Thermal resistance of alkali-activated metakaolin pastes containing nano-silica particles

In the current investigation, the opportunity of employing nano-SiO2 (NS) to modify fire resistance of metakaolin-based geopolymer pastes has been explored. Metakaolin (MK) was partially substituted with NS at ratios of 0.5%, 1%, 2%, 3% and 4%, by mass. After curing for 28 days, the specimens were subjected to high temperatures altered from 400 to 1000 °C with a step of 200 °C for 2 h. The workability of different mixtures has been investigated. Mass loss and compressive strength of various specimens prior and after exposure have been measured. The new formed geopolymer phases have been identified using X-ray diffraction and scanning electron microscopy. The results displayed that the incorporation of NS reduced the workability. The incorporation of 0.5% NS enhanced the compressive strength and fire resistance of MK-based geopolymer pastes, whilst including extra amounts of NS led to the occurrence of adverse effects.