Study of the evolution of properties of mortar under sulfate attack at different concentrations

Abstract

In this study, the samples of ordinary Portland cement mortar were fully immersed in sodium sulfate solutions of different concentrations (0%, 5% and 15%) for up to 270 d. The evolution of the properties of the samples (compressive strength, static modulus of elasticity, stress–strain behaviour, hardened density, water permeability coefficient and length change) was monitored. The surface deterioration of the samples was also observed and the morphological features of the products were investigated using scanning electron microscopy. Water immersion was found to improve for the properties of the samples and reduce the water permeability coefficient. Moreover, at the initial stage of sodium sulfate attack, the presence of sulfate ions had a positive effect on the evolution of the properties due to the formation of ettringite and gypsum. Afterwards, the samples immersed in sodium sulfate solution showed a degradation in the properties, induced by the expansion of expansive products and the generation of micro-cracks. Furthermore, the mortar immersed in sodium sulfate solution showed higher expansion and a larger hardened density than the mortar immersed in water. An increase in the concentration of the sodium sulfate solution was found to reduce the time needed to reach peak properties and to accelerate deterioration of the properties at the late stage.