Effects of sulfate and magnesium ion on the chloride transportation behavior and binding capacity of Portland cement mortar

Abstract

The chloride diffusion induced reinforcement corrosion seriously threatens the durability of concrete construction in marine environments. This paper investigates the effects of sulfate and magnesium ion in simulated seawater on the chloride transportation behavior and binding capacity of Portland cement mortar with and without fly ash (FA) and ground blast furnace slag (BFS). Chloride ion transport profile, binding capacity and corrosion products of mortar specimens exposed to NaCl, NaCl + MgCl2, NaCl + Na2SO4 and NaCl + MgCl2 + Na2SO4 solutions at different penetration depths were conducted respectively. Results indicate that the samples exposed to NaCl + MgCl2 solutions show the highest chloride content at the outmost layer (0–5 mm). The presence of magnesium ion and combined sulfate and magnesium ion in chloride salt accelerates chloride ingress and increase apparent chloride diffusion coefficient, while reduces the content of calcium hydroxide thus results in a reduction of the chloride binding. However, the sulfate ion in NaCl + Na2SO4 solutions inhibits the chloride diffusion, enhances bound chloride and refined the pore size due to the formation of Friedel’s salt (Fs) with chloride ion. Furthermore, the addition of BFS significantly improves the resistance to chloride ingress into mortar specimens.