Shear capacity of sustainable ultra-high performance concrete beam reinforced with macro synthetic fiber as a sustainable alternative for stirrups and steel fiber

The research aims to investigate using macro-synthetic fibers as a sustainable alternative to the traditional shear reinforcement (stirrups and steel fibers) in the development of sustainable ultra-high-performance concrete beams. This research also contributes to global efforts to combat climate change by creating sustainable cities with green structures, durable, lightweight, have very long service life, and required low maintenance. Twenty-six trial mixtures were prepared with a 234 cubes (50 mm) under heat curing at 90° for three days to achieve a compressive strength of around 150 MPa. Fourteen simply supported UHPC beams with dimensions (100 *150 *1150) mm without stirrups were prepared and tested under four-point loading with constant (a/d = 2.3) to investigate the shear behavior related to the first crack shear load and shear carrying capacity. Four studied parameters were used: two types of macro-synthetic fibers with three-volume fraction ratios (Vf) of (0.34, 0.52, 0.69) %, in addition to a third type hybrid with steel fiber in three volumetric ratios of 1.25%, as well as three longitudinal reinforcement ratio of (0.28%, 0.034%, 0.04%). The results revealed that the shear capacity of UHPC beams with macro-synthetic fibers in a volume ratio of 0.69% was superior to those with stirrups (8 mm every 140 mm), achieving one of the sustainable aims by replacing the stirrup steel. Also the steel fiber weight could be reduced by 56%, 42%, and 28% by hybridization it with macro synthetic fibers with (vf) of 0.69%, 0.52%, and 0.34% while maintaining an excellent shear capacity of 75%, 86% and 90%, respectively, from the shear capacity of steel fiber UHPC beams with 1,25% (vf). The shear carrying capacity increased by 17%, 53%, and 74% when the reinforcement ratio increased (0.028, 0.034 0.04) %. The small and medium volume fraction of macro synthetic fiber marginally affected the first crack load, while it increased by 27% when using a volume ratio of 69%, meanwhile, hybridization of this ratio with steel fiber improved the first crack load by 56%.