PRACTICAL APPROACH TO THE PREDICTION OF RUTTING IN ASPHALT PAVEMENTS: THE SHELL METHOD

This paper describes a true engineering method for predicting rut depth. It demonstrates how a mix design procedure based on creep testing can be used as a subsystem in an overall pavement management system. The proposed system makes it possible to calculate the decline in riding quality of a pavement as a function of time caused by permanent deformation. It is shown that (a) the service life of a pavement can be related to the bitumen properties, (b) the mix properties can be given as a function of the bitumen properties, (c) the total number of wheel loads of a given wheel-load spectrum can be expressed as an equivalent number of standard wheel loads, depending on the mix characteristics, (d) the influence of a varying contract area between the tire and the pavement is negligible in the case of a proper choice of the standard wheel, (e) the lateral distribution of wheel loads over the traffic lane and the occurrence of lateral swellings result in rut depth values (top to bottom) that are approximately equal to the reduction in layer thickness caused by the equivalent number of standard wheels in a single wheel path, and (f) the temperature variations must be corrected for by a proper calculation of average viscosities.