An Albany laboratory hopes its research will prolong the life of Oregon coastal bridges and help avert a complete bridge collapse like that experienced in Minnesota.
Bernie Covino and Sophie Bullard of NETL-Albany have conducted research projects in cooperation with the Oregon Department of Transportation since the mid-1990s.Their work focuses on cathodic protection on bridges where salt is a corrosive factor.
Cathodic protection isn't new technology. The process involves sending an electrical current through materials to prevent oxidation of other metals nn in this case, the steel reinforcing bars embedded in the concrete for the bridges.
The process involves thermally spraying molten zinc onto the concrete surfaces of a bridge to a thickness of about 15/1,000ths of an inch. Research at NETL-Albany (formerly the Albany Research Center) showed that the process may add 25 to 30 years to the useful lifespan of a bridge.
"There are about 10 Oregon bridges which are utilizing cathodic protection," Covino said. "In fact, ODOT is about to enter the second round of applying zinc to some of them."
Unchecked, oxidation of the reinforcing bars causes expansion and cracking of the concrete surrounding them, Covino said. Over decades, the underside of a bridge can lose enough concrete that the rebar is exposed, leading to bridge failure if unchecked.
The technique was first used on a bridge in California, Covino said.
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In addition to zinc, the researchers have studied a variety of anodes, including titanium, Bullard said.
"It's more expensive than zinc, but it could last a longer time," Covino added. "Also, you would only need to apply it about 3/1,000ths of an inch thick instead 15/1,000ths like with zinc. A problem is that while zinc turns gray with age and almost looks like concrete, titanium turns a dirty brown. It really doesn't look good."
The researchers' most recent project involves the Patterson Bridge over the Rogue River.
"It was coated with zinc within the last two years and we are monitoring to see if the cathodic protection system can be turned on and off intermittently," Bullard said. "If so, it could double the lifespan of the zinc and still offer protection for the bridge."
Bullard said she and Covino are looking at four different ways to reduce the amount of current that flows through the system. She monitors the cathodic protection process via computer. The project should last about one more year.
Once the Rogue River project is done, Covino and Bullard say their cathodic protection research will probably be over as well. The Albany center is now affiliated with the National Energy Technology Laboratory, whose focus is on research regarding the nation's energy supplies.
Covino said some of the newer bridges on the coast are using stainless steel rebar in hopes of extending bridge lifespans into the 100-plus-year range.