NEW ASPHALT OVERLAY DESIGN PROCEDURE

In Victoria, the design of asphalt overlays had for many years been based on a procedure which used maximum deflection measured under a standard wheel load, as its primary input. Some limitations to this procedure started to become obvious in the 1970's, with premature fatigue cracking of a number of asphalt overlays being observed. Whilst it is generally accepted that maximum deflections can be used as a guide to the magnitude of vertical compressive strains in a pavement structure, it was realized that horizontal tensile strains were the controlling factor for asphalt fatigue performance. A simple measure of the shape of the deflected pavement under a standard wheel load is now used in the new design procedure, to estimate the level of tensile strain developed in asphalt layers. The paper gives details of the new procedure together with an example of how it applies, in terms of predicting permanent deformation and fatigue cracking for different temperature environments. Examples of field measurements taken since adoption of the new design procedure are also included (TRRL/Author)