Influence of sulfate on the chloride diffusion mechanism in mortar

The deterioration of cement based materials in marine and salts lakes environment is complicated problem, due to the presence of chlorides and sulfate simultaneously. The influence of sulfate on the chloride diffusion mechanism was evaluated by scanning electron microscopy (SEM-EDS), mercury intrusion porosimetry (MIP) and X-ray diffraction (XRD). The total chloride profile was also used to illustrate the influence of chloride and sulfate salts concentrations on chloride diffusion. The results show that the chloride binding and formation of Friedel's salt are inhibited by the presence of sulfate. The presence of sulfate increases chloride diffusion in the short term, while it inhibits the chloride diffusion from a long-term perspective. The aggressive ions penetrate into the mortar causing mortar's porosity decrease, especially the pore <50 nm, which means the sulfate inhibits the chloride ions diffusion. The impact of sulfate on the chloride ions diffusion mechanism depend on chloride and sulfate salts concentrations, exposure time and diffusion depth. This study can provide a better insight for understanding the deterioration of cement-based materials under chloride-sulfate compound salts attack. (C) 2018 Elsevier Ltd. All rights reserved.