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.

Previous studies have reported the effects of aggregate gradation and angularity on the pavement performance of hot asphalt mixtures, while little work has been done on the role of aggregate gradation and morphology related to porous asphalt (PA) mixture performance. The primary objective of this article was to evaluate the effects of aggregate gradation and morphology on the mechanical properties and volumetric characteristics of PA mixtures. Ten PA mixtures, prepared by regulating the percentages of aggregate passing 9.5-, 4.75-, 2.36-, and $1.18\text{-}\mathrm{mm}$ sieves and using two types of aggregate sources, were compared by evaluating air voids, shear strength, Marshall stability, indirect tensile strength, and micromorphology. The analytic hierarchy process method was used to analyze the priority weights of various influencing factors on PA mixture performance. The results indicate that aggregate gradation had significant effects on the performance of the PA mixtures. There was an excellent linear relationship between the percentages of aggregate passing the 9.5-, 4.75-, and $2.36\text{-}\mathrm{mm}$ sieves and the respective mixture air voids. Increasing the proportion of $4.75–9.5\text{-}\mathrm{mm}$ aggregate particles in the PA mixes did not contribute to its moisture damage resistance. The percentage of $2.36–4.75\text{-}\mathrm{mm}$ aggregate fractions was the most critical influencing factor for the PA mixtures’ mechanical properties and volumetric characteristics. Additionally, aggregate morphology does affect PA performance. The permanent deformation resistance and moisture resistance were notably improved as the aggregate sphericity value increased. Based on the test results, the mechanical properties and volumetric characteristics of PA mixtures can be optimized depending on engineering requirements by regulating the aggregate gradation and type.

To investigate the effect of graphene on the fatigue properties of base asphalt mastics, graphene nanoplatelets (GNPs)-modified asphalt mastics and base asphalt mastics were prepared. A dynamic shear rheometer (DSR) was used to conduct the tests in the stress-controlled mode of a time-sweep test. The results showed that GNPs can improve the fatigue life of asphalt mastic. Under a stress of 0.15 MPa, the average fatigue life growth rate ($\overline{\omega }$) was 17.7% at a filler-asphalt ratio of 0.8, 35.4% at 1.0, and 45.2% at 1.2; under a stress of 0.2 MPa, the average fatigue life growth rate ($\overline{\omega }$) was 17.9% at a filler-asphalt ratio of 0.8, 25.6% at 1.0, and 38.2% at 1.2. The growth value (ΔT) of fatigue life of GNPs-modified asphalt mastics increased correspondingly with the increase of filler–asphalt ratio, the correlation coefficient R² was greater than 0.95, and the growth amount showed a good linear relationship with the filler–asphalt ratio. In the range of 0.8~1.2 filler–asphalt ratio, the increase of mineral powder can improve the fatigue life of asphalt mastics, and there is a good linear correlation between filler–asphalt ratio and fatigue life. The anti-fatigue mechanism of GNPs lies in the interaction between GNPs and asphalt, as well as its own lubricity and thermal conductivity.

This study aims to investigate the properties of novel waterborne epoxy modified asphalt emulsion with styrene–butadiene–chloroprene rubber (SBR/CR) and evaluate its performance improvement mechanism. To achieve this objective, Brookfield rotational viscometer tests and dynamic shear rheometer tests were first performed to characterize the rheological properties of new emulsion residues with time. Then, penetration, softening point, and ductility tests were adopted to evaluate the conventional performance of the new emulsion residue. Finally, the curing microstructures, functional group changes, and thermal stability of new emulsion were analyzed by using scanning electron microscopy, Fourier transform infrared spectrometry, thermal gravimetric analysis, and differential scanning calorimetry, respectively. The experimental results showed that the new emulsion residue showed an extremely high viscosity, and its viscosity value was more than 40 times that of general asphalt emulsion. The stiffness and thermal stability of new emulsion at high temperatures were significantly improved by crosslinking the epoxy system to form a three-dimensional polymer network. The incorporation of SBR/CR copolymer reduced the effect of waterborne epoxy cured products on the low-temperature elongation performance of new emulsion, resulting in improved thermal cracking resistance of the new emulsion system. The optimum dosage of waterborne epoxy for the new asphalt emulsion determined was 15% by weight of SBR/CR modified asphalt emulsion. Based on these results, it is evident that the waterborne epoxy asphalt emulsion together with the SBR/CR copolymer can form a durable emulsion system in both low- and high-temperature environments.