Influence of coarse aggregate grading types on the cost of concrete

Abstract

The effects of grades of coarse aggregates on the cost of concrete was studied. Several times in real life practice, the engineer at construction site is faced with the problem of not having the required grade of coarse aggregate for a given project. . This could be caused by several reasons such as; non-availability of desired grade, the different grades of coarse aggregate being obtained as a left over from a sister project, etc. In Nigeria, coarse aggregate for concrete is very expensive and thus, the engineer will think of how to use the available grade of coarse aggregate in his concrete mix design to achieve the desired results instead of discarding it. In this study, seven different grades of coarse aggregate were investigated. The fineness modulus of the fine aggregate and bulk densities of the various grades of coarse aggregate were determined. The results were used together with tables from American Concrete Institute (ACI) code to carry out concrete mix design on all the various grades of coarse aggregate to calculate the quantities of the different elements of concrete. From the mix design, the cost of the materials for producing one cubic meter of concrete was determined. The result showed that the Well graded aggregate had the highest bulk density of 1717Kg/m³ while uniformly graded retained on 10mm sieve had the least bulk density of 1580Kg/m³. Uniformly graded aggregate retained on 10mm sieve required the highest cost of N58,278.81 to produce a cubic meter of grade 25 concrete while the cost was least at N56,242.52 when uniformly graded retained on 20mm sieve and Gap-graded without 5mm size were used. This suggests that the larger the size of coarse aggregate (within the size limits studied) the less the cement paste required and hence the less the cost.