Chloride diffusion and time to corrosion initiation of reinforced concrete structures

Abstract

The diffusion mechanism for chloride ions in concrete with varying water/cement ratio (w/c) is studied by chloride ion spray testing. A new model of chloride diffusion coefficient, which varies with the ingress depth of chloride ion and w/c, is developed. A spatial time-dependent reliability model of time to corrosion initiation (TCI) for reinforced concrete (RC) structures is developed, considering spatial variability of geometric, material and environmental parameters. The test results show that the chloride diffusion coefficient increases as w/c increases, and chloride diffusion velocity decreases as penetration depth increases. It is found that the probability of corrosion initiation considering spatial variability is 13.1–18.5% greater than that without consideration of spatial variability. This indicates that neglecting spatial variations in 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 TCI based on a time-dependent chloride diffusion coefficient is 16.7% less than that obtained for a constant chloride diffusion coefficient. This suggests that it is more appropriate if penetration depth and w/c is considered when determining the time-dependent chloride diffusion coefficient.