Improving microwave absorption efficiency of asphalt mixture by enriching Fe3O4 on the surface of steel slag particles

In order to improve microwave absorption which would be used for in situ repair of asphalt pavement, Fe3O4 was enriched on the surface of steel slag particles through an activated carbon-reduction method. The surface modified steel slags were then added into asphalt mixture to replace fine aggregates. The results showed that the microwave heating rate of modified steel slag was 84.3 °C/min. That was 34.1 and 65.1% higher than that of the control group of unmodified steel slag and fine basalt aggregate, respectively. Within the microwave frequency band of 2–4 GHz, the real part and imaginary part of the complex permittivity of the modified steel slag asphalt mixture (MSAM) increased by 6.4–12.5 and 4.7–13.7%, respectively, comparing those of the ordinary steel slag asphalt mixture (OSAM) and the ordinary basalt asphalt mixture (OBAM). Meanwhile, the real part and imaginary part of the complex permeability of the MSAM increased by 9.8–31.9% and over 6.2 times, respectively. Besides, the microwave heating rate of the MSAM increased by 44.2 and 82.1%, respectively, comparing those of the OSAM and the OBAM. Simulation indicated that after microwave heating for 15 min, the temperature within the OBAM ranged from 62.23 to 125.48 °C. Moreover, the temperature field distribution of numerical simulation was similar to that of the test results. Since microwave absorption was sharply enhanced in the asphalt pavement, it is expected to promote the microwave heating technology in the asphalt pavement.