New void formers created from 100% recycled agricultural plastic

The outcome

Void formers are 3D geometric shapes that are strategically placed in concrete structures to reduce the amount of concrete used in construction. Traditional void formers are made from a range of materials including polystyrene.

Led by Swinburne University of Technology, the project proved that recycled plastics from used bunker tarp (traditionally used in grain farming) could create an excellent quality void former product.

The need

Thousands of tonnes of agricultural plastics are disposed of into landfill every year. For example, tarps, bulka bags and bale twine, that are used to protect grain, are often sent to landfill or left to decay on farmland.

After several harvest seasons, these plastic materials become redundant as they are usually damaged and heavily contaminated with vegetation and dirt. They can be difficult to reuse or recycle.

The research project looked at the suitability and performance of using recycled plastic waste streams, in particular bunker tarp, to create void formers for the construction industry. There was limited evidence on how well recycled plastics could be used in this type of construction product.

The research results have benefited ROBOVOID by confirming that the concept is feasible. Also, the technical data shall benefit other potential users of these recycled plastics in other applications.

Developing the solution

The research project focused on 3 sources of recycled plastics including bunker tarps, bulka bags and bale twine. These 3 products are made from polypropylene, are all mainly used in farming grain and are traditionally sent to landfill at the end of life.

GT Recycling collects these products as waste and converts them to pellets to enable the manufacture of new plastic products. To determine the feasibility of these pellets being used to make void formers, lab-based testing was conducted to understand the possible variations in melt density, strength and degree of shrinkage.

Analytical studies and factory-based trials were also conducted to determine design optimisation and functionality. Ultimately the bunker tarp recycled plastic was determined to be the preferred material for creating new void former products.

The project successfully utilised advanced 3D-printing methods for the complex components of developing the prototype from recycled plastics. The 3 project stages included:

• Lab-based testing: Differential scanning calorimetry, Rheology/viscosity/MFI testing, Thermogravimetric testing, Fourier Transform Infrared Spectroscopy (FTIR), Tensile and Dynamic Mechanical testing, Density testing, Shrinkage tests
• Analytical studies: Moldflow analysis of plastic flow during production, Finite element analysis of part functionality during usage, Parametric design optimisation of part and tooling based on the analytical results.
• Factory-based trials: Injection moulding trials, production optimisation and part functionality tests.

The partnership

Swinburne University was the project lead. Historically, they have worked with ROBOVOID Pty Ltd to conduct a full range of experimental investigations on various plastic void formers in concrete applications. The work was expanded upon in this project to replace the virgin plastic with up to 100% recycled plastic.

GT Recycling recently invested in a new plant and equipment in Victoria to increase its plastic recycling capacity. GT Recycling provided recycled plastic pellets for the testing and trials of this project.

ROBOVOID provided product IP, engineering expertise and manufacturing capability. ROBOVOIDS’s void former has the capacity to take advantage of GT Recycling's current product outputs and materials, allowing the diversion of low value plastics into high volume applications.

Pathway to commercialisation

Recycled plastic ROBOVOID technology is being developed further and the research team has subsequently obtained a grant from the federal government for a 30-month CRC Project Round 8 worth $2,361,232. The project now has a broader spread of partners across the construction supply chain and a focus on:

• recycled plastic material characterisation (further work on additional material sources, combinations and with additives),
• structural testing, facade and fire testing, automated manufacturing and design guidance.

Further phases will include demonstration projects, certification and commercialisation activities.

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