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Rammed Earth

July 16, 2009

The right amount of water can make a green building material super-sturdy.


The sandcastle principle. I’m Bob Hirshon and this is Science Update.

To make a perfect sandcastle, you need just the right amount of water. It turns out the same is true for an ancient building material that’s making a comeback. It’s called rammed earth, and it’s a compacted mixture of sand, clay, gravel, and water. Civil engineer Charles Augarde of Durham University in England notes that unlike a sandcastle, rammed earth never totally dries out.

CHARLES AUGARDE (Durham University, England):
Even though we think of sand particles as very small; they’re not really very small when we compare them to clay particles, which are so small you can’t see them or feel them in your hands.

Those dense particles trap water inside. Now, Augarde and his colleagues have found that rammed earth’s strength depends directly on its water content. That’s useful information for green-minded engineers, who see rammed earth as a climate-friendly alternative to concrete. I’m Bob Hirshon for AAAS, the Science Society.