In the first U.S. application of a solar-powered anti-icing/de-icing system on bridges, Missouri DOT (MoDOT) is testing how well the sun melts away winter weather maladies on two structures.
The surface heating system prevents snow, ice, and especially black ice from forming on pavement while also serving as an alternate energy source.
Functioning similarly to radiant heating in a home's floor, the method involves installing tubing in the bridge deck and pumping a heated, antifreeze, water/glycol solution through the 5/8-inch polyethylene tubes to keep the deck from freezing. Waterproof solar panels mounted near the bridge provide energy to heat the solution and fuel each pump. The automated system is activated when the temperature drops to 38° to 40° F.
The test bridges are part of MoDOT's Safe & Sound Bridge Improvement Program, which is replacing 802 of the state's 10,267 bridges by the end of 2013. “We didn't want to tear up good decks, so we needed to find structures that were scheduled to get new decks,” says Dennis Heckman, a bridge engineer for MoDOT.
Both concrete bridges — which were chosen because they have right of way available, face south (making the most out of the sun's rays), and aren't shady — are located in urban areas and experience about 10,000 cars a day.
The new system is quite a change from the agency's widely used snowplow-with-ice-spreader method, which uses about 173,000 tons of salt each year and costs MoDOT about $20 million annually. For this project, MoDOT is paying $183,000 to design, supply, and install the systems, but it can sell back any unused energy to local utilities (local electricity company AmerenUE has expressed interest in purchasing the energy). Plus, the solar panels can also be used to power a bridge's lighting system.
The system may also extend the lifespan of bridges. “The use of rock salt shortens their useful lives,” explains Heckman. Water and chemicals are also among bridges' biggest enemies.
Pave Guard Technology Inc. of Lee's Summit, Mo., which developed the technology, has been installing the system for more than a decade in residential applications such as driveways, walkways, and patios, and anticipates that it will will double the lifespan of the Missouri bridges. The company is gaining the attention of potential commercial and government customers, and is in talks with several other state transportation departments and the Federal Highway Administration, whose approval is required to use federal funding. Government agencies are showing more interest in solar-powered radiant heating as they become plagued by the increasing costs of repairing potholes and replacing concrete and asphalt damaged by freeze/thaw cycles, says Pave Guard COO Tom Casey.
Construction is scheduled to begin this month. If the test bridges prove to be cost effective and dependable after two winter cycles, MoDOT will consider wider implementation, says Heckman.
— Matt Hirschfeld is a Chicago-based freelancer and former editorial intern of Public Works.
For a video demonstrating how the solar-powered heating system works on bridges, click here.