Methods for Improving the Microstructure of Recycled Concrete Aggregate: A Review

Concrete contribute to 33% of the total waste generated in Australia with the economic acceleration and the speed of urban development. Most of the concrete waste goes into landfills and considerably low quantity is recycled and reused as recycled concrete aggregate. Nevertheless, there are several limitations of re-using of recycled concrete aggregate, for instance high porosity, high water absorption rate, micro cracks in the interfacial transition zones. Due to those limitations, the concrete produced with recycled aggregate has low properties than the concrete made with natural aggregates. To improve the properties of recycled aggregate, many methods have been adopted. This paper provides an insight into the methods, advantages and disadvantages of methods to improve the properties of recycled aggregate, methods of autogenous healing under self-healing and autonomous healing under re-hydration, bacterial and micro-encapsulation methods, two-stage mixing approaches, which are used to increase the permeability of the recycled aggregate, which result in increased durability of the same, reduce the voids and the calcium hydroxide (Ca(OH)2) content of the recycled aggregate, to improve the nanomechanical properties of the interfacial transition zones, removal or strengthening of weak parts or weak mortar layers of recycled aggregate by, mechanical grinding, heat grinding, pre-soaking in water, pre-soaking in acid, micro-wave assisted removal of mortar, spraying of immersion of polymer emulsion, submergence in sodium silicate solution, use of fly-ash, silica fume, metakaolin and ground granulated blast furnace slag under mineral admixtures. Carbon-curing, carbon conditioning and other CO2 carbonation approaches and submergence with diammonium hydrogen phosphate solution under crystal forming approaches.