Effects of Maximum Size of Coarse Aggregate on Compressive Strength of Concrete

Abstract

Concrete is one of the commonly used construction materials throughout the world. Concrete is essentially a mix of coarse aggregate, fine aggregate and cementing materials. ACI method of concrete mix design is one of the widely used methods for proportioning quantity of coarse aggregate, fine aggregate and cementing materials in concrete. According to ACI method of mix design, the volume of coarse aggregate requires to proportion per unit volume of concrete depends on the size of the coarse aggregate and the fine aggregate gradation, expressed in terms of fineness modulus. But the strength and durability of concrete depends on aggregate size distribution (gradation) rather than maximum size of aggregate. In this thesis effects of coarse aggregate size on compressive strength of concrete are examined. The maximum sizes of coarse aggregate are chosen as 3/4 and 3/8 inch for mix design. The design strength of concrete is assumed 3000 psi and water cement ratio of 0.68 on the basis of design strength. The concrete is also assumed non-air-entrained type. The workability of concrete expressed as slump istaken 1-2 inch. The fine aggregate used in this experiment has fineness modulus of 2.5. Ordinary Portland cement is used as cementing material. Two sets of concrete cylinder are prepared with ACI mix design ratios and tested at 28 days. The average compressive strength of 3/4 inch and 3/8 inch aggregates are found 2471 psi and 2518 psi respectively. Experimental results have revealed that, maximum sizes of coarse aggregate have very little effects on compressive strength of concrete.