GB5 high-modulus asphalt mixtures are considered promising materials for high-performance pavements because of their favorable aggregate structure and desirable mechanical properties. However, high modulus values are commonly achieved using hard binders with low penetration grades, which increase mixture stiffness but also increase susceptibility to low-temperature thermal cracking. Therefore, improving low-temperature performance while maintaining adequate stiffness and modulus remains a significant challenge in pavement engineering.

This study experimentally investigated the performance of GB5 asphalt mixtures containing 60/70 penetration grade bitumen modified with zinc oxide nanoparticles (Nano-ZnO) and styrene–butadiene–styrene (SBS) polymer, with particular emphasis on low-temperature behavior. The rheological properties of the binders were evaluated using the Bending Beam Rheometer (BBR) test. In addition, the corresponding asphalt mixtures were assessed in terms of dynamic modulus, low-temperature cracking resistance using the Semi-Circular Bending (SCB) test, and moisture susceptibility through the Indirect Tensile Strength (ITS) test.



The results demonstrated that Nano-ZnO improved the low-temperature performance of the binder and enhanced the resistance of asphalt mixtures to thermal cracking. Furthermore, SBS improved the viscoelastic behavior of the binder, resulting in enhanced fatigue resistance and mechanical stability. The combined use of Nano-ZnO and SBS produced a synergistic effect and provided the best overall performance in terms of cracking resistance, moisture durability, and fatigue behavior.

The BBR results indicated that the optimum combination of 4.2% Nano-ZnO and 3.7% SBS reduced flexural creep stiffness by 80% and increased the m-value by 31%. The T12 mixture (4.9% Nano-ZnO and 4.2% SBS) exhibited a dynamic modulus exceeding 16 GPa. Moreover, the SCB test showed more than a 70% improvement in fracture resistance at −5°C, while the ITS results indicated at least a 10% increase in moisture resistance. Overall, Nano-ZnO/SBS-modified 60/70 bitumen can effectively replace hard low-penetration binders in the production of high-modulus asphalt mixtures.