Drop Weight Impact Resistance and Energy Absorption Capacity of Ultra-High-Performance Concrete Containing Steel and Polypropylene Fibers

Ultra-high-performance concrete (UHPC) incorporating steel fibers and polypropylene fibers was investigated to assess its workability, mechanical properties, and impact resistance. A significant reduction in flow was observed with increasing fiber content, with a 23.9% for steel fibers and 26.9% decrease for PP fibers as the content increased from 0% to 1.5%. Density showed an increasing trend with steel fiber content, while ultrasonic pulse velocity (UPV) exhibited a decreasing trend. In contrast, polypropylene fibers had a negligible or slightly decreasing effect on density and UPV. Mechanical properties improved with increasing fiber content. Compressive and tensile strength exhibited an increasing trend for UHPC containing steel and polypropylene fibers. However, polypropylene fibers caused a slight reduction in compressive strength, while flexural strength improved with increasing fiber content up to 1.5%. A drop-weight impact test was conducted to evaluate impact resistance parameters, including the number of blows, energy absorption, and toughness. UHPC containing steel fibers demonstrated superior impact resistance compared to UHPC with polypropylene fibers. The number of blows required for failure, impact resistance, energy absorption, and overall toughness were significantly increased with steel fibers. The study concludes that while both fiber types improve certain properties, steel fibers provide greater strength and impact resistance enhancements, making them more effective for applications requiring high durability and toughness.