Circular Concrete Technology: A Review of Recycled Plastic Fiber Reinforcement in Cementitious Composites

The exponential increase in global plastic waste has urged researchers to explore sustainable construction materials that align with the circular economy. This review provides a comprehensive analysis of the use of recycled plastic fibers (RPF) as reinforcement in concrete. Various forms of RPF—including polyethylene terephthalate (PET), polypropylene (PP), high-density polyethylene (HDPE), and mixed waste plastics—are evaluated for their effects on the fresh and hardened properties of concrete. Circular concrete technology, integrating recycled materials into cementitious systems, presents a viable pathway toward carbon reduction and waste valorization. This review focuses on the use of recycled Polyethylene Terephthalate (PET) fibers in concrete as a sustainable reinforcement alternative. Optimal fiber addition between 0.5% and 1.0% by volume enhances compressive and tensile strengths by up to 13% and 50%, respectively, due to improved crack bridging and ductility. Beyond performance benefits, PET fibers contribute to reduced landfill waste and embodied energy, promoting material circularity in construction. The influence of fiber type, geometry, aspect ratio, and dosage on mechanical strength, crack resistance, and durability is summarized. Additionally, microstructural interactions, interfacial transition zone (ITZ) characteristics, and long-term performance are discussed. Challenges related to fiber dispersion, bond behavior, and standardization are highlighted, along with recommendations for future research. The review concludes that RPF integration not only enhances concrete toughness and crack control but also offers a sustainable approach to waste management and resource conservation. The review concludes by identifying research gaps in durability, life cycle assessment, and field-scale implementation to fully embed PET-based concrete into sustainable infrastructure systems.