Bridge Repair and Maintenance is very important after completion and commissioning of the structure, various operations that may be required to do on it are:
- Maintenance and repair-to preserve the intended load-carrying capacity and to ensure correct functioning, durability, aesthetic appearance and continuity of safety
- Rehabilitation-restoring the structure to the original service level it once had but has now lost due to some reasons or other
- Improvements – for upgrading the service level viz.
(i) Increasing the load-carrying capacity
(ii) Increase in deck width
- Replacement or reconstruction – These works are required to be carried out when the whole structure or at least its major components are required to be replaced, being beyond the economic level of repairs/rehabilitation.
Damage analysis of structure before Bridge Repair and Maintenance Work:
- Before any kind of repair or rehabilitation related work, it is necessary to find out the cause of damage, and the area or extent of damage to the structure must be determined
- Otherwise, repair has to be carried out soon
- Investigation of the causes of the damages is done by collecting information, by visual observations, studying records and asking questions, supplemented by a laboratory and field testing and finally interpreting the information collected
- Investigations must include defects relating to materials, construction, design, etc.
- The answer to the following question should be available
- How long have the signs of damage been noticed?
- Have the signs changed with time?
- Was assumed loading in design, specifications complete and correct?
- Were there any special kind of occurrences, omissions during the construction?
- Could some defects have been ignored or unknown during construction?
Condition assessment for Bridge Repair and Maintenance:
The analysis of the results of the condition survey, detailed investigation and structural assessment should enable the engineer to know:
- Whether there is any risk of failure of the damaged structure.
- Whether damages are likely to develop further with time
- Whether or not an economically efficient repair plan can limit or carry damages and improve the effective service life of a structure
- Degree of urgency required in implementing repair
- Is it necessary to carry tests to ascertain load carrying capacity
Bridge Repair and Maintenance Plan:
The data from investigations form the basis of the following decision:
- Total replacement of the structural component in case the damages are found to be too extensive
- Partial replacement of the structural component and repair based on the severity of localized damage
- Extensive rehabilitation and/or strengthening
- Minor repairs
Flow Chart for a systematic approach for assessment of distress/ deterioration:
Bridge Repair and Maintenance for Foundation and Protection Works:
- Bridges with shallow foundations should be protected by stone or CC flooring with drop walls or curtain walls to protect the foundation from scour
- If heavy scour is noticed on the downstream of the drop walls, scour hole should be filled with boulders or wire crate filled with boulders
- The river bed between piers should not be pitched
- If warranted, piers and abutments can be protected individually by pitching stones around them.
- In very severe cases of scouring, piles are driven concentric to the foundation with boulders dumped in-between
Bridge Repair and Maintenance for Substructures:
The substructure may develop various kind of defects. The name of the defects and their remedies are:
- If the weathering is not deep, plastering with cement mortar will suffice
- Otherwise, guniting or cement or epoxy grouting may be resorted to
Leaching of Mortar:
- In the case of deep leaching, grouting by cement or epoxy mortar will be effective
Leaning / Bulging of Abutments, Wing Walls & Return Walls:
- Choked weep wholes should be cleaned to avoid build-up of hydrostatic pressure; if required, additional weep holes should be provided
- Backfill material may be changed with the proper filter medium to reduce the earth pressure
- If leaning is due to undermining/scour, it can be tackled as per maintenance of foundation stated above.
Cracks in Concrete:
- Vertical Cracks: may occur due to differential settlement of the foundation or excessive shearing stresses in the substructure. The cracks should be monitored with tell tales. If signs of propagation noted, a detailed study should be made to identify the causes before taking remedial measures.
- Horizontal Cracks: These are more serious, and these could be due to inadequacy of section, defect in construction, failure of backfill drainage or excessive horizontal loads etc. The remedial measures should be decided after identifying the cause. Generally grouting with cement or epoxy mortar and jacketing are used as remedial measures.
Common Repair Technique for Bridge Repair and Maintenance:
Cement Pressure Grouting:
- When cracks are dormant
- Cracks are active but cause determined and remedial action has been taken
- When the honeycomb is present in concrete structures
- Drill holes in structure along cracks
- Fix GI pipes in holes with rich cement mortar
- All cracks are sealed with rich cement mortar
- All holes except the adjacent ones plugged with a wooden plug
- Water injected in the bottom-most hole (1) under pressure
- When the clear water comes out through 2 and 9, the injection of water is stopped, and the plugs 1 and 9 are restored
- The process is repeated until all the holes are covered
- The same sequence is adopted for injecting the cement grout
- Allow curing for ten days
Epoxy is quick setting, low shrinkage, excellent adhesion, high strength, low viscosity to penetrate even hair crack
- The area to be grouted should be dry and free from oil, grease, dust and all loose and unsound materials
- The crack be cut open to a ‘V’ groove about 10mm deep Remove loose material by compressed air and seal groove fully using epoxy mortar at least one day in advance
- Drive nails into the cracks at 15 cm to 50cm interval along the crack
- Holes of 7 – 10 mm dia are drilled along the cracks and copper or pipe pieces of 6 – 9 mm dia is fixed as grout nipples around the nails
- The epoxy formulation is injected from the bottom-most pipe, keeping all other pipes, except the adjacent ones, blocked by wooden plugs – Measurement of crack repair is based on the quantity of epoxy consumed
Jacketing of Piers:
Shotcreting or Guniting:
- It is generally used for repair of large horizontal or vertical spalled concrete surface area like bridge deck, pier/abutment surface, etc.
- Shotcrete is mortar or concrete sent through a hosepipe and is pneumatically struck at high velocity on to the surface to be treated
- The force of the jet impinging on the surface compacts the material
- Generally, a relatively dry mixture is used so that it supports by itself without sagging or sloughing even for vertical and overhead applications