Multiscale analysis of chemical components and ageing effect on thermo-rheological behaviour of bitumen: Experiments and molecular dynamics insights

Bitumen ageing governs the long-term performance and durability of asphalt pavements, yet its mechanisms and consequences remain strongly binder-dependent and difficult to predict using single-scale descriptors. This study proposes a multi-scale framework that integrates chemical characterization, rheological testing, and molecular dynamics (MD) simulations to elucidate the ageing behaviour of five bitumen with different components. The results reveal that ageing induces systematic aromatic-to-resin-to-asphaltene transformation, and subfraction asphaltene A s2 shows the highest ageing susceptibility. Molecular bitumen models were constructed based on SAR-AD compositions and validated against experimental glass transition temperature (|ΔT g |≤4.9°C), density (|Δρ|≤0.008 g·cm −3 ), and surface free energy (|Δγ|≤1.38 mJ·m −2 ). MD results show that ageing leads to an increase in cohesive energy density (CED) and a reduction in fractional free volume and diffusion capacity. Furthermore, strong quantitative correlations are established between MD-derived thermodynamic ageing indices and experimental rheological indices, including energy-complex modulus, surface free energy-Glover-Rowe, and CED-viscosity, thereby providing a mechanistic link between molecular-scale evolution and macroscopic performance degradation of bitumen during ageing. The proposed framework enables source-specific, performance-oriented ageing assessment and offers a predictive pathway for rational binder selection and durability-oriented asphalt pavement design.