Multiscale modelling of bitumen-aggregate interfaces from molecular debonding to pull-off strength

Cohesive and adhesive debonding and their percentages determine an asphalt mixture's bond energy which controls the material damage process. This study aims to establish the link of the probability of cohesive debonding at the nanoscale and the percentage of cohesive cracking at the microscale. Using this link, this study also investigates the influence of external conditions on the debonding behavior of bitumen-aggregate interfaces, and proposes a modified bond theory to predict the tensile strength of the interfaces. The debonding process was investigated numerically using coarse-grained molecular dynamics (CGMD) simulations at nanoscale and experimentally by a novel pull-off test (POT) at microscale. Results show that the debonding behaviors show consistency between the simulations and the experiments under different conditions. Cohesive fracture increases with bitumen film thickness and reaches a plateau (∼80% and 100% at the nanoscale and microscale, respectively); They also increase with temperatures (rise from 72% to 81% at nanoscale and from 73% to 100% at microscale, respectively) while show no relationship with loading rates. The pull-off strength decreases with bitumen film thickness and temperatures, and increases with loading rates. The modified Kendall's model can effectively predict the debonding behavior and the pull-off strength at different conditions.