Time dependent diffusion in concrete—three laboratory studies

The rate of chloride diffusion into concrete decreases with time due to issues such as continued hydration and chloride binding. Data are presented from three projects where the specimens were continuously exposed to chloride solutions for periods ranging from 28 days to 3 years. Chloride profiles obtained from the specimens at various time intervals were used to calculate diffusion values using Crank's solution to Fick's second law. The time-dependant reduction coefficient, m, was determined using three methods, yielding different values. Since the reduction of calculated diffusion coefficients with time has great impact on service life predictions, and values are sensitive to the method used, it is imperative to also know how the diffusion and time-dependant reduction coefficients were obtained.