Sustainable Geopolymer Synthesis from Calcined Pumice: Reactivity, Mechanical Performance, and Water Resistance

This study investigates the feasibility of using calcined pumice as a sustainable precursor for geopolymer production. Natural pumice was calcined at different temperatures (600, 750, and 900 °C) and durations (1, 2, and 4 h). The effects of calcination were evaluated through color change, particle size distribution, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The results showed that calcination induced structural and mineralogical modifications in pumice, including increased disorder in the aluminosilicate network and partial recrystallization, which enhanced its reactivity. Consequently, geopolymer mortars produced with calcined pumice exhibited significantly improved compressive strength, with the highest strength of 53.5 MPa obtained for the sample calcined at 750 °C for 1 h, corresponding to an 84.5% increase compared to the mortar produced with raw pumice. In addition, calcination at 600 °C and 900 °C significantly improved water resistance. Considering mechanical performance, durability-related properties, and energy efficiency together, the calcination condition of 600 °C for 2 h was identified as the optimum treatment. These findings demonstrate that calcined pumice is a promising and sustainable precursor for geopolymer production.