Abstract
Currently, the researchers' endeavors focus on the incorporation of recycled waste tires from worn-out tires, such as tires-rubber particles in the concrete mix, which contributes to solving the accumulated waste tires problem. However, the crumb rubber inclusion can result in a significant reduction in mechanical properties. Moreover, in fiber-reinforced concrete (FRC), hybrid fibers are more effective in arresting cracks macro/micro than a single fiber type. Therefore, using hybrid fiber is essential to address the problems of strength decline and sustain ability, simultaneously. To this end, this study aims to examine the impact of polypropylene (PP) fiber and steel fiber hybridization on the fracture characteristics of plain and rubberized concrete prisms to identify the fibers' optimized mixture proportion. Prism specimens, measuring 100 x 100 x 500 mm (width x depth x length) were, therefore, prepared for this purpose. The variables involve different ratios of PP fiber (0%, 0.1%, 0.175, 0.25%, 1.0%) and steel fiber (0%, 0.75, 0.825, 0.9%, 1.0%) with/without crumb rubber (1-2 mm in size) with a partial replacement ratio of 20% by volume of fine aggregate (natural sand). In experimental studies, FRC prisms with crumb rubber achieved more significant improvements in the fracture characteristics than those with/without crumb rubber. By contrast, the concrete compressive and tensile strengths decreased due to the crumb rubber replacement. The specimen, reinforced with hybrid 0.1% PP-0.9% steel fiber-reinforced rubberized concrete, produced higher levels of fracture energy of approximately 3716.6 N/m, i.e., 13 times higher than that of plain concrete. More importantly, the most significant improvement in compressive and tensile strengths has been observed for the mixture with hybrid 0.1% PP-0.9% steel fiber.