This paper describes an investigation into the possible benefits of using overlays of improved bituminous materials (HDM and DBM50), together with a hot rolled asphalt wearing course, to strengthen and extend the life of roads. A study of how the relationship between elastic stiffness and frequency changes with age showed that the well established deflectograph method of assessing the structural strength of roads can also be applied to roads constructed with HDM and DBM50. A linear elastic model used to compare overlay requirements for HDM and DBM50 indicated that overlay thickness reductions of around 10 per cent would be possible when using the improved materials in conjunction with a conventional 40 mm conventional 40 mm wearing course. Measurements at two new construction sites and three road strengthening trials provided supporting evidence on the quality of overlays of the improved materials. Use of the improved materials for overlays should result in a saving in material cost of about 5 per cent or increased life. Greater cost savings should be possible on multi-lane trunk roads and motorways where inlays and overlays of the improved macadams in the nearside lane would enable a reduced thickness of overlay to be used over the remaining carriageway.
Abstract