Prototype sensors have been developed to detect the onset of corrosion in steel reinforced concrete using non-invasive techniques. These sensors are designed to be extremely simple and low cost. The sensors are embedded in the concrete and are powered and interrogated through the use of inductively coupled magnetic fields. A new conductivity sensor is proposed, based on the design of the corrosion sensor. The conductivity sensor design is examined using circuit simulations and initial experimental results. Both sensors could be used together in a corrosion monitoring system.
In this paper a new low cost, wireless unpowered sensor will be discussed that is designed to monitor the conductivity of concrete, which may provide information on the ingress of chloride ions during the life of the structure. A method of extracting temperature information from a previously developed corrosion sensor will also be presented. During a recent test, both a wireless corrosion sensor and a wireless conductivity sensor were placed in concrete and monitored throughout the duration of the curing process. Analysis of the data shows it is possible to determine temperature information based on the corrosion sensor response, allowing wireless in-situ temperature monitoring of the concrete during the cure. Monitoring curing temperature using the same sensor which would later be used for long-term corrosion detection would help reduce the cost of such a monitoring system.
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.
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