Author(s): Aginam C H, Chidolue C A, Nwakire C
Concrete has a far greater strength than mortar and sandcrete of the same cement: aggregate ratio. This exceeding strength is, most times, found to be triple (or more) that of mortar. Coarse aggregates, which are the interest of this study, make the difference. Three different types of coarse aggregates, with 20mm maximum size, were employed in the investigation, namely; crushed granite, washed gravel, and unwashed gravel. The grading and relative densities of the aggregates were studied. The mix ratio and water/cement ratio adopted for the study was 1:3:6 and 0.6 respectively. The target mean strength at 28 days was 15N/mm2 . Twelve concrete cubes (150mm x 150mm x 150mm) were cast for each coarse aggregate type of which four were crushed at each maturity age namely; 7, 14, 21, and 28 days. All cubes reached the target mean strength after 7 days of curing. The 28 day strengths of the concretes made with crushed granite, washed gravel, and unwashed gravel were 25.1 N/mm2 , 20.0 N/mm2 , and 16.9 N/mm2 respectively. Consequently, it was concluded that the strength of concrete depends greatly on the internal structure, surface nature and shape of aggregates.