Long Term Behavior of Portland-limestone Cement Mortars Exposed to Magnesium Sulfate Attack

摘要

Concrete made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. This work deals with the factors affecting thaumasite formation in cement mortars and particularly the limestone content, the curing conditions and the type of the sand. Three types of cement were examined: ⅰ) 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% MgSO_4 solution and cured at: ⅰ) 5℃ and ⅱ) 25℃. The status of the samples for a storage period of 5 years was reported based on visual inspection, mass measurements, ultrasonic pulse velocity measurements and analytical techniques. 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 at low temperature.