What is jacketing in RCC retrofitting?

Short Answer:

Jacketing in RCC retrofitting is a method used to strengthen and repair weak or damaged concrete members like columns, beams, and slabs. It involves adding a new layer of concrete, along with extra reinforcement, around the existing structural member to increase its load-carrying capacity and restore stability.

This technique is very useful in improving the performance of structures affected by aging, overloading, corrosion, or earthquakes. Jacketing provides confinement to the existing member, enhances durability, and helps in preventing future damage, especially in areas where reconstruction is difficult or costly.

Detailed Explanation:

Jacketing in RCC retrofitting

Jacketing is one of the most commonly used techniques in RCC retrofitting to strengthen and restore the original strength of deteriorated structural elements. Over time, structures may show signs of distress due to environmental exposure, corrosion of reinforcement, increased loading, or poor construction practices. Instead of replacing the entire element, jacketing allows strengthening in place.

Jacketing involves enclosing the existing RCC member with a new layer of concrete or steel along with additional reinforcement. The main goal is to improve the structural performance by increasing the size, stiffness, and load-carrying capacity of the element. It also helps to reduce deflection, control cracking, and enhance the life of the structure.

Types of Jacketing

There are mainly three types of jacketing used in RCC retrofitting:

  1. Concrete Jacketing
    • This is the most widely used method.
    • A new layer of concrete (usually 100 mm to 150 mm thick) with vertical and transverse steel is added around the existing member.
    • Before concreting, the old surface is roughened and cleaned, and bonding agents like epoxy or cement slurry are applied.
    • The new reinforcement is tied with the old one to work together under load.
  2. Steel Jacketing
    • Steel plates or angles are fixed around the member using bolts or welding.
    • The steel casing is then filled with grout to ensure proper bonding.
    • It is mostly used in urgent strengthening where time is limited or in industrial structures.
  3. FRP Jacketing (Fiber-Reinforced Polymer)
    • FRP sheets are wrapped around the member to provide additional strength and confinement.
    • It is lightweight, corrosion-resistant, and ideal for quick retrofitting.
    • Suitable for seismic zones and areas with space constraints.

Applications of Jacketing

  • Strengthening of columns that have lost strength due to corrosion.
  • Enhancing the load-carrying capacity of members in case of design changes or added floors.
  • Repairing earthquake-damaged structures by increasing ductility.
  • Extending the life of old buildings without dismantling.

Advantages of Jacketing

  • Improves Strength and Stability: Increases cross-section and reinforcement, making the member stronger.
  • Cost-Effective: Avoids demolition and full reconstruction.
  • Versatile: Can be applied to columns, beams, and slabs.
  • Fast Repair: Especially in steel and FRP jacketing, work can be done quickly.
  • Suitable for Emergency Repairs: Can be used in damaged buildings after disasters.

Important Considerations

  • Proper surface preparation is necessary for effective bonding.
  • Adequate curing is required for strength gain in concrete jacketing.
  • The compatibility of materials (old and new) must be ensured.
  • Experienced supervision is required for correct execution.

Jacketing is widely used in retrofitting of old buildings, bridges, parking structures, industrial sheds, and earthquake-affected structures. With correct planning and execution, it provides a long-lasting and reliable solution for structural rehabilitation.

Conclusion:

Jacketing in RCC retrofitting is a simple and effective method to increase the strength, durability, and performance of damaged or weak structural members. It involves surrounding the existing element with new concrete, steel, or FRP layers to improve its load capacity. Jacketing is suitable for columns, beams, and slabs, and is widely used in both regular and emergency retrofitting works. It extends the life of structures without costly reconstruction.