第五章-变形耐久性

低、负温强度发展冻融循环盐的腐蚀氯离子侵蚀钢筋锈蚀干燥、温差、热应力引起的裂缝碱－骨料反应对多年冻土的热挠动冻土融沉及隆起的影响风蚀1抗渗性(Permeability—渗透性)

Permeabilityreferstotheeasewithwhichwatercanpassthroughtheconcrete.Lowpermeabilityisanimportantrequirementforhydraulicstructuresandinsomecaseswatertightnessofconcretemaybeconsideredtobemoresignificantthanstrengthalthough,otherconditionsbeingequal,concreteoflowpermeabilitywillalsobestronganddurable.

2抗冻性(FreezeResistance/Weathering)

Damagetoconcretefromfreezingandthawingarisesfromtheexpansionofporewaterduringfreezing;Theresistanceofconcretetofreezingandthawingcanbeimprovedbyincreasingitsimpermeability.Thiscanbeachievedbyusingamixwiththelowestpossiblewater-cementratiocompatiblewithsufficientworkabilityforplacingandcompactingintoahomogeneous（均匀的）mass.Durabilitycanbefurtherimprovedbyusingair-entrainment.

3抗侵蚀性(ChemicalAttack)

Ingeneral,concretehasalowresistancetochemicalattack.Thereareseveralchemicalagentswhichreactwithconcretebuttwoformsofattackaremostcommon,namelyleachingandsulphateattack.Chemicalagentsessentiallyreactwithcertaincompoundsofthehardenedcementpasteandtheresistanceofconcretetochemicalattackthereforedependlargelyonthetypeofcementused.4碱骨料反应(Alkali-AggregateReaction)Certainaggregatescanreactchemicallywiththealkalinecontentofcementtoformalkalinesilicagel.Whenthishappenstheseaggregatesexpandorswell（肿胀）

resultingincrackinganddisintegrationofconcrete.

5混凝土的碳化(Carbonizition)

总之，混凝土的耐久性决定于材料的品质、内部密实度、施工质量三个方面。

Inordertoproduceadurableconcretecareshouldbetakentoselectsuitableconstituentmaterials.Itisalsoimportantthatthemixcontainsadequatequantitiesofmaterialsinproportionssuitableforproducingahomogeneousandfullycompactedconcretemass.

6、提高耐久性的措施：（1）合理选择水泥品种，优质骨料。（2）控制W/C和水泥用量，提高密实度。（3）掺外加剂。（4）加保护层。（5）提高施工质量

第五节混凝土的变形性能(Deformation)

1、化学收缩（chemicalshrinkage）2、干缩变形（dryingshrinkage

）3、温度变形temperature4、荷载作用下的变形1、化学收缩

化学收缩是指混凝土拌合物在水化过程中，由于水泥水化生成物体积比体积小，而产生的收缩。chemicalshrinkageInasetconcrete,ashydrationproceeds,anetdecreaseinvolumeoccurssincethehydratedcementgelhasasmallervolumethanthesumofthecementandthewaterconstituents.Ashydrationcontinuesinanenvironmentwherethewatercontentisconstant,suchasinsidealargemassofconcretethisdecreaseinvolumeofthecementpasteresultsinshrinkageoftheconcrete.Thisisknownasautogenousshrinkage(chemicalshrinkage)becauseasthenameimplies,itisself-producedbythehydrationofcement.

2、干缩变形

由于混凝土内部吸附水分蒸发，而引起凝胶体失水收缩，毛细管水分蒸发，混凝土系统内的颗粒受毛细管压力作用而产生体积收缩。dryingshrinkageWhenahardenedconcretecuredinwater,isallowedtodryitfirstloseswaterfromitsvoidsandcapillaryporesandonlystartstoshrinkduringfurtherdryingwhenwaterisdrawnoutofitscementgel.Thisisknownasdryingshrinkage

3、温度变形

和其他材料一样，也具有热胀冷缩的性质。混凝土的温度膨胀系数约为10

10-5。对大体积混凝土不利。Thetemperatureoftheenvironmenthaveasignificanteffectonboththerateandmagnitude（数量）ofshrinkageinasmuchastheyaffectthemovementofwaterinconcrete.

4、荷载作用下的变形（deformation）短期荷载作用下的变形

Concretedeformsunderload,thedeformationincreasingwiththeappliedloadandbeingcommonlyknownaselasticdeformation.Concre