Durability-Based Service Life Design of RC Structures-Chloride-Induced Corrosion

In this present study, chloride ion diffusion into cover concrete is modelled as a sub-diffusion process. A time-fractional partial differential equation is used to describe the sub-diffusion process and the numerical solution of this equation is obtained using explicit finite difference scheme. The parameters C-s, alpha and D-alpha involved in the solution are estimated by data fitting performed using genetic algorithm-based optimization technique in MATLAB. This study is carried out for predicting the chloride profiles of OPC concrete that are available in the literature, exposed to marine environment for a long time. The collected profiles correspond to both laboratory samples exposed to field exposure and sample drawn from a real existing structure. The initiation time of corrosion is then determined numerically by finding the time at which chloride concentration at rebar reaches the critical chloride concentration. The results of the sub-diffusion model are also compared with fib model, whose parameters are also fitted using optimization technique. Based on field observations reported in the literature, it is found that the initiation times of corrosion predicted by sub-diffusion model are less conservative and more realistic compared to the predictions of fib model.