Architects, engineers and contractors have long been aware that manufacturing cement and, by extension, concrete releases a lot of carbon dioxide into the atmosphere.
That knowledge has spurred a lot of research both in government laboratories and on campuses around the world.
The work is usually initiated in response to industry needs and is done by faculty members, although graduate students routinely play a role.
But one of the best ideas to come along in recent years is the brainchild of a couple of undergraduate students at the Massachusetts Institute of Technology (MIT). There, Carolyn Schaefer and Michael Ortega, both undergrads, initiated a class project that could mean lower carbon emission levels and fewer discarded plastic bottles.
They found by exposing plastic flakes to small, harmless doses of gamma radiation, then pulverizing the flakes into a fine powder, they could mix the plastic with cement paste to produce concrete that is up to 20 per cent stronger than conventional concrete.
The students had help of course and the research team ended up including MIT faculty members and a researcher from the Argonne National Laboratory as well as the undergrads.
Concrete is, after water, the second most widely used material on the planet. The manufacturing of concrete generates about 4.5 per cent of the world’s human-induced carbon dioxide emissions.
Replacing even a small portion of concrete with irradiated plastic could help reduce the cement industry’s global carbon footprint.
As the students were casting about, looking for ideas for a research project, they discovered that others have tried to introduce plastic into cement mixtures but the plastic weakened the resulting concrete.
They also found evidence that exposing plastic to doses of gamma radiation changes the material’s crystalline structure in a way that makes the plastic stronger, stiffer and tougher.
They wondered if it would be possible that irradiating plastic could actually work to strengthen concrete.
That was their "eureka moment."
The first step was to obtain flakes of polyethylene terephthalate — the plastic material used to make water and soda bottles — from a local recycling facility. Then Schaefer and Ortega manually sorted through the flakes to remove bits of metal and other debris.
Then they took the plastic to a cobalt-60 irradiator on campus. The irradiator emits gamma rays, a radiation source that is typically used commercially to decontaminate food.
They exposed various batches of flakes to either a low or high dose of gamma rays then they 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 and silica fume. Each sample contained about 1.5 per cent irradiated plastic.
Once the samples were mixed with water, the researchers poured the mixtures into cylindrical moulds, allowed them to cure, then subjected the resulting concrete cylinders to compression tests.
They found, in general, samples with regular plastic were weaker than those without any plastic. The concrete with the 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, by up to 20 per cent.
Michael Short, a faculty member who was advising the students, says the technology takes plastic out of the landfill and locks it in concrete. It also uses less cement to make the concrete, which makes for fewer carbon dioxide emissions.
The stronger concrete could be used any way conventional concrete is used.
Most of the time, the ideas for research projects come from people who are already expert in their field or from industry.
But this time, it was the kids who took over, coming up with an idea that could help reduce some of the carbon emissions that plague our warming world.
Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@dailycommercialnews.com.
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