Comparative Analysis of Aged-SBSMA Regeneration in Hot In-Place Recycling: Individual and Coupled Effects of Aromatic Oil and SBS/SBR Polymer Modifiers

Hot in-place recycling (HIR) technology provides an efficient approach to utilizing reclaimed asphalt pavement, with the main challenge being effective recycling of styrene-butadiene-styrene (SBS) modified asphalt (SBSMA). This paper investigates the recycling effects of aromatic oil (AO) and SBS/styrene–butadiene rubber (SBR) polymer modifiers on aged SBSMA during HIR, individually and in coupling. First, the individual effects were evaluated using conventional tests, dynamic shear rheometer, and bending beam rheometer. AO reduced asphaltene content and enhanced low-temperature performance. In contrast, SBS and SBR polymers significantly increased the rutting factor and viscosity while slightly lowering creep stiffness. However, SBS latex and SBR polymers also reduced the creep rate, raising the risk of low-temperature cracking. Next, the coupled effects were assessed using the same performance tests. The results showed that coupled recycling process significantly improved the low-temperature performance of recycled SBSMA while maintaining high-temperature performance. Then, fluorescence microscopy revealed that AO replenished missing light components and provided a favorable swelling environment for polymer modification. Finally, field testing through a trial section confirmed that coupled regeneration reduced the permeability coefficient and significantly enhanced crack resistance. This research provides a basis for the development of advanced polymer-modified rejuvenators.