Prediction of corrosion initiation period of steel reinforcement in concrete structures submerged in seawater

摘要

Service life prediction in term of durability is becoming one of the most important tasks in the design of reinforced concrete structures, mainly for structures exposed to marine environment. In this environment, chloride induced corrosion of steel reinforcing bars (rebar) is one of the major causes of deterioration of reinforced concrete structures. Assessment of the mechanism of deterioration due to the chloride-induced corrosion of rebar can be generally divided into two stages. The first stage is the initiation period corresponding to the time required for free chloride ion concentration at the reinforcement level to reach the threshold value. The second stage i.e. -propagation period- is related to the corrosion process of reinforcement leading to concrete cover cracking, delamination and spalling. In this paper a mathematical model for describing the penetration of chloride ion due to diffusion process is presented for two-dimensional rectangular system. The model takes into account most parameters that influence the mechanism of chloride penetration such as chloride binding capacity, time, temperature, as well as microcracks and applied stress dependences of chloride diffusion coefficient. The model can be used to predict the corrosion initiation period of rebar in a structure submerged in seawater with respect to threshold value of the free chloride ion concentration in the pore solution of concrete, which is predicted using Electrochemical Impedance Spectroscopy. Finite difference method is applied to solve the model and the results are then presented in the form of profiles of penetrated chloride ion concentration as function of time and the distance from concrete surface.