The Effect of High Temperatures on the Compression and Flexural Characteristics of Recycled Fiber-Reinforced Concrete

The objective of this experimental study is to examine the behavior of concrete reinforced with metallic fibers (CMF) and polypropylene fibers (CPPF) subjected to high temperatures, as well as the effect of temperature variations on their mechanical properties, by evaluating the residual mass loss as well as the residual compressive and flexural strength. Two optimal fiber contents were selected for this study: W = 0.2% in compression and W = 0.8% in flexure, while a control concrete (W=0%) of the same composition serves as a reference. The fibers are characterized by their mechanical strength and pull-out resistance. The concrete composition is determined using the experimental method known as the "Dreux-Gorisse" method. Compression tests are carried out on cylinders with a diameter of Ø16 cm and a height of H32 cm, while flexural tests are performed on prismatic specimens with dimensions [10x10x40] cm³. Fiber-reinforced concretes are subjected to different heating-cooling cycles, reaching maximum temperatures of 600°C and 800°C at 28 days of age. This study revealed that the residual compressive and flexural strength of fiber-reinforced concretes exposed to very high temperatures of 600°C and 800°C decreases compared to concretes not exposed to such temperatures (20°C). For all temperatures studied, concrete reinforced with metallic fibers (CMF) showed significantly higher strength than concrete reinforced with polypropylene fibers (CPPF). At 800°C, both metallic fiber concretes and polypropylene fiber concretes exhibited networks of microcracks, but no spalling occurred.