| Anode |
a. The site in a corrosion cell where the consumption of metal
occurs.
b. The positive current source introduced for a Cathodic protection
system. May be galvanic or impressed current anode. |
| Carbonation |
The process where carbon dioxide (CO2) reacts with
water in concrete pores to form carbonic acid, neutralizing the
high alkaline concrete, possibly causing corrosion of reinforcement. |
| Cathodic Protection |
(CP) The process in which a metal structure
is protected from corrosion using either galvanic (sacrificial)
or impressed current anodes. Metal becomes Cathodic and is protected
from corrosion. |
| Cathodic Prevention |
Name given to Cathodic Protection of a new
(usually concrete) structure where the CP is installed at the time
of construction. Less current is required to protect the structure
in these systems, resulting in a more economical outcome than later
installation of CP. |
| Chloride Corrosion |
Chloride is an aggressive ion that is responsible
for initiating many corrosion problems, especially in concrete structures
exposed to seawater or chloride rich environments. |
| Chloride Extraction |
The electrochemical process of removing Chloride
ions from a concrete structure (similar arrangement to CP) in a
corroding structure. Treatment commonly takes 4 to 8 weeks. |
| Concrete |
Mixture of cement (Portland cement), sand, aggregates
and water resulting in a reaction of the water and the cement to
form a hard binder. |
| Corrosion |
The process where a metal reverts back to its natural
state by oxidation (rusting). Requires oxygen and water. |
| Electrochemical |
The process of using an electric current to move ions. Cathodic
protection, realkalization, chloride extraction are all electrochemical
processes. |
| Half cell |
Often a pure metal in a solution of fixed concentration,
giving a reaction of a steady potential. Reference half cells are
used to measure the “corrosion potential” of a metal
or steel reinforcement in concrete. |
Impressed Current
Cathodic Protection |
A type of Cathodic Protection where a direct current power supply
(transformer rectifier) provides power to an invert anode to pass
current protecting a metal (making the metal Cathodic) |
| Ion |
An atom which has gained or lost electrons (eg Na+,Cl-,Fe2+) |
| Passivation |
Process by which a metal is protected from corrosion by a passive
layer usually due to a highly alkaline environment. (eg reinforcing
steel is passivated by the alkaline nature of concrete being pH
~12) |
| pH |
Measure of acidity and alkalinity (neutral 7, acid 0-7, alkaline
7-14) |
| Prestressing |
The process where a compressive stress is applied to concrete
by the stressed (stretched) wires or bars of steel. (Prestressed
or
post-tensioned) Extreme care
must be taken in the Cathodic protection of prestressed steel due to the possibility
of causing hydrogen embrittlement in the steel, resulting in brittle failure
of the prestressed reinforcement. |
| Reference electrode |
Another name for a half cell |
| Reinforced concrete |
Concrete containing reinforcing steel. Concrete is strong in compression
but weak in tension. Reinforcement adds tensile strength to concrete. |
| Realkalization |
An electrochemical process (sometimes referred to as desalination)
in which carbonated concrete is treated in a process similar to
Cathodic protection, to restore
the alkalinity and stop corrosion of the reinforcing steel. The process takes
3 to 7 days in most cases. |
| Rust |
Corrosion product of a metal as it corrodes |
Sacrificial Cathodic
Protection |
A type of Cathodic Protection where a more easily corroded metal
(anode) is connected to the metal being protected. Common sacrificial
anodes are zinc, aluminium or magnesium (or alloys of these metals)
which sacrifice themselves to protect the metal (steel) being protected.
The sacrificial anode is consumed and may need to be replaced in
time. |
| Titanium anode |
Titanium is “activated” in a coating process resulting in an invert
material ideal for long term use as an impressed current anode. Commonly used
as anodes for the protection of reinforced concrete and steel structures in water
or soil. |
