A group of undergraduate students at MIT found that adding bits of plastic that have been exposed to high levels of harmless gamma radiation to cement paste can make concrete as much as 20 percent stronger than traditional blends.

The students went to a local recycling facility to get flakes of plastic from ordinary single-use soda and water bottles. Different concrete samples were produced with plastic exposed to high levels of gamma radiation, low levels of gamma radiation, no radiation, and no plastic at all. The samples contained about 1.5 percent plastic.

When subjected to compression tests, they found that samples with regular plastic were not as strong as samples without plastic, but samples with irradiated plastic were up to 20 percent stronger than traditional concrete. Further study indicated that the exposure to radiation created a stronger crystalline structure in the plastic flakes that reacts with Portland cement and fly ash to make the concrete stronger.

The next steps include experimenting with different types of plastic and different doses of gamma radiation to find the mixture that produces optimum results.

Concrete is responsible for about 4.5 percent of the world's carbon dioxide emissions. Replacing 1.5 percent of that concrete with recycled, irradiated plastic could significantly reduce carbon emissions worldwide.