Experimental investigation of energy absorption in fiber-reinforced ultra high-performance concrete after exposure to elevated temperatures

This study investigates the hybrid synergetic impact of using fiber reinforcements to enhance energy absorption capacity in ultrahigh-performance concrete (UHPC) subjected to elevated temperature, up to 800 °C. The study conducted 19 different UHPC formulations with steel (St), polypropylene (PP), and polyvinyl alcohol (PVA) fiber combinations. Energy absorption results showed that the highest absorption capacity (5360 N.mm) was recorded at room temperature for the combination 1 %St+ 0.2 %PVA. At elevated temperature, the best performance combinations noted were: at 200 °C, 1 %St+ 0.6 %PP (4367 N.mm); at 400 °C, 0.5 %St (5045 N.mm); at 600 °C, 1 %St (4093 N.mm); and 800 °C, 1 %St+ 0.4 %PP (1830 N.mm). Triple fibers, namely, St with PP and PVA, always performed better than their corresponding single fiber mixes at every temperature interval. The triple hybrid combination (1 %St+0.2 %PP+0.2 %PVA) turned out to be the best in all temperature ranges, producing good compressive strength (155.10 MPa at 200 °C), excellent flexural strength (19.20 MPa at 600 °C), and a relatively stable energy absorption capacity (2281 N.mm). The findings of this research show that hybrid fiber reinforcement is much superior to mono-fiber Reinforcements in maintaining the energy absorption capacity of UHPC at elevated temperatures.