Extended life asphalt pavements: An approach for the new millennium

The challenge to extend the life of asphalt pavement to reduce the costs incurred by local, state, and federal agencies is not new. Classic fatigue theory is that asphalt pavement fails when repetitions from traffic loads cause cracks to propagate from the base of the asphalt toward the surface. Designers are now convinced that many of the pavement failures are due to "top down" cracking, and are proposing new "perpetual pavement" designs which will last fifty years or more. Pavement designers in the UK, France, and the US found that in their analysis of traditional thick pavement designs, top down cracking is the primary cause of fatigue failure. The thick course base will stiffen relatively quickly then level off at approximately twenty years. This very stable base mitigates the deflections caused by heavy or prolonged traffic, so that the majority of failures occur in the top three inches of pavement. Current SUPERPAVE designs cal! for a multi-layer elastic approach using an improved sub-base course with good drainage, a high modulus HMA base, then a high performance relatively thin wearing surface. The principle concept is that the thicker pavement design will reduce deflections to a level below which classic bottom-up fatigue cracking will occur With a high performance, thin lift-wearing surface the roads can be rehabilitated every fifteen to twenty years with a relatively inexpensive "mill and fill" operation. Based on this approach asphalt pavement life can be extended beyond fifty years which will substantially improve the life-cycle cost associated with asphalt road construction and maintenance.