混凝土氯离子扩散理论模型的研究Ⅱ--基于有限大体的非稳态齐次与非齐次扩散问题

Diffusion Model of Chloride in Concrete Ⅱ——Homogeneous and Inhomogeneous Diffusion in Finite Body

针对Ⅰ维大平板、Ⅱ维长方柱体和Ⅲ维长方体等有限大扩散介质,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混凝土构件的氯离子扩散理论齐次模型,可以作为自然扩散法的计算模型使用。同时,在指数函数的边界条件下获得了Ⅰ维大平板、Ⅱ维长方柱体、Ⅲ维长方体和正交各向异性Ⅲ维长方体等混凝土构件的氯离子扩散理论非齐次模型,满足实际混凝土结构的多种体形和复杂边界条件。并用大量的实测数据验证了有限大体的Ⅱ维和Ⅲ维氯离子扩散理论齐次模型,探讨了有限大扩散和无限大扩散对混凝土结构寿命的影响。

Based on the recently proposed diffusion equation, a model of chloride diffusion in finite 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. The deduced model can be applied to natural diffusion in one, two or three- dimensional conditions. Aimed to the geometries and boundary conditions in practical engineering, chloride diffusion models incorporated with inhomogeneous exponential boundary conditions are also deduced, among the diffusion in one, two or three-dimensional conditions and orthotropic diffusion are included. And the two and three-dimensional models of chloride diffusion in finite body with constant homogeneous boundary or inhomogeneous exponential boundary condition are verified by experimental data. The difference of the concrete prediction life by finite and infinite models is also discussed.