Performance of high-volume fly ash concrete after exposure to elevated temperature

The purpose of the present research is to investigate the sustainable performance of fly ash concrete at elevated temperature. Initially, the optimum level of cement replacement with class F fly ash was determined. The concrete mixes, i.e., plain concrete (0% fly ash), 25% fly ash, and optimum level of cement replacement with fly ash (i.e., 40%), were chosen to determine the residual compressive strength of concrete after a single heating-cooling cycle of elevated temperature ranging from ambient to 400 °Cat an interval of 200 °C under unstressed and stressed conditions. The microstructure by scanning electron microscopy (SEM) was also examined for all the concrete mixes. During the heating-cooling process, the hysteresis loop at 400 °C is found larger than the hysteresis loop at 200 °C and ambient temperature. The 40% fly ash concrete showed a lower reduction in the residual compressive strength after heating at 400 °C under the unstressed condition. The 40% fly ash concrete has shown maximum residual compressive strength than 25% fly ash and plain concrete after heating at 200 °C and 400 °C under the unstressed and stressed conditions. The SEM analysis indicates a massive change in the morphology at 400 °C for plain and fly ash concrete mixes.