硅烷憎水处理混凝土的氯离子电场迁移模型研究

Theoretical model for electronic migration of chloride ions in water repellent concrete

电场下的氯离子迁移试验常被用来评价混凝土中的氯离子扩散系数及抵抗氯离子侵蚀的能力。研究了硅烷憎水处理混凝土的氯离子电场迁移模型。以往的试验发现忽略普通混凝土中孔隙结构分布对离子迁移过程的影响将导致预测值和试验值不吻合。Stanish等人因此提出了考虑氯离子扩散迁移速度离散性的氯离子电场迁移模型,并较好地预测了试验结果。在Stanish模型的基础上,假设氯离子扩散系数而不是氯离子迁移速度符合对数正态分布,从而简化了氯离子电场迁移模型的理论表达式,并更清晰地反映了混凝土微观结构的随机性,计算结果表明两种假设等价。基于上述理论模型,对于饱水的硅烷憎水处理混凝土试件的电通量试验结果进行分析,证明上述理论模型适用于硅烷憎水处理混凝土试件。分析结果亦表明:硅烷憎水处理过的混凝土的电通量试验结果,只反映硅烷憎水性涂层对混凝土表面氯离子浓度的影响,并不反映憎水处理对内部混凝土的扩散系数的影响,硝酸银显色法并不适用于硅烷憎水处理混凝土的电通量试验。

Electrical migration test is a common method to evaluate concrete＇ s resistance to the chloride-ion penetration. However, it has been found that the existing migration models are not accurate enough to interpret the test results due to neglecting the effect of pore structure distribution in concrete on the migration process. Stanish et al. proposed a new model by considering the random characteristics of chloride migration velocity and found that the model prediction agreed well with the test results. Based on Stanish＇ s model, a simplified model is further developed herein by assuming that the chloride diffusion coefficient instead of the chloride migration velocity follows a logarithmic normal distribution. This assumption reflects more directly the random characteristics of concrete pore structures. It can simplify the solutions to a large extent with the same accuracy of prediction. This simplified model was verified to be also applicable to the migration tests of silane-based water repellent concrete. It was revealed that the silane-based water repellent only affected the surface chloride concentration during the migration tests. The measured electric flux can reflect the influence of silane-based water repellent on the penetration of chloride ions, however, the silver nitrate colorimetric method is inapplicable to evaluating the chloride resistance of concrete with silane-based water repellent.