In Kenya 1974/5 and in Malawi 1984/5 trial sections of bituminous-surfaced low volume roads were constructed using as-dug laterite in place of stone or stabilized material as a base course.
The laterite did not conform with any accepted specifications but performed equally well when compared with adjoining sections of road using stone or stabilized material as a base.
The construction procedures employed are described. A period of 4–6 weeks between the compaction of the base and its surfacing is considered essential if the road is to perform satisfactorily. During this period it is exposed to the weather and traffic or to periodic watering and rolling. This treatment fills any cracks with dust or mud and closes them by the kneading action of rubber-tyred traffic. The bituminous surfacing is applied where the base has dried out to about half the optimum moisture content and is extended about 1.5 m beyond each edge of the carriageway.
In 1984, $40000 US per km was saved in Malawi in this way, approximately 70% being in convertible currency without incurring additional maintenance or vehicle operating costs.