Upcycling steel slag into construction materials

Steel slag is a byproduct generated by the steel manufacturing industry. It poses environmental contamination and health hazards without effective treatment. Upcycling steel slag as a construction material has attracted attention because of its desirable physicochemical properties (strength, durability, and resistance to corrosion). This study provides an overview of the currently available steel-slag upcycling methods for producing construction materials (cement, concrete, and asphalt mixtures). Specifically, this review comprehensively summarises the applications of steel slag in cement, concrete, and asphalt mixtures. It provides valuable insights into the long-term performance of steel-slag-based construction materials. When used in cement and concrete, the active components (CaO and Fe₂O₃) in steel slag promote the hydration reaction of cement. This results in the formation of hardened products and an improvement in the mechanical properties of concrete. To optimise the performance of the cement and concrete upcycled from steel slag, it is crucial to control the proportion and fineness of steel slag particles and ensure effective curing conditions and mix design. In asphalt mixtures, the high alkalinity of steel slag improves its adhesion to the asphalt materials. However, owing to the presence of free calcium oxide (f-CaO) in steel slag, the pavement with asphalt upcycled from steel slag causes an expansion associated with the service life of the pavement. The current limitations of steel slag upcycling in construction materials are discussed, and future research directions are recommended. It is anticipated that this review would support the sustainable implementation of steel slag as a raw material for construction.