Residual strength and microstructure of fiber reinforced self-compacting concrete exposed to high temperatures

Abstract One of the most important processes of physical deterioration in the concrete structures is the exposure to high temperatures that influences their durability and stability during service life. Hence, due to the importance of continuous service of the structure and safety of the residents, it is necessary to identify and evaluate properties of concrete materials after being exposed to high temperature conditions. This study implemented an experimental program to evaluate the effect of fly ash, steel fibers, and curing conditions on the mechanical properties, fracture energy, and microstructure of the self-compacting concrete at high temperatures. The study also evaluated physical-mechanical properties, including compressive strength, splitting tensile strength, flexural strength, fracture energy, ultrasonic plus velocity, weight loss, and images of SEM before and after exposure at 23, 110, 200, 400, and 600 °C. Experimental results showed that the loss of compressive strength of the specimens up to 200 °C is almost insignificance, but it will be 40% and 64% when the temperature increases by 400 °C and 600 °C, respectively. The steel fibers prevent the cracks expansion and contribute to the spalling and mechanical residual strength. However, as temperature increases, the slope of the ascending part (flexural hardness) of the load-deflection curves and fracture energy decrease. Moreover, microstructure analysis represents a close relationship between mechanical properties and different cracks and pores structure of the fibers-aggregates-cementitious matrix interface. Therefore, data obtained from the results of this experimental study were used to develop models, which predict mechanical strength of fiber reinforced self-compacting concrete and provide simplified relationships as a function of temperature.