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Corrosion of Reinforcing Steel Bars and its Control

Concrete is the most used construction material. Concrete is used in nearly every type of construction. 
Traditionally, concrete has been primarily composed of cement, water, and aggregates.
Steel reinforcements are often included to increase the tensile strength of concrete; such concrete is called reinforced cement concrete (RCC) or simply reinforced concrete (RC).The quality of steel used in RCC work is as important as that of concrete.

Steel reinforcement used in concrete may be of the following types:
1.Mild steel and medium tensile steel bars (MS bars)
2. High-yield-strength deformed steel bars (HYSD bars)
3. Hard drawn steel wire fabric
4. Structural steel conforming

Corrosion of Rebars

  • The primary factors controlling the corrosion rate  of steel rebars are the availability of oxygen, electrical resistivity and relative humidity of the concrete, pH, and prevailing temperature.
  • Carbonation is another cause for corrosion. Carbonation-induced corrosion often takes place in buildings that are exposed to rainfall, are shaded from sunlight, and have a low concrete cover over the reinforcing steel.
  • Corrosion can also occur when two different metals are in contact with concrete.
  • When corrosion takes place, the resulting rust occupies more than three times the original volume of steel which can eventually cause delamination, cracking, and spalling of concrete cover.
  • The presence of corrosion also reduces the effective cross-sectional area of the steel reinforcement and leads to the failure of a concrete element and subsequently the whole structure.

Controlling Corrosion:

Control measures to reduce the occurrence of corrosion includes the following:

1. Decreasing the water-cement ratio of concrete and using pozzolans and slag to make the concrete less permeable
2. Providing dense concrete cover using controlled permeability formwork (CPF), thus protecting the embedded steel rebars from corrosive materials
3. Including the use of corrosion-inhibiting admixtures
4. Providing protective coating to reinforcement
5. Using of sealers and membranes on the concrete surface

Following types of reinforcements can be used to control corrosion:

1. Fusion-bonded epoxy-coated reinforcing bars used in RC bridges with a satisfactory performance

2. Galvanized reinforcing bars whose protective zinc layer does not break easily and results in better bond

3. Stainless steel bars whose initial cost is high but the life cycle cost is lower

4. Fibre-reinforced polymer bars (FRP bars) are aramid fibre (AFRP), carbon fibre (CFRP) or glass fibre (GFRP) reinforced polymer rods. They are non-metallic and hence non-corrosive.

5. Basalt bars are manufactured from continuous basalt filaments and epoxy and polyester resins using a protrusion process offering a corrosion-resistant alternative to steel reinforcement.