1.1 Background
1.1.1 Reinforcing steel is compatible with concrete
because of similar coefficients of thermal expansion
and because concrete normally provides the steel with
excellent corrosion protection. The corrosion protection
is the result of the formation of a passive oxide film on
the surface of the reinforcing steel by highly alkaline
portland cement contained in the concrete. This
passive oxide film can be compromised by (1)
excessive amounts of chloride or other corrosive ions
and gases, or (2) the steel not being sufficiently
encased by the concrete.
1.1.2 Corrosion occurs as a result of the formation of
an electrochemical cell. An electrochemical cell
consists of four components: an anode, where
oxidation occurs; a cathode, where reduction occurs; a
metallic path, where electrons flow; and an electrolyte
(concrete), where ions flow. The anodic and cathodic
areas occur as a result of coupling dissimilar metals,
exposure to different environmental conditions, or both.
If any one of the four elements of the electrochemical
cell is eliminated, corrosion can be prevented.
1.2 Cathodic Protection
1.2.1 The basic principles of corrosion can be used to
understand the theory of CP. CP reduces the
corrosion of a metal surface by making the protected
surface the cathode of an electrochemical cell.
1.2.2 CP is a proven technique for controlling
corrosion of steel in chloride-contaminated concrete
structures. However, CP neither replaces lost steel nor
returns corroded reinforcing steel to its original crosssection.
1.2.3 CP of reinforcing steel in atmospherically
exposed concrete is described in NACE SP0290.
Many of the practices described in that document are
relevant to buried and submerged elements. Other
anode types are also applicable to buried and
submerged elements, as the soil or water provides a
somewhat homogenous medium for the anode system,
which need not be fixed directly to the concrete. The
application of CP to prestressed concrete cylinder
pipelines is described in NACE SP0100.
1.3 Scope and Limitations
1.3.1 The provisions of this standard should be applied
under the direction of a registered Professional
Engineer or a person certified by NACE International
as a Corrosion Specialist or a CP Specialist. The
person's professional experience should include
suitable experience in CP of reinforced concrete
structures. Under certain circumstances, a CP system
may either become a structural component or
significantly affect the serviceability and structural
performance of a reinforced concrete structure;
therefore, such impact by the CP system should be
reviewed by a qualified registered Structural Engineer
or the equivalent.
1.3.2 The guidelines presented here are limited to CP
systems for new or existing buried or submerged
reinforced concrete elements.
1.3.3 When the reinforcing steel is bonded to facility
grounding, as commonly required by the National
Electrical Code,6 the resulting galvanic corrosion cell
and the possible adverse affects on the quantity and
distribution of CP current to the reinforcing steel shall
be considered.
| ANSI : | ANSI Approved |
| File Size : | 1
file
, 130 KB |
| ISBN(s) : | 1575902230 |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 16 |
| Published : | 11/07/2008 |
