Production of cleaner high-strength cementing material using steel slag under elevated-temperature carbonation

The feasibility of making a cleaner cement via elevated-temperature carbonation of steel slag was investigated. Two types of steel slags were examined, a high-lime ladle steel slag (LSS) and a low-lime electric-arc furnace steel slag (ESS). In comparison to ambient-temperature (23 °C) carbonation, the optimized elevated temperature (55 °C) carbonation process improved the compressive strength of LSS and ESS binders by 72% and 48%, reaching a 12-h paste strength of 91.2 MPa and 39.9 MPa respectively. Meanwhile, LSS and ESS recorded 15% and 9% CO₂ uptake under the optimized carbonation scenario. Serving as the commercial benchmark control, ordinary Portland cement (OPC) paste conventionally hydrated for 28-d recorded an average strength of 43 MPa. The mineralogical and microstructural changes in the steel slag binders under the two carbonation curing scenarios (ambient and 55 °C) were examined by quantitative X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis coupled with a mass spectrometer, mercury intrusion porosimetry, nitrogen adsorption and desorption, and scanning electron microscopy. The analyses revealed that the degree of carbonation and the formation of reaction products were enhanced under the elevated temperature curing conditions, leading to a finer pore structure as well as the development of larger and more crystalline calcium carbonate crystals that contributed to the superior strength of the final product. The sustainability assessment including the embodied carbon analysis confirmed that the carbonated steel slag binder is a cleaner alternative to OPC. This study highlights the wide-ranging prospects to incorporate less reactive, and otherwise landfilled, steel slags into construction cement materials.