CO2-treatment of recycled concrete aggregates to improve mechanical and environmental properties for unbound applications

Concrete is the most significant building material worldwide due to its excellent mechanical properties and durability. In this regard, recycling and reusing the demolished concrete as new construction materials can greatly contribute to achieving sustainable development. One of the most promising ways to reuse such waste concrete is to produce recycled concrete aggregates (RCA). However, using RCA may bring some drawbacks, such as lower density, lower elastic modulus and strength, and a higher water absorption capacity. In the meantime, a strategy of RCA carbonation using carbon dioxide (CO2) to improve the mechanical properties and durability of RCA has emerged. In this study, the carbonation effect was investigated further for unbound applications of RCA with an emphasis on the two aspects - mechanical and environmental improvement of RCA by the CO2-treatment. Crushing value and column leaching tests were conducted for the original and CO2-treated RCA specimens for this purpose. The aggregate crushing value (ACV) was dropped by more than 2% points between the original and CO2 treated RCA, which demonstrates the strength improvement by the carbonation using CO2. The analysis of leachate water from the original and CO2-treated RCA specimens also showed remarkable changes in the concentrations of major elements. In particular, the concentrations of certain heavy metals, such as As and Cd, were reduced by about 50% from their original values after the CO2-treatment. Those results suggest that the carbonation by CO2-treatment can potentially not only improve the mechanical properties of RCA but also alleviate the environmental concern of using RCA for unbound applications, such as aggregates for base course and fill materials. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Research has shown that carbonation treatment of recycled concrete aggregates (RCA) with carbon dioxide (CO2) can significantly improve their mechanical properties and alleviate environmental concerns related to their unbound applications.