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For steel reinforcing bar
in concrete, the steel rebar may corrode when the passive (non-corroding)
steel surface is exposed to chloride ions which de-stabilize the normal
oxide film on the rebars embedded in the alkaline concrete environment.
The chloride ions may result from the use of deicing salts, exposure to
sea water or marine fog, or from chloride added to the fresh concrete.
The electrochemical corrosion cell is set up when two different parts of
the rebar mat, which are electrically bonded together, act as the anode
and cathode, as shown in Figure 1
.
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The electrolyte in this
case is the concrete, which will normally contain enough moisture to
conduct the electrical corrosion current. Since the steel corrosion
products, the iron oxides, occupy a larger physical volume than the
uncorroded steel, the rebar corrosion will exert tensile stresses on the
surrounding concrete, with the stresses increasing until cracks,
delaminations, and eventually potholes or spalls are formed.
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To know more about Cathodic
Protection of Steel in Concrete Click
Here.
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