Alaska is currently developing a pavement management system for their road system. An important input to the system is the determination of flexible overlays based on the structural adequacy of the existing pavement. The current overlay procedure (asphalt institute method) does not always show a need for overlays, despite the poor surface condition of the pavement and high traffic volumes. Therefore, an improved procedure that considers not only traffic but also surface distress, structural properties of the pavement, and effects of a freezing and thawing of the base, subbase, and subgrade layers is needed. This report recommends two such methods: a simplified mechanistic method using equations developed in Pennsylvania, and a mechanistic procedure using a back-calculation computer program known as ELSDEF. A comparison of these methods showed that the asphalt institute procedure was inappropriate and under designed the overlay for the road sections. The Pennsylvania equations were slightly more conservative than the mechanistic method using ELSDEF, except for cases where the pavement fatigue life had been utilised completely by past traffic loads. It is recommended that alaska utilise the mechanistic approach to design overlays and ELSDEF as the back-calculation procedure. The Pennsylvania equations can be used in cases not requiring considerable accuracy.
Abstract