The behaviour of recycled aggregate concrete at elevated temperatures

Recycled concrete aggregate (RCA) obtained from crushed concrete has different properties than those of natural aggregate. A considerable number of investigations have been conducted on the physical and mechanical properties of RCA concrete. However, little attention has been directed at studying the performance of concrete made with RCA at elevated temperatures, despite the fact that coarse aggregates play an important role in the behaviour of concrete under fire exposure. In this paper the compressive behaviour of RCA concrete exposed to high temperatures is compared with that of conventional concretes made with two different natural aggregates: river gravel and crushed limestone. The concrete specimens were heated under four different temperatures: 20°C (ambient temperature), 250°C, 500°C, and 750°C. The residual compressive and tensile strengths, moduli of elasticity, damage and failure patterns of concretes were observed and analyzed. The results indicate that RCA concrete exhibits good performance under elevated temperatures. No spalling or disintegration was observed when RCA concrete was heated up to 750°C. The ratios of residual to initial compressive and tensile strengths of RCA concrete were greater than those of river gravel concrete under all elevated temperatures. The same trend was observed when comparing RCA concrete with crushed limestone concrete at 500°C or greater. The relative residual moduli of elasticity for all concretes with the three different aggregates types showed same trends with a marginal improvement for RCA concrete at 500°C. The results presented in this paper could be directly used in the design of reinforced concrete structure consisting of recycled aggregate concrete