Converting ladle slag into high-strength cementing material by flue gas carbonation at different temperatures

The aim of this study is to explore the feasibility of valorization of steelmaking ladle slag into a high-strength cementing material through a carbonation-activation step that uses flue-gas, so that a closed-loop recycling solution can be achieved. Flue-gas (20% CO₂) carbonation was carried out at ambient (23°C) and elevated (55°C) temperatures. After 24 h of flue gas carbonation at 55°C, ladle slag compacts achieved an average compressive strength of 74.7 MPa with a CO₂ uptake equivalent to 12.1 wt.%. In comparison, conducting carbonation at the ambient temperature recorded lower values for strength and CO₂ uptake, and yielded a less refined and more porous microstructure. Nevertheless, carbonated compacts under both ambient and elevated temperatures achieved better strength performances at all testing ages than the hydrated OPC control reference specimens. The CO₂ in flue gas precipitated as calcite in the paste matrix regardless of curing temperature; however, the elevated temperature of 55°C was found to additionally promote the precipitation of aragonite crystals. In an environmental impact assessment model that uses conventionally-cured OPC as the industry-standard baseline with global warming potential (GWP) of 1204.4 kg CO₂-eq/m³, the alternative use of carbonation-activated ladle slag was found to greatly reduce the overall GWP to a range between 39.2 and 247.5 kg CO₂-eq/m³, even when taking the increased curing temperature into consideration. This work presents a possible future scenario where high-strength cementing material could be produced by recycling locally sourced slag, stack-captured flue gas, and waste heat energy from steel plants.