Mechanisms of interfacial load transfer in the fracture process of carbon nanotube-reinforced bitumen composites

Abstract

Carbon nanotube (CNT)-reinforced bitumen composites exhibit great fracture resistance in civil engineering. However, fundamental load-transfer mechanisms at the composite interface remain unclear. In this study, molecular dynamics (MD) and density functional theory (DFT) methods are employed to investigate the nanoscale interaction and load-transfer mechanisms at the bitumen-CNT interface. Force-controlled pull-out simulations combined with newly designed sliding simulations are utilized to evaluate the fundamental contributions to interfacial shear strength (ISS) for the first time. The results reveal a non-uniform distribution phenomenon of ISS, with interfacial friction prevailing at the embedded section and van der Waals (vdW) attraction distributed at the entrance of the bitumen-CNT interface. For defect-free CNTs, the ISS is governed by vdW attraction, and the interfacial friction approaches zero. However, with the introduction of defects and functional groups on CNT surfaces, the interfacial friction increases, even surpassing the contribution of vdW attraction. In addition, the fundamental interaction behavior of π–π stacking between CNTs and bitumen molecules is also studied. Findings from this study challenge the traditional perspective of the uniform distribution of ISS, and contribute to elucidating the fundamental load-transfer mechanism.