Some Geological Considerations and Durability Analysis on the Use of Crushed Pyroclastics from Abakaliki (Southeastern Nigeria) as Concrete Aggregate

Samples of pyroclastic rocks from Abakaliki area (Nigeria) were subjected to geological and geochemical tests to determine the suitability and durability of the rocks as concrete aggregate. Petrographic analysis shows fine-grained texture and predominance of plagioclase (21–60 %) and shaley-muddy lithic fragment, while geochemical analysis classifies the rocks as alkaline. Analysis indicates that the pyroclastics would likely perform marginally well as concrete aggregates, especially in heavy Portland cement concrete and bituminous concrete. This is due to appreciably high values of natural moisture content, low bulk density, relative density and specific gravity, which suggests low durability, high voids and less aggregate absorption in concrete and bitumen mixes. The rocks are rated as moderate to high strength material on the basis of their unconfined compressive strength values, but are very likely to have low durability as buttressed by poor sulphate soundness test results, probably due to high amount of weak minerals. Analyses reveal that the Abakaliki Pyroclastics are not completely satisfactory as concrete aggregates source, despite their origin, texture, strength and economic availability. Hence, caution is required when they are used in concrete projects.