Multi-scale characterization of lignin modified bitumen using experimental and molecular dynamics simulation methods

Lignin, as a major waste from biofuel and paper industries, could be utilized as a modifier to enhance the relevant performance of bitumen. However, the effects of lignin on the thermodynamics properties and molecular structure of bitumen are rarely studied. Meanwhile, the potential modification mechanism of lignin modified bitumen is still unclear. Molecular dynamics (MD) simulation and laboratory experimental methods are combined to explore the influence of lignin on the thermodynamics characteristics, rheological properties as well as the molecular structure of bitumen. The lignin modified bitumen with different dosages of lignin (10, 20 and 30 wt%) were prepared. DSR results from a macroscale view reveal that lignin could significantly improve the modulus, elastic recovery and rutting resistance of bitumen, but it adversely affects the fatigue performance. Meanwhile, the MD simulation results from a microscale perspective show that lignin could increase the density, cohesive energy density, shear viscosity, modulus and adhesive strength of bitumen. However, the free volume, diffusion coefficient and self-healing ability of lignin modified bitumen are weakened with the increase of lignin dosage. The MD simulations results are consistent with the experimental data. Furthermore, the correlations between the microscale and macroscale properties of lignin modified bitumen indicate that the physical and rheological properties of bitumen both depend on the molecular structure dramatically. The findings of this research can provide insights for an in-depth understanding of the effect of lignin on bitumen.