Accelerated carbonation of ladle furnace slag: A dual approach to CO2 utilization and waste valorization in sustainable cement applications

The cement industry contributes nearly 8 % of global anthropogenic CO₂ emissions, largely driven by energy-intensive clinker production and limestone calcination. Innovative pathways to reduce this carbon footprint are critical for meeting global climate targets. This study explores the valorization of ladle furnace slag (LFS) through accelerated CO₂ carbonation, transforming it into a reactive supplementary cementitious material (SCM) that simultaneously enhances cement performance and sequesters CO₂. LFS was exposed to 100 % CO₂ for up to 72 h, achieving a CO₂ uptake of 3.3 g per 100 g slag. Incorporation of carbonated LFS at 25 % and 50 % replacement levels in cement pastes revealed significant improvements in hydration kinetics, microstructure, mechanical strength, and durability. Microstructural characterization identified the formation of nano-crystalline CaCO₃ polymorphs, which intensified pozzolanic reactivity and particle bonding. Compared to uncarbonated slag, carbonated LFS accelerated early hydration and enhanced long term strength exhibiting a 22.8 % compressive strength increase at 64 days for 25 % replacement. Reductions were observed in water absorption (7.8 %), porosity (5.2 %), and carbonation depth (17.7 %). These results demonstrate that CO₂ carbonation pretreatment not only captures carbon but also upgrades industrial waste into a high-performance, low-carbon SCM. This dual-function strategy aligns with circular economy principles and advances sustainable cement production through CO₂ utilization. • Carbonated ladle furnace slag captures CO2 and enhances cement performance. • Accelerated carbonation achieves 3.3 g CO2 uptake per 100 g slag. • Carbonated slag boosts hydration and increases compressive strength by 23 %. • Durability improved with reduced water absorption porosity and carbonation depth. • Valorization of industrial waste supports circular economy and CO2 utilization.