Massachusetts Institute of Technology (MIT) undergraduate students have 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 plastic with cement paste to produce concrete that is up to 20 percent stronger than conventional concrete.
Concrete is, after water, the second most widely used material on the planet. The manufacturing of concrete generates about 4.5 percent of the world’s human-induced carbon dioxide emissions. Replacing even a small portion of concrete with irradiated plastic could thus help reduce the cement industry’s global carbon footprint.
Reusing plastics as concrete additives could also redirect old water and soda bottles, the bulk of which would otherwise end up in a 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.”
The team includes Carolyn Schaefer ‘17 and MIT senior Michael Ortega, who initiated the research as a class project; Kunal Kupwade-Patil, a research scientist in the Department of Civil and Environmental Engineering; Anne White, an associate professor in the Department of Nuclear Science and Engineering; Oral Büyüköztürk, a professor in the Department of Civil and Environmental Engineering; Carmen Soriano of Argonne National Laboratory; and Short. The new paper appears in the journal Waste Management.
“This is a part of our dedicated effort in our laboratory for involving undergraduates in outstanding research experiences dealing with innovations in search of new, better concrete materials with a diverse class of additives of different chemistries,” says Büyüköztürk, who is the director of Laboratory for Infrastructure Science and Sustainability. “The findings from this undergraduate student project open a new arena in the search for solutions to sustainable infrastructure.”
An idea, crystallized
Schaefer and Ortega began to explore the possibility of plastic-reinforced concrete as part of 22.033 (Nuclear Systems Design Project), in which students were asked to pick their own project.
The students learned that others have tried to introduce plastic into cement mixtures, but the plastic weakened the resulting concrete. Investigating further, they found evidence that exposing plastic to doses of gamma radiation makes the material’s crystalline structure change in a way that the plastic becomes stronger, stiffer, and tougher. Would irradiating plastic actually work to strengthen concrete?
The team is planning to experiment 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 percent of concrete with irradiated plastic can significantly improve its strength. While that may seem like a small fraction, Short says, implemented on a global scale, replacing even that amount of concrete could have a significant impact.
“Concrete produces about 4.5 percent of the world’s carbon dioxide emissions,” Short says. “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.”
“This research is a perfect example of interdisciplinary multiteam work toward creative solutions, and represents a model educational experience,” Büyüköztürk says.