Stronger concrete, waste diversion from landfills, reduced carbon dioxide emissions. MIT undergraduates accomplished all three by reinforcing concrete formulations with plastic flakes.

The researchers exposed flakes of polyethylene terephthalate — material used to make water and soda bottles — to harmless gamma radiation doses. The flakes were then pulverized into a fine powder and mixed with cement paste. The result: concrete that is up to 20 percent stronger than conventional concrete. The radiation treatment, performed in MIT’s cobalt-60 irradiator, alters and strengthens the material’s crystalline structure.

“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.

“Concrete produces about 4.5 percent of the world’s carbon dioxide emissions. Take out 1.5 percent of that, “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,” says assistant professor Michael Short. Source: MIT Newsand 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.”

Samples composed of 1.5 percent irradiated or control plastic, Portland cement and either flyash or silica fume were subjected to compression tests. Those containing the control, non-irradiated plastic proved weaker than samples without any plastic. Concrete with fly ash or silica fume was stronger than concrete made with just Portland cement. The inclusion of irradiated plastic strengthened the concrete even further, increasing its strength by up to 20 percent compared with samples made just with Portland cement.

X-ray diffraction, backscattered electron microscopy and X-ray microtomography techniques were next applied. High-resolution images revealed that samples containing irradiated plastic, particularly at high doses, exhibited crystalline structures with more cross-linking, or molecular connections. In these samples, the crystalline structure also seemed to block pores within concrete, making the samples denser and therefore stronger.

“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, a research scientist in the department of civil and environmental engineering. “The method has the potential to achieve sustainable solutions with improved performance for both structural and nonstructural applications.”