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.
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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