Flexible pavements are widely used throughout the world and are required to meet more stringent demands as traffic loads increase and as the highway network is extended into areas with more extreme climates. The requirements to provide satisfactory performance are universal but the ways in which this can be achieved have to be the subject of a detailed site evaluation followed by the design of materials with the appropriate properties. The detailed site evaluation should include an appraisal of projected traffic flows, particularly commercial traffic, the expected axle loads and their aggressiveness, and of climatic conditions with maximum and minimum road temperatures and critical climatic periods being important factors. The materials, the aggregate and the binder, are selected to provide adequate resistance to rutting, the principal form of deterioration of flexible pavements in heavily trafficked locations. In some countries, various forms of modification of bitumen are used which markedly change the rheological properties of the binder resulting in a lower temperature susceptibility. The investigations carried out as part of the United States Strategic Highway Research Program (SHRP) in the development of the SUPERPAVE design procedure have led to the development of some test procedures which may be suitable for modified binders. The decision on the materials to be used has, of course, to take into account the cost and the maintenance implications for that form of construction and in many countries the whole life performance is a major consideration in selecting the mixtures to be used. In all new construction and maintenance operations, it has to be borne in mind that the resources of primary aggregates are finite and every effort should be made to recycle and to re-use materials derived from highways and from other sources in order to ensure sustainable development. In many countries the quality assurance of mixtures is now controlled through the International Standards Organisation documentation (ISO 9000). The introduction of this form of quality assurance changes the responsibilities of the client and the supplier and has increased confidence between the two parties. Also, there is growing interest in the development of performance specifications in place of the conventional recipe-based and end-result specifications. For the covering abstract see ITRD E118727.
Samenvatting