The primary cause of steel corrosion in concrete is due to carbonation or chloride. Corrosion is the electro-chemical process that results in the formation of rust. The amount of rust formed due to steel corrosion is greater than the amount of original steel. This increase in the amount of steel inside the concrete creates cracks in the concrete. Sometimes this causes the concrete cover to collapse.

step by step process

The following step by step procedure will guide you to repair RC beam and column damage potion.

step 1 (provide support)

Beams and columns carry heavy loads. So the first step is to relieve part of its load. This is done by providing supports or props at the beam column joints. Remove the damaged concrete until the steel reinforcement is no longer visible.

step 2 (Cause Analysis)

In this step, the steel is checked for the type of rust. it is done by phenolphthalein test, This test will help to find out whether it is carbon induced corrosion or chloride induced corrosion.

pay attention:

  • Here we are dealing with only carbon induced corrosion of steel. Because chloride induced corrosion is difficult to identify and it calls for replacement of entire concrete near steel.

step 3 (proper chipping)

If the steel is completely corroded, remove 15 mm to 25 mm of concrete around the steel. This will help to clean the steel thoroughly and all-round.

step 4 (clean)

Clean concrete and steel surfaces thoroughly using water or any rust removal solution.

Step-5 (new steel fixing)

Check the percentage of steel corrosion. If 15% or more of the steel is affected by rust, bond the excess steel to the old steel. We can also weld to old steel instead of bonding it. Apply the necessary shear reinforcement to the beams and binders to the pillars.

step rate 6 (apply bonding coat)

After fixing the excess steel with the old steel, apply an appropriate bonding coat to the surface of the old concrete and steel. Bonding coats are used to bond the new concrete to the old concrete. The 4 categories of bonding coats commonly used for repair works are as follows:

  • epoxy based bonding coat
  • acrylic based bonding coat
  • Styrene Butadiene Rubber (SBR) Based Bonding Coat
  • Lingosulfate Based Bonding Coat

Step-7 (Formwork vs. Wire Mesh)

If the amount of the beam or the damaged part of the column is too large, it is suggested to assemble the formwork for the column and use expanded wire mesh for the beam.

Step-8 (place new concrete)

Prepare a fine-grained concrete mix composed of cement, sand, coarse aggregates (size 10 mm and below) and super-plasticizers. The water-cement ratio should not exceed 0.5. Place this concrete within the spaces in the member. Remember that the concrete must be poured before the bonding coat dries.

pay attention:

  • If the area to be repaired is small, use polymer modified cement mortar instead of concrete.
  • In case of large area repair work, shotcrete/gunite The method of pouring concrete is suggested.

Step-9 (apply finishing coat)

Apply cement plaster of proportion 1:3 (Cement : Sand) As a finishing coat. This must be done within 48 hours of placing the concrete.

Step-10 (Treatment)

Carry out repair work for at least 7 days.

Step-11 (waterproof coat)

To protect the repaired member from further attack by water, apply a final coat of waterproof paint to the surface of the member.

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.