Understanding the chloride binding and diffusion behaviors of marine concrete based on Portland limestone cement-alumina enriched pozzolans

Abstract

This work studies the chloride binding and diffusion of marine concrete produced with Portland limestone cement and alumina enriched pozzolans. The chloride binding capacity, the effect of binder chemic composition on chloride binding and the role of chloride binding in chloride diffusion are investigated. The results show that the addition of alumina enriched pozzolans benefits the formation of hemicarboaluminate that has low density and high filling efficiency, which helps to densify the matrix. The densified microstructure significantly restrains the chloride diffusion, and the penetration depths can be well indicated by the evaporable water content. The chloride binding capacity depends on CaO to Al2O3 (C/A) ratio of binder. There exists a critical value of C/A ratio, generally ranging from 3 to 7, to maximize the chloride binding capacity. For the C/A ratios less than the critical value, the alumina in the system is excessive and the chloride binding capacity is more closely linked to the calcium content; for the C/A ratios more than the critical value, the calcium is sufficient and the chloride binding capacity highly depends on the alumina content in the system. The numerical modelling results show that the chloride binding obviously retards the chloride diffusion in concrete. However, in the early exposure ages, this retardation is less remarkable due to long duration required for chloride binding equilibrium in concrete pore solution. For a prolonged exposure time, the chloride diffusion retarded by chloride binding is expected to be more remarkable.