Feb 18, 2016

Plastic fantastic in concrete mix

Plastic fantastic in concrete mix

The engineering team at James Cook University has shown how to walk the walk when it comes to recycling plastic.

Plastic fibre from industrial waste has been successfully used to reinforce concrete footpaths, replacing more traditional steel mesh reinforcement, in a joint JCU-Fibercon project.

JCU College of Science, Technology and Engineering (CSTE) senior lecturer Dr Rabin Tuladhar said the 50mm-long recycled plastic fibres could be mixed in concrete trucks.

“You don’t have to put steel in the formwork, so it saves a lot of labour and cost,” he said. “You just mix the fibre into the concrete in the truck and pour it straight into the formwork.”

Dr Tuladhar said the product had been trialled at JCU’s Douglas Campus, Townsville, in a 100m long concrete footpath near the planned Science Place building and another along Parkinson Rd.

It helped prevent shrinkage cracks in concrete, a significant problem in the dry tropics, he said.

“It also improves post-cracking performance in concrete. The fibres hold the crack together and don’t let it grow or expand.”

While the use of plastic fibre in concrete is nothing new, it is virgin plastic that has been used rather than recycled material.

Dr Tuladhar said also much of the previous research work on the potential use of recycled plastic fibres in concrete had focused on polyethylene terephthalate (PET) plastics.

This was limited to laboratory tests with extremely low production rates and the PET fibres were found to degrade when embedded in concrete.

The JCU project used recycled polypropylene (PP) fibres from industrial plastic wastes such as offcuts and packaging, he said.

This is melted into granules, then extruded and hot drawn in the production process. Diamond-shaped surface indents are then placed on the fibre surface to improve its bonding with the concrete matrix.

“This process of producing recycled plastic fibres is suitable for large-scale commercial production,” Dr Tuladhar said.

Researchers tested properties including tensile strength and whether the material degrades over time, as well as calculating the savings in carbon emissions to be made.

Dr Tuladhar said the life cycle assessment showed the manufacturing of recycled plastic fibre produced 90 per cent less CO2 and eutrophication (contamination of water bodies with nutrients) compared to steel required to achieve equivalent reinforcement. It also reduced plastic wastes going into landfills, contributing to sustainable development.

Dr Tulahdar said Fibercon had sponsored a PhD project, running from 2012 to the end of 2015, on the plastic fibres and was now commercialising the product.

Meanwhile JCU would extend its research in the area, he said.

This could include looking at surface modifiers to improve bonding in concrete and testing the feasibility of using PET plastics with modifications to avoid degradation.

The JCU-Fibercon project won the Manufacturing, Construction and Infrastructure category of the Australian Innovation Challenge for 2015.

More technical details are available in published papers:

  1. Post-cracking performance of recycled polypropylene fibre in concrete, Construction and Building Materials (2015): https://goo.gl/jKgDMg
  2. A life cycle assessment of recycled polypropylene fibre in concrete footpaths, Journal of Cleaner Production (2015): https://goo.gl/OjL4Oj
  3. Fiber preparation and mechanical properties of recycled polypropylene for reinforcing concrete, Journal of Applied Polymer Science (2015): https://goo.gl/aJCeHL
  4. Use of macro plastic fibres in concrete: A review, Construction and Building Materials (2015): https://goo.gl/2PWtdn

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