中文摘要：

基于Fick第二定律，建立了考虑扩散系数时变性、荷载对扩散系数影响和氯离子结合能力的氯离子扩散方程；通过求解扩散方程得到考虑多因素影响的混凝土方桩使用寿命预测模型；并分析了桩的保护层厚度、裂缝控制宽度、表面氯离子浓度和临界氯离子浓度等因素对桩的使用寿命的影响．分析结果表明：得到的氯离子扩散方程与实测数据吻合较好；对于设计使用寿命为50年的混凝土方桩，保护层厚度应大于45mm，桩身裂缝宽度不宜大于0．1mm．

英文摘要：

A diffusion equation of chloride ion in concrete was put forward based on Fick＇s second law. In the equation, the influences of time-dependence of chloride diffusivity, the effect of load on diffusion coefficient and chloride ion binding capacity of concrete were taken into consideration. A prediction model of service life of reinforced concrete （RC） square piles was established. The effects of cover thickness, cracking width, surface chloride ion concentration and the chloride threshold level on service life of RC square piles were analyzed. The analysis results indicate that the diffusion equation of chloride ion of this paper agrees well with the experimental data. It suggests that the cover thickness should be greater than 45 mm and the cracking width should not be greater than 0.1 mm if the design service life of RC square piles is 50 years.