Sustainable Portland Cement Alternative: Alkaline Activation of Ladle Furnace Slag as a Precursor for Eco-Friendly Building Materials

Portland cement (OPC) and steelmaking industries exhibit high production levels, and their industrial processes are not considered environmentally friendly, generating approximately 4%–7% of CO2 emissions worldwide. Both industries introduced several improvements in their industrial processes; however, the steelmaking industry still generates large volumes of solid waste. Ladle furnace slag (LFS), one of these residues, shows exciting properties to be used as part of the next generation of sustainable building materials. However, due to technological barriers in its valorization process, its final destination is landfilling. This article explores a safe and high-value application to valorize LFS as a high calcium content precursor in alkaline-activated (AA) systems, focusing on the effect of the SiO2/Na2O molar ratio of the activator, defined as the activator module (Ms), on physical-mechanical performance, volumetric instability, and the microstructure evolution. The microstructural characterization (chemical/mineralogical qualitative and quantitative) of the raw/activated samples using different techniques [X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and Raman] of the raw/activated samples, compressive strength, and volumetric instability tests were evaluated. Our results show low mechanical performance, reaching compressive strength values up to 11.5 MPa after 60 days. LFS mineralogical characterization reveals the feasibility of activating the LFS and the formation of a CASH-type gel with a high degree of polymerization (up to Q4 units). Therefore, LFS presents an interesting potential as a high-Ca content precursor in AA systems for potential use in low-strength cement-based formulations.