Influence of Petrogenesis on Suitability of Some Pelitic Rocks as Construction Aggregates in South-Eastern Nigeria

Ten rock samples, collected from five studied Albian rock quarry units, were subjected to hand specimen and X-ray diffraction studies to determine their petrography and also to two degradability test versions of soaking and drying to simulate their resistance to intra-seasonal and inter-seasonal weathering that occurs in south-eastern Nigeria. Nine of the samples, which are pelitic in composition, were further subjected to Los Angeles abrasion (LAAV) and aggregate impact value (AIV) tests to determine their mechanical properties. Field and petrographic studies revealed that the quarry units are made up of rocks of varying petrogenetic origins namely: hydrothermal alteration of pelites and volcanic bomb, contact metamorphism of pelites, low-grade regional metamorphism of pelites and volcanic/igneous activity. Results of the degradability tests revealed that the rocks that formed through regional metamorphism of pelites showed significant deterioration (≥1 %) in both short soaking/partial drying and long soaking/complete drying test while three of the hydrothermally altered pelites that contain sizeable amount of soluble minerals, showed significant deterioration (≥1 %) in only long soaking/complete drying test. Results of the LAAV and AIV tests showed that all the rocks satisfy the mechanical property criteria for construction of all sections of pavements. However, a combination of the petrographic, degradability, LAAV and AIV test results reveal that the regional metamorphosed pelites are not suitable for construction of base and wearing surface of pavements and structural concretes. The results also reveal that only the contact metamorphosed pelites and hydrothermally altered volcanic bomb are suitable for construction of all types of civil engineering structures.