Evaluation of selected basement complex rocks from Ado-Ekiti, SW Nigeria, as source of road construction aggregates

The petrographical and physical properties of major Precambrian basement rocks in Ado-Ekiti, Nigeria, were evaluated with a view to determine their suitability as road construction aggregates. Fifty rock samples were collected and subjected to petrographic evaluation and laboratory tests (water absorption capacity, specific gravity, Los Angeles abrasion value, aggregate crushing value, aggregate impact value and ten percent fines, flakiness index and unconfined compressive strength). Petrographical analysis revealed that the rocks (migmatite gneiss, quartzite, granite and charnockite) were predominantly acidic, rich in quartzo-feldspathic minerals. Opaque minerals in the rock units ranged between 0.6 and 2.3 % with maximum value in fine-grained charnockite. The specific gravity of the rock aggregates ranged between 2.65 and 2.74. All water absorption capacity values conform to recommended standard value of water absorption capacity <2 %. The aggregate crushing value of the rocks ranged between 17.6 and 28.4 % with minimum from quartzite (17.60–18.40 %) and highest in migmatite gneiss (27.70–28.40 %). The aggregate impact value ranged between 11.0 and 19.0 %, with the lowest value (11.0–11.6 %) from quartzite and highest in charnockite (18.4–19.0 %). Other properties including Los Angeles abrasion, ten percent fines, flakiness index and unconfined compressive strength ranged 17.4–29.8 %, 96.96–131.63 kN, 13 and 24.9 and 138.98–167.52 MPa, respectively. Based on physical and mechanical properties of the rock aggregates in this study, quartzite, and fine-medium grained granites were considered most suitable for road aggregates production as the tests were within the acceptable limits for general road aggregates purposes. Porphyritic granite, the migmatite gneiss and charnockites showed results for which most values were outside, at the margin or slightly within the acceptable limits for general road stone purpose. The geotechnical assessment provided by this study revealed that not all the Precambrian basement rocks would yield aggregates that are satisfactory for use as road aggregates.