Method Of Concrete Column Repair For Damages and Cracks: Before starting the repair of a concrete column, the axial dead load, axial live load, horizontal load and its associated moments must be known.
Here are the common methods of concrete column repair for damages and cracks:
Encasement or enlargement of the column cross section (jacketing). This method involves encasing the damaged column in a new layer of concrete or another material, such as fiber-reinforced polymer (FRP). This can help to increase the strength and stiffness of the column, and also protect the reinforcing steel from corrosion. Concrete Column Repair
Cathodic protection. This method uses an electrical current to prevent the reinforcing steel in the concrete from corroding. Anodes are attached to the steel, and a cathode is placed in the surrounding concrete. The current flows from the anode to the cathode, and this prevents the formation of rust on the steel. Concrete Column Repair
Re-alkalization. This method is used to reverse the effects of concrete carbonation, which is a process that can lead to the corrosion of the reinforcing steel. A chemical solution is injected into the concrete, which helps to raise the pH level and neutralize the carbonic acid that has caused the concrete to carbonate. Concrete Column Repair1
Chloride extraction. This method is used to remove chloride ions from the concrete. Chloride ions are a major cause of reinforcing steel corrosion, so removing them can help to prevent further corrosion. This method involves injecting a chemical solution into the concrete that can bind to the chloride ions and remove them from the concrete. Concrete Column Repair
Confinement using steel plate, carbon, or glass fiber materials. This method involves wrapping the damaged column with a steel plate, carbon fiber, or glass fiber material. This helps to prevent the concrete from cracking further and also helps to protect the reinforcing steel from corrosion.
Addition of shear collars. This method involves installing steel collars around the damaged column. These collars help to increase the shear capacity of the column and prevent it from failing.
Addition of a steel plate assembly. This method involves installing a steel plate assembly around the damaged column. This assembly helps to increase the moment capacity of the column and prevent it from failing. Concrete Column Repair
Supplemental columns. This method involves installing additional columns to support the damaged column. This is a more drastic measure, but it can be necessary to ensure the safety of the structure.
The best method for repairing a concrete column will depend on the specific damage and the severity of the problem. It is important to consult with a structural engineer to determine the best course of action.
Here are some additional things to consider when choosing a method of concrete column repair:
- The cost of the repair
- The time it will take to complete the repair
- The impact of the repair on the surrounding area
- The likelihood of the repair being successful
It is also important to make sure that the repair method is properly implemented to ensure the long-term safety of the structure.
Repairs to concrete columns can be divided into two categories. Surface or cosmetic repair only covers local deterioration and structural repair restores or strengthens the affected columns. If the deterioration does notsignificantly reduce the cross section, the conventional concrete repair can successfully be employed. Concrete Column Repair
Methods of Concrete Column Repair for Damages and Cracks
Columns may be repaired by using one or more of the following methods:
- Encasement or enlargement of the column cross section (jacketing).
- Cathodic protection to stop reinforcing steel corrosion.
- Re-alkalization of the reinforcing steel to stop corrosion.
- Chloride extraction to retard the reinforcing steel corrosion.
- Confinement using steel plate, carbon, or glass fiber materials. Addition of shear collars to increase the shear capacity of intermediate floors.
- Addition of a steel plate assembly to increase moment capacity.
- Supplemental columns.
- The application of a protection system to prevent future corrosion.
Following parameters are important for the design and the execution of the column repair:
Unloading Columns
In those cases where the column deterioration is significant, unloading the column is usually required so that the entire cross section of the repaired column is capable of carrying the reintroduced design load. Without this unloading, the new repair will hardly carry any load.
Drying shrinkage of new material may further reduce this share of load. Unfortunately, it can be difficult and expensive to unload columns, especially in high-rise buildings. If the existing load on a column is not removedbefore the repair, the jacket will only provide confinement to the existing column. The percentage of direct load taken by jacket will be very small (less than 25 percent of the jacket strength).
If it is not possible to remove the load from the column, then a supplemental column system can provide an alternative method of support in combination with the repair of the existing column.
Redistribution of the Load
In case of corrosion of reinforcement and significant concrete deterioration, the load is redistributed in the structure before repair to a new pattern which must be considered while designing the repair. Even the adjoining members may have been affected by this redistribution.
Supplemental Reinforcing Steel
The column ties can not usually be disturbed during the repair as it may cause buckling of the longitudinal bars. Hence, the supplemental vertical bars may be placed outside the original cage with extra ties. When the supplemental bars are placed outside the tie bars, the column dimensions should be increased to provide adequate over. Hairpin ties, usually of stainless steel, are used to laterally support the supplemental bars. Concrete Column Repair
Concrete Removal
The removal of concrete within a column cage must only be done if the column is unloaded. Otherwise, the longitudinal bars may buckle and compression failure of column may take place.
Corroded Reinforcing Steel
It is not necessary to remove the corroded reinforcing bar with reduced cross-sectional area if the loss is supplemented with additional reinforcing bars. The lap length of such a splice must be provided corresponding to the area lost by corrosion to either side of the corroded portion of the reinforcing bar that is supplemented.
The partially corroded reinforcing bars that are left in place must be thoroughly cleaned by sandblasting to obtainable metal. The bars with excessive corrosion must be replaced with fresh reinforcement having full laps on both sides. Concrete Column Repair
Corroded Ties
The corroded ties can be replaced by adding stainless steel hairpin ties that are anchored into the concrete. It is often necessary to deposit extra material around columns to provide adequate cover over the supplemental ties.
Low-strength Concrete
Where the concrete strength is low, resulting in insufficient load-carrying capacity, several alternatives are available:
- Shore the column and remove and replace the in-place concrete.
- Shore the column and increase the size of the column to reduce the bending stresses, and to increase the confinement on already placed weak concrete.
- Wrap the column with carbon- or glass-reinforced plastic.
- Install a supplemental column.
