High-temperature performance of slag-based Fe-rich alkali-activated materials

Fe-rich alkali-activated materials have been studied for their suitability for high-temperature application up to 1000 °C. The evolution of compressive strength, mineral composition and microstructure was monitored using FT-IR, XRD, TGA and SEM-WDS for the pastes and mortars obtained by alkali activation of fayalite and wüstite non-ferrous slags. For both binders, the changes in compressive strength revealed moderate fluctuations below 400 °C due to water evaporation, a sharp drop in strength to 25 MPa at 600 °C due to collapse of the original gel structure, and reinforcement of the strength above 600 °C due to sintering densification and formation of gehlenite-åkermanite or diopside-albite ceramic. An extensive reaction of the quartz aggregate with a sodium-rich binder resulted in the formation of an iron silicate phase that contributed to a further increase in the strength up to 70 MPa by increasing both temperature and time of heating.