LONG-LIFE FLEXIBLE ROADS

A longer design life for flexible pavements, which carry the heaviest volumes of traffic, will yield a lower whole life cost. This will require strategies for design that decrease the need for maintenance and thereby cause less disruption to the road user. This paper reviews the current philosophy and criteria for design and considers information on the performance of roads that has been collected since the last revision of UK design standards, in 1984. This has demonstrated that the deterioration of thick, well-constructed, fully-flexible pavements is not structural, and that deterioration generally occurs at the surface in the form of cracking and rutting. The evidence suggests that fatigue and structural deformation originating deep within the pavement structure are not the prevalent modes of deterioration. It also shows that changes that occur to the structural properties of the bituminous materials over the life of the road are crucial to the understanding of its behaviour. These changes can help to explain why conventional mechanisms of deterioration do not occur. They imply that a road built above a minimum strength will remain structurally serviceable for a considerable period, provided that non-structural deterioration in the form of cracks and deformation are detected and remedied before they have a serious impact on the structural integrity of the road.