Rejuvenating aged asphalt with modified waste cooking oil: Nano-scale surface characteristics, thermal behavior, and their statistical correlation

Modified waste cooking oil (MWCO) presents a sustainable solution for recycling aged asphalt. In this study, a comprehensive investigation was conducted to elucidate the effects of thermo-oxidative aging and rejuvenation on the surface microstructure, adhesion behavior, and thermal properties of asphalt. Atomic force microscopy (AFM) was employed for qualitative and quantitative characterization of the nanoscale evolution during asphalt aging and rejuvenation processes. This involved an analysis of the morphology of bee-like structures, surface feature depth, roughness, and adhesion force. Furthermore, thermal stability and low-temperature performance were analyzed through thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. Finally, Pearson correlation analysis was applied to reveal the intrinsic relationships between the nanoscale structural parameters and macroscopic thermal performance parameters of asphalt. The results indicated that thermo-oxidative aging coarsened the bee-like structures, increased surface roughness, broadened surface height distribution, and reduced adhesion force. Aging enhanced the thermal stability, raised the glass transition temperature (Tg), and broadened the breadth of the glass transition, indicating deteriorated low-temperature performance and reduced system homogeneity. The incorporation of MWCO reversed these aging-induced changes: the bee-like structures refined, surface roughness decreased, the surface height distribution became narrower, and the adhesion force rebounded. TGA results showed that the thermal decomposition temperatures and residual mass of rejuvenated asphalt decreased, and DSC results indicated a reduction in Tg and a narrowing of the glass transition interval, confirming the recovery of low-temperature flexibility and system compatibility. Pearson correlation analysis revealed significant correlations between nanoscale structural parameters and macroscale thermal properties, highlighting the fundamental role of nanoscale surface characteristics in governing the macroscopic behavior of asphalt. This study provides profound insights into the nanomechanical and thermal mechanisms underlying asphalt aging and MWCO rejuvenation, offering a multiscale framework and quantitative basis for evaluating and optimizing sustainable asphalt rejuvenators.