Availability of natural gravel for road construction in Ghana
Most road pavements in Ghana have for many years been built of natural gravel as the subbase and base layers. Natural gravel are the most economical material for road construction when available within economic haulage distances. However, there has been a gradual shift to the use of a blend of natural gravel and other materials (stabilization) or crushed stone as the layer materials for subbase and base. In addition, various studies have been done to improve the engineering properties of natural gravel underscoring the difficulty of finding suitable material for construction in Ghana. However the extent of the problem is unknown. This study evaluated some material properties (CBR, grading and Atterberg limits) of natural gravel samples from 454 borrow pits distributed throughout the country for their suitability or otherwise for road construction as a subbase, base and Otta seal. Each material property was compared with G30, G40, G60 and G80 MoT specifications. The ones meeting the criteria were denoted as passed or failed if otherwise. The results showed that it is difficult getting natural gravel meeting the specification for G80 base material. However, there is significant improvement when a relaxed specification of G60 is used. This indicated grading plays a very important part in deciding whether a natural gravel material meets specification or not. Generally Western Region had the greatest difficulty of meeting grading requirement. The overall proportion of samples meeting the requirements of subbase and base are 26% and 2% respectively. It is almost impossible to find a natural gravel pit meeting the requirements of Otta seal without processing. Most natural gravel in the country will need two cycles of screening for them to meet the gradation requirement for Otta seal.
A Thesis Submitted to the Department of Civil Engineering, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirement for the award of the Degree of Master of Science, 2008