Hygro-mechanical behaviour of cement paste and mortar during drying

The hygro-mechanical behaviour of cement paste and mortar during drying was investigated to assess the impact of the presence of aggregates. Samples were cast, and then subjected to air-drying and moderate oven-drying at 38 & DEG;C after a long maturation period. Shrinkage and mass variation were monitored and compressive and bending tests were carried out as a function of the drying conditioning mode and composition. The results show that the drying shrinkage of mortar is considerably lower than that of cement paste due to the presence of aggregates in the mixture, as expected, and tends more quickly to stabilisation. However, their relative losses in mass remain close for a given drying conditioning mode. Moreover, the cracks appear on air-dried cement paste, also visible on oven-dried cement paste after the application of hydraulic oil providing sufficient contrast, and then become imperceptible in the case of mortar. The presence of aggregates that leads the compressive strength and in particular the Young's modulus to rise at the initial (saturated) state accentuates the increase of compressive strength and limits the impact of drying-induced micro-cracking on the Young's modulus and bending strength at the dried state. Furthermore, the intensification of the rapid drying process of mortar from 38 to 60 & DEG;C leads mainly to a slightly lower drying shrinkage reached more quickly to stabilisation and a higher bending strength. All these results show that the performance of cement-based materials is influenced by their drying process and composition.