Properties and Performance Evaluation of Hot Mix Asphalt Mixtures Incorporating Recovered Carbon Black as a Filler

Asphalt pavements are increasingly exposed to higher traffic loads and extreme weather conditions, demanding durable and sustainable materials to enhance performance. This study evaluates the potential of Recovered Carbon Black (rCB), a by-product of tyre pyrolysis, as a sustainable filler in AC14 Hot Mix Asphalt (HMA). The primary objective is to improve rutting resistance and moisture susceptibility while supporting environmentally responsible waste management. Five mixtures were tested: a control mix (M0), a conventional 1% hydrated lime mix (M1L), two rCB-modified mixes with 1% and 2% rCB by weight of total aggregate (M1C and M2C), and a hybrid mix combining 1% rCB with 1% lime (M1C1L). SEM-EDS analysis confirmed uniform dispersion of rCB within the asphalt matrix, showing carbon-rich particles (>93%) integrated into the mastic, enhancing structural cohesion. Resilient modulus (RM) tests, conducted at 15℃, 20℃, 25℃, 32℃, and 40℃, demonstrated the viscoelastic sensitivity of asphalt mixtures, with RM decreasing as temperature increased. The control mix recorded the highest RM (22,360 MPa at 15℃, 1,521 MPa at 40℃), while the 1% rCB mix achieved 17,366 MPa and 822 MPa at corresponding temperatures. Although rCB-modified mixtures exhibited lower stiffness than lime-modified mixes, they delivered better rutting and moisture resistance. Hamburg Wheel Tracker results showed that the 2% rCB mix achieved the lowest rut depth (7.32 mm at 20,000 cycles, a 43.8% improvement over the control). These findings demonstrate that rCB enhances durability by mitigating permanent deformation and moisture damage while promoting circular economy practices. Incorporating rCB as a filler offers a sustainable alternative to conventional additives, paving the way for high-performance and environmentally friendly asphalt pavements.