The project is being funded through Waka Kotahi’s Hoe ki angitū Innovation Fund. 

WSP Petone-based research manager for transport Matt Sharp is confident that lab trials will result in a sustainable recycling process that brings Aotearoa New Zealand a step closer towards a circular economy in road surfacing.  

“When a chip-sealed stretch of road reaches its use-by date, it’s usually milled up and disposed of in clean fill. That’s hardly a win for roading sustainability,” says Matt.  

“In this feasibility project, we’re looking at whether we can extract, and re-use, bitumen and aggregate from old chip seal in a way that doesn’t harm the planet and preserves usability.” 

Chip seal will be familiar to most Kiwi drivers. It’s made up of bitumen (derived from crude oil) and crushed stone aggregate but can’t currently be recycled effectively. 

With eighty-eight percent of New Zealand roads constructed with chip seal, there’s a vast amount of raw material that may ultimately be able to be recycled.         

Another, related, Hoe ki angitū-funded project about to begin at WSP Research will see wood-lignin added to bitumen. In this way, researchers hope to create a lower-carbon road surface binder. 

Matt says while using lignin as an ‘extender’ or ‘filler’ for bitumen has been investigated in international studies and trialled overseas, it’s never been seriously considered in New Zealand. 

New Zealand is entirely dependent on imported bitumen for its road surfaces. That’s a problem for several reasons – not least of which is its high carbon footprint, and escalating price forecasts. 

“In this project, we’ll trial using lignin as a partial replacement for bitumen in New Zealand’s roading context. We expect this to result in a significant reduction in the carbon footprint of the road surface.  

WSP researchers are also involved in a Hoe ki angitū-funded project with waste minimisation group UsedFULLY, where fibres from recycled textiles and clothing will be trialled in chip seal bitumen. 

“We’re excited to get underway and thank Waka Kotahi for the opportunity to progress these important pieces of research. Work like this is critical in the development of more sustainable, circular roading materials and helping decarbonise the country’s transport system,” says Matt.