Evaluation of recycled aggregates for sustainable flowable concrete in prestressed concrete structures

Flowable concrete (FC) is characterised by its high self-compaction ability and improved form-filling, which are important for producing high-quality concrete. Recycled concrete aggregates (RCA) are expected to grow as a sustainable alternative to natural aggregates (NA) in concrete mixes, offering environmental benefits, economic advantages, and waste reduction. RCA are representing a key path towards sustainable concrete construction. Present studies show a number of complex issues when considering their use in prestressed structural elements. characteristics of FC incorporating RCA. This review highlights the fresh, mechanical, durability, and structural performance and sustainability properties of FC. It discusses the essential aspects of using RCA in FC, including benefits, challenges, and material properties, with a specific focus on Prestressed Concrete (PSC) applications. This paper concludes that including RCA typically results in lower workability, stiffness, and durability due to the presence of adhered mortar and increased porosity. These effects can be effectively mitigated through proper design of the optimised concrete mix, treatment of the aggregates, and use of supplementary cementitious materials (SCMs). Overall, structural evaluations show that PSC structures made with moderate levels of RCA can achieve nearly the same ultimate strength and failure modes as those made with conventional concrete (CC) but typically offer lower serviceability than CC. Existing evidence for the PSC applications remains limited in scope and is largely experimental, based on laboratory experiments.