Substituting steel slag for mineral materials in road construction has potential economic and environmental benefits. Due to the excellent thermal conductivity of steel slag, it is often used in functional pavements. However, there are few studies on the thermal conductivity characterization of steel slag asphalt mixture (SSAM). For this reason, the thermal conductivity of SSAM was first qualitatively evaluated by microscopic characterizations. The thermal conductivity was the quantitatively evaluated by the heating wire method. Theoretical calculations were used to verify the reliability of the quantitative characterization. Finally, the effects of steel slag on the volume indices and the road performance of SSAM were studied. Results showed that active minerals such as iron oxides make the steel slag thermally conductive, while a large number of protrusions and micropores on the surface of the steel slag may be detrimental to thermal conductivity. The thermal conductivity first increases and then decreases with the steel slag content. The asphalt mixture with 60% steel slag replacing aggregate of 3–5 mm (6.6% of the mixture) had the highest thermal coefficient of 1.746 W/(m·°C), which is only 4.78% different from the theoretical value. The porosity and water absorption of SSAM gradually increased with the content of steel slag. The road performance test indicated that steel slag increased the high-temperature performance of the asphalt mixture to a certain extent, but weakened the low-temperature performance and moisture resistance. After comprehensive consideration of the thermal conductivity and road performance, it is recommended that the optimum content of steel slag is not more than 60%.

Asphalt pavements are prone to cracking in low-temperature environments, and microwave heating (MH) can heal the cracks effectively. This research mainly investigates the different MH effects on the self-healing properties of asphalt mixtures. With this objective, the three-point splitting test is conducted to generate the cracks. A microwave oven is employed to heat the samples, and a thermal camera measures the surface temperature. Results indicate that heating power and time show a positive linear correlation with healing efficiency, and the HI of the samples can reach over 80%. The HI of the samples decreases with the heating cycle, but the sample with reasonable power and time still has a HI higher than 70% after 5 cycles. The temperature peaks on thermal images indicate that uneven heating exists during heating, but the heating uniformity is within an acceptable range. The healing efficiency level (HEL) suggests that asphalt mixtures have very low inefficient healing behavior if the heating time is below 45 s, but HEL can reach 86.14% at 700 W after 60 s. Furthermore, although the HI of strength shows ideal results, the recovery of other crack parameters, including stiffness, fracture energy, flexible index, and crack resistance index, are not satisfactory.

In recent years, the potential of waste engine oil (WEO) as a rejuvenator for aged asphalt binders has gained significant attention. Despite this interest, understanding WEO’s regeneration mechanism within aged asphalt binders, particularly its diffusion behavior when mixed with both aged and virgin asphalt binders, remains limited. This study adopts a molecular dynamics approach to constructing models of virgin, aged, and rejuvenated asphalt binders with different WEO contents (3%, 6%, 9%, and 12%). Key properties such as the density, glass transition temperature, cohesive energy density, solubility parameter, viscosity, surface free energy, fractional free volume, and diffusion coefficient are simulated. Additionally, models of rejuvenated asphalt binder are combined with those of aged asphalt binder to investigate mutual diffusion, focusing on the impact of WEO on the relative concentration and binding energy. The findings reveal that WEO notably decreased the density, viscosity, and glass transition temperature of aged asphalt binders. It also improved the molecular binding within the asphalt binder, enhancing crack resistance. Specifically, a 9% WEO content can restore the diffusion coefficient to 93.17% of that found in virgin asphalt binder. Increasing the WEO content facilitates diffusion toward virgin asphalt binders, strengthens molecular attraction, and promotes the blending of virgin and aged asphalt binders.