Impact of Aggregate Gradation on Properties of Portland Cement Concrete

2013PDFTech ReportRangaraju, Prasada RaoBalitsaris, MarcusKizhakkumodom, HarishClemson University. Department of Civil EngineeringUnited States. Federal Highway AdministrationSouth Carolina. Dept. of TransportationSouth CarolinaPortland cement concreteAggregate gradationSpecificationsCompressive strengthModulus of elasticityPerformance testsCoarse aggregatesFHWA-SC-13-03SPR 689Increasingly, aggregates in South Carolina are failing to meet the standard requirements for gradation for use in portland cement concrete. The effect of such failed aggregate gradations on concrete properties and the consequent effect on short- and long-term performance of the structures are poorly understood. Furthermore, a rational basis to accept or reject concrete containing such out-of-specification aggregate is not available at the present time. The goal of this project was to provide SCDOT with guidance on determining whether concrete containing aggregate with an out-of-specification gradation should be accepted or rejected. The principal objective of this investigation was to study the influence of variations in aggregate gradations on selected properties of concrete. The experimental methodology for this research study consisted of using aggregates size fractions that are sieved into individual size fractions and recombining them in definite proportions to create a range of gradations, some within the bounds of the acceptable gradation (Control-1, Control-2, Control-3) and some out-of-specification gradations. Concrete specimens were prepared with such aggregate gradations and a range of fresh and hardened properties of concrete were evaluated. Results from these studies indicated that deviations in fine aggregate gradation from the Control-2 gradation had relatively larger influence on properties of concrete compared to coarse aggregate. Also, the differences in gradations of aggregates within control gradations (i.e. between Control-1 and Control-3 gradation) had more significant influence on properties of concrete, compared to the out-of-specification gradations. In general, the effects of deviations in gradations from the Control-2 gradation had minimal influence on compressive strength and modulus of elasticity of concrete. However, properties such as slump of fresh concrete, split tensile strength and rapid chloride ion permeability were more significantly influenced by the deviations in the gradations.95