Dynamic Viscoelastic Responses Of Macro And Meso Structures For Asphalt Concrete

In order to analyze tire footprints in different conditions and calculate dynamic responses of asphalt pavement with vehicle braking,a tire-pavement coupling simulation system,which can use a viscoelastic constitutive model of asphalt concrete considering temperature dependence,was established.The user subroutine of the material model was programmed by the FORTRAN language,and viscoelastic parameters of the material model were recognized based on dynamic strain data of dynamic impact tests,whose validity was verified by using test data in the literature.The tire-pavement coupling simulation system was established to analyze tire footprints in static and dynamic conditions at different temperatures of asphalt concrete layer,whose calculation accuracy of the numerical simulation was verified.Based on measured temperature data at different depths of an actual pavement structure and the corresponding simulation model,thermal parameters of each layer in the pavement structure were recognized.Field distributions of the viscoelastic parameters in the asphalt concrete layer of the coupling simulation system were obtained by using the heat transfer analysis and the user subroutine.Average braking decelerations of trucks at a chosen intersection were calculated according to the investigation data.Based on the tire-pavement coupling simulation system,peak values of dynamic shear strain in the asphalt concrete layer at the intersection were calculated,which considered the coupling effect between axle loads and temperature fields.In order to consider temperature and rate dependence of asphalt concrete in mechanical analysis,new material constitutive equations using nonlinear material parameter fields were proposed,and user subroutines of these equations were programmed and verified.Material models of the Burgers viscoelastic parameter fields and the stiffness modulus fields,which can quantitatively characterize the temperature and rate dependence of asphalt concrete,were respectively proposed and compiled by the FORTRAN language.Parameter values of the two nonlinear material parameter fields were respectively recognized by uniaxial compression test data of asphalt concrete at different temperatures and strain rates.According to the obtained parameter values of the constitutive equations,data of small beam bending and uniaxial compression tests under different working conditions were respectively used to verify the generality of these parameter values for asphalt concrete.The results show that all simulation results using the two nonlinear material parameter fields are close to test data,and prediction effects of the Burgers viscoelastic parameter fields are more acceptable.In order to analyze the viscoelastic mechanical response for meso structure of asphalt concrete,the 3D numerical model of the meso structure was established,which considered temperature dependence of asphalt mortar.The meso structure of asphalt concrete,which included asphalt mortar,aggregate and pore,was established based on the algorithm of packing aggregates.A viscoelastic constitutive model of asphalt mortar considering temperature dependence was established based on dynamic impact tests and finite element analysis,whose validity was verified.According to uniaxial dynamic compression and small beam bending tests,3D numerical models of the meso structure for the asphalt concrete specimens,whose working conditions were same as those of the tests,were founded.The good agreements between simulation results and test data shows that the 3D numerical model of the meso structure for asphalt concrete,where the viscoelastic constitutive model of asphalt mortar considering temperature dependence was used,can be used to predict the macro nonlinear mechanical behavior.