Concrete often cracks due to shrinkage, impact or loading, and then the moisture gets in, corrodes the reinforcing or spalls in freeze-thaw cycles. Michelle Pelletier, a University of Rhode Island master's degree candidate, has figured out a way to make it "self-healing", and says this will reduce greenhouse gas emissions.
According to the URI news release:
Michelle Pelletier embedded a microencapsulated sodium silicate healing agent directly into a concrete matrix. When tiny stress cracks begin to form in the concrete, the capsules rupture and release the healing agent into the adjacent areas. The sodium silicate reacts with the calcium hydroxide naturally present in the concrete to form a calcium-silica-hydrate product to heal the cracks and block the pores in the concrete. The chemical reaction creates a gel-like material that hardens in about one week.
Sodium silicate is often used to seal concrete and make it waterproof, known as silicate mineral paint; the trick here is the encapsulation. It is also a major component of those beloved magic rocks of our childhood.
The big deal here is that our infrastructure is crumbling due to lack of maintenance and with the economic crisis, it is just getting worse. If water gets into concrete and at the reinforcing, it can fail early.
"Building concrete is routinely fixed with steel reinforcement bars to compensate for low tensile strength, but they are extremely susceptible to corrosion," Pelletier said. "We are exploring if the release of the agent will result in corrosion inhibition by two mechanisms. First, the reduced water transport due to the filled pores and reduced interconnectivity within the matrix may result in less moisture reaching the metal and ultimately less corrosion. Also, silicates can deposit on the surface to form a protective film which may also help with reducing the corrosion rate of the steel rebars."
Pelletier suggests that self-healing concrete could reduce CO2 production, 10% of which comes from the mining, production and transport of concrete.
"If self-healing concrete can lengthen the life of the concrete and reduce maintenance and repairs, it will ultimately reduce the production of excess amounts of concrete and result in a decrease in CO2 emissions," she said.