Numerical simulation of electrochemical mechanism of steel rebar corrosion in concrete under natural climate with time-varying temperature and humidity

Abstract In order to analyze and predict the corrosion ratio and rust layer distribution of steel rebar embedded in reinforced concrete under time-varying climatic conditions, a self-balancing steel corrosion model was established by connecting the environmental temperature, humidity, external chloride ions and oxygen concentration to the potential distribution and current density of the steel using finite element method. The model covered the whole corrosion process of steel rebar in concrete under natural climate, including the steel rebar depassivation, steel corrosion propagation and the rust layer expansion on the surface of steel rebar. In the proposed model, the microcell and macrocell corrosion were coupled by electrochemical polarization, and the cathode-to-anode area ratio was determined by the time-varying chloride distribution at the rebar surface. Taking the diffusion of chloride ions and oxygen in concrete into account, the distribution of corrosion potential of reinforcement, the change of corrosion current density of reinforcement, and the distribution of rust layer on the surface of reinforcement can be obtained based on the variation of natural temperature and humidity. The proposed model was validated utilizing the experimental data from the literatures. On this basis, a discussion about the influence of long-term climatic environments on the corrosion kinetics were conducted. The results suggest that environmental temperature and relative humidity affect the steel corrosion process mainly by affactting the chloride and oxygen diffusion coefficients, concrete resistivity, and concentration of dissolved oxygen in concrete pore solution. The corrosion current density of steel in concrete is sensitively influenced by the environmental temperature more than relative humidity. Although the initial exposure time has a significant impact on the accumulation process of chloride on steel surface within one climatic cycle, it has little influence on the final chloride distribution at the end of the period. However, the initial exposure time remarkably influences the evolution profile of rust layer thickness during the climatic cycle. The steel rebar initially exposed to a higher temperature suffers from more severe corrosion than that initially exposed to a lower temperature.