concrete

Super-cements similar to the ancient concrete used to build the pyramids might defeat even the U.S. Air Force's largest non-nuclear bunker buster to date.

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.

The use of concrete dates back to ancient Rome, and the recipe hasn't changed much since then. Neither have some of concrete's drawbacks. In particular, the slow deformation known as "concrete creep" has afflicted structures from the Pantheon to the Pentagon. But MIT scientists believe they have solved the mystery of concrete creep, and thus opened the door to structures that will last tens of thousands of years.