Influence of Mineralogy and Fabric on the Engineering Properties of the Miango Granite Porphyry, North Central Nigeria

Abstract

The major problem associated with the use of rock aggregates in engineering construction, is the difficulty of predicting their probable field performance. This is mainly due to the inadequate understanding of the decisive factors that control their engineering behavior. The mineralogy and fabric of the Miango granite porphyry was studied to assess their influence on engineering properties. The uniaxial compressive strength and aggregate crushing values show that the rocks are weak while other tests such as aggregate impact strength, water absorption, and absorption under saturation, soundness and specific gravity values are fairly good. However, thin section studies revealed three distinctive features which greatly influence the physico-mechanical properties: (a) abundant fractures of varying sizes (b) Sericitization of the orthoclase and or plagioclase feldspars (c) intergrowth of quartz and or orthoclase feldspars. The quartz grains shows extensive cracking which further reduces their mechanical strength. The strength loss of the granite porphyry could be attributed to the presence of the fractures on the quartz grains and the sericitization of the orthoclase and plagioclase feldspars. Geotechnical characterization of the rocks shows that they can be utilized as roadstone or could be polished and used as facing stones because of their non disintegration to sulphate attack and the large feldspar phenocrysts in the rock.