The increasing accumulation of plastic waste has raised significant environmental concerns, necessitating innovative recycling strategies. In the construction sector, Engineered Cementitious Composites (ECC) have demonstrated superior mechanical performance and durability through fiber reinforcement. This study investigates the partial replacement of Polyethylene (PE) fibers, a costly reinforcement material in ECC, with Polypropylene (PP) fibers to assess its impact on strength, ductility, and crack behavior. A series of four-point bending tests were conducted on Plain Concrete (PCC), ECC, and Modified Cementitious Composite (MCC) beams incorporating varying fiber contents. Experimental results showed that ECC beams exhibited high ductility and failure loads of approximately 50 kN, while MCC beams, despite improved ductility, suffered reduced load capacity (19.4–21.3 kN) and increased crack widths (up to 4.92 mm). The findings suggest that while PP fibers offer cost and sustainability advantages, their use as a direct replacement for PE significantly affects structural performance. Further research is needed to optimize fiber combinations and mix designs to enhance the mechanical properties of MCC while maintaining economic feasibility.