Assessment of concrete strength by comparing river and manufactured sand used in Jimma area.

Abstract

In ordinary structural concretes the aggregate constitutes 60 to 75 percent of the volume of hardened mass. Aggregates, which majority of them occurs naturally, are subjected to a wide range of variability and quality problems. Thus by assessing the quality of the aggregate we can say a lot about the quality of the concrete produced by it. Fine aggregate constitutes 30 to 40 percent of the overall aggregate volume available in the hardened concrete. With this in mind this study focuses on the assessment of fine aggregate material available in Jimma area to satisfy the requirements for compressive and tensile strength of concrete. Mostly used fine aggregate materials in Jimma town are natural and manufactured sand. Thus experiment has been undertaken to investigate the suitability of both types of fine aggregate materials to produce C-25 and C-30 concrete. Initially samples were taken from natural and manufactured sand and checked if they can satisfy physical requirements set by different standards. Then five combinations of natural sand and manufactured sand at an interval of 25% replacement (i.e. 100 NS +0 MS, 75 NS + 25 MS, 50NS + 50MS, 25NS + 75MS and 0NS+100 MS) were prepared for C-25 and C-30 grade concrete. The properties of these mixes were assessed both at the fresh and hardened state. The test results showed that for both, C-25 and C-30 concrete grades, the concrete mix with 50%MS+ 50% NS achieved a higher compressive strength than using with other proportions of manufactured and natural sand. But the manufactured sand has a gradation problem which is due to the lack of controlled production procedure and quality inspection. The mix proportion with 100% natural sand showed compressive and tensile strength below the requirements for C-25 concrete grade.