Composites Come on Strong
Sometime in the near future, we’ll drive super-lightweight cars across bridges that won’t corrode or collapse under their own weight and park at homes built and insulated with manufactured materials that are stronger, lighter and possibly cheaper than wood, steel or concrete.
Or so say those who tout the wonders of composites.
For the past decade, engineers, professors and entrepreneurs have been experimenting with these superplastics and carbon fibers that they say will eventually replace steel in construction projects.
“You have something here that’s as thin as paper, but as strong as steel and that can create lots of possibilities for everyday use,” said John Scalzi, a structural engineer at the National Science Foundation.
Composites are not new. Ancient Egyptians mixed straw with mud to strengthen bricks. In the 1850s, French gardener Joseph Monier used wire mesh to reinforce cement walls. A century later, researchers experimented with early forms of fiberglass, now the most common composite in boats and cars. Today, graphite composites are in high-end tennis rackets, golf clubs and mountain bikes.
And now more sophisticated composites originally used by the military and the aerospace industry are being adapted for everyday use. They were developed because they are lighter and stronger than the metals they replace. Several portions of the Stealth bomber were made of composites. And parts of the new Boeing 777 wide-body commercial airplane contain composites.
Researchers are looking to use the super-strong, lightweight materials to build suspension bridges that would last 10 times longer than the steel-and-concrete structures we now drive across.
“The average motorist won’t notice the difference when they drive over a composite bridge, but for people like us who know about it, it’s an incredible breakthrough to put something like this together,” said Freider Seible, professor of structural engineering at UC San Diego.
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Japan, China and Scotland have used composites to build bridges and reinforce concrete structures, but applications in the United States are just beginning.
There are dozens of universities around the country that have poured resources into researching composites, and several are embarking on construction projects. Engineers in Minnesota are working to replace a pier in Maine. Researchers in Dayton are repairing roads.
In California, ever since the 1989 Loma Prieta quake violently shook the Bay Area, engineers and entrepreneurs have been exploring ways to use composite materials in earthquake retrofitting projects to shore up weakened highway bridge decks and repair walls of buildings.
Composites are made from the mixture of two essential ingredients: high-strength fibers that have been woven into tape or sheets and polymers that bind the fabric into a rigid and lightweight matrix. Carbon, graphite and glass are the most typical fibers used. Epoxy, polyester and aramids are the most common polymers.
The combination of these materials makes composites stronger and more resistant to corrosion than steel and lighter than aluminum.
A piece of composite material big enough to fill a shopping cart can be lifted by two 6-year-olds, Scalzi said.
Because the composites are so light, they would be less likely to collapse under their own weight during an earthquake, researchers say. Unlike steel, the materials are not susceptible to deterioration from exposure to salt, water or air.
“These materials have very unique characteristics,” Seible said. “They weigh one-fifth of steel and are multiple times as strong, so you’ll need less equipment and manpower to use them, which will simplify a lot of construction aspects.”
The problem with the composites is the price tag. Carbon fiber composite costs $10 to $15 a pound on the low end, while steel averages about $1.50 a pound, Seible said.
In California, one of the leading states in studies of construction with composites, Caltrans has begun trial applications of the materials. Carbon fiber jackets have been wrapped around concrete beams at the Santa Monica viaduct near the intersection of the San Diego and Santa Monica freeways, and sheets as thin as wallpaper have covered small sections of the Golden State Freeway near Griffith Park.
“Our interest is that there’s new technology that can reduce costs because now we’ll have more than one type of material to choose from,” said Jim Roberts, chief structures engineer for Caltrans.
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Structural engineers at UC San Diego are working on a 450-foot-long, all-composite suspension bridge that would link the two parts of the campus separated by Interstate 5.
“We’re looking at replacing bridge deck components and we’re working with UCSD to create a cable bridge,” said Roberts.
“I don’t think these will necessarily replace steel and concrete, because they’re such cheap materials, but they’re certainly going to be part of the future in construction.”
