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Linear Polarization Resistance Testing - Ltbp Protocol - Fld-Dc-Nde-005

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

	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 (i_corr)	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.

Page Owner: Office of Research, Development, and Technology, Office of Corporate Research, Technology, and Innovation Management

Topics: research, infrastructure, structures
Keywords: research, structures, LTBP Program, bridge performance, bridge testing, bridge inspection, Bridge, bridge inspection, Long-Term Bridge Performance Program, LTBP, testing protocols, data collection
TRT Terms: research, infrastructure, Facilities, Structures
Scheduled Update: Archive - No Update needed

This page last modified on 03/24/2017

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

Linear Polarization Resistance TestingLTBP Protocol #: FLD-DC-NDE-005

1.

Data Collected

2.

Onsite Equipment and Personnel Requirements:

3.

Methodology

4.

Data Collection Table

5.

Criteria for Data Validation

6.

Commentary/Background

7.

References

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