Study on the Performance of Modified Asphalt Mixture Incorporating MSWI Bottom Ash

To achieve the valorization of municipal solid waste incineration (MSWI) bottom ash and investigate its engineering feasibility as an aggregate replacement in asphalt mixtures, this research adopted MSWI bottom ash in three particle size fractions (2.36–9.5 mm, 9.5–16 mm and 2.36–4.75 mm) to replace basalt aggregate in SBS-modified AC-20 asphalt mixtures. Five dosages of MSWI bottom ash (0%, 7.5%, 15%, 22.5% and 30%) were designed, and high-temperature stability, low-temperature cracking resistance, moisture stability, dynamic modulus and fatigue resistance were tested. The results indicate that the incorporation of MSWI bottom ash causes different degrees of performance degradation. At a dosage of 30%, the dynamic stability of Groups I, II and III decreased by 37.5%, 49.3% and 27.5%, respectively, while the fatigue lives decreased by 48.1%, 60.3% and 31.3%, respectively. The failure strain of Group III at 30% was 2007 microstrain, still slightly higher than the specification limit, whereas Groups I and II dropped to 1825 microstrain and 1575 microstrain. The freeze–thaw splitting tensile strength ratios of Groups I and III at 30% were 81.6% and 84.1%, both meeting the 80% requirement, while Group II decreased to 78.7%. Overall, the 2.36–4.75 mm fraction produced the smallest deterioration, followed by the 2.36–9.5 mm fraction, whereas the 9.5–16 mm fraction showed the most significant reduction. Considering both pavement performance and resource utilization efficiency, MSWI bottom ash is recommended to replace basalt aggregate at dosages not exceeding 30% for the 2.36–4.75 mm fraction and 22.5% for the 2.36–9.5 mm fraction. In addition, the asphalt–aggregate ratio should be adjusted with the slag dosage to compensate for the high absorption of MSWI bottom ash.