第五章-變形耐久性

低、負(fù)溫強度發(fā)展凍融循環(huán)鹽的腐蝕氯離子侵蝕鋼筋銹蝕干燥、溫差、熱應(yīng)力引起的裂縫堿－骨料反應(yīng)對多年凍土的熱撓動凍土融沉及隆起的影響風(fēng)蝕1抗?jié)B性(Permeability—滲透性)

Permeabilityreferstotheeasewithwhichwatercanpassthroughtheconcrete.Lowpermeabilityisanimportantrequirementforhydraulicstructuresandinsomecaseswatertightnessofconcretemaybeconsideredtobemoresignificantthanstrengthalthough,otherconditionsbeingequal,concreteoflowpermeabilitywillalsobestronganddurable.

2抗凍性(FreezeResistance/Weathering)

Damagetoconcretefromfreezingandthawingarisesfromtheexpansionofporewaterduringfreezing;Theresistanceofconcretetofreezingandthawingcanbeimprovedbyincreasingitsimpermeability.Thiscanbeachievedbyusingamixwiththelowestpossiblewater-cementratiocompatiblewithsufficientworkabilityforplacingandcompactingintoahomogeneous（均勻的）mass.Durabilitycanbefurtherimprovedbyusingair-entrainment.

3抗侵蝕性(ChemicalAttack)

Ingeneral,concretehasalowresistancetochemicalattack.Thereareseveralchemicalagentswhichreactwithconcretebuttwoformsofattackaremostcommon,namelyleachingandsulphateattack.Chemicalagentsessentiallyreactwithcertaincompoundsofthehardenedcementpasteandtheresistanceofconcretetochemicalattackthereforedependlargelyonthetypeofcementused.4堿骨料反應(yīng)(Alkali-AggregateReaction)Certainaggregatescanreactchemicallywiththealkalinecontentofcementtoformalkalinesilicagel.Whenthishappenstheseaggregatesexpandorswell（腫脹）

resultingincrackinganddisintegrationofconcrete.

5混凝土的碳化(Carbonizition)

總之，混凝土的耐久性決定于材料的品質(zhì)、內(nèi)部密實度、施工質(zhì)量三個方面。

Inordertoproduceadurableconcretecareshouldbetakentoselectsuitableconstituentmaterials.Itisalsoimportantthatthemixcontainsadequatequantitiesofmaterialsinproportionssuitableforproducingahomogeneousandfullycompactedconcretemass.

6、提高耐久性的措施：（1）合理選擇水泥品種，優(yōu)質(zhì)骨料。（2）控制W/C和水泥用量，提高密實度。（3）摻外加劑。（4）加保護(hù)層。（5）提高施工質(zhì)量

第五節(jié)混凝土的變形性能(Deformation)

1、化學(xué)收縮（chemicalshrinkage）2、干縮變形（dryingshrinkage

）3、溫度變形temperature4、荷載作用下的變形1、化學(xué)收縮

化學(xué)收縮是指混凝土拌合物在水化過程中，由于水泥水化生成物體積比體積小，而產(chǎn)生的收縮。chemicalshrinkageInasetconcrete,ashydrationproceeds,anetdecreaseinvolumeoccurssincethehydratedcementgelhasasmallervolumethanthesumofthecementandthewaterconstituents.Ashydrationcontinuesinanenvironmentwherethewatercontentisconstant,suchasinsidealargemassofconcretethisdecreaseinvolumeofthecementpasteresultsinshrinkageoftheconcrete.Thisisknownasautogenousshrinkage(chemicalshrinkage)becauseasthenameimplies,itisself-producedbythehydrationofcement.

2、干縮變形

由于混凝土內(nèi)部吸附水分蒸發(fā)，而引起凝膠體失水收縮，毛細(xì)管水分蒸發(fā)，混凝土系統(tǒng)內(nèi)的顆粒受毛細(xì)管壓力作用而產(chǎn)生體積收縮。dryingshrinkageWhenahardenedconcretecuredinwater,isallowedtodryitfirstloseswaterfromitsvoidsandcapillaryporesandonlystartstoshrinkduringfurtherdryingwhenwaterisdrawnoutofitscementgel.Thisisknownasdryingshrinkage

3、溫度變形

和其他材料一樣，也具有熱脹冷縮的性質(zhì)?；炷恋臏囟扰蛎浵禂?shù)約為10

10-5。對大體積混凝土不利。Thetemperatureoftheenvironmenthaveasignificanteffectonboththerateandmagnitude（數(shù)量）ofshrinkageinasmuchastheyaffectthemovementofwaterinconcrete.

4、荷載作用下的變形（deformation）短期荷載作用下的變形

Concretedeformsunderload,thedeformationincreasingwiththeappliedloadandbeingcommonlyknownaselasticdeformation.Concre