Development of an Embeddable Microinstrument for Corrosivity Monitoring in211 Concrete

摘要

The aim of this program was the development of a small and completely embeddable211u001emicroinstrument for corrosivity measurement in concrete. It should contain all 211u001ethe electronics for the electrochemical measurmeents, the means for data transfer 211u001ebetween engineer and device, and sensors sensitive to the different corrositivity 211u001eparameters. The goals of the work reported here were to develop and test the 211u001erequired sensors and electronics in a laboratory setting. Sensors for the 211u001emeasurement of corrosion rate, corrosion potential, chloride concentration, and 211u001econcrete conductivity were developed and tested in laboratory-scale slabs. The 211u001etests included electrochemical chloride driving as a method for test acceleration 211u001eand wet/dry cycling. The corrosion sensor consists of a piece of reinforcing 211u001esteel as working electrode, another rebar piece or a platinized Nb-mesh as 211u001ecounterelectrode, and an Ag/AgCl electrode as reference electrode. The 211u001econductivity sensor is based on a modified Wenner four-pin method and made of 211u001efour parallel Au wires. Both sensors work very well. Chloride introduced into the 211u001econcrete electrochemically induced corrosion on the corrosion sensor, as seen by 211u001ea decrease in potential and in the polarization resistance. The potentials 211u001erecovered after more than 1000 h of electrochemical chloride removal, but the 211u001ecorrosion resistance did not regain its original value. The change in chloride 211u001econtent was monitored by a silver/silver chloride chloride sensor. The only 211u001epresent drawback of the microinstrument is the construction of a long-term 211u001ereliable reference electrode. The best candidates seem to be Ni/W galvanic couple 211u001eand lead.