Durability of cement mortars incorporating limestone filler exposed to sodium sulfate solution

With the purpose of investigating the influence of both fineness levels and replacement ratios of limestone filler on sodium sulfate attack, cement mortar and paste specimens incorporating the material were exposed to 5% sodium sulfate solution for 1 year. The resistance of mortar specimens to sulfate attack was evaluated by visual appearance, expansion and compressive strength measurements. Additionally, microstructural observations such as XRD and SEM/EDS were also performed on paste samples stored in similar conditions of sulfate attack. Experimental results demonstrated that the worst performance was noted in the mortar specimens with high replacement ratio as well as high fineness level of limestone filler, showing extensive surface damages in addition to significant expansion and strength loss. Thus, it was observed that both high replacement ratio and high fineness level have potentially a negative effect in resisting sodium sulfate attack. This phenomenon is likely attributed to thaumasite formation as a result of sulfate attack rather than gypsum formation. The present study may suggest useful information on both reasonable replacement ratio and fineness level for the application of limestone filler in sulfate environments.