Factors affecting the corrosion of reinforcement

Reinforcement corrosion occurs due to the presence of chlorides and sulfates over a significant limit in reinforced cement concrete construction and when sufficient alkali is not received within the concrete to maintain the steel in a positive state.

Factors affecting corrosion of reinforcement in concrete structure
corrosion of reinforcement

The following factors are responsible for corrosion of steel reinforcement in concrete structure.

1. Quality of Concrete

Concrete consists of coarse aggregates, fine aggregates, cement and water. Right quality of material with proper w/c ratio, right mixing, adequate compaction by tamping or vibration and proper curing yields good quality concrete. If any of the above steps are not done in a specified manner, it will result in not so good concrete and there is a possibility of corrosion of the reinforcement.

High strength concrete, i.e. dense concrete is impervious to a large degree and generally resists the carrion of embedded steel.

2. Cover Thickness of Concrete Reinforcement

The reinforcement is protected by a suitable concrete cover over it. The greater the thickness of the cover, the greater the degree of protection against various climatic and other environmental conditions. For different structural members, the thickness of the cover should be different depending on their importance and degree of risk. The evenness of the concrete cover on the reinforcement is also very important for its corrosion protection.

3. Reinforcement conditions

The surface condition of steel reinforcement, when placed in concrete, affects its corrosion rate. If the reinforcement is contaminated with salt or is badly corroded, the corrosive action on the reinforcement is promoted rapidly once it is applied to the concrete.

4. Impact of environment and other chemicals

Chemicals are the main source of the spoilage process, either from the environment or from within the material making the concrete. The attack of chemicals causes cracks in the concrete, which is the first sign of deterioration. The effects of chemicals are mainly due to the presence of salt, carbonation, chloride attack and reaction of sulfates with tricalcium aluminate (C).3a) present in cement.

Concrete is an intimate mixture of cement, aggregate and water which is highly alkaline in green state. The hydration of cement develops calcium hydroxide which raises the pH value to 12.5. In such alkaline conditions, the reinforcing steel is covered with a film of oxide that protects the steel.

5. Porosity of Concrete

The penetration of aggressive chemicals is possible due to the permeability or porosity of the concrete. The porosity of concrete depends on the size, distribution and consistency of the capillary pores. It depends on the w/c ratio for a given degree of hydration. Porosity also depends on other factors, such as

  • age of concrete
  • degree of compactness
  • Aggregate Size and Grading
  • type of cement

6. Effect of High Thermal Stress

normal concrete 100 . can withstand temperatures up to0C. Beyond this temperature the corrosion of concrete starts. Concrete in industrial plants and power stations requires special protective measures otherwise thermal cracks may develop in the concrete. Cracked concrete structures are affected by environmental chemicals and the process of corrosion is triggered.

7. Freezing and Thawing Conditions

In colder regions, moisture tends to accumulate in the pores of the concrete. Ice formation gives rise to volumetric expansion which can be the pressure of the burst in addition to the surrounding solid mass. This results in the development of cracks in the concrete and can cause corrosion of the reinforcement.

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.