FRACTURE RESISTANCE AND SELF-HEALING POTENTIAL OF VERY THIN ASPHALT OVERLAY ENHANCED BY MICROWAVE HEATING

Very-thin asphalt overlay mixtures require a careful balance of competing demands, such as enhancing skid resistance, reducing noise, and improving rutting resistance, due to their reduced thickness. Achieving this balance involves reducing the nominal maximum aggregate size (NMAS) and incorporating coarser aggregate gradations. This design complexity is particularly critical for semi-dense graded very-thin overlays, which are more susceptible to cracking. In this context, investigating the healing potential of very-thin asphalt overlays through microwave heating offers a promising opportunity to extend pavement life while minimizing economic and environmental impacts. This study investigates and compares the cracking resistance and self-healing capabilities of two mixtures by applying Fracture–Healing–Fracture (FHF) cycles using Semi-Circular Bending (SCB) testing under microwave heating. The mixtures examined include a semi-dense aggregate gradation (BBTM8) designed for very-thin overlays, and a dense-graded aggregate mixture (ACL 16+) intended for binder courses and containing 50% reclaimed asphalt pavement (RAP). As a result, the ACL mixture exhibited a fracture toughness (KIC) value of 37.1 N/mm³⁄², attributed to its denser gradation, larger NMAS, higher stiffness, and greater RAP content. In contrast, the initial KIC value of the BBTM8 mixture was 18.4 N/mm³⁄². However, following microwave heating, the KIC value of the BBTM8 mixture increased significantly and approached that of the ACL mixture, aided by its higher air void content. The FHF cycle results revealed that the BBTM8 mixture demonstrated higher fracture resistance and more efficient recovery performance than the ACL mixture.