NEXCO-West’s mobile survey setup
FLIR A6701sc camera used to create infrared delamination maps
rise more rapidly during the day and fall faster at night, which is easily detected by the IR camera.
Inspections are performed with a truck-mounted infrared camera while driving across the bridge at 50 miles per hour with traffi c. Matsumoto says it only takes a few minutes for the infrared camera to record an entire scan of one lane of a one-mile long bridge.
The camera employed in NEXCO-West’s scanning system is a FLIR A6701sc MWIR science camera. “We use the A6700 series camera because it can photograph high resolution thermal images while driving at high speed,” explains Matsumoto. This camera’s cooled Indium Antimonide detector offers integration times as fast as 0.48 µs, allowing the team to record 640 x 512 pixel thermal images without any motion blur. Matsumoto says they typically set the camera for a 10Hz frame rate, which allows it to record a crisp thermal image every two meters at highway speed. The camera is connected to a laptop inside the vehicle that is running NEXCO-West’s Infrared Bridge Assessment System (IrBAS) software, so the team can see real-time analysis and recognize potentially delaminated areas.
Better Decisions, Safer Bridges
The subjectivity and potential inaccuracies of the chain drag method warrant reexamination of this traditional form of bridge deck inspection. Infrared scanning provides more objective results, while making the system mobile avoids the disadvantages inherent to traffi c lane closures, including safety hazards, traffi c delays, and increased emissions. An additional advantage to NEXCO-West’s comprehensive and objective data collection method is it allows state highway agencies to monitor long-term bridge performance. “NEXCO-West’s infrared mapping will support data-driven decision- making for bridge management and ultimately, will help bridge owners avoid expensive catastrophic repairs,” Matsumoto says. By superimposing defi ciency maps onto earlier records, engineers would be able to determine the condition and rate of degradation on bridges. This would help them predict the progression of deterioration and make plans for rehabilitation work.
Laptop shows live-streaming infrared through NEXCO-West’s IrBAS software
Thermal image used to create bridge deck defi ciency map
Thermal bridge scan (left) and IrBAS processed image used to create deck defi ciency map (right)
Example of temperature differential for sound and damaged concrete Source: “Comparison of Infrared Cameras for Concrete Bridge Deck Scanning: - Vol.2 Field Test at Haymarket Bridge”, December 2014, NEXCO-West USA, Inc
Processing the Data
After the team has collected data on each lane of the bridge, they can begin processing it. “Most of the data analysis and reporting processes are automated by the IrBAS software, which saves signifi cant time and cost preparing defi ciency maps,” says Matsumoto. The software uses the defi ciency map to calculate the percentage of delaminated deck area and then classify the condition states based on American Association of State Highway and Transportation Offi cials (AASHTO) criteria.
There are three damage categories: 1. Indication: Delamination is present within 4 cm of the concrete surface 2. Caution: Delamination is present within 2 cm of the concrete surface
3. Critical: Delamination is reaching the concrete surface Deck areas that rate Indication are considered satisfactory, while Caution areas require close monitoring. Any area rated as Critical requires immediate action.
Author Contact Details Flir • For more information about thermal imaging cameras or about this application, please visit: www.fl
ir.com/research
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