Locking plastic in concrete

ADDING plastic bottles to concrete could lead not only to lower carbon emissions, but improve structural performance, according to a new study.

A team from MIT in the US found that substituting concrete with irradiated plastic and fly ash can improve the material’s strength by up to 15%, compared to traditional concrete.

About 1.5% of concrete was replaced with recycled plastic in tests, which the group says could have a significant impact on the global scale, as concrete is responsible for around 4.5% of global anthropogenic CO₂ emissions. Locking plastic waste in buildings or pavements would also reduce the amount sent to landfill.

While previous studies have investigated incorporating plastics into concrete, these often resulted in a weaker material. However, in work published in Waste Management, the researchers found that exposure to gamma radiation changed the plastic’s crystalline structure, making it stronger, stiffer, and tougher.

In their method, flakes of polyethylene terephthalate are subjected to gamma radiation from a cobalt-60 irradiator. Samples are then ground and mixed with traditional Portland cement powder and fly ash, a byproduct of coal combustion.

X-ray diffraction, backscattered electron microscopy, and X-ray microtomography analyses were undertaken at MIT and Argonne National Laboratory. They showed that samples containing irradiated plastic exhibited crystalline structures with more cross-linking, which also seemed to block pores within concrete – making samples more dense, and therefore stronger.

Kunal Kupwade-Patil, a research scientist in MIT’s Department of Civil and Environmental Engineering, said: “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.

“Within the parameters of our test programme, the higher the irradiated dose, the higher the strength of concrete, so further research is needed to tailor the mixture and optimise the process with irradiation for the most effective results,” he added.

Waste Management: http://doi.org/cf9n