Flexural behavior of lightweight concrete beams encompassing various dosages of macro synthetic fibers and steel ratios

In this study, thirty-two lightweight concrete (LWC) beams were casted and tested as simply supported beams under four points' loading. The investigated parameters were the volume fraction (Vf) of discontinuous structural synthetic fiber (DSSF) and longitudinal steel reinforcement ratio (ρ). The modulus of rupture of structural LWC is low due to the weak lightweight aggregates used. Therefore, the feasibility of compensating for this shortcoming and providing post-cracking toughness characteristics using DSSF is of great interest. The behavior of each beam was evaluated in terms of cracking, failure mode, flexural strength, ultimate deflection, stiffness, toughness, and energy absorption. The results revealed measurable enhancements on majority of the aforementioned performance characteristics of LWC beams can be achieved when adding DSSF at Vf = 0.55% and 0.77%. The enhancements were attributed mainly to the effectiveness of the used DSSF in providing internal confinement/cracks arresting mechanism and toughness characteristics after cracking and even after reaching the peak strength. The experimental results of this study compared very well with predicted values using the ACI 318-14 in terms of cracking moment, service load deflection, and moment capacity.