| Asphalt mixture is a typical viscoelastic-plastic multiphase composite material with complex rheological properties.Asphalt pavement is widely used in road construction at home and abroad due to its good road performance.Under static load conditions,we can fully understand the influence of the deformation law of asphalt mixture on the permanent deformation of asphalt pavement by studying its linear and nonlinear creep deformation characteristics;under dynamic load conditions,since the strain of asphalt pavement under the load of most wheels is very small,it is of great practical significance to study the stress-strain response of asphalt mixture in the linear viscoelastic range for improving the pavement structure design,preventing pavement diseases and prolonging the service life of pavement.This paper focuses on the creep and dynamic viscoelastic properties of asphalt mixture,the main work and conclusions are as follows:1. To accurately describe the complete three-stage creep deformation of asphalt mixture,a nonlinear viscoelastoplastic creep model was proposed by using variable-order fractional calculus.Unlike the classic constitutive model,which was based on a full-time criterion,the components of the model only participate in the constitutive model during the corresponding creep phase.The differential order of the variable-order fractional-order element in the model was no longer constant,but a variable that changes with time,which reflects the changes of the mechanical properties of the material during the creep process.Whereas the tertiary creep phase was modeled by the viscoplastic element with time-varying viscosity,which was attributed to damage evolution.2. MTS-809 testing machine was used for uniaxial creep compression test on AC-13C(AH-70~#)asphalt mixture at 25°C under six constant stress levels of 0.7?1.7MPa.The model was used to perform piecewise nonlinear fitting on the test results by the Levenberg-Marquardt optimization algorithm.It is shown that the model is in good agreement with the experimental results and is applicable to describe the entire creep process which consists of primary,steady and tertiary stages.Moreover,the physical meaning of the model parameters is clear,the variation of the differential order of the variable-order fractional-order element is highly consistent with the experimental results.The differential order of the variable-order fractional-order element is constant during the decay creep stage,indicating that the creep performance of the asphalt mixture exhibits a linear viscoelastic characteristic in the small strain range;the differential order increases during the steady-state creep stage,indicating that the viscosity of the asphalt mixture increases during creep,and the higher the stress level,the more prominent the viscosity.At the same time,it is verified that the segmented treatment is an effective method to simulate the creep behavior of asphalt mixture.3. UTM-30 testing machine was used for uniaxial compression dynamic modulus test on AC-13C(AH-70#)asphalt mixture in a non-destructive state within a small strain range.The temperature and frequency dependence of dynamic viscoelastic parameters such as dynamic modulus and phase angle were analyzed based on the test result;based on the time-temperature equivalence principle,a dynamic modulus main curve is constructed by using the Sigmoid function model and the generalized Sigmoid function model,the results show that the generalized Sigmoid function model can more accurately describe the asymmetric characteristics of the dynamic modulus main curve;AC-13C(SBS)asphalt mixture dynamic modulus test was added,the results show that the addition of SBS modifier can improve the deformation resistance of asphalt mixture;finally,the Wiechert model is introduced,and the expressions of the relaxation modulus and storage modulus in the form of Prony series of the model are given.The conversion of the storage modulus and relaxation modulus is realized by the storage modulus main curve and equation calculation. |
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