Creep behaviour and post-creep compressive properties of concrete under 24-h high temperatures

Some concrete structures are exposed to the long-term high temperatures due to the special characteristics of service environment. This study attempts to investigate the creep behaviour and post-creep compressive properties of concrete under sustained high temperatures. The heating duration was set to 24 h to allow full development of high-temperature damage. Firstly, the concrete was applied initial loads before being heated. The creep behaviour of concrete at 24-h high temperatures (including free thermal strain, transient thermal strain and short-term creep) was tested. Subsequently, the concrete was continued to be loaded until failure without unloading. The variation patterns of post-creep compressive strength, peak strain and stress-strain curves of concrete were analysed. Furthermore, an innovative four-phase stress-strain relationship model for concrete at high temperatures considering creep was established and validated. The results show that preload contributes to the maintenance of compressive strength of concrete at high temperatures. The higher the temperature, the more pronounced is this beneficial effect. The peak strain of concrete does not vary monotonically with increasing temperature due to the creep. At initial stress levels of 20%, 40% and 60%, the peak strain decreases, remains basically unchanged and increases with increasing temperature, respectively. The developed stress-strain relationship model can accurately reflect the compressive behaviour of concrete with preload at sustained high temperatures.