Anti-aging Properties Of Nano-modified Asphalt Based On AFM Characterization

Recently,nano-modified asphalt has has attracted much attention become of its wide application in road traffic fields.Among them,asphalt aging is an important factor affecting the performance of asphalt pavement,which is accompanied by the whole life stage of asphalt mixture from production,mixing,storage and transportation to paving service.Hence,It is vital for analyzing the aging behavior of asphalt systematically.In the past,researchers paid more attention to the study on the properties of asphalt before and after aging by traditional means,but less on the microscopic level of asphalt.Therefore,in this paper,the anti-aging behavior and anti-aging mechanism of nano-modified asphalt were deeply discussed by means of atomic force microscope(AFM).In this paper,A-70 base asphalt as the research object,nano-graphene and montmorillonite as modifiers,two kinds of nano-modified asphalt have been prepared,respectively.The short-term and long-term aging characteristics were studied.The micro-morphology and mechanical properties of asphalt before and after aging were analyzed and discussed by traditional AFM method.The main conclusions are as follows:(1)Graphene-modified asphalt with content of 0.5%,1% and 1.5% was prepared by melt blending method.Through the analysis of conventional physical indexes(asphalt penetration,ductility,softening point,viscosity and its rate of change),it is concluded that the addition of graphene can improve the asphalt’s high temperature stability and anti-aging performance.By analyzing the changes of complex shear modulus(G*)and phase Angle(δ),it is concluded that the addition of graphene increases the elastic components of asphalt and improves the high temperature stability of asphalt.Infrared spectroscopy(FTIR)results show that there is only physical blending between graphene and asphalt without chemical reaction,and the aging resistance of graphene-modified asphalt is revealed by the S=O functional group.The AFM morphology results show that the number of "honeybee structure" of graphene-modified asphalt is more than that of base asphalt,and the volume of graphene-modified asphalt is smaller.At the same time,the roughness of the asphalt is reduced by graphene,and the decrease of graphene-modified asphalt is less than that of base asphalt before and after aging.AFM micromechanical properties showed that with the deepening of asphalt aging,the adhesion force of asphalt decreased and Young’s modulus increased,but after aging,graphene-modified asphalt had higher adhesion force and lower Young’s modulus,which indicated that graphene-modified asphalt had better aging resistance.(2)The montmorillonite modified asphalt with the content of 2%,4% and 6% was prepared.With the addition of montmorillonite,the penetration degree and softening point of bitumen are increased,while the ductility and viscosity are decreased.DSR results show that the rutting resistance and aging resistance of montmorillonite-modified asphalt are better than that of base asphalt.FTIR results also show that there is no chemical reaction between montmorillonite and asphalt,but the content of carbonyl and sulfoxyl functional groups in the aging modified asphalt is low,which indicates that the modified asphalt has good aging resistance.The AFM results showed that the addition of montmorillonite affected the size and quantity of honeybee structure.As the aging process deepens,the adhesion force of asphalt decreases,but the reduction rate of adhesion force of montmorillonite-modified asphalt is less than that of base asphalt.(3)The influence of modifier on the microstructure of asphalt is analyzed and discussed by means of "liquid-solid phase transition theory" and "diffusion theory" of material science.The "honeybee structure" of asphalt,consisting of asphaltene and wax,and its formation goes through two stages: nucleation and growth.In the nucleation stage,the nano-modifier acts like asphaltene and reduces the nucleation barrier.At the same time,the addition of modifier makes the asphalt viscosity increase and hinders the migration of particles.Therefore,the bee structure in modified asphalt is abundant and small in size.