Macro and micro polypropylene fiber effect on reinforced concrete beams with insufficient lap splice length

For longer spans of reinforced concrete elements, design codes dictate the use of sufficient lap splice length. Insufficient lap splice length decreases the flexural strength and ductility of reinforced concrete (RC) beams, while fiber addition improves their load-carrying capacity, ductility, and durability. The main purpose of this study was to examine the effects of micro and macro fibers on the lap splice length of RC beams. In this regard, the effect of fiber addition on RC beams having insufficient lap splice length under bending test has been studied in detail. Mixtures were prepared with different fiber ratios (0.5% micro polypropylene (PP), 0.25% micro polypropylene-0.25% macro-synthetic polypropylene (MS), 0.5% macro-synthetic polypropylene by volume of concrete) and performed on half-scale RC beams with various lap splice lengths. In beams with insufficient lap splice length, the addition of MS fiber improved the energy absorption capacity at around 30% and the load-carrying capacity at about 18%, while the effect of PP was limited. Damage analysis of the beam illustrates that MS fiber addition on RC beams inhibits crack propagation and improves load-carrying capacity.