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1. Concrete Corrosion Fundamentals PowerPoint Presentation
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1. Concrete Corrosion Fundamentals

1. Concrete Corrosion Fundamentals

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1. Concrete Corrosion Fundamentals

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  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 >10

  3. Causes of Reinforcement Corrosion

  4. Causes of Concrete Deterioration

  5. Causes of CorrosionChlorides • Airborne, marine, industrial, groundwater, cast-in • Cl– can penetrate through the passive film • At Cl- > “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 CorrosionCarbonation • CO2 gas dissolves in pore water  Carbonic Acid • Neutralises Alkalis in Concrete, pH ~ 9 • Passive Film dissolves • General corrosion starts

  7. Anodic Reaction (Oxidation) Fe  Fe2+ + 2e- Secondary Reactions Fe2+ Fe(OH)2, Fe3O4, Fe2O3 Corrosion Reactions Depassivation due to: Chlorides CO2 (carbonation) Cl- Cl- +ve Ions +ve Ions e- e- Anode Cathode Cathodic Reaction (Reduction) O2 + 2 H2O + 4 e-  4OH- High pH Maintained Anodes and Cathodes Oxygen & Moisture Oxygen & Moisture Fe Fe++ Rebar Cathode

  8. Rebar loss Spalling Cracks with Rust Staining Delamination Corrosion Damage

  9. Corrosion Damage