Research On Viscoelastic-plastic Model Of Asphalt Mixture Based On Triaxial Test Of Confining Pressure

During the service of asphalt pavement,the pavement surface bears repeated traffic loads,resulting in significant three-dimensional stress and strain inside the structure.However,the traditional uniaxial test can not accurately simulate the three-dimensional tensile-compression combined stress state of pavement structure,and it is difficult to objectively characterize the mechanical behavior of materials.Therefore,in this paper,the viscoelastic and viscoplastic models of asphalt mixture are obtained through the strength,creep and creep-recovery tests under various confining pressures,and the validity of the viscoplastic model is verified by the repeated load permanent deformation test.The main research contents are as follows:(1)The creep test of AC-13 asphalt mixture under different temperature,confining pressure and stress conditions.According to the similar geometric shape of creep curves under different temperature and stress conditions,the time-temperature and time-stress equivalent equations of asphalt mixture under different confining pressures were established,and the joint displacement factor of time-temperature-stress was solved.At the same time,the main curve parameters of creep compliance are solved in the form of Prony series,and the main curve equation of creep compliance is established,which provides an important reference for the subsequent study of nonlinear viscoelastic mechanical behavior of asphalt mixture.(2)Based on Schapery nonlinear viscoelastic model,the solving formulas of viscoelastic model parameters g0,g1 and g2 of asphalt mixture are derived.Multiple stress creep-recovery tests under different confining pressures were carried out,and the parameters of nonlinear viscoelastic model were solved by restoring creep compliance.The influence of complex stress on the viscoelastic model parameters is analyzed by using the triaxial stress ratio that characterizes the combined effect of confining pressure and axial stress,and the prediction model of viscoelastic parameters changing with the triaxial stress ratio is established.(3)According to the viscoplastic mechanical properties of asphalt mixture,the creeprecovery tests under different confining pressures were used to obtain the variation laws of axial,circumferential and volumetric strains of asphalt mixture under different confining pressures to consider the influence of confining pressure on viscoplastic deformation.The constant loading stress creep-recovery and constant loading time creep-recovery tests under different confining pressures were carried out.Considering the influence of time and stress on viscoplastic deformation,the parameters of viscoplastic model were solved,and the viscoplastic deformation characteristics under complex stress state were characterized.Finally,the variation law of permanent deformation with loading times is analyzed.The error between the measured value of irreversible viscoplastic deformation and the predicted value of the model is compared by using the repeated load permanent deformation test,and the validity of the viscoplastic model of asphalt mixture is verified.