Page 12 - Riem-Vol6_nº2

184 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 2
Cathodic protection for concrete structures
5. A case study of impressed cathodic
protection for a concrete structure
A cathodic prevention system was installed during the construc-
tion of the new general cargo wharf of the Aveiro Port, Portu-
gal. The cathodic protection system was installed in the tidal and
splash zones of the front beam of the wharf. This area is con-
sidered the greatest corrosion risk zone due to the proximity of
the water. The wharf has a length of 250 m. The total area of
reinforced concrete to be protected was 1046 m2. Mesh tapes
of Ti/MMO, with 0.5 mm wide and 20 mm thick, were used as
anodes. The tapes were installed with a spacing of 250 mm and
connected, by welding, to another titanium tape used as a cur-
rent distributor (see Figure 7).The tapes were fixed to the rein-
forcement before the concrete casting. Appropriate spacers were
used, aiming at avoiding a short circuit
The control and monitoring of the cathodic protection system was
carried out manually through a Control Central Unit. This unit was
essentially composed of three power supplies, one per zone, volt-
meters and ammeters to measure the intensity of the supplied
voltage and current and high impedance voltmeters for the steel/
concrete electrode potential measurements (see Figure 7).
Before starting the current application, tests were performed in
order to verify the functionality of all system components and to
ensure the correct connection of all circuits. The system was en-
ergized in the constant current mode. Initially, a low protection
current was applied aiming at allowing a slow polarization of the
system. In each subarea, different current values were applied in
order to evaluate the influence of the protective current on the po-
larization and depolarization of each part of the structure.
The relationship between the depolarization values (potential CP
off) and the current density obtained in each subarea is presented
in Figure 8. These results indicate that the required current density
for obtaining 100-mV depolarization, after 72 h of interruption of
the current, is about 3.5 mA/m2. As the system was designed to
provide much higher current densities than the maximum recom-
Figure 8 – Mean values of depolarization (72 h)
as a function of applied current density
mended, the need to increase the current does not present prob-
lems of anode or other system components’ durability.
6. Conclusions
Cathodic protection is an effective technique to avoid premature
deterioration and to extend the service life of concrete structures
subjected to high risk of premature degradation such as those ex-
posed to a high aggressive environment or presenting high con-
struction quality problems.
The present review showed that despite the application of cathodic
protection being suited to structures exposed to different condi-
tions and states of preservation, it has been especially applied in
new atmospheric structures subjected to corrosion by chloride ions
or in old structures presenting a severe ongoing corrosion process.
The impressed current cathodic protection method is used more in
concrete structures than the sacrificial anode method. However,
the latter is prudentially used to protect elements subjected to a
continuous wetting. In general, the application of the sacrificial an-
ode method presents higher simplicity and easier monitoring.
The selection of both cathodic protection methods should be made
on a detailed study of the concrete structure to be protected taking
into account the environmental conditions to which the structures
are exposed. In addition, the ease of anode installation, the cost,
the aesthetic, the required lifetime and the maintenance are factors
to be considered for an effective cathodic protection design. The
application of both must be made with the assistance of qualified
personnel.
7. References
[01] CHESS, P. Corrosion in reinforced concrete
structures. In: CHESS, P. (Ed.). Cathodic protection
of steel in concrete. London: E & FN Spon, 1998. p. 1-36.
[02] NATIONAL ASSOCIATION OF CORROSION
ENGINEERS. RP0209-2000: impressed current
cathodic protection of reinforcing steel in atmospherically
exposed concrete structures. Houston, 2000. 11p.
[03] BEAMISH, S.; EL-BELBOL, S. Appraisal of
corrosion-damaged structures. In: CHESS, Paul
(Ed.). Cathodic protection of steel in concrete. London:
E & FN Spon, 1998. p. 18-36.
[04] BROOMFIELD, J. International development and
growth. In: seminar on cathodic protection
of reinforced concrete structures,
1994, London. Proceedings… London: SCPRC, 1994.
Paper 6.
[05] PEDEFERRI, P. Cathodic protection and cathodic
prevention. Construction and Building Materials,
Oxford, v.10, n. 5, p. 391-402, 1996.
[06] BERTOLINI, L. et al. Three year tests on cathodic
prevention of reinforced concrete structures.
In: ANNUAL CONFERENCE AND EXPOSITION,
CORROSION/97, 52., 1997, New Orleans.
Proceedings… Houston: National Association of
Corrosion Engineers, 1997. Paper 244.
[07] EUROPEAN COMMITTEE FOR STANDARDIZATION.
EN ISO 12696: Cathodic protection of steel in
concrete. Brussels, 2008. 45p.