A numerical study on chloride diffusion in freeze-thaw affected concrete

Abstract

Existing concrete in cold or coastal regions is attacked by chloride penetration under freeze-thaw cycles (FTCs). The combined deterioration process accelerate the damage evolution of concrete and reduces the service life of concrete structures. This paper presents a mesoscopic numerical model, which is 2-D and 3-phases, to investigate the mechanism of chloride diffusion under FTCs in a quantitative manner. Unlike most of existing models, the present model considers the FTCs-induced damage affected chloride diffusion by adopting a time-dependent variable of porosity, which can not only reflect how freeze-thaw action affects the concrete pore structure, but also couple the freeze-thaw process together with the chloride diffusion process at time scale. The reliability of the proposed model is validated against a third-party experiment. Based on the obtained concentration distribution profiles, a series of significant influencing factors, i.e., w/c ratio, ITZ effects, external chloride concentration, aggregate volume fraction and inner temperature are clarified. A grey relational analysis is further conducted to rank the correlative degrees of influencing factors on diffusivity of chloride under FTCs. The findings of this study can bring insights to the preparation technique of concrete in cold or coastal regions as well as the durability prediction on existing concrete structures suffering chloride attack and freeze-thaw action.