The long-term reliability of a threshold corrosion sensor is demonstrated using data collected during two series of exposure tests. The sensors were embedded in concrete and interrogated in a wireless manner using inductive coupling. The frequency signature of the sensor changes after a steel sensing wire corrodes, providing a convenient and noninvasive technique for determining when a threshold amount of corrosion has occurred in a reinforced concrete structure. In the first series of exposure tests, the sensors were embedded in concrete prisms, which were exposed to a variety of temperature and moisture conditions over a six-month period. In the second series of tests, the sensors were embedded in reinforced concrete slabs. The slabs have been subjected to sustained loads and alternating wet and dry cycles for the past year. Data from both test series indicate that the threshold sensors are functioning as designed.
The prototype sensors provide a low-cost method to detect the onset of corrosion in concrete structures using a noninvasive approach. The embedded sensors are wirelessly powered by inductive coupling and do not require batteries. Unlike traditional techniques for detecting corrosion which require an electrical connection to the embedded reinforcement, the sensors are self-contained and provide information about the environmental conditions within the concrete in the vicinity of the sensor. The sensors were originally envisioned to provide binary information about the onset of corrosion based on the characteristic frequency of the impedance response. However, more complicated signal processing is required to determine the state of the sensor. The viability of the corrosion sensors is being evaluated through a comprehensive series of laboratory tests using small-scale concrete prisms and large-scale reinforced concrete members.