Civil Engineering Reference
In-Depth Information
5.3 Aluminium-zinc-indium galvanic anodes
At about the same time as the humectant was under development, a
proprietary aluminium-zinc-indium alloy thermal spray was developed
(Funahashi and Young, 1999). This was aimed at boosting the galvanic current
throw without the use of a humectant for inland de-icing salt applications.
The original material was electric arc sprayed using a wire with a core of
powdered metal. Later developments of other proprietary aluminium-zinc-
indium anodes use a solid wire and are now widely offered in Europe and
the Middle East.
5.4 Applying thermal sprayed metals
The anode is applied using either flame spraying or electric arc spraying.
The latter is now more common as deposition rates are far higher than
flame spraying. There is a standard for thermal spraying anodes on concrete,
see American Welding Society (2002). After initial surface preparation by
a light grit blast, the zinc or Al-Zn-In is sprayed onto the surface of the
concrete using flame or electric arc equipment. The coating application rate
and thickness must be carefully controlled as thick coatings can debond due
to thermal shock of the hot 'splatters' of zinc (or Al alloy) hitting the cold
surface. Coatings are usually a few tenths of a mm thick (typically 0.3 mm).
Zinc vapour can lead to 'zinc flu' if breathed in. Therefore all operatives
must be suitably protected and the area shrouded to contain the zinc
overspray.
This anode system has a life-expectancy of up to 25 years and has a
medium to high cost of installation compared with other anode systems.
Like a conductive paint there is little visual or other impact. The grey colour
means it has limited acceptability on buildings.
References
American Welding Society. 'Specification for thermal spraying zinc anodes on
reinforced concrete'. AWS/ANSI Standard. 2002; AWS C2.20/C2.20M:2002.
Apostolos, J. A. Parks, D. M., and Carello, R. A. 'Cathodic protection using metallized
zinc'.
Materials Performance
. pp. 22-28. 1987.
Bennett, J. E. 'Chemical enhancement of metallized zinc anodes performance'.
Corrosion 98
. Mar 1998. Paper No. 640, San Diego CA..
Covino, B. S. Cramer, S. D. Bullards, S. J. Holcomb, G. R. Russell, J. H. Collins,
W. K. Laylor, H. M., and Cryer, C. B.
Performance of Zinc Anodes for Cathodic
Protection of Reinforced Concrete Bridges
. FHWA/Oregon DOT Report. FHWA-
OR-RD-02-5. Mar 2002.
Funahashi, M. and Young, W. 'Three-year performance of aluminium alloy galvanic
cathodic protection systems'.
NACE Corrosion 99
(Paper No 550) Apr 1999.
Kessler, R. J. and Powers, R. G. 'Zinc metalizing for galvanic cathodic protection
of steel reinforced concrete in a marine environment'.
Corrosion 90
. Apr 23-27
1990; Paper 324: Las Vegas Nevada. NACE International, Houston, Texas.
