开裂状态下沿海干湿区桥梁粉煤灰混凝土氯离子扩散模型

Chloride Diffusion Model in Cracked Fly Ash Concrete Bridge Subjected to Coastal Drying-wetting Cycles

为了明确沿海干湿交替区域桥梁结构混凝土在开裂状态下的氯离子侵蚀机理，结合现有研究提出了考虑表层对流影响的开裂混凝土氯离子传输的修正扩散模型。以粉煤灰掺量、裂缝宽度为主要影响因素，对3组混凝土梁进行了氯盐干湿循环试验研究，借助15次和30次干湿循环后的取样结果，分析了裂缝宽度对表层对流区深度的影响，并用修正扩散模型拟合氯离子浓度分布的适用性，探讨了粉煤灰掺量、裂缝宽度对氯离子扩散特性的影响规律。研究结果表明：表层对流区深度在8～15mm之间，且其随裂缝宽度叫的增大而增大；用修正扩散模型分析开裂混凝土（W〈0．30mm）的氯离子浓度分布是可行的，其综合效应系数K在1～20之间；龄期衰减指数m随粉煤灰掺量的提高而增大，而氯离子扩散系数则随粉煤灰掺量的提高而降低；裂缝宽度对氯离子扩散系数的影响可用W的二次多项式函数进行描述。

In order to define the mechanism of chloride penetration in bridge with cracked concrete under the condition of drying-wetting cycles, based on the existing works, a revised diffusion model which took surface convection effect into account was proposed to predict chloride transport in cracked concrete. With fly ash content and crack width as main influence factors, a test study of chloride drying-wetting cycles was carried out for three kinds of concrete beams. Based on the sampling results obtained after 15 and 30 cycles, the influence of crack width on surface convection depth and the applicability of chloride concentration distribution fitted by revised diffusion model were analyzed. The effects of fly ash content and crack width on chloride diffusivity were discussed. The results show that the depth of surface convection is about 8 to 15 mm, and it increases with the increase of crack width （w）. It is verified that the revised diffusion model is suitable to analyze chloride concentration profiles in cracked concrete with crack width less than 0. 3 mm, and its integrated effect coefficient, K is near 1 to 20. The age-related degradation exponent, m increases with the increase of fly ash content, while chloride diffusion coefficient declines. The crack effect on chloride diffusion coefficient can be described with a quadratic polynomial function of crack width.