DESIGN AND ASSESSMENT OF LONG-LIFE FLEXIBLE PAVEMENTS

Improved strategies for design and condition assessment are required for flexible pavements, which carry the heaviest volumes of traffic, to decrease the need for maintenance and thereby cause less disruption to the road user. The current philosophy and criteria for design are reviewed, and information that has been collected since the last revision of standards in 1984 on the performance of roads is considered. Results demonstrate that the deterioration of thick, well-constructed, fully flexible pavements is not structural and that deterioration generally starts 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. They imply that a road built above a minimum strength will remain structurally serviceable for a considerable period, provided an appropriate condition assessment strategy is adopted to enable nonstructural deterioration, in the form of cracks and surface deformation, to be detected and remedied before it can have a serious impact on the structural integrity of the road.