Cracks in concrete are unsightly and expensive. They start off small but they can grow pretty quickly, and if water gets in the steel reinforcing underneath can be damaged and lead to structural failure. You can replace the concrete, but then it’s only a matter of time before cracks form again. So wouldn’t it be great if the concrete could just…heal itself? This idea is not actually as far-fetched as it might seem. Self-healing concrete is not new, and previous research has tried to accomplish this via three main processes. The first is autogenous healing. When water flows into a crack, cement particles in the crack are hydrated and calcification occurs due to dissolved carbon dioxide in the water. However, this only works for very small cracks and requires water. The second is the incorporation of a polymer matrix into the cement. When the polymer is exposed to humidity it releases a foam-like substance to fill the crack. Unfortunately, since this material behaves very differently to the concrete it can sometimes only make the cracks worse. The third method is bio-based: using calcium carbonate-producing bacteria to patch up the concrete. Bacteria are pretty good at this, but there are a few drawbacks, like increased nitrogen being released into the environment and needing a highly concentrated calcium source.
But now there’s a new kid on the block: fungi. A team of researchers at Binghamton University, State University of New York conducted an experiment analysing the interactions of various species of fungi with concrete. They found a fungus called Trichoderma reesei that is able to produce calcium carbonate, and can survive the drastic pH change that occurs as concrete dissolves. The idea is that this fungus will be mixed into the concrete. It will remain in a dormant spore state until a crack appears, exposing the spores to water and oxygen. When enough water and oxygen seep in, the fungus will wake up and begin growing and multiplying. As it does this it will precipitate calcium carbonate to fill up the crack. Once the crack is filled and no more water and oxygen can enter, the fungus will return to a spore state. The research is still in its early stages and the main challenge now is to make sure the fungus can survive within the concrete and throughout the concrete-making process, but bio-based concrete-healing is definitely a new technology to look out for. Self-healing concrete – coming soon to a neighbourhood near you?
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Emi Schutz Archives
March 2018
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