Concrete has shaped the modern world. Other than water, it is the most widely used material on the planet so it's unsurprising that scientists are constantly working to make it safer, stronger and more environmentally friendly. A team of MIT students have discovered a clever technique that uses irradiated plastic bottles to make a new concrete up to 20 percent stronger than regular concrete.
The students were initially exploring ways to reduce the global carbon footprint of the concrete industry, which accounts for 4.5 percent of the world's man-made carbon dioxide emissions. They also wondered if there was a way to recycle the huge amount of plastic that goes into landfill every year and use it to improve concrete production.
Other research into incorporating plastics into cement has been unsuccessful, with the plastic weakening the concrete, but the team wondered if there was a way to treat the plastic so it could ultimately strengthen concrete?
The research revealed that exposing the plastic to gamma radiation actually made it stronger. The irradiated plastic was then ground into a power and mixed with cement. The subsequent concrete was up to 20 percent stronger than concrete made without the irradiated plastic.
"We have observed that within the parameters of our test program, the higher the irradiated dose, the higher the strength of concrete, so further research is needed to tailor the mixture and optimize the process with irradiation for the most effective results," says Kunal Kupwade-Patil, one of the research scientists working on the project.
Examining the plastic-infused concrete using backscattered electron microscopy and X-ray microtomography the team discovered that crystallinity of the concrete was fundamentally altered to become denser with the addition of the irradiated plastic. It's also worth noting that the final product doesn't hold any radioactivity.
"There's no residual radioactivity from this type of irradiation," explains Michael Short, assistant professor in MIT's Department of Nuclear Science and Engineering. "If you stuck something in a reactor and irradiated it with neutrons, it would come out radioactive. But gamma rays are a different kind of radiation that, under most circumstances, leave no trace of radiation."
Despite the irradiated plastic only consisting of 1.5 percent of the concrete mix, the researchers suggest that on a global scale this would still have a significant impact on carbon emissions, as well as reducing plastic landfill and creating a stronger concrete product. There is no mention of how much energy (or carbon emissions) go into recycling and irradiating the plastic so we do remain slightly skeptical of the overall emission reduction resulting from the process.
"Concrete produces about 4.5 percent of the world's carbon dioxide emissions," says Short. "Take out 1.5 percent 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."
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