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As of March 2025, the innovative Polyrok concrete technology developed by RMIT University in partnership with Coles and Australian recycling firms continues to gain attention for its ability to recycle soft plastics into durable construction materials. First commercialized in 2021, Polyrok has already diverted over 1.3 billion pieces of soft plastic from landfill, and researchers see strong potential for adoption in the United States, where soft plastic recycling remains a major challenge.
Soft plastics — including wrappers, cling wrap, plastic bags, and flexible packaging — have long been the bane of recycling systems. They tangle sorting machinery, contaminate paper streams, and fetch low market value. In Australia, the REDcycle program collected these materials from households, but a 2022 collapse of the program left heaps of soft plastics in storage. Against this backdrop, RMIT engineers sought a high-volume, high-value outlet: concrete.
Led by RMIT senior lecturer Dr. Jonathan Tran, the team developed a plastic aggregate called Polyrok. The material replaces a portion of mineral aggregates — such as gravel or crushed stone — with shredded, cleaned soft plastic. The challenge was making plastic and concrete bond effectively. Tran explained that while glass can be easily ground into sand replacement, plastic repels cement paste. “Mixing concrete and plastic is difficult, as the two don’t naturally bond,” he said.
The researchers used X-ray computed tomography to analyze the internal structure of test mixes and optimize the ratio of plastic to conventional aggregate. They aimed to balance strength with acoustic energy absorption — a valuable trait for car parks and road surfaces. The resulting Polyrok concrete is lighter than standard concrete, offering easier handling on site, while maintaining structural integrity.
The first real-world use of Polyrok was at a Coles supermarket car park in Horsham, Victoria, in 2020. The concrete incorporated more than 900,000 pieces of plastic bags and soft packaging recovered through the REDcycle program. RMIT reported that the material performed well under both load and weather conditions, validating the laboratory findings.
This project demonstrated that soft plastic could be permanently locked inside concrete, preventing it from degrading into microplastics. Because the plastic is encapsulated in cement, it doesn’t leach or break down over time — a key advantage over landfill or incineration.
On February 15, 2021, Coles announced a much larger deployment at its Cobblebank supermarket in Melbourne’s west. The project used over 6.5 million pieces of soft plastic in the concrete for the store’s floor slab and pavement areas. At the time, it was described as the largest-ever commercial application of Polyrok.
Coles sourced the soft plastic from the same REDcycle program, which had collection bins in many of its stores. The partnership extended beyond construction: it created a circular economy loop where retail plastic waste flowed directly into building materials for the retailer’s own properties.
Since the partnership began, Tran said Replas, RED Group, and Coles had diverted more than 1.3 billion pieces of soft plastic from landfill. He also noted a local factory in Melbourne had the capacity to convert 105,000 tonnes of soft plastics into dense plastic aggregate each year. This volume could supply a significant portion of the concrete needed for new infrastructure projects.
The RMIT research team included Dr. Rajeev Roychand and Dr. Thomas Loh. Tran said they hoped to explore producing sustainable concrete structures using RMIT’s new large-scale concrete 3D printer at the Bundoora campus. This could allow on-demand fabrication of precast elements using recycled plastic aggregate, further reducing transportation emissions.
The United States generates about 9.4 million tons of plastic waste annually, according to the EPA, with the vast majority ending up in landfills. Soft plastics account for roughly 40% of that stream, or about 3.8 million tons per year. Current recycling rates remain below 10% for plastic overall, and soft plastics are particularly underrepresented.
Polyrok offers a potential pathway for American municipalities and retailers. U.S. concrete producers already use recycled materials such as fly ash, slag, and silica fume; adding plastic aggregate could be a natural extension. The American Concrete Institute (ACI) has published guidelines for alternative aggregates, and several states (California, Oregon, Minnesota) have begun exploring plastic-bearing concrete in pilot projects.
However, challenges remain. U.S. collection systems for soft plastic are fragmented. While some retailers collect plastic bags and wraps, most curbside programs don’t accept them. A dedicated aggregation and processing network
