混凝土浇筑层面的渗透特性与微裂纹结构特征

Permeability and micro-cracks of concrete layer interfaces

混凝土的宏观渗透性能与其内部微裂纹结构密切相关。本文开展了一系列室内试验研究混凝土浇筑层面的微裂纹结构及渗透特性。采用不同间隔时间浇筑形成有层面的混凝土方法制备了6组混凝土试件,分别进行宏观渗透性能试验和荧光显微结构观测。试验结果表明:随着形成层面的混凝土浇筑间隔时间延长,混凝土的渗透系数、电通量、初始电流及交流电导都逐渐增大,表明混凝土浇筑层面的抗渗性能逐渐降低;荧光显微观测结果表明微裂纹长度服从对数正态分布;表征裂纹方向的渗透变量λ曲线亦随之由圆形逐渐趋向于椭圆,表明裂纹网络由各向同性逐渐趋于各向异性,同时裂纹网络的优势方向逐渐趋于顺浇筑层面方向;渗透变量曲线极值λmax与渗透系数、初始电流及等效电导隙宽呈线性正相关,相关系数分别为0.85、0.80和0.95,而λmax与交流电阻呈线性负相关,相关程度为0.76。

The permeability of a concrete is closely related to its internal micro-cracks. This paper presents an experimental study focusing on characterizing micro-cracks within concrete layer interfaces and examining its effect on the permeability of the concrete. Six concrete specimens were prepared with layer interfaces formed by placing the concrete at different time intervals. Permeability tests were performed and micro-cracks of the concrete layer interfaces were characterized through fluorescence microscopic observation.The results show that the specimens will have greater permeability if they have layer interfaces formed bylonger time intervals, may indicating higher opening of the layer interfaces. Consequently, higher chargepassed,initial current and AC conductivity are also observed with the longer intervals. The fluorescence mi-cro-images reveal that the length of micro-cracks obeys logarithmic normal distribution. A parameter λ,quantifying the orientation of micro-cracks,indicates the micro-crack distribution changes from isotropic toanisotropic with increasing time interval of concrete placement. Meanwhile,the predominant direction of micro-cracks tends to follow the layer interface. The maximum value,λmax,is positively linearly correlated with permeability coefficient,initial current and equivalent conductive width,with correlation coefficients of0.85, 0.80 and 0.95, respectively. Whereas, λmax is negatively linearly correlated with AC resistance,with a correlation coefficient of 0.76.