MECHANISTIC DESIGN OF ASPHALT PAVEMENTS AND VERIFICATION USING THE HEAVY VEHICLE SIMULATOR --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

The first approach to the mechanistic design of asphalt pavements in South Africa was presented at the fourth international conference on the structural design of asphalt pavements in 1977. This approach was discussed in some detail and a number of examples were given as verification. Several improvements have since been made, mainly as a result of differences found in practice and from extensive testing carried out with the heavy vehicle simulator (hvs) on pavements throughout South Africa. These tests covered a wide variety of designs, materials, traffic and environmental conditions. The current mechanistic design method is described in the paper. The method takes account of fatigue and deformation in bituminous materials (different approaches being used for thin asphalt surfacings and thick bituminous bases), crushed-stone materials, cementitious materials of various strengths, natural gravels and soil subgrades. The degree of sophistication in the characterization of these materials may range from the selection of data from tables, up to repeated load triaxial and beam bending tests. The models used are based on simple linear elastic computer programs such as chevron, and a purpose-modified program mecde, up to the multi-loading program elsym. The criteria for distress used for different materials were developed and improved over a period of time from both laboratory and field tests. Rut deformation limits are based on laboratory repeated-load measurements and the results of tests with the hvs. The limits for cementitious materials are treated in two phases -the pre-cracked and post-cracked phases. A wide variety of different base types have been tested, using the fleet of four hvss. These include pavement with crushed-stone bases, bituminous bases, cementitious bases and natural gravel bases, and concrete pavements. The hvs test consists of applying a variety of wheel loads and measuring the elastic deflection and permanent deformation of the individual pavement layers. A large number of repetitions are then applied at a selected wheel load. During the test numerous indicators are used: these include deflection and deformation with depth; surface deflection and curvature, and rutting; state of cracking; surface profile; temperature; and density and moisture conditions in the pavement. The large volume of data on the behaviour of different pavement types has led to a high degree of confidence in the use of mechanistic design in South Africa. It has also been possible to modify designs in practice and to reduce pavement costs without a loss of confidence that the pavement will carry the expected traffic. In this way many millions of rands have been saved in South Africa, thus justifying many years of research into mechanistic design.(a) for the covering abstract of the conference see IRRD 815640.