Research On The Viscoelastic Properties Of Asphalt And Asphalt Mixture In The Process Of Ageing

As the main high-grade construction materials, while at the same time is a complex viscoelastic materials, through a long period of usage, due to the impact of traffic load, natural and human factors will result in the deterioration of asphalt pavements and reduce the service life of the road. The research on the viscoelastic properties of asphalt and asphalt mixtures in the ageing are very important for understanding the deformation law, predicting the service life of asphalt pavement and understanding the aging mechanism. Based on the dynamic mechanical, creep and fatigue damage, the viscoelastic constitutive model of asphalt and asphalt mixtures are establish by combining thermodynamics theoretical in this pape.Firstly, the viscoelastic characteristics of asphalt are study by dynamic shear rheology test in this paper. The effects of ageing type, temperature and loading frequency on the complex shear modulus and phase angle of base asphalt and modified asphalt are investigated. The findings indicate that the complex modulus was increased, while the phase angle was decreased by aged, which suggests that asphalt became more elastic in the process of ageing, which results in the enhancement of resistance to deformation. The complex modulus was increased by aged, but it grew more slowly than base asphalt. Modifier improved the resistance of asphalt, whereas the complex modulus of modified asphalt grew more slowly than base asphalt. Adopting the Time-Temperature equivalence principle, the complex modulus master curves of asphalt in the ageing can be obtained. It suggests that the complex modulus is increased in the whole working frequency or temperature range. In contrast with base asphalt, the modified asphalt in the enhancement of resistance to deformation at a high temperature or low frequency and in the reduction of resistance to crack at a low temperature or high frequency.Secondly, the viscoelastic characteristics of base asphalt and modified asphalt are investigated by the Dynamic Shear Test, and suitable models are selected to describe such viscoelastic characteristics. Results demonstrate that the total and permanent deformation of base asphalts are decreased during loading period. Due to the modifier, the deformation of asphalt is decreased, and the elastic and retardant elastic deformations are increased, which result in the reduction of irrecoverable deformation for asphalt. The relationship of creep stiffness modulus and loading time can be characterized by a power function for asphalt, and a relationship between the stiffness and loading time can be established for asphalt. The elastic strain and inelastic strain are both chosen as state variables. On the basis of Biot theory and by introducing a dissipation potential. Burgers model can be used to describe the viscoelastic characteristics for base and modified asphalt in the process of ageing.Thirdly, the Dynamic Modulus Test is applied to study the dynamic viscoelastic characteristics of base and modified asphalt mixtures. This Study Shows That the dynamic modulus of asphalt mixtures is increased with frequency decreasing and temperature increasing. The phase angle is decreases at a low temperature with the frequency increasing, while the phase angle increases firstly and then decreases with the frequency increasing at a high temperature. Due to modifier, the phase angle is decreased of asphalt mixtures and the dynamic modulus is increased. Adopting the Time-Temperature equivalence principle, the dynamic modulus master curves of asphalt in the ageing can be obtained. It suggests that the dynamic modulus are increased in the whole working frequency or temperature range. An indirect tensile test was used to evaluate the fatigue resistance of the modified asphalt mixtures in the process of ageing, and fatigue predictive equations were found at two temperatures. Results indicate that the fatigue life of asphalt mixtures is increased with the ageing in the stress control mode.Finally, the viscoelastic characteristics of asphalt mixtures in the process of ageing are studied by compression creep test, and suitable viscoelastic models are exerted to describe such properties. It indicates that the total deformation and irrecoverable deformation of mixtures are increased as temperature rise, while the total deformation and permanent deformation are decreased as ageing deepen. The relationship of creep stiffness modulus is decreased as temperature rise, and modulus are increased as ageing deepen. The revised Burgers model is more appropriate to the viscoelastic characteristics research of asphalt mixtures in the process of ageing, and the correlation coefficient reached over0.978. The model demonstrate that the coefficient of elasticity of asphalt mixtures increases, and coefficient of viscosity increases at20℃and40℃and decreases at a low temperature, which result in the enhancement of resistance to deformation at a high temperature and in the reductiont of resistance to crack at a low temperature for asphalt mixtures.