Chloride diffusion and time to corrosion initiation of reinforced concrete structures

Abstract

The diffusion mechanism for chloride ion in concrete with different water-cement ratio (w/c) is studied by chloride ion spray test. A new model of chloride diffusion coefficient which changes as the ingress depth of chloride ion and w/c is developed. A spatial time-dependent reliability model of time to corrosion initiation (T_CI) for reinforced concrete (RC) structures is developed considering spatial variability of geometrical, material and environmental parameters. The test results show that chloride diffusion coefficient increases as w/c increases, and chloride diffusion velocity decreases as the penetration depth enhances. It is found that the probability of corrosion initiation for spatial variability is 13.1%∼18.5% higher than that without consideration of spatial variability. This indicates that neglecting spatial variations for evaluating probability of corrosion initiation time overestimates the structural reliability. It is also found that the probability of corrosion initiation for future climate change is 9%∼11% higher than that obtained from constant temperature. The mean value of time for corrosion initiation based on time-dependent chloride diffusion coefficient is 16.7% earlier than that obtained from constant chloride diffusion coefficient. This suggests that it will be more appropriate if the effect of time-dependent chloride diffusion coefficient considers penetration depth and w/c.