Speed and reloading effects on pavement rutting

This paper concentrates on two factors that affect the permanent deformation (rutting) of unbound pavement layers. These factors are the loading speed and stress history. The loading speed has a simultaneous two-way effect: the permanent response of the unbound material itself, and the change in the stress state depending on the resilient properties of the upper-bound layers. The modelled examples show that the dominating factor in the speed effect is the change in stress state due to the change in the resilient properties of the bound layers, whereas the speed effects on the unbound material itself have a smaller role. In addition, the effect of loading speed depends greatly on the temperature, varying from 10–15% at 10°C to 20–25% at 25°C. The measured effects can be estimated reasonably well with modelling. Unloading—reloading cycles at various load levels have little effect on the permanent deformation. The effect is usually so small that it can be neglected in calculations, but the preloading history itself has a clear effect on the permanent deformation.