Joints are like an after-school program for cracks in concrete. If we fail to provide a place for cracks to occur safely, under supervision, and in aesthetically pleasing configurations, we as a society will be faced with complete anarchy in our walls and slabs.  This horrifying chaos could lead to unwed, underage cracks begetting more cracks and, possibly even more alarming, cracks on crack.

Sometimes, despite the provision of joints and reinforcing in concrete to resist tension, construction goes horribly wrong. Say the mix is off, or the wrong strength is used by mistake, or perhaps someone throws an empty can on the ground and it rolls into the formwork whereupon it gets cast into the underside of the slab, weakening it in a place where it ought to be strong. Or imagine if something were to explode unexpectedly, blasting a wall with forces it wasn’t designed to resist. Concrete is a pretty forgiving medium but there are limits. In any of these situations cracks can start to form that either weaken a structure or at the very least damage it aesthetically.

Image courtesy popsci.com

Until recently the solution to a lot of these crack problems was rehab – tearing out the offending concrete and recasting or patching it -usually an expensive proposition.  Sometimes people drip high-strength epoxies into the cracks hoping the glue will hold everything together, but this tactic engenders a new set of problems.  For example, if the glue is stronger than the concrete it puts a whole new set of stresses on the material.

Now there is another way. Researchers at the University of Newcastle in the UK have invented a bio-based material that patches up the cracks in concrete structures, restoring buildings damaged by seismic events or that have deteriorated over time.  They’ve “custom-designed a bacteria to burrow deep into the cracks in concrete where they produce a mix of calcium carbonate and a special bacteria glue that hardens to the same strength of the surrounding concrete” (Dillow).  That’s right, people.  Bacteria glue to the rescue!

Image courtesy en.citizendium.org

“BacillaFilla,” as the researchers call it, is a genetically modified version of Bacillus subtilis.  Apparently Bacillus subtilis (what a great name for a bacteria by the way – it sounds unobtrusive and subtle and as though it’s found below tiles) is everywhere around us and easily encountered in common soil.  The Newcastle researchers “have tweaked its genetic properties such that it only begins to germinate when it comes in contact with the highly-specific pH of concrete. Once the cells germinate, they are programmed to crawl as deep as they can into cracks in the concrete, where quorum sensing lets them know when enough bacteria have accumulated” (Dillow).

When the bacteria reach the deepest part of the crack and their spidey sense tells them they’ve reached an appropriate population size, they start to morph.  The cells begin to develop bacterial filaments, to produce calcium carbonate, and to “secrete a kind of bacterial glue that binds everything together. Once hardened, the bacteria is essentially as strong as the concrete itself, restoring structural strength and adding life to the surrounding concrete.  The bacteria also contains a self-destruct gene that keeps it from wildly proliferating away from its concrete target, because a runaway patch of bacterial concrete that continued to grow despite all efforts to stop it would be somewhat annoying” (Dillow).  So unlike the brute force approach of tearing out an entire zone of concrete, or the “coat everything with epoxy and cross your fingers” route, BacillaFilla has a kind of emergent intelligence that lets it assess and repair each unique crack. 

BacillaFilla could be used to improve the longevity of concrete structures, which means we’d need to build fewer of them.  That’s bad news for architects but good news for the planet because a lot of energy goes into the production of new concrete.  The material might also be deployed where earthquakes have damaged buildings, reducing the number of structures that would need to be torn down.  I also wonder if the bacteria could be tweaked so as to first build concrete structures and then maintain them over time? 

WU XING:

I’m filing BacillaFilla under earth because they’re living in the soil and etc.

Cited:

Dillow, Clay. “Bacteria Can Fill Cracks in Aging Concrete.” Popsci.com. 11/16/10.  Accessed 11/30/10.  URL.