Synergism and Mechanisms of Aging Resistance in the Use of Graphene and Carbon Nanotubes in Bitumen Composites

Thermal oxidation has a significant effect on the durability of bitumen composites reinforced with carbon nanomaterials. However, the mechanisms of aging resistance and the effect of aging on the chemical properties, morphology, micromechanical properties, and rheology of bitumen with carbon nanomaterials are still unclear. This study investigated the mechanisms of aging resistance underlying the synergistic effects of graphene and carbon nanotubes (CNTs) on the durability of bitumen composites. The antiaging properties of bitumen with hybrid graphene/CNT were also compared to those of bitumen with only graphene or/and bitumen with only CNT. Compared with control bitumen, bitumen with graphene, and bitumen with CNT, the bitumen with hybrid graphene/CNT had significantly improved aging resistance as shown by the much lower chemical aging indexes and the lower rheological aging index. The three-dimensional spatial network structure formed by graphene and CNT in bitumen has dual mechanisms underlying the improvement it provides in resistance to aging: the structure effectively confines the thermo-oxidation reactions in bitumen molecules and the structure acts as a barrier to inhibit the penetration of oxygen molecules and reduce their diffusion rate, thereby inhibiting the generation of free radicals. This study reveals the antiaging mechanisms of carbon nanomaterials in bitumen composites, providing a theoretical basis for the application of carbon nanomaterials in pavement engineering.