A research team from MiT has found that concrete is stronger when irradiated plastic is used as a raw material. While previous studies have found that plastic flakes are useable as a construction ingredient, the resulting concrete has always been weaker. The use of waste plastic as a construction material would reduce carbon dioxide emissions, as well as redirecting discarded PET bottles from landfill.
“There is a huge amount of plastic that is landfilled every year,” says Michael Short, an assistant professor in MIT’s Department of Nuclear Science and Engineering. “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.”
As the construction industry journal Durability and Design noted, “the students obtained polyethylene terephthalate (the plastic that makes up most bottles) and used MIT’s cobalt-60 irradiator, which emits gamma rays (a radiation that is typically used to decontaminate food and doesn’t leave traces of radiation).”
“There’s no residual radioactivity from this type of irradiation,” Short says. “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.”
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After irradiating the plastic flakes, the researchers then used them to make four different types of cylindrical concrete samples. The first was a traditional form of concrete, with fly ash or silica fume as a raw material. The second was concrete made without fly ash or silica fume. The third substituted 1.5% concrete for regular nonirradiated plastic flakes, and the fourth used the Gamma ray treated plastic, also at 1.5% substitution rate.
The results, as the MiT website reports, are potentially game-changing. “They found that, in general, samples with regular plastic were weaker than those without any plastic. The concrete with fly ash or silica fume was 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 team has now published their results in the peer-reviewed journal, Waste Management.
“At a nano-level, this irradiated plastic affects the crystallinity of concrete,” Kunal Kupwade-Patil, a research scientist at MiT‘s Department of Civil and Environmental Engineering, says. “The irradiated plastic has some reactivity, and when it mixes with Portland cement and fly ash, all three together give the magic formula, and you get stronger concrete.”
The team is now planning to experiment with different types of plastics, along with various doses of gamma radiation, to determine their effects on concrete. And while 1.5% may seem like an insignificant amount of concrete to replace, on a global level the change could make a big difference, given that the world uses 100,000,000,000 tons of concrete every year.
As Short says, “Concrete produces about 4.5 percent of the world’s carbon dioxide emissions. 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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Photo credit: MiT, Urbanghosts, and Wired
