Corrosion Monitoring of Steel Reinforced Concrete Structures Using Embedded Instrumentation The ECI-2 is an embeddable non-destructive evaluation (NDE) corrosion-monitoring instrument. It is capable of measuring parameters important to long term corrosion monitoring including linear polarization resistance (LPR), open circuit potential (OCP), resistivity, temperature and a potential related to chloride ion concentration ([Cl-]). Each ECI-2 Instrument is a digital peripheral connected on an embedded local area network. The instruments communicate with each other and an external data logger using the SDI-12 industry standard protocol. The ECI-2 has many applications in the construction and maintenance of commercial and civil structures. These structures can include but are not limited to high rise buildings, parking garages, bridges, dams, spillways, flood control channels, piers, pylons, and erosion control structures. During construction, engineers, builders, and supervisors can monitor parameters such as chloride concentration, resistivity, and temperature.
These parameters can identify errors at an early stage of construction. One error that may be detectable is the use of sea water or contaminated water during mixing of the concrete ([Cl-]). The moisture content and temperature of the structure can be monitored during the curing process to ensure maximum strength of the concrete. Once construction is complete the instrument can be used to conduct long term monitoring of corrosion conditions over time.
The Industrial Challenge
Extremely large construction efforts costing millions to billions of dollars and spanning several years. In the United States alone repairs for corrosion damage to federal bridges are estimated at $50 billion annually. These structures are vital to commerce and the standard of living of millions of people in the United States and billions of people worldwide. Worldwide estimates to repair reinforced concrete structures are $200/m2 of exposed surface.
Premature or unexpected failures of these structures are often catastrophic in terms of time, money, and lives. The high costs of corrosion due to replacement and premature failures mandate the need for integrated in-situ NDE systems. These NDE systems should provide information based on changes in the structure’s corrosion condition to effect timely maintenance interventions.
The Smart Structure Solution
Until now corrosion monitoring in steel reinforced structures has been conducted using embeddable probes. The probes measure analog signals that can be interrogated using electronic devices external to the structure. Since the signals produced by these probes are small in amplitude, they are subject to corruption from nearby EMI sources such as power lines, radios, cell phones and therefore must have limited lead lengths. To address these limitations, Smart Structures has developed a fully embeddable corrosion monitoring instrument incorporating all required electrodes and signal processing electronics. The ECI-2 approach allows the leads connecting the low-level analog signals to signal processing electronics to be kept short (approximately 1 inch). Short analog signal leads allow for a higher signal to noise ratio and more accurate and repeatable measurements. The ECI-2 communicates with other instruments and an external datalogger using a digital protocol which is highly resistant to corruption from nearby EMI sources.
The ECI-2 embeddable corrosion instrument packs 5 sensors into one small package that can be easily installed and placed wherever needed to provide adequate coverage of structure during construction.
The ECI-2 During Installation in a Bridge Deck
The instruments are modular and uniquely addressable allowing the system to be easily scaled to the needs of the specific structure. The ECI-2 is less susceptible to electromagnetic interference (EMI) than other corrosion probes on the market by virtue of its extremely small lead lengths.
Many embedded corrosion probing systems rely on external electronics to drive (stimulate) the embedded probe and to measure the resulting signals. Often these measurements have to be made over cables of up to 10 meters in length which can act as antennas for EMI sources such as power lines, cell phones and radio waves. The leads between the electrodes and data acquisition electronics in the ECI-2 are only about 1 inch in length and are converted to digital data right at the source. The data is transmitted over a digital network, which is relatively immune to interference.