In the 1970s, earth/sand and gravel roads constituted most of the rudimentary road network of Botswana. These roads carried very light but nationally important traffic, generally less than 200 vehicles per day, over vast distances of the country. A common characteristic of many of these unpaved roads is that they traverse the semi-arid, Kalahari Desert regions of the country where their proper maintenance was nearly impossible due to lack of water and suitable wearing course materials. One type of surfacing that has proved to be an economic and practical alternative to traditional surfacings in Botswana is the Otta seal, a graded aggregate seal. This type of surfacing allows the use of relatively inferior, naturally occurring, unscreened gravels in circumstances where the use of traditional bituminous sprayed surfacings using relatively expensive crushed rock would generally be unaffordable or simply not possible due to the unavailability of such materials. Today the Botswana paved road network is about 7000 km and 2400 km of this is Otta seal. This paper provides a success story about innovative approaches by tailoring a type of bituminous surfacing (the Otta seal) to the prevailing environment. (a) For the covering entry of this conference, please see ITRD abstract no. E217100.
Abstract