1. Concrete Corrosion Fundamentals - PowerPoint PPT Presentation

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1. Concrete Corrosion Fundamentals

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* * Concrete not only provides physical protection to reinforcement or prestressing, but good quality concrete also provides electrochemical protection. – PowerPoint PPT presentation

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Title: 1. Concrete Corrosion Fundamentals


1
1. Concrete Corrosion Fundamentals
2
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

3
Causes of Reinforcement Corrosion
4
Causes of Concrete Deterioration
5
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

6
Causes of Corrosion Carbonation
  • CO2 gas dissolves in pore water ? Carbonic Acid
  • Neutralises Alkalis in Concrete, pH 9
  • Passive Film dissolves
  • General corrosion starts

7
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

8
Corrosion Damage
9
Corrosion Damage
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