Effect of air-entrainment and phase transition on chloride diffusion in partially frozen concrete

In some regions concrete is partially frozen for several months each year, yet there is paucity of information about the effect of air entrainment on chloride diffusivity and binding in partially frozen concrete. To address this issue, concrete without and with entrained air were subjected to chloride diffusion under constant exposure temperatures of +5, 0, −5, and −15 °C and their total and free chloride concentrations were determined. The entrained air reduced chloride diffusivity by 18% when the concrete evaporable water was either unfrozen or nearly fully frozen, but when it was partially frozen it reduced it by only 3%. Non-air entrained concrete exhibited higher binding capacity than air entrained concrete under all the test temperatures. After freezing, the effect of temperature on concrete diffusivity cannot be captured by Arrhenius law alone. A procedure is proposed to account for this deviation and the predicted diffusion coefficients agree reasonably with the experimental values.