SCREENING EAGLE PM8500 Corrosion Potential Profometer User Guide

SCREENING EAGLE PM8500 Corrosion Potential Profometer

Product Information

The PM8500 is a device used for measuring the potential of concrete structures. It features various keys, a BT dongle USB-C, a battery port, and a top button for device control. The device has LED indicators that provide information about its status and behavior during operation.

Keys – Overview

• BT dongle USB-C: Used for Bluetooth connectivity.
• Battery Port: Allows for easy battery installation/removal.
• Top Button (Device ON/OFF): Used to power on/off or reboot the device.

LED – Behavior

• Turn on, awaiting Bluetooth connection: LED is inactive.
• While measuring (rod/wheels): LED remains on.
• Turn Off: LED is inactive.
• Errors/Device in boot loader mode:
  • Green: Single quick blink indicates battery level >20%.
  • Red: Single quick blink indicates battery level -200mV.

External Factors

The measured potential of the concrete can be influenced by several external factors:

• Moisture: Higher moisture levels lead to more negative potential values.
• Cover: Increasing concrete cover results in more positive potentials. Very low concrete cover can indicate high levels of corrosion.
• Coarse Grid: High electrical resistivity leads to more positive potentials.
• Oxygen Content: Decreasing oxygen concentration and increasing pH-value at a steel surface make the potential more negative.
• Temperature: High temperature lowers concrete resistivity, while low temperature increases it.

Product Usage Instructions

Preliminary Operations

Prepare the Electrodes

To prepare the rod electrode:

1. Remove the cap with the wooden plug.
2. Soak the rod in water for about an hour to saturate and swell the wood.

To prepare the wheel electrode:

1. The wooden plug should not be removed.
2. Immerse the wheel in water for an hour to allow the water to soak into the plug. Remove the wheels from the legs before doing this.

The felt hoops and felt hoop connector should be saturated before measuring. In normal use, the thin felt is on the wooden spigot side.

Ensure that water is dripping slowly from the water tank through the 1mm nozzle (red mark). Apply pressure by blowing air through the bike valve if necessary.

Prepare the saturated solution by mixing 40 units by weight of copper sulphate with 100 units by weight of distilled water. Add an additional teaspoon of copper sulphate crystals into the electrode.

Fill the electrode as completely as possible, minimizing air in the compartment to ensure proper contact with the wooden plug, even when measuring in an upward direction.

Connect to Rebar

Ensure that the device is properly connected to the rebar before proceeding with measurements.

Preliminary Operations – Coated Surfaces Pre-moistening

Measurements cannot be made through electrically isolating coatings like epoxy resin, sealing sheets, or asphalt layers.
However, it is possible to measure through thin dispersion coatings, which may cause a slight shift in potentials. Measure potentials at a few locations in such cases.

Dried-out concrete skin can impair the contact between the pore solution of the concrete and the probe, increasing the electrical resistivity of the concrete.

Always follow safety instructions when handling copper sulphate as indicated on the packaging.

Keys -Overview

Top Button

LED -Behaviour

Measurement Principle

Half Cell Potential

• Under normal conditions reinforcement steel is protected from corrosion by a thin, passive film of hydrated iron oxide
• This passive film is decomposed due to the reaction of the concrete with atmospheric carbon dioxide (CO2, carbonatation), or by the penetration of substances aggressive to steel, in particular chlorides.
• At the anode, ferrous ions (Fe++) are dissolved, and electrons are set free. These electrons drift through the steel to the cathode, where they form hydroxide (OH-) with the generally available water and oxygen. This principle creates a potential difference that can be measured by the half-cell method.
• The basic idea of potential measurement is to measure the potentials at the concrete surface. For this purpose, a Cu/CuSO4 reference electrode (with a known potential) is connected via a high-impedance voltmeter to the steel reinforcement and is moved in a grid over the concrete surface.

Typical Reference Values

Half Cell Potential

• Typical orders of magnitude (for information only) for the half-cell potential of steel in concrete measured against a Cu/CuSO4 reference electrode are in the following range (RILEM TC 154-EMC)
• Probability of corrosion rises with low (negative) potentials. Active corrosion can be expected at locations where a negative potential is surrounded by increasingly positive potentials. I.e. locations with a positive potential gradient. Potential differences of around +100mV within a 1m distance, together with negative potentials, can be a clear indication of active corrosion
• The actual potential absolute value (corrosion threshold) may vary on different structures.
• ASTM C 876-09 suggests two different thresholds:

External Factors

Half Cell Potential

Moisture
Moisture has a large effect on the measured potential leading to more negative values

Cover
The potential becomes more positive with increasing concrete cover.
Very low concrete cover can lead to more negative potentials which would seem to indicate high levels of corrosion

Electrical resistivity
Low electrical resistivity leads to more negative potentials and the potential gradients become flatter –coarse grid is needed.
High electrical resistivity leads to more positive potentials and potential gradients become steeper –fine grid is needed.

Temperature
High temperature will cause concrete resistivity to be lower and low temperature will cause concrete resistivity to be higher

Oxygen content
With decreasing oxygen concentration and increasing pH-value at a steel surface its potential becomes more negative

Preliminary operations

Prepare the electrodes

Rod Electrode: Remove the cap with the wooden plug and soak it into water for about an hour to allow the wood to saturate and swell.
Wheel Electrode: The wooden plug is not intended to be removed. Immerse the wheel in water for an hour to allow the water to soak into the plug. Only the wheels should be immersed, therefore, please remove them from the legs before doing it.
The felt hoops and the felt hoop connector must be saturated before measuring. In normal use (with water and cupper solution), the thin felt is on the wooden spigot side.
The water should be dripping out slowly from the water tank throughout the 1mm nozzle (red mark). The bike valve should provide a high pressure; if water is dripping out from this valve, please apply some pressure blowing with your mouth.

Copper Sulphate
Prepare the saturated solution by mixing 40 units by weight of copper sulphate with 100 units by weight of distilled water. Add an additional teaspoon of copper sulphate crystals into the electrode.
The electrode should be filled as completely as possible with a minimum of air in the compartment. This ensures that the solution is in contact with the wooden plug even when measuring in an upwards direction.

Connect to rebar
The ground cable must be connected to the reinforcement. The connection should be made with the least possible resistance – grind it and connect cable with welding tongs.
The connection should be tested for continuity. This requires at least one other point of the reinforcement to be exposed and to check the resistance between the two with an Ohmmeter – not more than 1 Ω above the resistance of the cable used.
A secure connection can be also obtained by drilling a 25 mm hole into the concrete above the rebar, then drill a 4 mm hole into the rebar and insert a self tapping screw with attached lead into the hole in the steel

When handling copper sulphate be careful to take note of the safety instructions on the packaging

Coated surfaces

It is not possible to make a measurement through an electrically isolating coating (e.g. an epoxy resin coating, sealing sheets or asphalt layers.)
It is possible to make a measurement through thin dispersion coatings, however this can cause a small shift of the potentials. To do this, potentials should be measured at a few locations

• in the first place through the coating and
• with the coating removed

If there is no alteration of the potential, or if a shift of the potential can be compensated by a correction (e.g. V = ± 50 mV), then a measurement can be made directly on the coating. If not, then the coating must be removed before making the measurement.

Pre-moistening

The contact between the pore solution of the concrete and the probe can be impaired by a dried out concrete skin. This can greatly increase the electrical resistivity of the concrete.
It is recommended to moisten the surface approximately 10 to 20 minutes before carrying out the measurement.
If this is not possible, it must be ensured that the sponge on the Rod Electrode or the felt hoops on the wheel electrode are sufficiently moistened. In this case, when making a measurement, the probe must be held against the surface until a stable end value is reached. This is only possible with the Rod Electrode.
In the case of the wheel electrode with its continual automatic measurement, it is not possible to monitor whether or not the measured value is stable. Therefore, it is recommended to pre-moisten the surface in sections and to measure in intervals of a few minutes.

Maintenance and Cleaning

To guarantee consistent, reliable and accurate measurements, the instrument should be calibrated on a yearly basis. The customer may, however, determine the service interval based on his or her own experience and usage.

• Do not immerse the instrument in water or other fluids.
• Keep the housing clean at all times.
• Wipe off contamination using a moist and soft cloth.
• Do not use any cleaning agents or solvents.
• Do not open the housing of the instrument yourself.

Rod Electrode

• Unscrew the two caps, wash with water and carefully clean the inner side of the tube.
• Clean the copper rod using emery cloth.
• Refill the electrode with copper sulphate

Wheel Electrode

• Remove the felt hoops and wash in lukewarm water.
• Remove the plastic filling screw and pour the copper sulphate solution into a container. (This can be reused)
• Flush out several times with water.
• Dissolve 1-part citric acid in 10 parts hot water and half fill the wheel.
• Replace the filling screw.
• Leave for 6 hours, shaking occasionally.
• Pour out the citric acid solution (no special disposal procedure is required) and flush out several times with water.
• Refill the electrode with copper sulphate solution.
• Replace the felt hoops. The felt hoop connector must be in place between the dampening nozzle and the wooden plug of the wheel electrode.
• When not in use, store the wheel electrode with the wooden plug facing upwards.

Settings

Potential Map

• The potential map provides an area mapping of the measured potential values
• The cells where no potential value was measured are displayed in black
• Zoom and scroll to any desired location, change the color palette and the potential thresholds to enhance the readability and highlight the desired details.
• Text notes can be added to any cells

Statistic View

Distribution and cumulative distribution are shown in the same view.
On the horizontal axis, the potential values are displayed; the vertical bars show the percentage of the respective potential values measured and stored.
In the upper part, the median, standard deviation, minimum and maximum values are shown, together with the number of measurements.

The cumulative distribution graph is used to determine the active and the passive potential thresholds that will affect the Chipping Graph, discriminating actively corroding areas from passive areas where no corrosion is to be expected.
If the surface under test has both actively corroding as well as passive rebars, then the curve will typically exhibit a central region with a lower gradient (flatter). The two points where the gradient changes can be marked on the screen by dragging the two vertical cursors.
The red cursor will define the maximum (most positive) potential value expected of the active distribution. Active corrosion is to be expected in the region of the left hand (more negative) straight section.
The green cursor will define the minimum (most negative) potential of the passive distribution.
If the surface under test has both actively corroding as well as passive rebars, then the two states exhibit two distinct partially overlapping distributions, with the corroding areas centered on a more negative potential.

Chipping Graph

The Chipping Graph View provides an area mapping of the measured potential values with a fixed green/yellow/red color palette referring to the thresholds set in the Cumulative Distribution View.
An immediate overview is then provided discriminating the actively corroding areas (red) from the passive areas (green) and the uncertain regions (yellow).

Basic Mode

The Basic Mode shows directly the Chipping Graph at the same time as the measurement is done.

For that purpose, the threshold limits have to be preset:

• Manually
• Selecting the ones included in the ASTM C876-09, Appendix X1, assigning a 90% probability of corrosion ongoing to the areas more negative than -350 mV, and a 90% probability of no corrosion to the areas more positive than -200 mV.

Advanced Mode

The Advanced Mode is recommended for expert users that want to create their own threshold limits based on the total measured values.
The process is the following: Potential map Statistic View Setting the threshold limits Chipping Graph

For more information on the product use of the product, please refer to the Profometer PM8500 documentation
It is available for download on

www.screeningeagle.com/en/products/profometer- pm8500

For safety and liability information, please download at https://www.screeningeagle.com/en/about-us/gtc-and-certificates Subject to change. Copyright © 2023 by Proceq SA, Schwerzenbach. All rights reserved.

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References

• Screening Eagle Technologies - Protect The Built World - Protect The Built World
• Profometer PM8000
• Profometer PM8500
• Certificates and General Terms & Conditions (GTC) - Protect The Built World

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