Concrete & Asphalt Bridge Deck Delamination

The nation’s deteriorating highway infrastructure requires new computerized Non-Destructive Evaluation (NDE) test methods, which provide analytical data to establish maintenance demands. Applying new non-destructive tools, specifically designed to quantify the extent and number of defects in the infrastructure, will allow maintenance priority assessment and provide the knowledge necessary to establish resource-planning parameters for maintenance scheduling.

The overall size of the camera system, cost size, and sensitivity have improved dramatically in the last few years. For example a quality (hand held) thermal imaging radiometer system and software had an average price of >$57,000.00 in 2000 and an average thermal sensitivity of .1 degree C or 100 millikelvin. In 2000 the cost of such a system was typically > $100,000.00. Average weight of one of the cameras itself was 6 to 15 pounds. Today a Bridge delamination detection system will cost < $20,000.00, the camera itself weighs less than 8 ounces, and has a thermal sensitivity of < .038 degrees C or 38 millikelvin. Numerous hand held cameras are available today for < $7000.00 and have better sensitivity than those systems manufactured in 2000. Most of these cameras utilize a microbolometer based sensor that detects electrical resistance across each pixel based on emitted radiation from the scene. There are currently four basic microbolometer arrays available commercially. They are as follows, 160 x 120, 384 x 288, 320 x 240 and 640 x 480. They are not all the same and vary by manufacturer. The definition of the term bolometer means resistor.

Thermal imaging systems are also currently being tested to find cracks in steel bridge structures under paint. These inspections are typically being conducted at night and in shaded areas. The small amount of friction created by the crack, from molecular movement is conducted to the surface of the paint and then radiated to the surface. This radiation then travels at the speed of light, 186,000 miles per second to the sensor in the thermal camera and is converted to an image we can then interpret. These inspections are more efficient when solar radiation is not introduced into the scene.