Flex Behavior of Green SNFRC Circ Beams with Double-Layers of Spirals and Uniformly Distributed Reinf

Abstract

Green Concrete has emerged as a promising sustainable alternative to Ordinary Portland Cement (OPC)-based concrete. Partial OPC replacement by Ground Granulated Blast-Furnace Slag (GGBS) promotes enhanced sustainability without adversely impacting mechanical characteristics. Macro-synthetic fibers can radically improve concrete’s post-cracking behavior. Combining the two creates Synthetic Fiber-Reinforced Green Concrete (SNFRGC). Moreover, Glass Fiber-Reinforced Polymer (GFRP) rebars address the steel reinforcement corrosion potential. This research experimentally investigated the flexural behavior of circular beams made from SNFRGC reinforced with GFRP and hybrid steel-GFRP uniformly distributed rebars in single-layer and double-layer configurations. An experimental program consisting of 18 large-scale beams of a 1,760 mm clear-span length and 260 mm cross-sectional diameter was executed. Moreover, the clear shear span-to-overall depth was 2.1 for the test beams. The average concrete compressive strength was 32 MPa reinforced with 1% by volume macro-synthetic fibers. The displacement-controlled flexural testing was conducted via a four-point loading setup. The influence of varying the following parameters was observed: (a) the reinforcement configuration (single layer vs. double layers), (b) reinforcement material (all-steel, all-GFRP, and hybrid), (c) number of longitudinal rebars (6, 12, 16, and 20), (d) spiral rebar diameter (10 and 12 mm), and (e) spiral pitch (45, 60, 65, 75, 80, 85, and 95 mm). Ductile elastoplastic behavior manifested with pure flexural and mixed flexural-shear cracks was observed for all tested specimens. Steel-reinforced beams exhibited concrete crushing failure modes subsequent to observable steel reinforcement yielding. In the GFRP-reinforced specimens, the failure mechanisms were initiated through compression concrete crushing and cover spalling followed by GFRP tension rebar rupture. The failure mechanism in the hybrid-reinforced specimens was associated with steel yielding, followed by concrete crushing and cover spalling, then GFRP tension rebar rupture. The double-layered hybrid-reinforced beams exhibited up to 33% higher load-carrying capacity than their all-GFRP reinforced counterparts. Moreover, double-layered hybrid-reinforced beams outperformed their all-GFRP reinforced counterparts in ductility; the difference ranged between 27 and 254%. The improved ductile behavior is a direct outcome of the steel rebars within the hybrid reinforcement. Hence, hybrid-reinforced beams can be regarded as a promising substitute for traditional steel-reinforced beams. This is especially important in harsh environments where such hybrid reinforcement configurations substantially enhance the infrastructure sustainability.