Damage Mechanism Of Asphalt Binder By Multi-factor Coupled Aging

Asphalt,as a binder material in pavement structure,is subjected to long-term and frequent traffic loading and environmental erosion during pavement use,resulting in more pavement diseases in the service life of asphalt pavement,which seriously reduces the service life of asphalt pavement,increases the frequency of asphalt pavement repair and maintenance,and increases the maintenance cost during pavement operation.The systematic study of the damage mechanism of asphalt binder by the coupled aging effect of oxygen,ultraviolet light,water and temperature provides a perfect scientific basis for the study of asphalt anti-aging prevention and control measures,which is of great theoretical guidance and practical significance to extend the service life of asphalt pavement.The purpose of this thesis is to investigate the damage mechanism of multi-factor coupled aging on asphalt binder,focusing on the damage mechanism of ultraviolet radiation on asphalt binder,the erosion mechanism of water-soluble salt medium on asphalt binder.Through viscosity performance tests and molecular dynamics simulations,the degree of influence of thermal-oxygen-UV aging on the rheological properties,microstructural transformation and aggregation behavior of asphalt binder materials is jointly analyzed by using the non-uniform state thermodynamic parameters such as energy,dispersed phase density,glass transition temperature of the system and material viscosity performance index.By combining the universal findings of microstructure characterization tests and molecular dynamics simulation results,we analyze the damage mechanisms of the water-soluble salt media on the internal microscopic indicators of asphalt such as groups and chemical bonds,and analyze the deep-seated causes of the universal findings of microstructure characterization tests with the diffusion and adsorption behaviors of water-soluble salt molecules in the gel structure of asphalt,as well as analyze the damage mechanisms of the water-soluble salt media on asphalt bonding and evaluate The extent of damage.The results of UV radiation on the damage mechanism of asphalt binder show that the saturated and aromatic fractions provide the active force for asphalt molecules,and the gums and asphaltenes provide the bonding force for asphalt molecules.As the UV aging time progresses,the light fraction in the asphalt molecule gradually transforms into the heavy fraction.The UV aging enhances the adhesion of asphalt molecules by increasing the heavy components and increasing the distribution width of the asphalt molecules,which improves the high temperature resistance of asphalt.At the same time,UV aging reduces the low-temperature resistance of asphalt by reducing the free volume of the lighter components and increasing the glass transition temperature,resulting in a solid state of asphalt molecules at low temperatures and making it difficult for rheological behavior to occur.In addition,among the factors affecting the viscosity of asphalt molecules,the influence of asphalt molecular structure and molecular weight is significantly greater than that of molecular activity.The addition of short branched chain hydrocarbon molecules to the UV-aged asphalt molecules can effectively reduce the viscosity of asphalt molecules,improve the mobility of asphalt molecules,and enhance the low-temperature resistance of UV-aged asphalt.The results of the study on the erosion mechanism of asphalt binder by water-soluble salt media show that: the thermal movement of water-soluble salt molecules in heterogeneous diffusion behavior has the characteristics of temperature sensitivity and asphalt species sensitivity,and the polarity,deformation,and structural morphology of molecules are the reasons for this characteristic,and the spatial configuration of complex soluble salt molecules have a larger diffusion potential and difficult to occur diffusion behavior.In addition,sulfate and nitrate physisorption and chemisorption occur on the asphaltene surface,where chemisorption takes the form of phenolic hydroxyl groups as characteristic recognition sites and chemical reactions catalyzed by activation energy,resulting in the transformation of the phenolic hydroxyl structure,and aqueous soluble salt media such as nitrate and sulfate oxidize the hydroxyl groups on the aromatic core structure within the asphalt molecule to carbonyl groups.At the same time,the nitrate and sulfate media induce oxidation of sulfur derivatives(e.g.,thioether groups,etc.)in the asphalt resulting in the formation of sub-maple characteristic functional groups.Ultimately,this results in an increase in the carbonyl and maple group content within the salt-soluble aged asphalt,with the oxidation of sulfate being more pronounced.Studies have shown that water-soluble sulfates and nitrates determine the degree of damage to the asphalt binder,and water-soluble chloride salts determine the depth of damage to the asphalt binder.