The Kiwi town making roads out of plastic

Plastic that used to be put on a boat to get recycled 10,000km away is now hitting the road - literally.

Liardet St in New Plymouth has been resurfaced with asphalt partly made of used plastic.

"It looks just like an ordinary road surface, but there's actually the equivalent of more than 83,300 yoghurt pots inside," said David Langford, infrastructure manager for New Plymouth District Council.

Instead of shipping it to China, the plastic now only has to travel about 10 to 15km to find a second life.

Around 500kg of plastics of type three to seven were used in the 90m of resurfacing - only about 0.5 percent of the total weight of the asphalt, called Plas Mix, but there are plans to up that ratio if the road holds up to traffic.

Plas Mix was developed by Road Science, a division of Downer.

"It's probably actually a little bit better than normal asphalt," Road Science technical development manager Darcy Rogers told RNZ.

"There are three killers for roads - there's water, heat and traffic. And through our testing, we've actually found that adding plastic increases the resistance to those three aspects."

It might be a New Zealand first, but plastic roads have already been trialled in India, Australia, Indonesia and the UK. There are concerns however when they deteriorate - as all roads eventually do - they could release microplastics into the environment.

"Testing has shown the new material is stronger and should perform better than standard asphalt while also being cost-effective," added Langford, "but the proof is in a real-world trial on our roads. So we'll be monitoring closely how it performs over the next several months."

Tests in the lab suggested it would last two decades, Stuff reported. Both plastics and traditional asphalt are manufactured using petroleum of one type or another.

Instead of paying to have 200 tonnes of plastics taken away every year, Langford hopes New Plymouth could become a hub for recycled plastics from around the region.

"That will be much more sustainable in the long-run, saving our ratepayers money and cutting our carbon footprint as well as taking a huge step towards us becoming a zero-waste district."

China's decision last year to cut down the amount of recycling it accepts from overseas prompted the council's move to try something different.

"Instead of stockpiling or landfilling these plastics, we took this as an opportunity to innovate and come up with a better solution, which is where the idea to put it into asphalt came from," said Langford.

Overseas efforts at plastic-asphalt hybrid roads have tended to be more expensive than traditional kinds, the Guardian reported in 2016. Road Science's Plas Mix reportedly costs the same - about $45 per square metre.