Effect of curing temperatures on hydration, mechanical and microstructural properties of metakaolin-blended cement mortars

Through this work, the effect of curing temperature on metakaolin-cement mortar blend was investigated. Mortar mixtures with different substitution rates of metakaolin (MK), i.e. 5, 15 and 25% of Portland cement (PC) at four different constant curing temperatures (10, 15, 20, 40 °C), were considered for the present investigation. Isothermal calorimetry and compressive strength tests were performed on mortars made with various dosages of PC and MK at different temperatures. The microcalorimetry curves obtained for the mortar blend with 25% MK mortar at different temperatures show that, with the increase in curing temperature, there is an acceleration of the hydration rate and particularly an earlier appearance of the main peak of hydration. The analysis of the effect of MK dosage on the time of the main hydration peak showed that the increase of the MK dosage enabled to increase in the reactivity of the binder at all temperatures considered. The compressive strength results also enabled to detect an optimal content of MK giving the higher mechanical performances, which was dependent on the age of the mortars and the curing temperature. The influence of curing temperature on the microstructure of the mortar matrix was further verified in terms of SEM-EDS and water porosity study.