Comparative Engineering Properties of Basalt and Porphyritic Granite in Tokbet-Katul, Pankshin Sheet 190 SE, North-Central Nigeria

Abstract

This study investigates the geological characteristics and compares the engineering properties of basalt and porphyritic granite in Tokbet-Katul, Pankshin Sheet 190SE, North-Central Nigeria, to evaluate their suitability for construction applications. Field geological mapping was conducted to document lithological units and structural features. Representative rock samples were collected for petrographic analysis using polarized light microscopy and geotechnical testing including specific gravity, density, porosity, water absorption, uniaxial compressive strength (UCS), aggregate crushing value (ACV), aggregate impact value (AIV), soundness, flexural strength, and hardness tests. Petrographic analysis revealed porphyritic granite composed of quartz, feldspars, biotite, and some accessory minerals, while basalt comprised plagioclase, pyroxene, olivine, and opaque minerals. Structural analysis showed dominant NNE-SSW joint trends in granite and NNW trends in basalt. Geotechnical results indicated granite has higher specific gravity (2.95 vs 2.85), UCS (34 MPa vs 31 MPa), flexural strength (10.24 vs 9.45 MPa), and hardness (6.4 vs 6.1). Basalt demonstrated better ACV (19.15% vs 22.26%) and soundness (7.20% vs 7.45%). Both rocks exhibited very low porosity (<0.08%) and water absorption (<0.7%). Both rocks meet international standards for construction materials. Porphyritic granite is superior for high-strength structural applications requiring compressive and flexural resistance, while basalt is better suited for road aggregates and environments requiring resistance to crushing and weathering cycles. The comparative evaluation provides essential baseline data for optimal utilization of these locally available resources in engineering projects.