Page 582 - Corrosion Engineering Principles and Practice

544 C h a p t e r 1 3 C a t h o d i c P r o t e c t i o n 545

distinction has to be made in the applicability of remedial measures
between new and existing structures. Unfortunately, the options in
the following list of remedial measures are more limited for fixing
existing aging structures than for designing new constructions [11]:

• Repairing the damaged concrete
• Modifying the external environment, for example, choosing a
different deicing agent or changing deicing salt practices
(however this will not remove salt already in the concrete).
• Modifying the internal concrete environment, for example,
realkalization of concrete, chloride extraction, addition of
corrosion inhibitors, and so on.
• Creating a barrier between the concrete and the external
environment.
• Creating a barrier between the rebar steel and the internal
concrete environment, for example, epoxy coating and
galvanization.
• Applying CP to the rebar structure.
• Alternatively, more corrosion-resistant rebar materials, for
example, stainless steel.
• Alternative methods of reinforcement, for example, fiber-
reinforced polymer composites.

The following sections describe how CP can be used to protect
reinforced concrete structures against corrosion by using either an
ICCP system or sacrificial anodes.

13.4.1 Impressed Current Cathodic Protection
ICCP consists in polarizing the rebar with a DC current source
(rectifier) to a cathodic potential where anodic dissolution of the rebar
is minimized (Fig. 13.20). Three basic methods are available for
controlling the output of a rectifier:

• Constant current mode: In this mode the rectifier maintains a
constant current output. The output voltage then varies with
changes in the circuit resistance. The potential of the
reinforcing steel can be measured with a reference cell as a
function of the applied current to ensure that certain protection
criteria are met.
• Constant voltage mode: In this mode a constant output voltage
is maintained by the rectifier. The applied current then
changes with variations in circuit resistance. Low concrete
resistance, often associated with increased risk for corrosion
damage, can result in increased current output. It should be
noted that in this mode, the rebar potential is not necessarily
constant. It can again be monitored with a reference cell.