Reinforcement steel or rebar is a major material of construction. It is almost impossible to construct any structure without steel. Nowadays most of the old buildings or houses are deteriorating and their service life is also getting reduced day by day. In many cities, due to the scarcity of land, experts have started a new trend. They repair or rehab the buildings or houses and make them stable for few more years for use. Repairing begins with the determination of the causes of damage, evaluation of the extent of damage, evaluation of residual strength, estimate of additional strength needed, selection of repair material, selection of repairing methods, and it ends with the execution of repairing methods and testing. We have already discussed the right steps for repairing of a concrete structure.
During the repairing of concrete, reinforcement steel needs to be prepared first before you execute any repairing methods. Reinforcement steel is one of the most important components which provides strength to the building or house. Hence repair corroded steel in concrete and proper care should be taken towards reinforcement steel while you carry out the repair.
Removing Concrete Around Steel
Corroded Steel in Concrete
The reinforcement steel gets exposed during the repair, and it requires special treatment. When reinforcement steel gets exposed for more than one-third of its periphery, then concrete should be entirely removed from around the steel. Sometimes when concrete is subjected to load, the concrete should be removed at least equal to nominal maximum size of the aggregates of the repair material plus one-fourth inch (6 mm) deep. Otherwise, it is advisable that the concrete should be removed at least 1 inch (25 mm) deep.
Also Read: Classification of Loads on Structure
Most of the time, reinforcement steel will have rust. In this case, it should be fully exposed, and surrounding loose concrete must be removed. The reinforcement steel should be exposed up to the extent where the concrete is well bonded to the steel, or steel is not affected by corrosion. There are many causes of corrosion in concrete, i.e. moisture, leakages, an inadequacy of concrete cover, effect of chemicals, etc. It is also necessary to evaluate the causes of corrosion. If the corrosion is a result of chloride contamination, it is advisable to remove all the affected concrete or consult the structural consultant. If you do not remove contaminated concrete, there is a chance of redevelopment of corrosion, and the time and efforts towards repairing will become unproductive.
Cleaning of Reinforcement
The loose concrete, scale, rust around the steel should be removed by wire brush and If possible, use high pressure water jet or sandblasting. It is not necessary to clean the steel to a new metal condition, just remove all the loose or poorly bonded concrete as it affects the bond between the repair material and the reinforcement steel. Nowadays chemicals are also used for removing rust. Refer following table.
|Name of Construction Chemical||Product Description||Make||Prize|
|Sika Rustoff 100||Rust remover and passivation||Sika India Pvt. Ltd.||Rs 350/Kilogram|
|Dr. Fixit Rust Remover||Liquid for cleaning re-bars & steel surfaces||Pidilite Industries Limited||Rs 200/litre|
|Reebaklens||Reebaklens is a combination of acid based material, corrosion inhibitors and dispersing agents and is supplied as a clear blue solution.||Fosroc Chemicals (India) Pvt. Ltd.||Rs 3,000/Unit|
Due to the corrosion,
If the cross-section of reinforcement steel has got reduced up to 80 percent of original diameter, it is advisable to consult with the structural engineer as soon as possible.
You can carry out work by simply replacing the corroded bars with rebaring method, if the repairing work is small. i.e. small patch repair or where RCC member does not transfer major load.
Rearing method is a technique which helps to place the new reinforcement steel in the concrete in place of old reinforcement steel without breaking concrete. Always use it for important structure and where loss of area is substantial. i.e. around 50%
If the diameter of exposed steel is allowable, then carry out cleaning work and apply rust remover and anti-corrosive coating on steel. Apply bonding agent on the concrete. It helps to achieve good bonding between old concrete and new concrete.
Location of Corroded Steel
Sometimes location of corroded steel plays an important role. i.e. if the corrosion is found in the stirrups at the junction of beam and column, it needs to be repaired as soon as possible as everyone knows that the junction of beam and column is a very critical portion of a structure. It is serious and add new stirrups by rebaring. Except that, you can carry out repair if the area is small and corrosion is in a moderate limit.
Whether the repairing work is small or large, it is necessary to prepare the reinforcement steel as mentioned above. Remember that the good repair always saves your time, effort and cost, if you do it properly.
But if you repair corrosion affected concrete without removing rust, the repair is meaningless and cracks and spalling will occur again.