混凝土氯离子扩散理论模型的研究Ⅰ——基于无限大体的非稳态齐次与非齐次扩散问题

Diffusion Model of Chloride in Concrete Ⅰ——Homogeneous and Inhomogeneous Diffusion in Infinite Body

针对无限大的扩散介质,以综合考虑氯离子结合能力、氯离子扩散系数的时间依赖性和结构微缺陷影响的实际混凝土氯离子扩散新方程为基础,在常数边界条件下,推导出一维、二维和三维氯离子扩散理论的齐次模型。同时,根据指数函数的边界条件,在理论上导出了一维氯离子扩散理论的非齐次模型,能满足混凝土结构工程的实际边界条件。最后论证了引进氯离子结合能力、氯离子扩散系数的时间依赖性和劣化效应系数等参数对于描述混凝土氯离子扩散行为的必要性,探讨了采用多维扩散理论模型的意义,并通过实验确定了混凝土的指数边界条件函数。结果表明,采用氯离子扩散理论非齐次模型有利于提高混凝土结构耐久性设计的安全性。

Based on the recently proposed diffusion equation, a model for chloride diffusion in infinite body with constant homogeneous boundary condition is mathematically deduced. The diffusion equation considers effects of concrete chloride binding capacity, time dependence of diffusion coefficients, and defects in microstructures, and the deduced model can be applied to natural diffusion in one-two-or three-dimensional conditions. Aimed at the boundary conditions in practical engineering, one-dimensional chloride diffusion model incorporated with inhomogeneous exponential boundary conditions is deduced. Necessity of introducing parameters, such as concrete chloride binding capacity, time dependence of diffusion coefficients, and defects in microstructures into research of chloride diffusion is demonstrated. In addition, the significance of multidimensional diffusion model is also discussed. The inhomogeneous ex- ponential boundary conditions are verified by experimental data. Results show that it is favorable for the durability design of concrete structures for introducing inhomogeneous model.