Chapter 3: Corrosion of Metal in Concrete Flashcards
1. Explain the corrosion theory and process in concrete 2. Identify factors affecting metal corrosion in concrete.
Concrete Durability Issues: Effects
leakage, settlement, deflection, wear, spalling, disintegration, cracking, delamination,
Concrete Durability Issues: Cause
Defect, Damage, Deterioration
Concrete Durability Issues: Damage
Overloading, chemical spill, earthquake, fire
Concrete Durability Issues: Deterioraton
Freeze-thaw, erosion, metal corrosion, alkali-aggregate, sulfate attack
What is corrosion:
electro-chemical process that involves the transfer of charge electrons form one site to another
3 Essential Conditions for Corrosion to occur?
- Anode: electron density greater than cathode
- Cathodes: takes electrons from anode and gives it back
- Electroyltes: transfers electrons through water and porous solution in aggreagtes
Anode Formula+ explanation
Fe= 2e + Fe++
Iron loose electrons and changes charges
Cathode Formula + explanation
2e + h20 + 0 = OH
absorbs electrons and reacts with water and oxygen to form hydroxide
Rust formula + explanation
Fe++ (+) 2OH = Fe(OH)2
hydroxide goes back to anode and reacts with charge Iron to create rust
Explain Corrosion Process
Iron in anode loses electrons due to electron density in rebar during manufacturing. Cathode takes electrons as it has low amounts and reacts with water and oxygen to form hydroxide. Hydroxide goes back to anode to react with charge iron to create rust
Factors affecting corrosion
water
oxygen
temperature
PH
chloride ions
concrete permeability
tidal zone
How does rust affect concrete
creates tension in concrete as rebar expands. Occupies 5-6 times volume
Passive Layer
small layer around rebar to prevent corrosion due to concrete PH
chlordies sources
admixtures, aggregates, cement, SCM’s, mix water, environment
