Influence of Quantity and Quality of Fines in Dug-up Gravel on the Performance Characteristics of Concrete

Abstract

The effects of quantity and quality of fines in the two earlier identified dug-up gravels as aggregates, on the performance characteristics of concrete were investigated. This aims at providing scientific solutions to the failure of concrete structures resulting from use of poor quality aggregates. Gravel A (Tiwantiwa) and gravel B (Majeroku) which were two major gravel sources in Ile-Ife and Ikire areas of Osun State were procured. The quantity and quality characteristics of the fines in the gravels were determined through gradation, chemical and mineralogical composition analyses. Each of the gravel was sieved into fines (? 2 mm) and non-fines (2 mm ? particle size ? 20 mm). The fines (F) and non-fine (NF) were later re-combined at varying percentages as coarse aggregate portion to make concrete cubes and beams for compressive and flexural strength tests using 1:2:4 mixes. The results showed that the gravels were absent of deleterious chemical compounds or minerals, but contained some level of impurities. At 28-day, the average compressive strength of concrete made with 0% F + 100% NF as coarse aggregate for both gravels A and B was 18.5 N/mm² and 16.1 N/mm². These values were decreasing as the quantity of fines in the coarse aggregate increased up to 100% F with 0% NF. There is good agreement between the experimental and modelled strengths. The recommended characteristic strength of concrete made with both gravels at fines content not exceeding 20%, at 28-day and 56-day curing ages are 14 and 18 N/mm² respectively.

Keywords: Dug-up gravel, fines and non-fines, compressive and flexural strengths, characteristic strength,                              failure of concrete structures, organic matters, water absorption, coefficient of determination