Towards sustainable recovery of waste plastics with the Australian construction industry: Transition scenarios and environmental impact evaluation

This research investigates sustainable plastic waste recovery opportunities with the Australian construction industry, addressing the critical challenge of plastic waste repurposing through viable construction applications. The study employs a methodical approach combining systematic literature review, interviews, surveys, case studies, and life cycle assessment to achieve four interconnected objectives: prioritizing construction applications for recycled plastics (RPs), identifying critical factors to facilitate plastic waste valorisation, assessing environmental impacts of high-incorporation RP applications, and developing recommendations for construction and demolition (C&D) plastic waste management. First, the research systematically evaluates and prioritises construction applications utilising RPs based on engineering properties and environmental benefits. Mechanical recycling emerges as the primary conversion method, with RPs being incorporated in three forms at optimal incorporation rate (OIR): fibres (0.25-2.5% of binder in composites), aggregates (25-60% in non-structural applications; 2.5-25% in structural composites), and melted forms (20-25% cement substitution in bricks; 50-60% in wood-plastic composites). Wood plastic composites (WPC) demonstrate the highest feasibility with mature commercialisation and optimal incorporation rates. RPs-bonded bricks show 55% less CO2 emissions than conventional cement bricks, while RPs fibre reinforcement in concrete paving reduces equivalent CO2 by 93%. Second, the study identifies market demand as the critical driver for RP adoption in Australian construction, primarily stimulated by local governments. Analysis reveals significant gaps between current plastic recycling rates (13.9%) and the 2030 national target (68%), necessitating urgent improvement measures. Major barriers include insufficient public acceptance, inadequate standards for construction applications using RPs, and limited price advantages without considering enhanced properties and extended service life. The research recommends life cycle cost analysis to demonstrate long-term economic benefits. Third, a comprehensive life cycle assessment of WPC made with recycled high density polyethylene (rHDPE) quantifies environmental benefits with primary inventory data. Production of one ton of rHDPE pellets generates 961.12 kg CO2-eq—60.58% less than virgin HDPE production and 38% below national plastic recycling emissions. South Australia's renewable energy (71% of the grid) contributes to these environmental advantages, suggesting further benefits through further renewable energy adoption. The assessment reveals that separating plastic types at Materials Recovery Facilities (MRFs) rather than at recycling plants significantly reduces environmental impacts while offering financial benefits. Importantly, the study exposes inadequacies in the widely adopted "zero burden" approach in environmental impact assessments, which underestimates the environmental impacts of products using secondary materials. Fourth, examination of C&D plastic waste management practices identifies systemic challenges: limited circular economy knowledge among project management, insufficient on-site resources (budget, schedule, space), and disconnection between project environmental responsibilities and stakeholder benefits. The research recommends enhanced training programs, dedicated resource allocation, embedding recycling criteria in tendering processes, and implementing incentive and responsibility assigning mechanisms similar to the Container Deposit Refund and Extended Producer Responsibility scheme applied to municipal wastes. This research makes significant theoretical contributions to environmental assessment methodologies and pro-environmental behavioural research while providing practical recommendations for industry stakeholders and policymakers. By establishing the foundation for sustainable plastic waste recovery in construction, the study supports Australia's transition toward circular plastic economy goals. Future rese rch directions include investigating the financial feasibility of construction applications containing RPs, improving plastic flow data management, enhancing standards for RP construction applications, and restructuring recycling operations through improved sorting capabilities at MRFs.