High-modulus asphalt mixtures are critical for long-life pavements due to their excellent deformation resistance. This study systematically compares three modification approaches—unmodified low-penetration-grade asphalt, natural asphalt modified asphalt, and polymer modified asphalt combined with two gradation systems (HFM-20 and HFM-16). Performance was evaluated through dynamic modulus, wheel tracking, and four-point bending fatigue tests. Results show that the natural asphalt modified mixture exhibits the best overall performance, combining high modulus, high rutting resistance, and excellent fatigue life, making it the preferred solution for long-life pavements. The polymer modified mixture demonstrates outstanding high-temperature performance, while the unmodified hard-grade asphalt shows high stiffness. HFM-20 gradation better leverages the advantages of hard-grade asphalt, whereas HFM-16 provides a compensatory effect for softer binders. Microstructural characterization (FTIR, SARA, XRF) reveals that natural asphalt’s organic components are fully compatible with petroleum asphalt. Higher asphaltene and resin contents enhance adhesion and high-temperature deformation resistance. The gel-type structure of natural asphalt, classified by the Gaestel colloidal instability index ( I c ), provides superior rutting resistance compared to sol-type materials. The inorganic fraction, primarily calcium carbonate, forms a natural mastic structure that balances stiffness and flexibility. These synergistic microstructural features underpin the exceptional performance of natural asphalt modified mixtures. The findings have been successfully applied to the Wuyue Expressway expansion project, providing a technical basis for material selection and structural design of high-modulus asphalt mixtures.
Dong et al. (Mon,) studied this question.