Investigation of the Effect of Weathering of Selected Charnockite Rocks in Nigeria on Its Engineering Properties

Abstract

The effect of alteration in the petrographic characteristics of charnockite on its strength, its engineering properties and transformations of the specific gravity which took place during weathering has been examined in this study. This study characterized selected samples of un-weathered and weathered charnockite rocks of Ijare, Ondo State, Nigeria. The physical properties determined were specific gravity, density, porosity, water content and water absorption while the mechanical properties investigated include the point load strength index. Results from the analysis carried out reveal: the point load index of 5.74Mpa and 3.72Mpa for unweathered and weathered samples; average uniaxial compressive strength of 136.90Mpa and 65.50Mpa for unweathered and weathered samples; slake durability of 98.80% and 97.80% for unweathered and weathered sample; Schmidt rebound value of 49Mpa and 45Mpa for both the unweathered and weathered samples respectively. The rock samples were also subjected to petrographical analysis whose result shows that weathering increases some investigated physical properties like porosity, water content and water absorption of the rock while decreasing the specific gravity and density. The result of the tests shows the bulk and dry densities increase for both the weathered and unweathered samples; increased degree of weathering equally results in a major reduction in the strength of the charnockite rock which is directly associated with changes in mineralogy and associated porosity. The point load strength, uniaxial compressive strength test and rebound hardness result values decreases because of weathering. Weathering processes also affected the physical properties of rock, mineralogy, chemical composition as well as the mechanical properties of the rock thereby reducing the strength and mechanical behavior of the rock materials.