Process for Repair of Shear Cracked Beam

1. Remove the loose concrete by means of hammer and pack the concrete by means of low viscous epoxy injection grouting using 12mm dia NRV nozzles.
2. Patch repair the area as per following steps:-

1. Target the damaged area and remove the unsound concrete from the surface using a chipping hammer. The cut should be made in order to remove all the loose concrete and also draft should be given for better bonding of new material. Mark the perimeter of the repair area and give it a simple geometric shape like square or rectangular using a saw cutter. Cut 250 mm extra sound concrete around the spalled/damaged area. Refer image below for better understanding.

• Rub the rusted reinforcement bar with wire brush and wash it as necessary. Given conditions may be followed depending on repair area:-
• Repair area is large (greater than 5 sqm) use abrasive material along with rust remover chemical (Pidilite or Equivalent) for rubbing the corroded steel bar. Apply rust remover spray on corroded steel bars in order to completely scrap off the rust and corrosion generating chemical agents.
• Repair area is small (less than 10 sqm) use water jet only.

• Now the diameter loss of reinforcement is checked. Solution to this can be provided as if:-
• Diameter loss is less than 20%, then additional steel of the type originally used is welded to the place where corrosion has occurred. The amount of steel reinforcement added is same as loss %.
• Diameter Loss is 20%-40%, then additional steel is added to the entire reinforcement of same diameter and lap length of 50 X diameter of bar.
• Diameter loss is greater than 40% patch repair method is ineffective and not recommended and structure repair methods are used after complete structural adequacy analysis.

• Apply anti-corrosive zinc coating/Primer to the old as well as newly added reinforcement bars to prevent further rusting.
• In order to increase its adhesive properties between new and old concrete, epoxy or acrylic based adhesives can be used (Fosroc-Nito Bond EP or Equivalent). For smaller regions acrylic bonding agent is used and for larger sections epoxy bonding agent is used. This helps in binding the new incoming surface (old hardened concrete and green concrete/repairing mortar) and helps in improving surface strain carrying capacity.
• If the filling depth is less than 25mm, filling is done in single layer of PMC (Polymer Modified Concrete/Mortar of Fosroc or Equivalent). Else up to 50 mm depth, a layer of 25mm PMC is filled and when it is about to settle, another layer of epoxy adhesive is laid and new layer of PMC is applied. But when the filling depth is between 50mm to 100mm spalled section is filled with self-compacting micro concrete with help of designed shuttering plates. If required filling depth is more than 100mm then, spalled section should be filled with micro concrete mixed with 4mm-6mm crushed course aggregates.

3. Once the patch repair work is completed now strengthen the beam as per following steps:

3.1 Removal of loose concrete from the member so as to prevent from the deterioration or de-bonding issues that entire loose particle from the concrete should  remove  below 25mm from  beams junction. After removal of  loose concrete entire surface should be wetted by spraying water. Propped the slab during chipping by hydraulic jacts at 1 @1sqm each.

3.2 After the removal of the loose mass of concrete for surface preparation the existing reinforcement is exposed to the atmosphere which is treated with the anti-corrosive treatment to avoid corrosion in the steel.

3.3 Based on the design aspect additional reinforcement is added to beam with maintaining of proper alignment and cover with a lap length of 50Xdia of bar= 1 meters.

3.4 After anti-corrosive treatment to existing reinforcement, the Nito Bond EP Chemical is applied to the old concrete to prepare a bond between the old and new placed concrete.

3.5 After the application of the nito bond ep the the ties and shear connector should be laid as per design.

3.6 Placing of Concrete M25 through guniting is carried as per required thickness based on design aspect.

3.7 Once the guniting done after period it should be de-shutter the joints of the shuttering occurs in column it should be filled with cement mortar layer .

3.8 For imparting durability water should be properly cured to casting surface that it should achieve strength. At suitable intervals curing of the surface to be done.