U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000


Skip to content
FacebookYouTubeTwitterFlickrLinkedIn

Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

 
REPORT
This report is an archived publication and may contain dated technical, contact, and link information
Publication Number:  FHWA-HRT-16-007    Date:  January 2016
Publication Number: FHWA-HRT-16-007
Date: January 2016

 

Long-Term Bridge Performance (LTBP) Program Protocols, Version 1

Long-Term Bridge Performance Program Logo

Linear Polarization Resistance Testing
LTBP Protocol #: FLD-DC-NDE-005


1.

Data Collected

 
1.1 Rate of corrosion of reinforcement in concrete.  

2.

Onsite Equipment and Personnel Requirements:

 
2.1 Equipment:  
2.1.1 PRE-PL-LO-004, Personal Health and Safety Plan.  
2.1.2 Linear polarization resistance (LPR) measurement system (manual or computer-operated potentiostat), including reference (half-cell) and counter electrode in portable probe configuration.  
2.1.3 Low-resistance electrical leads with connectors.  
2.1.4 Surfactant solution.  
2.1.5 Digital camera.  
2.2 Personnel: PRE-PL-LO-005, Personnel Qualifications.  

3.

Methodology

 
3.1 Test preparation:  
3.1.1 LPR testing is conducted at identified point locations, and the data can be used to correlate with indications of the presence and rate of corrosion from other test methods, such as resistivity and chloride profiles. Select locations based on other survey data, including half-cell and resistivity mapping, as well as visual damage survey (delaminations, spalls, and repairs).  
3.1.2 Use the local rectangular grid (FLD-OP-SC-001, Data Collection Grid and Coordinate System for Bridge Decks) to locate and document test points on the deck.  
3.1.3 Ensure the bridge deck is in a saturated-surface-dry condition (PRE-OP-SP-001, Site Preparation).  
3.2 Establishing electrical continuity:  
3.2.1 Provide positive electrical contact to the steel reinforcement to ensure electrical continuity between the electrical contact (tap) point and the reinforcement in the concrete surveyed section. This can be accomplished by providing multiple contact points at geometrically distributed points along the element being investigated.  
3.2.2 Depending upon reinforcement distribution, electrical continuity may not be expected over joints between spans, precast or cast-in-place (CIP) segments, and between structural components not cast monolithically. Carefully review structural and as-built drawings to determine the number and location of contact points to service the surveyed section.  
3.2.3 Using a high-impedance multimeter, measure the electrical resistance between the distributed points.  
3.2.4 Note that nonmetallic coatings, such as epoxy on concrete surfaces or reinforcement, asphalt, or polymer membranes may be electrical insulators and should be evaluated before proceeding with LPR measurements. Some organic coatings have been noted to uptake moisture over several years of service and may no longer preclude the flow of current, permitting measurements to be taken. However, interpretation may not be straightforward, since the area of bar polarized may be called into question. Results of tests on coated reinforcement should be taken in context with other measurements.  
3.2.5 If direct resistance between distributed contact points (after subtracting the lead-wire resistance) is only a few ohms and stable, then adequate conductivity should exist for LPR measurements.  
3.3 Placing the probe:  
3.3.1 Placing the half-cell/counter electrode assembly (probe) in contact with the concrete surface immediately over a reinforcing steel bar to which electrical continuity has been established. Avoid placing the probe on nonconductive obstructions (e.g., asphalt or coating splotches) that may influence the reading.  
3.3.2 Prior to executing a polarization test, if possible, observe the open circuit potential with the test instrument to ensure that readings are stable. The test should not be run if open circuit potential values drift more than 5 mV/min.  
3.3.2.1 If potential moves steadily in one direction, consider whether the concrete is adequately saturated or if there is an external source of electrical current that is affecting the reinforcement.  
3.3.2.2 If potential values jump erratically, this generally indicates an incomplete circuit; items to check include electrical connections, seating of the probe and reference cells, and electrical continuity of reinforcement between tap site and test location.  
3.3.2.3 Values of open circuit potential should be similar to those observed in measurement of half-cell potential at the same location, though the magnitude of reading may differ if a different type of reference electrode is used (for example copper–copper sulfate (Cu–CuSO4) versus silver–silver chloride (Ag-AgCl)).  
3.4 Manual testing: For the manual three-electrode polarization resistance (3LP) system, collect readings, and polarize the reinforcement through hand-driven operations:  
3.4.1 Monitor the electrical potential until stable. Stability corresponds to variations smaller than +/‑5mV per minute. Once stable potential is established and recorded, the system is ready to report relative potential versus the open-circuit potential (OCP).

NOTE— If readings are not stable, it may indicate an incomplete electrochemical circuit due to loose connections, inadequate moisture content, or interference by an external electrical source. Check connections, eliminate extraneous sources of electrical fields, and establish adequate moisture content.
 
3.4.2 Zero the meter by engaging the offset switch and turning the knob until potential value reads 0mV.  
3.4.3 Apply electrical current to polarize the reinforcement at a slow, steady rate in increments until the offset potential reaches +4, +8, and +12 mV from OCP. Record the current required to achieve the offset at the precise moment each noted increment is reached. The complete polarization procedure should take no longer than 2 minutes.  
3.4.4 Once complete, remove the current by rapidly turning the current knob back to zero and allow the reinforcement to depolarize. Continue to monitor the potential.  
3.4.5 Within 3 minutes, the potential should return to the original OCP (or “0” if offset is still engaged). If it does not, retake the measurement because the associated “drift” in OCP will influence the estimated corrosion rate. A period of 10 minutes must elapse before repeating the readings to ensure adequate depolarization.  
3.5 Automated testing: Some field instruments and laboratory potentiostats can be programmed to perform the polarization process automatically:  
3.5.1 If possible, program the system to monitor and collect the OCP by recording potential at 1-second intervals for at least 1 minute before and after the test.  
3.5.2 Program automated systems to conduct a potentiostatic linear polarization resistance procedure, which induces a current from the counter electrode that causes the electrical potential of the reinforcement to shift from the OCP (i.e., polarize) by at least +12 mV and no more than +20mV, at a rate of 10 mV per minute.  
3.5.3 Some devices are equipped with a “guard ring” electrode that induces a separate current into an electrode that surrounds and attempts to contain the primary counter electrode current into a specified polarization area. Such instruments are known to give significantly different corrosion rate values than the methods outlined above and are believed to underestimate the actual corrosion rate. Therefore, if used for the purposes of this program, such test devices must be operated with the guard ring electrode disabled.  
3.6 Storing data, documents, and images:  
3.6.1 FLD-DS-LS-001, Data, Document, and Image Storage—Local, for local storage.  
3.6.2 FLD-DS-RS-001, Data, Document, and Image Storage—Remote, for remote storage.  
3.7 Reporting: Transfer all metadata, data, documents, and images to Federal Highway Administration (FHWA), and/or upload all metadata, data, documents, and images into the Long-Term Bridge Performance (LTBP) Bridge Portal.  

4.

Data Collection Table

 
4.1 Table:  
# Field Name Data Type Accuracy Unit Field Description Row Color
1 State
Text
 
 
State Code, e.g., Virginia = VA
Green
2 NBI structure number
Text
 
 
Item 8, structure number, from NBI Coding Guide
Green
3 Structure name
Text
 
 
Descriptive name for the bridge, e.g., Route 15 SB over I–66
Green
4 Protocol name
Text
 
 
Title of the protocol
Green
5 Protocol version
Text
Month and year
 
Month and year the protocol version was published; e.g., May 2015
Green
6 Personnel performing data collection activities
Text
 
 
First name(s) Last name(s)
Green
7 Date data were collected
Text
Exact date
 
mm/dd/yyyy
Green
8 Ambient air temperature
Number
1
°F
Numeric means negative and positive integers, range: -50 to 150
Green
9 Deck surface temperature
Number
1
°F
Numeric means negative and positive integers, range: -50 to 150
Green
10 Equipment name
Text
 
 
 
Green
11 Equipment manufacturer
Text
 
 
 
Green
12 Equipment model name and number
Text
 
 
If available
Green
13 Comments (equipment)
Text
Unlimited
 
 
Orange
14 Reinforcement locating equipment name
Text
 
 
 
Green
15 Reinforcement locating equipment manufacturer
Text
 
 
 
Green
16 Comments (reinforcement locating equipment)
Text
Unlimited
 
 
Orange
17 Test site
Text
 
 
Location of the test on the bridge (e.g., shoulder and lane 1)
Blue
18 Location of test site (x-coordinate)
Number
1
ft
Longitudinal distance from the local grid origin
Blue
19 Location of test site (y- coordinate)
Number
1
ft
Transverse distance from the local grid origin
Blue
20 OCP (before test)
Number
1
mV
 
Yellow
21 Applied current readings
Number
0.0001
mA
 
Yellow
22 Corresponding potential
Number
1
mV
 
Yellow
23 Length of probe
Number
0.1
in.
 
Yellow
24 Reinforcement size
List
 
 
#3, #4, #5, #6, #7, #8, #9
Yellow
25 Range of polarization (offset) vs. OCP
Number
1
mV
 
Yellow
26 Scan rate
Number
0.1
mV/sec
 
Yellow
27 Depolarization OCP
Number
1
mV
 
Yellow
28 Polarized bar surface
Number
0.01
in.2
 
Yellow
29 Corrosion current density (icorr)
Number
0.01
mA/ft2
 
Yellow
30 OCP (after test)
Number
1
mV
 
Yellow
31 Metal loss
Number
0.000001
in./yr
 
Yellow
32 Comments
Text
Unlimited
 
 
Orange
4.2 Table Key:  
Column Descriptions
#
Sequential number of data item
Field Name
Data field name
Data Type
Type of data, such as text, number, predefined list, binary large object (BLOB), or PDF file
Accuracy
Accuracy to which the data are recorded
Unit
Unit in which a measurement is taken and recorded
Field Description
Commentary on the data or list of items in a predefined list
Row Color Key
Green
Data items only entered once for each protocol for each day the protocol is applied
Pink
Logical breakdown of data by elements or defect types (not always used)
Blue
Data identifying the element being evaluated or the type of defect being identified
Yellow
LTBP data reported individually for each element or defect identified
Orange
Comments on the data collection or data entered

5.

Criteria for Data Validation

 
5.1 Linear polarization resistance at any given location should correlate to measurements taken with the simpler half-cell potential test protocol (FLD-DC-NDE-003, Half-Cell Potential Testing). Corrosion rates can be calculated as corrosion current density, as total current is applied over the length and surface area of a reinforcement bar immediately below the probe, and translated into estimated metal loss using Faraday’s Law. Measurements of 0.1 μA/cm2 or less indicate negligible corrosion rate, whereas measurements greater than 5 μA/cm2 indicate very rapid corrosion.  

6.

Commentary/Background

 
6.1 The purpose of this protocol is to provide a standard procedure for using linear polarization resistance measurements for evaluating the instantaneous corrosion rate, as compared to other methods on which metal loss is measured over a finite period of time.  
6.2 The LPR technique is rapid and relatively nonintrusive; it requires only localized damage to the concrete cover to enable an electrical connection to be made to the reinforcing steel. Monitoring the relationship between electrochemical potential and the current generated between electrically charged electrodes allows the estimation of the corrosion rate. The data provide the instantaneous corrosion rate of the steel reinforcement at the test location, giving more detailed information than a simple half-cell potential (HCP) measurement.  
6.3 Reinforcement corrosion is mainly due to chloride ingress, causing depassivation and leading to corrosion when oxygen and moisture are present in the steel-concrete interface. Acid attack and carbonation could also provoke corrosion.  
6.4 This technique is used for estimating corrosion rates and is sensitive to very low corrosion rates; a rate of less than 0.1 millionths of an inch per year (mpy) can be detected.  
6.5 Periodic monitoring allows onset of corrosion and subsequent rate of corrosion to be evaluated.  

7.

References

 
7.1 LTBP Protocols:  
7.1.1 PRE-PL-LO-004, Personal Health and Safety Plan.  
7.1.2 PRE-PL-LO-005, Personnel Qualifications.  
7.1.3 PRE-OP-SP-001, Site Preparation.  
7.1.4 FLD-DC-NDE-003, Half-Cell Potential Testing.  
7.1.5 FLD-OP-SC-001, Data Collection Grid and Coordinate System for Bridge Decks.  
7.1.6 FLD-DC-PH-002, Photographing for Documentation Purposes.  
7.1.7 FLD-DS-LS-001, Data, Document, and Image Storage—Local.  
7.1.8 FLD-DS-RS-001, Data, Document, and Image Storage—Remote.  
7.2 External: None.  

 

 

 

Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000
Turner-Fairbank Highway Research Center | 6300 Georgetown Pike | McLean, VA | 22101