Long term behavior of Portland limestone cement mortars exposed to magnesium sulfate attack

Concrete and mortar made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. This work deals with the long term behavior of limestone cement mortars in relation to the limestone content, the curing conditions and the type of the sand. Three types of cement were examined: (i) Portland cement (PC), (ii) Portland limestone cement containing 15% w/w limestone and (iii) Portland limestone cement containing 30% w/w limestone. Mortar specimens were prepared using calcareous and siliceous sand. The specimens were immersed in a 1.8% MgSO4 solution and cured at: (i) 5 °C and (ii) 25 °C. The status of the samples for a storage period of 5 years are reported, based on visual inspection, compressive strength, mass measurements, ultrasonic pulse velocity measurements and analytical techniques, including X-ray diffraction, thermal analysis and scanning electron microscopy. It is concluded that mortars containing limestone, either as sand or as a main constituent of the cement, suffer from the thaumasite form of sulfate attack (TSA) at low temperature. In some cases, the TSA leads to almost complete damage of the specimens after only 60 months of exposure. At 25 °C the specimens do not show any signs of conventional sulfate attack, even after 60 months of exposure to sulfate solution.