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| Project Title: |
Evaluation of the ACT (Accelerated
Test Method) for Post-Tensioning Grouts |
| Investigator: |
Dr. Andrea
Schokker |
| Research Assistants: |
Alex Pacheco |
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| Funding Agency: |
CAPES Foundation (Brazil) |
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| Project Duration: |
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| References: |
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Recent problems with corrosion in poorly grouted post-tensioning tendons
has led to a more concerted effort to develop grouts that provide good
corrosion protection. An Accelerated Corrosion Method (ACT) is specified
in the Post-Tensioning Institute Guide Specification for Grouting of Post-Tensioned
Structures (February 2001). This method uses an electrochemical technique
know as a potentiostatic test. A constant electric potential is applied
to the test specimen and the current is measured at 30 minute intervals
during testing.
The objective of this research is to standardize the ACT test and to
investigate the following variables: IR compensation, curing time, and
specimen fabrication process. The IR or voltage drop is due to the intrinsic
electrical resistance of the grout. Since this resistance varies between
grouts, the polarization potential may vary if IR compensation is not
used. Previous testing with the ACT did not include this effect. Other
electrochemical testing will also be investigated in this study including
potentiodynamic curves.
EQUIPMENT
Two identical sets of equipment are available for data acquisition. Each
set is going to be responsible for the monitoring of eight different corrosion
cells or stations, making a total capacity of 16 stations.
The data readings are performed sequentially by a signal multiplexer,
which sends the readings to a controller and potentiostat circuit boards
installed in a microcomputer.
FIGURE 3.1 - Experimental setup schematics
FIGURE 3.2 - Experimental setup
The test stations consist of a specimen - the working electrode (WE),
a platinum wire - the counter electrode (CE), and a saturated calomel
electrode - the reference electrode (RE). All electrodes are immersed
in an electrolyte solution (5% NaCl in water).
FIGURE 3.3 - Corrosion cell schematics: (i) perspective,
(ii) elevation
EXPERIMENTAL TECHNIQUES
The experimental setup available for this work allows a variety of standard
electrochemical techniques for corrosion studies. The following table
presents the techniques that can be used for the purposes of the intended
research.
TABLE 4.1 - Types of experiment
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Type of Experiment
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Used for
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| Potentiostatic |
General purpose, passivation |
| Potentiodynamic Scan |
Mechanistic studies, passivation behavior |
| Polarization Resistance |
Rapid corrosion rate measurement |
| Rp/Ec Trend |
Inhibitor studies. Time dependance |
| Tafel |
Corrosion rate measurement |
| Cyclic Polarization |
Study of passivation, pitting |
| Corrosion Behavior Diagram |
Mechanistic studies |
| Corrosion Potential |
General purpose |
FIGURE 4.1 - One specimen severely corroded and another
one still intact
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