2. Content
Mechanism of Corrosion in Reinforcement
Causes of Corrosion
Preventive Measures of Corrosion in Reinforcement
Some Factors affecting on Corrosion
3. MECHANISM OF CORROSION IN REINFORCEMENT
Corrosion of steel reinforcement is electromechanical process shows on following
picture. Corrosion may starts when cover layer is destroyed.
4. The process can be describe as following reaction:
(1) 2 Fe + 2 H2O + O2 → 2 Fe(OH)2
This reaction includes the dissolution of iron, the reduction of
oxygen and formation of rust:
(2) Fe → Fe2+ + 2 e- anodic
(3) 2 H2O + O2 + 4 e- → 4 OH- cathodic
5. CAUSES OF CORROSION
1. Cracks in Concrete
2. Presence of Moisture
3. Permeability of Concrete
4. Carbonation
5. Chlorides
6. Sulphate Attack
7. Alkali-Aggregate Reaction
8. Inadequacy of Cover
6. Cracks in Concrete
Water can easily enter to the reinforcement through cracks of concrete
For normal atmosphere, crack shouldn’t be > 0.30 mm.
For unsafe atmosphere, crack shouldn’t be > 0.20 mm.
8. PREVENTIVE MEASURES OF CORROSION IN
REINFORCEMENT
1. Avoiding heavily congested reinforcement especially at the intersection of
beams and columns.
2. Avoiding the steel to come into contact with bricks, soil, wood and other
porous non-alkaline materials
3. Avoiding the use of materials which accelerate the process of corrosion i.e.
aggregates with high salt contents, water containing salts, etc.
4. Cleaning the reinforcement with wire-brush to remove the rust scales before
placing of concrete
5. Maintaining a high degree of workmanship
6. Proper structural design with due provision of cover
7. Providing cathodic protection to the reinforcement by some suitable method
9. 8. Providing surface coatings with paints, tars, asphalts, etc.
9. Use of high quality and impermeable concrete
10. Using stone pebbles in place of badly made cover blocks
11. Using the correct water-cement ratio
