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U.S. Department of Transportation
Federal Highway Administration
Research and Development
6300 Georgetown Pike
McLean, VA 22101-2296
Cathodic protection (CP), the technology used to mitigate corrosion of metals embedded in concrete, is
the only rehabilitation technique that has been proven to stop corrosion in salt-contaminated bridge
decks regardless of the chloride content of the concrete. This technology is based on the principle of
applying an external source of current to counteract the internal corrosion current produced in
reinforced concrete components. During CP, current flows from an auxiliary anode material through
the electrolyte (concrete) to the surface of the reinforcing steel.
Various materials in various configurations are used as auxiliary anodes for CP resulting in various types of CP systems. The selection of the anode material and its configuration is paramount to the success of the system. The primary objective of this 5-year study was to determine the effectiveness of various materials and configurations when they are used as auxiliary anodes on highway structures during a long-term evaluation.
The findings of the study summarize the protection provided by the systems evaluated and estimate the expected service life for the anode materials in similar environments. This report will be of interest to engineers involved in bridge design, bridge performance evaluation and prediction, and bridge maintenance and rehabilitation.
| T. Paul Teng, P.E. Director, Office of Infrastructure Research and Development |
This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof. This report does not constitute a standard, specification, or regulation.
The United States Government does not endorse products or manufacturers. Trade and manufacturers' names appear in this report only because they are considered essential to the object of the document.
SI* (Modern Metric) Conversion Factors
3-1. Arc-Sprayed Zinc Impressed-current CP Systems
3-2. The AC Resistance Between Reference Cell and Reference Cell Ground
3-3. The Current Density of Concrete Surface Area During Each Evaluation
4-1. Titanium Mesh Impressed-current CP Systems
4-2. Results of Depolarization Testing (in percent)
4-3. Titanium Ribbon Impressed-current CP Systems
4-4. Arc-Sprayed Titanium Impressed-current CP Systems
5-1. Conductive Coating-Based Impressed-current CP Systems
5-2. Current Density Variation
6-1. Slotted Conductive Polymer-Based Impressed-current CP Systems
6-2. Mounded Conductive Polymer Impressed-current CP Systems
7-1. Conductive Coke Breeze-Based Impressed-current CP Systems
8-1. Arc-Sprayed Zinc Galvanic CP Systems
8-2. Polarization Testing
8-3. Zinc with Adhesive Galvanic CP Systems
8-4. Expanded and Bulk Anode Galvanic CP Systems
Cathodic protection (CP) is a technology used to mitigate corrosion of metals embedded in concrete. Based on extensive Government and private industry research, the Federal Highway Administration (FHWA) concluded that CP is the only rehabilitation technique that has been proven to stop corrosion in salt-contaminated bridge decks regardless of the chloride content of the concrete. This technology is based on the principle of applying an external source of current to counteract the internal corrosion current produced in reinforced concrete components. During CP, current flows from an auxiliary anode material through the electrolyte (concrete) to the surface of the reinforcing steel.
Various materials in various configurations are used as auxiliary anodes for CP, resulting in various types of CP systems. The selection of the anode material and its configuration is critical to the success of the system. The primary objective of this study was to determine the effectiveness of various materials and configurations when used as auxiliary anodes on highway structures during a long-term evaluation.
Twenty highway structures (19 bridges and one tunnel) protected by one or more CP system(s) were included in this study. The structures were located in 11 States and one Canadian Province. These structures were protected by a total of 19 impressed-current and 5 galvanic CP systems. The following types of systems were monitored for a period of 5 years:
Based on the age of the system, three to eight evaluations were planned for each structure. Most of the structures were selected by FHWA based on previous studies performed under the Strategic Highway Research Program (SHRP). Additional structures were added to the program as they became known to the research team. Structures that could not be properly evaluated were excluded from the study. This study was funded under the continuation of the SHRP program.
Findings
A summary of the findings of this study is presented in tabular form below. The first four columns provide information on the systems evaluated in this study. The fifth column provides a rating for the protection provided by the systems (i.e., excellent, good, fair, or poor). Based on the results of this study and the experience of the authors, an estimate of expected service life for the anode materials in similar environments is presented. In this summary, the protection provided by the system is based on the actual operation of the system. On some structures, the systems were operated at insufficient output current and this resulted in poor performance. If these system had been operated at higher output currents, their performance would have been rated higher.
Table 1. Summary of findings
| Anode Material & Configuration | Environment | No. of Systems | Age of Systems (years) | Protection Provided | Estimated Service Life (years) |
|---|---|---|---|---|---|
|
Impressed-current Cathodic Protection Systems
|
|||||
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Arc-sprayed zinc
|
Semi-marine & deicing | 2 | 2 | Poor(1) | 10 to 15 |
|
Arc-sprayed zinc
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Marine | 1 | 1 | Excellent | 7 to 12 |
|
Arc-sprayed zinc
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Deicing | 1 | 8 | Not determined(2) | 10 to 15 |
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Titanium mesh
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Deicing | 3 | 6 to 12 | Excellent | >25 |
|
Titanium mesh
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Marine | 1 | 1 | Excellent | >25 |
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Titanium ribbon
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Deicing | 1 | 9 | Excellent | 15 to 25 |
|
Arc-sprayed titanium
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Semi-marine & deicing | 1 | 1 | Poor(1) | Not determined(3) |
|
Arc-sprayed titanium
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Marine | 1 | 1 | Poor | Failed in 1 year |
|
Conductive paint
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Deicing | 2 | 4 to 9 | Good | 5 to 10 |
|
Conductive polymer slotted
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Deicing | 1 | 12 | Fair | 5 to 10 |
|
Conductive polymer
mounded
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Deicing | 1 | 15 | Poor | 5 to 10 |
|
Coke breeze
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Deicing | 3 | 5 to 9 | Excellent | 10 to 15 |
|
Galvanic Cathodic Protection Systems
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|||||
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Arc-sprayed zinc
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Marine | 3 | Excellent | 7 to 10 | |
|
Zinc foil with adhesive
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Deicing | 1 | 1 | Excellent | 7 to 10 |
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Expanded zinc mesh &
bulk
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Marine | 1 | 3 | Good | 15 to 20 |
(1) Systems operated at insufficient current output.
(2) No instrumentation installed to allow determination.
(3) System operated intermittently to allow proper evaluation.
Cathodic protection (CP) is a technology used to mitigate corrosion of metals and has been used on
ships and pipelines for many decades. The first use of this technology on a bridge deck dates back to
1973.(1) Based on extensive Government and private industry research, the Federal Highway
Administration (FHWA) concluded that CP is the only rehabilitation technique that has been proven to
stop corrosion in salt-contaminated bridge decks regardless of the chloride content of the concrete.(2)
This technology is based on the principle of applying an external source of current to counteract the
internal corrosion current produced in reinforced concrete components. During CP, current flows from
an auxiliary anode material through the electrolyte (concrete) to the surface of the reinforcing steel.
Various materials in various configurations are used as auxiliary anodes for CP, resulting in various
types of CP systems. The selection of the anode material and its configuration is critical to the success
of the system. The primary objective of this study was to determine the effectiveness of various
materials and configurations when used as auxiliary anodes on highway structures during a long-term
evaluation.
The secondary objective of this research was to identify the most appropriate laboratory and field test
method(s) for evaluating and monitoring the performance of CP systems.
Twenty highway structures (19 bridges and one tunnel) protected by one or more CP system(s) were
included in this study. The structures were located in 11 States and one Canadian Province. These
structures were protected by a total of 19 impressed-current and 5 galvanic CP systems. The following
types of systems were monitored for a period of 5 years:
Based on the age of the system, three to eight evaluations were planned for each structure. Most of the
structures were selected by FHWA based on previous studies performed under the Strategic Highway
Research Program (SHRP). Additional structures were added to the program as they became known
to the research team. Structures that could not be properly evaluated were excluded from the study.
This study was funded under the continuation of the SHRP program. Because the last installment of
funds was not available to the project, two to six evaluations were actually performed. When possible,
two trips were scheduled in similar seasons to allow a comparison of data from similar temperature and
moisture conditions. Only sections of highway structures protected by the CP system were evaluated
on each structure.
During each evaluation, visual and delamination surveys were performed when possible. The operating
condition of all system components was documented and polarization and/or depolarization testing was
performed. When present, current flow in null probes and current probes was measured. Rectifier
data for all impressed-current systems was documented on arrival and at departure from the site.
Cores were collected during select evaluations to ascertain the chloride ion content in areas protected
by the CP system. On some structures, controls were established to allow comparison between
protected and unprotected areas. In such cases, the designated control areas were surveyed for
visually observable damage and the presence of delaminations.
The ability of CP technology to stop corrosion is well established, so the focus of this effort was to
ascertain the effectiveness of each material and configuration to serve as an anode for CP of reinforced
concrete bridge structures. In order to evaluate the effectiveness of a material in a particular
configuration, the design and installation of the system were reviewed first, when available, to ensure
that flaws had not predestined the system to fail. Next, monitoring and maintenance of the system,
when available, were reviewed to ensure that the system had been operated and maintained in a manner
in which the system could be effective in mitigating corrosion.
Although a significant amount of data has been collected during this study, analysis of the data was limited to ascertaining the long-term performance of the CP systems. In the interest of brevity, only the data necessary to support the findings of the study are presented in the report. Data from test methods to ascertain the condition of system components are not provided, and only conclusions drawn from the data are discussed. Only when such data were considered to be informative or unique were they included.
In this study, standard test methods and generally accepted industry practices were used in evaluating
the long-term performance of the CP systems. Under certain circumstances, some of the test methods
and practices encountered problems with implementation and data interpretation. Although many of
these issues are known to many users, very little discussion is found in literature. This chapter lists all
test methods and practices used in this study and the problems encountered in their use.
Test methods and practices common to both the impressed-current and galvanic CP systems are discussed first. This is followed by a discussion of methods used for impressed-current CP systems and galvanic CP systems.
2.1. Test Methods: Impressed-current and Galvanic Systems
The following test methods and practices common to both the impressed-current and galvanic CP systems are described below.
2.1.1. Visual Survey
During each evaluation, a visual survey of the section of the structure or component protected by the CP system was performed. In some instances, a visual survey of control areas set up adjacent to the protected area was also performed. All signs of corrosion-induced damage, concrete deterioration, deterioration of anode material, and anomalies were documented. In some structures, access was insufficient to conduct a visual survey of the entire cathodically protected area. In such structures, visual survey was limited to accessible areas. Only the results of the visual survey that impact the long-term performance of the system being evaluated are discussed in this report.
2.1.2. Delamination Survey
Sounding techniques using a hammer or a chain were used to detect delaminations or disbondment of the protected surface. In many instances, overlays were present and the hollow-sounding areas detected could have resulted from corrosion-induced damage or disbondment of the overlay from the original concrete. When possible, cores were collected to differentiate between delamination and disbondment. The results of the delamination survey are not discussed in the report if no hollow-sounding areas were detected.
2.1.3. Electrical Continuity Testing
Three test methods that can be used to perform electrical continuity testing. The most commonly used technique is the direct current (DC) method. The other two techniques are alternating current (AC) measurement and the half-cell technique.
In the DC method, resistance and the voltage difference between two embedded metals are measured. When this technique was developed, there were concerns that the resistance measured could be impacted by currents flowing between the embedded metals. To overcome the impact of these currents, the method requires measurement of resistance in both directions. If no currents are involved and the meter is exclusively measuring DC resistance, the resistance in both directions would be equal. Under generally accepted criteria for the test method, it is required that the resistance measured in the two directions not differ by more than 1 ohm and the voltage difference between the two points not exceed 1 millivolt (mV). The maximum allowable value of the resistance measured in each direction is dependent on where the measurement is made. When the DC technique is used directly on exposed reinforcement, as is the practice during construction of the CP system or condition evaluation of the structure, the maximum allowable resistance in each direction is 1 ohm (some in the industry use a criterion of 3 ohms). When the technique is used in an installed CP system, and the wires connected to the system grounds and the grounds of instruments such as the reference cells, current probes, null probes are used for the resistance measurement, the maximum allowable resistance in the each direction is dependent on the run of the wires.
Although the basis for the evaluation criteria for this technique is very sound, there are exceptions, such as when this criterion fails to detect continuity. When currents generated by various sources such as corrosion cells or stray currents are present in the reinforcement system targeted for testing, the DC technique fails to detect continuity. The presence of these currents results in the measurement of resistance and voltage representative of the electrical network associated with the current and the resistance of the target embedded metals. This problem is most prevalent when electrical continuity measurements using this technique are made in structures that are cathodically protected, are experiencing very active corrosion, have the presence of stray currents, or have some internal source of current.
In this report, the primary concern is measuring electrical continuity of elements in cathodically protected structures that have been de-energized. When a CP system is de-energized, the cathodically protected reinforcement is depolarizing and trying to reach a stable state. In this condition, the DC technique is very prone to impact by currents generated during the stabilizing of the system. Some systems stabilize very quickly and DC electrical continuity measurements produce valid results within hours of the system's being de-energized, whereas some systems take more than 24 hours to fully stabilize. Also, after a system is de-energized, corrosion cells may be initiated, depending on the corrosiveness of the environment, resulting in corrosion currents' flowing in the target element. When anode materials such as zinc are used for impressed-current systems, if they are in contact with the steel, although the system is de-energized, they will form a galvanic couple with the steel and produce currents in the element that impact DC measurements.
At the start of this study, the DC technique was used exclusively to detect continuity of system grounds and the grounds of embedded instruments. As unexpected results were encountered, AC and half-cell techniques were used in addition to the DC measurements to ascertain the presence or lack of continuity.
In the AC technique, only one AC resistance measurement is made between the target elements. Similar to the DC technique, the maximum allowable AC resistance to signify the presence of continuity is dependent on where it is used. As AC currents are capable of shorting through discontinuities when an appropriate capacitance is generated across the discontinuity, the AC resistance measurement may incorrectly identify continuity when none exists.
The half-cell technique is based on the concept that a reference cell will measure the same potential (of the same target area) even when different grounds are used, as long as these grounds are electrically continuous. The technique requires that the potential of the target area not differ by more than 1 mV when various grounds are used to measure it in order for continuity to be present between the grounds used in the test. This technique works only if the potential of the target area is stable and not changing with time.
2.1.4. The AC Resistance Measurements
The AC resistance measurements between anode and system ground were used to obtain circuit resistance of the system and to detect the presence of shorts between the anode and the embedded steel protected by the CP system.
The AC resistance measurements between reference cells and their respective grounds were used to identify malfunctioning reference cells. When the AC circuit resistance is very high, it may be indicative of the failure of certain types of reference cells. High circuit resistance in conjunction with no response by a reference cell to changes in CP current indicates a malfunctioning reference electrode. High resistance also makes the reference cell prone to noise pick-up and makes the measurement of accurate potentials somewhat difficult.
The Ontario Ministry of Transportation, which developed the voltage probe, recommends the use of AC resistance measurement between the voltage probe and the system ground, as well as the voltage probe and the anode, to determine its reliability.
2.1.5. Chloride Ion Content Analysis
Core samples were collected from protected areas of the structures during one of the evaluations. Powdered concrete samples were collected from various depths in the cores and analyzed for total chloride ion content in accordance with the standard test method prescribed by the American Association of State Highway and Transportation Officials (AASHTO) T-260(3), "Sampling and Testing for Chloride Ion in Concrete and Concrete Raw Materials." The results of the chloride ion content analysis at the steel depth, when available, are presented in the text to provide some idea of the corrosivity of the environment in which the cathodic protection system was operating.
2.2. Test Methods: Impressed-current Systems
When the impressed-current systems were evaluated, the as-found operating parameters were documented first. These included measuring output voltage, output current, and back electro-magnetic force (BEMF). In most rectifiers, meters are provided to measure the output voltage and the output current. An external meter was used to verify the accuracy of the meters in each rectifier. The output settings of each zone in each rectifier evaluated were also documented. This was followed by the measurement of the instant-off potentials of all embedded reference cells and voltage probes present and of currents in current probes and null probes. After these measurements were recorded, the system was de-energized.
Once the system was de-energized, all anode, system ground, reference cell, reference cell ground, null probe, and current probe connections, as appropriate, were removed from terminals connected to the rectifier and the measuring instrument circuits. Subsequently, electrical continuity testing and AC resistance measurements were performed. The connections were removed from the rectifier and the instrumentation to ensure that the internal circuits of the rectifier and the instrumentation did not impact the results of the tests.
Upon sufficient passage of time after the system was de-energized, static potentials of all embedded reference cells and currents in the current probes and null probes were measured.
After all measurements were completed, the system was re-energized and rectifier operating parameters were documented. Adjustments to output current or other corrections were made, when necessary, to some systems for which permission had been obtained.
In some systems, during certain evaluations, one or more circuits were found to be powered off. In such instances, all data to be collected while the system was de-energized were collected and, when possible, the system was energized. Instead of measuring polarization decay, polarization development was measured.
2.2.1. Instant-Off Potential Measurement
There are several methods for measuring instant-off potentials in impressed-current systems using embedded or external reference cells. Many rectifiers are equipped with instrumentation to measure instant-off potentials. In this study, all instant-off potentials were measured using an external meter and one of the following two methods:
When possible, the accuracy of the rectifier instrumentation in measuring instant-off potentials was verified by comparing the measurements made using an external multimeter with measurements obtained with one of the methods listed above.
Before any measurements were made, an oscilloscope was used to identify the output waveform and detect the presence of electrical noise in the system. When necessary, the scope-null method was used to verify the data obtained by the peak-hold method. When noise was detected, an attempt was made to eliminate it by the use of capacitors. Sometimes we were successful in eliminating the noise. When noise was detected and could not be eliminated, the manual interrupt technique was used. Also, rectifiers with filtered outputs and no mechanism for interruption of the current required the use of the manual method.
2.2.1.1. Peak-Hold Method
In this technique, the ability of the multimeter to store the highest potential measured by a reference cell in a 1-millisecond (ms) window is used. The highest potential measured by a reference cell is expected to occur when the current in the CP system momentarily goes to zero. In a rectifier with unfiltered output, the output current goes to zero when the AC cycle reverses polarity. In a rectifier with a filtered output, an internal current interrupter is used to interrupt the current for a given period of time. The peak-hold function of the multimeter is used to measure the peak potential that signifies the instant-off potential of the reference cell.
2.2.1.2. Manual Current Interrupt Method
In the manual method, the output current of the rectifier is interrupted manually and the potential difference between the reference cell and the steel is measured 1 second after the power interruption using a multimeter.
2.3. Test Methods: Galvanic Systems
The evaluation of galvanic systems was performed by measuring the CP current generated by the anode and/or the polarization development and/or decay. The output current can be measured as a voltage drop across a resistor connected between the anode and the system ground or as a current density of a rebar probe. Polarization development and decay measurements are made using embedded reference cells, rebar probes, and/or external reference cells. The system must be equipped with a resistor or a rebar probe for the current measurement to be made.
Many galvanic systems are equipped with rebar probes. Rebar probes contain a piece of reinforcing steel with a known surface area that is embedded in the concrete element to be protected. The rebar probe is connected to embedded steel via a fixed resistor. The resistor allows the measurement of current received by the probe. When a switch or other mechanism is installed to allow the rebar probe to be disconnected or connected to the structural steel, it can be used for polarization development or decay measurement. When a rebar probe is used, the connection or disconnection of the rebar probe to the structural steel does not impact the system operation. In Florida, where galvanic systems are commonly used to protect marine bridge substructures, two rebar probes are often used adjacent to one another. At any time, one probe is connected to the reinforcing steel and the other is not. During evaluation, the connected probe is used to perform depolarization (polarization decay) testing and the other probe is used to perform polarization (polarization development) testing. When rebar probes are not installed, the system must be disrupted if polarization development or decay testing are done, and a mechanism must be available to disrupt the system.
A total of four arc-sprayed zinc-impressed-current CP systems were evaluated. Two of these, the Yaquina Bay Bridge and the Depoe Bay Bridge, were in a similar environment and the other two, the Queen Isabella Causeway and the Upper Salt Creek Bridge, were in a very different environment. Table 3-1 lists pertinent information on the four CP systems:
Table 3-1. Arc-Sprayed Zinc Impressed-current CP Systems
| Structure Name and Location | Year CP System Installed | Element(s) Protected | Area Protected (m2) | Instrumentation | Age at Last Evaluation | Average Chloride Ion Content at Steel Depth (ppm)* |
|---|---|---|---|---|---|---|
| Yaquina Bay Bridge, Newport, OR | 1996 | Super- and substructure elements | 19,461 m2 | 2 reference cells per zone | 2 years | NA |
| Queen Isabella Causeway, South Padre Island, TX | 1997 | Tie beam & footings in bent | 127 m2 | 3 reference cells & 2 null probes | 13 months | 317 at center footing |
| Depoe Bay Bridge, Newport, OR | 1996 | Super- and substructure elements | 5600 m2 | 2 reference cells & 1 null probe per zone | 2 years | NA |
| Upper Salt Creek Bridge, Redding, CA | 1988 | Deck | 302 m2 | Potential wells | 8 years | 278 |
Note: Chloride ion content information was obtained from cores collected during this study.
NA - Not available
* parts per million
3.1.1. Yaquina Bay Bridge, Newport, Oregon
The historic Yaquina Bay Bridge was constructed in 1934 and carries northbound and southbound traffic over Yaquina Bay in Newport, Oregon.
3.1.1.1. Structure Information
The roadway is 8 meters wide and 994 m long. The substructure in each span comprises columns supported by two arches running parallel to the bridge, one on each side. The two ends of the arches are supported by footers at each pier. Diaphragm walls connect the two arches at a regular interval.
In 1989, a corrosion condition evaluation of the structure revealed that the bridge deck was in poor condition and required extensive rehabilitation. Thirteen hundred square meters of delaminated concrete were found. Corrosion-induced damage was also noted on the substructure elements.
3.1.1.2. CP Information
Arc-sprayed zinc was applied to various superstructure and substructure elements. These included the deck soffit, diaphragm, columns, arches, and piers. Prior to the installation of the CP system, areas of unsound and high-resistivity concrete were removed and repaired with pneumatically applied mortar. A very stringent quality-control plan was enforced during the rehabilitation. All elements of the structure to receive CP were enclosed and the environment inside the enclosure was controlled. Control of temperature and air quality was exercised to ensure good adhesion of arc-sprayed zinc to the concrete surface.
The system contains 58 zones, 55 of which are monitored and controlled by 8 rectifiers located on piers 4, 6, and 9. The first three zones have not been energized. Each of the 55 zones is instrumented with a graphite reference cell and a silver-silver chloride reference cell. Zones 4 and 8 have an additional graphite reference cell, and zones 10 and 14 have an additional silver-silver chloride reference cell. Twelve null probes, 6 each, were installed in zones 18 and 21. There is some confusion about the location of one set of these null probes. Although, the rectifier label states that the null probes are located in zone 16, the null probe wires are labeled zone 18 and the system ground of zone 18 is used for the measurement. For the purpose of this report, it is assumed that the probes are located in zone 18. System installation was completed in 1996.
The rectifiers are equipped with remote monitoring units (RMUs). These units provide system-operating parameter control and monitoring services, remotely or locally. As these rectifiers are not equipped with meters to directly read system-operating parameters, a portable computer must be connected to the RMUs during field evaluations.
3.1.1.3. Field Evaluations
Evaluations were performed on the following dates:
|
First evaluation
|
September 26 and 27, 1996 | < 1 year old |
|---|---|---|
|
Second evaluation
|
September 17 and 18, 1997 | ~ 1 years old |
|
Third evaluation
|
October 26 to 28, 1998 | ~ 2 years old |
3.1.1.4. Findings
System Component Evaluation
Electrical continuity between system grounds and reference cell grounds, and between reference cell grounds of the same zone were evaluated. The results of the DC continuity testing indicate significant lack of continuity, whereas more detailed analysis of AC continuity data suggests the presence of continuity. When the DC and the AC data are analyzed together, only a couple of discontinuities are observed out of the 400 measurements made in the three evaluations.
The impact of AC resistance on the performance of embedded reference cells has been a topic of significant discussion in the industry. Task Force 29 Report - Guide Specifications for Cathodic Protection of Concrete Bridge Decks(4), prepared by the American Association of State Highway & Transportation Officials-Association of General Contractors-American Road & Transportation Builders Association (AASHTO-AGC-ARTBA), requires that the AC resistance between reference cells and their grounds not exceed 10,000 ohms when embedded in concrete. As a significant number of reference cells were installed on this site, a summary of AC resistance data for these cells is provided in table 3-2.
Table 3-2. The AC Resistance Between Reference Cell and Reference Cell Ground
| Reference Cell Type | No. of Measurements | AC Resistance (ohms) | |||
|---|---|---|---|---|---|
| Minimum | Maximum | Average | Standard Deviation | ||
| Graphite | 115 | 320 | 32,000 | 4912 | 2736 |
| Silver-silver chloride | 115 | 740 | 76,000 | 9568 | 11,141 |
These data suggest that the average AC resistance was within the prescribed limits for proper reference cell operation. Of the 230 measurements, 7 for the graphite and 51 for the silver-silver chloride reference cell were in excess of 10,000 ohms. The impact of the higher resistance on the ability of the reference cells to perform reliably could not be determined from data collected in this study. In general, the resistance of the reference electrodes increased with time.
The current flow through the null probes was measured as a voltage drop across a 10-ohm resistor provided in the RMU. It should be noted that the null probe did not have a separate ground and the system ground was used for the purpose. During the first evaluation, zone 18 was not energized and thus only the null probes in zone 21 were evaluated. No null probes were tested in the second evaluation. The data for the null probes in zone 21 during the first evaluation shows the expected shift in current when the CP system is powered off. Many of the probes exhibited reversal of current flow, suggesting that the CP current was sufficient to shut off the macrocell current and provide a cathodic current to the probes. During the third evaluation, all null probes had the same reading and did not exhibit any change with the power off. The reason for this behavior was not determined.
The AC resistance between the anodes and the system grounds measured for each zone varied from 0.18 to 2.10 ohms, and averaged 0.49 ohms. These measurements are considered to be in the normal range.
Several zones during each trip were not powered up. It was learned that there was some problem in powering up the zones after a depolarization test had been remotely conducted using the RMUs.
System Performance
Visual and delamination surveys were conducted in certain sections of two zones during the first evaluation. A snooper was required and one lane of the bridge had to be shut down. The closing of the lane resulted in significant traffic backups and the research team was asked to avoid closing the lane in future evaluations. Thus, visual and delamination surveys were not performed during the second and third evaluations. A visual survey of the zinc surface indicated the formation of a white product. Analysis of the product by the Oregon Department of Transportation (DOT) indicated that it comprised zinc, chloride ions, and a small amount of sulfur. Some rust staining was observed in one area where no repairs were performed on cracks. No delaminations were noted in the areas tested.
The installation of the first 15 zones was not completed at the time of the first evaluation and thus these zones could not be evaluated. The first three zones were never energized. The remaining 12 zones were installed and energized by the second evaluation. One zone during the second evaluation and six zones during the third evaluation were observed to be powered off. It was later determined that some problems had been experienced in setting the output currents to these zones using the RMUs.
The true root mean square (TRMS) value of all rectifier output current and voltages was measured using an external multimeter. With a few exceptions, all zones were set to the same output current. During the first evaluation, the measured output current averaged 0.54 amps (A), with a standard deviation of 0.08 A. Similarly, during the second evaluation, the measured output current averaged 0.52 A, with a standard deviation of 0.02 A. During the third evaluation, 5 of the 55 zones were observed to be at a much higher current output than the remaining 50 zones. The measured output current for the remaining 50 zones averaged 1.00 A, with a standard deviation of 0.21 A. The output current for two of the five zones ranged from 10.00 to 11.00 A, and the other three zones were measured at 1.79 A. A summary of current densities is provided in table 3-3 below:
Table 3-3. The Current Density of Concrete Surface Area During Each Evaluation
| Evaluation | No. of Measurements | Current Density (mA/m2) of concrete surface area | |||
| Minimum | Maximum | Average | Standard Deviation | ||
| First | 39 | 0.93 | 2.55 | 1.36 | 0.35 |
| Second | 54 | 0.90 | 1.82 | 1.23 | 0.24 |
| Third | 49 | 1.38 | 37.09 | 4.19 | 7.68 |
The average current densities presented in table 3-3 are significantly lower than the generally recommended range of 10.75 to 16.13 mA/m2. The output voltages were in the acceptable range.
The BEMF and the instant-off potentials were measured using the soft interrupt provided in the rectifier. A laptop computer was connected to the rectifier and a command was sent from the laptop computer to the rectifier for current interruption. Upon receipt of the command, the rectifier momentarily interrupted the output current. The peak-hold technique was used to measure the BEMF and the instant-off potentials. Prior to use of the peak-hold technique, a portable oscilloscope was used to verify the BEMF and instant-off measurements in the first few zones during the first trip.
Twenty of the 39 BEMF measurements made during the first trip were less than 500 millivolts (mV) and 4 of these were close to zero. A low BEMF can imply either insufficient CP current or a near short, and a zero BEMF can imply a short. Eleven of the 20 zones with the low BEMF measurements did not meet the 100-mV depolarization requirement in 24 hours. One of the zones exhibited negative depolarization. No BEMF measurements were made during the second evaluation. In the third evaluation, only two zones had BEMF less than 500 mV, one of which still did not meet the 100-mV depolarization criteria. It should be noted that the output current during the third evaluation was approximately double the output current during the first evaluation and may have resolved the low BEMF measurements for zones experiencing insufficient current during the first evaluation. Also, near shorts in an impressed-zinc system may be eliminated with time due to excessive consumption of zinc in that area. At least one zone is probably experiencing a near short or a short.
Depolarization data do not exhibit expected behavior. Only in 11 zones did depolarization measured by both reference electrodes exceed the 100-mV criterion and increase with an increase in current. In 18 zones, the average depolarization exceeded 100 mV, but one or more reference cell(s) exhibited a decrease in depolarization with an increase in current. There were 31 zones in which one or more reference cell(s) did not meet the 100-mV requirement in one or more trips. Either the current density was not sufficient and/or input/output (IO) measurements contained errors from spikes that were picked up during measurement.
3.1.1.5. Conclusions
All components of the system were functioning normally. The current outputs of most zones needed to be increased to obtain sufficient CP. If the system were continuously operated at these low current densities, then it would not be expected to provide complete protection and some corrosion-induced damage would be expected in the future.
3.1.2. Queen Isabella Causeway, South Padre Island, Texas
The Queen Isabella Causeway bridge structure on Park Road (PR) 100 links South Padre Island to the mainland of Texas at Port Isabel and spans the Laguna Madre.
3.1.2.1. Structure Information
The 4.0-km-long structure carries four lanes of traffic going east/west. It comprises 150 spans, 3 continuous steel plates, and 147 simple prestressed concrete girder spans. The spans are supported by 150 bents that are numbered from 1 to 150 from west to east. Construction of this structure was completed in 1973.
In 1997, a corrosion condition evaluation was conducted for the tie beams and footings located in bents 19 through 24. The footings exhibited cracks and spalls, the majority of which were located on the south footings. Spalls were mostly located on the sides of the footings. Cracking was the predominant mode of deterioration on the tie beams. The concrete cover depth ranged from 71 to 121 mm for the tie beams and from 58 and 108 mm for the footings. A corrosion potential survey of the members revealed a few areas where the potentials were more negative than -350 mV copper sulfate electrode (CSE). These areas were typically found in the proximity of cracks or construction joints.
3.1.2.2. CP Information
The tie beam and the three footings in bent 19 were protected with impressed-current arc-sprayed zinc. The entire surface of the tie beam and the footings was sprayed with zinc, with the exception of the bottom surface of the footings, covering approximately 127 m2 of concrete surface area. The instrumentation consisted of three silver-silver chloride reference cells and two null probes. Two reference electrodes were embedded in the footings and one reference electrode was embedded in the tie beam. One null probe was installed in one of the footings and the other was installed in the tie beam.
Prior to the application of the anode, spalls and cracks were repaired and the concrete surface was sandblasted. The system was energized on October 7, 1997.
3.1.2.3. Field Evaluations
Data were collected during energization of the system and subsequently field evaluations were performed on the following dates:
|
Energization
|
October 7, 1997 | |
|---|---|---|
|
First evaluation
|
December 17 and 18, 1997 | 2 months old |
|
Second evaluation
|
February 9 to 11, 1998 | 4 months old |
|
Third evaluation
|
April 1 to 3, 1998 | 6 months old |
|
Fourth evaluation
|
June 3 to 6, 1998 | 8 months old |
|
Fifth evaluation
|
November 9 to 12, 1998 | 13 months old |
The energization of the system was performed by the contractor.
3.1.2.4. Findings
System Component Evaluation
Data collected during energization indicate that all system components were responding well, with the exception of reference cell 1. The other two reference cells exhibited increased polarization with an increase in output current, and the null probes also experienced an increase in current flow with an increase in output current. The flow of current reversed in the null probes as the cathodic current was applied.
Electrical continuity testing was performed at the rectifier using DC and AC techniques. Continuity testing was performed during the depolarization test when the power to the system was off. It was performed between the grounds of reference electrodes in each zone and between the grounds of reference electrodes and the system ground of the subject zone. It should be noted that all measurements were made at the rectifier, which was installed at one end of the bridge. The bent was located at a significant distance from the end of the bridge and the lengths of the wires connecting the zone to the rectifier were in excess of a quarter of a mile.
The reference cell ground of reference cell 1 was found to be discontinuous and the reference cell was observed to be unstable in all five evaluations. The null probes performed well and often exhibited reversal in current flow when the cathodic current was terminated and/or exhibited reduction in current flow when the system was powered down.
Accurate measurement of instant-off potential was made difficult by the presence of electrical noise or current flow in the system. The peak-hold method could not be used to collect instant-off data. Manual interrupt had to be used. Even during manual interrupt, an external electrical signal could be observed on the oscilloscope. In two out of the five evaluations, accurate instant-off potentials could not be obtained.
The AC resistance between the reference electrodes and the reference cell grounds for all three electrodes in all five evaluations was equal to or less than 10,000 ohms. The AC resistance between the anode and the system ground averaged 5.16 ohms.
System Performance
On bent 19, which was protected with impressed-current zinc, an approximately 0.1-m-wide band of whitish products was observed at the bottom of the side faces of the footings. This band of whitish products indicates accelerated consumption of the sprayed zinc coating at the location.
The rectifier output voltage and BEMF were observed to be in the acceptable range, and the average concrete current density for the three field evaluations ranged from 11.65 to 24.57 mA/m2. The average was 15.15 mA/m2. Polarization decay for all operating embedded reference cells averaged 152 mV in 4 hours.
3.1.2.5. Conclusions
With the exception of one reference electrode, all other system components were performing adequately. Depolarization test results exceeded the 100-mV criterion for the two operating reference cells. The null probes indicated that the current supplied by the CP system was adequate to overcome the corrosion current in the protected area. The band of whitish products at the bottom of the side faces of the footers suggested that at high tide when this section of the footers was submerged, current leaked from the anode to the bay water. Such current leaks result in accelerated consumption of the anode in the affected areas.
3.1.3. Depoe Bay Bridge, Newport, Oregon
The Depoe Bay Bridge carries northbound and southbound traffic of Pacific Highway 101 over Depoe Bay in Newport, Oregon.
3.1.3.1. Structure Information
The arch bridge was built in 1926 and was widened in 1939. The bridge has four lanes, with a total
length of 99 m and a 15.2-m-wide roadway.
3.1.3.2. CP Information
In 1996, arc-sprayed zinc was installed on the sidewalk soffit, sidewalk brackets and beams, deck soffit, longitudinal deck girders, transverse deck beams, arch ribs, struts, and columns of the Depoe Bay Bridge. Three rectifiers control 14 zones for a total protected area of 6032 m2. Sprayed zinc was applied in zones 1 through 13, for an approximate total zinc-protected area of 5600 m2.
Zones 1 through 13 are instrumented with a graphite reference cell and a silver-silver chloride reference cell. Every zone is instrumented with a null probe.
Delaminated concrete was removed and repairs were performed using shotcrete before the CP system was installed.
3.1.3.3. Field Evaluations
Evaluations were performed on the following dates:
|
First evaluation
|
September 28 and 29, 1996 | < 1 year old |
|---|---|---|
|
Second evaluation
|
September 19 and 20, 1997 | ~ 1 years old |
|
Third evaluation
|
October 27 and 28, 1998 | ~ 2 years old |
3.1.3.4. Findings
System Component Evaluation
Three field evaluations have been conducted on this system. The last evaluation was conducted after the system had been in service for about 2 years. At the time of the first evaluation, the arc-sprayed zinc had been shorted to the reinforcing steel and was functioning sacrificially because the rectifiers had not been installed. The rectifiers were found to have been installed during the second evaluation, but some measurements could not be obtained for cabinet 1 since it was not accessible. During the third evaluation, the zones controlled by cabinets 1 and 2, with the exception of zone 1, were found to be de-energized.
Electrical continuity testing of the reference cell grounds to the system grounds and of the reference cell grounds to the reference cell grounds indicated that the reference cell grounds of both cells in zone 3 and the silver-silver chloride reference cell in zone 13 were discontinuous.
In general, the AC resistance between the reference cell and its ground for the silver-silver chloride reference cells were found to be much higher than the graphite reference cells. The AC resistance between the silver-silver chloride reference cell of zone 4 and its ground was 92,000 ohms. The AC resistance for the graphite reference electrodes averaged 2873 ohms and the silver-silver chlorides averaged 19,337 ohms, excluding the one measuring 92,000 ohms.
During the second evaluation, null probe measurements could only be taken from cabinet 2, which controls zones 6 through 10. The null probe currents either reversed or went to zero upon de-energization. Similar behavior was noted for zones 11 through 13 during the third evaluation. The current flowing through the null probes for the zones in cabinet 2 during the third evaluation was positive when the system's power was off. The currents decreased when the system was powered up, but did not reverse, indicating that the cathodic current was not sufficient to overcome corrosion currents.
Information from Oregon DOT indicated that some problems were being experienced in setting operating parameters using the RMUs. These monitoring units were similar to the ones at Yaquina Bay Bridge.
System Performance
The output voltage and BEMF measurements were in the acceptable range. The anode to system ground AC resistance averaged 0.42 ohms during the first evaluation and 0.52 ohms during the third evaluation.
The average current density for the operating zones was 1.21 mA/m2 during the second evaluation and 1.46 mA/m2 during the third evaluation. The average depolarization for zones 5, 6, and 11 did not exceed 100 mV; all other zones exceeded 100 mV during the second evaluation. During the third evaluation, depolarization did not exceed 100 mV in three of the four operational zones.
3.1.3.5. Conclusions
With the exception of two discontinuities, all other components of the system were operational. Due to problems with the RMUs in setting the output parameters, the system was not operating continuously and was not providing protection as would be desired. Also, the operating current densities were not sufficient to overcome the ongoing corrosion in the bridge elements.
3.2. Zinc Strip
3.2.1. Upper Salt Creek Bridge on Southbound I-5, Redding, California
The Upper Salt Creek Bridge carries southbound I-5 in Redding, California.
3.2.1.1. Structure Information
The bridge is 11.4 m long and 3.6 m wide, with a deck surface area of 446 m2. Construction of the Upper Salt Creek Bridge was completed in 1966.
3.2.1.2. CP Information
A metallized zinc CP system was installed on the southern half of the bridge deck (zone 1) on a total surface area of 223 m2 in 1998.
The metallized zinc system comprises a grid of 150-mm-wide and 0.61-mm-thick arc-sprayed zinc strips at 300 mm on center. The zinc strips were sprayed on the prepared concrete deck surface. The power connection to the zinc strips was achieved with brass pads installed flush with the concrete surface and in contact with the arc-sprayed zinc strips. A 110-mm-thick asphalt concrete overlay was then placed on the deck.
There were no embedded reference cells or rebar probes installed in the system. However, potential wells were installed on the bridge deck to facilitate potential measurements using an external reference electrode. A constant voltage rectifier was used to power the system.
3.2.1.3. Field Evaluations
Evaluations were performed on the following dates:
|
First evaluation
|
October 31 to November 4, 1994 | ~ 6 years old |
|---|---|---|
|
Second evaluation
|
November 26 and 27, 1996 | ~ 8 years old |
3.2.1.4. Findings
System Component Evaluation
No instrumentation was installed in this system. A visual survey of the potential wells indicated that water was collecting under the asphalt overlay and shorting the potential wells with the zinc anode. Thus, the wells could not be used to measure potential of the embedded steel.
During the second evaluation, the system was found to be powered off. The power to the system was turned on and rectifier data were collected.
System Performance
The concrete current density during the first evaluation was 2.2 mA/m2 and the output voltage and BEMF were in the acceptable range.
3.2.1.5. Conclusions
The performance of this system could not be judged based on the data available. The concept of
installing potential wells was a good one, but the wells were not isolated properly from the anode.
Five CP systems installed on highway structures using titanium mesh as an auxiliary anode were
included in this study. Three of the systems were installed on bridge decks, one on the underside of a
roadway in a tunnel and one on bridge substructure elements. Table 4-1 lists pertinent information on
these five CP systems:
Table 4-1. Titanium Mesh Impressed-current CP Systems
| Structure Name and Location | Year CP System Installed | Element Protected | Area Protected | Instrumentation | Age at Last Evaluation | Average Chloride Ion Content of Steel Depth (ppm) |
| Wawecus Hill Road Bridge, Norwich, CT | 1992 | Deck | 1124 m2 | 1 reference cell & 1 null probe per zone | 7 years | 875 |
| Brooklyn Battery
Tunnel,
New York, NY |
1992 | Underside of roadway slab | 10332 m2 | 4 reference cells per zone | 6 years | 4170 top mat
515 bottom mat |
| Columbia Road Bridge, Westlake, OH | 1986 | Deck | 985 m2 | 3 reference cells & 4 current probes | 12 years | NA |
| 6th Street Bridge,
Sioux Falls, SD |
1991 | Deck | 1515 m2 | 1 reference cell per zone | 6 years | 239 |
| Queen Isabella Causeway, South Padre Island, TX | 1997 | Tie beam & footings in bent | 127 m2 | 3 reference cells & 1 null probe | 13 months | 1132 in the footing |
NA - not available.
Note: Chloride ion content information was obtained from cores collected during the study.
4.1.1. Wawecus Hill Road Bridge Over I-395, Norwich, Connecticut
The Wawecus Hill Road Bridge carries eastbound and westbound traffic over I-395 in Norwich, Connecticut.
4.1.1.1. Structure Information
The bridge comprises four simple spans, with a total length of 92.8 m. The bridge has a skew angle of approximately 57 degrees and a total width of 13.9 m (two 6-m-wide travel lanes and two 0.86-m-wide sidewalks). Construction of the bridge was completed in 1958. In August 1990, a condition evaluation of the structure revealed that the bridge deck was in poor condition and required extensive rehabilitation.
4.1.1.2. CP Information
Deteriorated concrete was removed by hydro-demolition and a monolithic low-slump dense concrete pour was used to patch the deteriorated areas and place an overlay. The thickness of the concrete placement varied from 40 mm to full depth. The titanium mesh anode was placed between the hydro-demolished surface and the overlay. A plastic spacer mesh was used to isolate the titanium mesh from the reinforcing steel exposed by hydro-demolition.
The CP system was subdivided into four individual zones, each zone had one span. A total deck surface area of 1124 m2 was protected by the CP system. In sections of the deck where additional steel was required, epoxy-coated rebars were used. The epoxy-coated rebars were made continuous to the black steel. Each zone was instrumented with two silver-silver chloride reference cells and two null probes. The system was installed and energized in 1992.
4.1.1.3. Field Evaluations
Evaluations were performed on the following dates:
|
First evaluation
|
July 6 and 7, 1995 | ~ 3 years old |
|---|---|---|
|
Second evaluation
|
June 18, 1997 | ~ 5 years old |
|
Third evaluation
|
July 29 and 30, 1999 | ~ 7 years old |
4.1.1.4. Findings
System Component Evaluation
The DC electrical continuity test data for each evaluation exhibited discontinuity. Electrical continuity data obtained during the last two evaluations using the AC and the half-cell potential method suggest the presence of electrical continuity.
The AC resistance measurement between the reference cells and their respective grounds indicated that one reference cell in zone 1 had AC resistance in excess of 100,000 ohms throughout the study, and the resistance of the other reference cell in the same zone increased with time to similar levels. Such high resistances can cause an error in potential measurement due to pickup of electrical noise. The AC resistances for the remainder of the reference cells were within the AASHTO-prescribed limits, with the exception of one reference cell in zone 4 and one in zone 3, which exhibited resistances in excess of 10,000 ohms at times.
Three of the eight null probes were not functional. One had a broken wire and two others had shorts. The remaining null probes exhibited reversal of current flow when the system was powered down.
The readings taken from the rectifier meters were in good agreement with the external meter used to validate them.
System Performance
No corrosion-induced deterioration was observed on the top or bottom surfaces of the deck. Hollow-sounding areas were detected over less than 0.1 percent of the top deck surface. It is suspected that the hollow-sounding areas resulted from disbondment of the overlay.
The average concrete current density for the three evaluations ranged from 8.61 to 12.06 mA/m2. With the exception of zone 1, all other zones were running at a current density lower than the generally recommended 10.75 mA/m2. The anode-to-steel AC resistance averaged 0.66 ohms for all zones and the output voltage and BEMF were in the acceptable range.
In general, the 100-mV polarization decay criterion was met for all zones. Some fluctuations in polarization decay for zones 1 and 3 were noted. Reference cell 2 in zones 1 and 3 did not meet the 100-mV criterion in two of the three evaluations. Depolarization measurements made with external reference cells in potential wells also exceeded 100 mV. The null probe data suggest that the system is putting out sufficient current to reverse the macrocell in areas where the null probes are located.
4.1.1.5. Conclusions
With the exception of the three null probes, all other components were functioning properly. The system was providing adequate protection for the reinforcement.
4.1.2. Brooklyn Battery Tunnel, New York, New York
The Brooklyn Battery Tunnel, built beginning in 1940 and completed in 1950, connects Battery Park in lower Manhattan with the Red Hook section of Brooklyn.
4.1.2.1. Structure Information
The Brooklyn Battery Tunnel consists of two parallel tubes that are 2780 m long between the entrance and exit portals. Each tube is 9.5 m in diameter and is subdivided into three conduits by a roadway slab and a ceiling slab. The lower conduit serves as a fresh air duct, the middle conduit serves as the roadway, and the upper conduit serves as the exhaust duct. The roadway slab is 6.1 m wide and 360 mm thick. The top surface of the roadway slab is covered by 100 mm of asphalt pavement.
In 1990, a condition survey revealed that the roadway slab was in poor condition. Spalled concrete exposing severely corroded rebars was observed.
4.1.2.2. CP Information
Following a 1990 condition survey of the roadway slab, deteriorated asphalt on the top surface and concrete on the top and bottom surfaces were repaired. All delaminated and unsound concrete from the roadway slab was removed. At some locations, reinforcing steel bars on the bottom mat of the steel experiencing significant loss of cross section were removed and replaced with epoxy-coated rebar. The epoxy-coated rebar was tied to the existing steel reinforcement by welding.
In 1992, a titanium mesh anode was installed on select rehabilitated sections of the soffit of the roadway slab. A total of 10,332 m2 of concrete surface area was protected by the CP system. The titanium mesh anode was secured to the concrete surface with plastic fasteners and encapsulated in a shotcrete overlay. There were problems with the development of the bond between the shotcrete and the original concrete. Several unsuccessful attempts were made to improve the bond. As a last resort, it was decided that plastic pins would be installed to hold the overlay in place. The CP system comprises 42 zones that are controlled by 14 rectifiers (7 rectifiers in each tube). Each rectifier is equipped with an RMU. Each zone is instrumented with an embedded graphite reference cell and a current probe.
4.1.2.3. Field Evaluations
Evaluations were performed on the following dates:
|
First evaluation
|
July 17 and 18, 1995 | ~ 3 years old |
|---|---|---|
|
Second evaluation
|
June 9 and 10, 1997 | ~ 5 years old |
|
Third evaluation
|
September 23 to 25, 1998 | ~ 6 years old |
4.1.2.4. Findings
System Component Evaluation
Three field evaluations have been conducted on this system. The last evaluation was conducted after
the system had been in service for about 6 years. At the time of the first evaluation, a contractor was
attempting to restore the mechanical bond of the disbonded overlay by anchoring it to the original
concrete surface with plastic fasteners. The sections of the soffit of the roadway slab, which were not
rehabilitated, were found to be in poor condition and widespread spalling with exposed and corroded
rebar was visible.
Access to the rectifiers was restricted due to other ongoing rehabilitation work in the tunnel. In the first, second, and the third evaluations, access was available to three, six, and nine rectifiers, respectively.
The anode-to-system ground data indicated that there were no electrical shorts between the anodes and the system grounds. In the rectifiers evaluated, generally no continuity was detected between system grounds and between reference cell grounds and their respective system ground using the DC method, whereas, AC measurements suggested the presence of continuity. The DC continuity data suggest that currents from some source are flowing in the roadway slab. Considering the amount of corrosion damage that is observed in the area not yet rehabilitated, it is suspected that corrosion in areas not receiving sufficient current is ongoing.
System Performance
The significant lack of bonding between the overlay and the roadway slab, the localized presence of moisture in the roadway slab, and the possibility of freeze-thaw damage render the CP system inefficient, ineffective, and/or non-functional. Lack of bonding impairs the efficient and effective current distribution to all steel to be protected in the roadway. Current flow from the anode to the steel occurs only in areas with sufficient bond. If moisture from the roadway slab finds its way between the overlay and the roadway slab, it could enhance current distribution locally. However, unless the overlay were watertight, it would be difficult for water to completely fill the cavity produced by the disbondment, as the tunnels are inclined. Thus, the CP system is providing protection only in areas of good bonding and in isolated areas where moisture has completely filled the cavities caused by disbondment. It is believed that moisture is not present everywhere or all the time.
Measurement of rectifier output parameters indicates that a CP current is being impressed to each zone. The average current density for each evaluation varied from 29.60 to 34.33 mA/m2 of concrete surface area. The current densities impressed on the system are significantly higher than normally encountered for corrosion mitigation. The output voltage and BEMF are in the acceptable range except for one zone (the output voltage, current, and BEMF for this zone indicate that a short or a near short is present). The average anode-to-system ground resistance was 0.30 ohms.
The results of the depolarization testing for all evaluations can be summarized as follows:
Table 4-2. Results of Depolarization Testing (in percent)
| First Evaluation | Second Evaluation | Third Evaluation | |
|---|---|---|---|
|
> 100 mV
|
9 | 11 | 15 |
|
0 to 100 mV
|
73 | 11 | 73 |
|
Negative Depolarization
|
18 | 78 | 12 |
Depolarization test results indicate that the distribution of CP current varies as a function of environmental conditions, especially the presence of moisture between the overlay and the original concrete.
4.1.2.5. Conclusions
Considering the higher level of current densities being impressed on the roadway slab, the results of the depolarization testing, and the DC continuity data, it was clear that the system was not performing efficiently and effectively. The primary reason for the lack of performance was improper installation of the system. One cannot expect a CP system to perform when the majority of the overlay is disbonded.
4.1.3. Columbia Road Bridge, Westlake, Ohio
The Columbia Road Bridge is located on Columbia Road over I-90 in Westlake, Ohio.
4.1.3.1. Structure Information
The bridge has four spans, with a total length of 83 m and a roadway width of 24 m. The total deck area is approximately 1970 m2. The substructure consists of two reinforced concrete piers and two reinforced concrete abutments. Construction of the Columbia Road Bridge was completed in 1974.
Before the CP system was installed, the deck had delaminations over 1 percent of its surface area and the average chloride ion content at the steel depth was 178 ppm.
4.1.3.2. CP Information
In 1986, a CP system utilizing a titanium mesh anode was installed on the two southbound lanes. The southbound lanes were divided into two independent zones, each 83 m long and 6 m wide. The deck was overlaid with 64 mm of superplasticized dense concrete. The anode was not installed on the northbound lanes. These areas were overlaid, however, and were designated as the controls. Each zone was instrumented with two silver-silver chloride reference cells, two rebar probes, and two Corrosometer® probes.
4.1.3.3. Field Evaluations
Evaluations were performed on the following dates:
|
First evaluation
|
September 8 and 9, 1994 | ~ 8 years old |
|---|---|---|
|
Second evaluation
|
March 25, 1997 | ~ 11 years old |
|
Third evaluation
|
April 22 and 23, 1998 | ~ 12 years old |
4.1.3.4. Findings
System Component Evaluation
Electrical continuity data reflected good continuity of system grounds to reference cell grounds and system grounds to system grounds. The AC resistance data for one reference cell during the first evaluation was close to 100,000 ohms and two others exceeded 10,000 ohms. The AC resistance for these three reference electrodes increased to above 100,000 ohms during the second evaluation and remained at very high levels. Two of these three exceeded 500,000 ohms during the second evaluation.
The corrosion probes were observed to be functioning as intended with the exception of one that was missing a resistor since the first evaluation and another probe that exhibited a broken wire during the third evaluation.
System Performance
The output voltage and BEMF values were in the acceptable range and the average anode-to-system ground resistances varied from 0.30 to 0.34 ohms.
No corrosion-induced deterioration of the deck surface of the protected area and the control area was observed during the first evaluation. Only non-corrosion-induced spalls were observed in the protected area during the first evaluation. Evaluations before the start of this study had noted some bond failure between the overlay and the original deck concrete. However, corrosion-induced spalls were found on the deck soffit and, in general, the soffit of the protected area exhibited more spalling than the control area during all evaluations. During the third evaluation, delamination on the deck surface measuring 0.09 m2 in the protected area and 0.45 m2 in the control area was observed. It is not known whether these delaminations were corrosion-induced. Rust stains were visible on the unprotected sidewalks and the median.
The average concrete current density varied from 8.04 to 13.08 mA/m2 during the three evaluations. Every reference cell tested met the 100-mV criterion during each evaluation. All corrosion probes tested exhibited reversal of current with system power up and power down. The corrosion probes installed in the control area exhibited high macrocell current, indicating ongoing corrosion in the control area.
4.1.3.5. Conclusions
All components of the system were functioning properly and the system was providing adequate protection to the top mat steel. There were indications that corrosion was ongoing in the unprotected section of the deck, and this section may experience corrosion-induced damage in the future. The corrosion-induced damage on the soffit of the protected area was of concern. It was not known whether this damage existed at the time of the installation of the system and has remained constant, or whether it has increased with time while the deck was cathodically protected. In this study, sufficiently detailed information was not collected on the soffit damage to ascertain whether it increased with time.
4.1.4. Bridge over Big Sioux River, Sioux Falls, South Dakota
The Sixth Street Bridge is a four-lane structure over the Big Sioux River in Sioux Falls, Minnehaha County, South Dakota.
4.1.4.1. Structure Information
The bridge has a total length of 71 m and a roadway width of 15 m. Construction of the bridge was completed in 1975.
A condition evaluation of the bridge revealed that more than 10 percent of the deck surface area was delaminated and the average chloride ion content at the steel depth exceeded 2600 ppm.
4.1.4.2. CP Information
In 1991, a CP system utilizing a titanium mesh anode was installed on the deck, the two sidewalks, and the curb barriers that separate the sidewalks from the deck. The CP system was installed to control corrosion on 1515 m2 of concrete surface area. This area was divided into six zones with zones 1 through 4 located on the deck and zones 5 and 6 on the sidewalks and curb barriers. Each zone was instrumented with a silver-silver chloride reference cell. The deck was overlaid with 64 mm of low-slump dense concrete, and a thin overlay of pre-bagged fast-setting material was installed on the curb and the curb barriers.
Before the CP system was installed, delaminated concrete was removed, and repairs were performed using A45 Class concrete.
4.1.4.3. Field Evaluations
Evaluations were performed on the following dates:
|
First evaluation
|
September 16 and 17, 1994 | ~ 2 years old |
|---|---|---|
|
Second evaluation
|
July 29 to August 1, 1996 | ~ 4 years old |
|
Third evaluation
|
May 15 and 16, 1998 | ~ 6 years old |
4.1.4.4. Findings
System Component Evaluation
Electrical continuity testing, AC resistance measurements, and unstable potentials identified one bad reference cell ground and one non-functional reference electrode. The reference cell ground was corrected by shorting to another ground. All other components of the system were observed to be performing normally.
System Performance
The system output voltage, BEMF, and anodes-to-system ground resistances were found to be in the acceptable range. The average anode-to-system ground resistance varied from 0.53 to 0.65 ohms.
Before installation of the CP system, the chloride ion content in the concrete at the steel depth was several times higher than the threshold required to initiate corrosion. During the 4-year span of the evaluations, the system has been operating at current densities ranging from 8.93 to 9.90 mA/m2. At these current densities, all embedded reference cells (except one that was not operational) met the 100-mV depolarization criterion. The reference electrode in zone 5 exhibited a depolarization value of 372 mV in the first evaluation and depolarization values in excess of 400 mV in the remaining two evaluations. Such high depolarization is of concern, especially at a current density of less than 10 mA/m2.
At the time of the last field evaluation, a few longitudinal cracks were observed on the overlay surface and minor cracking was evident on the sidewalks and deck underside. Hollow-sounding areas were detected in all evaluations in zone 5. System installation reports indicate that disbondment of the thin overlay installed on the sidewalks has been a problem from the time of the system installation. In conjunction with the high polarization values for zone 5, this suggests that disbondment of the overlay is concentrating the current in that zone to sections with good bond, hence the high depolarization values.
4.1.4.5. Conclusions
All system components, with the exception of one reference electrode, were functioning normally and the system was providing adequate protection. The disbondment of the thin overlay was of concern. If the amount of area disbonded increases with time, the effectiveness of the CP system will be reduced in the subject zone.
4.1.5. Queen Isabella Causeway, South Padre Island, Texas
The Queen Isabella Causeway is a 4.0-km-long bridge structure on PR 100 that links South Padre Island to the mainland of Texas at Port Isabel and spans the Laguna Madre.
4.1.5.1. Structure Information
The causeway carries four lanes of traffic going east/west. It comprises 150 spans, 3 continuous steel plates, and 147 simple prestressed concrete girder spans. The spans are supported by 150 bents that are numbered from 1 to 150 from west to east. Construction of this structure was completed in 1973.
In 1997, a corrosion condition evaluation was conducted for the tie beams and footings located in bents 19 through 24. The footings exhibited cracks and spalls, the majority of which were located on south footings. Spalls were mostly located on the sides of the footings. Cracking was the predominant mode of deterioration on the tie beams. The concrete cover depth ranged from 71 to 121 mm for the tie beams and from 58 and 108 mm for the footings. A corrosion potential survey of the members revealed a few areas where the potentials were more negative than -350 mV CSE. These areas were typically found in the proximity of cracks or construction joints.
4.1.5.2. CP Information
The tie beam and the three footings in bent 21 were protected with a titanium mesh anode. The titanium mesh anode was installed on the entire surface of the tie beam and the footings with the exception of the bottom surface of the footings. The titanium mesh anode was encapsulated in a cementitious overlay. The total surface area covered with the titanium mesh was approximately 127 m2. The instrumentation consisted of three silver-silver chloride reference cells and two null probes. Two reference electrodes were embedded in the footings and one reference electrode was embedded in the tie beam. One null probe was installed in one of the footings and the other in the tie beam.
Spalls and cracks were repaired and the concrete surface was sandblasted prior to the application of the anode. The installation of the concrete overlay encapsulating the titanium mesh was done three times. The first two times the overlay was installed, the overlay and the mesh had to be removed. The first application involved trowel-applied Sikatop® 123. This product is intended for patch repair rather than overlay application. Two days after the application of the system, the overlay exhibited very severe cracking and was removed. The second application involved trowel-applied Emaco® S88-CA manufactured by Master Builders. Two days after the application of the overlay, hammer sounding was conducted to test for delaminations. Delaminated areas amounted to 25 percent of the concrete overlay. Seven days later, the delaminated areas had increased to 75 percent and were prevalent in the vertical and overhead orientations. The overlay was again removed. The main reason for the failure of the second trial was inadequate surface preparation. The surface preparation for the third trial included scabbling with hand-held milling machines in addition to sandblasting. The concrete overlay was dry-mix shotcrete applied for the third and final application of the overlay.
4.1.5.3. Field Evaluations
CONCORR, Inc. personnel were present during the initial energization of the system; subsequent evaluations were performed on the following dates:
|
Energization
|
October 7, 1997 | |
|---|---|---|
|
First evaluation
|
December 17 and 18, 1997 | ~ 2 months old |
|
Second evaluation
|
February 9 to 11, 1998 | ~ 4 months old |
|
Third evaluation
|
April 1 to 3, 1998 | ~ 6 months old |
|
Fourth evaluation
|
June 3 to 6, 1998 | ~ 8 months old |
|
Fifth evaluation
|
November 9 to 12, 1998 | ~ 13 months old |
4.1.5.4. Findings
System Component Evaluation
During energization of the system, all components, with the exception of the RMU, were functioning properly. By the time of the second evaluation, the RMU problem had been rectified. The DC electrical continuity data erroneously indicated that there was a lack of continuity. This was attributed to the flow of corrosion currents in the reinforcing steel when the system was off. During the second evaluation, a 0.14- m2 hollow-sound area was identified. The hollow sound in this area was attributed to disbondment of the encapsulation.
System Performance
The average concrete current density for the three field evaluations ranged from 12.37 to 22.93 mA/m2.
Polarization decay for all embedded reference cells was in excess of 100 mV and averaged 255 mV
for all evaluations in 4 hours. The null probes exhibited a reduction in current to zero or reversal upon
system power off. The output voltages and BEMF measurements were in the acceptable range. The
AC resistance between the anode and the system ground averaged 4.5 ohms.
Only one structure with a titanium ribbon anode installed as an auxiliary anode was included in this
study. Pertinent information is provided in table 4-3:
Table 4-3. Titanium Ribbon Impressed-current CP Systems
| Structure Name and Location | Year CP System Installed | Element Protected | Area Protected | Instrumentation | Age at Last Evaluation | Average Chloride Ion Content of Steel Depth (ppm) |
|---|---|---|---|---|---|---|
| Rte. 229 Bridge, Southington, CT | 1989 | Deck | 2057 m2 | 1 Reference Cell per zone | 9 years | 1103 |
Note: Choride ion content information was obtained from cores collected during this study.
4.2.1. Route 229 Bridge Over I-84, Southington, Connecticut
The bridge on Route 229 over I-84 (bridge number 1242) in Southington, Connecticut, was constructed in 1960.
4.2.1.1. Structure Information
The bridge has five spans, with a total length of 125 m and a curb-to-curb roadway width of 16.5 m. The bridge consists of four lanes (two northbound and two southbound) and a 1.5-m-wide sidewalk on each side.
In 1986, a comprehensive condition evaluation of the bridge deck was conducted. Visual and delamination survey results indicated that 10 percent of the deck surface area was patched, spalled, or delaminated. The chloride ion content at the steel depth varied from 199 ppm to 3100 ppm and approximately 90 percent of the area surveyed using the half-cell potential technique exhibited active potentials (i.e., potentials more negative than -350 mV).
4.2.1.2. CP Information
During the summer and fall of 1989, an impressed-current CP system utilizing 6.4-mm-wide titanium ribbon as the anode material was installed. The anode ribbon was placed below the top mat epoxy-coated reinforcing steel at a spacing of 305 mm on center. The CP system was powered by a single 10-circuit rectifier and protected 2057 m2 of concrete surface divided into 10 zones. Each of the 10 zones was instrumented with one silver-silver chloride reference cell. All reference cells were cast-in-concrete cubes and these cubes were placed adjacent to the epoxy-coated rebar. Design drawings specified chloride-contaminated concrete for the manufacture of these cubes. System grounds were installed on the top epoxy-coated reinforcing steel mat. Bond cables between the top mat of reinforcing steel and the bottom mat of reinforcing steel were installed to ensure continuity between the two mats.
Zones 1 through 5 have one common header wire and the ground for zone 6 was found to be discontinuous soon after installation of the system. To resolve this problem, all system grounds were shorted.
As part of the rehabilitation project, the concrete below the top mat reinforcement was removed, the top mat of steel was replaced with epoxy-coated rebar, and the bridge deck was resurfaced with a monolithic concrete pour. With the exception of some locations where full-depth (184-mm-deep) repairs were required, the depth of the concrete repairs averaged 114 mm.
4.2.1.3. Field Evaluations
Evaluations were performed on the following dates:
|
First evaluation
|
July 10 and 11, 1995 | ~ 6 years old |
|---|---|---|
|
Second evaluation
|
June 17 and 18, 1997 | ~ 8 years old |
|
Third evaluation
|
June 27, 1998 | ~ 9 years old |
4.2.1.4. Findings
System Component Evaluation
The AC, DC, and potential continuity test data do not show a clear pattern of continuity. The AC resistance measurements in some cases exceeded 50 ohms and, in many cases, exceeded 10 ohms. The level of discontinuity detected in this system was higher than normally encountered. The potentials measured by the reference cells did not indicate any lack of electrical continuity and exhibited correct movement of the steel potential with the change in the system current. The use of epoxy-coated rebars in the top mat probably complicated the detection of and the presence of continuity. All reference cells were functioning as expected. The AC resistances between the reference cells and their respective grounds were less than 10,000 ohms for all of the evaluations.
System Performance
Three field evaluations were conducted and the system was in its ninth year of service at the time of the
most recent evaluation. A small amount of delamination was detected during the first and the last
evaluations. Cores were collected from the delaminated areas and it was determined that the
delaminations were a result of failure of the bond between the overlay and the original concrete.
The 100-mV polarization criterion was satisfied in 4 hours at all locations in all evaluations except for zone 7 during the third evaluation. The stability of this reference cell was suspect. The system was operating at an average current density ranging from 2.9 to 3.3 mA/m2 from one evaluation to another.
4.2.1.5. Conclusions
With the exception of one reference cell, all other system components were functioning normally. The presence of epoxy-coated rebar in the top mat was making it difficult to interpret continuity data using DC, AC, and half-cell techniques.
4.3. Arc-sprayed Titanium
Two experimental installations of arc-sprayed titanium anode were included in this study. Both systems were installed in only one of the zones in each of the two bridges. Pertinent information on each system is provided in table 4-4:
Table 4-4. Arc-Sprayed Titanium Impressed-current CP Systems
| Structure Name and Location | Year CP System Installed | Element Protected | Area Protected | Instrumentation | Age at Last Evaluation | Average Chloride Ion Content of Steel Depth (ppm) |
|---|---|---|---|---|---|---|
| Depoe Bay Bridge, Newport, OR | 1996 | Super- & Substructure Elements | 6032 m2 | 3 reference cells & 1 null probe | 2 years | NA |
| Queen Isabella Causeway, South Padre Island, TX | 1997 | Tie beam & footings in bent | 127 m2 | 3 reference cells & 1 null probe | 13 months | 598 in the footing |
NA - not available.
Note: Chloride ion content information was obtained from cores collected during the study.
4.3.1. Depoe Bay Bridge, Newport, Oregon
The Depoe Bay Bridge carries the northbound and southbound traffic of Pacific Highway 101 over Depoe Bay in Newport, Oregon.
4.3.1.1. Structure Information
This arched bridge was built in 1926 and was widened in 1939. The bridge has four lanes, with a total length of 99 m and a 15.2-m-wide roadway.
4.3.1.2. CP Information
In 1996, arc-sprayed titanium was installed on the sidewalk soffit, sidewalk brackets and beams, deck soffit, longitudinal deck girders, and transverse deck beams of the Depoe Bay Bridge. Arc-sprayed titanium zinc was applied only in one zone (zone 14) to protect 451 m2. Arc-sprayed zinc was applied in zones 1 through 13.
Zone 14 was instrumented with two graphite reference electrodes, a silver-silver chloride reference electrode, and a null probe. Delaminated concrete was removed and repairs were performed using shotcrete before the CP system was installed.
4.3.1.3. Field Evaluations
Evaluations were performed on the following dates:
|
First evaluation
|
September 28 and 29, 1996 | 0 years old |
|---|---|---|
|
Second evaluation
|
September 19 and 20, 1997 | < 1 year old |
|
Third evaluation
|
October 27 and 28, 1998 | > 1 year old |
4.3.1.4. Findings
System Component Evaluation
Three field evaluations have been conducted on this system. The last evaluation was conducted after the system had been in service for about 2 years. At the time of the first evaluation, the rectifier installation had not been completed and the arc-sprayed titanium system was not operational. It was determined during the second evaluation that the rectifiers had been installed.
Electrical continuity testing of the reference cell grounds to the system grounds and the reference cell grounds to the reference cell grounds indicated that the expected continuity was present. The AC resistance between the anode and the system grounds was found to be in the reasonable range. The AC resistance between the reference cells and their respective grounds averaged 1500 ohms for the graphite and 19,000 ohms for the silver-silver chloride reference electrode.
System Performance
Null probe currents went to zero when the system was powered off. All reference cells met the 100-mV criterion during each evaluation, and the system was operating at an average current density of 1.0 mA/m2. The system had not been operated continuously due to problems experienced in setting the output parameters via the RMU.
4.3.1.5. Conclusions
All system components were functioning properly. The effectiveness of the system was being compromised due to interruption of the operation of the system.
4.3.2. Queen Isabella Causeway, South Padre Island, Texas
The Queen Isabella Causeway is a 4.0-km long bridge structure on PR 100 that links South Padre Island to the mainland of Texas at Port Isabel and spans the Laguna Madre.
4.3.2.1. Structure Information
The structure carries four lanes of traffic going east/west. It comprises 150 spans, 3 continuous steel plates, and 147 simple prestressed concrete girder spans. The spans are supported by 150 bents that are numbered from 1 to 150 from west to east. Construction of this structure was completed in 1973.
In 1997, a corrosion condition evaluation was conducted for the tie beams and footings located in bents 19 through 24. The footings exhibited cracks and spalls, the majority of which were located on the south footings. Spalls were mostly located on the sides of the footings. Cracking was the predominant mode of deterioration on the tie beams. The concrete cover depth ranged from 71 to 121 mm for the tie beams and from 58 to 108 mm for the footings. A corrosion potential survey of the members revealed a few areas where the potentials were more negative than -350 mV CSE. These areas were typically found in the proximity of cracks or construction joints.
4.3.2.2. CP Information
The tie beam and the three footings in bent 20 were protected with arc-sprayed titanium. The arc-sprayed titanium anode was installed on the entire surface of the tie beam and the footings, with the exception of the bottom surface of the footings. The total surface area covered with the titanium anode was approximately 127 m2. The instrumentation consisted of three silver-silver chloride reference cells and two null probes. Two reference electrodes were embedded in the footings and one reference electrode was embedded in the tie beam. One null probe was installed in one of the footings and the other in the tie beam.
Before the anode was applied, spalls and cracks were repaired and the concrete surface was sandblasted.
4.3.2.3. Field Evaluations
CONCORR, Inc., personnel were present during the initial energization of the system; subsequent evaluations were performed on the following dates:
|
Energization
|
October 7, 1997 | |
|---|---|---|
|
First evaluation
|
December 17 and 18, 1997 | ~ 2 months old |
|
Second evaluation
|
February 9 to 11, 1998 | ~ 4 months old |
|
Third evaluation
|
April 1 to 3, 1998 | ~ 6 months old |
|
Fourth evaluation
|
June 3 to 6, 1998 | ~ 8 months old |
|
Fifth evaluation
|
November 9 to 12, 1998 | ~ 13 months old |
4.3.2.4. Findings
System Component Evaluation
During energization of the system, all components, with the exception of the RMU, were functioning properly. By the time of the second evaluation, the RMU problem had been rectified. The DC electrical continuity data erroneously indicated that there was a lack of continuity. This was attributed to the flow of corrosion currents in the reinforcing steel when the system was off.
System Performance
A visual survey of the condition of the arc-sprayed titanium was conducted during two evaluations
(second and fifth). During the second evaluation, sprayed titanium was observed to have disbonded at
the south end of the tie beam and at the sides of the footing. During the last evaluation, the condition of
the sprayed titanium had deteriorated significantly. Approximately one-third of the coating had
disbonded, exposing the concrete surface. At the time of the survey, it was raining and water was
observed under the titanium coating.
The average concrete current density for the field evaluations ranged from 24.11 to 44.64 mA/m2. Of
the three reference electrodes, one never exceeded 100 mV, one exceeded 100 mV in each evaluation,
and one varied from negative polarization to values in excess of 100 mV. Considering the excessive
disbondment of the coating, it is expected that CP current is only being impressed in areas of good
bonding, hence the variation in the polarization of the three reference electrodes. Also, the current
densities impressed on this system are significantly higher than those encountered in the protection of
steel embedded in concrete. Lack of polarization of the steel at such high current densities is indicative
of either non-uniform current distribution by the anode or current leakage into the ground through the
bay water.
4.3.2.5. Conclusions
The anode material in this system had significantly deteriorated and the system was not considered to be functional.
5.0. CONDUCTIVE COATING-BASED IMPRESSED-CURRENT CP SYSTEMS
Two conductive paint impressed-current systems were evaluated in this study. Both systems were installed on bridge substructure elements and both were located in Virginia. Pertinent information is provided in table 5-1:
Table 5-1. Conductive Coating-Based Impressed-current CP Systems
| Structure Name and Location | Year CP System Installed | Element Protected | Area Protected | Instrumentation | Age at Last Evaluation | Average Chloride Ion Content of Steel Depth (ppm) |
|---|---|---|---|---|---|---|
|
Maury River
Bridges, Lexington, VA
|
1991 & 1992 | 14 piers & pier caps | 1530 m2 | 2 reference cells per zone | 4 years | 281 in southbound structure |
|
James River Bridge, Richmond, VA
|
1987 | 93 hammerhead pier caps | 7900 m2 | 1 reference cell & potential wells | 9 years | 394 |
Note: Chloride ion content information was obtained from cores collected during this study.
5.1. Maury River Bridge, Lexington, Virginia
The Maury River Bridge on I-81 is located in Rockbridge County in Lexington, Virginia.
5.1.1. Structure Information
The bridge comprises one northbound and one southbound structure. Each structure carries two lanes of traffic and is supported by seven piers. The length and width of each structure are 215 m and 8.8 m, respectively. Construction of the bridge was completed in 1967.
Significant corrosion-induced delaminations (more than 14 percent) and spalls were encountered on the piers of the two bridges during a survey conducted in 1991. The distress on the piers was due to leakage of chloride-laden water through the joints.
5.1.2. CP Information
The piers were cathodically protected with an impressed-current system. The CP systems on the northbound and southbound structures were installed in November 1991, and July 1992, respectively.
The CP system utilized platinized wire as the primary anode and a conductive carbon-based coating as the secondary anode. For aesthetic purposes, a topcoat of white paint was applied to the black conductive coating.
The CP systems on the two structures are controlled by two 7-circuit, full-wave, unfiltered rectifiers. Each circuit controls one pier. Both rectifiers are located on the south end of the southbound structure. Two embedded graphite reference cells were installed in each pier for monitoring purposes.
Delaminated concrete was removed from the pier caps and repairs were performed using shotcrete.
5.1.3. Field Evaluations
Evaluations were performed on the following dates:
|
First evaluation
|
March 2, 1995 | ~ 3 year old |
|---|---|---|
|
Second evaluation
|
June 12 and 13, 1996 | ~ 4 years old |
5.1.4. Findings
System Component Evaluation
Electrical continuity testing using the DC technique detected continuity among all expected elements with one exception: Cell 2 on circuit 3 of the southbound rectifier had a discontinuous ground. The anode-to-structure data indicated that there were no shorts between the anode and the structure steel.
The AC resistance measurements between the anode and ground ranged from 13 to 89 ohms, significantly higher than values reported earlier (1.65 to 2.30 ohms). The significant increase in AC resistance with time