Corrosion behaviour of steel rebar in mortars subjected to magnesium sulfate and sodium chloride mixtures at 5 and 20 °C

Although exposure to sulfate and chloride ions separately is known to result in deterioration of concrete and corrosion of steel rebars, the effects of both ions being simultaneously present are ambiguous, with some studies showing the presence of chloride to be beneficial, while in others attack was accelerated. This paper describes an investigation into the corrosion activity of steel rebars embedded in cement mortars made with CEMI and CEMI blended with 10% limestone filler subjected to combined sulfate (0.6% SO4−2 and 0.152% Mg+2 as Epsom salt) and chloride (0.5 and 2.0% Cl−) at both 5 and 20 °C. Evaluation was made by means of linear polarization resistance (LPR) and visual inspection of the mortar specimens and the rebar surfaces. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis were also carried out on selective materials collected from steel-mortar interfaces. Mortar specimens stored in composite sulfate and 0.5% chloride solution at 5 °C showed deterioration due to thaumasite formation and the associated rebars suffered greater corrosion than for other mixtures. It is concluded that thaumasite formation resulting in the loss of chloride binding in the cement mortars is a crucial factor in accelerating steel corrosion.