Alternative materials for rural road construction

The report was announced as part of a webinar conducted by Austroads in July. The three speakers at the webinar were Institute of Public Works Engineering Australasia’s roads and transport directorate manager Mick Savage (project manager), the Australian Road Research Board’s (ARRB) chief technology leader for sustainability and resilience Tyrone Toole (project leader), and Zia Rice, ARRB’s senior professional for future transport infrastructure.

Kieran Sharp, Lincoln Latter and Michael Moffatt were the other participating ARRB team members, with Austroads’ Eliz Esteban the moderator. The review team comprised stakeholders from road and traffic authorities, among others.

{{quote-A:R-W:250-I:2-Q:“Overall, there is a need to more effectively manage the available natural resources and consider the consumption of these resources for longer-term asset planning.” -who:Tyrone Toole}}Toole said the construction materials industry could benefit if the report’s findings were implemented nationally. There would be significantly lower costs of supply through substantially lower processing and transport costs.

“Demand could increase as transport and processing cost savings would be available to fund additional processing and supply,” Toole said.

Toole noted “a significant backlog of works exists in the roads sector” and said “an optimum outcome would be the use of cost savings to fund more projects”.

He said the study was commissioned in the backdrop of a shortage of quarry products, due to environmental restrictions and high transport costs of construction materials.

“Overall, there is a need to more effectively manage the available natural resources and consider the consumption of these resources for longer-term asset planning,” Toole said.

Key aims of the study

Toole explained the study was commissioned to consider:

• The increasing shortage of quality quarried materials and natural gravels for road construction and maintenance, with these being finite resources, and current sources being exhausted.
• The transportation of gravel quarry products over longer distances, resulting in escalating costs for road construction and maintenance. Some agencies are now paying for access to previously free materials.
• The exacerbation of the problem by the trend towards tighter environmental and quarry operation legislation and land access requirements.

Toole said the study focused on rural roads, although the use of marginal and substandard materials was also possible in other cases, including towns and industrial areas, where traffic levels were not excessive.

The report states there would be a reduction in construction and maintenance costs, particularly in remote and rural areas – including local government sub-division roads, and similar applications, where traffic loading is light.

“For unsealed roads, for most conditions they require a sufficient quantity of plastic soil fines to help bind the surface, thus reducing surface wear, leading to gravel loss, and pothole formation,” Toole said, adding that too much of the fines would lead to slipperiness loss of strength, and loss of shape.

Toole said what often was termed a ‘marginal material’ for a sealed road might be suitable for an unsealed road.

“For sealed roads the need is to provide a sufficiently strong road base that will tolerate stresses applied by heavy traffic, with a need to withstand these under prevailing moisture conditions,” he said.

“The implications of using marginal pavement materials for sealed roads has the potential to reduce the whole-of-life costs for the sealed road network,” he said.

The report concludes that there is a strong case, based on both national and international evidence, that supports the wider use of marginal and non-standard road pavement materials in sealed roads. Toole said “a life cycle of 20 years is achievable,” depending on future operating conditions.

It also identifies evidence from studies of unsealed roads, demonstrating the effective selection of unsealed road wearing course materials, and the benefits of good quality construction and maintenance practices.

Increased focus on the quality of design, materials testing, and construction is seen as a pre-requisite to optimise the use of marginal and non-standard materials.

The project findings support the wider use of preliminary materials assessment techniques and the report proposes a materials assessment protocol for low volume roads.

Each section of the report provides summarised ‘take home’ messages for asset managers to aid the application of the report’s findings in different circumstances.

To view the webinar and supporting documents, visit the Austroads website.

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