Transient creep strain of fly ash concrete at elevated temperatures

Accurate modelling of transient creep strain (TRC) is crucial for reliable fire performance assessments of concrete structures, since it is the largest strain component for structural concrete subjected to thermal exposure. Nonetheless, the mechanism underlying TRC is still not fully understood and most of the available models were established based on ordinary Portland cement concrete. As the most widely used supplemental cementitious material, the effect of fly ash on the development of TRC still requires further study. For this paper, steady state tests and transient state tests were carried out on ordinary Portland cement concrete (CEM I 52.5 as per BS EN 197-1, water/cement = 0.5) and fly ash concrete (class F fly ash as per BS EN 450-1, 25% replacement percentage), respectively. It was found that replacing 25% ordinary Portland cement with class F fly ash in concrete can mitigate the development of TRC above 400°C. Based on the experimental results, one assumption of the influence mechanism of class F fly ash on TRC is made and a TRC model for fly ash concrete (class F, 25% replacement percentage) at elevated temperatures is proposed.