Effect of carbonation on chloride diffusion in concrete

Concrete and paste were immersed in a 3.5% NaCl solution for 650 d after they were quickly carbonated for 0, 14 and 28 d. The free and total chloride contents in different depths of concrete were tested to calculate the chloride apparent diffusion coefficient and the chloride binding capacity. The pore structure and corrosion production of paste attacked by different corrosion regimes were analyzed by mercury intrusion porosimeter (MIP) and differential thermal analysis (DSC), respectively. The results indicate that the chloride content and the chloride apparent diffusion coefficient increase after quick carbonation, however the chloride binding capacity of concrete reduce simultaneously; and the carbonation influence increase with time. Quick carbonation of concrete coarsens its pore structure that the capillary pore (≥ 30 nm) amount of paste increases by 11% and the most probable pore size increases by 17 nm, but it decreases the Friedel'S amount in concrete and reduces the chemical chloride binding capacity of concrete.