Embedded Corrosion Instrument (ECI)
ElectraWatch ECI:
The Embedded Corrosion Instrument - ECI - is an electronic corrosion sensor that provides early warning of conditions that damage steel reinforcement, leading to cracking, spalling, and other deterioration of concrete structures. By monitoring five key factors in corrosion, and by communicating these through a digital network, the ECI provides comprehensive, real-time information on structural conditions. This helps facilities managers to avert crises, save money on maintenance, and build a detailed record on each structure.
The ECI is designed to monitor bridges, buildings, dams, erosion control structures, flood control channels, parking garages, piers, pylons, roadways, and spillways. A non-destructive evaluation (NDE) device, it gathers and delivers all data without requiring inspectors to cut samples, interrupt use of a structure, or even visit the site.
The ECI monitors five key factors in corrosion - linear polarization resistance, open circuit potential, resistivity, choloride ion concentration, and temperature. This provides more comprehensive data than prior generations of corrosion monitors. It also reveals correlations among the causes and signs of corrosion, yielding a fuller, more certain picture of the threat.
ECI Measurements:
Linear Polarization Resistance (LPR) and Open Circuit Potential (OCP): The ECI-1 measures linear polarization resistance by using a steel working electrode, stainless steel counter electrode, and manganese dioxide reference electrode. The working electrode is a sacrificial component made of black steel, designed to corrode at the same rate as the ASTM 615/A-compliant steel that it monitors. Defective areas in protective coatings over structural steel, such as epoxy or stainless steel cladding, may be expected to demonstrate corrosion characteristics comparable with those of black steel.
The ECI control module initiates the measurement of open circuit potential between the working and reference electrodes in the potentiostat circuit, and applies the appropriate potentiostat drive potential between the counter and working electrodes. A zero resistance ammeter in the potentiostat circuit measures the cell current.
The ECI scans cell current and drive potential over a range about the OCP, and uses the resulting data to calculate polarization resistance. The corrosion rate of reinforcement steel may be expected to be inversely proportional to this figure. If LPR is high and OCP remains small in magnitude, managers may anticipate that the reinforcement steel in a structure is passive, suffering corrosion at a relatively low rate. As steel begins to depassivate, due to an increase in chloride ion concentration or other corrosive environmental conditions, LPR will decrease and OCP will become increasingly negative.
Resistivity: The ECI-1 uses four stainless steel electrodes to measure resistivity in the concrete that surrounds it. A galvanostat circuit drives a stepped current through the outer pair of these electrodes, and measures the potential between the inner pair at each step. Electronics within the ECI then perform a linear regression to calculate the resistance between the inner pair of electrodes. The ECI multiplies this figure by the cell constant of its resistivity sensor to derive the resistivity of the concrete in units of ohms-cm. This provides information on the relative amount of moisture in the concrete. Structure managers may also use this resistivity parameter with the geometric cell constant of the working, counter, and reference electrodes to correct for ohmic resistance errors in polarization resistance measurements.
Chloride Ion Concentration: The ECI-1 uses a silver/silver-chloride ion specific electrode in combination with its reference electrode to measure chloride ion concentration. Over time, a potential will develop between the Ag / AgCl and reference electrodes. The magnitude of this potential is related to the chloride concentration in the concrete surrounding the instrument. The ECI reports chloride measurement results as a potential.
Temperature: The ECI-1 includes an on-board solid state sensor, which provides information on the temperature within the concrete surrounding it.
The ECI integrates processing electronics with its sensors, and so can use digital, rather than analog communications. This eliminates data corruption by electro-magnetic interference from power lines, radio waves, and cellular telephones. Digital technology also makes it possible to connect multiple ECI monitors to a single datalogger, saving potentially tens of thousands of dollars in support electronics per project.
With these advances, the ECI has earned success and acclaim around the world. It has been integrated into a wide range of structures, in regions as diverse as Australia, Singapore, and the United States. It has gained media coverage in Better Roads Magazine, the MIT Technology Review, and other leading publications.
