Influence of compatibility between light oil and isocyanate compounds on rejuvenation properties and mechanisms of aged SBS modified bitumen

Reactive rejuvenators can restore both aged base bitumen and degraded styrene–butadiene-styrene (SBS) in aged SBS modified bitumen. This study investigated light oil-isocyanate compatibility mechanisms using epoxidized soybean oil (ESO), aromatic oil (AO), fluid catalytic cracking (FCC) slurry, methylene-bis(4-cyclohexylisocyanate) (HMDI), and isophorone diisocyanate (IPDI). Macroscopic results show that FCC-based rejuvenators limit rapid high-temperature property deterioration but provide limited mid- and low-temperature rejuvenation. ESO improves mid- and low-temperature properties but severely compromises high-temperature properties, whereas AO provides balanced restoration across temperatures. Fourier transform infrared (FTIR) spectroscopy and fluorescence microscopy indicate that isocyanates repair SBS, with efficacy depending on light oil type. Light oil type most strongly affects bitumen peak structure, which is directly related to asphaltene enrichment capacity. ESO’s strong dissolving capacity hinders SBS repair by isocyanates. Thus, light oil selection should consider compatibility, which substantially influences the properties of rejuvenated bitumen.