This paper describes a programme of co-operative research between the British Aggregate Construction Materials Industries, the Refined Bitumen Association and the Department of Transport, that has led to the development of design curves for roads with one of two different improved roadbase materials. Previous pilot-scale investigations showed that improved macadams with more filler and a harder grade of binder compared with normal dense bitumen macadam have considerable potential. These materials for use in roadbase and basecourse construction have been evaluated in five motorway and trunk road reconstruction contracts. Analysis of the production process showed that it might cost up to 10 per cent more, but its superior load spreading ability allows a thinner depth of construction to be specified and the overall cost saving is likely to be at least 12 per cent. There are situations where additional filler is not readily available or where its use leads to longer mixing times and a reduction in productivity of the mixing plant; the additional filler may be omitted and the resultant material will still be more cost effective than normal dense bitumen macadam. Analysis of the structural properties of material taken from the five reconstruction sites provided a basis for design curves relating thickness of construction to cumulative traffic loading over the design life of the pavement.
Samenvatting