Numerical simulation of chloride-induced corrosion initiation in reinforced concrete structures with cracks

Steel corrosion is a major problem with concrete structures. For concrete structures exposed to chlorides, once a critical chloride concentration is reached at the steel surface, corrosion starts to occur. For a given cover thickness, the corrosion initiation time depends on the chloride diffusivity. For different kinds of concrete, the diffusivity D_o at the un-cracked state has been measured. However, in reinforced concrete design, concrete members are allowed to crack in tension. Once cracking occurs, chloride can also diffuse through the crack at a faster rate governed by the crack diffusivity D_cr. Recent experiments have shown that D_cr is a function of the crack width. In the present study, finite element analysis is performed to study the effect of cracking on corrosion initiation in concrete with different values of D_o. For various crack width and cover thickness, the time for critical chloride concentration to be reached at steel intersected by the crack is determined. Based on the simulation results, we will derive the empirical equation for an effective diffusion coefficient (D_eff) which can be employed directly in the solution of the one-dimensional diffusion equation to calculate the corrosion initiation time. The study will provide a convenient but accurate approach for predicting corrosion initiation under real world situations where cracks are present in a concrete structure.