Chemo-physical characterization and molecular dynamics simulation of long-term aging behaviors of bitumen

To further explore the long-term aging behaviors of bitumen from the multiscale perspectives, the experimental characterization and molecular dynamics (MD) simulation methods were performed. Series of chemical properties for the virgin and various aged bitumen were evaluated using the TCL-FID, ATR-FTIR, Elemental analysis and GPC tests. The molecular models of virgin and aged bitumen were established firstly, and the influence of long-term aging on the thermodynamics properties was predicted from the MD simulation results. The experimental results revealed that with the aging degree deepened, the resin and asphaltene fractions both increased dramatically, which resulted in the increment of average molecular weight and the more uneven molecular weight distribution in aged bitumen. Moreover, the aging of bitumen led to the increase of the oxidized functional groups (C=O and S=O) index, oxygen content, aromaticity and polarity, while the carbon, hydrogen element contents and the H/C ratio reduced. The density values from MD simulation agreed well with the experimental results, which significantly validated the reliability of molecular models for the virgin and different aged bitumen binders. The MD simulation results demonstrated that the long-term aging remarkably improved the cohesive energy density, solubility parameter and activation energy, however it deteriorated the surface free energy, work of cohesion and self-diffusion coefficient of the bitumen molecular system. This study develops the molecular models of virgin and aged bitumen with different long-term aging degrees, and provides a fundamental understanding regarding the influence of long-term aging influence on the chemo-physical and thermodynamic properties of bitumen.