[01] Bruce Roy Thulane Vilane, Department of Agricultural and Biosystems Engineering, Faculty of Agriculture, University of Swaziland, Luyengo Campus, Swaziland. [02] Ndlangamandla Sabelo, Department of Agricultural and Biosystems Engineering, Faculty of Agriculture, University of Swaziland, Luyengo Campus, Swaziland.

Aggregate grading is an important element in concrete mixing and the resultant compression strength. An experiment was conducted to determine the effect of aggregate size on the compressive strength of concrete. The experiment had three treatments, which were the aggregate sizes (9.5 mm, 13.2 mm and 19.0 mm) and the control. A constant mix of 1:2:4 with a water/cement ratio of 0.5 was used throughout the experiment. Tests that were conducted included the slump and compressive strength tests. Fresh concrete batches were formulated from each of the coarse aggregate sizes and the slump test was conducted to test for workability. Three cubes (150 mm × 150 mm) were cast from each batch and the compressive strength was determined using a concrete load testing machine (Pro-Ikon cube press) after 7 days curing. The results reflected that workability (slump) increased with increasing aggregate size. The concrete made from the 9.5 mm, 13.2 mm and 19.0 mm aggregate sizes had workability (slumps) of 10 mm, 13.5 mm and 20 mm, respectively. The mean compressive strength for the 9.5 mm, 13.2 mm, and 19 mm were 15.34 N/mm², 18.61 N/mm² and 19.48 N/mm², respectively. The 9.5 mm and 19.0 mm aggregates had compressive strengths that were significantly different (P<0.05; 0.034), while the 13.2 mm and 19.0 mm aggregate sizes had compressive strengths that were not significantly different (P>0.05; 0.585). It was concluded that concrete workability (slump) was directly proportional to aggregate size. The mean concrete compressive strength increased with increasing aggregates size.

Aggregate Size, Concrete, Compressive Strength

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