This study indicates two issues of available time-dependent diffusion coefficient function; non-smoothness of diffusion coefficient decay, and inconsistency of stable time of diffusion coefficient. A naturally logarithmic apparent diffusion coefficient function is thus developed for closed-form solutions of chloride transport model. The developed model is validated with experimental data, and its generality is ensured by comparing with the finite difference approach. From the study, the stable time of the developed diffusion coefficient appears 2.87-3.21 years after exposure, and the stable time of surface chloride appears 5 years after exposure. Such early appearance of these stable times behaves different from other studies, causing different long-term chloride prediction and concrete service life. Using the developed model, the influence of cover depth and percent fly-ash is determined in service life prediction. Additionally, this study develops a model to predict environmental impact in terms of eutrophication potential, currently considered as an emerging global issue. The developed eutrophication potential model shows that the increase of fly-ash replacement of 0% to 50% reduces such eutrophication potential due to concrete production by as much as 38%. Moreover, the relationships between the service life and the eutrophication potential for normal and fly-ash concrete tend to be linear.

Naturally logarithmic apparent diffusion coefficient, stable time, service life, fly-ash concrete, eutrophication potential