Towards sustainable geopolymers: Utilization of diverse calcined clays as alternative precursors

Geopolymers have emerged as a promising alternative to conventional cement-based materials due to their lower carbon emissions and alignment with sustainability goals. However, the limited availability of aluminosilicate sources remain a critical barrier to widespread adoption. This study investigates the potential use of calcined local clays as precursors for geopolymer production.Red, white, yellow, green, and black clay samples were characterized using X-ray diffraction (XRD), revealing the presence of illite , smectite , and kaolinite . The clays were then calcined at temperatures of 600–900°C for 1, 2, and 3 hours, and their pozzolanic reactivity was evaluated via the Strength Activity Index (SAI) and rapid, relevant and reliable (R³) test. Optimal calcination conditions were identified, and clays were further examined using XRD, X-ray fluorescence (XRF), and SEM-EDX techniques. Geopolymer pastes prepared with NaOH solutions of varying molarities (6–12 M) showed low early compressive strengths (<5 MPa). Improved performance was achieved using a NaOH/Na₂SiO₃ ratio of 1:1, with compressive strength increasing to 7.8–36.3 MPa at 7, 28, and 90 days. Additional FT-IR and SEM-EDX analyses provided insights into the reaction mechanisms. The study also explored the influence of SAI values, and iron content on geopolymer performance. The results confirm that calcined clays , when optimized, can serve as effective precursors in sustainable geopolymer production. • The study focuses on the influence of calcination parameters on alternative and widely available clays. • Geopolymer production was studied and compressive strength of mortar specimens at 3, 7, 28 and 90 days were investigated. • This research demonstrates the feasibility of using commonly available clays in geopolymer production