Short Answer:

Reinforcement corrosion occurs when steel bars inside concrete react with moisture and oxygen, usually due to the presence of water, chlorides, or carbonation. This reaction forms rust, which expands and causes internal pressure in the concrete, leading to cracks and spalling.

Corrosion reduces the cross-sectional area of steel, weakens the bond between steel and concrete, and significantly lowers the strength and durability of the structure. Over time, it can lead to severe damage or even failure if not identified and repaired early.

Detailed Explanation

Reinforcement Corrosion 

Reinforced Cement Concrete (RCC) structures rely on the combined strength of concrete and steel. The steel provides tensile strength, while the concrete offers compression resistance. When reinforcement bars inside the concrete begin to corrode, it poses a serious risk to the overall durability and safety of the structure.

Corrosion of reinforcement is one of the most common causes of damage in concrete structures worldwide. It not only affects the steel itself but also causes damage to the surrounding concrete, eventually leading to structural deterioration if not controlled. Understanding how reinforcement corrosion affects durability helps in designing long-lasting and reliable concrete structures.

How Reinforcement Corrosion Affects Durability

1. Loss of Cross-Sectional Area of Steel

• Corrosion reduces the diameter of the reinforcement bars.
• This leads to a loss in tensile strength, which is essential for the structural performance of RCC.
• As the steel weakens, the structure becomes more vulnerable to cracking and collapse.

2. Expansion and Cracking of Concrete

• When steel corrodes, it produces rust that occupies 2 to 4 times the original volume of the steel.
• This expansion creates internal pressure, which causes cracking and eventually spalling (surface peeling) of concrete.
• Cracks make the concrete more porous, allowing more water and air inside, which accelerates further corrosion.

3. Reduced Bond Strength

• Corroded steel bars lose their grip with the surrounding concrete.
• The bond strength between steel and concrete reduces, causing slippage of reinforcement under load.
• This weakens the load-carrying capacity of the structure.

4. Accelerated Deterioration

• Once corrosion begins, it usually progresses rapidly if not treated.
• The cracks and voids created by corrosion act as entry points for more moisture and harmful chemicals, worsening the condition.
• This results in a cycle of damage that continues unless proper repairs are made.

5. Compromised Load-Carrying Capacity

• Structural elements like beams, columns, and slabs depend on strong reinforcement.
• As corrosion reduces steel area and bond, the element can no longer carry the designed load safely.
• This could lead to structural instability or collapse in severe cases.

6. Decreased Life Span and Increased Maintenance Cost

• Corrosion reduces the life of a structure, sometimes by decades.
• It also leads to expensive maintenance, repair, and rehabilitation work.
• Early detection and treatment are essential to prevent major financial losses.

7. Impacts on Safety and Functionality

• Cracks and spalling from corrosion not only reduce strength but can also affect aesthetics and usability.
• In some cases, it poses a direct safety hazard to users and occupants of the structure.

Conclusion

Reinforcement corrosion severely affects the structural durability of RCC structures by reducing steel strength, creating cracks, and weakening the bond with concrete. Over time, it compromises load-bearing capacity and shortens the life of the structure. Preventing corrosion through quality materials, adequate cover, and timely maintenance is essential for ensuring the long-term safety and reliability of concrete structures.