Air Force Academy Cadets Seek to Improve Corrosion Management Processes on U.S. Bridges

As part of the Bridge Watch cadet senior design program, Air Force Academy cadets 1St Class Ryan O’Reilly and Meng-Chieh Kuo (a Taiwanese Air Force exchange cadet) ready a reloadable anode cartridge and steel reinforcing rods to be cast into a concrete test article.  Photos courtesy of the U.S. Air Force Academy.

As part of the Bridge Watch cadet senior design program, Air Force Academy cadets 1St Class Ryan O’Reilly and Meng-Chieh Kuo (a Taiwanese Air Force exchange cadet) ready a reloadable anode cartridge and steel reinforcing rods to be cast into a concrete test article. Photos courtesy of the U.S. Air Force Academy.

By Cynthia Greenwood

In 2007 the failure of the I-35W Saint Anthony Falls Bridge in Minneapolis killed 13 individuals and injured 145 more.  The American Society of Civil Engineers (ASCE) estimates that over two hundred million trips are taken daily across deficient bridges in the nation’s 102 largest metropolitan regions. The nation spends approximately $12.8 billion annually on upgrading and replacing structurally deficient bridges, while the estimated total cost to address currently identified deficient bridge needs is $76 billion, ASCE reports.

“The cost of repairing or replacing bridge decks represents a major portion of this spending,” said Retired Lt. Colonel Kevin Gibbons, operations manager for Sabreliner Aviation at the U.S. Air Force Academy (USAFA) Center for Aircraft Structural Life Extension (CAStLE), under the Department of Engineering Mechanics. “If the functional life of the bridge deck could be increased, these staggering costs could be greatly reduced.”

Three cadet project design teams at the U.S. Air Force Academy (USAFA) and their sponsors in the Department of Engineering Mechanics and the Department of Civil and Environmental Engineering have engaged in a program called Bridge Watch to cut the maintenance costs per bridge in half by improving corrosion management, reduction, and repair processes.

“A very significant factor contributing to these structural deficiencies is bridge deck corrosion,” said Ret. Lt. Col. Gibbons, who has co-led a series of cadet design teams since 2013 committed to addressing the problem.

 

Underpinning the Bridge Watch program is the idea that replaceable sacrificial anodes may contribute to increasing the functional life of bridge decks, thereby reducing the cost of bridge deck maintenance over time.Currently sacrificial zinc anodes are used to prolong a bridge’s life expectancy by 10 to 15 years. The zinc anodes are positioned so they will corrode in place of the embedded steel reinforcement that forms the bridge deck backbone structure. This process, in which one material is sacrificed in order to protect another, underlies cathodic protection, an electrochemical means of preventing corrosion.

The research project developed in spring 2013 when a cadet design team conducted interviews and maintenance visits with bridge inspectors and bridge maintainers in the city of Colorado Springs, Colorado, and at the Air Force Academy. The cadets and their sponsors at USAFA and CAStLE engaged in a discussion centered on addressing the shortcomings of the traditional method of using sacrificial anodes to protect bridges. The 2014-2015 cadet team began considering the benefits of monitoring sacrificial anodes over the long-term life of a bridge, Ret. Lt. Col. Gibbons explained.

Early on in the program, the 2014-15 cadet design team developed methods to monitor the remaining useful life of built-in sacrificial anodes embedded in cathodically protected structures. “Since built-in sacrificial anodes are becoming more common in highway bridge decks, this effort has broad applicability to the nation’s critical transportation infrastructure,” said Ret. Lt. Col. Gibbons.

Since the Bridge Watch program’s earliest phase, the cadets have narrowed the scope of their project to encompass developing efficient replacement strategies for sacrificial anodes embedded in steel-reinforced concrete bridge decks. In its current phase, the 2015-16 cadet design team is incorporating the monitored anode capability with a strategy of using non-destructive means of replacing the anodes, when necessary. “The current study complemented the previous team’s work since the remaining life data from monitored anodes could be used to develop a bridge deck anode replacement schedule,” said Cadet 1st Class Cameron Fierro.

Cadet 1st Class Evan Richter and Cadet 2nd Class Kyra Schmidt prepare a steel-reinforced concrete specimen for monitored-sacrificial anode integration and follow-on corrosion testing for the Bridge Watch senior design project. (Photos courtesy of the U.S. Air Force Academy)

Cadet 1st Class Evan Richter and Cadet 2nd Class Kyra Schmidt prepare a steel-reinforced concrete specimen for monitored-sacrificial anode integration and follow-on corrosion testing for the Bridge Watch senior design project. (Photos courtesy of the U.S. Air Force Academy)

The rate of bridge degradation due to corrosion as well as the rate of sacrificial anode corrosion varies dramatically based on location, climate, and local conditions. “If bridge maintenance experts could collect accurate anode life data specific to a location, it would allow each maintenance crew to create a schedule that is tailored to their specific bridge and responsive to the actual state of the anodes of that particular bridge,” Fierro explained.

“By knowing the remaining time that an anode can be effective in preventing the corrosion of structural components, agencies could develop schedules tailored specifically for their region to ensure that they are providing proper, timely maintenance to their bridges as efficiently as possible, thus saving them time and money from a lifecycle perspective,” explained Cadet 1st Class Brett Fabian.  “The actual corrosion rate data would be extremely valuable to update design life calculation assumptions on existing structures as well as to inform designers of the actual corrosive environment for new structures in a specific location.”

“The Bridge Watch technology is pioneering in that it is capable of anode health monitoring and providing useful, quantitative data that allows precise and efficient anode replacement for both new and old bridges,” said Ret. Lt. Col. Gibbons.

The Bridge Watch team has received its primary financial support from the DoD Corrosion Policy and Oversight Office, which has covered the cadet senior design capstone program’s research and development over three academic years.  “In addition to financial support, the cadets have received management and technical guidance, and mentorship, from the Corrosion Office, for which they are very grateful,” said Ret. Lt. Col. Gibbons.

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