Detection of Water and Ice on Bridge Structures by AC Impedance and Dielectric Relaxation Spectroscopy Phase I


John Evans

April 2009

Report no. CTS 09-12

We have carried out a preliminary evaluation of two approaches to low-cost sensing systems for monitoring ice and water on bridge deck surfaces. These sensing systems are based on the measurement of impedance of the sensor in contact with or close proximity to ice, water or aqueous solutions of deicing chemicals. Impedance analysis at lower frequencies allows for the determination of the presence of solutions of deicing electrolyte (a sort of "conductivity measurement"), while high frequency dielectric relaxation using time domain reflectometry (TDR) probes the physical state of precipitation and deicing chemicals on the deck or road surface (via dielectric relaxation).

While we originally expected that both measurements would be required to reliably determine the condition of a bridge deck surface with regard to the presence of frozen water or deicing solutions, we have found that the TDR approach is adequate for this task. This suggests that a significant reduction in both the cost of development of practicable sensors and supporting software/electronics can be realized, as well as the ultimate cost of deploying a system based on TDR alone can be realized. As such, TDR becomes the focus for the next phase of development of these sensors.

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