| In western China,the ecological environment is fragile,and the construction temperature of conventional hot mix asphalt mixture is high,which pollutes the environment along the line greatly.Warm mix asphalt is gradually widely used as a green environmental protection technology.However,due to the high altitude,intense ultraviolet radiation,prominent ultraviolet aging problem,and the water stability of warm mix asphalt pavement is lower than that of conventional pavement,so water damage is an important factor affecting the durability of warm mix asphalt pavement.Macroscopically,it is water damage,but the basic cause is the adhesion damage of asphalt binder on the micro level.The existing water damage indicators are macro physical evaluation methods,which have strong subjectivity and great variability of test results.In this paper,the adhesiveness of warm mix asphalt under ultraviolet radiation is studied systematically.The adhesiveness mechanism of warm mix asphalt under ultraviolet aging is analyzed in depth.The adhesion characterization method on micro-level is proposed,and the correlation between the adhesiveness of warm mix asphalt and the road performance of mixture is analyzed.The experimental results provide a theoretical basis for evaluating the ultraviolet aging performance of warm mix asphalt,and have guiding significance for proposing a more accurate evaluation method of water damage of warm mix asphalt.In order to scientifically study the adhesiveness of warm mix asphalt under ultraviolet radiation,an indoor ultraviolet aging simulation experimental equipment was developed based on the principle of photochemistry effect.Two experimental schemes are designed,one is ultraviolet aging,the other is ultraviolet aging coupled with oxygen.The aging degree of warm mix asphalt was evaluated by the changes of rheological properties and characteristic functional groups after aging.Therefore,a scientific and reasonable experiment and evaluation scheme has been established for the work of this subject.In this paper,a kind of base asphalt and two kinds of warm mixing agents(Evotherm and Sasobit)were used to prepare warm mixing asphalt with different components.The rheological properties and adhesion properties of warm mixing asphalt under different aging processes of ultraviolet aging time,short-term aging and long-term aging were studied and analyzed by using dynamic rheological parameters and surface free energy.The microstructure,morphology and chemical change process of warm mix asphalt after UV aging were analyzed by atomic force microscopy(AFM),fourier transform infrared spectroscopy(FTIR)and gel permeation chromatography(GPC).The adhesion mechanism of warm mix asphalt under ultraviolet aging condition was preliminarily explained.(1)The warm mix asphalt prepared by Evotherm warm mixer based on physical viscosity reduction method and Sasobit warm mixer based on chemical viscosity reduction method did not form new functional groups with the addition of warm mixer,which indicated that only physical reaction occurred between warm mixer and base asphalt.(2)The dynamic shear rheological parameters of different Warm-Mix asphalts were investigated.The results showed that the short-term and long-term aging parameters of the two kinds of warm mix asphalts were close,but the ultraviolet aging parameters became larger obviously.The results show that ultraviolet radiation has a greater impact on the aging of warm mix asphalt.The ultraviolet radiation aging causes more loss of viscous components of asphalt,which shows that warm mix asphalt hardens macroscopically.After 150 hours of ultraviolet aging,the aging tends to be stable.Compared with the changes of parameters under the condition of oxygen isolation and photo-oxygen coupling,the changes under the condition of photo-oxygen coupling are greater than those under the condition of oxygen isolation,which shows that oxygen participation can make aging more serious.(3)The surface free energy of different warm mix asphalts was investigated.The results show that the surface free energy of Evotherm warm mix asphalt is larger than that of base asphalt,while that of Sasobit warm mix asphalt is smaller than that of base asphalt.After short-term aging,long-term aging and ultraviolet aging,the surface free energy of the two kinds of warm mix asphalt decreased.The adhesiveness and cohesiveness of the two warm mix asphalts deteriorated with the prolongation of ultraviolet aging time,and gradually stabilized after 150 hours.At the same time,under the same aging conditions,the adhesion performance of the two warm mix asphalts under the photo-oxygen coupling condition is worse than that under the oxygen isolation condition.(4)Atomic force microscopy(AFM)morphology analysis showed that the surface of warm asphalt showed bee-like structure.With the prolongation of ultraviolet aging time,the total area of bee-like structure of warm mix asphalt decreases gradually,but the single area increases.This is because bee-like structure begins to aggregate,and the valley bottom area representing micro-cracks increases gradually.The decrease of light components and the formation of micro-cracks will reduce the effective area of contact with stone,resulting in the decrease of adhesion work of warm mix asphalt.Using flourier transformation infrared spectroscopy(FTIR)and gel chromatography(GPC)to analyze the chemical change process of warm mix asphalt,it is known that ultraviolet aging makes Aromatics and resin gradually change to asphaltene.The general trend is that asphaltene increases,resin decreases,the decrease of resin and the flocculation and precipitation of some asphaltenes lead to the decrease of adhesion.(5)On the basis of the study of rheological and adhesion changes and mechanism after ultraviolet aging,the relationship between the adhesion properties and the changes of nano-adhesion force,surface roughness,bee area ratio,carbonyl index,sulfoxide index and large molecular weight was analyzed.The nano-adhesion force,surface roughness and peak area ratio were used to characterize warm mix asphalt under ultraviolet aging conditions.The micro-evaluation index of adhesion performance was verified and analyzed with the macro-pavement performance of warm mix asphalt mixture.The results show that the micro-evaluation index of adhesion performance proposed in this paper has high accuracy,little human influence and reliable results,which has a good practical significance for the study of water damage of warm mix asphalt. |
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