Flexural properties of fiber-reinforced concrete using hybrid recycled steel fibers and manufactured steel fibers

This study investigates the flexural properties of fiber-reinforced concrete (FRC) using a hybrid mix of recycled steel fibers (RSF) from waste tires and manufactured steel fibers (MSF). The aim of this study is to demonstrate hybrid steel fiber reinforcement as a more environmentally sustainable alternative to traditional single-fiber systems, by assessing whether hybrid reinforcement can achieve or surpass the performance of conventional single-manufactured steel fiber reinforcement. Using a novel four-stage methodology, this paper presents a comprehensive and detailed evaluation of mechanical and ductility performance through three-point bending tests, digital image correlation (DIC), CT-scans, and scanning electron microscopy (SEM). The results from flexural stress-deflection curves were used to evaluate the flexural strength and toughness. This was followed by an in-depth eight-stage DIC analysis and Surface Damage Index (SDI) curves throughout the test. CT-scan images were used to quantify the proportion of fibers classified as pulled-out, ruptured, or bridging the crack, while SEM analyzed the efficiency of fiber reinforcement through microstructural evaluations, further validating the findings of this study. Results show that hybrid reinforcement significantly enhances both toughness and ductility while reducing surface damage. MSFs in the hybrid system improve post-peak ductility and energy absorption by bridging large cracks, while RSFs prevent micro-cracks, increasing pre-peak rigidity. CT-scan analysis reveals that the inclusion of RSFs reduces pulled-out MSFs by 26 %, further boosting flexural performance. SEM confirms the superior bond of MSFs with the concrete matrix in hybrid samples. Additionally, higher fiber content in FRC enhances toughness and ductility while reducing surface damage. This research advances our understanding of hybrid fiber-reinforced concrete and promotes more sustainable construction practices through the use of recycled steel fibers. By leveraging the combination of new methodologies, the study effectively targets gaps in the current research landscape, offering a comprehensive approach to improving performance and sustainability in construction materials.