Viscoelastoplastic Continuum Damage Constitutive Model Of Asphalt Mixtures Under Compression Loading

In recent years,due to the increase in traffic volume and the intensification of the overload phenomenon,pavement diseases have also emerged.Some newly built asphalt pavements even start to show oil flooding,cracks,crazing,potholes,rutting,and other diseases soon after opening to traffic.The pavement structure mechanical response analysis reveals the pavement disease mechanism and the core of the pavement structure design,where the pavement material mechanical parameters and intrinsic structure relationship are the basis of mechanical response analysis.Asphalt mixture is a composite material composed of binder and aggregate,which has the memory characteristics of viscoelastic material,and its mechanical properties are closely related to temperature,load,and loading rate.Accurate analysis of the viscoelastic mechanical parameters and intrinsic structure relationships of asphalt mixtures is a prerequisite for establishing and developing pavement design theories consistent with the actual working conditions.Based on the continuous damage mechanics,the asphalt mixture viscoelasticplastic damage mechanics model has been gradually developed to consider both viscoelastic and viscoplastic deformation under the damage condition.Although the model has been gradually promoted in North America,the pavement structure and mix type in China are quite different from those in North America,so it is crucial to further study the implementation and validation of the model in northern China,especially for the matrix,SBS and crumb rubber modified asphalt mixes commonly used in Inner Mongolia.In this thesis,a mechanical principal structure model of asphalt mixture viscoelastoplastic continuum damage under compression loading is constructed.It has significant potential applications in analyzing pavement deformation,predicting the magnitude of permanent deformation of pavement structures,and preventing and inhibiting pavement damage.The following research work is carried out in the thesis.(1)For the uniaxial compression complex modulus test results of three different types of asphalt mixtures with matrix,SBS,and rubber powder,the master curve models of dynamic modulus and phase angle,storage modulus and loss modulus,and storage compliance and loss compliance in the frequency domain were constructed based on the generalized Sigmoidal model,respectively,according to the approximate Kramers-Kronig relations,The master curve models of all the master curves were obtained while ensuring that all the master curves of each viscoelastic response function are obtained on the premise that all the models have the same shift factor.The master curves are verified by using Black and Wicket plots.(2)based on satisfying the linear viscoelasticity,the continuous relaxation spectrum model is derived from the stored modulus master curve model based on the integral transformation theory,and the relaxation modulus master curve in the time domain is obtained from the results of the continuous relaxation spectrum based on the numerical integration method;similarly the continuous retardation spectrum model is derived from the stored compliance master curve model,and the creep compliance master curve in the time domain is obtained from the results of the continuous retardation spectrum based on the numerical integration method.The master curve of the time-domain viscoelastic response function obtained by the continuous spectrum method is compared with the results obtained by the discrete spectrum method based on the Prony series,and the results show that both methods can construct the master curve of the time-domain viscoelastic response function.(3)Based on uniaxial constant strain rate compression tests at different temperatures and strain rates,stress-reduced time master curves and shift factor results at different strain levels were obtained,thus demonstrating the validity of the time-temperature superposition principle(TTSP)at large strains;strength master curves and strain master curves of asphalt mixtures were constructed,and the ultimate strength and strain of the mixtures under arbitrary conditions could be predicted using these curves.The stress-strain curves under other conditions can be predicted by using the stress-reduced time master curve,and the prediction results show a good correlation compared with the measured stress-strain curves.(4)Based on the strain decomposition principle,the total strain is decomposed into viscoelastic deformation and viscoplastic deformation,and the Shcapery nonlinear viscoelastic model with damage is constructed to characterize the viscoelastic deformation based on irreversible process thermodynamics,work potential theory,elastic-viscoelastic correspondence principle and time-temperature superposition principle at larger strain.The damage property curves were obtained from the uniaxial constant strain rate compression results at a lower temperature(5 ℃),and the viscoelastic model could be calibrated by combining the relaxation modulus and creep compliance results.Based on the simplified Perzyna viscoplastic rheology theory,the Uzan viscoplastic model was constructed to characterize the viscoplastic deformation by considering strain hardening;the viscoplastic model was calibrated by repeated loading creep recovery test in two modes:fixed stress changing time and fixed time changing stress.The viscoelasticplastic continuum damage model under compression loading was obtained by combining the Shcapery nonlinear viscoelastic model with the Uzan viscoplastic model containing the damage.In this paper,the viscoelasticplastic continuum damage constitutive model is constructed based on the mechanical response of three asphalt mixtures under compression loading,enabling a comprehensive and systematic study of asphalt mixtures’ mechanical properties.This paper’s results provide a reference for further improving the structural design theory of asphalt pavements and provide a relevant basis for the maintenance and repair of pavements.