Effect Of Anisotropy And Viscoelastic Properties Of Asphalt Mixtures On The Response Of Asphalt Pavements

Because of its excellent road performance,asphalt mixture has been favored in the construction of high-grade highway in China.With the development of economy,the service performance of asphalt pavement has attracted more and more attention.Asphalt mixture is regarded as isotropic elastic material in the design code of asphalt pavement in our country,which can not represent the real properties of materials and can not accurately reflect the service performance of pavement.Based on the measured anisotropy and viscoelastic properties,the finite element modeling analysis is carried out to study the influence of asphalt mixture anisotropy and viscoelasticity on pavement structure response under different external conditions.Firstly,a test scheme is designed to obtain the anisotropic and viscoelastic parameters of asphalt mixture,and the gradation test of asphalt mixture is carried out for subsequent test.A dynamic modulus test with four temperatures and six frequencies in two directions is designed to obtain the anisotropy and variation of asphalt mixture.Based on the linear viscoelastic principle,a one-dimensional viscoelastic model of asphalt mixture is selected to derive the three-dimensional stress-strain increment relationship,and a creep test is designed to obtain viscoelastic parameters to provide a basis for viscoelastic pavement modeling.The gradation design of three kinds of asphalt mixtures was carried out,and qualified asphalt mixtures were obtained and the specimens were made.Secondly,the measured anisotropy and time-domain viscoelastic parameters of asphalt mixtures are accurately obtained by experiments.The dynamic modulus test was carried out to obtain the dynamic modulus in different directions under multi-temperature and multi-frequency and calculate its anisotropy.The results show that the measured anisotropy increases with the increase of temperature and loading frequency.Quantitative analysis of the loading process of creep test shows that the creep compliance of asphalt mixture is underestimated at the neglect of loading stage,and a data processing method considering loading stage is proposed.The results show that the creep compliance is seriously underestimated at the neglect of loading stage,with an average error of 33.77%.Viscoelastic parameters are obtained on the basis of chemical loading stage.Then,three pavement models,isotropic elasticity,anisotropic elasticity and isotropic viscoelasticity,are established to analyze the pavement response under four temperature and three speed conditions.The results show that the structure of elastic pavement is significantly affected by temperature and is limited by vehicle speed,while the viscoelastic pavement is significantly affected by vehicle speed and temperature,and the increase of temperature and the decrease of vehicle speed have adverse effects on pavement;at the same time,anisotropy has adverse effects on pavement mechanical indexes,but different indexes are affected differently,and the tensile strain at bottom and compressive stress at top of the layer increase to a certain extent.Big,the other indicators did not change significantly.The structural response of viscoelastic pavement is related to the load duration.Under single load,the other indicators are smaller than those of elastic pavement except the tensile stress of base course,and the base course of viscoelastic pavement is unsafe.Under long-term uninterrupted load,the tensile strain at the bottom of base course and the tensile stress at the bottom of base course are larger than those of elastic pavement,which indicates that ignoring viscoelastic leads to unsafe pavement.Comparing the effects of viscoelasticity and anisotropy on pavement structure,it is found that the negative effects of the latter are limited,while the negative effects of the former on pavement response are significant and far greater than those of the latter.The effect of viscoelasticity on pavement response should be given priority.Finally,the deviation degree is proposed to characterize the three-dimensional modulus characteristics of asphalt mixture,which is well related to the structural response of elastic pavement and viscoelastic pavement.It shows that the deviation degree can change the dynamic modulus changes of asphalt mixture caused by the changes of temperature and speed and the modulus differences in different directions into a unified characterization of pavement space characteristics.The anisotropic state of the asphalt pavement surface is characterized by the change of the anisotropic state and is related to the response of the pavement structure.