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12 November 2012

Plastic waste set in concrete

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Because plastic is widely available and not biodegradable, it is a material of choice to include as a component of light concrete

In Europe more than 12 million tonnes of mixed plastic waste are dumped on landfills every year, according to a report from NUMIX scientists. The recycling of plastic into usable products has proven difficult. That’s because plastic waste contains many different types of plastic that have to be treated in different ways for recycling.  Now, a new method designed to create expanded construction nodules from mixed plastic waste may replace the expanded clay traditionally used in light concrete that is not used for structural part of a building and often contains air bubbles.

"If you look at the volume of light-weight concrete that is now produced in Europe, we could potentially use all the mixed plastic waste," Alessandra Passaro tells He is the coordinator of the EU funded NUMIX programme, which developed the new technology, and a materials engineer at CETMA, a research organisation based in Brindisi, Italy.

The wide availability of plastic waste an advantage combined with the fact that it is not biodegradable.  "We performed a lot of tests to make sure that mixed plastics could be used in concrete," says Passaro, adding that researchers expect that the plastic will survive at least a hundred years.

However, promoting the technology, which CETMA patented, has still proven difficult, according to Passaro, despite the fact that:" [this] aggregate has a cost that is similar to the aggregate made with expanded clay," he says. Economic incentives, such as subsidies for recycling mixed plastic waste are lacking or have been cancelled because of the financial crisis, points out Passaro.

To their surprise, the researchers found that there is also a psychological barrier to adopting this technology.  But there is more interest at the European level for the clay aggregate, because it is viewed as a more sustainable and ecofriendly material. "The presence of European standards that would have taken into account the possibility of using mixed plastic aggregate would have been of help," comments Passaro. 

Roger Morton, Director of Axion Recycling Ltd, a London, UK-based company that also sells mixed plastic waste to companies that process it further to convert it into high-grade plastic waste and also for the production of fuel, agrees that the introduction of mixed plastic waste in concrete might meet with resistance in the market. "Concrete is a very long-lasting material and people would be nervous about an unknown component that may prove to cause problems," he tells, “You want a lot of evidence that the material will remain strong and not crack.” But he agrees that the technology is interesting for non-supporting structures.

However, there is a need to evaluate the ecological impact and sustainability of using plastic waste in the cement industry. "What we call ‘fluff’, paper and plastic waste, is used as fuel in the production of cement. So we have to find out what is more sustainable: burning the plastic waste or use it as a filler in concrete," explains Christian Rech, an engineering consultant at cement manufacturer Cimalux, in Esch-sur-Alzette, Luxembourg. In addition, the recyclability of concrete matters too.  Some local authorities, such as Zürich, require that concrete be recyclable. This means that using plastic filler in concrete will then require extra processing for separating out the plastic. Rech also wonders how the aggregate will behave in case of fire and whether it will affect its resistance against heat.  He concludes: "These are all points that still have to be clarified.”

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