Traditionally, the owners and managers
of a structure have monitored corrosion through visual
inspection or the use of analog probes. Unfortunately,
however, these techniques are subject to severe limitations.
Visual inspection is costly, labor-intensive, and fails
to reveal deterioration within a structure.
Analog probes, by contrast, can be embedded within concrete.
To gather data from these devices, however, inspectors
must tour a structure and insert a reader into each
probe site. Like visual inspection, this process is
expensive and labor-intensive, and it generates data
only at the time of each visit. To address this issue,
engineers may wire the probes to send their readings
to a datalogger. Because these transmissions are analog,
however, they’re highly vulnerable to electro-magnetic
interference. The greater the distance between the probe
and the datalogger, the more their connecting wire functions
as an antenna, suffering electro-magnetic interference
from power lines, radio waves, and cell phones. Also
very importantly, each analog probe has historically
measured only one or two parameters of the corrosive
environment.
Virginia Technologies has designed the ECI to solve
these problems. Embedded in a structure during construction,
the ECI monitors the corrosive environment within steel-reinforced
concrete. Because its sensors are integrated with on-board
processing electronics, the ECI carries its signals
only a short distance – approximately one inch
– before analog-to-digital conversion. This maximizes
the signal-to-noise ratio, prevents electro-magnetic
interference, and facilitates more accurate, repeatable
measurements.
From each ECI, those measurements are automatically
transmitted to a datalogger. This eliminates the need
for inspectors to take manual readings. That, in turn,
minimizes the costs of inspection and makes it economically
feasible to gather corrosion data continuously, rather
than every few months. In this way, the ECI ensures
that warning signals are received at the earliest possible
date – when the costs of remediation are lowest.
The ECI also transmits its readings to the datalogger
via digital signals, rather than analog wave-forms.
This makes it possible to place each ECI up to 200 feet
from the nearest datalogger – rather than 30 feet,
as in the case of analog probes. In this way, the ECI
facilitates coverage of a far larger area by each datalogger,
minimizing the cost of supporting electronics. With
the flexibility offered by this greater distance, structure
managers are also able to place dataloggers in more
favorable, sheltered locations. Furthermore, because
ECI readings are digital, maintenance engineers can
download them remotely, and integrate them into computerized
structure management systems.
Finally, and perhaps most importantly, the ECI monitors
not one or two, but 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 sensors. It also reveals correlations among the causes
and signs of corrosion, yielding a fuller, more certain
picture of the threat.
In all of these ways, the ECI represents a substantial
advance in the technology of corrosion monitoring for
steel-reinforced concrete structures.
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