Sustainable pavements: ARRB

Margaret Brownjohn from the Australian Road Research Board takes a look at lifecycle assessment and promoting the uptake of innovative recycling materials in roads.

Sustainable development spans economic, social, environmental and governance aspects. Sustainability is no longer a “nice to have”.

The infrastructure industry in Australia is now driving outcomes that help reduce its ecological footprints. Many state and territory governments are also doing their bit to promote sustainability.

They have policy targets that govern procurement decision making. This includes reducing their annual greenhouse gas emissions, local jobs creation and diverting waste away from landfill.

Many states and territories are also requiring that major infrastructure projects undergo an Infrastructure Sustainability Council of Australia rating. This is an independent assessment process to assess innovation, sustainability and continuous improvement and compared to business-as-usual.

ASSESSING SUSTAINABILITY

A challenge in promoting the uptake of more sustainable pavement technologies is communicating its whole-of-lifecycle sustainability and lifecycle asset performance to transport practitioners. Often there are win-win commercial and sustainability outcomes from the use of innovative pavement technologies.

As part of the National Asset Centre of Excellence (NACoE) partnership between Transport and Main Roads in Queensland and the Australian Road Research Board (ARRB), a number of innovative pavement technologies have been developed, tested and trialled for application on Australian roads.

ARRB conducted a study where the lifecycle sustainability costs and benefits of different pavement technologies were assessed. This included quantification of greenhouse gas reductions over the pavement lifecycle.

These included the following technologies:

EME 2

Reclaimed asphalt pavement (RAP)

Crumbed rubber in binders

Foam bitumen stabilised (FBS) Bases

Local marginal materials.

EME 2 is a high-strength asphalt used in high-traffic urban arterials and motorways. It often reduces the base layer thickness by up to 30 per cent, which means lower use of virgin materials. It also means fewer lifecycle emissions due to less use of materials, haulage and construction emission. Approximately three per cent of lifecycle emissions and lifecycle cost savings are achievable with the use of EME 2 in an urban context.

RAP is a reprocessed pavement containing reused asphalt. This means less use of virgin materials and less clearing of trees for quarries. There may also be fewer emissions from haulage. 5.1 per cent lower emissions and lifecycle cost savings are also achievable. This is particularly notable where landfill levies and fees are applicable in regions like Queensland, which has an escalating levy each year.

The use of crumbed rubber in binders promotes local and circular economies, which both create jobs. Crumbed rubber also reduces the imports of materials like polymer modified binders. It may be hauled large distances and still achieve lifecycle greenhouse gas reductions.

FBS is a processed pavement base with increased strength and resilience to flood events. This reduces the risk of rehabilitation required after a flood. Because of its stiffer and thinner base, it also has lifecycle emissions reductions.

Marginal materials are locally sourced materials. They are beneficial where higher performing virgin materials are expensive and required to be hauled long distances. Due to reduced haulage, up to 22 per cent reduction in lifecycle emissions are achievable. It also promotes local industries in rural areas.

All technologies achieved lifecycle greenhouse gas reductions and commercial savings in the right context. General findings included that high durability and resilient pavements have good whole-of-lifecycle sustainability performance.

The largest emissions reductions are also achievable through vehicle technologies, such as electric vehicles. But every year of delay adds to cumulative emissions in the atmosphere and over the pavement lifecycle.

Future work will include quantifying the benefits of additional sustainable materials, including, but not limited to, the use of recycled glass and warm asphalt. The tool provides a framework in which pavement options may be assessed on a project-by-project basis for smarter procurement decision making.

If you are interested in finding out more about this work and its potential application, or customisation to your needs, contact ARRB at sustainability@arrb.com.au