Multiscale investigation of aged asphalt rejuvenation by treated waste cooking oil: Molecular diffusion kinetics, interfacial fusion, and microstructural restoration

• The multi-scale framework links molecular dynamics to microstructural recovery. • Treated waste cooking oil (TWCO) showed excellent compatibility with aged asphalt. • Rejuvenated asphalt exhibited restored diffusion coefficients surpassing aged systems. • TWCO disrupts polar clusters, reducing oxidized functional groups. • The TWCO-rejuvenated system exhibited enhanced interfacial adhesion. This study presents a comprehensive investigation into the rejuvenation mechanisms of aged asphalt using treated waste cooking oil (TWCO) through an integrated molecular dynamics and experimental approach. The reliable point-contact diffusion models were established and validated by density and glass transition temperature calculations, confirming the accuracy of our molecular representations. Differences in solubility parameters between systems were quantitatively analyzed to assess compatibility. Temperature-dependent molecular mobility was characterized through mean square displacement and diffusion coefficient calculations across virgin, aged, and rejuvenated asphalt systems. The layered-contact diffusion models were developed to calculate fusion coefficients, providing quantitative metrics for evaluating TWCO’s effectiveness in restoring the diffusion and fusion capabilities of aged asphalt. Furthermore, interfacial binding energies between heterogeneous material systems were computed to investigate interface stability. Experimental validation was conducted using Fourier-transform infrared spectroscopy to track functional group evolution and atomic force microscopy to assess microstructural recovery. Key findings demonstrated that the solubility parameter differences between TWCO and aged asphalt, as well as between rejuvenated and virgin asphalt, were consistently below 2.1 (J·cm −3 ) 1/2 , indicating excellent compatibility. Across all simulated temperatures, the diffusion coefficients of rejuvenated asphalt exceeded those of aged asphalt, confirming partial restoration of molecular diffusion capacity and microscopic mobility in the aged system. Moreover, compared to the virgin-aged asphalt interface model, the TWCO-rejuvenated system exhibited significantly enhanced fusion coefficients, interfacial energy, and work of adhesion. After TWCO incorporation, the peak intensities of polar functional groups in aged asphalt progressively diminished, while surface homogeneity improved—evidenced by increased quantity yet reduced size of “bee-like structures” and lower roughness parameters. This work provides fundamental insights into the diffusion-fusion mechanisms of TWCO in aged asphalt at multiple scales and establishes a robust computational-experimental framework for developing sustainable asphalt recycling technologies.