Dual mitigation of extruded plastic sack waste in green concrete via microsilica and recycled polypropylene fibers

The accumulation of industrial packaging waste poses a severe environmental threat. To promote a circular economy, this study investigates valorizing extruded plastic sack (EPS) waste as a partial aggregate replacement in concrete (5–20% by volume). A dual-mitigation strategy using waste polypropylene (PP) fibers (0.5%) and microsilica (10%) was employed to offset the anticipated mechanical deficiencies of the smooth-surfaced plastic. Specimens were tested for mechanical strength, water absorption, and workability. Results indicate that increasing EPS replacement significantly decreases mechanical performance due to a weak interfacial transition zone (ITZ); at 20% replacement, compressive strength fell by approximately 78%. However, the dual-mitigation strategy proved effective: microsilica refined the bulk matrix via pore-filling and pozzolanic reactions, while PP fibers bridged microcracks initiated at the EPS surface. The optimal composite (5% EPS, 10% microsilica, 0.5% fibers) not only recovered the compressive strength loss but exceeded the control specimen’s tensile and flexural strengths by 3.6% and 15%, respectively. This approach successfully transforms a brittle, waste-laden matrix into a ductile, eco-efficient composite suitable for semi-structural applications.