Atomic insight into the nano-cracking behaviour of bitumen: considering oxidative aging effects

Abstract

Experimental understanding of the nanoscale cracking mechanism in bitumen is challenging. This paper adopts molecular dynamics simulation to study the loading-induced cracking behaviour from four aspects: (1) stress-displacement states; (2) morphology evolution; (3) energy contribution; and (4) the relationship with chemical compositions. Simulation results indicated that the nano-cracking process can be divided into the following stages: increase of free volume (stage I), formation of nanovoids, (stage II), nucleation and propagation (stage III), filamentation (stage IV) and separation (stage V). The density drop was observed in the area where saturates agglomerated, which potentially caused the formation of nanovoids. Energy analysis indicated that the cracking behaviour was related to the non-bond interaction, especially van der Waals interaction. Oxidative aging increased the intermolecular bonding and reduced the molecular mobility, which resulted in larger tensile strength but lower ductility. In addition, the effects of temperature on the nano-cracking behaviour were also presented.