Recycled glass for new pavements and roads

The outcome

Building upon existing research in the field, the research project successfully trialled a new road base mix for lower trafficked roads that contains a much higher percentage of glass fines. With the Department of Transport (DoT) updating its specification for the use of recycled glass in roads, local and state government can use much more recycled glass in Victoria’s expanding road and footpath network.

The research found that up to 25% recycled glass (RG) can be initially recommended for incorporation as a supplementary material in unbound crushed concrete pavement subbase applications. Depending on the results of future field trials, it may be possible to increase the percentage of RG added in the future of up to 30% content.

Up to 25% RG (by mass) can be initially added to crushed concrete (CC4 and CC3) for use in cement treated applications for pavement subbase applications. Depending on the results of future field trials, it may be possible to increase the percentage of RG added in the future.

The need

In Victoria approximately 300,000 tonnes of recycled glass, 1.4 million tonnes of crushed brick and 3.5 million tonnes of crushed concrete are available for processing annually into new products. In total this is 5.2 million tonnes of material that would go to landfill or be stockpiled around the state.

DoT manages a road network of 151,000 kilometres, from major freeways to minor local roads. Approximately 50,000 kilometres of this road network is located in metropolitan Melbourne and requires the use of bound pavements (cement treated) with asphalt for pavement bases and sub-bases. There are also similar requirements for municipal roads.

Traditional pavement base and sub-base materials are becoming scarce in Victorian regions. In some cases, the use of these materials is unsustainable from both an environmental and economical perspective.

The reuse of recycled materials in new applications, such as lower traffic roads, has significant carbon savings compared with virgin quarried materials. The use of recycled materials in new products also reduces stockpiling by creating more demand.

Developing the solution

Geotechnical tests were undertaken on the triple blends to obtain critical information about the physical properties of the proposed mixes and these included:

• pH
• plasticity index and linear shrinkage
• foreign materials content
• particle size distribution
• hydrometer
• organic content
• particle density and water absorption
• flakiness
• modified compaction
• permeability
• California Bearing Ratio
• Repeated Load Triaxial (RLT)
• wheel tracker tests

To ensure the project ran efficiently it was important:

• to ensure all equipment was available and fully calibrated
• that the operators are well-trained for all advanced testings
• that all parent materials are collected at the start of the project
• for representative samples to be prepared for each test
• to start analysing the data in parallel with testing
• there were regular meetings with the industry partner during the experimental phase.

A technical testing breakthrough was the wheel tracker test used for the first time for determining the performance of RG and other recycled products in pavement applications. The test method was found to be effective for evaluating the performance of recycled materials.

The partnership

Swinburne University of Technology was the project lead and they have been actively undertaking research with DoT and the Construction and Demolition industry since 2006 on the use of various recycled demolition materials as pavement sub-bases.

Alex Fraser Group provided materials and understanding of various blends, processing and market expertise. The company also offered technical and consultative expertise on recycled materials such as RG, CC4 and CC3 produced in various classes from the Clayton and Laverton sites.

Existing research on demolition materials indicate the recycled materials are of high quality and with engineering properties equivalent or better than that of traditional quarry materials. Knowledge gained and a track record on these past projects plus an established team at Swinburne enhanced the research project outcomes.

Pathway to commercialisation

The ever-expanding road network in Victoria and in Australia plus the ongoing restoration of pavements provides a huge potential market for the commercialisation of the specification.

Currently, up to 25% recycled crushed glass can be incorporated as a supplementary material in concrete pavement sub-base applications. Depending on the results of future field trials, it may be possible to increase this percentage to 30%.

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