Frost damage progression studied through X-Ray tomography in mortar with Phase Change Materials

The potential of using phase change materials (PCM) in cementitious materials to mitigate damage due to thermal loadings has been recently focus of intensive research. In the case of PCM with transition temperatures near to the freezing point of water, their potential to delay frost in a cementitious matrix has been largely investigated through the monitoring of internal temperature changes when exposed to repeated cycles of subzero and ambient temperature. Yet, the effect of these admixtures to prevent damage in cement-based materials has not been directly studied. In this paper,mortars cylinders of two different sizes and containing 0, 10 and 30%of PCM replacement by volume of aggregates were subjected to frost salt scaling during freeze and thaw cycles. Prior to the start of the weathering and after cycles 1, 3, 7 and 15 the cylindrical specimens were subjected to X-ray microtomography to monitor morphological changes due to frost action, such as chipping and cracks. Compressive and flexural strength, coefficient of thermal expansion and apparent porosity of the undamaged composites were also investigated. Results suggest that the improvement of frost scaling resistance of the mortars with incorporated PCM is a trade-off between resulting mechanical proper-ties, thermal volume stability and porosity of the composite, as evinced from the better performance of mortars with 10%of PCM replacement.