OCCURRENCE AND ENGINEERING GEOLOGICAL PROPERTIES OF ‘BUSH’ GRAVEL IN ADO-EKITI AREA, SOUTHWESTERN NIGERIA

Abstract

The occurrence and engineering geological properties of ‘Bush’ gravel in Ado-Ekiti Southwestern Nigeria were investigated using engineering index properties. This was done with a view to determine the suitability of the gravels as engineering construction aggregates using the physical and mechanical properties of the gravel. A generalized mapping was done to know areas where there are bush gravel in Ado Ekiti, Twenty five gravel samples were collected and subjected to laboratory analyses (Specific Gravity (SG), Particle Size Distribution (PSD), Flakiness Index (FI), Water Absorption Capacity (WAC), Aggregate Impact Value (AIV) and Aggregate Crushing Value (ACV). A set questionnaire was administered to stakeholders in construction industry based on the performance of ‘Bush’ gravel compared to Bedrock aggregate. A generalized engineering geological map of ‘bush’ gravel in Ado Ekiti area was produced based on the lateral extent to know where the gravels are mineable and un-mineable. Based on the physical and mechanical properties of the gravel, a strength characteristics map was produced to show areas in Ado-Ekiti where the gravels are acceptable for various engineering construction works such as concreting aggregate, pavement construction, and highway construction. The specific gravity of the gravel ranged between 2.51 to 2.68, Water Absorption Capacity ranged from 0.63% to 2.03% in which about 98% of the Water Absorption Capacity value conform to the recommended standard value of Water Absorption Capacity <2%, the Particle Size analysis gave gravel content varying from 79% to 99% and the sand content from 1% to 21%. (Which were presented as grading curves and they show reasonable fallout from the gradation limit and a grading curve for the gravels indicate that they are coarsely graded). The Flakiness Index ranged from 10.1% to 30.9%, Aggregate Crushing Value ranged between 21.2% to 43.7%, while the Aggregate Impact Value ranged from 33% to 60%. The analyses show that significant correlation exists between AIV and ACV with correlation coefficients (r) of 0.76, WAC and SG with correlation coefficient (r) of -0.77, ACV and WAC have a correlation coefficient (r) of 0.44, FI and AIV gave coefficient (r) of 0.42, ACV and SG gave coefficient of -0.69,SG and AIV gave coefficient of -0.56. From the results obtained, the bush gravel appeared in large deposit in the area mapped and they are available for mining. Waste proportion of the bush gravel varied from 1% to 21% with most of them falling between 10 & 15%. The market price as at early 2017 shows that bush gravel is about 44% cheaper as compared to bedrock aggregate price which makes it more economical, if bush gravel can be appropriately sieved, organic materials are removed and if they are segregated into different sizes. They will then be a good alternative to bedrock aggregate for different engineering construction works