Modeling Of Creep And Fatigue Damage Of Asphalt Mixture

With the rapid development of expressways,asphalt mixture has been widely used as the main road material of high-grade highways.More and more researchers have begun to analyze the distresses of asphalt pavement,such as rutting,cracking,loosening,and potholes,and these distresses are closely related to the mechanical response of asphalt mixture under static load and dynamic load.Therefore,it is of great scientific and practical value to study the constitutive model of asphalt mixture and analyze the mechanical behavior of asphalt mixture under static and dynamic loads.The dense graded asphalt mixture samples were prepared,in which the AH70#ordinary road asphalt are selected.Based on the fractal theory,the fractal dimension was used to measure the grading of the mixture.The type C grading and a resonable asphalt-aggregate ratio of 4.6%are determined based on the measurements of Marshall stability and porosity of the asphalt mixtures.In order to investigate the static and dynamic mechanical properties of the asphalt mixtures,the MTS809 testing machine and the DTS-30 multi-purpose testing machine were used to preform the creep and fatigue tests under stress control.The nonlinear creep behavior,dynamic viscoelastic properties and fatigue damage evolution of the asphalt mixtures were investigated and some conclusions can be drawn as follows:(1)The measured creep data of the asphalt mixtures were analized.According to the creep rate,the creep process can be divided into two stages:decaying creep stage and stable creep stage,and the higher the stress,the greater the creep rate in each stage.Moreover,it can be seen from the isochronous stress-strain curve that the creep of asphalt mixtures shows obvious nonlinear characteristics.(2)Based on the viscoelastic constitutive theory,the three-parameter solid model and Burgers fluid model were used to fit the creep test data.Although the fitting result of the Burgers model is better than the three-parameter solid model,the two models are not good enough to completely describe the mon-linear creep behavior of the asphalt mixtures.Based on the strain decomposition theory,the viscosity coefficient of the Burgers model was modified to obtain a new viscoelastic-plastic model,the physical significance of the modified coefficient was also discussed.It is shown that the proposed model can well reproduce the two stages of the creep process.(3)The frequency sweep tests were conducted to the asphalt mixture samples at different temperatures to investigate the effect of temperature on the dynamic viscoelastic characteristics.The dynamic storage modulus master curve was obtained by the time-temperature superposition principle,and the Prony series of relaxation modulus of the material was then obtained.Based on the theory of Schapery pseudo-variables,the strain response of the asphalt mixture under cyclic stress was analyzed.It is found that the stress vs.pseudo-strain curves eliminate the hysteresis loops of the stress-strain curves.The stress vs.pseudo-strain curve is in a linear relationship,which slope is defined to be the pseudo-stiffness.In the absence of damage,the pseudo-stiffness is 1 kPa,while the pseudo-stiffness gradually decreases with the fatigue cycle if the fatigue damage occurs.The damage,defined by the change of the pseudo-rigidity,increases with the rising fatigue cycles.The predictions of the proposed damage model agrees well with the experimental results.