基于纳米压痕试验的混凝土微观耐久性表征

利用纳米压痕和扫描电镜研究了不同冻融循环下混凝土的微观性能，揭示了冻融循环所导致混凝土退化的机理．纳米压痕结果显示，混凝土浆体的压痕模量与硬度的相关系数很大，并且都不满足正态分布．本文利用核密度估计来计算浆体微观性能的概率密度函数．根据浆体和骨料的性能差异，用阶跃函数来拟合界面过渡区的微观力学性能，同时利用扫描电镜观察界面过渡区的形貌．采用以上两种方法研究不同冻融循环下的混凝土，发现在不同的尺度下，冻融循环对混凝土的影响不同：在纳米尺度下，由于水的参与，高密度水凝胶会进一步形成；而在微米尺度下，由于冻融循环中水结冰膨胀和材料多相性，微裂纹进一步扩展，导致断裂能量降低，混凝土表现出宏观退化．

Microscopic Characterization of Concrete Durability Using Nano-Indentation Tests

Nano-indentation and scanning electron microscopy (SEM) were used to reveal the intrinsic microscopic properties of concrete and deterioration mechanism of concrete due to cyclic freezing/thawing (F/T) damage. Characterization results on the 0 F/T cycle mortar indicates that, the hardness and indentation modulus are highly correlated by Pearson's correlation coefficient and their histograms fail to comply with the normal distribution. The kernel density estimation was utilized to provide a global distribution function instead of several Gaussian curve additions. The nanoscale mechanical properties at the neighbor of interfacial transition zone (ITZ) were approximated by Heaviside function, and a procedure for determining ITZ was made by considering the difference of mechanical properties. Studying different F/T degradation samples indicates that, the multi-scale nature of concrete leads to material degradation or enhancement of concrete at different length scales. At the nanometer scale, more High Density Calcium-Silicate-Hydrate (C-S-H) is present as observed from the kernel density estimations of different F/T samples; while at the micrometer scale, more cracks are developed according to the SEM observation, resulting in the decrease of fracture energy.