Steel slag (SS) is industrial waste, and there is a large amount of SS to be treated in China. Its disposal generates severe environmental pollution. One of the best ways to use SS is as a road base material. This paper reviews the possibility of using SS in semi-rigid base and evaluates the performance of SS base course. The interaction between three stabilizers (cement, lime–fly ash, and cement–fly ash) and SS is analyzed, and the influence of modifier content on the performance of base course is evaluated. The potential laws between SS, curing time, and unconfined compressive strength, as well as drying shrinkage and temperature shrinkage, are discussed and their effects on the performance of the base course are revealed. The finite element method, discrete element method, and molecular dynamics can be used to analyze the freeze-thaw, rutting resistance, and crack development of SS base. In addition, compared with traditional macadam base, the CO₂ emissions for the use of SS base are slightly more, one of the disadvantages of its use in production, transportation, and compaction. However, considering the overall mechanical, economic, and environmental benefits, it is recommended to use SS in semi-rigid base course. The future research scope of SS as base material is suggested.

In order to reuse waste resources (waste engine oil and waste asphalt mixture), the regeneration process of waste oil on aged asphalt is systematically explained. The BA was treated by aging test, and the basic mechanical properties, molecular dynamics simulation, and infrared spectrum test were carried out on this basis. The results showed that the WEO can restore the physical properties of the aged asphalt, and the recommended amount of WEO is 3%. The density of the asphalt model corresponds to the actual situation of the asphalt. The aged asphalt components are more aggregated. After the WEO was added, the components of asphalt aggregation were reduced and the diffusion ability was improved. Finally, infrared spectroscopy tests were conducted on asphalt specimens, and the results showed that the process of rejuvenated asphalt was dominated by physical reactions. Consequentially, the results of this study build a bridge between the performance and simulation of aged asphalt rejuvenated by WEO. Consequentially, the results of this research promote the recycling of WEO and waste asphalt pavement materials, ultimately advocating the sustainability of pavement construction.

This study established the ratio of the base layer’s elastic modulus to that of the surface layer Rm as a key variable to systematically investigate how the base layer’s elastic modulus influences the mechanical response and service life of flexible pavement. A three-dimensional finite element model of a three-layer pavement system was analysed, using EverStressFE, with a constant surface layer modulus and a variable base layer modulus. The analysis included two important interfacial bonding conditions: full bonding and full slip. It also considered that the actual wheel loads are not uniform but rather follow concave and convex distribution patterns. The mechanical responses, including deflection at the top of the asphalt layer, tensile strain at the bottom of the asphalt layer εxx, and vertical compressive strain at the top of the subgrade εzz, were quantified to predict fatigue life (for cracking) and rutting life (for permanent deformation). The results indicated that the maximum deflection reached 0.53 mm under a full slip condition with a convex load distribution at Rm = 0.75. Critical tensile strains at the bottom of the asphalt layer were most severe under full slip with a convex load, reaching 348 × 10−6, while the fully bonded, concave case resulted in a much lower value of 83 × 10−6. Similarly, the maximum vertical compressive strain on the subgrade was 365 × 10−6 for the fully slipped, convex case compared to 250 × 10−6 for the fully bonded, concave case. A lower Rm value under full slip with a concave load distribution significantly reduced the pavement lifespan, with predicted fatigue life decreasing by over 60% and rutting life by nearly 45% compared to the fully bonded case. On the other hand, a convex load distribution greatly increased the pavement’s bearing capacity by raising the critical strain thresholds and lengthening the expected service life. These findings underscore the paramount importance of interface bonding and load distribution patterns, suggesting that they can outweigh the influence of the base layer’s modulus alone on pavement design.