Microwave Heating and Self-Healing Performance of Asphalt Mixtures Containing Metallic Fibres from Recycled Tyres

Abstract

This study investigates how recycled metal fibres from End-of-Life Tyres (ELTs) affect both microwave heating efficiency and crack healing properties in dense asphalt mixtures. The aim is to improve tyre recyclability by using their fibres in asphalt and exploring their self-healing potential with microwave heating. To achieve this, four dense asphalt mixture designs were studied in the laboratory. Each mixture used the same aggregate gradation and bitumen content, but with three different percentages of metallic fibres by binder volume (i.e., 1.5%, 2.5%, and 3.5%), along with an asphalt mixture without fibres serving as a reference material. The microwave heating properties of the asphalt mixtures and their individual components (i.e., aggregates and bitumen) were measured at six different heating times, ranging from 10 to 60 s. Based on the microwave heating results, the cracking and subsequent self-healing properties of the mixtures were evaluated by exposing them to microwave radiation at three heating times: 30, 40, and 50 s. The main results indicated that adding metallic fibres to facilitate microwave heating of the asphalt mixture is unnecessary because healing can be triggered predominately through the aggregates used. Unlike previous studies, it was observed that the healing level of asphalt mixtures, both with and without metallic fibres, increases with the accumulation of crack-healing cycles. Finally, it was determined that the advised microwave heating time for laboratory-sized mixtures, with or without fibres, is 40 s.