The GalvaPulse is used to measure the corrosion rate of reinforcement in concrete for the following typical applications:
- Monitoring corrosion activity in reinforced concrete structures
- Service life estimation
- Evaluating the efficiency of corrosion arresting measures such as application of inhibitors, membranes, or electrochemical removal of chlorides
- Condition surveys of suspect reinforced structures, especially structures in wet environments where the classic potential mapping may provide misleading or insufficient information
- Measuring corrosion activity in repaired areas
The GalvaPulse evaluates the corrosion rate of reinforcement by measuring polarization resistance using the galvanostatic pulse technique, as described below.
A current pulse I is imposed on the reinforcement from a counter electrode placed on the concrete surface. A guard ring confines the current to an area A of the reinforcement below the central counter electrode.
The applied current is usually in the range of 5 to 400 A and the typical pulse duration is 5 to 10 seconds. The reinforcement is polarized in the anodic direction compared to its free corrosion potential, Ecorr. The resulting change of the electrochemical potential of the reinforcement is recorded as a function of time using a reference electrode (Ag/AgCl). A typical potential response for reinforcement actively corroding is shown in the right figure above.
When the current is applied to the system, there is an ohmic potential drop IRo as well as change in potential due to polarization of the reinforcement, IRp. The polarization resistance of the reinforcement Rp is calculated by curve fitting to the transient portion of the potential data. By means of the Stern-Geary equation for active corrosion (Icorr = (26 A)/Rp) and Faraday’s law of electrochemical equivalence, the corrosion rate is estimated as:
Corrosion Rate ( m/year) = 11.6 Icorr /A
where A is the confined area (in cm2) of the reinforcement below the central counter electrode. The factor 11.6 is for black steel.
The value of Ro, the electrical resistance of the concrete between the counter electrode and the reinforcement, is also determined.
Accuracy and Variation
The half- cell potential is measured to an accuracy of ±5 mV with the Ag/AgCl electrode. The electrical resistance is estimated to be measured with an accuracy of ± 5 %.
The accuracy of the corrosion rate estimation can only be evaluated by comparison with actual mass loss measurement of the reinforcement subjected to long term corrosion conditions. One such laboratory investigation produced the following comparison between corrosion rates calculated from measured mass loss measurements and from the GalvaPulse.
||Corrosion Rate (µm/year)
Reference: Baessler, R. and Burkert, A., “Laboratory Testing of Portable Equipment,” Brite/Euram Project Integrated Monitoring System for Durability Assessment of Concrete Structures, BAM (Federal Institute for Materials and Testing), Berlin, Germany, 2001
The findings support the general conclusion that the GalvaPulse is accurate well within a factor of two for estimating the corrosion rate in anodic areas. In addition, other uncertainties should be taken into account when evaluating on-site test results, e.g., the actual area of the reinforcement being polarized and the variation over time in corrosion rates due variation in temperature and moisture conditions.
In passive regions (corrosion rates < 1 µm/year), the GalvaPulse will overestimate the corrosion rate by a factor of 3 to 4. Such areas are, however, not interesting in terms of corrosion.
In a long term field study, 30-year old bridge columns subjected to deicing salts were examined regularly over a 20-year period since corrosion began. The chloride levels and moisture content in the concrete of the bridge were high. When the last measurements were performed, the temperature was 15 C and the following test results were obtained.
The fairly constant corrosion rate measured over the 20-yr period corresponds to a cross section loss of the reinforcement of 20 years times 0.22 mm/y = 4.4 mm. Removal of concrete at several locations at the bottom of the columns revealed approximately 4 mm cross section loss of the reinforcement.
The GalvaPulse Features
- Reliable evaluation of reinforcement corrosion in anaerobic concrete environment
- Lightweight, handheld equipment, easy to operate
- Two operation modes: one for speedy measurement using only half-cell potentials and electrical resistance (1 to 2 s/test), and another for corrosion rate, half-cell potentials and electrical resistance (5 to 10 s/test). The first mode is normally used to identify the anodic and the cathodic areas, while the second mode is used in anodic areas, where the corrosion rate is a decisive parameter to be measured
- Testing on rough or curved surfaces
- Storage capacity of up to 20,000 records in the handheld computer
- Easy-to-use Windows based software for presentation of the test results in 2D or 3D color graphics
- Portable system including calibration unit and a check block with embedded stainless steel and corroding black steel bars
Evaluation of corrosion rate in balcony slab of seaside condominium with the GalvaPulse
Highway bridge column being tested for corrosion rate with the GalvaPulse
Corrosion activity being evaluated on a bridge wall with the GalvaPulse
GalvaPulse (older model) testing in progress for corrosion activity of a heavily corroded column
Examples of the Graphic Displays to View GalvaPulse Data
Following testing, the handheld computer is connected to a PC with the installed Windows based GalvaPulse viewing and reporting software. The records are transferred to the PC and data can be viewed using 2D or 3D graphic displays. Here we see 3-D displays of the corrosion rates(above), the half-cell potential (above right), and the electrical resistance (right). Such plots permit the display of a large amount of data in a concise manner for preparing test reports.
The GalvaPulse-5000 Ordering Numbers
|Handheld computer with installed GalvaPulse software and pulse generator
|Calibration unit for pulse generator
|Measuring cell with 3 meter cable
|Sponge for measuring cell
|Reinforcement conductivity meter
|Cable for data transfer to PC
|Two adjustable reinforcement clamps
|Two reinforcement adaptors
|12 mm and 18 mm drill bits
|10 mm Allen key
|Sponge for grinding of electrode rings
|Hammer and chisel
|Measuring tape and chalk
|GalvaPulse data viewing and reporting software
|Supplied separately with the GP-5000 Kit
|Cable drum with 15 meters of cable
|Check block with embedded a corroding bar and a stainless steel bar