Mechanism And Simulation Study Of Steel Bar Corrosion In Concrete Exposed To Chloride Environment

Corrosion of reinforcement in concrete is one of the main factors that affect the durability of structures. Corrosion mechanism,corrosion rate prediction and corrosion propagation are several difficult points in the field of concrete durability.The ingress of chloride ion is considered to be one of the main reasons that cause early corrosion of reinforcement in concrete. Chloride ion could destroy the high alkaline environment around the steel bar, thus causing the depassivation and corrosion of reinforcement. Corrosion of reinforcement in concrete caused by chloride ion is a common phenomenon in marine environment or area using deicing salt.In this paper, the transportation mechanism of corrosive medium in concrete is analysed and illustrated. Commonly, the transportation patterns of corrosive medium in concrete mainly include diffusion, permeation, capillary absorption and electromigration. The transportation mechanism of corrosive medium in cracked concrete is a little different, which is commonly analysed by the revised dual porosity medium model. Corrosion of reinforcement in concrete could be devided into two types, macrocell and microcell, which cause pitting corrosion and uniform corrosion respectively. When transverse cracks exist, the steel bar in cracked region becomes active earlier. In this case, corrosion of steel bar is based on macrocell corrosion.By using Nernst-Planck equation and Tafel equation, we set up mathematical models of net current density in electrolyte, net current density in electrode, anodic current density and cathodic current density. To measure the effect of chloride ion content on corrosion rate, influential factor fCl and FCl are introduced, which could revise the model of anodic current density. Based on the model above,COMSOL Multiphysics is utilized to simulate the corrosion process of reinforcement in concrete under chloride attack, and the outcome is in good agreement with existing test data,which could serve as reference for the analysis of durability of concrete structures in chloride environment.The coupling process of ion transportation and steel bar corrosion in sound and cracked concrete exposed to chloride environment is investigated. By numerical simulation, we obtain the variation rule of chloride content, corrosion current density,corrosion depth and electric potential on reinforcement surface concerning location and time. The outcome shows that the closer the reinforcement surface is to solution boundary,the higher the chloride content is, which results in bigger corrosion current density,bigger corrosion depth and lower electric potential. With the exposure time going on, chloride content,corrosion current density and corrosion depth become bigger, while electric potential becomes lower.The achievements in this paper could be used to predict the corrosion rate and corrosion morphology of reinforcement in concrete structures exposed to chloride environment, which could serve as reference for the analysis of durability and service life prediction of concrete structures under chloride environment.