混凝土孔结构及其分形维数与氯离子扩散性能的关系

Relationship Between Pore Structure,Fractal Dimension and Chloride Diffusion Performance of Concrete

氯离子扩散系数是研究海洋环境下混凝土结构耐久性的重要参数之一。通过开展不同水胶比混凝土的压汞试验和盐雾扩散试验,研究了混凝土内部孔隙率、孔径分布及临界孔径对氯离子扩散系数的影响规律。结合Menger海绵体模型,建立孔体积分形维数与氯离子扩散系数的关系。结果表明:孔隙率和临界孔径与无量纲化氯离子扩散系数的相关性很高,可作为反映混凝土氯离子扩散性能的重要参数;通过数学分析计算得到的孔表面分形维数分布在2.56~3.86之间,孔体积分形维数分布在2.85~2.98之间;基于压汞法和分形理论计算得到的孔体积分形维数可以作为评价氯离子扩散系数的指标,在孔径小于10 nm、10~100 nm、100~1000 nm以及大于1000 nm四类区间,氯离子扩散系数随孔体积分形维数的增加而下降。

Chloride diffusion coefficient is one of the important parameters to study the durability of concrete structures in marine environment.Through mercury intrusion test and salt spray diffusion test of concrete with different water-binder ratios,the influences of porosity,pore size distribution and critical pore size on chloride diffusion coefficient in concrete were studied.The relationship between the fractal dimension of pore volume and the chloride diffusion coefficient was established based on Menger sponge model.The results show that the porosity and critical pore size are highly correlated with the dimensionless chloride diffusion coefficient,which can be used as important parameters to reflect the chloride diffusion performance of concrete.The distribution of fractal dimension of pore surface calculated by mathematical analysis is 2.56~3.86,and that of pore volume is 2.85~2.98.The fractal dimension of pore volume calculated by mercury intrusion test and fractal theory can be used as an index to evaluate the chloride diffusion coefficient.The chloride diffusion coefficient decreases with the increase of the fractal dimension of pore volume in four ranges of pore size less than 10 nm,10~100 nm,100~1000 nm and more than 1000 nm.