.Unpublished Heart

Written by Philip Proefrock on 24/06/09

Any engineer would look at this image and say, "That can't be concrete!" But it is; and it could represent a way to make bridges and other structures safer and longer lasting.

There is a lot of work being done to improve concrete, right now. And while it is not the most beloved green building material, it has properties that make it eminently useful for engineers and architects for a number of purposes. Given that there is not going to be a sudden moratorium on using the stuff, it's better to have improvements that can keep from having it go from useful building material to landfill.
Professor Victor Li at the University of Michigan has developed a self-healing concrete that can help alleviate the need for demolition and replacement of concrete after it has been subjected to heavy stress. By devising a concrete that controls the way it cracks under stress, the concrete can withstand tensile strain hundreds of times more than ordinary concrete. Beyond its remarkable flexibility, this concrete can then heal itself, as well.

"In Li's lab, self-healed specimens recovered most if not all of their original strength after researchers subjected them to a 3 percent tensile strain. That means they stretched the specimens to 3 percent beyond their initial size. It's the equivalent of stretching a 100-foot piece an extra three feet—enough strain to severely deform metal or catastrophically fracture traditional concrete."

The new concrete needs only exposure to moisture and carbon dioxide in order to heal the microscopic cracks that are formed after the concrete has been stressed. The cracks expose dry cement in the structure, and this reacts with CO2 and moisture to form calcium carbonate 'scars' which quickly heal the concrete.
"The professor says this new substance could make infrastructure safer and more durable. By reversing the typical deterioration process, the concrete could reduce the cost and environmental impacts of making new structures. And repairs would last longer."

Link: Michigan Today (thanks KGS!)