New, performance-related specifications for wearing course materials for unpaved roads have been derived from an extensive investigation of existing unpaved roads in South Africa and Namibia. These specifications identify the most suitable materials in terms of a number of newly defined parameters, determined from standard particle size distribution analyses, plasticity tests, material hardness and the material strength. They are more reliable than the specifications currently available, and an indication of the consequences of using materials outside the specifications can be obtained from a simple chart. The use of these specifications can result in higher materials location and construction construction costs, however, substantial reductions in the total life-cycle costs of the road are indicated. Potential annual savings in road user costs of more than 20 per cent are possible in South Africa. Extensive research on the use of dust palliatives and the role that they can play in the phased construction of a road has also been conducted. Laboratory investigations followed by controlled field experiments have led to a greater understanding of the performance mechanisms of each product. The research found that the products are material and climate dependent and that application and maintenance procedures should be strictly controlled. (A)
Samenvatting