Abstract This study explores hybrid fibers' impact, combining steel and polypropylene fibers, on Engineered Cementitious Composites (ECC) concrete strength. Recognized for enhanced ductility, crack resistance, and tensile strength, ECC's mechanical properties are further improved through fiber hybridization. The experimental program systematically added hybrid fibers to ECC mixtures, varying content and aspect ratios. Compressive strength tests gauged resistance to axial loads, while tensile strength tests assessed parallel force resistance. The study illuminates hybrid fibers' interplay with the ECC matrix, revealing their combined impact on compressive and tensile strength. Preliminary results exhibit a significant enhancement in ECC's mechanical properties with hybrid fibers, holding implications for superior tensile strength, crack control, and durability in structural design. The study contributes valuable insights to fiber-reinforced concrete, showcasing the effective utilization of hybrid fibers to optimize ECC performance in diverse applications. In this study, three steel fiber percentages (0.5%, 1.0%, and 1.5%) with a constant 0.5% polypropylene fiber were tested at two ages (7 days and 28 days). Models displayed notable increases in compressive and tensile strength over time, but with 1.5% steel fiber, both strengths decreased with age. The higher steel fiber proportion may induce flocculation, leading to a weakened interfacial transition zone and impeding strength development.
