| The development and utilization of high-performance modified bitumen are important means to improve the disease resistance of bituminous pavements,extend the life of the pavement,and reduce maintenance costs.However,there are still problems with modified bitumen,such as a difficult balance between hightemperature performance and low-temperature performance,aging,and water damage.Nano-modification is a promising method to improve the performance of bitumen.The addition of carbon nanomaterials to bitumen can improve its performance by acting as a toughening agent,crack barrier,and reinforcement.However,it is still a great challenge to further improve the performance of bitumen by modulating its microstructure.In this paper,the microscopic damage mechanism of carbon nanomaterial-modified bitumen was studied based on the composite mechanics theory.Analysis of the morphology and synergistic effects of carbon nanomaterial on bitumen properties.The performance enhancement mechanism of carbon nanomaterials/SBS composite-modified bitumen was explored.The specific studies are as follows:Firstly,the microscopic damage mode and fracture mechanism of carbon nanomaterial-modified bitumen were investigated.The deformation behaviors of carbon nanotube-modified bitumen and graphene-modified bitumen representative units in parallel and orthogonal planes under tensile and shear loading were investigated by molecular simulation to elucidate the interfacial behaviors and load transfer mechanisms of carbon nanomaterial-modified bitumen.It was found that graphene with orthotropic surfaces had better load-bearing and load-transfer capabilities;graphene interlayer sliding and bitumen matrix fracture were the damage modes of graphene-modified bitumen during tensile and shear loading.Carbon nanotubes with parallel faces can carry and transfer tensile loads more efficiently,while carbon nanotubes in an orthogonal plane can carry and transfer shear loads more efficiently.The tensile damage of carbon nanotube-modified bitumen is adhesion damage,and the shear damage is cohesive damage.Secondly,the effect of the morphology of carbon nanomaterials on the viscoelastic properties of bitumen and the modification mechanism were investigated.The results showed that carbon nanotubes or graphene significantly improved the stiffness,rutting resistance,elastic recovery performance,and low-temperature performance of bitumen and improved the pavement’s service life.The optimal doping of carbon nanotubes was 1.5 wt.%,and that of graphene was 1.0 wt.%.The two-dimensional surface morphology of graphene made its interfacial bonding performance with bitumen stronger,and its modification effect on bitumen was significantly better than that of carbon nanotubes.When high-doped carbon nanomaterials are added to bitumen,the main way they change is through particle contact.When low-doped carbon nanomaterials are added to bitumen,the main ways they change are through bulk-fill and physical-chemical changes.Thirdly,the effect of the synergistic effect of graphene and carbon nanotubes on the properties of bitumen was investigated.To address the challenges of poor dispersion of nanomaterials in bitumen and weak interfacial interactions between nanomaterials and bitumen,one-dimensional carbon nanotubes and two-dimensional graphene were selected as modifiers to build three-dimensional spatial network structures in bitumen matrix through the morphological and dimensional differences between graphene and carbon nanotubes to promote mutual dispersion.The results showed that the synergistic effect of graphene and carbon nanotubes significantly improved the macroscopic mechanical properties of bitumen and greatly optimized the dispersion of graphene and carbon nanotubes in the bitumen matrix.The maximum synergistic effect of graphene and carbon nanotubes is achieved when the content of graphene is 0.2 wt.% and the content of carbon nanotubes is 0.8 wt.%.The synergistic modification mechanism of carbon nanomaterials is mostly the threedimensional network structure formed by graphene and carbon nanotubes in the bitumen matrix.This structure is similar to the cross-linked structure of nano-rivets that are held together by hydrogen bonds,and it has many advantages as a structure.Finally,the mechanism of performance enhancement of carbon nanomaterials/SBS composite-modified bitumen was investigated.Carbon nanomaterials were found to improve the durability of SBS-modified bitumen,with the best mechanical properties of carbon nanotube/SBS composite-modified bitumen,which had 21.6 times higher low-temperature fracture energy,4.51 times higher rutting resistance,and 6.45 times higher fatigue resistance than SBS-modified bitumen.The carbon nanotube/SBS composite modified bitumen exhibits the best anti-aging performance and resistance to water damage,and it still has a strong resistance to fatigue cracking under high strain conditions after aging and has excellent durability.The micro-nano structure constructed by carbon nanomaterials and SBS in the bitumen matrix improves the load-bearing capacity and stress transfer efficiency of bitumen. |
