Suitability of Natural Gravels in Ghana for Otta Seal Construction

Abstract

Otta seals are bituminous chip seals constructed to upgrade low-volume gravel roads to surfaced standards using natural gravel or crushed rock containing some amount of fines for the seal coat. Currently, the Department of Feeder Roads in Ghana is piloting Otta seal field trials as a precursor to a more extensive application of the technology nationwide. However, the success of the application will depend on the availability of natural gravel of the required quality to support the construction. This study evaluated natural gravel samples from over 150 gravel deposits distributed throughout Ghana to establish their suitability for Otta seal construction. Particle size distribution, strength of the coarse particles, and the plasticity of the fines were used to assess the gravels in line with Otta seal requirements. Most (about 80%) of the gravels met strength requirements measured by the 10% Fines Value (both dry and wet) but failed Otta seal grading and Atterberg limits requirements. However, after the gravels had been screened to remove out-of-specification sizes and reduce the quantities of fractions with excessive contents, about 75% met Otta seal requirements. On average, screening did not result in more than 32% wastage in gravel quantity. It is recommended that the amount of gravel wastage must be factored into the cost of materials for costing of the construction.