Toward circular asphalt materials: Rheological and microstructural insights into the rejuvenation of SBS-modified binders

SBS modified asphalt (SBSMA) pavement experiences natural aging, reducing strength and increasing cracking susceptibility. To address environmental pollution and promote recycling, rejuvenators are used to restore aged asphalt. However, conventional methods, such as adding virgin asphalt or replenishing missing components, are often ineffective. To achieve simultaneous rejuvenation of SBS molecules and the asphalt matrix, this study developed a novel composite rejuvenator by blending polymeric diphenylmethane diisocyanate (PMDI) with aromatic oil (AO) at varying ratios. Dynamic shear rheological (DSR) tests, Christensen-Anderson (CA) model fitting, Fourier transform infrared spectroscopy (FTIR), and fluorescence microscopy (FM) were used to characterize rejuvenation. Results demonstrated that the combined use of AO and PMDI effectively rejuvenates both aged asphalt components and SBS modifiers, with optimal efficiency at a 3 % dosage (AO:PMDI = 7:3). At low temperatures (5 °C), aromatic fraction replenishment and reconstruction of flexible polybutadiene (PB) segments in SBS molecules significantly enhanced the ductility of aged SBSMA. Under medium and high temperatures (25 °C, 60 °C), restored SBS crosslinking structures endowed the asphalt with superior elasticity, improving rutting resistance by 57 % at 25 °C. FTIR and FM analyses revealed the reaction mechanism involving isocyanate groups and validated the optimal rejuvenator ratio. This composite rejuvenator demonstrates comprehensive rejuvenation capability for SBSMA while meeting engineering performance requirements, presenting an efficient solution for SBSMA rejuvenation.