Reactions, Phase Evolution, and Microstructure of Ambient-Cured Geopolymer with Delithiated β -Spodumene

This research examines the feasibility of using delithiated β-spodumene (DβS), a lithium refining by-product with great pozzolanic properties, as a substitute for fly ash (FA) in geopolymer mortar made with 75% FA and 25% ground granulated blast-furnace slag (GGBS). DβS is incorporated at replacement levels of 25%, 50%, and 75% of the total binder, substituting the FA portion by mass, while the GGBS content remains unchanged, to evaluate its effects on the mortar properties. A comprehensive set of mechanical and durability tests coupled with detailed microstructural characterizations were conducted to assess the effect of DβS content on the geopolymer. Workability, compressive strength, flexural strength, water absorption, drying shrinkage, and sulfate attack resistance were thoroughly assessed. Microstructural characterization was conducted using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR). The results show that the mix with 75% DβS exhibits better fresh and hardened properties, with a 55% increase in workability, a 68% improvement in 28-day compressive strength, and a 46% enhancement in 28-day flexural strength, relative to the control mix. Durability assessments reveal a 2% decrease in water absorption and a 59% decrease in drying shrinkage, while sulfate resistance tests indicate a 68% reduction in compressive strength loss and a 97% reduction in length change after 28 days of sulfate exposure at 75% DβS content. Microstructural analyses confirm the enhanced development of calcium aluminum silicate hydrate and sodium aluminum silicate hydrate phases in the 75% DβS mix compared to the control mix. SEM further revealed a denser microstructure with lower porosity and greater geopolymerization in the mix. These findings highlight the significant potential of DβS in enhancing the durability and mechanical properties of geopolymer mortar while also providing a sustainable solution for mitigating the DβS landfilling problem by recycling it into geopolymer materials.