Downer begins large scale trial of shredded plastic in asphalt

Downer was recently awarded a 10-year contract from the New Plymouth District Council in New Zealand for term maintenance.

The contract covers urban and rural roads in the district and includes road maintenance, CBD cleaning, water and wastewater reticulation renewals, as well as small to medium bridge maintenance.

Downer said this contract presented the right opportunity for the first large-scale trial of Plas Mix, which was delivered last month in New Plymouth.

Plas Mix is raw shredded plastic that goes into asphalt. Common types of plastics used are containers for margarine, yogurt, cottage cheese, butter, bottles for cleaning products and more.

“The creation of Plas Mix is a collaboration between two commercial companies actively working together to solve significant local and global waste minimisation issues. The team are tasked with developing a meaningful outcome that can successfully repurpose waste plastic while not compromising the integrity of the pavement solutions,” Downer’s Murray Robertson said.

Enviro NZ who are working with Downer said the main benefit of Plas Mix is the prevention of waste to landfill, which in turn eliminates the need to transport materials thousands of kilometres overseas for processing.

The trial in New Plymouth was the first example where plastic has been used to surface a public road in New Zealand.

The trial consumed 500 kilograms of hard plastic waste in 100 square metres of road. Downer said this is the equivalent plastic waste 1300 people would generate in one week.

Downer’s road science laboratories have gone to great effort to identify the optimum plastic mix and the size needed for a successful product. It is laid and paved in the same way as traditional asphalt.

One of the benefits Downer found in testing was that the performance of asphaltic road surfacing was actually enhanced by adding the plastic, especially in the areas of waterproofing and rutting.

“Developing practical and cost effective solutions to sustainability challenges remains front and centre for our team. Reducing solid waste from entering landfills, while reducing our carbon footprint and providing high quality cost effective outcomes is a challenging yet motivating assignment for us,” said Mr. Robertson.