Preparation and Performance of SBR/SiO₂-Modified Emulsified Asphalt Mixtures Incorporating Recycled Aggregates

To address the technical bottlenecks associated with the poor overall performance of emulsified asphalt mixtures incorporating high-proportion (84 wt%) recycled asphalt pavement (RAP) aggregates, this study proposes a synergistic modification strategy using styrene-butadiene rubber (SBR) and nano-silica (SiO₂), coupled with the regulation of cement and polyester fiber contents. Through systematic rheological characterization and performance testing, the results demonstrate that SBR/SiO₂ modification is able to enhance the high-temperature properties of the emulsified asphalt binder, as evidenced by a reduced penetration, a lower phase angle, and an increased complex modulus. Meanwhile, this modification also slightly affects the low-temperature performance of the asphalt binder by boosting its ductility and reducing its creep stiffness (S); however, the m-value was decreased. Fourier transform infrared spectroscopy (FTIR) results demonstrate that the synergistic effect between SBR and SiO₂ is physical in nature. The optimal formulation for the asphalt mixtures was ultimately determined as follows: 3.9% binder modified by 3.5 wt% SBR and 3 wt% nano-SiO₂, 1.5 wt% cement, and 0.3 wt% polyester fiber, achieving a splitting strength of 0.82 MPa, a dynamic stability of 4683 times/mm, a flexural strain of 2526 με, and a freeze–thaw splitting ratio of 83.3%. This research establishes a basis for the high-value utilization of RAP aggregates in emulsified asphalt mixtures and contributes to the advancement of low-carbon, sustainable pavement materials.