Post-High-Temperature Exposure Repeated Impact Response of Steel-Fiber-Reinforced Concrete

The response of plain and fibrous concrete to the scenario of fired structures exposed to repeated impacts from falling fragmented building elements and other objects is experimentally investigated in this study. The experimental program included the casting and testing of specimens with 0%, 0.5%, and 1.0% hooked-end steel fibers (SFs) under the ACI 544-2R repeated-impact test. The impact test was conducted using cylindrical disk specimens, while 100 mm cubes were used to evaluate the residual compressive strength and weight loss. From each mixture, six disks and three cubes were heated to high temperatures of 200, 400, and 600 °C, while a similar set of specimens were tested without heating as a reference group. The results show that SF could significantly improve cracking impact resistance and dramatically boost failure impact numbers. The retained percentage improvements were the highest for specimens heated to 600 °C, which were approximately 250% at the cracking stage and 1680% at the failure stage for specimens with 1.0% SF. The test results also show that the repeated-impact resistance dramatically deteriorated at high temperatures, where the maximal residual cracking and failure impact numbers after exposure to 200, 400, and 600 °C were approximately 20% and 40%, 4% and 7%, and 2.2% and 4%, respectively.