As cement hardens through a process called hydration, the molecules within the mixture develop millions of microscopic crystals, like those seen in this screenshot from the NASA video below. These interlocking crystals help the cement molecules bind with each other, as well as other concrete ingredients like gravel, sand, and small rocks. (Credit: NASA ScienceCasts)

Concrete, in one form or another, has been a staple of human construction for some 5,000 years. Now, researchers have finally b