FRENCH EXPERIENCE WITH GRAVE-BITUME, A DENSE BITUMINOUS ROAD BASE

The report gives background information about the development in France of grave-bitume, a roadbase material with high resistance to permanent deformation under traffic. The required properties are obtained by providing a strong aggregate matrix coated with a hard binder. The quantity of binder used is less than that for alternative French bituminous materials. The method of determining the mixture composition is described and the techniques involved in laying and compacting grave-bitume discussed; in France considerable emphasis is placed on the high level of compaction necessary to obtain satisfactory performance and the compaction plant used is considerably more powerful and expensive than that normally used in the United Kingdom. Details are given of the construction at three sites where grave-bitume was used as a roadbase or overlay material. The cost per unit thickness of grave-bitume is certainly not less than that of dense roadbase macadam used in UK but there is evidence from laboratory studies to suggest that its structural performance may be better; there is potential for incorporating some of the essential features of grave-bitume in the development of improved dense coated macadams. /Author/TRRL/