Chloride-Induced Corrosion of Reinforcing Steel in Concrete: Electrochemical Modeling of Initial and Limiting Corrosion Rates

The high alkalinity of concrete can prevent reinforcing steel in concrete from corroding. However, corrosion will commence when the [Cl^-]/[OH^-] ratio reaches a threshold of about 0.6. The aim of this paper is to evaluate the corrosion rate of steel due to chloride penetration and the availability of oxygen in the concrete pores. The corrosion process is very complex and modeling is often based on observation or speculation rather than detailed modeling of the chemical processes involved.

The limiting corrosion current was modeled based on the cathodic reaction and oxygen diffusion in the rust layer around a reinforcing bar. The corrosion current was calculated for different boundary conditions, concrete properties, and concrete cover thicknesses. The results indicate that only the boundary condition and concrete quality have a significant impact on the corrosion rate. Using good quality concrete with a low water-cement ratio is effective in reducing corrosion damage. Concrete with a high water-cement ratio has higher porosity and permeability resulting in increased diffusion of oxygen and water absorption that cause the corrosion current to increase. The corrosion current predicted by the electrochemical model compares favorably with experimental and field measurement results available in the literature.