Friday, August 13, 2010

Watching concrete crack: A new strength record

A small slab of a special concrete laced with short, twisted wires set a tensile strength record a few weeks ago in the civil engineering Structures Lab, the researchers involved say. Tensile strength is essentially resistance to stretching.

This stuff has about 100 times the stretchiness of conventional concrete. It can withstand 5,000 pounds per square inch after it starts cracking. It's the combination of strength and stretchiness that makes the material unique, the researchers say.

Postdoctoral researcher Kay Wille and professor emeritus Antoine Naaman invited me to watch one of their tests. They put a specimen of their concrete in a machine that pulls it apart until it fractures. I videotaped it. I was expecting something dramatic.

Turns out the drama was in what didn't happen. The material didn't break in half. It slowly cracked in scratches so tiny we could barely see them without a microscope. Wille first knew they were happening because he heard them.

There's more detail in the video. Naaman even offers to test anyone else's plate-like specimen purported to be stronger than theirs. (That buzz in the background is the natural din of the lab.)

Wille and Naaman are working on this new "ultra-high performance fiber reinforced material" with associate professor Gustavo Parra-Montesinos and professor Sherif Al Tawil.

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