Space tech for concrete

Concrete dates back to the Roman Empire, but its properties continue to mystify. A NASA supercomputer may help map the variations that go into a typical batch

What do you do with one of the world8217;s fastest computers? You can forecast hurricane patterns. Or simulate how stars form, how nuclear bombs explode, or how a spacecraft handles solar winds. Or you can learn to mix concrete.

Don8217;t laugh. Researchers at the National Institute of Standards and Technology in Gaithersburg, Maryland, are using a million hours of processor time awarded to them on the National Aeronautics and Space Administration8217;s fastest supercomputer to analyze the billions of possibilities created by the collisions of tiny particles of sand, gravel and cement whenever a cement truck pours a sidewalk.

The different size and shape of each particle8212;which scientists blow up to the size of weather balloons on their projection screens8212;have a profound effect on the strength and durability of concrete and the time it takes to harden. All of these, in turn, are critical factors when engineers create the right recipe for what has become a prime structural material in some of the tallest buildings.

The use of concrete dates to the Roman Empire, but thousands of years later, many of the material8217;s properties remain a mystery. 8216;8216;Several things about it are not really understood8212;the durability, for one thing, is really not known how to predict,8217;8217; said Edward J. Garboczi, a member of the NIST team working on the project.

NIST is trying to create concrete that8217;s more durable and easier to pour at construction sites. NIST researchers need NASA8217;s supercomputer because of the nearly incalculable variations that go into making a typical batch of concrete.

Concrete is a mixture of sand, gravel and cement. The cement is made by mixing and heating limestone, clay and other materials. The particles that make up the mix also come in all shapes and sizes, which affect the durability of the finished concrete. Cement particles can range from 10 microns to 200 microns across 25,400 microns in an inch. The stones that make up the gravel can be anywhere from a half a millimeter to 2 inches in diameter.

With 10,240 processors, NASA8217;s supercomputer8212;named Columbia8212;is the nation8217;s fourth most powerful in industry rankings, said Bryan Biegel, deputy chief of NASA8217;s Advanced Supercomputing Division. The 120 million computer takes up 15,000 sq ft in a temperature-controlled room at the Ames Research Center, California.

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With Columbia, NIST will be able to scale up the work, modelling concrete blocks 10 times bigger and using the supercomputer to see8212;for the first time8212;how the size, distribution and shape of particles affect the flow and durability of concrete. NIST will use the models as the basis for computer simulations in its Immersive Visualization Laboratory8212; a dark room where computer simulations are projected onto garage door-sized screens. They show what happens when millions of particles of sand, cement or any of concrete8217;s ingredients are mixed and poured.

In that lab, micron-sized particles of sand, created during a concrete research project in 2003, look like balls the size of weather balloons on screen. Polymer fibers, millimeters long in real life, look like huge necklaces of pearls. With a visor linked to the computer, the images become three dimensional and can be set in motion and manipulated, making viewers feel as if they have stepped onto a futuristic 8216;8216;holodeck.8217;8217; The detail will be much greater with the help of the Columbia supercomputer.

Meanwhile, concrete experts say this project is long overdue. 8216;8216;There8217;s a lot, lot, lot we have to learn,8217;8217; said Surendra Shah, a civil and environmental engineer at Northwestern University in Illinois. 8216;8216;We should have been doing this 20 years ago, but people haven8217;t realized the importance of the research.8217;8217;

LAT-WP