Valorisation of ladle steel slag in building material

Abstract The global cement industry is a major contributor to anthropogenic CO₂ emissions, driven by energy-intensive processes and the widespread use of clinker. To address this challenge, the valorisation of industrial by-products such as steel slag has emerged as a sustainable pathway for developing low-carbon construction materials. This thesis focuses on the utilization of aluminum-killed ladle slag (AKLS)—a chemically complex and traditionally underutilized by-product of secondary steelmaking—as a supplementary cementitious material. Three industrial AKLS batches sourced from Calcetek (produced in 2024 and 2025) were systematically characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), isothermal calorimetry, and mechanical testing. The study investigates the impact of slag batch variability and chemical activation strategies on hydration behavior, phase development, and compressive strength evolution. Chemical additives such as tartaric acid, citric acid, sodium carbonate, sucrose, and gypsum were introduced to enhance reactivity and control hydration kinetics. The results demonstrate that slag reactivity is highly dependent on batch composition, particularly the CaO/Al₂O₃ ratio, free lime content, and the presence of calcium sulfide. While unactivated AKLS exhibited low hydration and mechanical performance, the application of tailored additives significantly improved cumulative heat release and promoted the formation of crystalline hydration products such as portlandite and ettringite. Tartaric acid, in particular, enabled delayed but intensified hydration, leading to improved strength gain and reduced shrinkage. This study highlights the feasibility of transforming AKLS into a functional binder component by combining material-specific formulation with chemical activation. It contributes to a growing body of research supporting industrial symbiosis and carbon reduction through circular use of metallurgical residues in cementitious systems.