Mitigating Corrosion of Steel Bridges
Michelle Riedinger stood on the runway, which she had prepared to simulate a 100-foot section of roadway. A city truck had sprayed the road section with water, and Riedinger had set up meteorological instruments and LiDAR to record whatever came next.
Riedinger, who is a junior studying civil and environmental engineering, turned to watch as a U-Haul truck came barreling toward the test section at 50 miles per hour. In less than two seconds, the truck passed through the test section, lifting a plume of water high into the air. Even with the naked eye, Riedinger could see that the plume traveled much farther than she had expected, all the way to the tree line about 100 yards away.
“I was shocked at how much difference speed makes,” says IIHR Research Engineer Bill Eichinger. At 30 or 35 mph, the spray doesn’t go very far, but around 50 mph, it begins to loft much higher. Eichinger explains that when a vehicle goes by, a huge burst of turbulent kinetic energy is released that entrains the droplets in the air and lofts them. “The burst is short-lived, but very intense,” Eichinger says.
Steel Bridge Weathering
Why should we care about how high the water lofts when a vehicle passes by? Turns out, it makes a huge difference to the weathering of steel bridge piers.
In the spring, melting snow floods the roadways, laced with salt left over from winter road treatments. When vehicles go by, they lift the brine high into the air, and droplets land on bridge girders.
“You know, salt and steel — not a good combination,” Eichinger says. “You get rust.”
The Federal Highway Administration sponsored the research project to verify the agency’s computer model. Eichinger credits his students, especially Riedinger, for their excellent work collecting the data. He thinks the sponsor will appreciate the results he and his team have gathered. “We’ve got data that I think they will really like on the turbulent kinetic energy, which is something that’s missing in their model.”
Students played a number of roles in the experiments. Haowen Xu and Heng-Wei (David) Tsai recorded the experiment with video cameras. Brandon Willis helped analyze and interpret the data to generate the values needed to determine atmospheric stability and turbulent kinetic energy.
Riedinger says the results were somewhat surprising. “I never would have thought that [speed] was an issue.” She says that the results indicate a serious problem with corrosion of bridges from road salt. One solution could be porous pavements, which Riedinger says decrease the spray.
Riedinger says the research project was an intriguing one that allowed her to put her classroom skills to work in the field. “I love being involved with this project,” she says. “I’m very glad that I had the opportunity to get involved in this project with Bill.”