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 ()
Sponsored
Climate
Deep-sea corals may not be flashy, but they deserve a second look. Oceana

Ignoring Deep-Sea Corals Is Risky for the Oceans, and for Us

By Nathan Johnson

The deep sea might be cold and dark, but it's not barren. Down here, an incredible diversity of corals shelters young fish like grouper, snapper and rockfish. Sharks, rays and other species live and feed here their whole lives.

Brightly colored coral gardens, far beyond the reach of the sun's rays, don't just nurture deep-sea life. They also help advance medical research and understand climate change.

Keep reading... Show less
Energy
Kristian Buus / Greenpeace

Green Groups Balk at England’s Plan to Fast Track Fracking

Government ministers published proposals Thursday that would speed the development of fracking in England, igniting opposition from environmental groups and local communities, The Independent reported.

Keep reading... Show less
Energy

Before Royal Wedding Sermon, Rev. Curry Stood With Standing Rock Pipeline Opponents

Bishop Michael Curry, who delivered a passionate wedding sermon to royal newlyweds Prince Harry and Meghan Markle on Saturday, also gave a powerful message about two years ago to Dakota Access Pipeline protesters at Standing Rock, North Dakota.

On Sept. 24, 2016 at the Oceti Sakowin Camp, the reverend offered the Episcopal Church's solidarity with the water protectors, noting that, "Water is a gift of the Creator. We must protect it. We must conserve it. We must care for it."

Keep reading... Show less
Climate
Coral bleaching like this (in the Great Barrier Reef) is killing the largest reef in Japan. Oregon State University / CC BY-SA 2.0

Only 1% of Japan’s Largest Reef Still Healthy After Historic Bleaching Catastrophe

In a sobering reminder of the impact of climate change on marine biodiversity, a survey by the Japanese government found that barely more than one percent of the coral in the country's largest coral reef is healthy, AFP reported Friday.

The reef, located in the Sekisei Lagoon near Okinawa, has suffered mass coral bleaching events due to rising sea temperatures in 1998, 2001, 2007 and 2016.

Keep reading... Show less
Sponsored
Energy

Train Carrying 250,000 Liters of Fuel Derails on Kenyan Coast

A cargo train carrying 250,000 liters (66,000 gallons) of super petroleum, or unleaded gasoline, derailed off its tracks after taking a sharp turn along Kenya's eastern coast, forcing the closure of a major highway over the weekend, according to local reports.

The accident occurred early Sunday in Kibarani in Mombasa County, and prompted authorities to completely close off Makupa Causeway, the main link between the mainland and Mombasa Island, fearing a fire would break out after spillage of the highly flammable liquid, The Star, Kenya reported.

Keep reading... Show less
Politics
The farm bill's historic conservation provisions are important for preserving grassland biodiversity, like this black-footed ferret and prairie dog. USFWS Mountain-Prairie / CC BY 2.0

Farm Bill Harmful to Endangered Species and Conservation Fails in House

A farm bill with dangerous consequences for endangered species and conservation efforts failed to pass the House on Friday, The Guardian reported.

The 2018 version of the major agricultural bill was criticized by environmental groups because it would have allowed the Environmental Protection Agency (EPA) to approve new pesticides without assessing their impact on wildlife protected under the Endangered Species Act. The bill would also have cut funding for land conservation programs by $800 million over the next ten years.

Keep reading... Show less
Sponsored
Animals
Pixabay

Controversial Kangaroo Cull Underway in Canberra

By Stephanie Koorey

May is late autumn in the southern hemisphere, and as we creep closer to winter, Canberra, Australia's capital city, is carrying out its annual, and controversial, kangaroo cull. With some pride, the city is known as the "bush capital" due to its wide corridors of native grasslands and gumtree and casurina tree woodlands, and an abundance of accompanying wildlife. As the city sprawls, it is displacing native habitats. At the same time, suburban lawns and sports ovals offer appealing alternative spaces for some animals, particularly our largest and most mobile grazing species, the eastern grey kangaroo. Due in part to the near disappearance of the kangaroo's main natural predator, the dingo or wild dog, and declines in traditional Indigenous hunting, kangaroo populations have exploded over recent decades.

Keep reading... Show less
Food
pxhere

Opinion: The 2018 Farm Bill Battle Lines Have Been Drawn: Here’s What You Can Do

Last week, the Republican-drafted Farm Bill, called the Agriculture and Nutrition Act of 2018 (H.R. 2), failed spectacularly on the House floor when Republicans tried to leverage the farm bill to placate conservatives' agenda on immigration. Nevertheless, H.R. 2, which generally benefits large commodity producers while compromising long-term food security, provides a helpful view into where the policy battles are being fought on the road to passage.

Keep reading... Show less
Sponsored

mail-copy

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