Mechanical and performance-related properties of bitumen-beneficiated indurated shale aggregates for use in road construction in southeastern Nigeria

In most developing countries, the use of marginal quality aggregates had resulted in premature distress on the road pavements not visible until years after construction. Abakaliki region is endowed with low-grade indurated shales that have tremendous potentials for use in road construction but require beneficiation in order to improve their quality and durability before use. It is, therefore, necessary to develop process of improving the aggregate properties to achieve satisfactory results. This study presents results of laboratory testing of the physico-mechanical properties of shales and when treated with bitumen. The concept was based on the principle of using coating process on the aggregates with a bituminous film. The aggregates can be rendered water-proofed so that their strength in dry condition could be retained even after wetting. The results of mineralogical and chemical analyses revealed that the shales have no remarkable differences in their mineralogy with predominance of quartz, clay minerals, and feldspar and high silica, aluminum, and alkali content, respectively. The strength and resistance to abrasion attrition of the aggregates were critical factors that determined the quality of the aggregates. The aggregates when tested in dry condition performed marginally when compared with standard criteria as the presence of moisture further downgrade the aggregate properties. When beneficiated, bituminous materials reduced the aggregate absorption capacity by blocking the capillaries within the aggregates with hydrophobic film, and increased the aggregate resistance against weathering. The treated aggregates showed potential for appreciable gain in strength which qualifies the aggregates for use as road construction.