MIT students fortify concrete by adding recycled plastic

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Betonmischung (Foto: © Norbert Lorenz / http://www.pixelio.de)

Cambridge, Massachusetts, USA — Discarded plastic bottles could one day be used to build stronger, more flexible concrete structures, from sidewalks and street barriers, to buildings and bridges, according to a new study. 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.

“There is a huge amount of plastic that is landfilled every year,” says MIT assistant professor Michael 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.”

To answer that question, the students first obtained flakes of polyethylene terephthalate — plastic material used to make water and soda bottles — from a local recycling facility. The team exposed various batches of flakes to either a low or high dose of gamma rays. They then ground each batch of flakes into a powder and mixed the powders with a series of cement paste samples, each with traditional Portland cement powder and one of two common mineral additives: fly ash (a byproduct of coal combustion) and silica fume (a byproduct of silicon production). Each sample contained about 1.5 percent irradiated plastic.

The team finally analyzed their samples using X-ray diffraction, backscattered electron microscopy, and X-ray microtomography. The 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 more dense and therefore stronger. “At a nano-level, this irradiated plastic affects the crystallinity of concrete,” research scientist Kunal Kupwade-Patil 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.”

“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,” Kupwade-Patil says. “The method has the potential to achieve sustainable solutions with improved performance for both structural and nonstructural applications.”

The full story can be read under news.mit.edu.

Source: Massachusetts Institute of Technology