Investigation of the effects of re-curing on mechanical properties of basalt-polypropylene hybrid fiber concretes after exposure to high temperature

Fiber reinforced concretes have attracted significant attention in recent decades due to their superior flexural and toughness properties compared to traditional concrete in civil engineering structures. In addition, cementitious materials can undergo significant mechanical deterioration under high temperature. Therefore, the investigation of the properties of FRC for fire-resistant design has become an important research topic in recent years. On the other hand, there is very little research on the repair of FRCs damaged by fire. In this study, high temperature resistance of mixtures prepared using basalt and polypropylene fibers was investigated. In addition, the ability of FRCs exposed to high temperatures to regain their properties by applying water re-curing process was investigated. In this context, ultrasonic pulse velocity (UPV), compressive and flexural strength of FRC series after different stages were investigated. In the use of water curing single basalt fiber, 18.56% and 13.82% increase in relative compressive strength was obtained after 600 °C and 800 °C, respectively. These increase rates were determined as 22.25% and 22.81% in relative flexural strength. Recovery was more significant in the hybrid mixture formed with 0.2% polypropylene fiber. 29.22% and 15.93% recovery was reported in relative compressive strength after 600 °C and 800 °C, respectively. It was determined that re-curing significantly increased the mechanical properties of FRC mixtures.