Interfacial Failure Mechanism of Bitumen Reinforced with Carbon Nanotubes: A Micro-Nano Analysis

Carbon-based nanomaterials have been widely used as bitumen modifiers because of their excellent mechanical and functional properties. Among carbon-based nanomaterials, carbon nanotubes (CNTs) have attracted particular attention because of their high aspect ratios and strong reinforcing potential. However, the interfacial failure mechanism of CNT-reinforced bitumen at the micro- and nanoscale remains unclear. This study employs molecular dynamics simulations to investigate the interfacial failure behavior of CNT-reinforced bitumen at the micro- and nanoscale. Utilizing the LAMMPS platform, a representative volume element model of CNT-reinforced bitumen was developed to evaluate both tensile and shear loading across two distinct CNT alignments: parallel and orthogonal. Through these models, the interfacial mechanical responses, crack evolution, and atomic-scale interaction morphologies were examined to elucidate the fundamental load-transfer behavior. The findings indicate that CNTs aligned parallel to the interface offer superior performance in tensile load bearing and transfer, whereas CNTs aligned orthogonal to the interface exhibit greater resilience under shear stress. During tensile deformation, failure is primarily driven by a loss of interfacial adhesion, as demonstrated by the observed crack propagation patterns and shifts in the atomic interaction morphology. In contrast, shear-induced damage is largely localized within the bitumen matrix, indicating that the cohesive failure remains the dominant degradation mode. These simulation results are further compared with direct tensile tests and SEM observations, which provide experimental evidence for interfacial sliding, CNT pull-out, and local matrix fracture in CNT-reinforced bitumen. Additional rheological characterization further demonstrates that CNT-modified bitumen has enhanced overall viscoelastic performance and deformation resistance compared with base bitumen. By detailing at the atomic scale the toughening mechanisms of CNT-reinforced bitumen, this work provides a theoretical framework for understanding and optimizing CNT-reinforced bitumen for pavement engineering applications.