5 Maintenance and repair methods for RCC Construction

 

5.1 Repair Stages

To ensure durability and effectiveness, RCC repairs must follow systematic stages:

1. Concrete Removal and Surface Preparation

• Damaged, loose, or cracked concrete is removed by chipping, saw-cutting, or hydro-demolition.

• Removal should expose clean, rust-free reinforcement.

• Surface prep includes:

  • Cleaning with wire brush, air blower, or water jet.

  • Roughening the surface to improve bonding.

2. Fixing Suitable Formwork

• Formwork holds the repair material until it sets.

• Should be leak-proof, strong, and easy to remove.

• Used especially in vertical or overhead patching.

3. Bonding/Passive Coat Application

• Apply bonding agents (e.g., epoxy resin) between old and new concrete to improve adhesion.

• Apply passivating coat (zinc-rich or polymer coating) on rebars to prevent corrosion.

4. Repair Material Application

• Use non-shrink repair mortar, polymer concrete, or epoxy mortar depending on damage type.

• Compaction and curing are critical to performance.

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5.2 Repair Options

1. Grouting

• Low-viscosity cementitious or chemical grout is injected into cracks/voids.

• Restores integrity and prevents further water ingress.

2. Patch Repairs

• Suitable for localized spalling or honeycombing.

• Involves removal of damaged concrete and recasting with compatible mortar.

3. Carbonated Concrete Repair

• Carbonation reduces concrete pH, leading to rebar corrosion.

• Steps:

  • Remove carbonated layer.

  • Apply alkaline repair mortar or coating.

  • Protect rebars with anti-corrosion agents.

4. Cleaning Corroded Steel

• Manual (wire brushing), mechanical, or sand blasting used to remove rust.

• Apply zinc-rich primer or epoxy to prevent re-corrosion.

5. Concrete Overlays

• Apply new concrete layer over existing surface.

• Improves load-carrying capacity.

• Requires excellent surface preparation and bonding.

6. Latex Concrete

• Latex-modified concrete has better flexibility and bonding.

• Suitable for water-retaining structures or floor overlays.

7. Epoxy Bonded Mortar/Concrete

• Epoxy acts as both binder and structural adhesive.

• High strength, excellent for crack injection and bonding new concrete to old.

8. Polymer Concrete

• Uses resin (e.g., polyester/epoxy) instead of cement.

• High strength, chemical-resistant—used in industrial areas.

9. Corrosion Protection (Jacketing)

• Reinforced concrete or steel jacket added around structural members.

• Purpose: Increase strength, protect rebar, and prevent failure.

• Used for columns, beams, piers.

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5.3 Building Cracks and Prevention

Cracks in RCC occur due to shrinkage, thermal movement, load, or corrosion.

Dormant Crack Repair (Inactive cracks)

Cracks that no longer expand can be sealed and repaired.

Common methods:

1. Epoxy Injection:

   • Inject low-viscosity epoxy resin into fine cracks.

   • Provides monolithic restoration of strength.

2. Grooving and Sealing:

   • Crack edges are cut, cleaned, and filled with flexible sealant.

   • Used for non-structural surface cracks.

3. Stitching:

   • Steel “U” shaped bars installed across crack.

   • Prevents further crack opening.

   • Embedded in epoxy or non-shrink grout.

4. Grouting:

   • For wider cracks or honeycombing.

   • Can be cement-based, polymer, or epoxy grout.

5. Guniting / Shotcreting:

   • High-pressure spraying of mortar or concrete.

   • Used for large surface restoration (walls, beams).

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5.4 Strengthening Methods for Live Cracks

Live cracks are active and need structural interventions to stop movement and restore strength.

1. Addition of Reinforcements

• Extra rebars or steel meshes added during repair.

• Used in beams, slabs, and joints.

2. Jacketing

• RCC or steel jacket added to column or beam to increase cross-section and load capacity.

• Example: RCC jacketing for earthquake-damaged column.

3. Brackets & Collars

• Steel brackets provide support at beam-column joints.

• Collars are used at column bases or beam ends to prevent buckling and rotation.

4. Supplementary Members

• Shoring: Temporary vertical support to relieve structural load.

• Underpinning: Strengthening of foundation to stop settlement or cracks.

• Propping: Temporary or permanent supports to carry load during repair.