Can Microplastics (MPs) Replace Conventional Mineral Aggregates? A Brief Review

Microplastics (MPs) are an increasingly pervasive pollutant, prompting interest in using them as a waste valorization feedstock in cementitious composites-most commonly as partial replacements for mineral aggregates. This review critically assesses the technical feasibility and implications of this approach based on current experimental and analytical evidence. Across the literature, MPs differ fundamentally from natural aggregates in stiffness, density, and surface chemistry, which weakens particle packing and interfacial bonding. Consequently, MP-aggregate substitution typically reduces workability and compressive strength and degrades durability-related performance, including resistance to chloride ingress, carbonation, and freeze-thaw action, with adverse effects generally increasing at higher replacement levels. While isolated benefits such as reduced unit weight and occasional post-cracking responses have been reported under specific mix designs, untreated MPs usually behave as mechanically inactive inclusions and stress concentrators rather than effective reinforcement. Major uncertainties remain regarding long-term durability and the risk of secondary MP release. Overall, MP-based aggregate replacement should be considered a conditional, application-specific strategy, currently most defensible for non-structural or function-driven applications under carefully defined performance and environmental criteria.