Basics in Building Construction

Building Components And Types

Lesson 15 : Reinforced Cement Concrete

Corrosion Of Steel In Concrete

Corrosion sometimes occurs to reinforcing bars placed in concrete. This is of course not a serious problem for majority of reinforced structures. The term corrosion is used to indicate the conversion of metals by natural agencies into various compounds. The term rusting is used to refer corrosion of ferrous metals.

Causes of Corrosion

Following are the factors responsible for causing corrosion of steel in concrete:

1. improper construction methods,
2. inadequate design procedure,
3. insufficient cover to steel from exposed concrete surface
4. permeability of concrete which depends on various factors such as water-cement ratio, size of aggregate, curing, grading of aggregates, etc.
5. poor workmanship,
6. presence of moisture in concrete,
7. presence of salts,
8. type of atmospheric conditions surrounding the region of concrete,
9. unequal distribution of oxygen over the steel surface, etc.

Effect of Corrosion

The action of corrosion of steel in concrete is very slow and except under exceptional circumstances, such corrosion does not decrease the life of concrete member. It should, however, be remembered that action of corrosion becomes more intensive when it is combined with adverse effects of internal and external stresses. One important effect of corrosion is the formation of cracks and these cracks usually progress or advance most rapidly where shearing stresses are the greatest and where slipping occurs due to loss of bond.

Prevention of corrosion

To minimize the chances of development of corrosion of steel in concrete, the following preventive measures may be taken:

1. avoiding the steel to come into contact with bricks, soil, wood and other porous non-alkaline materials,
2. avoiding the use of materials which accelerate the process of corrosion, i.e. , aggregates with high salt contents, water containing salts etc.,
3. maintaining a high degree of workmanship,
4. proper structural design with due provision of cover,
5. providing cathodic protection to reinforcement by some suitable method,
6. providing surface coatings with paints, tars, asphalts, etc.
7. use of a high quality and impermeable concrete, etc.