Enhancing strength and ▫$CO_2$▫ uptake in lignite-based fly ash geopolymer mortar through supercritical carbonationPodnar, Tinkara Marija (Avtor) Knez, Željko (Avtor) Kravanja, Gregor (Avtor) geopolymerfly ashcarbonationCO2 fixationsupercritical CO2high pressure reactorThis 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.Elsevier B.V.20252025-07-25 10:27:55Članek v reviji93908UDK: 66.02COBISS_ID: 241936131DOI: 10.1016/j.supflu.2025.106695ISSN pri članku: 1872-8162sl© 2025 The Author(s)