The Effect of Maximum Coarse Aggregate Size on the Compressive Strength of Concrete Produced in Ghana

Abstract

An experiment was conducted to determine the effect of different sizes of machine crushed gneisses used in Ghana for concrete production on the compressive strength of concrete. Coarse aggregate samples of maximum sizes of 10mm, 14mm and 20mm were used to produce concrete at constant water/cement ratio of 0.63. In all the experiments, the concreting procedures and materials were kept constant whiles the maximum coarse aggregate sizes were varied. A total of 36 concrete cubes were crushed at 7, 14, 21 and 28 days to determine their compressive strengths.The results show that the smallest coarse aggregate size gave the highest compressive strength and lowest slump at constant water/cement ratio.  A regression analysis also shows that the relationship between the maximum coarse aggregate size and the compressive strength follows a polynomial with R²= 1; indicating that the model is reliable. The optimum maximum coarse aggregate size for the best compressive strength of 28 day concrete was therefore found to be 8mm for the water/cement ratio of 0.63. The analysis further shows that as heterogeneity increases the compressive strength of concrete reduces.

Keywords: Gneiss, compressive strength, aggregate sizes, slump, heterogeneity.