Long-Term Performance of Modified Nature Asphalt–Derived High Modulus Asphalt Mixtures under Heavy Loads and Humid-Hot Climates

High-modulus asphalt mixtures (HMAMs) are potential materials for achieving long-life pavement performance, and understanding their long-term performance degradation mechanism is crucial for analyzing pavement performance degradation under long-term exposure to traffic and environmental coupling conditions. This paper aims to examine the long-term evolution of high- and low-temperature performance and water stability in HMAMs derived from modified nature asphalt, prepared using microparticle suspension technology, under heavy load and humid heat conditions. Four asphalt mixtures (AC-13, BBME-13, SMA-13, SBSAC-13) were prepared, and then their dynamic moduli were tested. A test plan for the long-term performance of the mixtures was designed, and the performances of HMAMs with different gradations and time were analyzed. Furthermore, corresponding long-term performance degradation models of HMAMs were established. The results show that the HMAMs of modified natural asphalt have better high-temperature performance than HMAMs of high-modulus agent/SBS-modified asphalt. However, following prolonged thermal aging and freeze-thaw cycles, the low-temperature performance shows the opposite trend. In addition, thermal aging had the same effect on the long-term low-temperature performance of both types of HMAM, with the HMAMs of modified natural asphalt being less affected by long-term freeze-thaw cycling. The long-term bending tensile strain attenuation of HMAMs can be simulated using an exponential function. Both types of HMAMs display similar water stability under dry-wet cycles and dynamic water erosion condition. The variations in residual stability during dry-wet cycles can be accurately represented using a power function.