“Can we use plastic waste to build roads, buildings, and more?”

To answer this question, Stanford University engineers Zhiye Li, a postdoctoral scholar in civil and environmental engineering, and Michael Lepech, a professor of civil and environmental engineering, conducted a detailed study on the current challenges of recycling plastics in a circular economy, as well as its long-term durability and environmental costs for use in infrastructure.

After analysing two specific case studies where plastic waste was used – facade panels on the San Francisco Museum of Modern Art, and a pavement in a California Department of Transportation road project – Lepech and Li used a mix of computer modelling, scientific research, experimental and field data, as well as interviews with recycling industry stakeholders to reveal the potential of recycled glass fibre reinforced polymer composite – a tensile plastic commonly used in car, boat, and plane parts – as a promising material for reuse in buildings.

Their findings were published in a white paper commissioned by the National Academies of Sciences, Engineering, and Medicine (NASEM), which was included as an appendix to its recent report to Congress, the U.S. Department of Transportation, and the U.S. Environmental Protection Agency.

Biggest obstacles for repurposing plastic waste into infrastructure applications?

According to Lepech, one of the biggest challenges comes from the difficult economics and logistics of managing plastic waste streams in municipal solid waste. This is mainly because plastic waste material flow is highly variable, with its mass changing from month to month; the type of plastic can also vary.

Big opportunities?

“The recycling of entire buildings made of polymer composites at the end of their useful lives could be a game changer,” says Lepech. “That’s because the amount of material, along with its likely uniform composition, would make recycling it into another infrastructure application significantly easier.”

Li lists out the recommendations given in their white paper: “Improve waste sorting, encourage and support plastic upcycling innovation, set up a performance database of certain plastic blends, and establish predictable models for these materials’ durability under different use conditions.”

Lessons for other circular economy efforts

“Upcycling of recycled plastics in infrastructure sets an example of creating value by creating demand,” Li explains. “The recycled plastic blended construction material needs to achieve certain performance requirements and maintain lower environmental impacts than conventional construction materials. Our paper shows that for a use case that has a longer lifespan – such as certain blended plastic composite building panels or asphalt pavement, the needed quality and sustainability requirements are more achievable.”

Upcycling plastic waste – is it profitable?

Lepech observes that companies that are part of a circular economy value chain may see regulatory advantages, such as extended protection of an explicit or implicit license to operate or greater flexibility with regulatory agencies. There are obvious operational efficiencies since they won’t be relying on virgin fossil resources. In terms of risk management, there could be reduced potential for environmental emergencies such as oil spills, and the benefit of lower insurance premiums.

He adds that such companies can profit from targeting markets that value environment-friendly or sustainable products.

Beyond buildings and roadways

“Upcycling plastic waste in infrastructure has attracted increasing interest because it creates something of high value for which there is large potential demand,” says Li. While there are many applications for reusing plastic, there aren’t many that would use as much plastic waste or last as long. Though packaging consumes more than 60% of global recycled plastic, it has a short lifespan. Again, while some automotive parts can be made with recycled plastic, they require relatively little plastic to produce.

Image: The Stanford researchers analysed a California road project that used plastic bottles in asphalt. (Image credit: Caltrans)

Branko Miletic

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