Determination of Optimum Characteristics of Binary Aggregate Mixtures

Abstract

To obtain an efficient and economic concrete mix, determination of the optimum proportions of binary aggregate mixtures of coarse and fine aggregates is necessary. This study was aimed at obtaining the appropriate percentages of binary aggregate mixtures that will yield optimum binary aggregate properties of maximum bulk density, minimum specific binary aggregate volume and minimum void ratio. Two coarse aggregate types (Granite Chippings & Gravel) and three fine aggregate types (River Dredged Sand, Granite Dust & Dolomite Dust) were selected to give six binary aggregate mixtures - Granite Chippings + River Dredged Sand, Granite Chippings + Granite Dust, Granite Chippings + Dolomite Dust, Gravel + River Dredged Sand, Gravel + Granite Dust, and Gravel + Dolomite Dust. Individual aggregate types were characterized and the binary aggregates mixtures were tested for both loosed and rodded aggregate conditions. From the study, the optimum coarse aggregate volume fraction that will give the maximum binary aggregate bulk density was determined for each binary aggregate mixture. Results of the study revealed that at the optimum coarse aggregate volume fraction, specific binary aggregate volume and void ratio were minimum for all the binary aggregate mixtures. Further analysis of the results showed that binary aggregate mixtures of Gravel produced a better mixture than binary aggregate mixtures of Crushed Granite and consequently likely better concrete mix. It is concluded that to obtain a concrete mix that is both economical and efficient in terms of strength, workability, durability and shrinkage, concrete mixes should be designed at the optimum binary coarse aggregate volume fraction obtained in this study.

Keywords: binary aggregate mixture, bulk density, specific binary aggregate volume, void ratio, coarse aggregate volume fraction