氯离子在混凝土中扩散效应分析的MCA模型

MCA Model for Analyzing Diffusion Effect of Chloride Ions in Concrete

氯离子侵蚀引起的钢筋锈蚀是影响混凝土结构发生耐久性失效的主要原因之一,研究氯离子在混凝土中的扩散机理具有重大意义。以组成混凝土的三相复合特点,采用细观尺度模拟和元胞自动机相结合的方法,提出用于描述混凝土氯离子时变扩散效应的MCA模型,并对影响模型计算效率和应用限制的元胞尺寸进行讨论。根据已有的氯离子浓度实测结果对所提出的模型进行验证。利用MCA模型对影响氯离子扩散效应的各细观结构参数进行分析。理论和试验结果表明:推荐采用的元胞尺寸为最小骨料粒径的0.707倍;MCA模型模拟的氯离子浓度平均值与试验值偏差不超过10%,且随时间和深度的变化规律与试验结果一致;模型具有描述材料变异性的能力,能够准确描述氯离子在截面内的浓度分布;界面扩散特性对氯离子扩散效应影响最为显著,骨料含量次之,氯离子扩散效应随界面扩散特性的增加而增加,随骨料含量的增加而减小,而骨料分布形式基本不会对氯离子扩散效应产生影响。

The corrosion of steel bars caused by chloride ion erosion is one of the main reasons that affect the durability of concrete structures.It is of great significance to study the diffusion mechanism of chloride ions in concrete.In this paper,based on the three-phase composite characteristics of concrete,and the method of micro-scale simulation and cellular automata,an MCA model was proposed to describe the time-varying diffusion effect of concrete chloride ions and to discuss the cell size that affects the computational efficiency of the model and the application limitations.The proposed model was verified based on the existing measured results of chloride ion concentration.On this basis,the MCA model was used to analyze the meso-structure parameters that affect the effect of chloride ion diffusion.Theoretical and experimental results show that the recommended cell size is 0.707 times the minimum aggregate particle size.The deviation between the average value of chloride ion concentration simulated by the MCA model and the test value does not exceed 10%,and the change rule with time and depth is consistent with the test results.The model has the ability to describe material variability and can accurately describe the concentration distribution of chloride ions in the cross section.The interface diffusion characteristics have the most significant impact on the chloride ion diffusion effect,followed by the aggregate content.The chloride ion diffusion effect increases with the increase of the interface diffusion characteristics and decreases with the increase of aggregate content while the aggregate distribution form has little impact on the chloride ion diffusion effect.