Time-to-Corrosion Initiation of Chloride-Exposed Reinforced Concrete Considering Time Dependence of the Diffusion Coefficient

Previous research reported an equation whereby the fraction of electrochemically independent, identically exposed reinforced concrete elements for which corrosion initiation has resulted after a given time can be calculated. The approach considers that all relevant variables (surface Cl⁻ concentration, effective Cl⁻ diffusion coefficient [D], concrete cover, and critical Cl⁻ concentration threshold to initiate corrosion) conform to a distribution rather than being discrete, as is now known to be the case. Upon inputting distribution parameters for the above variables into the equation, the fraction of elements that have initiated corrosion after a designated time is determined. Upon repeating the calculation for different times, a cumulative distribution function plot for occurrence of corrosion initiation results. Previously, the mean and standard deviation of the above variables were assumed to be constant with time. It is generally recognized, however, that D decreases with time according to a power law expression in response to progressive cement hydration. In the present study, the extent of corrosion initiation was investigated considering this time dependence for D. Implications of the results with regard to the evolution of corrosion initiation are discussed.