March 7, 2013 2:23 pm
Concrete, a slushy mix of cement, rocks and sand, has built empires. The Assyrians and Babylonians used it. So did the Egyptians. Though the specific formula has changed with time, today, concrete is the “single most widely used material in the world,” says Chemistry World [pdf], used in everything from bridges and highrises to, in some cases, benches, lights and coasters.
But concrete can crack, and when it does, water and salt can get inside, further breaking down the material’s integrity. But recent research has resulted in self-healing concrete, says Mike Orcutt for Technology Review. With a special polymer coating and the power of the sun, says Orcutt, a new type of concrete can heal tiny cracks before they get a chance to grow.
The new coating contains polymer microcapsules, filled with a solution that, when exposed to light, turns into a water-resistant solid. The idea is that damage to a coated concrete surface would cause the capsules to break open and release the solution, which then would fill the crack and solidify in sunlight.
Dr Chung …and his colleagues knew from laboratory tests that when two substances called methacryloxypropyl-terminated polydimethylsiloxane and benzoin isobutyl ether are mixed in the presence of sunlight, they are transformed into a protective waterproof polymer that sticks readily to concrete. The challenge was to pack these chemicals up in a way that would keep them safe until they were needed, and then release them. The solution the team came up with was to put the healing balm inside tiny capsules made of urea and formaldehyde. These would screen the chemical mixture from sunlight and keep it safely stowed away. They would, however, be weak enough to rupture and release their contents when the concrete near them cracked.
This isn’t the first case of self-healing concrete, but the reliance on sunlight as the source of energy to drive the chemical reaction that does the healing is a good step.
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