Recycling plastic into concrete

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Researchers at the BAM Federal Institute for Materials Research and Testing in Berlin, have developed a technique for turning plastic ash from incineration plants into a form of concrete that is suitable for building roads.

Incineration is an increasingly popular method of waste disposal. Although it reduces the volume of waste by around 95 percent, the products are still often disposed of in landfill sites.

The researchers used material from a modern waste-to-energy plant in Hamburg. The ash left behind in the furnace is already often reused in coarse form to construct roads, but has previously contained too many impurities to be strong enough for use in concrete.

The most harmful impurities are aluminium and glass, which cause cracks to appear in the concrete. To remove glass, transparent particles were automatically detected and removed mechanically, while storage in sodium hydroxide solution and subsequent washing, reduces the aluminium content to less than 0.4 per cent.

The results were tested by producing concretes where the usual aggregates were replaced by bottom ashes treated in various ways. The engineering properties of the concrete, such as workability, compressive strength, elasticity and porosity, were assesseded, demonstrating that treating the bottom ash improves the quality of the concrete produced.