuseofthesetwomethods（SEM-AFM）isdiscussed.Finally,thecorrelationbetweenthemicrostructureandthemacroscopicalengineeringanddurabilitypropertiesofcementproductsisdiscussed.

2.Experimentalprocedure

2.1.Materialsandsamplepreparation

Threetypicalcementitiousand/orpozzolanicadditionswereexamined;

asilicafume,alow-calciumflyash,andahigh-calciumflyash.Thesilicafume（SF）originatedfromNorway（ElkemMaterialsA/S,Kristiansand）andisatypicalhighlypozzolanicmaterial.Thelow-Caflyash（FL）wasproducedisDenmark（distributedbyDanaskeI/S,Aalborg）andiscategorizedasnormalpozzolanicmaterial.Thehigh–Caflyash（FH）wasproducedinGreece（PublicPowerCorporation,Ptolemais）andisacementitiousmineraladmixture.Thus,thechoiceofthesematerialscoversalmostalltherangeofcementitious-pozzolanicby-productsusedinconcrete.SFandFLwereusedastheyweredeliveredfromtheproducers,whereasFHwaspulverizedpriortouse,tomeettheFLmeanparticlesize.Anormalportlandcement（350m2/gBlaine’sfineness）wasused.

Themainphysicalpropertiesandchemicalanalysesofthematerials,determinedbyX-raysedimentationtechnique,showedthatthemeanparticlediameterofflyasheswas13um,similartothecementparticles.SFparticles,asreportedintheliterature,areabout100timessmallerinsize（0.1umaveragediameter）.

Fourpastespecimenswerecastinsmallplasticcontainers.Thepastesweremadeofnormalportlandcement（control）,cementplus10%silicafume,cementplus20%low-calciumflyash,andcementplus20%high-calciumflyash.Awater-to-cementratio（W/C）of0.5wasretainedforallpastes.First,thecementamount（10g）wasaddedandthenthecorrespondingamountoftheadditive.Thesematerialsweremixedbyhandfortwomin;

thenthecorrespondingamount（5g）ofthewaterwasaddedandthefreshpastewasfurthermixedfor2min.Onedayafterthecasting,1mlofwaterwasaddedtoallspecimens.Thecontainerswerehermeticallysealedandplacedat20℃constanttemperature.Microscopyanalyseswereperformedaftersixmonths.

2.2.Atomicforcemicroscopy

Materialparticlesandpastesampleswereexaminedbyatomicforcemicroscope（RasterscopeTM4000,DanishMicroEngieeringA/S）runninginnoncontactmode（0.1nNforce）.Theparticlesinthecement,silicafume,andflyashesweredispersedbyultrasonictreatment;

thesilicafumeindistilledwaterandtheothercomponentsinacetoneinordertoavoidhydartion.Thespecimenswerepreparedbyleavingonedropofthesuspensiontodryatroomconditionsonablockofhighlyorientedpyrolyticgraphite（HOPG）.Thesamplesfromtepasteswereremovedbyhammerstrokefromthepastespecimens,oven-driedat105℃for24h.SmallpiecesofmaterialwerethengludeontoAFMsampleholdersandslightlypolishedindrycondition.Allspecimenswereexaminedatroomconditions（～20℃,1atmand40-60%relativehumidity）.

2.3.Scanningelectronmicroscopy

Alloftheaboveparticlesandpasteswerealsoexaminedbymeansofscanningelectronmicroscope（LEO435VP）.Surfacemicrographsof8,000magnificationsizewereobtainedandcanbeusedasageneraloverviewofthematerials.

3.Resultsanddiscussion

3.1.Cement,silicafume,andflyashparticles

TypicalSEMmicrographsinFigs2-5.

AsobservedbySEM（Fig.1a）,cementparticleshaveandirregularpolygonalshape.Particlesizesrangefrom15tolessthan0.5um.FromAFM（Fig.2）,someparticlesofsize1to0.5umndiameterarerounded,withaglobularsurface,whereasothersarepolygonal.However,someirregularparticlesofsizelessthan0.1umindiameterwereobserved（Fig.2,right）.

SilicafumeparticlesaretoosmallinsizetobeimagedindetailbySEM（Fig.1b）.FromAFM（Fig.3）,thesilicafumeinvestigatedhasparticlediametersofabout0.1um,inagreementwithpreviousreporteddimensions.Twoparticleshapesarepresent,onespheroidandonecylindrical.Itisverycharacteristicofthematerialthatallparticlesarecomposedoftwocomplimentaryparts（hemispheresorsemi-cylinders）.Thisfeaturecanbeexplainedfromtheproductionofsilicafume,wherethereductionofquartztosiliconatabout2000℃producesagaseousSiO,whichistransportedtolowertemperatrues,whereitisoxidizedandcondensed.ThisparticularshapecanhelpinSFidentificationincementpasteduringthehydrationprocess.

Ingeneral,flyashesconsistofglassyspheresofvarioussizes.Duetothelowerproportionofsurfacedepositsconsistingofalkalisulphatecrystals,FLtendstoshowacleanerappearanceinSEM（Fig.1c）.FortheFH,manyoftheparticlesareplerospherescontainingnumeroussmallerparticles,butaftergrinding,smallersizeparticlesareproducedhavinganirregularshapelikethecementparticles（Fig.1d）.UsingAFMtechnique,itisobserved（Fig.4）thattheFLconsistsprimarilyoflargespheroidparticles（approximately3um）withasmoothsurface,likefoundpreviously,andofsmaller（inonedimension）.Thesenano-sizeparticlesmaybecorrelatedwiththeearlypozzolanicactivityoftheflyashes.

3.2.Pastemicrostructure

SEMmicrographsforallmaturepastesaresummarized