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 simultaneously has a 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 of speed effect is the change in stress state due to the change in resilient properties of bound layers, while the speed effects on the unbound material itself have a smaller role. In addition the effect of loading speed greatly depends on the temperature, from 10 %...15 % at +10 ºC and 20...25 % at +25 ºC. The measured effects could be estimated reasonably well with modelling. The unloading – reloading cycles at various load levels has 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.