Performance evolution of Fe3O4 used in the production of sustainable self-healing asphalt materials

Studies have shown that the sustainable self-healing ability of asphalt materials under microwave radiation is related to the microwave absorption of the constituent materials. As a typical absorbing material, Fe3O4 and its derivatives have the potential to heal the micro cracks of asphalt materials multiple times by themselves, and enhance the sustainable self-healing properties. However, former researchers have neglected the fact that Fe3O4 will be gradually oxidized at high temperatures, such as 100 °C, resulting in the changes in material properties, microwave absorption and heat-generating capability. Therefore, the effects of different temperatures on the properties of controllable synthesized Fe3O4 were studied at 125 °C (mixing temperature of WMA), 150 °C (mixing temperature of HMA), 175 °C (mixing temperature of HMA with modified binder) and 200 °C (extreme mixing temperature). The phase compositions, chemical structure of synthesized Fe3O4 were characterized firstly. Then, their electromagnetic parameters, reflection loss were studied at a microwave frequency ranging from 1 to 18 GHz. Additionally, heat-generating abilities of them were characterized at usual microwave frequency of 2.45 GHz. Finally, the effects of different content of Fe3O4 on the rheological properties of pure asphalt were studied. The results show that the proportion of γ-Fe2O3 in the samples gradually increase with exposure temperature, and the static magnetic properties gradually deteriorate. The reflection loss of the modified asphalt decreases firstly and then increases. The F-150 modified asphalt has the strongest microwave absorption capacity. Under the 2.45 GHz microwave radiation, the F-150 modified asphalt presents the strongest heat-generating capability and is consistent with the results of reflection loss. It can be seen that the ratio of γ-Fe2O3 and Fe3O4 in F-150 has the best attenuation effect on microwave radiation, and Fe3O4 is more suitable as microwave absorber for self-healing enhancement of HMA.