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

  • alternatives to bitumen
  • chip seal recycling
  • barriers to more efficient use of pavement aggregates in New Zealand
  • rubber in roads
  • epoxy modified open graded porous asphalt (OGPA).

Alternatives to bitumen

A review was undertaken in 2021 to investigate potential alternatives to petroleum bitumen for construction of road surfacings in New Zealand. The review provides a high-level overview of available materials and materials in development. The review recommendations, based on current available alternatives, are for further investigation into the feasibility of recycling chip seal materials, both as millings and through bitumen and aggregate recovery. Also, the use of lignin or chemically modified lignin appears to be the most promising starting material for development of a practical, renewable alternative to bitumen.

Bitumen alternatives report [PDF, 815 KB] 

Chip seal recycling

A preliminary investigation was undertaken in 2021 into current and emerging technologies for recycling of chip seal road surfacings. The intention of this research was to explore possible approaches for the development of a chip seal recycling practice comparable to the current practice of recycling reclaimed asphalt pavement (RAP). The investigation recommends that further research is undertaken in the following areas:

  1. Utilisation of chip seal millings in asphalt pavements via small-scale in-situ recycling and placement of asphalt (or ex-situ processes similar to RAP). This would potentially have a short-term, immediate impact on the recycling rate of chip seal surfaces;
  2. Extraction and recovery processes for separation of bitumen and aggregate from chip seal millings which can be scaled up, and are commercially and environmentally viable;
  3. Life Cycle Assessment sensitivity studies of the new processes conceptualised in (1) and (2) to help understand the constraints required for a viable process;
  4. Potential sustainable, environmentally friendly, rejuvenating agent from renewable materials for modifying the extracted, aged bitumen to enable its use in both asphalt and chip seals.

Chip seal recycling report [PDF, 892 KB] 

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 (Waka Kotahi, 2020) [PDF, 148 KB]

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 (WSP New Zealand Ltd) [PDF, 854 KB]

Research Report 679: The reuse of end-of-life tyres to enhance the performance of chipseal binders

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 published research reports

Resources and tools

Life cycle assessment of pavements (LCAP) tool