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Repair of corroded or deteriorated steel reinforcement and prestressing stands is one of the techniques past which deteriorated structural elements are rehabilitated to regain its original load carrying capacity. Corrosion of reinforcements is frequent due to chemic attacks, fire, and accidental cutting.

After the cause of steel damage is determined, it tin be repaired by either replacing deteriorated bars or supplementing partially deteriorated bars. Before commencement of repair process, the reinforcement bars are exposed to evaluate their condition and fix steel confined for the repair methods.

It is necessary to consider proper procedure to expose and gear up damaged steel confined otherwise the repair method would not meet the immovability requirements.

Contents:

  • Procedure for Repair Reinforcements
    • i. Remove Concrete Around Steel Bars
    • 2. Clean and Inspect Reinforcement
    • 3. Mild Reinforcement or Prestressed Strand Repair
    • 3.1 Repair Mild Reinforcements
    • 3.ii Repair Prestressing Steel

Procedure for Repair Reinforcements

1. Remove Concrete Around Steel Confined

The removal of concrete around steel confined should exist conducted cautiously to prevent further damage to reinforcements. This can exist achieved past firstly determining location, depth, size, and ratio of steel confined using bar locator or covermeter, and secondly using proper concrete removal method.

Often, proper shoring should be provided release the fellow member from loads. The shoring has to be checked before physical removal begins. Vibration of reinforcement should be avoided to prevent damage to its bond with physical around repair zone. Moreover, intendance should be expert to avert cut steel confined during concrete removal procedure.

Damaged and lose concrete is removed around steel bars. If all deteriorated concrete is removed and steel confined are partially exposed, then it is non required to remove the unabridged concrete effectually the bars.

However, concrete removal process should continue to clear a space of maximum aggregate size dimension plus 6mm backside steel bars when they should loose rust, corrosion, or not bonded properly to physical.

Exposing Reinforcements
Fig. 1: Exposing Reinforcements

two. Clean and Inspect Reinforcement

After removal of concrete, steel bars are cleaned and advisedly inspected to find out whether they are capable of performing their designed office. Wire brushing tin can exist used if the area cannot be accessed easily otherwise sandblasting is more often than not desired to clean steel bars from droppings and other contaminants.

Damaged Reinforcement
Fig. 1: Damaged Reinforcement

3. Mild Reinforcement or Prestressed Strand Repair

The repair of reinforcements includes the repair of balmy reinforcement and prestressed strand. Replacement of reinforcements or supplemental reinforcements are the two methods which can exist used for both types of steel repair:

iii.1 Repair Mild Reinforcements

Afterward exposing and cleaning reinforcements, a determination should be made whether to supersede steel confined or supplementing partially damaged reinforcements.

A. Replacement of Reinforcements

When replacing reinforcement is selected, deteriorated parts of bars are cut out and so mild reinforcing steels are spliced in. The length of the lap needs to exist according to applicable codes such as ACI 318.

It is possible to use welded splice instead to lap splice. Similarly, weld splice must be conducted according to codes such every bit ACI 318 and American Welding Society.

One should be aware that weld splice is non suitable for bars greater than 25mm. This is because welding process may lead to expand embedded bars and causes cracking of surrounding physical.

Butt welding is usually avoided due to the high degree of skill required to perform a full penetration weld because the dorsum side of a bar is non commonly accessible.

Mechanical connection is another method which tin be used to splice steel bars. It should too adapt the requirements of ACI 318. Commercially bachelor propriety mechanical connection devices tin can be constitute in ACI 339.3R.

Replacement and Coating of Bars
Fig. 3: Replacement and Coating of Bars

B. Supplemental Reinforcements

Supplemental reinforcement is used when embedded steel confined lost cross department or inadequate, or the fellow member need to exist strengthened. It is the responsibility of engineer in charge to decided whether supplemental reinforcement is used or not, and each member need its own decision.

Deteriorated confined should be cleaned and physical need to exist removed to permit the placement of supplemental bars side by side to damaged reinforcement. The length of supplemental bars is equal to the length of deteriorated portion of deteriorated confined plus lap splice length of each side.

Moreover, if coating such as epoxy, polymer cement slurry, or zinc-rich coats is applied to reinforcement to prevent corrosion in the time to come, then coating thickness should be smaller than 0.3mm to refuse lose of bond evolution at the deformations.

Finally, spillage of coating on parent physical should be prevented since it would decrease bond development.

Supplemental Reinforcement
Fig. 4: Supplemental Reinforcement

3.ii Repair Prestressing Steel

Deterioration or damage to the strands or bars can result from affect, blueprint error, overload, corrosion, or fire. Fire may anneal cold-worked, high-strength prestressing steel.

The unbonded high-strength strands may need to exist de-tensioned before repair and re-tensioned after repair to restore the initial structural integrity of the member.

A. Bonded Strands

Because the prestressed strand is bonded, only the exposed and damaged section is restressed following repairs. The repair procedure requires replacing the damaged department with the new section of strand connected to the existing ends of the undamaged strands.

The new strand section and the exposed lengths of the existing strand must be post-tensioned to match the stress level of the bonded strand.

Expose and Clean Tendons
Fig. 5: Expose and Clean Tendons
New Tendons are Installed
Fig. 6: New Tendons are Installed
Post Tensioning Operations
Fig. 7: Mail service Tensioning Operations
Cementitious Materials Poured
Fig. 8: Cementitious Materials Poured

B. Unbonded Tendons

The strands are protected against corrosion by the sheathing, corrosion-inhibiting material, or combination thereof. The master cause of unbonded tendon failure are corrosion of the end connections.

A deteriorated portion of a strand tin can exist exposed by excavating the concrete and cutting the capsule. Unbonded tendons can be tested to verify their ability to carry the design load.

This can exist done by attaching a chuck and coupler to the exposed end of the strand and performing a lift-off test. This usually requires at least 20 mm of free strand beyond the bulkhead.

If there is excessive corrosion in the strand, failure occurs and the strand must be replaced or spliced. Shoring of the span being repaired and adjacent spans upwardly to several bays away may be required before removing or re-tensioning unbonded prestressed strands.

The strand is cut on both sides of the deterioration and the removed portion of the strand is replaced with a new section. The new strand is spliced to the existing strand at the location of the cuts. The repaired strand is then prestressed.

Carbon cobweb or equivalent systems are available to supplement the reinforcement in prestressed, post-tensioned, and mild steel reinforced structures.

This system is normally glued onto the exterior surface. Unless the component being reinforced is unloaded, the strengthening system only provides reinforcement for future loadings.

Fiber wrapping is commonly used for reinforcing columns, especially in convulsion zones. At that place are systems available that recover the dried and damaged protective barrier inside the capsule.