SOUTHFIELD (WWJ) – Michigan Department of Transportation Director Kirk Steudle said that when he was a student at Lawrence Technological University in Southfield, one of his favorite classes was informally known as “smash lab,” where you’d test all sorts of materials to their breaking point.
Well, Thursday at Lawrence Tech it was smash lab on steroids, as the university and MDOT tested the load-bearing strength of a new kind of concrete bridge — one reinforced with strands of carbon fiber composites instead of steel.
The problem with steel reinforced concrete is that steel rusts, according to Charles Elder, project manager for graduate research projects and an adjunct engineering professor at Lawrence Tech. And when steel rusts it expands, causing cracks in the concrete. Water can enter those cracks, expanding when it freezes and making the cracks even bigger. And all this is hastened by Michigan’s use of corrosive salt on its roads in winter.
Replacing steel with carbon fiber solves the rust problem, giving you a bridge that will last 90 to 120 years instead of the 50-year lifespan of steel reinforced concrete bridges.
But first, engineers have to make sure that the carbon fiber reinforced bridges are strong enough to stand up to traffic.
So Thursday, Lawrence Tech used a huge hydraulic press in its Center for Advanced Materials Research to apply weight to a 31-foot-long section of bridge comprised of five carbon fiber reinforced beams. Lots and lots and lots of weight. And eventually, after about a half hour, under 254,000 pounds of pressure, the bridge section collapsed. (That’s roughly equivlaent to the weight of two fully loaded semi-trailer trucks, concentrated in a section of the bridge about five feet long — in other words, nothing that’s likely to happen in real life.)
Lawrence Tech and MDOT officials say the tests address a critical need. Fully 200,000 bridges in the United States — one out of three of then — are rated either structurally deficient or functionally obsolete. And 25 percent of U.S. bridges are more than 50 years old. And the cost of fixing this $20 billion problem grows at $500 million a year.
Elder said Lawrence Tech is also working with the Michigan Economic Development Corp. to develop carbon fiber manufacturing capacity in Michigan, which would make the new bridges a job creator beyond the construction industry.