Effect of carbonation on chloride diffusion in fly ash concrete

The part above the sea water of marine concrete structures is subjected to chloride penetration and carbonation over a long period of time. Compared with the concrete structures in the general atmosphere, marine concrete structures are more susceptible to reinforcement corrosion. In this study, experiment of chloride penetration into concrete after carbonation under wet and dry cycle mechanism was carried out. Effect of concrete carbonization on chloride diffusion was deeply studied through analysis of the distribution of chloride ions, chloride diffusivity coefficient and microstructure of concrete. The results showed that: carbonation changes the original filtering mechanism of concrete, causes a re-distribution of microstructure, slows down the decay of chloride ion concentration, increases the content of free chloride ion and brings adverse effect to chloride-penetration resistance of concrete. After carbonation, chloride diffusivity coefficient increases in common and it will increase with the increasing of carbonation time. The adverse effect to chloride-penetration resistance of concrete caused by carbonation is more significant to concrete with higher fly ash amount.