The precarious state of U.S. bridges and the significance of infrastructure monitoring systems were highlighted by the Interstate 35W bridge collapse
The precarious state of U.S. bridges and the significance of infrastructure monitoring systems were highlighted by the Interstate 35W bridge collapse in Minneapolis, officials from Applied Sensor Research and Development Corp. contend. Aiming to monitor public structures with tiny wireless sensors, they have entered a Maryland Industrial Partnerships contract with University of Maryland Civil Engineering Professor Dr. Dimitrios Goulias to test sensors that measure temperature, a key factor in concrete’s stability throughout its lifespan.
Hardening at the wrong temperature can cause concrete to become unstable and crack, creating safety hazards and expensive repairs. During the Chesapeake Bay Bridge renovation in 2002, officials spent $60 million on general repairs that included repaving with concrete. According to The Washington Post, the new pavement began to crack shortly thereafter, and an additional $7 million was funneled into the project. Later, inspections proved that the cracking was a result of low curing temperatures.
Many current structural heath inspection processes, particularly in the U.S., are completely manual and labor intensive, contends Jacqueline Hines, president of Annapolis, Md.-based ASR&D. The sensors we are developing will provide a continuous wireless monitoring capability.
Workers embed the sensors in a structure before concrete is poured. The sensors then relay temperature measurements to a software program that provides strength predictions and thermal gradients. Depending on the readings, construction workers can insulate or cool the structure as it hardens to maintain optimal temperatures. The team will study how the sensors work in differing concrete mixes on current construction sites, either on or nearby campus. Further, Prof. Goulias and ASR&D staff will study how construction equipment, such as cranes and front loaders, affect the wireless signal of the sensors.
Throughout a structure’s service life, the wireless sensors, lasting 30 to 40 years or longer, also monitor temperature changes due to environmental factors or incidents such as vehicle fires or explosions. If a vehicle fire or an explosion occurs in a tunnel or a bridge, our sensors can monitor how hot the concrete gets. Concrete exposed to extremely high temperatures can become almost sand-like and lose its structural integrity, says Hines.
Temperature is not the only indicator for concrete failure: crucial instigators can include stresses in the form of reinforcement corrosion, vibrations and traffic loads. Hines notes that her company is investigating other types of sensors to monitor such factors, using these devices as well to provide a wireless link to interface with other sensor technologies.