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CIVILENGINEERING MATERIALS Thispageintentionallyleftblank
WOODHEADPUBLISHING SERIESINCIVILAND STRUCTURALENGINEERING CIVILENGINEERING MATERIALS FromTheorytoPractice QIANGYUAN ZANQUNLIU KERENZHENG CONGMA Elsevier
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Copyright © 2021CentralSouthUniversityPress.PublishedbyElsevierLtd. AllRightsReserved.
Nopartofthispublicationmaybereproducedortransmittedinanyformorbyany means,electronicormechanical,includingphotocopying,recording,orany informationstorageandretrievalsystem,withoutpermissioninwritingfromthe publisher.Detailsonhowtoseekpermission,furtherinformationaboutthe Publisher’spermissionspoliciesandourarrangementswithorganizationssuchasthe CopyrightClearanceCenterandtheCopyrightLicensingAgency,canbefoundatour website: www.elsevier.com/permissions
Thisbookandtheindividualcontributionscontainedinitareprotectedunder copyrightbythePublisher(otherthanasmaybenotedherein).
Notices Knowledgeandbestpracticeinthis fieldareconstantlychanging.Asnewresearch andexperiencebroadenourunderstanding,changesinresearchmethods,professional practices,ormedicaltreatmentmaybecomenecessary.
Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledge inevaluatingandusinganyinformation,methods,compounds,orexperiments describedherein.Inusingsuchinformationormethodstheyshouldbemindfulof theirownsafetyandthesafetyofothers,includingpartiesforwhomtheyhavea professionalresponsibility.
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1.Fundamentalsofmaterials1
1.1 Compositionandstructure1
1.2 Physicalproperties5
1.3 Mechanicalproperties11
1.4 Durability15 Exercises16
2.Inorganiccementingmaterials17
2.1 Portlandcement17
2.2 Calciumsulfoaluminatecement37
2.3 Calciumaluminatecements41
2.4 Alkali-activatedcement47
2.5 Magnesium-basedcements52 Exercises56
3.Portlandcementconcrete59
3.1 Introduction59
3.2 Typesofconcrete62
3.3 Rawmaterials64
3.4 Concreteatfreshstate113
3.5 Mechanicalproperties129
3.6 Deformation137
3.7 Durability146
3.8 Mixdesign163
3.9 Self-compactingconcreteanditsapplicationinhigh-speedrail171
3.10 Steam-curedconcrete190 Exercises202
4.Metal205
4.1 Introduction205
4.2 Structuralsteel206
4.3 Standardsandselectionofbuildingsteel220
4.4 Corrosionandpreventionofsteel232
4.5 Nonferrousmetals234 Exercises238
7.Asphalt287
7.1
8.Cement-basedcomposites327 8.1
Preface Civilengineeringmaterialsarethebasicsforconstruction.Human civilizationisbuiltonallkindsofbuildingsandinfrastructuresthataremade upofvariousmaterials.Theproperunderstandinganduseofmaterialsare ofparamountsignificancetotheengineers,whichdeterminethequalityof thebuildingsandinfrastructure.Forthepastdecades,governmentsand constructionindustriesallaroundtheworldhavemadeahugeinvestment inconstructionworks,andmassiveamountsofcivilengineeringmaterials havebeenmanufacturedandconsumed.Inordertomeettherequirements ofnewstructures,traditionalandnewlydevelopedcivilengineering materialshavebeeninnovativelyputintouse,andnewknowledgeand experienceshavebeengenerated,whichareinvaluabletoacademiaand industry.Theuseofnewmaterialsandnewtechnologiespromotethe developmentofstructure,andthedevelopmentofstructureencouragesthe useofnewmaterialsandtechnologies.Itistherighttimetowritea textbookdedicatedtocivilengineeringmaterials,whichincludesthenew knowledgeandexperiencesinthis field,andthefundamentaltheoryfor materialsaswell.Sincealmosthalfoftheglobalconstructionworkshappen inChina,someChineseexperiencesareintroducedparticularly.
Thisbookcoversawiderangeofmaterials,fromorganictoinorganic, frommetaltononmetal,andfromtraditionaltonewlydeveloped. Materialsareintroducedbasedontherelationsamongcomposition, structure,andproperties.Firstly,fundamentalsofmaterialsareprovided fromtheperspectiveofmaterialsscience,andthenthematerialsdescribed subsequentlycanberelatedtothesebasictheories.Specifically,seventypes ofcivilengineeringmaterials,i.e.,inorganicbinder,concrete,metal, asphalt,wood,polymer,andcomposite,aredescribedinthisbook.Most importantly,thenewknowledgeandexperiencesobtainedrecentlyin China,especiallyinthe fieldofhigh-speedrailway,areincorporatedinthis book.Forinstance,ultrahigh-performanceconcreteandself-compacting concretearenewlydevelopedmaterials,andhavebeenwidelyusedin theconstructionofinfrastructure.Steam-curedconcreteisatraditionalway forfastproductionofconcretemembers.Thishasbeenwidelyusedin Chinaforprecastboxgirdersandotherconcretemembers.Thebasic knowledgeandinnovativeapplicationofpolymer,wood,steel,composite, andasphaltarealsointroduced.
TheauthorsofthisbookarefromCentralSouthUniversityand ShenZhenUniversityinChina.QiangYuanfromCentralSouthUniversity isresponsiblefortheplanofthisbookandthewritingof Chapter3 andpart of Chapter8.KerenZhengfromCentralSouthUniversityisresponsiblefor thewritingof Chapters1and2.ZanqunLiufromCentralSouthUniversity isresponsibleforthewritingof Chapters4and5 andpartof Chapter8. CongMafromShenZhenUniversityisresponsiblefor Chapters6and7 ManymastersandPhDstudentshelpedwiththeeditingand fi gure drawingofthemanuscriptduringthepreparationofthisbook.Theauthors wouldliketoacknowledgeMs.YumanWang,Mr.ShenghaoZuo, Mr.TsegayeLakewBerihun,andMr.GhimirePrateekfortheircontributionstothisbook.
Thisbookisintendedforundergraduateandgraduatestudentsincivil engineeringormaterialscience.Itcanalsobeusedasageneralreference bookforprofessionalengineersandresearchers,oratoolbookfor professionalengineersandresearchers.
QiangYuan,ZanqunLiu KerenZheng,CongMa
CHAPTER1 Fundamentalsofmaterials 1.1Compositionandstructure 1.1.1Composition
1.1.1.1Chemicalcomposition
Thechemicalcompositionofamaterialcanbedefinedasthedistribution oftheindividualcomponentsthatconstitutethematerial.
Thematerialcanbeapuresubstance,whichcontainsonlyonechemical component;inthiscase,thechemicalcompositioncorrespondstothe relativeamountsoftheelementsconstitutingthesubstance.Normally,it canbeexpressedwithachemicalformula.Foranexample,thechemical formulaforwaterisH2O,thusthechemicalcompositionofwatermaybe interpretedasa2:1ratioofhydrogenatomstooxygenatoms.
Foramixture,thechemicalisequivalenttoquantifyingtheconcentrationofeachcomponent.Componentrespondstochemicallyrecognizablespecies(FeandCincarbonsteel,H2OandNaClinsaltedwater). Therearedifferentwaystodefinetheconcentrationofacomponent,and therearealsodifferentwaystodefinethecompositionofamixture.Itmay beexpressedasmolarfraction,volumefraction,massfraction,molalityor normalityormixingratio.
1.1.1.2Phasecomposition Phase,inthermodynamics,referstochemicallyandphysicallyuniformor homogeneousquantityofamatterthatcanbeseparatedmechanicallyfrom anonhomogeneousmixture,andthatmayconsistofasinglesubstanceora mixtureofsubstances.Theconceptofphaseisalsointroducedtocharacterizethecompositionofmaterialscontainingmorethanonecomponent. Aphaseinamaterialhasuniformphysicalandchemicalcharacteristics,and differentphasesinamaterialareseparatedfromoneanotherbydistinct boundaries.Inmaterials,aphasemaycontainoneormorecomponents.In otherwords,amulticomponentmaterialcanexistasasinglephaseifthe
CivilEngineeringMaterials
ISBN978-0-12-822865-4
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Copyright © 2021CentralSouth UniversityPress.Publishedby ElsevierLtd.AllRightsReserved. 1
differentchemicalcomponentsareintimatelymixedattheatomiclength scale.Inthesolidstate,suchmixturesarecalledsolidsolution.
Thecomponentsorphasesininorganicmaterialscanbeminerals. Mineralsarenaturallyoccurring,inorganicsubstanceswithquantifiable chemicalcompositionandacrystallinestructure.Portlandcementclinkeris man-made,andcontainsmainlyfourphases:Alite,belite,aluminate,and ferrite;however,wealsocalledthesephasesasminerals.
1.1.2Structure
Generally,thetermstructureformaterialsreferstothearrangementof internalcomponentsofmaterials.Thestructureofmaterialscanbeclassified bythegeneralmagnitudeofvariousfeaturesbeingconsidered.Thethree mostcommonmajorclassificationsofstructureareasfollows: ①Atomic structure,whichincludesfeaturessuchasthetypesofbondingbetweenthe atoms,andthewaytheatomsarearranged; ②Microstructure,which includesfeaturesthatcanbeseenusingamicroscope,butseldomwiththe nakedeye; ③Macrostructure,whichincludesfeaturesthatcanbeseenwith thenakedeye.
Actually,mostpropertiesarehighlystructuresensitiveandthestructure virtuallydetermineseverythingaboutamaterial:itsproperties,itspotential applications,anditsperformancewithinthoseapplications.Therefore,itis veryimportanttounderstandthebasisforthestructureofmaterialstobe abletocontrolthepropertiesandreliabilityofengineeringmaterials.
1.1.2.1Atomicstructure Allmaterialsaremadeofatoms.Thereareonlyabout100differentkindsof atomsintheentireuniverse.However,thesesame100atomsformthousandsofdifferentsubstancesrangingfromtheairwebreathetothemetal usedtosupporttallbuildings.Itistheinteractionbetweenatomsand atomicbonding,toholdtheseatomstogetherandformdifferentsubstances. Accordingtotheirnature,thebondscanbecategorizedintotwoclasses basedonthebondenergy.Theprimarybonds(>100kJ/mol)areionic, covalent,andmetallic.ThesecondarybondsareofthevanderWaals,or hydrogen.
Ionicbondingoccursbetweenmetalatomsandnonmetalatoms.To becomestable,themetalatomtendstoloseoneormoreelectronsinits outershell,thusbecomingapositivelychargedion(akacations).Since electronshaveanegativecharge,theatomthatgainselectronsbecomesa negativelychargedion(akaanion).Asaresult,theatomsinanionic compoundareheldtogethersinceoppositelychargedatomsareattractedto oneanother.
Whereacompoundonlycontainsnonmetalatoms,acovalentbondis formedbyatomssharingtwoormoreelectrons.Nonmetalshavefouror moreelectronsintheiroutershells(exceptboron).Withthesemany electronsintheoutershell,itwouldrequiremoreenergytoremovethe electronsthanwouldbegainedbymakingnewbonds.Therefore,boththe atomsinvolvedshareapairofelectrons.Eachatomgivesoneofitsouter electronstotheelectronpair,whichthenspendssometimewitheach atom.Consequently,bothatomsareheldneareachothersincebothatoms haveashareintheelectrons.
Metallicbondingisatypeofchemicalbondingthatrisesfromthe electrostaticattractiveforcebetweenconductionelectrons(intheformof anelectroncloudofdelocalizedelectrons)andpositivelychargedmetal ions.Itmaybedescribedasthesharingoffreeelectronsamongastructure ofpositivelychargedions(cations).Metallicbondingaccountsformany physicalpropertiesofmetals,suchasstrength,ductility,thermalandelectricalresistivityandconductivity,opacity,andluster.
vanderWaalsbondingincludesattractionandrepulsionsbetween atoms,molecules,andsurfaces,aswellasotherintermolecularforces.van derWaalsbondingdiffersfromcovalentandionicbondinginthattheyare causedbycorrelationsinthe fluctuatingpolarizationsofnearbyparticles. vanderWaalsforceisadistance-dependentinteractionbetweenatomsor moleculesandcomparativelyweak.
Whentheatoms,ions,ormoleculeshaveanopportunitytoorganize themselvesintoregulararrangements,orlatticesbythebondsmentioned aboveinasolid,thesolidisclassifiedasacrystallinematerial.Hence,a crystallinesolidpossesseslongrange,regularlyrepeatingunits.
Ifthereisnolong-rangestructuralorderthroughoutthesolid,the materialisbestdescribedasamorphous.Quiteoften,thesematerialspossess considerableshort-rangeorderoverdistancesof1 10nmorso.However, thelackoflong-rangetranslationalorder(periodicity)separatesthisclassof materialsfromtheircrystallinecounterparts.Examplesofamorphoussolids areglassandsometypesofplastic.Theyaresometimesdescribedas supercooledliquidsbecausetheirmoleculesarearrangedinarandom mannersomewhatasintheliquidstate.Asshownin Fig.1.1,siliconand oxygenarebondedbycovalentbondtoformregularunit,silicon oxygen tetrahedron,whenthesilicon oxygentetrahedronsarearrangedinregular way,thesolidiscalledquartz,crystallineSiO2,whereassilicon oxygen tetrahedronsarearrangedinarandomway,theyformglass(amorphous SiO2).
Theatomicstructureprimarilyaffectsthechemical,physical,thermal, electrical,magnetic,andopticalproperties.
1.1.2.2Microstructure
Theterm “microstructure” isusedtodescribethearrangementofphases anddefectswithinamaterial,theappearanceofthematerialonthenm mmlengthscale.Acompletedescriptionofmicrostructuresinvolves describingthesize,shape,anddistributionofgrainsandsecond-phase particlesandtheircomposition.
Microstructurecanbeobservedusingarangeofmicroscopytechniques. Themicrostructuralfeaturesofagivenmaterialmayvarygreatlywhen observedatdifferentlengthscales.Forthisreason,itiscrucialtoconsider thelengthscaleoftheobservationsyouaremakingwhendescribingthe microstructureofamaterial.
Microstructuresdeterminethemechanical,physical,andchemical propertiesofmaterials.Forexample,thestrengthandhardnessofmaterials aredeterminedbythenumberofphasesandtheirgrainsizes.Theelectrical andmagneticpropertiesandalsothechemicalbehavior(corrosion)are determinedbythegrainsizeanddefects(vacancies,dislocations,grain boundaries,etc.)presentedinthematerial.Asaconsequence,thebehavior ofsuchmultiphasematerialisdeterminedbythepropertiesoftheindividualphasesandthefashioninwhichthesephasesinteract.Asageneral rule,themechanicalpropertiessuchasductility,strength,resistancetocreep andfatigueofengineeringmaterialsaredeterminedbytheir(micro)structureatdifferentgeometricscales.
Figure1.1 SchematiccomparisonbetweencrystallineSiO2(quartz)andamorphous SiO2(glass).
Themicrostructureofcement-basedmaterialsiscontrolledbytheir constituents,themixtureproportions,processing(e.g.,mixing,consolidation,andcuring),anddegreeofhydration.Thepropertiesofthehardened cement-basedmaterialsaredependentontheirmicrostructure;thecapillary porestructure(blackareasin Fig.1.2),whichincludestheinterfacetransitionzonebetweenthecementpasteandaggregatesusuallygovernsthe transportpropertiesofconcrete,whilelargervoidsreducethestrengthof concrete.
1.1.2.3Macrostructure Macrostructuredescribestheappearanceofamaterialinthescalemillimeterstometers,itisthestructureofthematerialasseenwiththenaked eye.Thetermmacrostructureissometimesusedtorefertothelargest componentsoftheinternalstructure.Grain flow,cracks,andporosityare allexamplesofmacrostructurefeaturesofmaterials.Macrostructurealso determinespropertiesofmaterials,especiallythemechanicalproperties.
1.2Physicalproperties Propertiesofamaterialrefertothefeatureswecansense,measure,ortest. Forexample,ifwehaveasampleofmetalinfrontofus,wecanidentify thatthematerialisgray,hard,orshiny.Testingshowsthatthematerialis abletoconductheatandelectricityanditwillreactwithanacid.Theseare someofthemetal’sproperties.
Physicalpropertiesarethosethatcanbeobservedwithoutchangingthe identityofthesubstance.Thegeneralpropertiesofmattersuchasdensity, specificgravity, fineness,thermalconductivity,heatcapacity,etc.,areexamplesofphysicalproperties.
Figure1.2 TheBSEandparticlespackingimagesofcement-basedmaterials.
1.2.1Densityandspecificgravity Mass(m)isafundamentalmeasureoftheamountofmatter.Thespacethe massoccupiesisitsvolume,andthemassperunitofvolumeisitsdensity. Hence,itissimpletocalculatedensityofanobjectbydividingitsmassbyits volume.However,thisisprettycomplicatedinthecaseofbuildingmaterials.
Alotofbuildingmaterials,suchaswood,cementitiousmaterials,and ceramics,areporous.Forporousparticles,themassisa finitevalue,but howaboutthevolume?Asshownin Fig.1.3,astackofporousparticles containsalotofpores,andtheseporescanbedividedintotwogroups,i.e., openporesandclosedpores.Whentheparticlesareimmersedinwater, watercanenteropenpores,butitcannotenterclosedpores.Hence, differentvolumesoftheporousparticlescanbedefined.Foraparticulate solid,itadditionallyincludesthespaceleftvoidbetweenparticles.
Envelopevolume:Thevolumesofthesolidandthevoidswithinthe particle,thatis,withinclose-fittingimaginaryenvelopescompletelysurroundingtheparticle.
Apparentvolumeorskeletalvolume:Thevolumesofthesolidinthe particlesandclosed(orblind)poreswithintheparticle.Thisvolume definitionexcludesvolumesofopenpores.
Trueorabsolutevolume:Thevolumeofthesolidintheparticle,which excludesvolumesofallpores.
Accordingly,wecandefinedifferentdensitiesforporousmaterialsas follows:
Apparentdensity:Themassofaparticledividedbyitsapparent(skeletal) volume.
Envelopedensity:Theratioofthemassofaparticletotheenvelope volumeoftheparticle.
Truedensity:Themassofaparticledividedbyitstrue(absolute) volume.
Foracollectionofdiscreteparticlesofsolidporousmaterial,thebulk densityistheratioofthemassofthecollectionofdiscretepiecesofsolid materialtothesumofthevolumesofthesolidsineachpiece,thevoids withinthepieces,andthevoidsamongthepiecesoftheparticular collection.Forpowdermaterials,bulkdensityisalsocalledbulkpowder density.
Weight(w)isameasureoftheforceexertedbyamassandthisforceis producedbytheaccelerationofgravity.Therefore,onthesurfaceofthe earth,themassofanobjectisdeterminedbydividingtheweightofan
Figure1.3 Aschematicpicturewellillustratesthephysicalmeaningofthesedensitydefinitions.
objectby9.8m/s2 (theaccelerationofgravityonthesurfaceoftheearth). Sincewearetypicallycomparingthingsonthesurfaceoftheearth,the weightofanobjectiscommonlyusedratherthancalculatingitsmass. Specificgravityistheratioofthedensityofasubstancecomparedtothe densityoffreshwaterat4 C.Atthistemperature,thedensityofwaterisat itsgreatestvalueandequals1g/cm3.Sincespecificgravityisaratio,ithas nounits.Specificgravityvaluesforafewcommonsubstancesareasfollows: Au,19.3;mercury,13.6;alcohol,0.7893;benzene,0.8786.Notethatsince waterhasadensityof1g/cm3,thespecificgravityisthesameasthedensity ofthematerialmeasureding/cm3.
1.2.2Fineness Finenessindicatesthe finenessorcoarsenessdegreeofpowderymaterials.It isoftenexpressedasstandardsievepercentageorspecificsurfacearea.
Finenesscanalsobeexpressedbypercentageofparticlesofvarioussizes oraveragevalueofunitweightmaterial.Thepopulationofparticlesof varioussizesistermedasparticlesizedistribution. D50 isusuallyusedto representtheparticlesizeofgroupofparticles,whichcharacterizesthe mediandiameterormediumvalueofparticlesizedistribution.Forinstance, if D50 ¼ 5.8 mm,then50%oftheparticlesinthesamplearelargerthan 5.8 mmand50%smallerthan5.8 mm.
Thespecificsurfaceareaisthesurfaceareaofthepowderymaterialper unitweight.Therearemanymethodstodeterminethespecificsurface area,suchasgasadsorption,organicmolecularadsorption,andairpermeability.Blaine’sairpermeabilityapparatusiscommonlyusedforcementitiousmaterials,whichconsistsessentiallyofameansofdrawingadefinite quantityofairthroughapreparedbedofcementofdefiniteporosity.
Fineness,PSD,andspecificsurfaceareaarefundamentalcharacteristics ofcementitiousmaterials,theyaffectthepropertiesofbuildingmaterialsin manyimportantways.Takingcementforanexample,the finessesaffectsits hydrationrate,waterdemand,workabilityoffreshconcretepreparedwith thematerial.
1.2.3Thermalconductivityandheatcapacity Thermalconductivityistheabilityofamaterialtotransferheat.Thermal conductivityisquantifiedusingtheunitofW/(m$K),andisthereciprocal ofthermalresistivity,whichmeasurestheabilityofmaterialstoresistheat transfer.Thermalconductivitycanbecalculatedasthefollowingequation:
where Q isheat flow,W; L islengthorthicknessofthematerial,mm; A is surfaceareaofmaterial,m2; T2 T1 istemperaturegradient,K.
Thethermalconductivityofaspecificmaterialishighlydependentona numberoffactors,includingthetemperaturegradient,thepropertiesofthe material,andthepathlengththattheheatfollows.Thethermalconductivityofthematerialsaroundusvariessubstantially,fromthosewithlow conductivitiessuchasairwithavalueof0.024W/(m$K)at0 Ctohighly conductivemetalslikecopper,385W/(m$K).
Thethermalconductivityofmaterialsdetermineshowweusethem,for example,thosewithlowthermalconductivitiesareexcellentatinsulating ourhomesandbusinesses,whilehighthermalconductivitymaterialsareideal forapplicationswhereheatneedstobemovedquicklyandefficientlyfrom oneareatoanother,asincookingutensilsandcoolingsystemsinelectronic devices.Byselectingmaterialswiththethermalconductivityappropriatefor theapplication,wecanachievethebestperformancepossible.
Heatcapacitydescribeshowmuchheatmustbeaddedtoasubstanceto raiseitstemperatureby1 C:
where C isheatcapacity; Q isenergy(usuallyexpressedinjoules); DT isthe changeintemperature(CelsiusorinKelvin).
Specificheatandheatcapacityarerelatedbymass:
where C isheatcapacity; m ismassofmaterial; S isspecificheat.
1.2.4Linearcoefficientofthermalexpansion Theaverageamplitudeoftheatoms’ vibrationwithinthematerialincreases whenheatisaddedtomostofthematerials.This,inturn,increasesthe separationbetweenatomsandcausesmaterialstoexpand.Itisusually expressedasafractionalchangeinlengthorvolumeperunittemperature change;alinearexpansioncoefficientisusuallyusedindescribingthe expansionofasolid.Thelinearcoefficientofthermalexpansion(a)describestherelativechangeinlengthofamaterialperdegreetemperature change.
where li isinitiallength; Dl isthechangeinlength; DT ischangein temperature.
Thermalexpansion(andcontraction)mustbetakenintoaccountwhen designingstructures.Thephenomenaofthermalexpansioncanbechallengingwhendesigningbridges,buildings,aircraft,andspacecraft,butitcan beputtobeneficialuses.
1.2.5Wettingandcapillarity Wettingistheabilityofliquidtoforminterfaceswithsolidsurfaces,or referstodescribehowaliquiddepositedonasolid(orliquid)substrate spreadsout.Todeterminethedegreeofwetting,thecontactangle(q)that isformedbetweentheliquidandthesolidsurfaceismeasured.Thesmaller thecontactangleandthesmallerthesurfacetension,thegreaterthedegree ofwetting.
Asshownin Fig.1.4,awettingliquidisaliquidthatformsacontactangle withthesolidwhichissmallerthan90degrees.Anonwettingliquidcreatesa contactanglebetween90and180degreeswiththesolid.Assumingthat therearenootherfactorsinvolved(e.g.,roughness),whenthecontactangle formedbetweenwaterandasolidsurfaceissmallerthan90degrees,thesolid ishydrophilic.Onthecontrary,watercreatesacontactanglebetween90 and180degreeswithasolid,whichmeansthatwatercannotspreadonthe solidsurfaceautogenously,thenthesolidishydrophobic.
Capillarityistheabilityofasubstancetodrawanothersubstanceintoit. Itoccurswhentheadhesiveintermolecularforcesbetweentheliquidanda substancearestrongerthanthecohesiveintermolecularforcesinsidethe liquid.Theeffectformsaconcavemeniscuswherethesubstanceis touchingaverticalsurface.Thesameeffectiswhatcausesporousmaterials tosoakupliquids.Capillaryforcespullawettingliquidtowardalow contactanglewiththesurfaceandwetsthesurface.Acompletelywetting liquidformsazero-contactangleintoacapillarybycreatingacurved meniscusattherisingliquidfront.Thisphenomenoncanbedescribedwith theYoung LaplaceequationandtheLaplacepressureinsideacapillary.
Figure1.4 Schematicillustrationofcontactangleofbothhydrophobicsurfaceand hydrophilicsurface.
1.3Mechanicalproperties 1.3.1Loadingandstrength Theapplicationofaforcetoanobjectisknownasloading.Materialscanbe subjectedtomanydifferentloadingscenariosandamaterial’sperformanceis dependentontheloadingconditions.Thereare fivefundamentalloading conditions:tension,compression,bending,shear,andtorsion(Fig.1.5).
Ifmaterialissubjectedtoaconstantforce,itiscalledstaticloading.Ifthe loadingofthematerialisnotconstantbutinstead fluctuates,itiscalled dynamicorcyclicloading.Thewaymaterialisloadedgreatlyaffectsits mechanicalpropertiesandlargelydetermineshow,orif,acomponentwill fail;andwhetheritwillshowwarningsignsbeforethefailureactually occurs.
Inmechanicsofmaterials,thestrengthofamaterialisitsabilityto withstandanappliedloadwithoutfailureorplasticdeformation.According todifferentloadingconditions,thestrengthincludestensilestrength, compressivestrength, flexiblestrength,shearstrength,andothers.
1.3.2Elasticityandplasticity Elasticityisthepropertyofsolidmaterialstoreturntotheiroriginalshape andsizeaftertheforcesdeformingthemhavebeenremoved.Whenaforce isappliedtoacertaincross-sectionalareaofanobject,thatobjectwill developbothstressandstrainasaresultoftheforce.
Figure1.5 Thefundamentalloadingconditionsandillustration.
Stressistheforcecarriedbythememberperunitarea;
where F istheappliedforce; A isthecross-sectionalareaoverwhichthe forceacts.
Strainistheratioofthedeformationtotheoriginallengthofthepart:
where L isthedeformedlength; L0 istheoriginalundeformedlength; d is thedeformation(thedifferencebetweenthetwo).
Stressisproportionaltostrainintheelasticregionofthematerial’ s stress straincurve(belowtheproportionalitylimit,wherethecurveis linear).Thecoefficientthatrelatesaparticulartypeofstresstotheresulted strainiscalledanelasticmodulus(plural,moduli).
Elasticmoduliarepropertiesofmaterials,notobjects.Theelastic modulus,alsoknownasthemodulusofelasticity,orYoung’smodulus,is essentiallyameasurementofthestiffnessofamaterial.Asaresult,itis commonlyusedindesignandengineeringapplications.
Plasticity,abilityofsolidmaterialto flowortochangeshapepermanentlywhensubjectedtostressesofintermediatemagnitudebetweenthose producingtemporarydeformation,orelasticbehavior,andthosecausing failureofthematerial,orrupture.Plasticityenablesasolidundertheaction ofexternalforcestoundergopermanentdeformationwithoutrupture. Plasticdeformationisapropertyofductileandmalleablesolids.
Mostofthebuildingmaterialsarenotpureelasticmaterials.Some materialsonlyhaveelasticdeformationifthestressisnotlarge,butplastic deformationwillhappentothemwhenthestressisbeyondalimit,suchas low-carbonsteel.Underexternalforces,somematerialswillhaveelastic deformationandplasticdeformationatthesametime,butelasticdeformationwilldisappearandplasticdeformationstillmaintainswhenthestress isremoved,suchasconcrete.
1.3.3Brittlenessandtoughness Brittlenessisapropertyofmaterialswhichenablesittowithstandpermanentdeformation.Castironandglassareexamplesofbrittlematerials. Theywillbreakratherthanbendundershockorimpact.Generally,the brittlematerialshavehighcompressivestrengthbutlowintensilestrength.
Toughnessmeanstheabilityofamaterialtodeformplasticallyandto absorbenergyintheprocessbeforefractureoccurs.Theemphasisofthis definitionshouldbeplacedontheabilitytoabsorbenergybeforefracture. Ductilityisameasureofhowmuchsomethingdeformsplasticallybefore fracture,butnotethatamaterialisductiledoesnotmakeittough.Thekey totoughnessisagoodcombinationofstrengthandductility.Amaterial withhighstrengthandhighductilitywillhavemoretoughnessthana materialwithlowstrengthandhighductility.Therefore,onewayto measuretoughnessisbycalculatingtheareaunderthestress straincurve fromatensiletest.Thisvalueissimplycalled “materialtoughness” andit hastheunitofenergypervolume.Materialtoughnessequatestoslow absorptionofenergybythematerial.
Itisthepropertyofamaterialwhichenablesittowithstandshockor impact.Toughnessistheoppositeconditionofbrittleness.Thetoughness maybeconsideringthecombinationofstrengthandplasticity.Manganese steel,wroughtiron,mildsteel,etc.,areexamplesoftoughnessmaterials. Thereareseveralvariablesthathaveaprofoundinfluenceonthetoughness ofamaterial.Thesevariablesarestrainrate(rateofloading),temperature, andnotcheffect.
1.3.4Hardness Hardnessistheresistanceofamaterialtolocalizeddeformation.Theterm canapplytodeformationfromindentation,scratching,cutting,orbending. Inmetals,ceramics,andmostpolymers,thedeformationconsideredis plasticdeformationofthesurface.Forelastomersandsomepolymers, hardnessisdefinedastheresistancetoelasticdeformationofthesurface. Hardnessmeasurementsarewidelyusedforthequalitycontrolofmaterials becausetheyarequickandconsideredtobenondestructivetestswhenthe marksorindentationsproducedbythetestareinlow-stressareas.Thereare alargevarietyofmethodsusedfordeterminingthehardnessofasubstance. Historically,itwasmeasuredonanempiricalscale,determinedbythe abilityofamaterialtoscratchanother,diamondbeingthehardestandtalc thesofter.Thereareafewdifferenthardnesstests:Mohs,Rockwell,Brinell,Vickers,etc.Theyarepopularbecausetheyareeasyandnondestructive(exceptforthesmalldent).
1.3.5Dynamicmechanicalproperties Alotofstructuresaresubjectedtodynamicloadduringtheirservicetime suchasbridges,rails.Dynamicmechanicalpropertiesrefertotheresponse ofamaterialtoaperiodicforce.Thesepropertiesmaybeexpressedinterms ofadynamicmodulus,adynamiclossmodulus,andamechanicaldamping term.Polymers,andparticularlyrubbers,areoftendeliberatelyselectedfor productswhicharetobesubjectedtodynamicmechanicalloading.
Stressanalysisinvolvestheuseofthefrequency-dependentdynamic moduliofthepolymers.Assume,forexample,thatthepolymerissubjected toasinusoidalstress s ofamplitude so andfrequency u,i.e., s ¼ s0sinut Stressanalysisconcernedwiththedynamicmechanicalpropertiesnormally assumesthatpolymersarelinearlyviscoelastic.Hence,thestrainresponse ε totheimposedsinusoidalstresscanbedescribedas ε ¼ ε0sin(wt d)where d isthephaseangle.Thisisshowndiagrammaticallyin Fig.1.6.The imposedstressandthematerialresponsedonotcoincide,andthephase angle d isthedifferencebetweenthetwocurves.
Notethatthestrainresponselagsbehindthestressbythephase angle owingtotheviscouscomponentofthematerial.Some,butnotall, oftheenergystoredduringthedeformationofthematerialisdissipated. Sincethematerialisassumedtobelinear,thestressisproportionaltothe strainatalltimes,i.e., s ¼ Ee,but E isafunctionofthefrequency u. Becausethestressandstrainarenotinphase, E mustbetreatedasa complexfunction:
Figure1.6 Thesinusoidalstress s andcorrespondingstrain ε responseforalinear viscoelasticmaterial.
whereand E 0 and E00 arethein-phaseandout-of-phasecomponentsofthe modulus.
Fromtheabovedefinitionsofthedynamicmoduliandbymanipulation ofthelinearrelationshipbetweenthesinusoidalstressandthecorrespondingstrainresponse,thephaseangle d canbeexpressedasfollows:
wheretan d iscommonlycalledthelosstangentordampingfactor; E00 and E 0 arethemostcommonlymeasureddynamicpropertiesofrubbers,representingtheelasticstiffnessanddampingorhysteresisproperties,respectively.Sometimesthe “argument” ofthecomplexmodulus jEj isused insteadof E*,andisgivenbythefollowingequation:
Atveryhighfrequencies(u ¼ 104 108 cycles/sorHz)rubberisvery stiffwithaglass-likemodulus.Atthesefrequenciesthepolymermolecules donothavetimetoreactinresponsetotheforcingoscillations.The dampingfactoristhensmallbutitincreasestoamaximumvalueinthe “leathery” transitionregionbetweentheglassymodulusandtheusual(low) moduluswhichischaracteristicofrubbersthataredeformedslowly(u < 1 cycle/sorHz).
1.4Durability Formaterials,durabilityistheabilitytoserviceforthelongtermwithout significantdeteriorationbyresistingtheeffectsoftheheavyuse,drying, wetting,heating,freezing,thawing,corrosion,oxidation,volatilization,etc.
Accordingtothedeteriorationmechanisms,thedeleteriousfactors mainlyconsistofphysicalactions,chemicalreactions.Physicalactions includewettinganddrying,changeintemperatures,andfreeze-and-thaw cycle.
Forcement-basedmaterials,chemicalreactionsleadingtodegradation includeacidattack,saltattack,alkali-aggregatereaction,carbonation,and reinforcementcorrosion.Twotypesofcorrosioncanbedistinguishedfor steelandothermetals:directreactionofthecorrosivecompoundwiththe metalandcorrosionthatoccursthroughthewaterpresentatthemetal surface.Forasphalt,plastic,rubber,andotherorganicmaterialswillbe damagedduetoaging.
Durabilityisoneofthemajorrequirementstobeconsideredintheuse ofbuildingmaterials.Moreknowledgeaboutdeteriorationmechanisms andthemeasurestocounteractthesearetobeprovidedinotherchaptersin thisbook.
Exercises 1. Pleasesummarizethefactorswhichinfluencethedurabilityofmaterials forcivilengineering.
2. Wateriseasytospreadoverthesurfaceofconcreteandtransportin concretebecauseitisahydrophilicmaterial,howtoimprovetheimpermeabilityofconcretewithoutchangingitsporosityandporestructure?
3. Whendesigningbuildingssuchasairportterminals,whythelinearcoefficientofthermalexpansionofusedmaterialsshouldbeconsidered?
4. Statethegeneralrelationshipbetweenthecomposition,structure,and propertiesofmaterials.
5. Completethefollowingformtodescribethechangeinpropertiesofa materialsasitsporosityincreases.(using [whenincreasing; Y when decreasing, whenunchanged,and?forunclear)
CHAPTER2 Inorganiccementingmaterials 2.1Portlandcement Portlandcementwasinventedin1824,anditsnameisderivedfromits similaritytoPortlandstone,atypeofbuildingstonequarriedontheIsleof PortlandinDorset,England.Nowadays,Portlandcementisthemost widelyusedman-madematerialbecauseoflowcost,easyavailabilityofraw materials,goodworkabilityoffreshcement-basedmaterials,andversatility.
Portlandcementisobtainedbygrindingclinkertogetherwithadequate gypsum.Clinkerisahydraulicmaterialwhichshallconsistofatleast two-thirdsbymassofcalciumsilicates.Clinkersarenodulesofasintered materialthatisproducedwhenarawmixtureofpredeterminedcompositionisheatedtohightemperature.Themainmineralphasescontainedin aPortlandclinkerarecalciumsilicates(Ca3SiO5,Ca2SiO4),aluminate (Ca3Al2O6)andalumino-ferrite(Ca4(AlxFex 1)4O10),brieflydenotedas C3S,C2S,C3A,andC4AF.
AccordingtoGB-175,clinkermakesupmorethan90%ofthecement, alongwithalimitedamountofcalciumsulfate(CaSO4,whichcontrolsthe settime),andupto5%minorconstituents(or fillers)asallowedbyvarious standards.
BlendedcementcanbedefinedasauniformmixofPortlandcement andblendingmaterialssuchas flyash,limestone,andslagtoenhanceits propertiesfordifferentuses.Blendedcementcanimproveworkability, strength,durability,andchemicalresistanceofconcrete.Moreover,the replacementofclinkerwithblendingmaterialscanreducetheCO2 footprintofcementandconcrete,andusesolidindustrialbyproductsinan eco-efficientway.
ThecompositionofPortlandcementisdefinedbythemasspercentages andcompositionoftherawsourcesoflime,iron,silica,andaluminaaswell asthetemperatureanddurationofheating.Itisthisvariationinrawmaterialssourceandtheplant-specificcharacteristics,aswellasthe finishing processes(i.e.,grindingandpossibleblendingwithgypsum,limestone,or
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