Will a new extra-large wheel tracking test bring Australia one step closer to all-recycled? Dr Didier Bodin, Dr James Grenfell, Jaimi Harrison and Shannon Malone of the Australian Road Research Board explain.
The road sector has been reusing and recycling materials in the roadbed for many years, as it continues to improve the sustainable management of virgin and recycled aggregate resources.
With Victoria’s big build well underway, developing wider recycled alternatives to quarried sand is critical. Crushed concrete and other demolition materials provide an excellent alternative to virgin quarry products.
The use of reclaimed asphalt pavement in asphalt mixes is a well-known example of recycling in road construction. That said, recycled aggregates have also been used in unbound granular base and subbase layers.
Victorian Department of Transport specifications for recycled subbase materials have been available for a long time. However, the department is currently working towards increasing the fit-for-purpose use of recycled material in road construction.
To achieve this, the transport department engaged the Australian Road Research Board (ARRB) to trial, test and research processes and mixes to extend the specification framework.
A couple of questions needed to be answered
First, can we use recycled aggregates in road base materials for lightly trafficked roads? And second, how do different blends of crushed concrete, crushed brick and crushed glass perform?
Maximising resource recovery for these major waste streams will not only reduce our reliance on virgin material, but reduce the amount of material sent to landfill and support the circular economy transition. This is a key factor given the Victorian Government is slated to release its Circular Economy Policy in 2020.
In the future, these materials can be recycled in granular roadbase materials, or if required, can be further improved through in-situ stabilisation.
The extra-large wheel-tracking test developed by ARRB for Austroads is the best approach to assess the performance of unbound granular material in the laboratory under simulated traffic conditions.
It consists of trafficking a 300-millimetre-deep specimen of material under a rolling wheel-load for at least 80,000 load passes (40,000 cycles). The deformation at the surface of the specimen is measured during the test to assess the rutting characteristic of the material.
Test specimens can be prepared at various density or moisture conditions. To benchmark the performance of various materials, specimens from each mix are compacted at equivalent field density and moisture content conditions.
Each specimen is sealed with a flexible epoxy membrane to preserve the specimen moisture conditions during testing.
Building on the experience with crushed concrete material as a subbase material in the field, the research methodology compares the performance of different blends in comparison with a crushed concrete as a control material.
A crushed concrete material was blended with different proportions of crushed glass and crushed brick to evaluate performance changes with increasing recycled material content.
All work was conducted in ARRB’s state-of-the-art research laboratories in Port Melbourne.
Performance
All of the mixes performed well within expectations compared to other aggregate sources tested in similar conditions during this and previous projects.
These encouraging results suggest the potential for increasing fit-for-purpose use of these 100-per-cent-recycled materials and blends for lightly trafficked roads.
More work is underway to perform similar assessments on crushed rock materials and blends with different recycled proportions.
Eventually, the hope is we could reach a point where we use these recycled materials as a granular base, and then just lay a thin surfacing over the top. This would be an important application for lightly trafficked rural roads which are managed by local councils.
Interested in finding out more about this work and its potential application, or customisation of a testing program to suit your needs?
Contact ARRB at labs@arrb.com.au
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