ADVANCES IN ASPHALT OVERLAY DESIGN PROCEDURES. SIXTH INTERNATIONAL CONFERENCE, STRUCTURAL DESIGN OF ASPHALT PAVEMENTS, VOLUME I, PROCEEDINGS, UNIVERSITY OF MICHIGAN, JULY 13-17, 1987, ANN ARBOR, MICHIGAN

In the Road Construction Authority of Victoria, the design of asphalt overlays for flexible pavements has for many years been based on the maximum deflection measured under a standard test load. Some limitations have been evident in procedures which relied solely on this principle, particularly with regard to the control of asphalt fatigue cracking. This paper describes theoretical and field studies which have resulted in modification of the former approach. Although maximum deflections appear to be related to vertical compressive strains in the pavement structure, they are not a reliable indicator of the potential for asphalt fatigue cracking. A simple measure of the deflected shape of the pavement surface under a standard test load is now used to estimate the level of tensile strain in asphalt layers, and thereby predict asphalt fatigue performance. The adopted measure has been called curvature function and is defined as the arithmetic difference of the deflection between the tyres of a standard dual truck wheel (D sub 0), and the deflection which is produced 200 mm from D sub 0 in the direction of travel (D sub 200). D sub 0 and D sub 200 were selected as they can be readily measured by locally available deflection measuring equipment. The paper includes details of the new procedures together with a worked example of their use in predicting the performance of pavements in terms of permanent deformation and fatigue cracking for different temperature environments. Experiences with use of the procedures since their introduction in 1982 are also discussed.