The project, led by researchers at the Center for Marine Debris Research at Hawaiʻi Pacific University with the Hawaii Department of Transportation and University of Hawaiʻi involvement, is testing recycled polyethylene from fishing nets and residential waste as a substitute for some petroleum-based polymer additives already used in road construction. Early findings from road dust, simulated stormwater and mechanical testing indicate that pavements containing recycled polyethylene did not release more plastic polymers than standard polymer-modified asphalt.
The findings are significant for Hawaii, where recycling is costly, landfill space is limited and marine debris poses a persistent environmental burden. Discarded fishing gear is among the most difficult waste streams to handle because nets are bulky, contaminated by salt and biological material, and often arrive from outside the islands after drifting across the Pacific. The research seeks to determine whether such waste can be locked into long-life infrastructure rather than transported, burned or buried.
Jeremy Axworthy, a researcher involved in the work, said the project examines whether recycled plastics can be responsibly used in Hawaii’s roads. The central question is not only whether the material can be added to asphalt, but whether the resulting pavement remains safe, durable and practical under tropical conditions that include heat, heavy rain and water damage risk.
Hawaii has largely relied on polymer-modified asphalt since 2020 to improve road strength and resistance to cracking, rutting and moisture. This type of pavement commonly uses styrene-butadiene-styrene, a virgin copolymer that is melted into asphalt binder before being mixed with heated rock and sand. Researchers are now testing whether recycled high-density polyethylene from local waste streams can partly replace that imported material.
The first trial sections were laid on a residential road on Oahu. The mixes included a standard control section, a section containing recycled polyethylene from Honolulu’s residential recycling stream and another using polyethylene recovered from derelict fishing nets. After about 11 months of normal traffic, researchers collected road dust and studied runoff under simulated stormwater conditions.
The team used pyrolysis gas chromatography-mass spectrometry to identify chemical signatures from different materials in the road dust. The analysis looked for styrene and butadiene from standard asphalt polymer, polyethylene from recycled plastic mixes and rubber particles from tyre wear. Microplastic-sized particles were found, but only a small share were identified as polyethylene, regardless of the pavement type.
Researchers believe the result may reflect how the plastic behaves when melted into the asphalt binder. Instead of breaking away as pure plastic fragments, particles appear to shed as a mixed material containing rock, binder and polymer chains. That distinction matters because one of the strongest objections to plastic roads has been the possibility that they may simply turn visible waste into harder-to-track microplastic pollution.
Tyre wear emerged as a much larger signal in the dust samples than polyethylene from the recycled asphalt. That finding aligns with broader research showing that vehicle tyres are a major source of road-related microplastic pollution. It also shifts attention towards the overall transport system, rather than recycled road material alone, when assessing the environmental burden from pavement use.
The project is still at an early stage. Researchers have not yet completed the long-term durability assessment needed to determine whether recycled plastic asphalt can match conventional pavement over years of traffic, storms and repair cycles. Durability will be crucial because a road material that fails faster would weaken the environmental case by requiring more maintenance, more asphalt production and more transport.
The work also highlights a wider policy dilemma. Plastic waste is often difficult to recycle profitably, especially in island economies far from major processing markets. Hawaii must handle local household plastic while also receiving marine debris carried by ocean currents. The Center for Marine Debris Research has developed removal and tracking programmes, including a bounty system that pays licensed commercial fishers to recover large derelict fishing gear before it reaches reefs and beaches.
The Bounty Project has removed tens of tonnes of large fishing gear from the Pacific, while broader clean-up work has recovered large volumes of plastic from Hawaii’s waters and shores. A single clean-up around Papahānaumokuākea Marine National Monument in 2021 recovered a 50-tonne mass of plastic waste, mostly fishing nets. Such events have strengthened calls for a system that connects detection, removal, sorting and repurposing.
If durability studies confirm the early environmental results, recycled-plastic asphalt could become one part of Hawaii’s waste strategy. It would not eliminate the need to reduce plastic use or prevent fishing gear losses at sea. But it could create a local end-use for material that is otherwise expensive to manage, difficult to export and harmful when left in marine ecosystems.
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