耦合多相传输的氯离子侵蚀混凝土数值模拟研究

Numerical Modeling of Chloride Penetration in Concrete Coupled with Multiphase Transport

氯离子侵蚀是导致氯盐环境中混凝土结构承载力下降的主要原因之一.为预测渗有氯盐混凝土中氯离子的传输和分布规律,建立了考虑温湿影响的多相耦合氯离子侵蚀模型,模型中考虑到了作为非饱和多孔材料的混凝土中热量、水分、气体与氯离子耦合运输过程,以及伴随发生的相变现象.相变过程既包括水分的蒸发与凝结,也涉及氯盐的溶解与沉淀.特别是氯离子的存在对材料组成成份的物理和热力学性能的影响在模型中也进行了考虑.为求解构成模型的耦合偏微分方程组,采用了有限元法和完全隐式差分法.模型预测与试验结果具有较好的一致性,展现出所发展的数值计算方法在重现氯离子侵蚀混凝土真实过程的能力,将可有效用于实际混凝土结构耐久性评估与设计中.

Chloride ions penetration is one of the major causes that reduce the carrying capacity of concrete structures exposed to chloride environment. To predict the transportation and distribution of chloride ions in chloride contaminated concrete,a coupled multiphase model of chloride ions penetration considering the effect of temperature and humidity is proposed that describes coupled heat,moisture,air and chloride transport including phase transitions in the unsaturated porous building material. The phase transitions involved in the model take into account both evaporation-condensation of water and dissolution-precipitation of salt. Particularly the effect of chloride on the physical and thermodynamic properties of the material composition is considered. To solve the set of coupled partial differential governing equations in this model,the finite element method and the fully implicit finite difference method are used. A good agreement between the model prediction and the experimental evidence is obtained,demonstrating the performance of the proposed approach to realistically reproduce the chloride ions penetration into concrete structures. Further,these results may be efficiently used for the realistic assessment and design for durability of concrete structures.