A fungus that grows on concrete and promotes the growth of calcium carbonate
could help repair roads and bridges, materials scientists say.
The United States has one of the most advanced economies in the world, yet the concrete infrastructure that supports it—roads, bridges, sidewalks, etc.—is slowly crumbling. This deterioration requires complex repairs, causes long delays, and in the most severe cases can lead to structural failure. It’s also an increasingly expensive problem. Small cracks left in disrepair develop into bigger ones that expose metal reinforcement structures, and when these are damaged, repairs can be costly and complex. According to the American Society of Civil Engineers (ASCE), this problem will cost the U.S. economy almost $4 trillion in lost business by 2025 if it’s not addressed.
Clearly, a better, cheaper way to repair concrete is desperately needed. Dr. Ning Zhang, Department of Plant Biology-School of Environmental and Biological Sciences, Rutgers University-New Jersey and few colleagues say they have discovered a secret ingredient that could one day keep the nation moving by repairing crumbling concrete automatically—MUSHROOMS!
Materials scientists have long hoped to find a “secret sauce” that helps concrete repair itself. One idea is to fill concrete with polymer fibers containing resin that leaks out to fills cracks. That looked promising for a while, but because concrete and resin have different thermal expansion properties, sometimes cracks can become worse. Calcium carbonate is a better filler for cracks because it bonds well with concrete and has similar structural properties. Various bacteria produce minerals of this kind but other by-products can damage roads and the environment.
So materials scientists need another option. Dr. Zhang and colleagues say they’ve found it in the form of a fungus called Trichoderma reesei. It can germinate in a wide range of conditions, forming a fibrous fungus that promotes the formation of calcium carbonate. Fungal spores are added to the concrete when it is mixed, then lie dormant until the concrete cracks. Water flowing into the cracks causes the spores to germinate, filling the cracks with fungal fibers that trigger the formation of calcium carbonate—which eventually fills the void.
Dr. Zhang’s group tested whether it would work in practice. The team poured concrete into petri dishes and allowed it to set. They then poured a growth medium onto each slab and added various kinds of fungi. They waited to see which of the fungi would grow in the highly alkaline conditions that concrete promotes. The results were revealing. Of all the fungi tested, only Trichoderma reesei flourished even when the pH rose to 13. Her team then studied its fibrous structure under a microscope and used x-ray diffraction to analyze the deposits it left behind. Electron microscope images clearly show the mineralized structures the fibers leave behind. “The data strongly suggested that T. reesei hyphae can promote calcium carbonate precipitation,” they said.
For Trichoderma reesei spores to survive when added to concrete while being mixed, the spores would have to sit in pores within the concrete. Dr. Zhang’s team measured the pores in the concrete they made and found that they were about one micrometer in diameter on average. But, since the Trichoderma reesei spores are bigger than the pores in the concrete (four micrometers in diameter vs. one), they would be crushed as the concrete sets. They said the problem could be solved by adding air bubbles to the mix, but this needs to be investigated further.
There is a significant upside: If Trichoderma reesei turn out to be the magic mushroom that can repair the U.S.’s crumbling infrastructure, it will be a major boon—it’s environmentally friendly, the fungus is benign as far as humans are concerned, and the process of forming calcium carbonate fixes carbon from the atmosphere—removing carbon dioxide … a greenhouse gas.
There is much work ahead to determine whether the spores will survive in concrete. But the early results provide reason to study this in more detail.
To read the entire article, please go to: https://www.technologyreview.com/s/608717/how-mushrooms-could-repair-our-crumbling-infrastructure/
To reference the Cornell University Library Paper “Screening of Fungi for Self-Healing of Concrete Cracks”, please go to: https://arxiv.org/abs/1708.01337
For the ISCP September 2015 VIDEO titled, “The Netherlands: Video healCON Project: Concrete with Self-Healing Powers” please go to: https://www.concretepavements.org/2016/09/08/the-netherlands-video-healcon-project-concrete-with-self-healing-powers/
ISCP reported on a ‘self-healing concrete’ in a May 2015 article titled “Self-Healing Concrete by Bacterial Mineral Precipitation”: A team of microbiologists at The Delft University of Technology (TU Delft) in the Netherlands, headed by Dr. Henk Jonkers, Civil Engineering and Geosciences, Materials Sciences and Sustainable Construction—TUDelft, Water Resources Section, is researching how the self-healing capacity of concrete structures can be improved by using calcite-precipitating bacteria and what conditions are necessary for these bacteria to thrive. Bacteria: By embedding calcite-precipitating bacteria in the concrete mixture, it is possible to create concrete that has self-healing capacities. As the pH value of concrete is very high, only the so-called alkaliphilic bacteria are able to survive. They have mixed several of these bacteria into a cement paste, and after a month, found the spores of three particular bacteria were still viable…To read this ISCP May 2015 article, please go to: https://www.concretepavements.org/2015/05/19/self-healing-concrete-by-bacterial-mineral-precipitation/