A Life Cycle Assessment of HDPE Plastic Milk Bottle Waste Within Concrete Composites and Their Potential in Residential Building and Construction Applications

Plastic waste management remains a significant global challenge, with limited recycling opportunities contributing to its status as one of the highest waste producers. In Australia, the recovery rate for plastic waste is 12.5%, resulting in a high percentage of plastics being landfilled. Common disposal methods, such as incineration and landfilling, are environmentally damaging, with incineration emitting harmful gases and landfilling causing contamination. Recycling, while preferable, faces difficulties due to contamination and infrastructure challenges. However, alternative solutions, such as integrating waste plastic into concrete, present an opportunity to both reduce plastic waste and enhance the economic value of recycled materials. This study evaluates the potential of waste plastic milk bottles (PMBs) in residential concrete by assessing their mechanical strength, environmental impact, and variability in greenhouse gas (GHG) emissions. This study demonstrated that replacing up to 10% of cement with silica fume-modified plastic milk bottle (SFPMB) waste granules maintained comparable compressive strength to traditional concrete. The addition of metakaolin to the SFPMB mix design (SFMKPMB) further improved the material’s strength by 28%. Life cycle assessment (LCA) results revealed reductions in global warming potential (GWP), human toxicity potential (HTP), and fossil depletion potential (FDP), with SFMKPMB showing the greatest environmental savings. A Monte Carlo simulation evaluated variability factors, revealing that additional transportation and energy requirements increased GHG emissions, though the SFMKPMB mix ultimately resulted in the lowest overall material GHG emissions. This study demonstrates the complexity of assessing “green” materials and highlights how material variability and energy use can influence the sustainability of waste-derived composites. Despite challenges, incorporating waste plastics into concrete offers a promising strategy for mitigating landfill waste and reducing environmental impacts, especially as renewable energy adoption increases.