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MIT Students Use Plastic For Stronger Concrete

Friday, October 27, 2017

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Researchers at the Massachusetts Institute of Technology have begun testing the impact of adding bits of irradiated plastic into cement. What they found could hold up to competition.

Recent graduate Carolyn Schaefer and MIT senior Michael Ortega had begun the research as part of a Nuclear Systems Design Project.

MIT News

Researchers at the Massachusetts Institute of Technology have begun testing the impact of adding bits of irradiated plastic into cement. What they found could hold up to competition.

“They wanted to find ways to lower carbon dioxide emissions that weren’t just, ‘let’s build nuclear reactors,’” said Michael Short, an assistant professor in MIT’s Department of Nuclear Science and Engineering. “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 Study

The students wanted to explore the idea of adding plastic that would normally end up in landfills, such as bottles of water or other drinks. In their preliminary research they found that others have mixed plastic into cement mixtures before, and the plastic had actually weakened the resulting concrete.

However, they also found that exposing plastic to doses of gamma radiation makes the materials’ crystalline structure change. In fact, the radiation makes the plastic stronger and stiffer.

So, the students obtained polyethylene terephthalate (the plastic that makes up most bottles) and used MIT’s cobalt-60 irradiator, which emits gamma rays (a radiation that is typically used to decontaminate food and doesn’t leave traces of radiation).

After batches of plastic flakes were exposed to either low or high doses of gamma rays the material was ground into a power and mixed to create a series of cement samples. Each sample ended up containing about 1.5 percent plastic.

Once those samples were mixed with water, they were poured into cylindrical molds, left to cure, and then the resulting concrete was subjected to compression tests.

They found that the samples with the irradiated plastic mixed in was 20 percent stronger compared with samples just made from Portland cement.

Further Research

After the compression tests, the samples were taken to the Argonne National Laboratory and the Center for Materials Science and Engineering at MIT where they were analyzed.

That analysis revealed that the cement mixture containing the irradiated plastic had a crystalline structure with more cross-linking, or more molecular connections. Those structures were also found to block pores within the concrete, thus making it stronger.

“At a nano-level, this irradiated plastic affects the crystallinity of concrete,” said Kunal Kupwade-Patil, a research scientist in the Department of Civil and Environmental Engineering. “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.”

The team plans to continue its research with different types of plastic and doses of radiation.

   

Tagged categories: Cement; concrete; Research; Research and development

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