Natural road construction materials of Southern Africa

Abstract

Naturally occurring materials, such as rock and soil, constitute a significant portion of the materials content and cost of a road. Most textbooks dealing with road construction materials, however, are mainly concerned with the manufactured materials used in such structures, such as bitumen and cement. Furthermore, where reference is made to natural materials in such publications it applies mainly to overseas countries. Since 1957 the author and other researchers in the National Institute for Transport and Road Research have devoted much effort to understanding the properties and performance of natural road construction materials in the variable Southern African conditions. It has been found that different types of rock perform differently in the various layers of a pavement and that these differences are greater in rocks than in soils. It has also been found that environmental conditions, such as climate and topography, play an important role in the performance of such materials in roads. Consequently the durability of natural materials is an important factor in their selection for use in roads.