双轴受压下水灰比对水泥砂浆氯离子扩散的影响规律

Influence of water cement ratio on chloride ion diffusion of cement mortar under biaxial compression

氯离子严重影响混凝土结构的耐久性,为研究水灰比对水泥砂浆氯离子扩散规律的影响,首先对水泥砂浆试块施加指定荷载,并采用快速氯离子迁移系数法(RCM法)测定水泥砂浆氯离子扩散系数,然后通过数字图像处理技术(DIC)、压汞法(MIP)和纳米压痕测定试块的应变云图、孔隙结构特征和界面过渡区力学性能,揭示氯离子扩散机理,最后建立氯离子扩散系数预测模型,并对其进行试验验证。结果表明:在受压应力水平增加时,水泥砂浆氯离子扩散系数先降低后提高,单轴加载的临界应力约为极限荷载的25%,双轴加载的临界应力约为极限荷载的50%;水泥砂浆中的孔隙率随着水灰比的增加而变大,水灰比越大,浆骨之间的界面过渡区厚度越大,硬度和弹性模量越小,对压荷载越敏感,成为水泥砂浆最薄弱的区域;荷载作用前后,无害孔和少害孔的孔隙率变化不大,随着荷载的增大,有害孔的孔隙率有降低趋势,而多害孔的孔隙率有所提升,使得水泥砂浆氯离子扩散系数变大。

Chloride affects the durability of concrete structures.In order to study the influence of the water cement ratio on chloride diffusion of cement mortar,first a specified load is applied to the cement mortar specimen,and the chloride diffusion coefficient of cement mortar is tested using the RCM method.Then the strain nephogram,porosity and interfacial transition zone(ITZ)of the specimen is studied through DIC,MIP and nano indentation.Finally,a prediction model is established for chloride diffusion coefficient.The results show that the chloride diffusion coefficient first decreases and then increases with the load.The critical stress under uniaxial loading is about 25%of the ultimate load,while that under biaxial loading is about 50%.The greater the water cement ratio is,the greater the porosity is,the thicker the ITZ is,and the smaller the hardness and elastic modulus are.Before and after the loading,the porosity of harmless holes and less harmful holes has little change.With the increase of load,the porosity of harmful holes tends to decrease,while the porosity of multi harmful holes increases,making the chloride ion diffusion coefficient of cement mortar larger.