From cultural icons to humble toilet blocks, many buildings have succumbed to concrete degradation. In a few years’ time that might all be in the past.
Curtin University estimates that building corrosion costs the Australian economy AUD$32 billion annually – about $1500 per person. Globally it’s estimated to be USD$2.5 trillion – about 3.4 percent of global GDP. Over the lifecycle of a building or piece of infrastructure, researchers estimate that maintenance costs rise to “50 percent more than the capital value of an asset”.
Given that the Ancient Romans managed to make concrete last for two millennia, you can’t help but wonder why corrosion such as concrete cancer is a part of daily life in the 21st-century. But, a joint research paper from Binghamton and Rutgers universities, points to a world where corrosion may be a thing of the past.
“I think self-healing concrete could definitely work, bringing down costly maintenance costs for vital urban infrastructure and housing,” says Congrui Jin, associate professor of mechanical engineering at New York State’s Binghamton University.
Jin, along with Binghamton’s professor Guangwen Zhou, associate professor David Davies, and Rutgers’ associate professor Ning Zhang worked together to determine what could make concrete heal itself, much like the body’s functions. To do that, the team turned to humble fungi.
The problem, however, is that concrete is not the best environment to support life. Its pH values (potential of hydrogen) sits between 11 and 13, akin to bleach or oven cleaner. It is an extremely harsh alkaline environment with a very limited capacity to support organic matter. So, only very special fungi can survive such hostile environments. Out of a total pool of 1.5 to 3 million fungi species, the team narrowed the list down to just 20. As the team found out, certain fungi could be found in very inhospitable climates.
“There are particular fungi species that, for some reason, have developed strategies to adapt to harsh ecosystems, such as geysers, deserts, or the deep sea” says Jin.
The breakthrough came in 2017, with the team finally honing in on a resilient fungus species, Trichoderma reesei, that could be sourced from plants in Canada’s Rocky Mountains, New Jersey’s Pine Barrens, and the Serpentine Barrens on the US state border between Pennsylvania-Maryland.
“Those places have very special environments where the soils are very alkaline, but they still manage to support different types of plants,” Jin says. “So we collected a number of different plants and isolated the fungi from their roots.”
The thing that made Trichoderma reesi so special was its ability to produce calcium carbonate within concrete. Researchers found that when small cracks first appeared, the fungi spores reacted with oxygen and water, filling voids with calcium carbonate, thereby strengthening the concrete in the process.
“This fungi has a remarkable ability to survive. It’s even more extraordinary that it can actually produce calcium carbonate under those conditions,” says Jin.
But, in the meantime, don’t hold your breath for this wonder-material to take root just yet. Jin explains that their discovery still needs further tests and observation, before it can be rolled-out for mass consumption – citing the heavy costs of growing the fungi at present. But, if the team manage to secure further research funding from the American National Science Foundation, concrete cancer might just be a thing of the past sooner than you think.