冻融循环作用下超高性能混凝土界面过渡区微观力学性能劣化研究

Investigation on degradation of micromechanical properties of interfacial transition zone of ultra-high performance concrete under freeze-thaw cycles

为了探究冻融作用下超高性能混凝土(UHPC)的抗冻性机理,利用纳米压痕技术对钢纤维-浆体以及细砂-浆体两种界面过渡区的微观结构和微观力学性能进行研究.研究表明:钢纤维-浆体界面过渡区中存在明显薄弱带,微观结构受冻融影响较大.冻融作用下水化硅酸钙、氢氧化钙的弹性模量和硬度相对变化幅度小于0.2.微孔洞体积分数随冻融循环次数增加呈指数增长,且孔径逐渐扩展到几十微米.钢纤维界面过渡区厚度经0～1500次冻融后从20μm逐渐扩展到65μm左右.随冻融循环次数增加,微孔洞体积分数呈指数函数增长,钢纤维界面过渡区厚度也逐渐扩展,因此可以用来有效地表征冻融作用下UHPC界面过渡区的微观力学性能劣化机理.

In order to explore frost resistance mechanism of ultra-high performance concrete（UHPC） under freeze-thaw（F-T） action, the microstructures and micromechanical properties of two interfacial transition zones（ITZ） of steel fiber-paste and fine sand-paste are investigated using nanoindentation technology. The experimental results demonstrates that there exits an obvious weak zone in the ITZ of fiber-paste, of which the microstructure is largely affected by F-T action. The relative variation of the amplitude of modulus and hardness of calcium silicate and calcium hydroxide is less than 0.2 under F-T action. The volume fraction of micropores increases exponentially as the increase of F-T cycles, and the pore size gradually extends to tens of microns. The thickness of ITZ between steel fibers and paste gradually increased from 20 to 65 μm after 0–1500 F-T cycles. Thus, the volume fraction of micropores and the thickness of ITZ in steel fibers can be used to effectively characterize the degradation of micromechanical properties of UHPC under cold climates.