STRUCTURAL BEHAVIOUR OF ROAD MATERIALS --BITUMEN, FLEXIBLE AND DURABLE. 3RD EUROBITUME SYMPOSIUM 1985, THE HAGUE, NETHERLANDS, SEPTEMBER 11-13, 1985

The first part of this report describes a method allowing the comparison of different materials to be used in the upper layer of flexible roads. This method is based on the concept of "equivalent thickness". The comparison of the structural behavior of different products is made on the basis of the materials' thicknesses which are necessary in order to ensure a well defined service life to the road structure. The input data needed for its application are physical characteristics (moduli and fatigue law) determined from dynamic laboratory tests. The thicknesses are calculated in order to limit the strains at the bottom of the layer under study, and by taking into account the traffic, the bearing capacity of the base as well as the climatic conditions. The characteristics measured on different mixes containing pure bitumen and modified binders are then presented. The equivalent thicknesses of these materials are calculated for different realistic values of the modulus of the base layer. The obtained results show that the qualitative ranking of the materials is almost independent of the stiffness of the base layer. The study leads to the definition of a structural equivalency factor from which it is possible to determine which thickness of material will give the same result as a fixed thickness of another one. This structural equivalency factor allows the pavement design methods for bituminous mixes to be adapted for "new" products.(a) for the covering abstract of the symposium see IRRD 815173.