Enhancing the quality of recycled coarse aggregates by different treatment techniques—a review

Generation of solid wastes due to industrialization and urbanization results in dumping of wastes in landfills causing contamination of soil, air, and water. One of the important solid wastes is construction and demolition wastes generated during destruction of engineering structures. These wastes reduce the percolation of rain water that recharges the underground water level table and affects the integrity of the environment. In recent times, concrete fractions recycled from the construction wastes have been used as an alternative to fine and coarse aggregates. However, the adhered mortar on the surface of recycled aggregates possesses micro-cracks resulting in the higher water absorption compared to the natural aggregates. Removal of adhered mortar and densification of micro-cracks on the surface of recycled aggregates are performed through various treatments to enhance the quality of recycled aggregates. This paper reviews various treatments and processing techniques to improve the quality of aggregates recycled from the construction wastes for its efficient utilization in the concrete. The review on various literatures infers that the microbial treatment to recycled aggregates was more effective in improving the properties of the concrete. Microbial treatment precipitates dense CaCO₃ crystals that clog the micro-cracks on the adhered mortar and reduces the porosity of the recycled aggregates. It is also observed that several advanced concrete mixing techniques strengthen the weaker interfacial transition zone (ITZ) in the recycled aggregate concrete without any additional surface treatments to recycled aggregates.