Steel Slag in Asphalt Pavements: A Review on Performance, Multifunctional Applications, and Volume Expansion Mitigation Strategies

Abstract To address the environmental challenges posed by steel slag (SS), integrating SS into asphalt pavements has emerged as a promising solution to manage waste and promote sustainable development. Therefore, this review aims to provide the current state of knowledge regarding the application of SS in asphalt pavements, including the physicochemical interactions between SS and asphalt binders, the influence of SS on road performance, strategies for mitigating volume expansion, and emerging multifunctional applications. First, SS has excellent physical properties and adhesion with asphalt, which enables it to comprehensively improve the performance of asphalt mixtures. This makes them a promising alternative to natural aggregates. However, despite its superior initial adhesion, free calcium and magnesium oxides (f-CaO and f-MgO) trigger delayed hydration reactions, leading to volume expansion and durability issues, which are the primary barriers to wide-scale application. Given that, this review critically evaluates various pretreatment methods, with their underlying mechanisms. Beyond enhancing road performance, SS also shows remarkable potential in smart pavement technologies, such as microwave-induced self-healing, de-icing, and temperature-regulating pavements. More importantly, the combined use of SS with recycled asphalt pavement represents a highly practical and sustainable strategy, as it balances pavement performance, reduces the demand for fresh asphalt binder, and maximizes the reuse of waste materials. Ultimately, through a comprehensive review of studies in recent years, this review aims to provide actionable reutilization strategies of steel slag and engineering insights for sustainable road infrastructure.