Thaumasite sulfate attack in Portland and Portland-limestone cement mortars exposed to sulfate solution

The resistance of a plain Portland cement and a Portland-limestone cement to sulfate attack at 5 °C was evaluated. The expansion of mortar bars exposed to a sodium sulfate solution was measured over time and different phases formed at various stages of the sulfate attack were identified using XRD. Results show that the mortar bars initially formed ettringite and gypsum causing some expansion, but expanded much more and ultimately disintegrated due to thaumasite formation. The opening up of the microstructure, caused by extensive cracking of the samples at the early stages was a prerequisite for the formation of thaumasite.