United States Department of Transportation
i
Development of a prototype version of an embeddable corrosivity measuring instrument for reinforced concrete.
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2002-01-01
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Edition:Final contract report;July 2000Nov. 2002.
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Abstract:To address the problem of safely and quantifiably detecting corrosion in a cost-effective and timely manner, the University of Virginia and Virginia Technologies, Inc. have developed a remotely accessible, networked, embedded corrosion instrument. The instrument measures the corrosion rate and open circuit potential of a sample of black steel reinforcement in the concrete of interest. It does not directly measure the corrosion parameters of the nearby bars in the reinforcement network but instead measures the corrosivity of the concrete environment nearby. The instrument also measures the conductivity of the concrete, which can be used to assess the moisture content of the concrete. An onboard temperature sensor records the internal temperature of the concrete and an Ag/AgCl ion specific electrode (ISE) can detect increasing changes in chloride concentration. These measurements combined provide a fairly comprehensive snapshot of the internal electrochemical corrosivity of the structure. The instrument also contains the necessary circuitry to stimulate and measure a strain gauge external to the instrument, which can be used to measure mechanical stresses caused by the buildup of corrosion products on the reinforcement steel. A rugged, environmentally sealed enclosure was designed and molded to provide protection for the electronics, a rigid mounting surface for the electrodes, and features for mounting the instrument to the rebar. A finite element analysis was performed for the enclosure embedded in a bridge deck to show that the Embedded Corrosion Instrument (ECI) could withstand the compressive and tensile forces encountered in the bridge without rupturing or compromising the integrity of the bridge. Successful laboratory tests of the prototype were performed that demonstrate its ability to detect changes in corrosivity, analyze them, and communicate them in a useable form to the operator. In the spring of 2002, four instruments were installed in the 29/460 interchange near Lynchburg, Virginia. Their functionality is being monitored via a wireless cellular connection. Thus, there is no need to visit the site to collect corrosion information. The entire system is powered directly from the rechargeable battery. The solar panel is used to maintain the charge level of the battery. A single battery is being used to power all of the microinstruments installed on a bridge. The most important achievements of the project are the development, demonstration, and field installation of a microinstrument prototype that can measure multiple parameters relevant to corrosivity and communicate this information via a wireless cellular connection to a central site. Specific recommendations include continued monitoring of the instruments installed in the 29/460 interchange, and expansion of microinstrument use to long-term laboratory measurements at the Virginia Transportation Research Council in studies of inhibitors and other corrosion mitigation strategies.
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