THE AGIP VISCOELASTIC METHOD FOR ASPHALT PAVEMENT DESIGN --PROCEEDINGS OF THE FIFTH INTERNATIONAL CONFERENCE ON THE STRUCTURAL DESIGN OF ASPHALT PAVEMENTS HELD DEFLT UNIVERSITY OF TECHNOLOGY, AUGUST 23-26 1982. VOL 1 AND 2. -- NETHERLANDS

In this paper a simplified viscoelastic method for pavement design based on the analysis of a three-layer system subject to moving loads is considered. The first layer is representative of all the asphalt layers, whose mechanical characteristics are described by a very simple analytical expression which can be obtained by uniaxial creep laboratory tests. The second and the third (semi-infinite) layers are considered elastic. All the layers are supposed to be rigidly bounded and incompressible (poissons ratio = 0.5). A computer program called pavis 3 (pavement viscoelasticity -three layers) has been developed to calculate strains at all points of the three-layer system, caused by the passage of moving loads. The load is supposed to be uniformly distributed on a round track. The following notable viscoelastic effects have been foreseen: -the lack of symmetry between strains calculated for positive and negative distances along the direction of load motion -the influence of speed -the difference between the maximum amount of longitudinal and transverse strains calculated at the base of the asphalt layers. An experimental validation of the above theoretical results has been performed by measurements carried out on a large test track in southern Italy. The new viscoelastic design method allows the determination of the critical tensile strains in the bituminous layers, under different temperature situations and speeds of commercial vehicles, thus furnishing the necessary parameters for the calculation of the fatigue life of flexible and semi-rigid structures. A complete subsystem for the prediction of permanent deformations in the asphalt layers is included. A computer program (morel) has been developed for the calculation of permanent deformations. Temperature and traffic conditions are taken into account by means of a nomograph.(a) for the covering abstract of the conference see IRRD 815640.