Optimising particle size in the accelerated carbonation of EAF slag for improved mechanical performance and CO₂ uptake

This study investigated how the particle size of electric arc furnace slag (EAFS) affects carbonation reactivity, CO 2 uptake, microstructural evolution, mechanical performance, energy efficiency, and leaching behaviour under accelerated dry carbonation. EAF slag was mechanically ground for various periods, mixed with 8 wt% water, compacted statically into 40 mm cubes, and then carbonated for 24 h. Mechanical activation reduced the mean particle size (D50) from 128 µm to 6 µm, increasing the specific surface area to 1137 m 2 /kg and enhancing carbonation reactivity. The highest carbonation performance was achieved after 20 min of grinding, yielding an average CO 2 uptake (UCO 2 ) of 5.41%, a degree of carbonation (DCO 2 ) of 17.79% and a maximum compressive strength of 75.03 MPa. The optimal grinding time was found to be between 12 and 14 min, corresponding to specific grinding energies of 0.34–0.40 kWh/kg. Within this range, the carbonated slags achieved compressive strengths above 71 MPa, average UCO 2 values of around 4.5%, and a degree of carbonation of around 15%. Leaching tests showed heavy-metal concentrations below toxicity limits. Overall, these results emphasise the importance of optimising particle size to produce low-carbon EAF slag-based construction materials.