Long-term field study of chloride ingress in concretes containing pozzolans exposed to severe marine tidal zone

Abstract

Chloride ingress in concrete is the most deteriorating factor for reinforced concrete structures exposed to marine environment. This phenomenon depassivates reinforcing steel in concrete and causes steel corrosion. To improve the durability and serviceability of concrete structures in harsh environments with high relative humidity, temperature and concentration of chloride ions such as in the Persian Gulf, the addition of silica fume and other pozzolans have been recommended by several investigations. In this paper, the chloride ion diffusivity and mechanical performance of concretes containing silica fume, metakaolin and natural zeolite, and those of concretes with different water-cement ratios (w/c) under in-situ tidal exposure condition were investigated. To achieve this objective, concrete specimens with w/c of 0.35, 0.40, 0.45 and 0.50 were fabricated. In addition, to examine the performance of pozzolans, other specimens with constant water-binder ratio (w/b) of 0.40 containing 5% silica fume, 5% metakaolin and 10% natural zeolite were prepared. All of the specimens were subjected to laboratory and tidal exposure in the field conditions. The results indicate that 10% natural zeolite, 5% metakaolin and 5% silica fume have similar effects on concrete strength and durability in harsh marine environments. In addition, it is concluded that at long time field exposure, chloride diffusion coefficient and surface chloride content of different mixtures reach to relatively similar amounts.