164 Damage to concrete structures
Figure 5.38 shows a typical microcell for corroding steel in a cementitious system. At the anode, iron ions go into solution. The remaining electrons are transported toward the cathode, where in the presence of water
and oxygen some hydroxyl ions are formed. These hydroxyl ions are transported through the electrolyte solution and react with the iron ions forming
iron hydroxide Fe(OH) 2 , which can be further oxidized to iron oxide Fe 2 O 3 .
The expansive formation of corrosion products leads to tensile stresses in
Concrete
Steel
e
–
e
–
Cathode
OH
–
Fe
2+
O 2
H 2 O
OH –
O 2
H 2 O
Fe 2 O 3
Fe(OH) 2
Figure 5.38 Corrosion microcell of steel in a cementitious system.
Cu
H 2 O
OH –
Anode
Cathode
Electrolyte
O 2
Fe
2+
Fe
e
–
Figure 5.37 Macrocell representation of a corrosion process.