Behavior of blended cement mortars containing nano-metakaolin at elevated temperatures

The effects of high temperatures up to 800 °C on the mechanical properties and microstructure of nano-metakaolin cement mortars were investigated in this study. The blended cement used in this investigation is ordinary Portland cement (OPC) containing nano-metakaolin (NMK). The nano-metakaolin was prepared by thermal activation of nano kaolin clay at 750 °C for 2 h. The mortar was prepared using blended cement: sand ratio of 1:3 and water/binder ratio of 0.6. The cement mortar pastes were cured under water for 28 days; then dried at 105 ± 5 °C for 24 h and then exposed to 250, 450, 600 and 800 °C for 2 h. The compressive and flexural strengths were measured for blended cement mortar and compared with the strength of pure OPC mortar. It was found that after an initial increase in compressive strength at 250 °C for the mortar specimens, the strength decreased considerably at higher temperatures.