Analysis Of Asphalt Damage Evolution Based On Viscoelastic Characteristics

The damage evolution refers to the relation curve of damage variable to time that can accurately describe variation of asphalt internal structure damage degree under the load. Over the years, researchers have paid close attention to the study of the evolution of asphalt damage, and proposed a variety of damage evolution functions. However, the existing damage evolution function does not reflect the viscoelastic characteristics in terms of describing the damage state of asphalt internal structure. The change regulation of modulus and energy and some special functions (such as Weibull function) are used as damage evolution functions in most of the studies, but the results are not satisfactory. Therefore, based on the viscoelastic model theory, the viscoelastic model parameters are considered as damage variables by analyzing the viscoelastic model parameters that characterize the internal structural damage states. The method of analyzing the change of the asphalt internal structure provides a new research idea for the analysis of asphalt damage evolution.In view of this, for analysis of the asphalt damage characteristics under static and dynamic load, the conventional fatigue and creep tests were carried out at different conditions of temperature and asphalt kind in this research. The study shows that with the increase of loading time, the viscoelastic parameters ( complex modulus, dissipated energy and cumulative dissipated energy) of asphalt show two stages in the asphalt fatigue process, except the phase angle exhibits three stages of change. Based on this, multistage fatigue tests / multistage creep tests which lay the foundation for parameter fitting of viscoelastic model of asphalt internal structure were designed.Secondly, based on the multistage fatigue test and the multistage creep test,the damage evolution curves of the inner variable principal curve cluster were analyzed. On this basis, the CAM model was used to analyze the change of asphalt internal structural state with damage. The research shows that the early stage of the load, coincident variables within the master curve of asphalt. With the loading time increasing, the complex modulus versus frequency of the asphalt is parallel to the vertical axis, and its spacing increases continuously. When the phase angle versus frequency principal curve moves in the opposite direction, the phase angle in the high frequency range is also decreased. While the complex modulus versus phase angle main curve cluster moves in the opposite direction to the longitudinal axis, the arc shape curve shows the trend of shortening at first and then increasing at the two ends. The arc main curve cluster of the loss modulus versus the storage modulus has a shortening tendency at arc and arc length. In the course of asphalt fatigue / creep damage, the model parameters including Gg*?fc?fd?Rd?md basic remain constant.With the increase of loading time, the model parameter R(k,me), which describe the relaxation time spectrum width of asphalt internal structure, show the trend of basically constant and the late increase from the fast to the slow.Finally, based on the classical constitutive model (The generalized Kelvin-Voigt model) and the fractional derivative model (The 1S2P1D model), the model parameters of the inner variable principal curve cluster were fitted. The variation of asphalt internal structural state with damage was further analyzed from the change rule of the model parameters that describe the internal structural state of asphalt. Based on this, the model parameters which have high sensitivity to damage were chosen as asphalt damage variables, and the asphalt damage evolution were expounded based on asphalt damage variables. It shows that there are obvious change regulations in the R of the CAM model parameter and the relaxation modulus E2., E3 and E4 of the generalized Kelvin-Voigt model parameters which characterize the core viscoelastic properties of asphalt. Combining with the meansquare difference analysis, the parameter of E2+E3/2 is selected as the asphalt fatigue / creep damage variable. And it is found that there is two distinct change phases during the asphalt fatigue damage process. In the first stage, parameter ofrelaxation modulus E2+E3/2 remains constant, and the effect of the thixotropy in the early stage of fatigue loading is eliminated from the point of the internalstructure steady state. In the second stage, it shows that the parameter E2+E3/2 decreases linearly and from fast to slow later which is verified to be the influence of the interface crack growth mechanism. During the course of asphalt creep damage,the modulus E2+E3/2 of asphalt relaxation exhibits two distinct stages of change.In the first stage of creep,the relaxation modulus E2+E3/2 decreases linearly slowly, and decreases rapidly at the second stage.In this paper, the variation process of internal variable principal curve cluster and the parameters of internal structural state model in asphalt damage process are expounded. It provides a theoretical basis for the prediction of asphalt damage evolution and the prediction of mechanical properties, and also provides a reference and basis for the study of damage evolution of other viscoelastic materials.