Waste Plastic as Partial Aggregate Replacement in Concrete: A Review of Mechanical, Durability and High-Temperature Performance

Abstract

Plastic waste has become an environmental problem because of its consumption, low biodegradability and accumulation in landfills and natural ecosystems. At the same time, infrastructure development is increasing the demand for natural aggregates used in concrete. This review examines the use of waste plastic as a partial replacement for fine or coarse aggregate and as discrete fibre, with particular emphasis on fresh properties, mechanical behaviour, durability and high-temperature performance. Published studies on polyethylene terephthalate (PET), high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene and electronic plastic waste were assessed. The literature reports reduced workability and density because plastic particles are lightweight, irregular and hydrophobic. Mechanical performance depends on plastic type, particle geometry, surface condition and replacement percentage. Low or moderate additions can improve crack resistance, tensile behaviour, impact performance and, in some cases, compressive strength; however, excessive replacement weakens the interfacial transition zone and reduces stiffness and strength. Under elevated temperatures, plastic may soften or melt, creating pores that reduce residual strength but may also release vapour pressure and limit explosive spalling. Overall, replacement levels of approximately 5–15% appear most promising. Further work is required on long-term durability, emissions, microstructure, structural elements and standardised mix-design procedures.