Research On Dynamic Viscoelastic Characteristics And Shear Modulus Predicting Methods For Asphalt Mixtures Based On Dynamic Mechanical Analysis (dma) Means

With the highway mileage growing, more and more early damage in asphalt pavement has emerged. Researches indicated that various damages of asphalt pavement are relevant to viscoelastic of asphalt mixtures. Asphalt mixtures are particulate composite materials consisting of uniformly distributed mineral aggregates, asphalt binder and air voids. The viscoelastic characteristics are contact with various components. At present, the studies on viscoelastic behavior of asphalt mixtures do not make full use of Superpave asphalt rheological data. Meanwhile, asphalt pavements often bear vehicle load. Therefore, this research on viscoelastic characteristics in wide-temperature-wide-frequency for asphalt mixtures based on dynamic mechanical analysis(DMA)and predicting according to the components properties are very necessary.Dynamic mechanical analysis (DMA) is an important method to study the viscoelastic properties of asphalts and aphalt mixtures under cyclic stress or strain. DMA is usually operated under conditions of small strain and small strain deformation consistent with the pavements. DMA was employed to obtain dynamic mechanical properties of asphalts and asphalt mixtures within different stress, strain, time, temperature and frequency region using a small sample, which can not be obtained from others method. Therefore, DMA method can evaluate the viscoelastic behavior of asphalt mixtures completely. To obtain the viscoelastic function master curve is prerequisite for viscoelastic behavior analysis of asphalt mixtures. According to domestic and foreign research results, a high advanced shear rheometer AR-2000 is used to obtain the DMA sweep test data. Asphalt mixtures is a simple thermal rheological materials determined by time-temperature superposition principle, and just horizontal movement can viscoelastic function master curve for asphalt mixtures, and master curve obtained by non-linear fitting covering the entire frequency range of engineering applications provides a sufficient basis for a comprehensive study of the viscoelastic behavior of asphalt mixtures.The glass transition temperature(T_g)for asphalts and asphalt mixtures are got using the DMA frequency spectrum and time-temperature superposition principle and overcome the shortage that dynamic mechanical temperature spectra may not cover the T_g. The dynamic frequency sweep (DFS) is an effective method to obtain T_g characteristic index of asphalt and asphalt mixtures. T_g of sphalts and T_g of asphalt mixtures are the same trend and good correlation. Meanwhile, there is good correlation between WLF equation in the C2 in WLF equation and T_g of asphalt and asphalt mixtures. The results show that the same index T_g can evaluate the lower temperature performance for asphalt and asphalt mixtures.Comparison of other rheological models, a CAM model with clear physical meaning of parameters is used to study viscoelastic behavior for asphalt mixtures in wide-temperature -wide-frequency based on their master curves. The viscoelastic behavior for asphalt mixtures in limit low frequency and limit high frequency and the viscoelastic ratio for asphalt mixtures at low temperature, intermediate temperature, intermediate-high temperature and high temperature are investigated using of CAM model. The results show that CAM model with good clear physical meaning and sensitive to volume index changes is effective model of quantitative study for asphalt mixture viscoelastic behaviors, can study the performance and provide application guidance for asphalt mixtures.To analyze the dynamic complex viscoelastic properties of asphalt mixtures, dynamic viscoelastic constitutive equation of asphalt mixtures dynamic properties was studied, consisting of generalized Maxwell model and fractional derivative Maxwell model, Burgers model and fractional derivative model, and the fitting results of classical viscoelastic model and fractional derivative model are analyzed. The results indicate that generalized Maxwell model fit less effective at both end of the curve, but fractional derivative Maxwell model with clear physical meaning parameters in some degree can fit the test data well and can describe the dynamic performance for asphalt mixtures in quantitative; Burgers model can not fit the dynamic creep curve accurately and the beginning of fitting deviation in creep curve is particularly evident, while fractional derivative Burgers model can describe the asphalt mixture dynamic creep curves accurately.It is concluded that the fractional derivative model can descirbe the dynamic viscoelastic behavior accurately. Considering the components of asphalt mixtures material impact on its viscoelastic behavior, an improved Hirsch model was derived. A micromechnical improved Hirsch model is used to predicte the shear modulus and phase angle of asphalt mixtures using Superpave asphalt rheological data and considering. The results show that there is a good correction between predicted value and measured value( R~2 > 0.89)and the improved Hirsch model is a simple and practical approach to estimate the complex shear module and phase angle for asphalt mixtures. If measured the volume index of asphalt mixtures, its viscoelastic function paramaters can estimate according to asphalt rheological data at same temperature and same frequency and its components fractions. This greatly reduces the experimental cost and time. Improved Hirsch model for provides an effective way to estimate dynamic shear modulus and phase angle for asphalt mixtures and investigate the viscoelastic behavior of asphalt mixtures.