Calcium-aluminate mortars at high temperatures: Overcoming adverse conversion effects using clinker aggregates

Abstract The effect of elevated temperatures on a calcium aluminate mortar with clinker aggregates is the subject of this paper. After an exposure period of 3 h at temperatures ranging from 25 to 1000 °C, specimens were tested in residual conditions in order to evaluate changes on the mechanical and microstructural properties. A simplified hydration model based on the chemical reactions of the principal minerals is proposed to predict the evolution of matrix composition from the early-age hydration. The improvement of the mechanical properties occurring due to the conversion reactions between 25 °C and 200 °C, is attributed to an increased hydration reaction of both cement and clinker aggregate. Furthermore, when compared to the metastable reactions, an improved interlocking effect at the reactive aggregate interface, and a more dense nature of the stable hydration products, were observed. These phenomena balance the adverse effects promoted by conversion reactions on porosity and mechanical properties.