Refined separation not only controls the variability of reclaimed asphalt pavement (RAP), but also improves the mixing ratio of RAP and the quality of recycled asphalt mixtures. This study examines RAP treated with various refined separation frequency parameters, analyzes the variation rules and the variability of RAP aggregate gradation, asphalt content, asphalt properties, and aggregate properties, and calculates the maximum mixing percentage of coarse RAP material by using the gradation variability control method and the asphalt content variability control method. The results show that the variability of gradation and asphalt content of coarsely separated RAP is considerable, and a refined separation process significantly reduces the variability of gradation and asphalt content of RAP; the agglomeration of RAP decreases with an increase in the refined separation frequency; and the RAP agglomeration of three kinds of RAPs (E1, E2, and E3) under a refined separation frequency of 55 Hz reduces by 6.40%, 4.30%, and 4.30%, respectively, as compared with that of coarsely separated RAPs. The asphalt content of the refined separation RAP gradually decreases with an increase in frequency, and the asphalt content of E1 and E2 (55 Hz) was only 0.95% and 1.10%, respectively. The maximum percentage of RAP in recycled asphalt mixtures was calculated using the gradation variability control method and the asphalt content variability control method, respectively. The maximum proportions of RAP were 45% and 33% for A1 (0 Hz), respectively, and the maximum proportions of RAP for E1 (55 Hz) were all 100%. The results of the two methods show that the process of refined separation can increase the maximum proportion of blended RAP materials. They also demonstrate that the refined separation process can increase the maximum blending ratio of coarse RAP materials, thereby improving the quality of the RAP, increasing the proportion of RAP blending, and ensuring the quality of the recycled asphalt mixture. In conclusion, the refined separation process holds promise for maximizing the potential value of RAP and optimizing its recycling, environmental, and economic benefits.

Whether reclaimed asphalt pavement can be reused multiple cycles has become a focal issue in the industry. This paper investigates the macroscopic physical property changes and microscopic four-component alteration mechanisms of multiple recycling asphalt, simulates the multiple recycling processes of asphalt mixtures through laboratory tests, determines the mix proportions of multiple recycling asphalt mixtures through Marshall test, and evaluates the pavement performance of the mixtures using high-temperature wheel tracking test, semi-circular bending test, and freeze-thaw splitting test. The results indicate that after multiple recycling, multiple recycling asphalt exhibits poorer rheological property; high-temperature performance of multiple recycling asphalt mixture is improved, and low-temperature performance of multiple recycling asphalt mixture is significantly degraded. The solubilization of rejuvenator in old asphalt intensifies with increasing rejuvenator dosage but decreases exponentially with the increasing number of recycling cycles. The high-temperature stability of recycled asphalt mixtures gradually increases with the number of recycling cycles, while water stability shows low sensitivity to the number of recycling cycles. After the third recycling, the Marshall volume indicators of the recycled asphalt mixtures can meet the regulatory requirement. After the second recycling, the low-temperature anti-cracking performance of the recycled mixtures deteriorates rapidly. In summary, when asphalt mixtures undergo multiple recycling, special attention should be paid to the restoration of their low-temperature property.

The force chain network within asphalt mixtures serves as the primary load-bearing structure to resist external forces. The objective of this study is to quantitatively characterize the contact force distribution and force chain topology structure. The discrete element method (DEM) was employed to construct simulation models for two stone matrix asphalt (SMA) and two open-graded friction course (OGFC) mixtures. Load distribution characteristics, including average contact force, load bearing contribution and contact force angle, and force chain topological network parameters, clustering coefficient, edge betweenness and average path length, were analyzed to elucidate the load transfer mechanisms. The findings of the present study demonstrate that the average contact force between aggregate–aggregate contact types in specific particle sizes significantly exceeds the average contact force of the same particle size aggregates. For SMA16 and OGFC16 asphalt mixtures, the load-bearing contribution of aggregates initially increases and then decreases with decreasing particle size, peaking at 13.2 mm. SMA13 and OGFC13 mixtures demonstrate a consistent decline in load bearing contribution with decreasing aggregate size. The analysis of the force chain network topology of the asphalt mixture reveals that SMA mixtures exhibited higher average clustering coefficients in force chain topological features in comparison to OGFC mixtures. It indicates that SMA gradations have superior skeletal load-bearing structures. While the maximum nominal aggregate size minimally influences the average path length with a relative change rate of 3%, the gradation type exerts a more substantial impact, exhibiting a relative change rate of 7% to 9%. These findings confirm that SMA mixtures have more stable load-bearing structures than OGFC mixtures. The proposed topological parameters effectively capture structural distinctions in force chain networks, offering insights for optimizing gradation design and enhancing mechanical performance.

Skid resistance durability is an important aspect of pavement durability. A full understanding of pavement polishing behavior is helpful to make improvement in material design to obtain better skid resistance durability. In this paper, the polishing behavior of stone matrix asphalt (SMA) with basalt, red sandstone, and limestone coarse aggregate, respectively, was investigated by a series of laboratory polishing tests. A British pendulum tester, a handheld three-dimensional (3D) laser scanner, and an interference principle based 3D optical microscope were employed to acquire the British pendulum number, 3D macrotexture, and 3D microtexture data, respectively. The test results show that the coarse aggregate lithology has significant influence on the wear behavior of macrotexture. No statistically significant microtexture degradation was recognized in the polishing tests for all the SMA mixtures with different lithology types of coarse aggregates. The skid resistance significantly changes due to polishing, and the skid resistance capability and degradation behavior are closely related to the coarse aggregate lithology. The selection of coarse aggregate lithology is important in SMA mixture design for achieving high polishing resistance. Among the three lithology types of coarse aggregates considered in this study, the basalt coarse aggregate can bring the best polishing resistance, followed by the red sandstone, which can bring similar performance to the basalt can do. The polishing resistance brought by limestone coarse aggregate is relatively low. The findings and conclusions enhance the understanding of the polishing behavior of SMA, which is helpful to improve the skid resistance of asphalt pavement in practice.