Implementation and verification of a mechanistic permanent deformation model (shift model) to predict rut depths of asphalt pavement

The shift model is implemented in the layered viscoelastic asphalt pavement analysis for critical distresses (LVECD) program to predict the rut depth of asphalt pavements. The rut depth measurements taken at the National Center for Asphalt Technology (NCAT) test track and the Federal Highway Administration Accelerated Facility (FHWA ALF) test sections are evaluated using the model. The model can successfully evaluate rut depth, which proves the capability of the model implemented in the LVECD program. The slight over-prediction of the NCAT sections can be explained by ageing in the field that increases the pavement's resistance to rutting. The simulation results support the hypothesis that triaxial stress sweep tests with confinement can represent the permanent deformation behaviour of asphalt concrete in the field. In this regard, excessive shear flow may be the reason for the under-prediction of the FHWA ALF mixtures. For better predictions, a correction factor (i.e. a transfer function) is suggested, which is quantified via the ratio of shear stress to shear resistance. After applying individual transfer functions, the permanent deformation model in the LVECD can evaluate the growth of the rut depth. Therefore, even though the shift model is a uniaxial model, the model can predict the rut depth of asphalt concrete by employing the transfer function.