Tiny Tuesday: Recycled Plastic for Stronger Concrete

Concrete production is responsible for about 4.5% of the world’s carbon emissions. As such, materials engineers are interested in reformulating the material to reduce its impact. One technique is to replace the most production-intensive ingredient, Portland cement (concrete’s binding agent), with fly ash (a byproduct of burning coal) – emissions reduction with no loss of strength. Another technique previously explored in this blog is autoclaved aerated concrete, which eliminates the large aggregate and adds hydrogen bubbles for a lighter block, resulting in a greater volume of concrete from the same amount of cement.

Recycled plastic is enticing as a material to replace even more Portland cement, but every formulation with plastic has produced a weaker concrete… until now. A team of MIT students has discovered that if polyethylene flakes are exposed to gamma radiation and then ground to a powder, the resulting crystal structure is actually beneficial to concrete. In fact, compression tests on concrete samples made with fly ash and 1.5% irradiated plastic showed a 15% higher strength than concrete made with Portland cement and no plastic. Gamma ray radiation leaves no radiation residue behind; it’s used commercially to decontaminate food. All this and more is explained in this MIT News article.

The article does not indicate when irradiated plastic concrete will hit the market, or how much more it will cost than regular concrete. Radiation uses specialized equipment and has some PR issues, so it may be difficult to achieve mass production. The MIT project team included an old professor of mine, affectionately known as Oral B.

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