Behavior of Cement-Based Alkali-Activated Lightweight Mortars at High Temperatures

Six lightweight cement-based or alkali-activated mortars are investigated after being exposed to 500, 750, and 1000 °C. In the three cement-based mortars, the binder is Portland cement, with/without fly ash or metakaolin, while in the remaining three alkali-activated mortars (all devoid of Portland cement), different combinations of fly ash and metakaolin are investigated. Replacing 40% of the cement with metakaolin and replacing 50% of metakaolin with coal fly ash enhance the resistance to high temperatures of the mortars. After the exposure to 1000 °C, the high residual compressive strength of cement-based mortars containing metakaolin comes from the formation of new crystalline phases, whereas in alkali-activated mortars the high residual compressive strength comes from their high densification.