Hawaii Is Finding A Clever Solution To Recycle Ocean Plastic

Hawaii may be known for its gorgeous beaches and crystal-clear waters, but the U.S. island chain happens to lie within the North Pacific Gyre, a huge system of circulating ocean currents that transports marine debris across the Pacific, concentrating it in certain areas. It means that Hawaiian islands like Oahu and Maui find themselves exposed to large amounts of marine debris carried by ocean currents, containing everything from fishing nets and ropes to bottles and food packaging. Intriguingly, some of the plastic waste polluting Hawaiian waters is now being tested for use in the state's road construction projects.

Since 2020, Hawaii has been using polymer-modified asphalt (PMA) for road construction. The material contains synthetic polymers that help make roads more resistant to damage from cracking and rutting. Researchers are now investigating whether some of these virgin polymers can be replaced with recycled plastic, including the material that's been removed from Hawaii's marine environment.

The project has so far involved using polyethylene, a type of synthetic polymer, recovered from items like household waste and discarded fishing nets. The plastic is processed and incorporated into the asphalt binder before the road is laid, giving waste that might otherwise end up in landfill, or potentially break down into nanoplastics in the ocean, a more useful existence in road infrastructure. Another benefit is that using recycled plastic reduces the need to produce and process virgin polymers, which should cut energy use and emissions linked to their production.

Initial tests of asphalt containing recycled polyethylene have shown promising results regarding resistance to rutting, while the findings on cracking resistance remain inconclusive. It should be noted, however, the road sections on Oahu had been in use only for around 11 months when researchers collected samples, so further research is required to find out how well the pavement performs over time with continued exposure to traffic and the elements. 

But durability isn't the only concern, as researchers also need to establish if the new material releases plastic particles as the road wears down due to traffic. So far, early analysis has found no evidence that asphalt containing recycled plastic sheds more polymers than conventional PMA. Although studied samples contained microplastics, only a small portion were found to be polyethylene. 

Researchers also discovered more polymers from tire wear than from the recycled polyethylene in samples of road dust. The findings offer some reassurance, but they don't tell us for certain if recycled-plastic asphalt is free of environmental risks. More testing needs to be carried out in order to better understand the amount of polyethylene that's released from the roads in real-world conditions, and if the level changes as the surface ages. Hawaii isn't the only U.S. state experimenting with this approach, as Texas is working on plastic roads to combat heatwave issues.