Review on high-strength recycled aggregate concrete: Mix design, properties, models and structural behaviour

High-strength recycled aggregate concrete (HSRAC) has been extensively studied in terms of mix design, properties, models, and structural behaviour. However, a comprehensive state-of-the-art review of HSRAC is still lacking. This paper addresses this gap by reviewing studies on mix proportion design, properties (including mechanical properties, durability, microstructure, environmental impact, and economic benefits), stress-strain models, and structural behaviour. To conduct this review, we used a systematic approach, searching for research articles with the keyword "High-strength/performance recycled concrete" in several databases, including the ASCE Library, ScienceDirect, China National Knowledge Infrastructure (CNKI), Google Scholar, and Scopus. Our initial search yielded 317 articles, from which 78 were selected based on criteria including the strength of high-strength concrete (defined as cubic compressive strength f(cu) >= 60 MPa) and the type of aggregates (coarse aggregates and crushed waste concrete). Our review indicates that a simple mix proportion design method for HSRAC with optimal performance, considering mechanical properties, workability, environmental impact, and cost, is still needed. We also found that the optimal content of ordinary recycled concrete aggregates (RA) for producing HSRAC is about 30%. To enhance RA use in most structural applications and HSRAC production, its performance is typically improved by removing or strengthening attached mortar. Furthermore, the study reveals that factors like superplasticisers, steel fibres, curing methods, sand ratio, paste- to-aggregate ratio, and aggregate size have been under-examined in HSRAC studies, and that existing stress- strain models for HSRAC have limited applicability, particularly for strengths over 70 MPa. Finally, the review highlights that the structural behaviour of HSRAC is similar to that of traditional high-strength concrete (HSC). This comprehensive review provides insights into the production of HSRAC with enhanced properties, environmental and economic benefits, as well as guidance for the design of HSRAC structures. It also suggests directions for future research into HSRAC.