PHYSICOMECHANICAL CHARACTERISTICS OF CHARNOCKITIC ROCK OF AKURE, SOUTHWEST NIGERIA

Charnockitic rock is one of the varieties of crystalline rocks that dot the face of the earth. Its reputation for aesthetics tends to impact a high economic value on it. This warrants more understanding of its petrographical, physical and mechanical parameters. Its field and petrographic relationship in Akure area has been reported but the physico-mechanical characteristics have not enjoyed discuss and reportage. Its petro-physico-mechanical characteristics were therefore studied so as to improve on the knowledge and understanding of the rock type in general and that of Akure area in particular. Petrographical analysis of the photomicrographs of the thin sections were analysed with the aid of ImageJ. Instron Universal Tester was used to determine the uniaxial compressive strength (UCS) while Schmidt Rebound Hammer and Roclab software were used for its estimations. The abrasion tester was used to determine the abrasion resistance (Ha) while the aggregate impact value (AIV) apparatus was used for the aggregate impact value. The results showed that mineralogically, the rock consisted of the following as major mineral: Plagioclase, biotite, quartz, hypersthene, hornblende, muscovite and orthoclase with the following respectively as modal composition: 32%, 16%, 16%, 16%, 11%, 4%, 3%, 1% and 1%. A value of 2.81g/cc was determined as the density while the Porosity, AIV and Ha were respectively 0.03, 11 and 33.40. The Young’s Modulus was evaluated to be 10.4KN/mm. The values of UCS from Instron Universal Tester, Rebound Value and Roclab were respectively 86MPa, 82MPa and 165MPa. Conclusively, the results of the petro-physico-mechanical tests on the rock samples corroborated one another with an indication of high physical and mechanical strength although the UCS was discovered to have been lowered by the observed microstructural characteristics.