Quantcast
Science
MIT News

Recycled Plastic Can Fortify Concrete, MIT Students Find

By Jennifer Chu

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.


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," said 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," said 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.

"They wanted to find ways to lower carbon dioxide emissions that weren't just, 'let's build nuclear reactors,'" Short said. "Concrete production is one of the largest sources of carbon dioxide, and they got to thinking, 'how could we attack that?' They looked through the literature, and then an idea crystallized."

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?

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. Schaefer and Ortega manually sorted through the flakes to remove bits of metal and other debris. They then walked the plastic samples down to the basement of MIT's Building 8, which houses a cobalt-60 irradiator that emits gamma rays, a radiation source that is typically used commercially to decontaminate food.

"There's no residual radioactivity from this type of irradiation," Short said. "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."

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.

Once the samples were mixed with water, the researchers poured the mixtures into cylindrical molds, allowed them to cure, removed the molds, and subjected the resulting concrete cylinders to compression tests. They measured the strength of each sample and compared it with similar samples made with regular, nonirradiated plastic, as well as with samples containing no plastic at all.

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 strengthened the concrete even further, increasing its strength by up to 20 percent compared with samples made just with Portland cement, particularly in samples with high-dose irradiated plastic.

The concrete road ahead

After the compression tests, the researchers went one step further, using various imaging techniques to examine the samples for clues as to why irradiated plastic yielded stronger concrete.

The team took their samples to Argonne National Laboratory and the Center for Materials Science and Engineering (CMSE) at MIT, where they analyzed them 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," Kupwade-Patil said. "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 said. "The method has the potential to achieve sustainable solutions with improved performance for both structural and nonstructural applications."

Going forward, 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 said, 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 said. "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 said.

Reposted with permission from our media associate MIT News.

Show Comments ()

EcoWatch Daily Newsletter

Sponsored
Climate
Sea ice in the Arctic Ocean. NASA

Not Enough Ice to Drill the Arctic! Offshore Oil Drilling a 'Disaster Waiting to Happen'

Last month, the Trump administration approved the first offshore oil drilling development in federal Arctic waters, which environmentalists fear will ramp up carbon pollution that fuels climate change.

But here's the ultimate irony: Hilcorp Alaska's project—which involves building a 9-acre artificial drilling island in the shallow waters of the Beaufort Sea—has been delayed because of the effects of climate change, Alaska Public Media reported.

Keep reading... Show less
Popular
Westend61 / Getty Images

EcoWatch Gratitude Photo Contest: Submit Now!

EcoWatch is pleased to announce its first photo contest! Show us what in nature you are most thankful for this Thanksgiving. Whether you have a love for oceans, animals, or parks, we want to see your best photos that capture what you love about this planet.

Keep reading... Show less
Insights
Dominion Energy's headquarters in Richmond, Virginia. VCU CNS

Cash Buys Elections—and Continued Fossil Fuel Dominance

By Wenonah Hauter

Last week, the fossil fuel industry successfully squashed several local measures it didn't like—thanks to the more than $100 million it shelled out to oppose them.

Keep reading... Show less
Fracking
Rick Rappaport

World’s Largest Fracked-Gas-to-Methanol Refinery Must Be Stopped: Submit a Comment Today!

Tuesday, a report written by the company proposing the world's largest fracked-gas-to-methanol refinery was released by the Port of Kalama and Cowlitz County, Washington. The proposed fossil fuel refinery is controversial because of the impacts on both local residents' health and our climate. Despite the company's claim that the refinery could result in a climate benefit, the refinery would consume a stunning amount of fracked natural gas—one-third as much gas as the entire state of Washington.

Keep reading... Show less
Sponsored
Business
Drinkworks

How Green Is the New Keurig Cocktail Machine?

This week, Keurig and Anheuser-Busch made headlines with the launch of the Drinkworks Home Bar, a pod-based appliance that makes cocktails, brews and ciders at the push of a button.

Look, I get it. An instant, no-fuss Old Fashioned—which normally requires muddling sugar, water and bitters and mixing in many other ingredients—sounds great!

Keep reading... Show less
Climate
The Climate Reality Project

First Look: 24 Hours of Reality: Protect Our Planet, Protect Ourselves

In many places, the leaves have fallen and the first frosts have turned the air crisp. The days are getting shorter. Most birds are well on their way south, and the holidays are just around the corner. And in just a few weeks, on Dec. 3-4, we'll present our eighth annual global broadcast of 24 Hours of Reality.

Keep reading... Show less
Sponsored
Climate
Student leaders behind the movement calling on the UN to highlight key data on imminent global collapse. Our Future Uncompromised

20,000+ Students to UN: Publicize Key Facts to Prevent Global Collapse

24,500 students representing every country in the EU have added their names to the list of young people fighting for a future for themselves and the earth.

The students, who organize under the banner of Our Future Uncompromised and attend the prestigious Schola Europaea network of international schools, are calling on the United Nations (UN) to "stop withholding" crucial scientific information that they say could help avert the duel catastrophes of resources depletion and climate change, the students announced Thursday in an email sent to EcoWatch.

Keep reading... Show less
Politics
Trump at Big Sandy Superstore Arena in Huntington, West Virginia on Aug. 3, 2017. SAUL LOEB / AFP / Getty Images

Trump Team Plans 'Sideshow on Coal' at UN Climate Talks

No one really expects the coal-friendly Trump administration to take significant action on climate change, but this is just trolling.

A new exclusive from Reuters claims that the president's team will "set up a side-event promoting fossil fuels" at the global climate summit this December, aka COP 24, in Katowice, Poland.

Keep reading... Show less
Sponsored

mail-copy

The best of EcoWatch, right in your inbox. Sign up for our email newsletter!