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Waka Kotahi NZ Transport Agency research

Waka Kotahi supports research to investigate best practice state highway corridor environmental management for resource efficiency and waste management. Recent research projects include:

  • Barriers to more efficient use of pavement aggregates in New Zealand
  • Recycled aggregate waste research
  • Rubber in roads
  • Epoxy modified open graded porous asphalt (OGPA)

Barriers to more efficient use of pavement aggregates in New Zealand

Recycled and alternative materials have been included in our road specifications (such as M/4) since 2006. The percentage of recycled and alternative materials used in highway improvement and maintenance projects remains low by international standards.

In 2017 we completed a discussion paper highlighting the issues around premium virgin aggregate materials and their availability across New Zealand:
Premium aggregate resource efficiency discussion paper (NZ Transport Agency, 2017) [PDF, 3.7 MB]

An update to some of the figures within the 2017 discussion paper which reflects more recent data can be found below:
Premium aggregate resource efficiency discussion paper (NZ Transport Agency, 2019) [PDF, 481 KB]

In 2018 Waka Kotahi commissioned a research project to better understand the barriers to increasing the uptake of recycled and alternative aggregate materials and to develop recommendations to overcome these.

The project was completed in two stages. Stage 1 involved an international literature review, an analysis of local case studies and online survey of industry members. Stage 2 consisted of a series of in-depth interviews with industry and agency representatives.

Research findings

Recycled aggregates on New Zealand roads: Barriers to uptake and drivers to change (WSP Opus Research, 2018) [PDF, 2.7 MB]

Summary of research findings

Barriers to more efficient use of pavement aggregates in New Zealand 2018/19: summary of findings (NZ Transport Agency, 2020) [PDF, 148 KB]

Recycled aggregate waste research

Together with local government, academia and industry partners, Waka Kotahi has co-funded a research project into the use of recycled aggregate at the Centre for Infrastructure Research at the University of Auckland. The aim of this project was to determine the size of the Auckland recycled aggregate market, the type of materials available, and what recycled materials might be suitable for use as aggregates in roading.

There were two work streams associated with the project. The first stream was to understand the nature and engineering performance of current recycled aggregate within the Auckland market. The second stream focussed on guiding roading providers, consultants, contractors and suppliers to increase their uptake of recycled aggregate materials.

This research aims to create a better understanding of what recycled materials the market can supply. This will ultimately reduce the need for virgin use, transport of quarried materials and landfill disposal costs for recyclable materials.

Rubber in roads

The Transport Sector Research Fund funded a research project to identify the barriers to using tyre-derived crumb rubber in bitumen binder in New Zealand roads. This project also aimed to understand the mechanisms to remove these barriers to create market demand for New Zealand waste tyre-derived products.

Internationally tyre-derived crumb rubber has become a common alternative additive to bituminous binders since the 1970s, addressing pavement performance issues as well as tackling the disposal problem of end-of-life tyres. While early trials of crumb rubber in both hot mixed asphalt (HMA) and chip seal pavements have resulted in mixed performances, technological advances and ongoing research and practices internationally have demonstrated that crumb rubber can be effectively incorporated into road surfacing.

In New Zealand, rubber has only been used in the form of natural rubber latex or styrene-butadiene-styrene block copolymer (SBS) from around the 1970s. To date crumb rubber from waste tyres has not been used to any extent (outside research trials) in normal road pavement maintenance or construction.

Find out more information on the current state of crumbed rubber in New Zealand:
Crumb Rubber Review - 2020 Update (WPS New Zealand Ltd, 2020) [PDF, 854 KB]

Epoxy modified open graded porous asphalt (OGPA)

Epoxy modified OGPA is now an established surfacing for Waka Kotahi that has be made in Auckland, Hamilton, Wellington and Christchurch by our major contracting partners.

Field performance on bridges and our lab testing suggests that we will be able to extend the average life of our low noise surfacing from 8 years to 40 years. This will reduce both maintenance costs and increase resource efficiency by extending the life cycle of the aggregates and bitumen related products used.

Low noise pavement investigation for epoxy modified open graded asphalt (EMOGPA) (AECOM 2020) [PDF, 175 KB]

OGPA and EMOGPA research summary (AECOM 2020) [PDF, 113 KB]

Waka Kotahi NZ Transport Agency published research reports

Resource efficiency case studies

Many of the Waka Kotahi state highway projects have incorporated resource efficiency initiatives successfully. The following case studies provide examples of recent projects.

Ngauranga to Aotea Quay upgrade [PDF, 502 KB] – clever re-use of existing infrastructure on SH1 in Wellington.

Newmarket Viaduct replacement project [PDF, 711 KB] – example of 100 percent recovery of non-contaminated materials.

Waitangi Wharf upgrade [PDF, 625 KB] – innovative design and resource efficient practices on Chatham Islands.

More case studies will be added as relevant projects are completed over time.

Useful links

WasteMinz link)

Ministry for the Environment link)

Greenroads project case studies link)

Infrastructure Sustainability Council of Australia case studies link)


For further information contact