Advanced characterization of ambient-cured geopolymer paste with delithiated β-Spodumene: effect of Na2SiO3–to–NaOH ratio on performance and microstructure

Delithiated β-spodumene (DβS), an industrial by-product from lithium refining, has demonstrated potential for enhancing mechanical properties of geopolymers due to its pozzolanic characteristics. Understanding the behavior of DβS-based geopolymer paste at different alkaline activator ratios from a microstructural perspective provides critical insights into the potential suitability of DβS for geopolymer mortar and concrete. This research evaluates the influence of varying Na₂SiO₃–to–NaOH ratios on the compressive strength and microstructural attributes of geopolymer paste made with 25% DβS and 75% fly ash. The findings reveal that the paste made with DβS and fly ash exhibits the maximum compressive strength at a Na₂SiO₃–to–NaOH ratio of 2, similar to that of the paste made with only fly ash. The generation of the amorphous sodium aluminosilicate hydrate phase is enhanced with increasing Na₂SiO₃–to–NaOH ratios. The highest amount of the sodium aluminosilicate hydrate phase formation in the DβS/fly ash and fly ash pastes occurs at ratios of 2 and 2.25, respectively. The findings of this study provide an insight to incorporate DβS as an alternative to FA in geopolymer binders and suggest the optimal alkaline ratio range for use in geopolymer mortar and concrete. This strategy not only enhances geopolymer properties but also mitigates the environmental issue of DβS disposal of in landfill.