4.1 Corrosion of steel Flashcards
Three types of protection for concrete reinforcement
Physical
Chemical
Electrical
What factors affect the effect of concrete cover?
Permeability
Degree of interconnected porosity
How does chemical protection protect concrete reinforcement?
High pH provides passivating oxide layer & cement matrix chemically binds harmful ions
How does electrical protection protect concrete reinforcement?
Prevents initiation of flow of corrosion currents
What happens at the anode during corrosion?
Dissolution of iron
Breakdown of passivating oxide layer
Hydroxyl ions from cathode react with ion to form rust
What happens at the cathode during corrosion?
Surplus electrons, oxygen and water react to form hydroxyl ions
What are the requirements for corrosion?
Oxygen
Water
How does oxygen contribute to corrosion?
Hydroxyl ions and rust
How does water contribute to corrosion?
Electrolytic process
For corrosion currents to flow between anode and cathode.
Two periods of time for corrosion
Initiation period
Propagation period
What happens in the initiation period
Ingress of deleterious agent
No corrosion
What does the initiation period depend on? (5)
Cover depth
Cement type
W/C ratio
Temp
Curing
What happens in the propagation period?
Sufficient oxygen and water and OH- ions cause spalling and cracking
What does the propagation period depend on?
Oxygen, Water, OH- concentration
