Efficacy of Various Accelerated Carbonation Techniques to Improve Recycled Concrete Aggregates: A Comprehensive Review

This study presents a critical review to evaluate the comparative efficacy of different accelerated carbonation techniques used to improve the properties of recycled concrete aggregates (RCA). Four different accelerated carbonation methods practised in the published research are standard accelerated carbonation (SC), pressurized accelerated carbonation (PC), flow through accelerated carbonation (FC) and wet carbonation (WC). These methods are comprehensively discussed and their effects on the physical and mechanical properties of carbonated RCAs are evaluated. The properties of carbonated aggregates such as porosity, water absorption, density, aggregate crushing value and compressive strength were evaluated with various carbonation parameters such as duration, pressure, gas flow rate, and particle size. Comparison of the methods revealed that wet carbonation achieved optimal efficiency in a shorter period, while standard carbonation effectively reduced porosity to a greater degree with longer carbonation duration. Longer CO2 exposure improved the effectiveness of standard, pressurized, and flow-through carbonation methods, whereas extended wet carbonation reduced performance, which is likely due to the dissolution of carbonation products in the solution. Wet carbonation is relatively simple and easy to control compared to the other methods, which needed a controlled environment for aggregate pre-conditioning and carbonation. Regarding the impact of accelerated carbonation on the properties of RCA, both positive and negative effects were observed and the underlying mechanisms behind these contrasting influences were critically analysed and discussed. While the effectiveness of accelerated carbonation depends on various factors, this study offers a comprehensive understanding of four distinct methods and their comparative performances based on the percentage improvements of different properties of RCA. Finally, some recommendations for future studies are provided based on the identified knowledge gaps.