This study explores the temperature changes and freeze–thaw cycles in certain typical high-altitude areas, finding that these areas encounter more than 120, or even more than 200, freeze–thaw cycles per year. Such frequent freeze–thaw cycles deliver significant impact on the performance of asphalt pavements, with cracks becoming a typical problem in high-altitude areas. Such factors as cold weather, large temperature differences, and frequent freeze–thaw cycles have adverse effects on the stress of asphalt pavement materials, resulting in cracks in pavements. By simulating the conditions of such frequent freeze–thaw cycles, this study explores the law of changes in the performance of roads made from asphalt and asphalt mixtures, as well as the low-temperature crack resistance properties of asphalt and asphalt mixtures in frequent freeze–thaw cycles. It is found that the performance of the three different types of asphalt binders used in the test shows basically no change after 50 freeze–thaw cycles, and the asphalt types have a significant effect on the low-temperature performance of asphalt mixtures. The modified asphalt shows a higher viscosity than the matrix asphalt, with better toughness than that of the matrix asphalt at low temperature. Frequent freeze–thaw cycles significantly influence the low-temperature splitting tensile strength and water stability of asphalt mixtures; with increased freeze–thaw cycles, the splitting strength and freeze–thaw splitting tensile strength ratio will gradually decrease to a significant level. The freeze–thaw conditions are found delivering remarkable influence on the low-temperature splitting tensile strength and water stability of asphalt mixtures. The research results of this study provide a basis for the selection of asphalt pavement materials as well as the optimal design of mixtures in high-altitude area like the Qinghai-Tibet Plateau.

Due to the harsh climatic conditions in high altitude and cold regions with large temperature differences, asphalt pavement is generally prone to cracking, and the cracks propagate rapidly, which reduces the service life and service level of the road. The factors influencing the fracture characteristics of asphalt mixtures were analyzed in this paper, and the mixtures with different aggregate gradations from various types of asphalt were prepared. The fracture characteristics were explored using the thermal stress restrained specimen test (TSRST) and low-temperature bending test, and the good consistency of the low-temperature fracture performance was identified according to the results of frost-break temperature, flexural strength, and fracture toughness. The frost-break temperature was confirmed as the best indicator of the material crack resistance and could be used as the index to evaluate the performance of asphalt mixtures at low temperatures. The frost-break temperature of matrix asphalt mixture is 8–10 °C higher than that of modified asphalt mixture, and AC asphalt mixture is 2–4 °C higher than that of SMA asphalt mixture. The excellent asphalt performance has a more important influence on the fracture characteristics of asphalt mixture. The asphalt mixture of the same type had similar fracture toughness at varying notch depths, the most deviation is 3.78% which shows that the initial crack depth has little effect on the fracture toughness of asphalt mixture at low temperature. The results of the study can provide a basis for the selection of asphalt pavement surface materials and the optimization of mixtures in high altitude and cold regions with large temperature differences.

Conventional polypropylene fibers, characterized by their smooth surfaces, exhibit relatively weak bonding with cement-based materials, limiting their effectiveness in enhancing these materials’ mechanical properties. This study investigates a graft-modified approach to activating polypropylene fibers, introducing amide groups onto their surfaces to improve fiber–matrix interaction. The active polypropylene fibers were produced using an ultraviolet (UV) grafting technique, where maleic anhydride was first used to graft carboxyl groups onto the fiber surfaces, followed by acylation with diethylenetriamine to introduce amide bonds. The optimal experimental conditions were identified by using the degree of amidation as the response metric. Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) confirmed successful amination and surface activation, with a marked increase in specific surface area. The water contact angle of the active polypropylene fibers decreased significantly from 106.3° to 39.9°, indicating greatly improved wettability by the cement slurry and enhanced bonding strength between the fibers and the cement matrix. To evaluate the effects of the modified fibers, cement-stabilized macadam specimens incorporating various fiber contents were prepared and tested to determine their mechanical properties and shrinkage performance. The results indicated that, compared to conventional polypropylene fibers, the activated polypropylene fibers increased the 28-day compressive strength of CSM by 6.56%, enhanced tensile strength by 4.94%, reduced the rebound modulus by 7.42%, decreased the drying shrinkage coefficient by 25.55%, and lowered the thermal shrinkage coefficient by 13.16%. These findings demonstrate that the chemical bonding between the active polypropylene fibers and the cement matrix is significantly enhanced, leading to improved overall performance in crack resistance, material toughening, and shrinkage mitigation.