Probability distribution of convection zone depth of chloride in concrete in a marine tidal environment

Based on a field experiment of concrete exposed to a marine tidal environment and according to measured chloride ingress data, diffusion coefficients of chloride ion in concrete after different exposure time are fitted by Fick-second law. Concrete with different types of admixture are tested in this paper, with water-cement ratios of 0.40, 0.45, 0.50, 0.55 and 0.60, respectively. Based on 270 group chloride ingress curves of test concrete, the convection zone depth of chloride and peak value of chloride concentration in concrete are acquired. According to chloride ingress curves of concrete with different water-cement ratio under the same exposure time, the probability distribution forms of convection zone depth of chloride are investigated by statistical test using the log-normal distribution, the normal distribution and the maximum value distribution, respectively. The statistical results show that the mean value of convection zone depths of chloride is in a range from 4 mm to 6 mmin this paper, disregarding the difference in exposure time, water-cement ratio and with or without the admixture in the specimens. The majority of convection zone depths of chloride in different exposure time and water-cement ratios, as well as the admixture, follow a Gumbel distribution, and the convection zone depth of chloride in total 270 specimens follows a Gumbel distribution with the mean value of 3.99 mm and the standard deviation of 1.05 mm. The exposure time, water-cement ratio and different admixture have negligible effect on the mean value and the probabilistic characteristic of convection zone depth of chloride, however, different admixture and lower water-cement ratio can significantly reduce the diffusion coefficients and peak values of chloride concentration in concrete.