Investigation of high-temperature resistance of natural pozzolan-based geopolymers produced with oven and microwave curing

•Geopolymers are more resistant to high temperatures than portland cement systems.•Pumice- and perlite-based geopolymers lost their volume stability at elevated temperatures.•Upon exposure to high-temperature geopolymer matrices melted partially and filled the cracks and pores. In this study, high-temperature resistances of oven- and microwave-cured pumice-, perlite-, fly ash- and burnt clay-based geopolymer were investigated and, the results were compared with that of the cement mortars. The effect of high-temperature on the matrix microstructure was investigated by SEM and changes in the crystal structure were monitored by XRD analyses. High-temperature experiments were carried out with 3 h exposure to 450, 600, 750 and 900 °C. The results indicated that both oven- and microwave-cured geopolymer mortars are more resistant to high-temperatures at all temperatures than their portland cement counterpart. However, it was also determined that pumice- and perlite-based mortars could not maintain their volumetric stability at elevated temperatures.