Turning shopping bags into streets: ECU research tackles plastic waste

Discarded shopping bags and spent milk bottles could be given a second life by becoming part of critical infrastructure, new research from Edith Cowan University (ECU) has found.

PhD student Mr Ali Ghodrati has noted that the integration of waste plastics into pavement material could offer a dual benefit of enhancing road performance and mitigating the environmental burden of plastic waste.

“Plastic waste has become a very concerning and dangerous problem all around the world. By repurposing these common household plastics, which would otherwise end up in landfills or oceans, recycling these plastics into pavement not only offers a practical solution to plastic pollution but also enhances the strength and longevity of our roads.”

Global plastic production reached approximately 460 million tonnes in 2019. However, only around 9% of plastic waste has been recycled globally; the other 12% has been incinerated, and almost 79% has ended up in landfills or the natural environment.

The research has estimated that plastic waste production is expected to exceed one billion tons a year by 2050.

While plastics have been used in pavements since the 1990s to improve a range of performance characteristics such as rutting resistance, stiffness, and durability, Mr Ghodrati said that incorporating waste plastics into this process could decrease dependency on virgin materials and could contribute to climate change mitigation through lowering the embodied carbon of road works.

Fellow author Dr Nuha Mashaan said the inclusion of waste plastics into infrastructure was a great example of turning an environmental liability into an asset.

“What excites us is the dual benefit; helping the environment while creating resilient and sustainable longer-lasting roads. It’s an innovation that has the potential to deliver real change for both communities and industry.”

ECU’s Dr Themelina Paraskeva pointed out that there are currently three ways in which plastics are incorporated into pavements; the wet method, the dry method and a mixed method. The incorporation method significantly affects the way that the plastics perform in the pavement and could potentially also contribute to micro plastic pollution.

“The wet processing techniques generally deliver better material compatibility and reduce long-term environmental risks, such as microplastic emissions. Dry processing, while easier to implement and more flexible in terms of plastic reuse, can lead to uneven dispersion and higher risk of microplastic release from road wear,” Dr Mashaan added.

She highlighted the potential of hybrid approaches to balance sustainability and performance, stressing the circular economy’s focus on reducing waste and improving resource efficiency by reusing, recycling, and repurposing materials.

One size does not fit all

“In road construction, not all plastics are suitable,” Dr Mashaan noted.

“The key factor is the melting point. Asphalt is typically mixed at temperatures between 140 and 180 degrees Celsius. Thermoplastics, such as those found in shopping bags or milk bottles, melt within or below this range. This makes them ideal, as they blend efficiently with bitumen without requiring additional energy or producing harmful by-products, unlike plastics with higher melting points.”

By incorporating waste plastics into asphalt, this method not only diverts plastic from landfills but also contributes to longer-lasting road surfaces, aligning with the principles of the circular economy.

Mr Ghodrati added that while the incorporation of waste plastics into pavement has the potential to lower greenhouse gas emissions, reduce the need for virgin materials, and cut down on long-term maintenance, challenges still remained.

“At higher concentrations, plastic additives can make the asphalt more brittle and prone to cracking. There are also important environmental considerations, including potential fume emissions, leaching behaviour, and the risk of micro- and nano-plastic release during service life, particularly under traffic and weathering.

“Most notably, while lab and small-scale trials are promising, more real-world testing across different climates and traffic conditions is urgently needed to fully validate the long-term performance and environmental safety of plastic-modified roads,” he added.

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