Mechanical and physical response of recycled aggregates high-strength concrete at elevated temperatures

The advances in concrete technology have enabled construction industry with the possibility to produce high-strength concrete (HSC) incorporating recycled aggregates. The envisaged structural applications of recycled aggregates high-strength concrete (RA-HSC) necessitates characterizing its behavior under different service conditions. Fire is among major hazards to which structures are susceptible during their service life. Therefore, characterization of the mechanical and material performance of RA-HSC at elevated temperatures is desirable. In this study, properties of HSC produced using recycled coarse aggregate (RCA) were investigated at high temperatures from 23 to 800 °C. Mechanical properties comprising compressive and splitting tensile strength, elastic modulus, and stress-strain response were investigated under different heating and test conditions. Additionally, visual observations and microstructural analysis were performed to illustrate the comparative high temperature damage to RA-HSC and natural aggregates high-strength concrete (NA-HSC). Results exhibit that the rate of drop in compressive and splitting tensile strength was lower in the case of RA-HSC compared to that of NA-HSC. Changes in the stress-strain response with an increase in temperature show that RA-HSC exhibits comparatively higher axial strains compared to NA-HSC above 400 °C. Visual investigations after exposure to elevated temperatures show that RA-HSC exhibits lower thermal cracking and fewer color changes compared to that of NA-HSC. For analytical fire resistance calculations, data obtained from high temperature material property tests was used to develop simplified equations for expressing mechanical properties of RA-HSC as a function of temperature.