A review of the advanced treatment techniques for enriching the recycled concrete aggregates for recycled-based concrete: economic, environmental and technical analysis

<p>Purpose – This study aimed to review various existing methods for improving the quality of recycled concrete</p> <p>aggregates (RCAs) as a possible substitution for natural aggregates (NAs) in concrete. It is vital as the old paste</p> <p>attached to the RCA weakens its structure. It is due to the porous structure of the RCA with cracks, weakening</p> <p>the interfacial transition zone (ITZ) between the RCA and binding material, negatively impacting the concrete’s</p> <p>properties. To this end, various methods for reinforcement of the RCA, cleaning the RCA’s old paste and</p> <p>enhancing the quality of the RCA-based concrete without RCA modification are studied in terms of</p> <p>environmental effects, cost and technical matters. Furthermore, this research sought to identify gaps in</p> <p>knowledge and future research directions.</p> <p>Design/methodology/approach – The review of the relevant journal papers revealed that various methods</p> <p>exist for improving the properties of RCAs and RCA-based concrete. A decision matrix was developed and</p> <p>implemented for ranking these techniques based on environmental, economic and technical criteria.</p> <p>Findings – The identified methods for reinforcement of the RCA include accelerated carbonation, bio</p> <p>deposition, soaking in polymer emulsions, soaking in waterproofing admixture, soaking in sodium silicate,</p> <p>soaking in nanoparticles and coating with geopolymer slurry. Moreover, cleaning the RCA’s old paste is</p> <p>possible using acid, water, heating, thermal and mechanical treatment, thermo-mechanical and electro-dynamic</p> <p>treatment. Added to these treatment techniques, using RCA in saturated surface dry (SSD) mixing approaches</p> <p>and adding fibres or pozzolana enhance the quality of the RCA-based concrete without RCA modification. The</p> <p>study ranked these techniques based on environmental, economic and technical criteria. Ultimately, adding</p> <p>fibres, pozzolana and coating RCA with geopolymer slurry were introduced as the best techniques based on the</p> <p>nominated criteria.</p> <p>Practical implications – The study supported the need for better knowledge regarding the existing</p> <p>treatment techniques for RCA improvement. The outcomes of this research offer an understanding of each</p> <p>RCA enrichment technique’s importance in environmental, economic and technical criteria.</p> <p>Originality/value – The practicality of the RCA treatment techniques is based on economic, environmental</p> <p>and technical specifications for rating the existing treatment techniques.</p>