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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

Half-Cell Potential Testing
LTBP Protocol #: FLD-DC-NDE-003


1.

Data Collected

 
1.1 Potential for electrochemical corrosion of steel 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 Concrete pachometer (cover meter).  
2.1.3 Permanent marker.  
2.1.4 Temporary chalk marker.  
2.1.5 Power source.  
2.1.6 Hammer drill.  
2.1.7 Depth measuring instrument or drill stop with precision to one-quarter inch or less.  
2.1.8 Stainless steel screw of appropriate length and diameter.  
2.1.9 Drill bit of appropriate diameter for the stainless steel screw.  
2.1.10 Concrete patching compound.  
2.1.11 Half-cell electrode; copper–copper sulfate (Cu–CuSO4) [units mV copper sulfate electrode(CSE)], silver–silver chloride (Ag–AgCl2) [units mV AgCl], or other.  
2.1.12 High-impedance portable voltmeter.  
2.1.13 Low-resistance lead wire with electrical clamps or plugs.  
2.1.14 Open-celled sponges.  
2.1.15 Surfactant (soap) solution.  
2.1.16 Cu–CuSO4 CSE reference electrode.  
2.1.17 Ag–AgCl2 reference electrode.  
2.1.18 Digital camera.  
2.2 Personnel: PRE-PL-LO-005, Personnel Qualifications.  

3.

Methodology

 
3.1 For concrete decks, identify the location and position of the test points using the local rectangular coordinate system (FLD-OP-SC-001, Data Collection Grid and Coordinate System for Bridge Decks). For other concrete elements, identify the location and position of the test points using the structure segmentation and element numbering system (FLD-OP-SC-002, Structure Segmentation and Element Identification System).  
3.2 Test Preparation:  
3.2.1 The half-cell potential test requires a direct connection to the reinforcing steel.  
3.2.1.1 Select a location in the shoulder area and use the pachometer (cover meter) to identify the location and measure the depth to the upper mat of reinforcing steel. Record the depth of the reinforcement detected. Mark the intersection of the longitudinal and transverse steel of the upper mat with the temporary chalk marker.  
3.2.1.2 Using the hammer drill, remove concrete down to the level of the upper mat of the reinforcing steel.  
3.2.1.3 Drill a pilot hole into the reinforcing bar and screw in the stainless steel screw.  
3.2.2 Ensure the bridge deck is in a saturated-surface-dry condition (PRE-OP-SP-001, Site Preparation).  
3.2.3 Apply water to the testing points immediately before surveying.  
3.3 Measurements:  
3.3.1 Connect the positive terminal of the high-impedance portable voltmeter to the stainless steel screw using the low-resistance lead wire with electrical clamps.  
3.3.2 Place the half-cell in contact with a wetted sponge on the concrete surface, then read and record (automatically if so equipped) the indicated potential.  
3.3.3 Apply consistent pressure to the half-cell as variability in contact pressure may influence the readings.  
3.3.4 Do not place the half-cell on individual exposed aggregate particles or other obstructions (e.g., asphalt or coating splotches) that may inordinately influence the reading.  
3.3.5 Monitor each point for at least 3 seconds before recording to ensure the reading is stable (not increasing). A variation of no more than +/- 5 mV per minute is necessary. If readings are not stable, this may indicate inadequate moisture or interference by an external electrical source, which should be evaluated and rectified before proceeding.  
3.3.6 In reinforced concrete, half-cell potential values for mild steel reinforcement commonly range from +50 to -600 mV CSE. Zinc and zinc coatings, as found on galvanized steel or in galvanic anodes for corrosion protection, will indicate more negative potentials in many cases. Regions where lack of oxygen restricts the cathode reaction to support corrosion may also produce unusually negative half-cell potential values. For valid interpretation, convert values for half-cell types other than Cu–CuSO4.  
3.3.7 If using a rolling wheel half-cell, the half-cell potential wheel must be rolled back and forth at least 3 inches to find the smallest negative number around each point (this generally corresponds to the location closest to the steel reinforcement).  
3.3.8 For comparison to other complementary test data at selected point locations, take additional detailed measurements. Take extra care to ensure proper probe contact and avoid exposed aggregate particles or other obstacles that may influence current flow. Select locations based on other survey data, including broad scale half-cell and resistivity mapping, as well as visual damage survey (for example, at locations showing delaminations, spalls, and repairs). Site restoration: When the half-cell potential testing is complete, fill in the hole flush with the surface of the surrounding area of the deck with a suitable concrete patching compound (approved by the bridge owner).  
3.4 Storing data, documents, and images:  
3.4.1 FLD-DS-LS-001, Data, Document, and Image Storage—Local, for local storage.  
3.4.2 FLD-DS-RS-001, Data, Document, and Image Storage—Remote, for remote storage.  
3.5 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
ºF
Range: -50 to 150
Green
9 Deck surface temperature
Number
1
ºF
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
 
 
 
Orange
14 Location of electrical connection to the reinforcing steel
Text
 
 
Descriptive location of the connection screw on the bridge (e.g., left shoulder 30 feet from joint 1 and 3 feet from the edge of the lane.)
Green
15 Location of connection screw (x-coordinate)
Number
1
ft
Longitudinal distance from the local grid origin
Green
16 Location of connection screw (y-coordinate)
Number
1
ft
Transverse distance from the local grid origin
Green
17 Test site
Text
 
 
Descriptive location of the test on the bridge (e.g., shoulder and lane1)
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 Half-cell potential (HCP) reading
Number
1
mV
Range: -999 to 99
Yellow
21 Comments
Text
 
 
 
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 Verification and comparison should be made with results obtained from other NDE methods including chemical/potential methods, acoustic methods, and electromagnetic methods.  

6.

Commentary/Background

 
6.1 The purpose of this protocol is to provide a standard procedure for using half-cell potential measurements to assess the probability of active steel corrosion in a reinforced concrete member.  
6.2 Traffic in the lanes outside of the work zone is permissible during data collection.  
6.3 The stainless steel screw should be of a length that when firmly connected to the reinforcing bar, the head of the screw protrudes about 0.5 inches above the top of the core hole. Thus, after the core hole is patched, the stainless steel screw will be available for future half-cell potential testing and a positive connection to the screw will be possible.  
6.4 The half-cell potential test measures the electrical potential between the embedded steel reinforcement in the concrete and a reference electrode, typically a copper electrode in a copper sulfate solution, electrically coupled to the concrete surface. The electrical potential is measured as a voltage using a high-impedance voltmeter. The reference electrode is connected to the negative terminal of the voltmeter and a direct connection to the steel reinforcement is connected to the positive terminal. The reference electrode is typically coupled to the concrete surface using a porous ceramic plug and an open-celled sponge wetted with surfactant solution. Measurements are taken at point locations by moving the electrode from one point to another on a grid on the concrete.  
6.5 Regions with a significantly lower negative potential compared to surrounding areas indicate a 90percent probability of corrosion. ASTM C876 gives guidelines for evaluating active corrosion probability in concrete structures containing uncoated mild steel reinforcement.  
6.6 HCP measurements do not give quantitative information about the rate of corrosion. The potential is influenced by cover depth, permeability and moisture content of concrete, and, therefore, a combination of HCP and resistivity measurements may help interpret the collected data. Coatings on concrete (isolating layers, asphalt, and paint) or reinforcement may influence or nullify HCP measurements.  

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 FLD-OP-SC-001, Data Collection Grid and Coordinate System for Bridge Decks.  
7.1.4 FLD-OP-SC-002, Structure Segmentation and Element Identification System.  
7.1.5 PRE-OP-SP-001, Site Preparation.  
7.1.6 FLD-DS-LS-001, Data, Document, and Image Storage—Local.  
7.1.7 FLD-DS-RS-001, Data, Document, and Image Storage—Remote.  
7.2 External:  
7.2.1 ASTMC876-09, Standard Test Method for Corrosion Potentials of Uncoated Reinforcing Steel in Concrete, ASTM International, West Conshohocken, PA, 2009.  

 

 

 

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