Cracking in concrete is unavoidable. There are certain limits of crack width that a structure may have. But it is of serious concern if exceeds the limit. There are several types of cracks that may exist in freshly poured concrete even in concrete has hardened more than 28 days.
The root cause of cracking needs to be identified first before adopting any repair strategy. And if it will not be repaired immediately that could be the cause of issue such as nonconformance or what we called NCR.
Here we discuss few crack repairing techniques in general.
1. Grouting
Grouting is the technique in which white cement or hydraulic cement is filled in the crack. First, the crack is chiseled to identify the actual depth of the crack. Groove made by chiseling is cleaned from small broken particles, dirt, and paint.
The grouting material is filled in the groove. When it set, the surface is sealed with sealing material so that it may not deteriorate or get a stain.
2. Injection
In this method of repairing, after cleaning the crack line, small nails are fixed in the cracked line at regular distance. Injection cord is hanged on each nail and the concrete filler is injected. When it hardens, injection cord is cut. The filler can be injected with pressure.
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3. Stitching
Stitching is similar to stapling of paper. Two holes are made on each side of the crack and staple is inserted. Similarly, more staple or fastener are inserted throughout the length of the crack. This technique is also known as sewing.
4. Reinforcement Addition
If the crack is wide or critical, that may lead to a brittle failure, it is necessary to reinforce it properly. For this, the concrete cover is removed and the surface is cleaned from dust. If reinforcement is rusted, it needs to be cleaned and painted with corrosion resistant emulsion. Additional reinforcement is drilled where required. Lastly, the surface is re-concreted and plastered.
5. Steel Plate and Bolts
Bridges and industrial buildings have severe and impact loadings. They are more prone to the environment and hazardous chemicals. Cracks in such structure may lead to strength failure due to creep. Ordinary repairing techniques are not effective for these structures. Steel Plates are bolted or riveted at the locations of crack to strengthen the cracked area.
6. Wire Mesh and Plaster
This technique is useful for the area where there are large numbers of hair cracks. Wire mesh is wrapped or fixed with nails on the cracked surface after cleaning. The surface is plastered again. This is also used in combination with bolts and plates.
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7. Fiber Reinforced Polymer (FRP) Strengthening
Fiber Reinforced polymer is the composition of fibers that are reinforced with a polymer matrix. Fiber Reinforced is an excellent retrofitting material that can be used as strips, plates, rods and spray. FRP is high strength, durable, light density and flexible material. FRP wrapping around cracked structure not only prevent cracking but it improves the overall structural strength.
FRP can be used at beam soffits, slabs and around openings. It is applicable to the areas where other retrofitting techniques are not applicable due to the complexity of structure. Fiber Reinforced Polymer improves building performance for both gravity and lateral loadings (wind and seismic).
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