Polymer and Steel Fiber-Reinforced Cementitious Composites under Impact Loading—Part 2: Flexural Toughness

In Part 1 of this paper, single-fiber pullout tests were described, and the bond-slip responses under impact loading were reported. Four different fiber types, including one straight polyolefin fiber, two lengths of a sinusoidally deformed polypropylene fiber, and a steel fiber with flattened ends, were investigated. In this Part 2, results from flexural tests on fiber-reinforced concrete beams with the same four types of fibers are reported. Both static and impact flexural tests were conducted. It was observed that, regardless of the loading rate, most fibers pulled out across a matrix crack. Among the three polymeric fibers tested, the longer of the two deformed polypropylene fibers was the most promising under both rates of loading. While beams incorporating polymer fibers exhibited an increase in the energy absorption capacity (or toughness) at higher rates of loading, steel fiber-reinforced beams demonstrated a drop in toughness under impact loading. Consequently, although in quantitative terms the steel fiber-reinforced concrete beams absorbed more energy than beams reinforced with polymer fibers at both loading rates, the differences diminished at higher loading rates. This was in agreement with the results of the bond-slip tests reported in Part 1, where it was shown that the pronounced viscoelastic nature of polypropylene fibers makes them particularly suitable for impact-type load applications.