Chloride Ion Sensor
The United States is replacing aging concrete infrastructure and simultaneously developing the tools and techniques to monitor new infrastructure as it ages. Currently, trained personnel base most infrastructure monitoring on individual sensor measurements or periodic visual inspection. Sensors are not distributed throughout the structure being monitored. They are used only for discrete general measurements, mostly due to economic limitations. These approaches do not detect degradation until it has already reached an advanced state. What is required is a robust, reliable, long lasting and cost-effective instrumentation package to measure the parameters of the physical processes that cause degradation in many locations throughout the structure. Detecting the onset and evolution of the process causing the degradation enables corrective action to be scheduled and implemented before significant corrosion occurs.
Researchers at The Johns Hopkins University Applied Physics Laboratory (JHUAPL) have developed the Wireless Embedded Sensor Platform (WESP) which is a package of electronics and antennas that is capable of monitoring various sensing elements and transmitting a signal on demand to a receiver. The Chloride Ion Sensor is one of the sensing elements that are coupled to the WESP. It measures chloride concentration in concrete to determine the effect of the chloride on the rebar. The measurement of the chloride ion is by the use of a molecular imprinted polymer (MIPS) membrane of polypyrrole and polystyrene sulfonate coated over inter-digitated AgCl electrodes. The MIPS allows only the chloride molecules to penetrate the polymer and become trapped. Once in the polymer they change the electronic characteristics of the electrodes and produce a signal in proportion to the amount of chloride present. The JHUAPL chloride ion sensor is 1 inch in diameter and ¼ thick. It is imbedded into the concrete structure near the rebar at the time of construction. Monitoring of the sensor is accomplished by passing a read out device over the concrete. The device powers the sensor and obtains the current status information. When the read out device is moved to another location the sensor deactivates. This allows for rapid and inexpensive monitoring of the structure without taking samples for further laboratory analysis.
US 7,063,781 [MORE INFO
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