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October 2, 2001

A public radio commentary

Recently while waiting for an appointment, I starred out the window and watched an ancient art: The making of concrete.

The origin of the word gives away its ancientness. It's made by combining the Latin prefix com meaning "together," and crescere meaning "to grow." The names comes about because when the ingredients making up concrete - water, gravel, sand, and a bit of cement - are mixed they turn into a hard, rigid solid.

The Romans discovered concrete by accident. A builder was making some mortar and he happened to be working near Mount Vesuvius, the famous volcano. He tossed in some volcanic ash and noticed that when his mixture dried it made a very hard substance.

From this serendipitous beginning the Romans fine tuned the recipe for concrete. They mixed horse hair to reduce the amount it shrank during hardening; and they also added blood, which made the stuff frost-resistant. Today we use plastics for horse hair and special chemicals instead of blood, but the same principles apply.

With these innovations Roman concrete reached a level of quality unmatched until this century. Just look at the Pantheon, the Temple of the Gods.

The Roman Emperor and builder Hadrian capped its rotunda with a 144 foot in diameter concrete dome. Michelangelo found it so beautiful he called it "angelic" and declared it "not of human design."

Although the Pantheon is the most visible example of Roman concrete engineering, example of Roman concrete engineering, they also made incredible structures underwater.

An amazing property of concrete is that it can dry and harden underwater. So, the Romans used it to make piers, breakwaters, and lighthouse foundations that differ little from the ones we build today.

In our age the concrete industry is so important that it now takes up about 10 percent of our gross national product. And it promises to take up even more.

Perhaps the most bizarre application for concrete is in making ships and submarines. Although not well known concrete will float if you add enough air to it. A concrete submarine can dive deeper than a metal one because concrete is very strong under pressure. Once submerged it would be hard to detect. A concrete submarine fools sonar into thinking its the ocean floor.

Now, concrete is becoming high tech. Engineers are inventing smart concrete that can conduct electrical signals. It'll be able to detect vehicles, perhaps even guide one down a highway. And when used in buildings it might even detect earthquakes. Although I note that the Romans needed no such thing: After 2000 years the concrete dome of the Pantheon is still standing.

Copyright 2001 William S. Hammack Enterprises