File:Concrete-engineerguy.ogv

Bill moves a piece of sewer pipe into his office to show how important the ancient material concrete is to our modern world. It, of course, wreaks havoc on his office.

Transcript: Transcript I find this piece of concrete absolutely amazing. This is a piece of sewer pipe and its used to hook together another pipe at 90 degrees. You just pass it through this hole and use a rubber gasket so it doesn't leak. This piece of pipe is about 50 inches tall and its about the same diameter, so that means it weighs about 1500 pounds or three-quarters of a ton. Now obviously its substantial, but its made from something that looks like dirt.

At my local hardware store I bought this bag of concrete. And, indeed, it does look like dirt. But its made of aggregate which is gravel and sand and cement. Cement is made of oxides of calcium, silicon and aluminum. And if you add a little bit of water, it will form a paste, and if you have aggregate in there you'll actually make concrete.

Now, concrete is an ancient material; it comes from the Latin words for "to grow together". The Romans discovered it by accident, a builder was making mortar and he had added volcanic ash from Mount Vesuvius to his mixture and he noticed he had a very hard substance. From there the Romans fine-tuned the recipe for concrete; they added things like horsehair so it wouldn't shrink when it set. They also added blood so it would be frost resistant.

The pinnacle of Roman concrete was probably the pantheon. This dome was made from concrete. Michelangelo said it was "angelic" and "not of human design."

Now there's a common misconception about concrete: And that is that when it hardens it's drying. That would imply that water is evaporating; nothing like that is happening. In fact, you can make concrete under water. The Romans made pier and lighthouses and breakwaters out of it. What's happening instead is something called hydration.

The water molecules are combing with the oxides forming larger molecules that then coalesce into a network. Now this will take a little bit of time to dry.