Concrete is one of those technologies that was used for centuries—in this case, by the Romans—and then had to be invented again centuries later. But once we rediscovered it, we were hooked. The only thing that humans consume more of, by volume, than water is cement, concrete's key ingredient. We use so much of the stuff that the cement industry is responsible, all on its own, for 5 percent of global carbon dioxide emissions.
The idea is simple enough: you mix together small particles (like sand) and slightly bigger particles (like tiny pebbles) with water and some sort of paste that will set and keep the whole thing together. (It's this last bit that's the tricky part.) The Romans made concrete of lime and volcanic rock, and they had some pretty good ideas about what it should be used for:
But at some point between the rule of the emperor Hadrian and the end of this past millennium, the recipe for Roman concrete was lost. In the second half of the 1700s, in England, engineers were experimenting once again with heating up limestone to create a powder that, when wet, would set and hold together. In 1757, the engineer John Smeaton found that the best limes to use in mortars were the ones with high amounts of clay, and he used this "hydraulic lime," to help build the third iteration of the Eddystone lighthouse, off the south coast of England:
Smeaton's lime set off a craze among builders in England to come up with a better "Roman cement." The key to making a good concrete was to improve on the composition of the paste that kept the whole thing together. In 1824, a paper in Leeds reported on some progress: "We hear that Joseph Aspdin, bricklayer of this town, has obtained a patent for a superior cement representing Portland stone."