Concrete is the world's most popular building material, and, because of that, scientists are constantly trying to make it better. We recently talked about a replacement for cement that showed promising results, now we're discussing the tensile strength of concrete.
Back in late 2012, a team of Dutch scientists began work on a new type of concrete additive. All concrete additives modify the physical properties of the concrete in some way, whether by making the concrete harder, set faster, or more resistant to cracking. However, what the Dutch team set out to do was to make a concrete that was "alive;" an additive that would not stop cracks, but heal the cracks after they formed. The scientists had to determine what type of micro-organism could survive in the harsh environment of concrete and also create material that repaired the concrete and, ultimately, they chose a bacteria called Bacillus. Bacillus thrives in alkaline conditions that are found in concrete and can remain dormant for decades. Waking the Bacillus up and feeding the bacteria was the next challenge they had to overcome. Henk Jonkers, the Dutch scientist responsible for this new technology, determined that calcium lactate set in biodegradable plastic was just the right choice as adding sugar, the simplest solution, would cause the concrete to weaken. So, the outcome is that if a crack develops in the concrete water will seep into the crevasse and dissolve the biodegradable plastic. This activates the bacteria and food. As a byproduct of the bacteria's activity, limestone is produced and within a couple of months your crack is healed.