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CHAPTERTHREE CIVILENGINEERINGMATERIALS Theimportanceofanunderstandingofthematerialsusedincivilengineeringiswidelyrecognized.Designers'ideascannotbecometruewithoutvariouscivilengineeringmaterialsofcorrectsizeandgoodproperties.So,knowledgeofvariouskindsofcivilengineeringmaterialsiscentraltoacivilengineer'scareer. IntroductiontoCivilEngineeringMaterials Civilengineeringmaterialscanbenaturalandmanmade.Theycontainrock,metals,timber,concrete,bituminousresemblingorcontainingbitumen沥青的；含沥青的,soil,polymers聚合物；高分子,bricksandblocksetc.Besidesthesetraditionalmaterials,newtypesofconstructionalmaterialsarealsoinvestigatedanddevelopedandwillbeappliedgradually. Nowgreencivilengineeringmaterialsandeveneco-materials环境材料forcivilengineeringarerecommendedbasedontheconsiderationofSustainableDevelopment可持续发展Thishasthebenefitsofreducingenergy,savingresourcesandprotectingtheenvironment,havingminimumharmtohumanhealth. Timber CharacteristicsofTimber Timberisoneoftheoldestknowncivilengineeringmaterials.Inadditiontoitsusefulnessasastructuralmaterial结构材料,timberhasalsofulfilledaroleintemporarystructures临时.Althoughtimberisakindofsustainableresource,theconsumptionspeedofforestsmustbesloweddownbecauseoftherelativeslownessoftreegrowth.（maybetenortwentyyears） Maturetrees,ofwhatevertype,arethesourceofstructuraltimber.Fromthecrosssectionoftrunk(Fig.3.1),wecanobservethebark,heartwood,pith,sapwoodandgrowthrings. Fig.3.1Crosssectionofthetrunk 1）Pith；2)Sapwood边材;3)Heartwood树木的心材;4)Growthrings年轮i5)Bark树皮 SometimesTheageofthetreecanbejudgedbygrowthrings,Butonlyapproximate BecausesometreesOneyearalsohavecanproduceseveralrings Timberisgenerallyclassifiedintotwotypes hardwoods阔叶树whichhavebroadleavesshedintheautumn,suchasangiosperm被子植物,dicotyledons双子叶植物,and softwoods软木材；针叶树材whichhaveneedle-like针状的leaves,broadlyevergreen(aplanthavingfoliagethatpersistsandremainsgreenthroughouttheyear),suchasconifers松柏类，针叶树,gymnosperms裸子植物；裸子植物类.Itshouldbenotedthatthetermshardwoodsandsoftwoodsdonotnecessarilyindicaterelativehar
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