Concrete, heal thyself!

Concrete, heal thyself! 

by MIKE HRYMAK | Jul 8, 2015

Superstitious steppers and their concerned mothers may soon breathe a sigh of relief if sidewalk cracks become a thing of the past. If so, that would just be one of many benefits stemming from the work of Dr. Hendrik Jonkers, a Dutch microbiologist at Delft University of Technology in the Netherlands. He claims to have developed a "self-healing" concrete mixture that can repair its own cracks organically. Not surprisingly, the news generated a lively media stir earlier this year.

By combining the standard concrete mixture with capsules of limestone-producing bacteria -- either Bacillus Pseudofirmus or Sporosarcina Pasteurii -- along with calcium lactate, Jonkers says he has birthed a more durable building product that bounces back after cracking. When the bacteria comes in contact with air and water, he explains, that activates the calcium lactate, which then turns it into calcite (an ingredient in limestone), thus sealing off the crack. For more, watch this video:

At the moment, it's still a pricey product, costing anywhere from $33 to $44 per sq. m. Calcium lactate is the inflationary culprit, notes Jonkers, who told Smithsonian.com in June that he is now also working on a cheaper, sugar-based alternative. He hopes to be able to produce the substitute in much larger quantities by mid-2016. For his work, Jonkers was named a finalist for the 2015 European Inventors Award, but finished out of the money at last month's awards ceremony in Paris. 

Healthy competition

Meanwhile, other groups around the world continue working on their own versions of self-healing concrete, competing for industry attention and research dollars. For instance, engineers at MIT are developing a sunlight-induced, self-healing protective coating that is intended to fix cracks on the surface before they get out of hand. (Read more about that coating here.)

Similarly, Dr. Victor C. Li, a University of Michigan research engineer, has been working nearly a decade on developing concrete with microfibers that bend instead of break -- if tiny tears do occur, the material expands and reinforces itself with calcium carbonate. As Li explained to Smithsonian.com, the advantage of products like his is that they can actually recover the original load-bearing capacity of the concrete rather than simply filling in the gaps with healing products. "I expect self-healing concrete to be in use within the next few years," he said last month. 

Sahmaran tests a 'healed' ECC specimen. (c/o Phys.org)

Of note, the American Concrete Institute is keeping tabs on R&D developments in Ankara, Turkey. There, Mustafa Sahmaran, Asst. Prof. of Civil Engineering, and Director of the Advanced Infrastructure Materials Research Laboratory at Gazi University, is currently working on self-healing Engineered Cementitious Composites. The way ECCs work is quite straightforward, he told Phys.org. "Cracks heal themselves with the help of two main mechanisms: ongoing hydration reactions of anhydrous cementitious materials resulting in further calcium-silicate-hydrate gels, and calcium carbonate precipitation," he explained. 

Sahmaran's technical paper on ECCs will be published in the ACI Materials Journal soon. It is already available online here.