BITUMINOUS BASES AND SURFACINGS FOR LOW-COST ROADS IN THE TROPICS

Mechanically stable materials for road bases are often not obtainable in developing countries and the technique of soil stabilisation has therefore been developed. In the middle east, aggregates are often scarce but oil products are readily available. The region has therefore provided some of the earliest examples of bituminous stabilisation, which originally consisted of thin running surfaces over compacted sand. Bituminous stabilisation can also enable local sand to be used for base construction, and various tests and design criteria have been proposed for such applications. The report describes full-scale experimental trials supported by laboratory research, which have enabled acceptance criteria for bitumen-stabilised sand bases for light/medium traffic to be proposed. Construction methods for bituminous stabilisation are also described. Details are given of methods of surface dressing, which is important both as an initial running surface on new bases and as A maintenance treatment. Premixed bituminous materials, both as bases and surfacings, might perhaps be considered as inadmissible for low-cost roads. Such roads, however, usually require progressive improvement because of the traffic growth which accompanies development. There is A growing use of strengthening overlays and the report briefly discusses premixed materials and their application. (A)