Though concrete structures are very strong, especially if reinforced with Thermo-Mechanically-Treated (TMT) iron rods, they usually fail prematurely if proper care and attention is not given to it.

Structural failure is the inability of a concrete structure to meet up with its intended performance, response and behavior under all expected environmental conditions. Structural failure shows its ugly head in form of unwanted deformations, cracking, spalling, severe honeycombing, displacement of supports and eventual collapse.

Some of the factors often responsible for the failure are use of inferior iron rods, corrosion, insufficient reinforcement, exposure to extreme temperature, structural damage, fire hazard, seismic damage, weather exposure, chemical damage and others. These factors are either environmental or production-induced.

When deterioration or damage occurs in concrete structures, the damaged members need to be replaced. However, before replacement is carried out, the existing structural elements should be demolished and removed to pave way for replacement.

Factors to Consider Before Replacing Damaged Concrete Members

The damaged existing structural members are only demolished after proper application of jacking to relieve imposed loads on them. The demolition should be done carefully in order not to damage existing iron rods.

Also, the structural members such as beam, columns, walls and braces which have been severely damaged should be completely replaced. Efforts should be geared towards replacing the damaged members with new ones that possess equal or higher strength.

This technique is used to repair and strengthen deteriorated buildings as well as to increase the lifespan of structures.

The engineers select repair materials that meet specifications and recommendations of applicable codes.

Replacement Procedure

• If the damaged structural member is load-bearing, shoring needs to be provided adjacent to it to withstand loads while the member is demolished and not present to carry the loads.
• The structural member must be carefully demolished using proper tools such as saws and chipping tools.
• If present, steel bars should not be damaged in order to splice them with new steel reinforcements which are going to be installed for the new structural member.
• The surface of the surrounding structure should be prepared to make sure adequate bond is generated between existing and new materials, for example, roughening surfaces.
• New reinforcing bars should be spliced to existing bars.
• If new reinforcing bars are required to be attached to the existing structure, these bars should be anchored to the existing structure by setting them into holes with epoxy.
• The depth of the holes needs to be adequate in order to make sure that the full potential of the steel bars is utilized. It is advised to consulate epoxy manufacturer for the proper depth of the bar and for the instructions for installing the epoxy.
• The new concrete can be poured using suitable means. For example, using formworks, or applying shotcrete.
• If formworks are employed, fresh concrete is poured through an access hole near the top of the formwork, and extra holes may be required to provide access for vibrators to consolidate concrete.
• Finally, proper curing regime is used to make sure that concrete achieves the designated strength.

Conclusion

Due to the fact that newly placed concrete would inevitably experience shrinkage and existing concrete would not undergo any movement, the concrete of new constructed member would develop cracks.

These cracks need to be repaired after significant amount of shrinkage has occurred for instance after two to four months. The shrinkage cracks should be repaired using epoxy or any other suitable repair materials.