Detection of Thaumasite Formation Using Differential Scanning Calorimetry

Thaumasite sulfate attack was studied on mortars containing portland-limestone cements and various supplementary cementing materials. The resistance of the mortar mixtures against deterioration was quantified by measuring expansion of mortar prisms for 2 years according to current Canadian standards. In order to characterize the products formed from thaumasite sulfate attack reactions in the mortar samples, differential scanning calorimetry (DSC) was employed, and the observations were verified using X-ray diffraction. It was observed that, for the studied mortar samples exposed to thaumasite sulfate attack, thaumasite could be identified using DSC due to its distinct endothermic peak located between 110 degrees C and 119 degrees C. In addition, endothermic peak ranges for ettringite or calcium silicate hydrates and gypsum were found as 88 degrees C-105 degrees C and 120 degrees C-134 degrees C, respectively. DSC was found to be a reliable technique in studying concrete and mortar affected by thaumasite formation, which may be used as a replacement or complement for X-ray diffraction.