Low-Cost Threshold Sensors for Corrosion Detection in Bridge Decks

A passive sensor prototype has been developed for detection of corrosion initiation in bridge decks. The sensor is designed to be embedded in concrete during construction and interrogated during routine inspections. It is scanned with a mobile external reader that measures inductively coupled impedance. The innovative design provides a low-cost, wireless and battery-free alternative for corrosion monitoring. The sensor incorporates two components; a resonant L-C circuit and a sacrificial corroding element. The exposed corroding element is not connected to the circuit components and affects the measured circuit response through inductive coupling. As the sacrificial element corrodes, the sensor response changes gradually indicating corrosion initiation within concrete. Consequently, the sensor platform can be used for either threshold or analog corrosion monitoring applications. The threshold information can be obtained using rapid interrogation and the measured output can be interpreted easily. In addition, the design allows for using corroding elements of different materials and geometries, hence, permitting the detection of multiple corrosion levels. The reliability of the passive sensor prototype was investigated in a long-term accelerated corrosion test. Sensors were embedded in reinforced corrosion specimens and successfully indicated the state of corrosion in adjacent reinforcement. The sensor response was not sensitive to variations in the environmental conditions, such as temperature and moisture content. Recent developments in the sensor design and the results of the long-term tests will be presented.

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