In the rural areas of developing countries, where many of the up-grading or new paved road construction projects are taking place, good quality surfacing aggregates is often unavailable and importation from an approved source may involve very long haul distances. Even if suitable aggregate is available, the cost of establishing a conventional quarry for low volume road in a remote area is often prohibitively expensive. These problems have led to the need to develop alternative designs to the more traditional single or double bituminous surface treatments (dressings) which utilise naturally occurring gravels and which do not sacrifice the overall quality and performance of the seal. This paper outlines the design and construction details of graded aggregate bituminous seals based on extensive experience of this type of surfacing in Southern and Eastern Africa. Particular attention is paid to the properties and characteristics of the aggregates and bituminous binders used in the construction of the seal in relation to its performance and cost effectiveness. The paper concludes that the use of graded aggregate seals enable more extensive use to be made of naturally occurring, often marginal quality, materials compared to the more conventional bituminous surface treatments. In favourable circumstances, the use of these seals can make a major contribution to the economic viability of up-grading gravel roads or constructing new, low-volume roads to bitumen surfaced standard, particularly in the remote areas of developing countries. (A)
Abstract