基于有限元法的混凝土输水管内硫酸根离子扩散分析

暴露于硫酸盐环境中的混凝土输水管易遭受硫酸盐化学侵蚀,导致其耐久性退化、提前失效;而环境中硫酸根离子传输进入混凝土是其化学侵蚀的前提.为获得混凝土内硫酸根离子的扩散进程,首先基于Fick定律及质量守恒定律,建立饱和混凝土管内硫酸根离子的扩散-反应模型.其次,将扩散-反应模型的边界条件齐次化,建立其有限元控制方程.然后,开展硫酸钠溶液中水泥砂浆圆柱试件的腐蚀试验,测定试件不同深度处的硫酸根离子浓度,与模型计算结果对比,以验证模型.最后,开展数值模拟研究,分析混凝土输水管外表面、内外表面暴露于浓度恒定或振荡的硫酸盐溶液情况下管内硫酸根离子浓度的时空分布.

Numerical Analysis on Sulfate Ion Diffusion in Concrete Pipe Based on Finite Element Method

The concrete pipe exposed to sulfate environment suffers from the chemical sulfate attack,causing the durability deterioration and premature failure of the pipe.The transport of sulfate ion from outside environment into concrete is the premise of chemical sulfate attack.In order to predict the sulfate diffusion progress in concrete,firstly,a diffusionreaction model of sulfate ion in the saturated concrete pipe was established by using Fick ’s law and mass conservation law.Secondly,the boundary conditions of diffusion-reaction model were transformed into homogeneous conditions,and a finite element governing equation of the model is further established.Then,a corrosion experiment of cement mortar column specimens immersed into sodium sulfate solution was carried out to measure the sulfate concentrations in the different depths of the specimens.The sulfate concentrations calculated by the established model were compared with that from the corrosion experiment to validate the model.Finally,an numerical simulation is performed to analyze the spatial-temporal distribution of sulfate concentration in concrete pipe in the cases of its outside surface,the outside and inside surfaces exposed to sulfate solution with constant or oscillatory concentrations.