Chloride binding capacity of green concrete mixed with fly ash or coal gangue in the marine environment

Abstract

Wide application of green concrete mixed with supplementary cementitious materials (SCMs) can result in the reduction of energy consumption and carbon dioxide emission from cement production. Adequate aluminum in SCMs can improve the chloride binding capacity of green concrete to decrease the free chloride concentration in pore solution, reduce the corrosion risk and enhance the structural durability. Thus, high-aluminum fly ash (FA) and coal gangue (CG) can be regarded as potential SCMs for reinforced concrete structures exposed to the marine environment. This study investigated the chloride binding capacity of FA and CG concrete in the marine environment and the effects of the environment (salt fog and tidal zone) and water to cement ratio (w/c) on the chloride binding capacity. The replacement ratios of cement by FA or CG were designed to be 0%, 10%, 20%, and 30%. The results indicated that FA and CG could significantly improve the chloride binding capacity and the optimal contents of both SCMs are in a range from 20% to 30%. The chloride binding capacity is time-dependent and can be described well by linear binding isotherm. Furthermore, the chloride binding capacity in salt fog is lower than that in the tidal zone and the binding capacity increases with an increase of w/c. Finally, a semi-empirical model was proposed to evaluate the chloride diffusion and predict the chloride concentration considering the effect of chloride binding.