Composites

Antoun Nabhan antoun@incellico.com
Sun, 21 Oct 2001 19:53:50 -0400


Watch this space for further materials science news. And yes, this is also 
Sept. 11-relevant. Less weight in airplanes and other high-speed, 
high-volume transporation devices means less kinetic energy and requires 
less on-board fuel. Seems like this is an avenue toward public safety. The 
other thing is that airlines have traditionally been financially precarious 
because 1) the economics of their business put them at the mercy of 
volatile fuel prices, and 2) they always have to buy enough fuel to get the 
airframe to its destination - a fixed per-trip cost - regardless of the 
number of passenger-miles they've booked on any given flight. Reduce that 
fixed cost by reducing weight and you attack one of the root difficulties 
of airline economics.

--A.


<http://www.techreview.com/magazine/sep01/innovation7.asp>

Bridge to Tomorrow
By Lauren Gravitz

It doesn't look much different from California's other arroyo crossings, 
but peek under the deck of the Kings Stormwater Channel Bridge on Route 86 
in Riverside County and you'll find something surprising: plastic, carbon 
and glass where steel girders and reinforced concrete ought to be. The 
California Department of Transportation's recent completion of the bridge 
could mark the beginning of a move away from traditional construction 
materials in favor of lightweight, rugged composites.

Though "polymer matrix composites" (fibers like carbon or glass encased in 
plastic) have found their way into a smattering of smaller structures in 
the past decade, the new bridge is the first to face the test of highway 
traffic and long-haul trucks. It boasts a fiberglass composite deck with a 
thin veneer of special concrete supported by carbon-fiber composite tubes 
just 355 millimeters in diameter. The materials are so lightweight two men 
can do what normally requires a crane. That translates into faster 
construction, which is critical when a busy bridge is out of commission, 
says the Federal Highway Administration's Eric Munley, a composites expert. 
"If you can replace the thing in a week, you're going to be very interested 
in composites," Munley says.

In fact, the Kings Stormwater bridge went up in one-third the usual 
timeóbut at twice the cost, because composites are relatively pricey. 
Still, says California Department of Transportation chief deputy director 
Jim Roberts, the materials' superior durability could make them worth the 
expense, not only for bridges but also for highway decking in areas where 
ice and salt readily do in steel and concrete. "All you have to do is get 
20 to 30 years out of it, and you're way ahead of the game economically," 
Roberts says. His department is planning to begin another composite bridge 
in San Diego in mid-2002.

Jim Cooper, the director of bridge technology for the Federal Highway 
Administration, is also optimistic: "It's my belief that composites will 
form a major construction material in the future." But until the cost of 
composites comes down, the gap between present and future may be a 
difficult one to bridge.

Lauren Gravitz is a freelance science writer based in Cambridge, MA.



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