Recovered Carbon Black as a Sustainable Alternative to Hydrated Lime in Asphalt Mixtures: Mechanical and Durability Perspectives

• rCB (1–2%) evaluated as sustainable filler replacing hydrated lime. • 2% rCB boosts four-point bending fatigue life by up to ∼60%. • Master curves show rCB mixes retain design-relevant stiffness. • Ageing index indicates moderated oxidative hardening with 1% rCB. The growing stockpiles of end-of-life tyres (EOLTs) present a critical environmental challenge and highlight the urgent need for circular economy solutions in infrastructure materials. Recovered Carbon Black (rCB), obtained through tyre pyrolysis, offers a sustainable pathway for valorising this waste stream while reducing reliance on virgin fillers in asphalt production. This study evaluates the potential of rCB to enhance both the environmental and mechanical performance of dense-graded asphalt mixtures designed for high-traffic pavements. Five mixtures were prepared: a control with natural fines, a conventional mix with 1% hydrated lime, and three rCB-modified variants with different proportions of rCB (1–2%) combined with lime. Mechanical performance was assessed through Indirect Tensile Resilient Modulus tests and Four-Point Bending Beam fatigue tests under both unaged and long-term aged conditions. Master curves were developed using time–temperature superposition and sigmoidal fitting to characterise viscoelastic properties. The findings indicate that while rCB substitution marginally reduces resilient modulus, it significantly extends fatigue life, by up to 63.8% at 2% dosage, and improves resistance to ageing-induced stiffening. These results underscore the dual benefit of rCB as both a sustainable alternative filler and a performance enhancer, enabling reduced environmental footprint and extended pavement durability. The study contributes to advancing sustainable material design strategies that align with circular economy principles and promote resilient, resource-efficient road infrastructure.