Each year, billions of tons of concrete become the stuff of buildings, highways, dams, sidewalks, and even artworks. The list goes on. Not only is the material ubiquitous, it has a long history. The Romans invented cement-based concrete more than 2,000 years ago and used the material to build architectural masterpieces such as the Pantheon. To Christian Meyer, a structural engineer at Columbia University, there’s just no question about it: “Concrete is the world’s most important material.” And it’s one of the simplest. A typical mix of concrete consists of 60 to 75 percent sand and gravel or crushed stone, 15 to 20 percent water, and 10 to 15 percent cement, which is prepared by roasting limestone, clay, and other ingredients. The cement is the paste that binds the components into concrete.