Synergistic effects of sulfur and polyphosphoric acid additives in warm mix bio-rejuvenated asphalt modification

In response to the growing demand for energy-efficient and sustainable materials in road construction, this research presents a pioneering method to enhance the engineering application of bio-oil rejuvenated asphalt . Initially, aged asphalt was rejuvenated by blending with 6% castor oil . Subsequent modifications included introducing varying concentrations of polyphosphoric acid (PPA) (0%, 0.5%, 1.0%, 1.5%), combined with differing sulfur levels (15% and 30%). The rheological properties of the resulting asphalt binders were assessed using rotational viscometer (RV), asphalt binder crack device (ABCD), and dynamic shear rheometer (DSR) tests, while fourier transform infrared spectroscopy (FTIR) test was employed to reveal the interaction mechanism. The study’s key findings reveal that incorporating 15% sulfur significantly reduces asphalt viscosity , effectively lowering the mixing and compaction temperatures by approximately 17 °C and 15 °C, respectively. Besides, rutting factor ( G * / sin δ ) and fatigue life ( N f ) results unveil a positive connection between PPA content, high-temperature stability, and fatigue resistance. Furthermore, the grey relational analysis emphasizes a strong correlation between G * / sin δ and R 3.2 (grey relational degree of 0.986), indicating that the recovery rate partially reflects high-temperature performance. The FTIR analysis demonstrates that bio-oil primarily contributes through physical blending, whereas PPA undergoes chemical transformations, and the combination of sulfur with asphalt results in both physical and chemical reactions. In conclusion, this research emphasizes the synergistic potential of bio-oil, sulfur, and PPA in enhancing recycled asphalt performance. For optimal warm mix efficiency and road performance, incorporation of 15% sulfur and 1.0% PPA in bio-rejuvenated asphalt is recommended. These findings provide substantial advantages in reducing reliance on petroleum asphalt and mitigating carbon emissions , contributing to sustainable infrastructure development.