Methods to improve microstructural properties of recycled concrete aggregate : a critical review

Recycled concrete aggregate is a demolition concrete waste, which could be an environmental-friendly building material and can be a serious contender for saving natural aggregate and reducing environmental pollution. Nevertheless, the use of the same is limited, as it has inferior qualities compared to virgin aggregate, such as low density, high porosity, high water absorption rate, micro cracks in residual mortar and at the interfacial transition zones. Thereby, the need of improving the properties of recycled aggregate is vital to enable a wider adoption of the same. This paper provides an insight into identifying knowledge gaps and as a critical review for the methods, technologies, its advantages and disadvantages for improving the microstructural and mechanical properties of recycled aggregate, such as self-healing methods of re-hydration, bacterial and micro-encapsulation, sequential mixing approaches, removal of adhered mortar, permeation of solutions, coating with solutions and CO2 carbonation approaches. The existing studies to improve the properties of the recycled aggregate, are limited and the density improvement techniques by permeation of chemicals and/or reactions have only been superficially studied.