Enhancing strength and CO₂ uptake in lignite-based fly ash geopolymer mortar through supercritical carbonation

This study demonstrates the potential of supercritical CO₂ curing to enhance the performance and sustainability of lignite-based fly ash geopolymer mortar offering a promising approach to reducing CO₂ emissions in the construction industry while improving material properties. The research comprehensively compared conventional curing (GEO-REF) with supercritical CO₂ curing (GEO-CO₂), revealing that GEO-CO₂ samples exhibited higher compressive and flexural strengths, achieving peak performance almost immediately after curing. Supercritical CO₂ exposure resulted in enhanced carbonation, with a depth of up to 7.6 mm and a carbonation rate of up to 67 %. XRD confirmed phase changes due to CO₂ curing, with GEO-CO₂ showing additional calcium carbonate-calcite, calcium carbonate-aragonite, and calcium silicate hydroxide compared to GEO-REF. Nitrogen adsorption/desorption studies indicated larger pore diameters but a reduced BET surface area in GEO-CO₂ samples, suggesting structural changes due to CO₂ exposure. TGA analysis revealed that supercritical CO₂ curing reduced water retention and enhanced carbonation, resulting in increased CaCO₃ content and changes in Ca(OH)₂ levels. • Supercritical CO₂ curing significantly improves mechanical properties of geopolymers. • GEO-CO₂ samples achieve peak compressive and flexural strengths post-curing. • Enhanced carbonation depth (7.6 mm) and rate (67 %) confirmed through analysis. • XRD and nitrogen adsorption reveal structural changes and phase transformations. • TGA indicates reduced water retention and increased CaCO₃ content in GEO-CO₂.