| Two Superpave test sections, constructed with different Superpave mixtures, were tested under a 134kN (34-kip) tandem axle load at the Kansas Accelerated Testing Laboratory (K-ATL). After about 80,000 repetitions, both sections showed severe channelized, permanent surface deformation, or rutting. This study deals with the finite element modeling of rut development on those two Superpave test sections.; Nonlinear properties of paving materials, such as, visco-elasticity and visco-plasticity of Superpave mixtures, and plasticity of the aggregate base and subgrade materials, which are considered to be the major contributors to rutting, were studied and mathematically modeled. A three-parameter creep model was used to characterize the nonlinear properties of the Superpave mixtures, and a two-parameter Drucker-Prager (DP) plasticity model was chosen for the aggregate base and subgrade materials. A set of uniaxial compressive creep tests was performed using a Superpave Shear Tester. Four 100 mm (4 in.) cores, cut from the off-wheel path locations on the test sections, were tested under three different levels of compressive loads and loading times. The creep test results were analyzed in the multiple regression technique to capture the parameters in the proposed creep model. With the specified material models described above, the Superpave test sections were modeled in a finite element software, ANSYS. The initial simulation results show that the proposed creep model can give very promising simulated rut profiles with both three-dimensional (3D) and two-dimensional (2D) finite element models. The 3D model, however, is very time consuming. A new approach for backcalculating the creep model parameters with the in-situ measured rut depth results is also presented in this study. The backcalculated creep model parameters were found to be better than those from the creep tests apparently because of discrepancy in the loading condition between the laboratory tests and the actural wheel load applications.; The simulation results with a 2D finite element model using these parameters checked closely with the in-situ measured rut depths up to 10,000 load repetitions on both Superpave test sections. It is, thus, concluded that the proposed creep model can be used to simulate the visco-elastic and visco-plastic properties of the Superpave mixtures in a finite element model. A detailed sensitivity analysis was then done for seven significant factors used in the proposed 2D finite element model. Finally, rut-depth prediction equations are presented based on the finite element simulation results in this study. The significant contribution of this study lies in its finite element simulation for capturing the nonlinear properties of paving materials, especially the Superpave mixtures. The approach is expected to be widely used in mechanistic pavement analysis and design. |
