Permanent deformation and rate effects in asphalt concrete: Constitutive modeling and numerical implementation

Rutting in asphalt concrete pavements is the primary distress mechanisms in pavements. The initial rut is caused by densification of pavement under the path of the wheel. However, the subsequent rut is a result of the shear flow of the fix. In properly compacted pavements the shear flow is considered to be the primary rutting mechanism.; Permanent deformation in asphalt concrete consists of rate dependent and rate independent components. In addition, the mix dilates under shear loading as the aggregates try to roll past each other. A successful constitutive model has to incorporate these features.; A four-component model for asphalt concrete is proposed. These four components are: elastic, viscoelastic, viscoplastic and plastic. The elastic model is a third order hyperelastic model, which captures the development of normal stresses under shear loading. The viscoelastic model is a generalized form of the Modified Kuhn model. The plasticity model is based on the theory of generalized plasticity. Finally, the viscoplastic model is based on Perzyna's theory of viscoplasticity.; A robust numerical scheme to time integrate the equations of the model is presented. The equations are time discretized using the backward Euler method. The resulting system of equations is solved using the predictor—corrector scheme and Newton Raphson method in multi dimensions. Finally, the model is implemented within the context of a finite element program, CASTEM 2000, to study boundary value problems.; Model results are compared to experimental observations. For the viscoelastic component, the creep and frequency sweep results are captured. For the permanent deformation, results of the Repetitive Simple Shear Test at Constant Height (RSST-CH), are used to calibrate the model and test its prediction for different stress levels. RSST-CH is also modeled as a boundary value problem to make correction to the model parameters. Finally, a pavement finite element mesh is constructed. It is shown, that the pattern of deformation in the finite element mesh is similar to that seen in the field.