OPTIMUM MIX DESIGN FOR MINIMUM STRENGTH REQUIREMENT USING LOCAL AGGREGATES FROM AKURE, ONDO STATE, NIGERIA

Abstract

There is a great concern for the integrity of reinforced concrete buildings in Nigeria because of the frequency of their collapse. Concrete as a major component of reinforced concrete structures depends on its constituents for strength. This project is to characterize the compressive strength of concrete produced from bush gravel and pitsand, which are commonly used in Akure metropolis. Some practice in Akure is the use of unwashed bush gravel using ratios of 1:2:2 (for flooring), 1:2:3 (for lintel), and 1:2:4 for columns. Various mixes for unwashed and sorted (size 10 -20mm) washed bush gravels were attempted. The results gave the following trends after 28days of curing. The ratio 1:2:4 gave an average compressive strength of 12.34N/mm2 for sorted washed gravels and 12.4N/mm2 for the unwashed. For ratio 1:2:3, the compressive strength dropped to 11.56 N/mm2 for unwashed gravel while it increased to 17.56 N/mm2 with the sorted washed gravel. The result of ratio 1:2:2 showed a compressive strength of 8.89N/mm2 and 21.78N/mm2 for unwashed and sorted washed gravel respectively. Meanwhile, this investigation has highlighted the flaws and provided an improvement in the use of local aggregates in concreting. It is recommended that for heavy load bearing concreting, bush gravel should be washed and sorted.