A rational approach to develop gradation of sustainable multi recycled aggregate using particle packing methods

Recycled aggregate has already been in use in construction industry, and research on use of multi-recycled aggregate in concrete is being actively pursued. This study investigates the potential use of three generations of recycled aggregate, by strengthening the aggregate skeleton in concrete using particle packing methods of gradation of aggregate. The gradation curves of multi recycled aggregates (MRA) developed using three particle packing methods viz., Modified toufar method (MTM), J D Dewar (JDD) and Compressible packing model (CPM) are compared with gradation stipulated for natural aggregate by Standard codes viz., Indian Standards (IS 383:2016), American society for testing and materials (ASTM C33/C33M-18) and european norms (EN 12620:2013). The particle packing methods increased the packing density of aggregates, reduced the void content and cement paste required to fill the voids in concrete. The proportions as per ASTM code yielded higher packing density compared to IS and EN codes. By juxtaposing the particle packing theories on the aggregate size fractions in various codes (for natural aggregates), it is possible to enhance packing density, reduce void ratio of recycled aggregates and the maximum cement paste thickness. This proposed methodology results in an efficient usage of recycled aggregate in developing sustainable concrete.