Treated recycled coarse aggregate concrete: A new mixture proportioning method based on packing densities

Abstract

In this paper, recycled coarse and fine aggregate collected from concrete rubble are treated with acid to remove the adhered cement mortar on the aggregates. These treated recycled aggregates both in fine and coarse aggregates are used to prepare concrete with water-cement ratio of 0.55 based on newly developed mix design method using packing densities. In this study two different recycled coarse aggregate sizes of 10 mm (40 % by mass fraction) and 20 mm (60 % by mass fraction) are used for various replacement levels of natural aggregates. The ratios of aggregates mixture of CA20, CA10 and FA are 38.4:25.6:36.0 by mass. For various packing densities, the recycled aggregates content is evaluated. Quantities for recycled aggregate concrete mixes made with 100 % recycled fine aggregate (RFA) and various replacement percentages of recycled coarse aggregate (RCA) for 0.55 w/c ratio are arrived at. Workability of concrete made with 100 % RFA in terms of slump (mm) can be enhanced by adding 5 % GGBS by mass of cement. Compressive strengths of concrete made with 0 to 100 % replacement of treated recycled fine and coarse aggregate ranges from 27.21 to 19.05 MPa. But when cement or silica fume is added to the recycled aggregate concrete then the compressive strengths are comparable to that of concrete made with natural aggregates.