Reclaimed asphalt pavement (RAP) mainly contains asphalt binder and aggregates, and the RAP materials used in paving roads could save virgin materials. This paper studied the following: asphalt mixture with different RAP material contents was prepared; then the indirect tensile test was carried out, and the mesoscopic model of the recycled asphalt mixture was reconstructed digitally. Discrete element method (DEM) of indirect tensile test was carried out to analyze the mechanical properties of recycled asphalt mixture in mesoscopic perspective. The results showed that there were some gaps between the simulation result of the digital specimen model and the test value of the recycled asphalt mixture, but the velocity vector and the law of force chain development of the recycled asphalt mixture could be explained in mesoscopic perspective. It proved that the virtual simulation test of the mechanical test was effective. The damage process of recycled asphalt mixture was analyzed in mesoscopic perspective, and the unification of mechanical response and macroscopic appearance was completed. Meanwhile, the simulation method of mesoscopic mechanics was an effective supplement to traditional tests, and guided tests method theoretically.

An ultrathin wearing course is an effective maintenance treatment for prolonging the service life of asphalt pavements, which have been widely used in the field of pavement construction and road maintenance. However, the repeated vehicle load and wear results in a decreased durability of ultrathin wear course cover pavement. Hence, the gradation of ultrathin wear course was designed using calcined bauxite in this study, and the water stability, low-temperature properties, resistance to permanent deformation, and salt erosion were investigated through a laboratory test. Results indicated that the addition of a nonammonia antistripping agent significantly improves the water stability of the asphalt mixture with calcined bauxite and its ability to resist salt erosion as well as improve its low-temperature deformation ability. At the same time, polyphosphoric acid improves the adhesion between asphalt and calcined bauxite aggregate and the high-temperature performance of asphalt mixture but has limited improvement in water stability and resistance to salt erosion. This research is conducive to the widespread use of calcined bauxite aggregates in road pavements and is of great significance for improving the durability of ultrathin wear course asphalt pavements.

Natural fibers have attracted increasing attention as eco-friendly and sustainable additives for improving the durability and mechanical performance of asphalt mixes. This paper presents a critical state-of-the-art review of the use of six kinds of natural fibers in asphalt mixes. This paper reviews the impact of six natural fibers such as lignin fiber, bamboo fiber, bagasse fiber, corn stalk fiber, basalt fiber, and wool fiber on the properties of bitumen binders and mixes. It examines the influence of these fibers on the physical properties, rheological properties, and fatigue performance of bitumen binders. In addition, the influence of fibers on the moisture stability, anti-cracking, and high- and low-temperature performance of asphalt concrete was analyzed. The review demonstrated that the recommended lengths of natural fibers in asphalt mixes are as follows: lignin fiber 0.8–1.2 mm, bamboo fiber 4–20 mm, sugarcane bagasse fiber 5–12 mm, corn stalk fiber 3 mm, and basalt fiber 6–30 mm. Adding lignin fiber and corn stalk fiber enhanced the high-temperature characteristic of bitumen. The high- and low-temperature properties of the binder were improved by adding bamboo fiber. The addition of basalt fiber and bamboo fiber can increase rutting resistance and fatigue life. Additionally, incorporating the bamboo fiber, bagasse fiber, basalt fiber and wool fiber improved the low-temperature cracking and fatigue resistance of the bitumen mixture. The high-temperature properties of the bitumen mixes were enhanced by using basalt fibers, lignin fibers, bamboo fibers and bagasse fibers. The moisture resistance of bitumen mixes were reinforced by the incorporation of basalt fibers, lignin fibers and bamboo fibers. In general, incorporating natural fibers provided a technical method for improving the performance of asphalt concrete in road applications.