Thaumasite formation in Portland-limestone cement mortars: Effect of wetting/drying cycles and continuous immersion in different sulfate sources

Abstract

Sulfate ions can induce the formation of thaumasite by sulfate attack (TSA). This attack mechanism destroys the binding capacity of the cement, resulting in surface wear and material deterioration. Research indicates that the manner of exposure to sulfates contributes to the generation of TSA, including continuous immersion and wetting/drying cycles. Although there are studies on different exposure conditions for the formation of TSA, most of them focus on the comparison with a single type of sulfate. Furthermore, the time of severe wear is quite variable. In this work, the effect of these different methods on the formation of thaumasite was studied in Portland-limestone cement (PLC) mortars exposed to Na₂SO₄ and MgSO₄ solutions at low temperatures (5 °C) for 455 days. Assessments included visual analyses, microstructure (XRD and FTIR) and monitoring changes in length and mass. The results indicated the formation of thaumasite in all mortars, intensified in the specimens under continuous immersion conditions, regardless of the type of sulfate. Delayed wear of wetting/drying cycles has been attributed to insufficient water for ion transfer and chemical reactions to initiate TSA.