Concrete Dreams How Liquid Stone Became the World's Most-Used Material

The largest unreinforced concrete dome in the world has a hole in the top of it, and for almost nineteen centuries rain has been falling through that hole onto the floor of the Pantheon in Rome. The dome has no steel inside it and no modern admixtures. It is a vast bowl of poured Roman material, forty-three meters across, and it has outlasted empires, earthquakes, fires, floods, and the centuries when nobody in Europe could have built anything like it.

Now compare that with a concrete bridge or parking structure built in the 1960s, which may already be crumbling, with rust-stained cracks and chunks missing from its beams. That contrast sits at the center of this story. Concrete is the most widely used man-made material on the planet. After water, it is the most consumed substance on Earth. Every year, humanity pours enough of it to wrap a substantial wall around the globe. It forms the foundations beneath your feet, the dam holding back your region's reservoir, and the stairwell you take when the elevator is broken. Yet most of us rarely give it a thought.

This is the story of how we learned to make it, how we forgot, how we learned again, and why the thing that built the modern world now sits near the center of the climate problem. It is also a story about bacteria, algae, and volcanic ash, and about whether one of the oldest building materials in the Western world might hold clues to its future.