We build things out of concrete when we want them to last, and that's why it's the most commonly-used building material in the world. But widespread as it is, concrete has slowly been letting us down. Through expansion and contraction the material inevitably cracks, and once water gets inside, problems start. If the water freezes, the ice will expand, worsening the crack. If the water reaches the rebar inside, it will begin to rust.
The solution to this comes not from the construction industry, but from Hendrik Jonkers, a microbiologist at TU Delft. In trying to solve the problem of cracks forming in concrete, Jonkers observed that the human body, including the bones, are capable of healing their own minor damage. Thus inspired, he set out to find a way that would allow concrete to heal itself naturally—and whaddaya know, he found it:
If Jonkers succeeds in commercializing his discovery, particularly the bit about having it retroactively applied, he will potentially save governments from spending billions. According to the European Patent Office, who named Jonkers a finalist for last year's European Inventor Award,
Because around 70% of Europe's infrastructure is comprised of concrete, maintenance is an extremely costly affair. HealCON, an EU FP-7 funded project, estimates the annual maintenance cost for bridges, tunnels and earth-retaining walls in the EU member countries at up to € 6 billion.
By the way, another interesting thing I learned by reading Delft's webpage on the material: Apparently in Dutch, the abbreviation for "Hendrik" is "Henk." Huh.