Polymer waste for cement-free paving
Plastic waste could be redirected from landfill and used to replace cement in concrete paving, according to a joint Latvian-Spanish EUREKA funded project known as SANDPLAST.
Researchers at the Latvian Technological Centre and the Institute of Polymer Mechanics at the University of Latvia, both in Riga, working with Spanish cement company Hormigones Uniland, based in Barcelona, have discovered that by melting polyethylene terephthalate bottles, cartons and yoghurt pots and mixing them with sand, crushed glass and gravel, they were able to create a cement-free binding substance for concrete blocks. The company was unable to go into detail regarding the manufacturing process as a patent is pending.
‘Twenty-five per cent of polymer waste is not suitable for recycling because it is either too dirty, contains a mixture of different types of polymers, or is simply economically unviable’, explains Dr Juris Balodis, project manager at the Latvian Technology Centre. ‘It is much more environmentally friendly to make useful products from this worthless fraction of polymer waste [than sending it to landfill].’
Balodis claims that polymer concrete bricks are more durable than those made from cement. ‘They resist temperature variations like freezing and thawing, as plastic does not absorb water’, he says. ‘This makes them ideal for outdoor use such as paving and street furniture.’
Paving bricks based on the composite were introduced to the Latvian market in 2003 at a slightly lower price than traditional paving bricks, thanks to Latvian state subsidies for waste processing which have kept the cost of production down.
But the SANDPLAST team is developing new machinery to accelerate productivity and make the technology commercial viable without subsidies.
‘The current rate [of production] is three bricks per minute, but we want to increase that to between 30 and 60 per minute,’ says Balodis. ‘It is not possible to increase productivity with the existing method of preparing the melted concrete polymer mass, therefore a new technology for preparation is underway to increase production within the next few years.’
Spin-off company, Partneris L.V., also in Riga, is currently working to develop new building products from polymer waste.
However, the bricks cannot be used in buildings as the polymer concrete binds poorly with mortar and does not meet fire regulation standards due to the material’s relatively low melting point.