Exploring the physical and mechanical characteristics of multi-generation recycled aggregate concrete at equivalent compressive strengths

Abstract

The concrete industry has been responsible for significant depletion of natural resources and at end-of-life significantly contributes to global waste production. To date experimental studies have typically explored the use of single generation recycled aggregates (RA) in concrete production, however, to move towards a circular economy the concrete industry needs to embrace the use of multi-generation recycled aggregate concrete (MGRAC). In this paper the physical and mechanical performance of 45 concrete mix designs over 4 generations of concrete production is explored. At each generation a series of mixes are conducted at various water to cement ratios (w/c) and with a range of blends of virgin and recycled aggregates from differing generations to capture the impact on material properties. The physical and mechanical properties are quantified for both the aggregates and the concretes at each generation. The results show that the physical properties and some mechanical properties of the concrete and RA decrease with respect to virgin aggregate concrete and virgin aggregate but, implementing a 50% replacement of VA can slow down intergenerational degradation. Furthermore, the blending RA from a range of generations can also slow intergenerational degradation but to a lesser extent. Effective aggregate properties are determined, and direct relationships confirmed indicating potential for informed mix design based on an understanding of a few simple aggregate properties.