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Pressure Point: The polymer fibers in flexible concrete help it resist 500 times as much stress as conventional concrete.  Courtesy Nicole Casal Moore/University of Michigan;

Flexcrete

Researchers have known for decades that concrete fixes itself as cement particles near a small crack mix with air and water to form calcium carbonate. But some fractures are too big to heal on their own. Now engineers at the University of Michigan have mixed a new concrete formula with reinforcing glue-like fibers that hold it together under pressure, allowing only hair-width cracks that can mend after a rainy day. Available in a few years, the remixed concrete will cost more than the standard stuff, but less maintenance could make it cheaper in the long run.