United States Department of Transportation
i
Development of an embeddable microinstrument for corrosivity monitoring in concrete.
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1999-07-01
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[PDF-2.69 MB]
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Edition:Final Contract, 10/96-6/99
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Abstract:The aim of this program was the development of a small and completely embeddable microinstrument for corrosivity measurement
in concrete. It should contain all the electronics for the electrochemical measurements, the means for data transfer between engineer
and device, and sensors sensitive to the different corrosivity parameters. The goals of the work reported here were to develop and
test the required sensors and electronics in a laboratory setting.
Sensors for the measurement of corrosion rate, corrosion potential, chloride concentration, and concrete conductivity were
developed and tested in laboratory-scale concrete slabs. The tests included electrochemical chloride driving as a method for test
acceleration and wet/dry cycling. The corrosion sensor consists of a piece of reinforcing steel as working electrode, another rebar
piece or a platinized Nb-mesh as counterelectrode, and an Ag/AgCI electrode as reference electrode. The conductivity sensor is
based on a modified Wenner four-pin method and made of four parallel Au wires. Both sensors work very well. Chloride
introduced into the concrete electrochemically induced corrosion on the corrosion sensor, as seen by a decrease in potential and in
the polarization resistance. The potentials recovered after more than 1000 h of electrochemical chloride removal, but the corrosion
resistance did not regain its original value. The change in chloride content was monitored by a silver/silver chloride chloride sensor.
The only present drawback of the microinstrument is the construction of a long-term reliable reference electrode. The best
candidates seem to be Ni/W galvanic couple and lead.
A micropotentiostat coupled to a zero-resistance ammeter and a microgalvanostat based on operational amplifiers were designed: and
heart of a complete measurement system, which includes on two double surface mount boards the ASIC, a microprocessor, control
circuitry, and connections to the external corrosivity sensors, as well as RF transceiver circuitry for the wireless communication with
the instrument.
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