This document discusses corrosion of steel reinforcement in concrete. It outlines the mechanisms of corrosion, including how steel becomes passive in high pH concrete but can become depassivated by chlorides or carbonation. Chlorides from deicing salts, seawater, or contaminated aggregates are common sources of corrosion. Corrosion causes cracking and deterioration of concrete structures like bridges and marine structures. Control methods focus on using low permeability concrete mixes with good cover to prevent ingress of chlorides and carbonation.

1. Corrosion of Steel
Reinforcement in Concrete
Presented by :
Group 4

2. Overview
• Introduction
• Mechanisms of Steel Corrosion
• Control of Corrosion

3. Introduction
• Corrosion is one of the principal causes of concrete
deterioration
• The damage is especially large in the structures
exposed to marine environment , contaminated
ground water, or deicing chemicals.
• Crores of rupees spent each year for maintenance
and repair of steel structures deteriorated due to
corrosion.

4. Cracking of concrete
• Heat of hydration
• Alkali-aggregate reactivity
• Carbonation
• Sulfate attack
• Acid and chemicals
• Reinforcement corrosion

5. Reinforcement corrosion
• Passivity
– High pH leading to formation of passive layer
– Chemical binding of chlorides
– Dense and impermeable structure of concrete
• Depassivation
– Chloride ingress
– Carbonation

6. Mechanisms of reinforcement
corrosion

7. Factors affecting reinforcement
corrosion
• Depassivation of steel
• Atmospheric pollutants
• Availability of oxygen and moisture
• Electrical resistivity of concrete
– Moisture
– Chloride and sulfate contamination

8. Mechanisms of Steel Corrosion
• Corrosion of steel in concrete is an electrochemical
process.
• The electrochemical potentials to form the
corrosion cells may be generated in two ways:
1. Two dissimilar metals are embedded in concrete, such as
steel rebars and aluminum conduit pipes, or when
significant variations exist in surface characteristics of the
steel.
1. Differences in the concentration of dissolved ions, such
as alkalies and chlorides.

9. Anodic and Cathodic Reactions
Anode: Fe 2e- + Fe2+
(metallic iron)
Cathode: (½) O2 + H2O + 2e- 2(OH)-
air water
• FeO (H2O)x
rust

10. Steel Passivity
• Ordinary iron and steel products are normally
covered by a thin iron oxide film that
becomes impermeable and strongly adherent
to the steel surface in an alkaline
environment, thus making the steel passive
to corrosion.
• This means that metallic iron is not available
for the anodic reaction until the passivity of
steel has been destroyed.

14. Sources of Chloride in Concrete
• Admixtures,
• Salt-contaminated aggregate,
• Penetration of seawater, groundwater, or
deicing salt solutions.

15. Corrosion of the Steel Reinforced
Concrete Structures
MARINE STRUCTURES BURIED UTILITIES
FOUNDATIONS BRIDGES & CULVERTS

17. Control of Corrosion
• Permeability of concrete is the key to control
the various processes involved in the
phenomena.
– Concrete mixture parameters to ensure low
permeability, e.g., low water-cement ratio,
adequate cement content, control of aggregate
size and grading, and use of mineral admixtures.

18. Control of Corrosion
Minimum concrete cover should be maintained.
Current practice for coastal structures requires a
minimum 50 mm of cover on conventional
reinforcement, and 70 mm on prestressing steel.

19. Control of Corrosion
• Waterproof membranes
• Overlay of watertight concrete
• Protective coatings for reinforcing steel