Improving the self-healing properties of bitumen mastic under microwave irradiation by heated oil-ground steel slag

Steel slag (SS) is a solid waste rich in iron elements with the potential for microwave heating. However, the low ferrite content and the barrier of the silicate layer limit the efficiency of microwave heating of SS. This study employs soybean oil as the grinding environment and utilizes heated oil milling technology to functionalize steel slag. This process facilitates the separation and purification of the iron phase from the SS, enabling the generation of additional Fe 3 O 4 through reduction reactions. The synergistic effect of heating and grinding promotes the conversion of Fe 3 + to Fe 2+ , which results in a 31 % increase in Fe 2+ content and a 34 % increase in saturation magnetization of heated oil grinding steel slag (HGSS). Through the targeted design of particle size and oleophilic surfaces, HGSS is uniformly and compactly dispersed in the bitumen, constructing a network structure with multi-refraction properties, which reduces the reflection loss by 26 %. Under the combined effect of phase and structural changes, compared to SS bitumen mastic, HGSS bitumen mastic showed a 20 % increase in temperature rise at 60 s of microwave heating, in addition to an 11 % increase in healing index. This study aims to enhance the microwave absorption performance of SS by optimizing its microstructure and composition, thereby improving the self-healing efficiency of steel slag-bitumen composite materials under microwave heating conditions and providing new insights into the high-value utilization of SS. • The Fe 3 O 4 content of steel slag is increased by heating grinding technology. • Activated steel slag has higher static magnetic properties and lower reflection loss. • Activated steel slag forms a uniform and dense Fe-phase network in asphalt. • Microwave heating efficiency and healing properties of asphalt mastic enhanced.