Microwave heating uniformity, road performance and internal void characteristics of steel slag asphalt mixtures

Steel slag (SS) has good microwave absorption and microwave heating potential. Firstly, SS was classified by the difference of microwave capacity, and high heat source (HHS) steel slag was selected to partially replace limestone to prepare steel slag asphalt mixture (SSAM) in this work. The morphology and elements of SS were analyzed by microcosmic tests. Then the surface temperature and thermal transfer process of SSAM were studied. In addition, the road performance of SSAM under different microwave cycles was evaluated. Finally, the influence of microwave heating on the air voids structures of SSAM was analyzed by X-ray computed tomography (CT). The results show that the surface temperature of SSAM prepared by HHS steel slag is not significantly reduced, and the uniformity of microwave heating is greatly improved. The metallic elements in SS are the reasons for enhancing the microwave absorption performance of SSAM. After microwave cycling, the road performance of the mixture continues to decline; CT scan results show that microwave heating can reduce the micro voids in SSAM but increase the ratio of large voids and extra-large voids, which causes the decrease of durability. Overall, this work contributes to improving the durability and sustainability of asphalt pavements under microwave irradiation.