Prospective application of coal gangue as filler in fracture-healing behavior of asphalt mixture

Coal gangue powder, which is an environmental waste, was used as filler to investigate its facilitation effect on microwave heating and self-healing of asphalt mixture. In this work, two types of fillers named coal gangue powder (CGP) and coal gangue ash (CGA) were utilized to prepare various mixtures to replace conventional limestone powder (LMP) by six rates of 0%, 15%, 35%, 50%, 75%, and 100%. Firstly, the micromorphology and composition properties of different fillers were performed by scanning electron microscopy (SEM) and X-ray fluorescence (XRF) test. Secondly, the semi-circular bending (SCB) test was conducted to analyze the low -temperature fracture performance of mixtures. Then, the microwave heating capacity and behaviors of fillers and mixtures were studied on the basis of infrared thermography imaging. Ultimately, the mixtures healing efficiency was evaluated with five fracture-healing-fracture cycles and the electromagnetic parameters were determined via a microwave network vector analyzer. Test results reveal that mixtures with appropriate CGA and CGP filler proportion both possess better microwave heating effect, while the excessive dosage of CGA or CGP filler will result in mixtures' uneven surface temperature distribution. It is found that 50% CGA or 50% CGP can be a prospective substitution because this rate not only obtains excellent healing effectiveness at 60-s microwave heating but also improve the low-temperature crack resistance of mixture. Moreover, the higher dielectric and magnetic losses of CGA and CGP provide an explanation for promoting microwave heating. The aforementioned results show that coal gangue powder waste has prominent application in asphalt mixture cracking and self-healing and thus improve its utilization in this method.