干湿交替下水分及氯离子在混凝土中传输的细观数值模拟

Mesoscale simulation of water and chloride transport in concrete subjected to drying-wetting cycles

氯离子侵蚀已成为影响海洋及近海环境中混凝土结构耐久性的主要因素。考虑材料组成的非匀质特性,将混凝土看作由粗骨料、硬化水泥砂浆及二者界面过渡区组成的三相复合材料的细观层次方法,是开展物质传输过程研究的新途径。建立非饱和混凝土中氯离子传输的一维非线性对流扩散方程,并利用伽略金加权余数法给出了该方程的有限元形式,采用适用于物质传输的细观格构网络模型开展了水分及氯离子在非饱和混凝土中传输过程及分布规律研究,分析了干湿循环周期和循环机制对水分及氯离子传输性能的影响规律。数值计算结果表明,干湿交替下,相同的干燥时间,非饱和混凝土内水分及氯离子的侵入深度主要取决于湿润时间,而干燥时间和循环周期数则影响混凝土表层氯离子含量,并在混凝土表层10 mm处有浓度集中现象。

Chloride-induced corrosion is one of the major deterioration mechanisms of reinforced concrete that may seriously influence durability of the structures in marine and offshore environment. With consideration of non-homogeneous characteristic of the material composition, the mesoseale method, in which concrete is described as a three-phase composite consisting of the coarse aggregate, hardened cement mortar and the interracial transition zone between them, is adopted to conduct the study of mass transport process. In the present paper, the one-dimensional nonlinear convection-diffusion equation of chloride transport is established, as well as its finite difference form by means of the Galerkin weighted residual method. Based on mesoscopic structure of concrete, the mesoscale lattice network model is developed, which is able to simulate the water and chloride transport process in unsaturated concrete. The transport property is investigated by analyzing the influence of the cycles and cyclic scheme of drying-wetting. Numerical calculation results show that the depth of water and chloride penetration into the unsaturated concrete mainly depends on the wetting time. The chloride ion content of concrete surface is influenced by the drying time and cycles. Additionally, it is found that there is a concentration of chloride in the depth of 10 mm.