How to Repair Rc beams and columns Damaged by steel corrosion? - Homeslibro - HOMESLIBRO

In this article, we will explain the repair process for Reinforced concrete beams and columns damaged by steel corrosion where the depth of the affected concrete has reached the reinforcement level. As the amount of steel rust exceeds that of the original steel, the concrete around the steel cracks. In some cases, the cover concrete may fall off. Corrosion can be caused by carbonation or chloride.

The following procedure is followed to repair these reinforced concrete members. The main difference between slabs from columns and beams is that for the latter, a more elaborate formwork must be used to place the concrete. Otherwise, we can place concrete with shotcrete

Repair of Cracks in Beams and Columns when Corrosion has Reached Reinforcement Level

Step 1: As these members carry heavy loads, first support the beam and column using supports to relieve part of its load. Then, remove the damaged concrete to expose the steel.

Step 2: Investigate the type of corrosion with phenolphthalein tests to determine whether the corrosion is due to carbonation or chloride effect. Also, determine the depth to which erosion has continued. If it's due to carbonation, it's worth fixing. But if it is due to chloride corrosion, the same corrosion can occur elsewhere if the concrete near the steel is not completely replaced. Here, we assume that carbonation is the only cause of corrosion.

Step 3: If the steel is completely corroded, remove 15mm to 25mm of concrete from the entire steel.

Step 4: Clean the concrete surface and steel surface thoroughly with water. A rust removal solution can also be used for steel. It dissolves the rust and adheres to the steel as a coating.

Step 5: When the steel is reduced by about 15% due to corrosion, place the necessary additional steel and bond it properly with the old steel or additional support. New steel can also be supported by spot welding to old steel. Place required shear reinforcements for beams and binders for columns.

Step 6: Apply proper bonding coat to the old concrete surface and steel surface.

Step 7: If necessary, attach the formwork to the column for concreting the removed area. For columns, it is easy to place formwork or self-compacting concrete for pouring concrete. For beams, it is more convenient to use expanded wire mesh

Step 8: Before the bond coat dries, compact the void space of the member with cement, sand, small coarse aggregate (10mm and below) and micro concrete with superplasticizer as required. Water-cement ratio should not exceed 0.5. In some cases, we may have to use self-compacting concrete. This is achieved by using concrete chemicals such as superplasticizers. For patch repairs or repairing small areas, we usually use simple polymer-modified cement mortar. For larger repairs, it is better if we use shotcrete to fill the removed area.

Step 9: Apply a 1:3 (finely sanded) coating within 48 hours of completing Step 8.

Step 10: Wet curing should be done for at least 7 days.

Step 11: After complete drying, a coat of waterproof paint is given to protect the member and match the surrounding surfaces. Note: In larger jobs, it is better to place concrete or mortar using shotcrete, also known as gunite.