Research On Dynamic Viscoelastic Mechanical Model And Viscoelastic Strain Separation Method Of Asphalt Mixture

As the main material of asphalt pavement surface,asphalt mixture is a typical viscoelastic-plastic material.The permanent deformation under dynamic creep test can better reflect the performance of asphalt mixture.The same as the permanent deformation,dynamic modulus is also a key parameter to characterize the performance of asphalt mixture,which reflects the viscoelastic response of asphalt mixture under dynamic load.Therefore,this paper establishes a dynamic viscoelastic model based on the complex modulus test of asphalt mixture under various confining pressures,and studies the flow time and viscoelastic strain separation combined with the permanent deformation curve of dynamic creep test,so as to provide reference for the subsequent establishment of viscoplastic model.The main conclusions of this paper are as follows:(1)Combination with pavement design standards,the complex modulus tests at various temperatures(5℃,20℃,35℃,50℃),multiple frequencies(0.1 Hz、0.5Hz、1Hz、5Hz、10Hz、25Hz)and multiple confining pressures(0 kPa、50kPa、100kPa、150kPa、20kPa)were performed on the AC-13 asphalt mixture.And the effects of various factors on viscoelastic parameters(dynamic modulus,phase angle,storage modulus,loss modulus)were analyzed.The phase angle and loss modulus change nonlinearly with temperature and frequency.(2)For the frequency domain master curves of dynamic modulus,phase angle,storage modulus,and loss modulus,two methods are proposed to establish a complex modulus master curve model that satisfies the viscoelastic theory and the KramerKronig relationship.①Combined with the test data of storage modulus and loss modulus,the generalized Sigmoidal model is used as the basis of the main curve model,the WLF time-temperature equation is combined,and the relationship between storage modulus and loss modulus is established according to the simplified KramersKronig relationship.The main curve model of complex modulus with uniform shift factor is established.②Combined with test data of the dynamic modulus and phase angle,the Sigmoidal model is used as the main curve,the time-temperature equation of quadratic polynomial is combined,and the relationship between dynamic modulus and phase angle is established according to the simplified Kramers-Kronig simplification.Both models can meet the accuracy requirements,and simplified models are recommended.(3)The main curve of creep compliance can be established from the main curve of storage modulus through the established continuous relaxation time distribution function,relaxation modulus main curve model and continuous delay time distribution function,combined with Euler formula,Riemann integral and written MATLAB program.The main curve of relaxation modulus,continuous delay distribution function and creep compliance under different confining pressures at reference temperature are drawn.(4)According to the comparison of different calculation methods of flow number,it is recommended to use Francken model for direct regression of permanent deformation curve and direct calculation of rheological times of asphalt mixture.It is proposed that the permanent deformation before the third stage of dynamic creep is used to directly separate the viscoelastic and viscoplastic strains,combined with the established creep compliance master curve to solve the Schapery viscoelastic model,and the viscoplastic model and the parameters of the viscoplastic model calculation method are proposed.