Valorization of Waste Polypropylene, Polyethylene Terephthalate, and Bushings and Insulator Ceramics to Develop Sustainable Cementitious Composites

Continuous and increasing generation of solid waste and its effective disposal have become critical challenges, particularly in recent years. The incorporation of waste materials into cementitious mixtures offers a promising solution to divert materials from landfills. However, understanding the impact of waste materials on the properties of cementitious mixtures is essential for their large-scale adoption. This research aims to enhance our understanding of the utilization of three waste materials: polypropylene (PP), polyethylene terephthalate (PET), and ceramic electrical insulators and bushings in cementitious mixtures.The hydrophobic nature of plastics, which causes low adhesion to cement matrix, poses a primary concern for their use in cementitious mixtures. Surface treatment of plastics is an effective method to improve their hydrophilicity. This research investigates ultraviolet (UV) irradiation and bio-grafting for surface treatment. Bio-grafting is a scalable, safe, and considerably faster surface treatment method which utilizes cooking oil and microwave radiation. The benefits of increasing the hydrophilicity of plastics through UV irradiation and bio-grafting on the ductility improvement of plastic-cement composites are established through spectroscopic observation of the plastic surfaces and three-point bend tests on plastic-cement composites. UV irradiation and bio-grafting successfully improved the oxygen functional groups at the plastic’s surface, increasing its hydrophilicity. The enhanced hydrophilicity improves plastic-cement adhesion, facilitating stress transfer at the interface, resulting in a significant enhancement in the energy absorption capacity and ductility of the composite. A size effect investigation reveals an increase in transition size, fracture energy, and effective fracture process zone length, along with a decrease in the brittleness number of cementitious composites with PET modified through bio-grafting, indicating a transition from essentially purely brittle to quasi-brittle behavior. Furthermore, the assessment of the fresh, hardened, and durability properties of concrete with ceramic aggregate against reference concrete with conventional limestone aggregates demonstrates that ceramics are an effective alternative. Ceramic aggregates have no significant impact on mechanical properties but result in improved workability and durability properties in terms of chloride resistance and capillary water absorption. Overall, the research output will contribute to the valorization of some commonly landfilled materials as ingredients in cementitious mixtures, promoting waste diversion from landfills.