The competitive diffusion process of chloride into mortar immersed in chloride-sulfate solution

The chloride and sulfate exist together in real environment, no matter marine or salts lakes, and the ratio of the chloride to sulfate is varied. To precisely predict the concrete durability under real environment, this paper mainly investigated the influence of sulfate on chloride ions diffuse into hardened cement paste. The Minitab software was used to calculate and design the content of compound impregnating solution in order to fully understand the effect of the concentration of chloride and sulfate on the chloride diffusion depth. The AgNO3-based colorimetric method and acid-soluble chloride test were used to determine the chloride diffusion depth and the chloride penetration profile. The evolution phase distribution from the outer to the inner were characterized by SEM, EDS and XRD. The results showed that chloride diffusion generally increased with increasing concentration of chloride. The presence of sulfates promoted chloride diffusion initially, while it delayed the chloride diffusion in the later. Chloride ions diffused into mortar mainly through ITZ and pores, and reacted with the hydration products to produce Friedel’s salt. Although the diffusion rate of sulfate ions is slow, it can alter the stability of the Friedel’s salt and block the pores, which has a long-term effect on chloride ion diffusion.