1. Concrete Corrosion Fundamentals

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1. Concrete Corrosion Fundamentals
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Reinforcement Protection by Passive Film

• Ca, Na, K hydroxides in hydrated cement raise the
  pH to 13.5
• A dense protective ? ferric oxide (Fe2O3)
  passive film forms around the reinforcement
• This passive film stops iron dissolution, and is
  stable at pH gt10

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Causes of Reinforcement Corrosion
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Causes of Concrete Deterioration
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Causes of Corrosion Chlorides

• Airborne, marine, industrial, groundwater,
  cast-in
• Cl can penetrate through the passive film
• At Cl- gt threshold, passive film breaks down,
  corrosion initiates
• Cl- threshold value is typically 0.05 by wt of
  concrete (0.02 prestressed concrete)
• Pitting corrosion
• Chlorides are main cause of reinforcement
  corrosion

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Causes of Corrosion Carbonation

• CO2 gas dissolves in pore water ? Carbonic Acid
• Neutralises Alkalis in Concrete, pH 9
• Passive Film dissolves
• General corrosion starts

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Corrosion Reactions
Anodes and Cathodes
Oxygen Moisture
Oxygen Moisture
Fe Fe
Rebar
Cathode

• Anodic Reaction (Oxidation)
• Fe ? Fe2 2e-
• Secondary Reactions
• Fe2 ? Fe(OH)2, Fe3O4, Fe2O3

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Corrosion Damage
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Corrosion Damage