Waste Plastic Could Strengthen Concrete

The need for concrete repairs could become a thing of the past if a recent discovery by MIT students becomes commercialised.

Undergraduate researchers there have found a way to create a cement aggregate that makes concrete up to 20 per cent stronger. The aggregate nature of the cement means that less cement is needed, and therefore there are fewer carbon emissions.

The even better news? It contains pulverised plastic, providing a new route to divert waste plastic somewhere other than landfill.

Michael Short, an assistant professor in MIT’s Department of Nuclear Science and Engineering told The Engineer: “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.”

The plastic used by the undergraduates was polyethylene terephthalate, a type of plastic that is used to make bottles (and we all know how bad plastic bottles are…). They even managed to source flakes of it from a local recycling plant, and clean it using a machine that is more often used to decontaminate food.

This irradiation served another purpose, however, as they hoped it could make the plastic stronger. And they were right. The cement mixed with high dose irradiated plastic was found to be 20 per cent stronger compared with samples made just with cement.

The reason for this? Apparently, the cement that contained the plastic had a more crystalline structure and more cross linking evident in it, which could be the reason behind the increased strength.

Kunal Kupwade-Patil, a research scientist in MIT’s Department of Civil and Environmental Engineering explained to The Engineer: “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.”

The quest to find a stronger concrete is an important one and we have covered other attempts in this area before. One recent study looked at how the structure of bubbles in the foam on a head of beer could be replicated in concrete to make it stronger.

Not that long ago another study found that the ancient Romans’ trick of using sea water in their mixes meant that it lasted longer than our modern day equivalent.

The strength of it has been known for a long time – Roman scholar Pliny the Elder described underwater concrete structures that become “a single stone mass, impregnable to the waves and every day stronger,” after all. Yet, it was a researcher this year who showed that the impressive strength of roman concrete was due to a silicate mineral called phillipsite that developed when salt water was used to mix the concrete.

Finding a way to increase the longevity of concrete is important if we are to reduce the overall carbon footprint of building work. Creating concrete creates a large amount of carbon dioxide, which is very hard to capture. We will be watching these developments with growing interest, as the need for more environmentally friendly options in construction become more necessary.