Irradiated plastic can help build stronger, more flexible concrete structures while reducing carbon emissions from the cement industry.
A team from Massachusetts Institute of Technology (MIT) found that, by exposing plastic flakes to small, harmless doses of gamma radiation, then pulverizing the flakes into a fine powder, they can mix the irradiated plastic with cement paste and fly ash to produce concrete that is up to 15 per cent stronger than conventional concrete.
Michael Short, an assistant professor in MIT’s Department of Nuclear Science and Engineering, said manufacturing of concrete generates about 4.5 per cent of the world’s human-induced carbon dioxide emissions so replacing even a small portion of concrete with irradiated plastic could help reduce the cement industry’s global carbon footprint
“There is a huge amount of plastic that is landfilled every year,” said Short.
“Our technology takes plastic out of the landfill, locks it up in concrete, and also uses less cement to make the concrete, which makes fewer carbon dioxide emissions. This has the potential to pull plastic landfill waste out of the landfill and into buildings, where it could actually help to make them stronger.”
Earlier research found that introducing plastic into cement mixtures weakened the resulting concrete. However, a couple of MIT students found research that exposing plastic to gamma radiation changes its crystalline structure to become stronger, stiffer, and tougher, and decided to investigate whether it could strengthen concrete.
They made a range of concrete samples, some with and without plastic. The ones with plastic were made with plastic that either hadn't been irradiated at all, had a low dose of gamma radiation or a high dose.
The team found that, in general, samples with regular plastic were weaker than those without any plastic. Samples made with fly ash or silica fume were stronger than concrete made with just Portland cement. And the presence of irradiated plastic along with fly ash strengthened the concrete even further, increasing its strength by up to 15 percent compared with samples made just with Portland cement, particularly in samples with high-dose irradiated plastic.
The next step for the team is experimenting with different types of plastics, along with various doses of gamma radiation, to determine their effects on concrete. For now, they have found that substituting about 1.5 per cent of concrete with irradiated plastic can significantly improve its strength. Short says that, while replacing 1.5 percent of concrete with plastic may seem like a small fraction, when implemented on a global scale, it could have a significant impact.
“Concrete produces about 4.5 per cent of the world’s carbon dioxide emissions,” he said.
“Take out 1.5 per cent of that, and you’re already talking about 0.0675 percent of the world’s carbon dioxide emissions. That’s a huge amount of greenhouse gases in one fell swoop.”
[Image: MIT]