Want better concrete? Just add plastic
Katie Camero | 31 October 2017
Concrete infused with plastic can create stronger, more flexible structures, reducing the material’s global carbon footprint and redirecting plastics from landfill, according to a study by MIT students.
Stemming from a class research project, Caroline Schaefer and Michael Ortega wanted to find ways to lower carbon dioxide emissions, and decided to tackle concrete manufacture, as it generates about 4.5 per cent of the world’s human-induced carbon emissions.
Their team exposed plastic used to make water and soda bottles to gamma radiation, pulverised the flakes into a fine powder, and then mixed the irradiated plastic with cement paste and fly ash.
Testing found the novel concrete was up to 15 per cent stronger than conventional concrete.
“There is a huge amount of plastic that is landfilled every year,” MIT assistant professor in the department of nuclear science and engineering Michael Short said.
“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. 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.”
Why does it perform better?
While previous studies have found that adding plastics to concrete can weaken the material, exposing plastic to doses of gamma radiation makes the material’s crystalline structure change, resulting in a stronger, stiffer and tougher plastic. The researchers hypothesised that this could lead to a stronger final concrete material.
They analysed their concrete samples with X-ray diffraction, backscattered electron microscopy and X-ray microtomography. The images revealed crystalline structures with more molecular connections that blocked pores within the concrete, making it denser and therefore stronger.
The team found that substituting 1.5 per cent of concrete with irradiated plastic could significantly improve its strength.
While it is a small amount, Dr Short said if implemented on a global scale it could have a significant impact.
“Concrete produces about 4.5 per cent of the world’s carbon dioxide emissions,” he said. “Take out 1.5 per cent of that, and you’re already talking about 0.0675 per cent of the world’s carbon dioxide emissions. That’s a huge amount of greenhouse gases in one fell swoop.”
To receive the most effective results, further exploration will be done to tailor the mixture and optimise the irradiation process to maximise performance.
The team said they plan to experiment with different types of plastics and various doses of gamma radiation to determine their effects on concrete durability.