Use of mineral admixtures to prevent thaumasite formation in limestone cement mortar

Abstract

Abstract Concrete made from limestone cement may exhibit a lack of durability due to the formation of thaumasite. The addition of minerals that improve the concrete durability is expected to slow down the formation of thaumasite. In this work the effect of natural pozzolana, fly ash, ground granulated blastfurnace slag (ggbs) and metakaolin on the thaumasite formation in limestone cement mortar is examined. A limestone cement containing 15% w/w limestone was used. Mortar specimens were prepared by replacing a varying part of the limestone cement with the above minerals. Siliceous and calcareous sand was used in order to study the effect of the sand type on the thaumasite formation. The specimens were immersed in a 1.8% MgSO4 solution and cured at 5 and 25 °C. The formation of thaumasite was checked and confirmed by visual inspection, strength tests, ultrasonic pulse velocity measurements, XRD and TGA. It is concluded that the use of specific minerals, as partial replacement of cement, inhibits the thaumasite formation in limestone cement mortar.