热带岛礁环境下全珊瑚海水混凝土结构服役寿命的可靠性

Reliability of Service Life of Coral Aggregate Seawater Concrete Structure in Tropic Island Reef Environment

基于修正氯离子扩散理论和可靠度理论的寿命分析软件ChaDuraLifeV1.0,选取4种配合比的全珊瑚海水混凝土（CASC）进行实验室海水浸泡试验,研究了不同混凝土强度、不同养护龄期和不同暴露时间CASC的表观氯离子扩散系数（Da）、表面自由氯离子含量（Cs）及Da时间依赖性指数（m）的变化规律,探讨了保护层厚度和混凝土强度对CASC服役寿命的影响,提出了适应于热带海洋环境CASC的最小保护层厚度和混凝土强度等级的要求。结果表明：CASC的Da和Cs随着暴露时间的延长分别呈幂函数的降低趋势和幂函数的增长趋势;对于失效概率为5%～10%的CASC,当保护层厚度为7.5 cm、混凝土强度等级为C50时,其使用寿命可达17～19 a。因此,建议海洋工程中的CASC结构,其保护层厚度至少为7.5 cm、混凝土强度等级至少为C50。这样,有利于延长CASC中Cl^-到达钢筋表面的距离和周期,降低钢筋对Cl^-腐蚀的敏感性,提高混凝土抗Cl^-扩散渗透能力,从而延缓钢筋起始锈蚀时间,降低锈蚀速率,达到延长CASC结构服役寿命的目的。

The coral aggregate seawater concretes （CASC） with four kinds of mixture proportions soaked in seawater were investigated via a service life prediction program named ChaDuraLife V1.0 based on the modified chloride diffusion theory and reliability theory.The change rule of Da and time dependence index of Da （m） in CASC at different concrete strengths, curing ages and exposure time were analyzed. The influences of concrete cover thickness and concrete strength grade on the service life of CASC were discussed. The requirements for the minimum concrete cover thickness and the concrete strength of CASC in the tropical marine environment were proposed. The results show that the decreasing relationship between Da of CASC and the exposure time and the increasing relationship between Cs and the exposure time both follow the power function. When the failure probability of CASC is 5%-10%, the concrete cover thickness is 7.5 cm and the concrete strength is C50, the service life can reach 17-19 years. Therefore, for the CASC structures in marine island and reef engineering, the concrete cover should be thicker than 7.5 cm and the concrete strength grade should be over C50. All of these measures can favour the increase of the time and distance required for C^l- to reach the reinforcement surface, thus reducing the reinforcement sensitivity to CF corrosion and enhancing the ability of concrete to resist CF diffusion. Therefore, the initial corrosion time delays, the corrosion rate reduces and the service life prolongs.