Engineering geological evaluation of some rocks from Akure, Southwestern Nigeria as aggregates for concrete and pavement construction

The importance of rocks and rock aggregates cannot be overemphasized in construction and concrete design globally. This study evaluated the physical and mechanical characteristics of fine grained granite, porphyritic granite, quartzite, granite gneiss, migmatite gneiss and charnockite from ten different locations in Akure for their suitability as construction materials. Field observation, water absorption, specific gravity, shape indices, aggregate impact value (AIV), aggregate crushing value (ACV), Los Angeles abrasion value (LAAV), compressive strength, tensile strength and petrography of the selected rocks were evaluated. The field studies indicate fresh outcrops with little signs of weathering. Porphyritic granite shows a higher water absorption value >1%, suggestive of its unsuitability as foundation materials in water logged areas. The higher flakiness and elongation indices of porphyritic granite, quartzite and migmatite gneiss are detrimental to the higher workability and stability of mixes. AIV (14.79–23.52%), ACV (18.32–28.93%) and LAAV (25.22–34.55%) showed that granite, granite gneiss and charnockite have good soundness and hardness with greater resistance to wear. Higher strength values of all the rocks were found to be satisfactory for use in the production of aggregates for civil constructions. Petrographic analysis revealed similarities in the compositions of the rocks, with quartz being the dominant mineral. The results show that all the rock types possess the required quality standards for use as construction aggregates in highway pavements and foundations. Some of the aggregates (GG1, GG2, GF, GC, MG1, CK1 and CK2) are also suitable for bituminous mixes. Quartzite should be avoided in load bearing masonry units due to its lower strength values. The most suitable rocks proven as road and building stones are fine grained granite, granite gneiss and charnockite because of their low water absorption, low flakiness and elongation indices, low abrasion values, higher strength values (tensile strength and unconfined compressive strength) and sound petrographic characters. Thus, adequate knowledge of rocks and rock aggregates is crucial in order to prevent continuous structural failure around the globe and make the environment friendlier.