Methodology on Repair / Rehabilitation of Existing Bridge Structures

The current methodology may be referred for the repair, rehabilitation and strengthening of the existing bridge structures. It shall be read in conjunction with the provisions specified in IRC SP: 40-1993 (Guidelines for Techniques for Strengthening and Rehabilitation of Bridges) for detailed understanding and implementation.

The broad methodology for repair and rehabilitation of existing structures along the project highway is described below:

1. Repair / Remedial Measures for Concrete Crash Barriers & Parapets

Observation

The crash barriers / parapets are generally well constructed and erected at site. However, at some locations improper finishing and partial damages have been observed.

Remedial Measures

• Surface Preparation: The damaged surface shall be prepared by mechanical methods such as chipping, sand blasting and compressed air cleaning.
• Minor Surface Repair: Edges and minor damaged portions of crash barriers / parapets shall be repaired using 1:4 cement mortar.
• Major Surface Repair: For severely damaged portions, repairs shall be carried out using concrete of same or higher grade matching the existing material. If the damage is extensive, the affected portion shall be demolished and reconstructed.

2. Restoration of Rusted / Exposed Reinforcement of Slab

Observation

Overall condition of slab is satisfactory; however, at some locations the concrete cover has spalled off exposing reinforcement bars to atmosphere.

Remedial Measures

• Surface Preparation: Concrete cover shall be removed by chipping, sand blasting and compressed air cleaning until reinforcement is fully exposed.
• Repair Procedure:
  • Rust from reinforcement shall be removed using sand blasting, wire brushing or needle hammer.
  • Reinforcement shall be protected against corrosion by epoxy coating or alkaline cementitious bond coat.
  • Where sufficient thickness is available, damaged portions shall be repaired using concrete one grade higher than the existing concrete.
  • If sufficient thickness is not available, polymer cement mortar shall be used.

3. Repair of Foundation

General methodology for repair and strengthening of foundations depends upon the site conditions and nature of distress.

Typical Repairs

• Scour and erosion protection.
• Repair of washed away or damaged protection works.
• Repair of foundations on soft ground subjected to erosion.
• Repair of serrated surfaces caused by high velocity flow carrying abrasive particles.

Observation

Excessive scour is one of the major causes of structural distress or failure in bridge foundations. The extent of damage depends upon stream bed material, discharge intensity, silt content, flow obliquity and shape of structure.

Remedial Measures

Scour around pier foundations shall be controlled using garlanding techniques by placing heavy concrete blocks, stone boulders, sheet piling or stone pitching around the foundation.

4. Repair of Substructure of Minor Bridges

Observation

Deterioration of joints, spalling and disintegration of abutment wall surfaces have been observed.

Remedial Measures

Damaged joints shall be repaired by epoxy mortar injection, surface protection treatment and plastering with 1:4 cement mortar on the affected surfaces.

5. Repair of Concrete

For partial depth repairs, deteriorated concrete shall be removed up to 75 mm to 100 mm depth and approximately 1 m × 1 m area depending upon extent of damage.

The repaired area shall be filled with elastomeric concrete or polymer concrete of one grade higher than existing concrete. Chicken mesh reinforcement fixed using U-clips shall be provided to improve bonding and durability.

6. Repair of Cracks

Observation

Cracks shall be examined to determine whether they are active or dormant.

Remedial Measures

• Active Cracks: Repair by stitching, jacketing, epoxy injection and epoxy mortar treatment.
• Dormant Cracks: Repair by grouting, jacketing and thin resurfacing treatment.

7. Repair of Drainage Spouts

Repair or replacement of drainage spouts shall be carried out based on actual site condition and approved drawings.

8. Replacement of Approach Slab

Replacement of approach slab shall be decided based on site condition, structural distress and recommendations of the Engineer.

9. Repair / Replacement of Bearings & Expansion Joints

Repair or replacement of bearings and expansion joints shall be carried out strictly in accordance with manufacturer’s specifications, approved drawings and vendor recommendations.