America’s infrastructure is in bad shape. Our roads are filled with pot holes. Sidewalks are cracked and crumbling. Bridges are literally falling apart. This problem is not going to fix itself… or is it?
Dr. Alan Richardson his team are using a ground borne bacteria, bacilli megaterium, to create calcite, a crystalline form of natural calcium carbonate. The goal – self repairing concrete.
Dr. Richardson grows the bacteria in a nutrient broth of yeast, minerals and urea, also known as carbamide. This mix is then added to concrete. Since the bacteria’s food source is mixed into the concrete the bacteria breeds and spreads out within the mixture, acting as a filler to seal the cracks and strengthen the concrete.
If the idea of having bacteria growing inside concrete weirds you out, there are others at work making self-repairing concrete mixes. Advanced Civil Engineering – Materials Research Lab at the University of Michigan has made a new type of concrete using microfibers in place of sand and gravel. The microfibers allow the concrete to be more flexible and that results in less cracking.
When cracking does occur however, the dried concrete absorbs moisture from the air; this allows the concrete in the crack to become softer and eventually expand to fill the crack. At the same time, the calcium ions within the crack absorb the moisture along with carbon dioxide from the air. This reaction forms a calcium carbonate material that is similar to the material found in seashells. If a snail gets a crack in its shell, the shell will repair itself overtime – this concrete mixture does the same thing. Science!
Self repairing cement is not actually really anything new; the Romans made it by mistake. But, you know what they say, history is bound to repeat itself — however this time the results look rather positive.
