A New Kind of Concrete Can Grow and Repair Itself. How? It’s Alive.

Concrete is one of the biggest greenhouse gas emitters in the world, so scientists are developing new strategies to mitigate its climate impact.
One of those strategies is to create a concrete that “self-heals,” and in a new study, scientists used synthetic lichen to patch cracks autonomously (meaning that outside nutrients don’t need to be applied for the repair to take place.
The lichen—actually a combination of cyanobacteria and fungi—can draw food from sunlight and the atmosphere while also using calcium ions to produce calcium carbonate, which is the same ultra-strong material found in seashells and millennia-old Roman concrete.

The production of concrete, as well as the key ingredient—cement—is one of the leading generators of CO₂ emissions on Earth, contributing to at least 8 percent of the world’s global budget. So, it’s no surprise that scientists and engineers are trying to figure out ways to lower this building material’s impact.

One solution is to not use it altogether—the creation of mass timber buildings in the U.S. has been rapidly increasing in recent years. Another is to devise some way to make concrete more sustainable, or even find ways for it to be a carbon negative building material. However, the area that’s gotten the most attention in the past few decades is figuring out how to make concrete longer-lasting, and even better than the widely used ultra-high performance concrete (UHPC).

The most common method for increasing concrete’s longevity is by ripping a page out of the Roman playbook and developing means for concrete to essentially “self-heal.” The reason why the 2,000-year-old aqueducts throughout Italy don’t look a day over 500 is because Romans used “lime clasts” mixed in with concrete that essentially filled cracks before they formed. Now, scientists from Texas A&M University are investigating ways to pull off a similar trick using lichen. The results of the study were published in the journal Materials Today Communications.

Of course, self-healing concrete isn’t new—headlines have popped up for years touting new techniques for making concrete long lasting, and some have even used microbes. But the authors of this new study say they’ve stumbled upon a technique that improves on previous attempts in one major way.

“Microbe-mediated self-healing concrete has been extensively investigated for more than three decades” Congrui Grace Jin, senior author of the study from Texas A&M, said in a press statement, “but it still suffers from one important limitation—none of the current self-healing approaches are fully autonomous since they require an external supply of nutrients for the healing agents to continuously produce repair materials.”

Lichen, often found clinging to trees and rocks, is actually a complex symbiotic system filled with cyanobacteria, fungi, and algae. The researchers created a synthetic lichen that consisted of a cyanobacteria that can use sunlight (as well as elements from the atmosphere) as food, and some fungi that naturally produce materials that can seal cracks. Specifically, the fungi can pull in ionized calcium, which spurs the production of calcium carbonate—the ultra-hard material found in seashells and coral. (Calcium carbonate is actually the same material that made Rome’s concrete extremely strong in antiquity.)

In lab tests, the synthetic lichen was able to fill cracks—even in concrete—relying on just sunlight and air for food. Using this autonomous repair system can not only extend the life of concrete, but also cut down on repair costs. The authors are now testing whether this synthetic fungi could repair existing cracks as well.

Challenges still remain for the widespread adoption of self-healing concrete. Right now, not many companies make the stuff, and it’s still more expensive to produce that typical, run-of-the-mill concrete. Some experts say it could still be a decade before self-healing additives really take off.

When that happens, though, the lichen will be ready.

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