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Researchers used recycled plastic and irradiated it with gamma rays; the result was a mixture of concrete with 1.5% of that material, 15% stronger

In an experiment conducted by the Massachusetts Institute of Technology (MIT), a group of researchers discovered that mixing plastic with a conventional concrete composition may make it 15% stronger. The use of plastic in this context has two additional benefits: it gives plastic that would be disposed a noble use and, by reducing the amount of cement required in the mixture, it lowers the total emission of carbon dioxide from the material production process. Overall, according to the Institute, the manufacture of concrete generates about 4.5% of global carbon footprint.

The idea of mixing plastic with concrete came to life from the need of finding alternatives for the impact on the environment due to production of concrete – the second most used material on the planet, just behind water. “There is a huge amount of plastic that is landfilled every year,” says Michael Short, professor at MIT, in a statement to the Institute. “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”, he summarized.

How is plastic mixture for concrete made?

The recipe is unorthodox. The plastic used in the cement starts out as flaked plastic of recycled origin. This plastic is then exposed to cobalt-60 irradiator, a tool that emits gamma rays usually applied for decontamining food. Next, the material is ground until it turns into powder, which is mixed with traditional cement paste with mineral additives that are coal and silicon byproducts. The proportions were a big challenge, but the ideal recipe turned out to be 1.5% of irradiated plastic in the mixture.

The team states that there is no risk of toxic radioactivity in human beings with that material. “There’s no residual radioactivity from this type of irradiation,” Short says. “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”, he explains.

The next step of the experiment will continue testing the use of new types of plastic and the optimal dosing of gamma rays to make them even stronger and eco-friendly.

Concreto feito de plástico. Crédito: MIT News

Concrete and environment

Concrete is most commonly used in the construction field, whether to erect buildings and houses, or in urban structures such as roads, bridges and dams. It is estimated that global concrete production is growing about 2.5% a year and, by 2050, it will have reached 3.74 billion tons annually.

Its production requires a large amount of energy, due to the intense heat needed to compose cement, its main material. Producing a ton of cement requires 4.7 million BTU of energy, equivalent to about 400 pounds of coal. This process accounts for 50% of all emissions from cement production, 40% from combustion of fuels for the kiln and 10% related to energy transmission.

The result is that for each ton of product, a ton of CO2 emissions is generated. “Concrete produces about 4.5% of the world’s carbon dioxide emissions,” Short reiterates. “Take out 1.5% of that, and you’re already talking about 0.0675% of the world’s carbon dioxide emissions.  That’s a huge amount of greenhouse gases in one fell swoop,” he completed.

Thus, the introduction of recycled plastic in its composition has a dual function: avoid more waste of material in landfills and reduce the large amount of carbon emissions produced during its manufacture.

Content published in September 28, 2018

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