The effect of bitumen emulsion on selected engineering properties of lateritic gravel and the potential for reducing erosion of unpaved roads

Thumbnail Image
Journal Title
Journal ISSN
Volume Title
In Ghana the road network accounts for the overwhelming proportion of both passenger and freight traffic. The network is about 40,000km long and is divided into three functional classes of feeder roads, trunk roads and urban roads. Over 82% of the network is unpaved and unpaved roads can be found in all functional classes of roads and distributed in all the regions of the country. One of the characteristics of unpaved roads is that they tend to deteriorate faster than paved roads. Like in many developing countries, the funds available for maintenance in Ghana is far below that required to keep the roads at the minimum level of service. The unpaved roads are also mostly low volume roads with average daily traffic levels not exceeding 100 even on trunk roads. Given the rather high rainfall in the southern parts of the country, it appears that the major cause of deterioration of unpaved roads in these parts of the country is rainfall-induced erosion. Any financially affordable effort that leads to a delay in the deterioration of these unpaved roads will therefore contribute towards an improvement of the road network. Stabilization is known to be a simple and often affordable method of improving the resistance of unpaved roads to erosion. This project therefore seeks to investigate first how stabilization of lateritic gravel using bitumen emulsion can affect certain engineering properties of lateritic gravel and then secondly to investigate the potential for using this material to reduce rainfall induced erosion on unpaved roads. The study first reviews the factors that affect the deterioration of unpaved roads, the effect of rainfall characteristics on erosion, the rainfall patterns and zones in the country and their effect on the formation of the different types of lateritic gravel. It also reviews the experience of the effects of cement, lime and bitumen emulsion on different lateritic gravel. An anionic bitumen emulsion produced locally was used in the laboratory investigation. The laboratory work consisted of an investigation of the effect of different percentages of the bitumen on the index properties, compaction characteristics, CBR and permeability of samples of lateritic gravel obtained from five borrow pits in two agro-ecological zones of the country The results established an optimal nominal bitumen content of about 2% for improved compaction and strength characteristics. A model pavement prepared with this optimum bitumen content was constructed and the rate of erosion of material from the pavement was compared with a non-stabilized model pavement in the H313 hydrological (rainfall simulation chamber) apparatus. The results showed a four-fold reduction in the amount of material eroded from the model pavement compared with the unsterilized material.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Philosophy in Civil Engineering