Travelling down a glass highway

Australians have become great recyclers of glass, even though not all glass is actually reusable. However, a purpose may just have been found for the growing stockpile of waste glass in many cities and towns.

Research at Swinburne University of Technology?s Centre for Sustainable Infrastructure is looking at ways to make this glass suitable for use in road construction. In Victoria alone, about 250,000 tonnes of non-recyclable glass ends up in landfill, so it represents a sizeable resource to supplement materials used in roads and footpaths.

Recycled glass is already used in road construction in Europe and the US, but each region needs to set its own standards according to local conditions, materials and climate.

In Victoria, VicRoads, which constructs State highways and freeways, and the Municipal Association of Victoria (MAV), which represents local councils that look after local roads, footpaths and bike paths, need to be confident that the new materials would not compromise quality and durability. Currently, crushed glass is allowed, but only up to a maximum proportion of three per cent.

Roads generally have three levels: a sub-base pavement, a base pavement and an asphalt top. The sub-base is the main load-bearing layer of the pavement; its role is to spread the load evenly over the earth beneath. The quality of the sub-base is crucial, as poor construction or use of the wrong materials can cause the upper surface to crack.

Materials used in a sub-base must comprise particles of a shape and size that interlock tightly when compacted to eliminate air gaps and movement.

Traditionally, quarry rock has been used. Authorities such as VicRoads require proof that any new material like crushed glass can withstand at least 20 years of heavy traffic.

This is where Swinburne comes in. Dr Arul Arulrajah, an associate professor in Civil and Geotechnical Engineering at Swinburne?s Centre for Sustainable Infrastructure, has previously assessed the suitability of crushed brick as a road construction material.

In 2009, supported by a consortium of government and industry groups including Sustainability Victoria, Visy, VicRoads, the MAV and the ARRB Group (formerly Australian Road Research Board), Dr Arulrajah led a team to compare different blends of recycled glass, crushed rock and concrete with traditional quarry materials.

Laboratory tests by Dr Arulrajah and his team, including Swinburne PhD students Younus Ali and Mahdi Miri Disfani, assessed the mechanical properties of each blend, including the particle density, particle size, plasticity (ability to be shaped), compactability, permeability and load- bearing capacity.

The finding ? that all the blends with up to 30 per cent glass matched or exceeded the VicRoads specifications ? didn?t actually come as a surprise to Professor Arulrajah, ?given that crushed glass is really just like coarse sand?.

Even so, it is one thing for a material to perform under the controlled conditions of a laboratory, and another for it to deal with real-world conditions. Associate Professor Binh Vuong, a senior research fellow with Swinburne?s Centre for Sustainable Infrastructure and a principal engineer at ARRB, has extensive experience in laboratory testing and field construction of recycled and quarry-produced materials. In his joint appointment with ARRB, Professor Vuong had already been involved in the laboratory testing process for recycled glass. His role now is to oversee the field testing of the blends.

The Alex Fraser Group, a materials recycler, offered the entrance to its Western Metropolitan Recycling Facility in Laverton, Victoria, as the site for a road trial. The road carries a large volume of heavy vehicles. Nine sections of road, each 80m long, were laid in November 2009, each using a different blend of recycled glass and recycled concrete or crushed rock, and designed and constructed to the specifications required for arterial and local roads.

After six months, the test roads are showing no visible signs of rutting or cracking, the symptoms of a weakening sub-base.

In May 2011, the surface was scrutinised in minute detail using an ARRB laser profiler. If the study shows the glass blends are of comparable performance to virgin quarry rock, the consortium backing the research will submit a report to VicRoads for its consideration. This may potentially lead to an adjustment in VicRoads? specifications, to allow higher percentages of crushed glass to be used in crushed roadmaking materials.

Peter Richardson, the general manager of recycling industries at the Alex Fraser Group, believes glass mixes will be competitive options for road builders. ?To take on a product, it has to make both commercial as well as sustainable sense. We have no doubt that this product will be competitive with other road-building materials.?

NOTES

As Quarry goes to print, the ARRB Group is analysing the results of its final detailed tests on the performance of the trial road surfaces before the research consortium submits its report to VicRoads.

This article is reproduced with permission of Swinburne, the research magazine of Swinburne University of Technology (www.swinburne.edu.au/magazine).

Swinburne University is continuing its research focus on recycled materials with the potential to replace quarried products. Associate Professor Arul Arulrajah welcomes industry inquiries, email aarulrajah@swin.edu.au

BOXOUT:

Through the looking glass …

? About 250,000 tonnes of waste glass are stockpiled each year in Victoria.

? Laboratory testing at Swinburne has shown that the glass has the right qualities to be incorporated into road base material.

? If road trials currently being evaluated are successful, road base materials could in future include up to 30 per cent recycled glass, absorbing all waste glass produced in Victoria.