To give you an idea of the scale of concrete production in the 21st century, here is a fun little factoid:
China used more concrete between 2011 and 2013 than the U.S. used in the entire 20th century. That’s a heck of a lot of concrete—6.6 gigatons to be exact.
So, any efforts to reduce the amount of concrete produced, and the CO2 emissions along with it, should be seen as a good thing, right? Right.
The good news is that a team of undergrads from MIT has discovered a method of using recycled plastic bottles to bulk up concrete mix, thus reducing both plastic waste and the ingredients used in concrete production. Not only that, but the team has found that the addition of the plastics to the concrete can result in an increase of strength by up to 15 percent, compared to standard concrete.
“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 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 process works by irradiating the plastic with small doses of gamma radiation before grinding the plastic into a fine powder, which is then mixed with cement.
By irradiating the plastic flakes from the bottles, the researchers found that the radiation alters the crystalline structure of the plastics and makes the plastic stronger, stiffer and tougher.
After several experiments varying the ratio of plastic, fly ash, silica fuma and Portland cement, they discovered the highest compression strength samples resulted from a mix of 1.5 percent irradiated plastic, fly ash and Portland cement. The compressive strength was observed to increase by 15 percent compared to other mixtures, such as those made with plain old Portland cement.
Further examination via various laboratory imaging techniques revealed that the samples containing the irradiated plastic demonstrated more cross-linking, or molecular connections. In these samples, the crystalline structure also seemed to reduce the porosity of the concrete, thus making the samples denser and stronger.
“Concrete produces about 4.5 percent of the world’s carbon dioxide emissions,” said Short. “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.”
That is indeed a lot of greenhouse gas. Best of luck to the MIT team.
For more concrete research, find out why the secret ingredient in Ancient Roman concrete is seawater.