Recycling Polyethylene Terephthalate (PET) Bottle Waste into Sustainable Building Materials: A Systematic Review of Technical Performance, Environmental Safety and Circular-Economy

Waste polyethylene terephthalate (PET) from single-use bottles is generated in rapidly increasing quantities, yet only about 15–35% of PET bottles are recycled. A systematic search of four databases (Scopus, Web of Science Core Collection, Google Scholar and PubMed Central) returned 798 records; after duplicate removal and two-stage screening, 69 studies met the eligibility criteria, of which 28 reported the quantitative performance data that underpin the ranges extracted here. Three recycling routes were compared, namely mechanical recycling, chemical recycling (glycolysis, methanolysis, hydrolysis, pyrolysis and gasification) and enzymatic hydrolysis. PET has been added to concrete, asphalt, bricks, insulation and panels and tested for mechanical strength, physical behaviour and durability under laboratory conditions, and the associated microplastic release, leaching of antimony and phthalate plasticisers, and fire behaviour were also assessed. Costs and market barriers were examined. The evidence indicates that PET is suitable for non-structural and semi-structural applications, and that the reported dosage windows are application-specific rather than reducible to a single range: roughly 5–15% by volume as an aggregate replacement in concrete, 2–10% in asphalt on bases that differ between studies, 25–40% by mass in PET–sand bricks and 0.5–2% fibre volume fraction in fibre-reinforced mortar. Each window is an envelope across studies that differ in PET form, dosage basis, mix design and test standard, and none is a specification. Long-term field testing, standardised leaching and microplastic-release methods, and full life-cycle assessments remain the principal research and application gaps. By linking technical performance to environmental safety, evidence quality and market readiness, this review supports evidence-based decisions for sustainable, circular construction.