Optimizing carbon sequestration and performance of a sustainable gypsum-based materials using steel slag waste

Building materials can act as carbon sequestration agents by capturing atmospheric carbon dioxide (CO 2 ) and enhancing their performance. This represents a promising approach to reducing the carbon footprint of the construction industry and mitigating the greenhouse effect through CO 2 utilization. However, gypsum-based materials tend to show a decline in performance after carbonation, a challenge that remains unresolved in current research. This study is the first to utilize the unique properties of basic oxygen furnace slag (BOFS), which is a type of steel slag waste, to address this issue. A comprehensive evaluation was conducted on bulk density, compressive strength, water resistance, water absorption, porosity, and environmental impact, complemented by advanced analytical techniques, including TGA, SEM, and XRD, to gain deeper insights into the underlying reaction mechanisms. The findings reveal that incorporating BOFS into gypsum-based materials and activating the system with an alkaline activator mitigated deterioration after carbonation while maintaining effective CO 2 sequestration. The results indicated that adding 20 % BOFS to gypsum-based blocks with a water-to-binder ratio of 0.20 generated sufficient carbonation products (CaCO 3 and SiO 2 -rich gel) after carbonation. These products effectively filled the internal pores of the specimens and induced subsequent hydration reactions, further improving their compressive strength and water resistance. Furthermore, based on life cycle assessment, these specimens achieved an ideal CO 2 uptake of 32 kg CO 2 eq per ton, reducing the global warming potential by 94.5 % compared to carbonated cement-based materials. This greener carbon sequestration agent offered promising potential for advancing sustainable building materials. • Incorporating BOFS in gypsum-based blocks can better utilize CO 2 to enhance strength. • Excessive water content hindered CO 2 ion migration and diffusion. • Optimal combination is 20% BOFS content and 0.20 w/b ratio. • Carbonated gypsum-based blocks had lower emissions compared to cement-based blocks. • Modified gypsum-based blocks sequestered up to 32 kg of CO 2 eq per ton.