Researchers at MIT have found that by exposing plastic flakes to small, harmless doses of gamma radiation, then pulverizing the flakes into a fine powder, they could produce concrete that is up to 15% stronger than conventional concrete.

Concrete is the second most widely used material, after water, on Earth. The manufacturing of concrete generates about 4.5% of the world’s human-induced carbon dioxide emissions. Replacing even a small portion of concrete with irradiated plastic could help reduce the cement industry’s global carbon footprint.

At the same time, reusing plastics as concrete additives would reduce the amount of plastic sent to landfill or left in the environment.

There have been previous attempts to introduce plastic into cement mixtures, but the plastic weakened the resulting concrete. However, exposing the plastic to doses of gamma radiation makes its crystalline structure change in a way that the plastic becomes stronger, stiffer and tougher.

The researchers irradiated flakes of polyethylene terephthalate – the plastic material used to make water and soda bottles – using a cobalt-60 irradiator that is typically used commercially to decontaminate food. The irradiated plastic was ground into a powder a mixed with normal Portland cement and one of two common additives, fly ash from burning coal or silica flume from silicon production. Each sample contained about 1.5% plastic.

Samples with non-irradiated plastic were weaker than conventional concrete. Adding fly ash or silica flume strengthened the concrete but the sample with irradiated plastic and fly ash was even stronger being about 15% stronger than concrete with no additives.