The basic repair procedures and materials for underwater concrete structures are similar to that of a typical concrete repair. But, conducting the repair procedures underwater brings many complex problems. The underwater concrete repair procedures are performed by highly qualified and experienced professionals, whose details and requirements are provided in ACI SP-8 and SP-65.
Before the repair of underwater concrete, proper evaluation of the present condition of the structure is essential for designing long-term repairs.
Steps in the Repair of Underwater Concrete
- Evaluation and Inspection of Underwater Concrete
- Preparation for Repair
- Formworks
- Repairing of Underwater Concrete
- Final Inspection of Repairs
Repair of Underwater Concrete
After proper preparation of the repair area, and providing proper formwork support, a suitable repair method with respective material is used to rehabilitate the structure.
The method used to repair underwater concrete is dependent on the type of repair. For example, a minor spall or crack can be repaired by a simple patch or crack injection system. For large repair works, where the load-carrying capacity of that element must be regained, the repair method must bring a new load path around the damaged areas.
Following methods and materials are used for the repair of underwater concrete:
- Preplaced Aggregate Concrete
- Tremie Concrete
- Pumped Concrete and Grout
- Free Dump Through Water
- Epoxy Grouting
- Epoxy Injection
- Hand Placement
- Concrete with Anti-Washout Admixtures
1. Preplaced Aggregate Concrete
Applications
- repairing railway and highway bridge piers
- for encasing and underpinning piers weakened by such factors as weathering, riverbed scour, exposed piling or cribbing, floating ice, and overloading
- repair of piers supporting control gates on spillways and hydroelectric outlet structures that have suffered damage from ice abrasion or freezing and thawing.
Procedure
- In this method, all the damaged or weakened concrete is initially removed to a predetermined depth or until a sound material is formed (which is greater). The corroded reinforcement rust is removed, or the bar is replaced or supplemented as the situation requires.
- Forms are placed and sealed at joints and at points of contact with concrete surfaces.
- Now, coarse aggregate is poured in the form of 2 to 4 ft lifts to avoid segregation.
- Next, the grout is pumped into the preplaced aggregate starting at the lowest points. It is pumped either through the forms or through preplaced vertical pipes as given in ACI 304R.
- Once the forms are full, it is a good practice to spill some grout over the top or through vent holes or a venting section at the top of the form, to expel out trapped air, water, or diluted grout.
- Once the concrete has achieved adequate strength, the form is removed.
2. Tremie Concrete
Applications
- At Tarbela Dam more than 90,000 yd3 (68,800 m3 ) of tremie concrete were placed to repair damage caused by cavitation (Holland, 1996).
- The Corps of Engineers has used tremie concrete to repair damage to stilling basins at several of its structures (McDonald, 1980).
- best suited for larger-volume repair placements where the tremie does not need to be relocated frequently, or for deeper placements where pumping is impractical.
Installation Procedures
- For successful tremie concreting, the concrete in the tremie must be separately placed from water.
- Once the concreting starts, the tremie must stay embedded in the concrete to prevent concrete from dropping into water or getting dispersed.
- ACI 304 R provides recommendations for tremie placement for concrete.
3. Pumped Concrete and Grout
Applications
- It can be used in most applications where tremie concrete is applicable but has the added advantage of having a smaller, more flexible hose that can reach difficult locations.
- Grouts are most commonly used to fill voids between concrete and forms or jackets such as in pile repair.
- repair smaller voids and larger cracks in and under concrete structures.
Installation Procedures
- The initial concrete or grout that is placed at the start of the pumping from the water and upon maintaining is separated throughout the placement.
- The separation must be reestablished whenever the pump outlet is relocated
4. Free Dump Through Water
Applications
- placing concrete containing anti-washout admixture underwater in new construction and repairing old concrete.
5. Epoxy Grouting
Applications
- Plastic jackets and underwater-curable, epoxy-resin systems are used for the repair of eroded or structurally damaged splash zone concrete and underwater concrete structures.
- Epoxy systems are used for patching, grouting, and crack repair.
- They are also used to bond such items as anchor bolts reinforcing steel, and protective safety devices to concrete under water.
- underwater Underwater-curable epoxy coatings are used to provide protection to concrete and other building materials from erosion and aggressive waters.
6. Epoxy Injection
Applications
- Non-moving joints can be bonded together with epoxy resins, just like a crack.
- Anchor bolts and reinforcing steel can be grouted into concrete structures in the splash zone and underwater with the injection process