Developing a multi-scale framework to predict and evaluate cohesion and adhesion of rejuvenated bitumen: Insights from molecular dynamics simulations and experiments

Rejuvenators are crucial for efficient asphalt pavement recycling, but their effectiveness varies widely based on factors like bitumen source, aging degree, and rejuvenator composition. This study aims to develop a multiscale evaluation methodology to assess the cohesive and adhesive performance of rejuvenated bitumen, integrating molecular dynamics (MD) simulations and experimental testing. Molecular models of rejuvenated bitumen are established to predict nanoscale cohesion energy and the linear amplitude sweep (LAS) tests for fatigue evaluation. Bitumen-aggregate interface models undergo MD simulations for adhesion assessment, validated by pull-off tension tests, while microstructural observations clarify debonding mechanisms. Results show that bio-oil is the most effective rejuvenator for restoring aged bitumen's cohesion, followed by engine-oil, naphthenic-oil, and aromatic-oil. LAS tests confirm these rankings for both bitumen and mastic, with Filler Wigro outperforming Wigro60K in reducing cohesive cracking risk. While aging decreases adhesion property, rejuvenators restore both cohesive and adhesive performance, with bio-oil achieving 44.4 % restoration of adhesion when adding 10 % by weight of bitumen. Additionally, MD simulations reveal that the work of adhesion (W_aa) negatively correlates with fatigue parameter (G*sinδ) and positively with fatigue life (N_f), and both Waa and the work of bonding adhesion (W_BA) decrease linearly with the pull-off tension strength (POTS) index. Bitumen TB is the most effective for improving cohesion crack resistance, whereas binder FB results in lower fatigue life. Overall, bio-oil proves most effective in restoring cohesion and adhesion across bitumen types and fillers, improving rejuvenated asphalt performance.