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

Purpose – This study aimed to review various existing methods for improving the quality of recycled concrete

aggregates (RCAs) as a possible substitution for natural aggregates (NAs) in concrete. It is vital as the old paste

attached to the RCA weakens its structure. It is due to the porous structure of the RCA with cracks, weakening

the interfacial transition zone (ITZ) between the RCA and binding material, negatively impacting the concrete’s

properties. To this end, various methods for reinforcement of the RCA, cleaning the RCA’s old paste and

enhancing the quality of the RCA-based concrete without RCA modification are studied in terms of

environmental effects, cost and technical matters. Furthermore, this research sought to identify gaps in

knowledge and future research directions.

Design/methodology/approach – The review of the relevant journal papers revealed that various methods

exist for improving the properties of RCAs and RCA-based concrete. A decision matrix was developed and

implemented for ranking these techniques based on environmental, economic and technical criteria.

Findings – The identified methods for reinforcement of the RCA include accelerated carbonation, bio

deposition, soaking in polymer emulsions, soaking in waterproofing admixture, soaking in sodium silicate,

soaking in nanoparticles and coating with geopolymer slurry. Moreover, cleaning the RCA’s old paste is

possible using acid, water, heating, thermal and mechanical treatment, thermo-mechanical and electro-dynamic

treatment. Added to these treatment techniques, using RCA in saturated surface dry (SSD) mixing approaches

and adding fibres or pozzolana enhance the quality of the RCA-based concrete without RCA modification. The

study ranked these techniques based on environmental, economic and technical criteria. Ultimately, adding

fibres, pozzolana and coating RCA with geopolymer slurry were introduced as the best techniques based on the

nominated criteria.

Practical implications – The study supported the need for better knowledge regarding the existing

treatment techniques for RCA improvement. The outcomes of this research offer an understanding of each

RCA enrichment technique’s importance in environmental, economic and technical criteria.

Originality/value – The practicality of the RCA treatment techniques is based on economic, environmental

and technical specifications for rating the existing treatment techniques.