Some useful tips to restore active cracks in concrete

Active cracks in concrete stand for live cracks which are broaden in length, width, and depth in due course. Because of overloading & thermal enlargement, these cracks are developed e.g. cracks owing to freeze-thaw. There are different types of processes to restore active cracks which range from drilling and plugging, stitching, external pre-stressing and flexible sealing of cracks.

Because of unrestrained growth, there is chance for a new crack to be developed next to the restored active cracks. So, primarily, it is essential to settle reason of crack formation.

How to restore active cracks in concrete

The following processes are commonly used for restoring active cracks in concrete structures.

1. Drilling and Plugging through Crack: This process is suitable for the cracks which are found in straight lines. Under this process, a hole is drilled adjacent to the crack and stuffed with grout. This grout builds the key to lock the crack so that it can’t expand further. The grout avoids leakages and loss of soil. This method is inexpensive and less time is required for that.

Another useful process for plugging the drilled hole is stuffing it with epoxy mortar or any epoxy formulation with reinforcement bars which are arranged in the drilled hole. The bars applied contain predetermined length and size to fasten the cracks across.

The method includes drilling a hole of 50 to 75mm diameter based on the width of crack following the position of crack. The hole should be must be sufficiently big to bisect the crack along its full length and arrange adequate repair material to structurally bear the loads enforced on the key.

If water tightness is mainly required over structural load transmission, then the drilled hole is stuffed with a flexible material having low modulus. If both properties are necessary, the first hole is stuffed with grout and the second hole is stuffed with a flexible material.

2. Stitching of Cracks: Under this process, holes are drilled in such a manner that entry and exit points are provided across the cracks. Through the holes, several U-shaped metallic staples are provided through the holes and the holes are secured firmly at the end with grout or epoxy.

3. External Prestressing: Post-tensioning method is used to close flexural cracks in reinforced concrete. It will stop the cracks to be expanded further or fixed entirely. The process offers compression force so as to correct the tendons and then supplementary residual compressive force.

This process needs anchorage of the tie-rods to the anchoring device tied to the beam.

4. Flexible Sealing: Under flexible sealing method, bond breaker is utilized for repairing active cracks.

Prior to apply a repair method for active cracks, it should be checked that whether it is essential to make the flexural or tensile strength better across the crack. To sustain the strength, it is required to set up an expansion joint close to the repaired crack so that further cracking can’t happen adjacent to the corrected one in due course of time.



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Published By
Rajib Dey
www.constructioncost.co
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Some useful tips to repair cracks in plaster walls

Cracks in plaster walls are normally occurred due to various factors like settlement, vibration or atmospheric conditions and in some cases for defective construction.

To repair cracks, the following items will be required :-

a. Blade for widening of cracks
b. Patching material usually putty
c. Painting brush
d. Paint scrapper
e. Flexible putty knife for filling
f. Fine grade sandpaper

THE CRACKS CAN BE REPAIRED IN THE FOLLOWIN WAYS

1. With the help of blade or putty knife, broaden and undercut opening to arrange grip for filler. If filler material is applied in very small quantity then there will be no tough bonding and too much quantity is not also recommended. In second option, opt for plastering initially.
2. Arrange the patching material to fill the crack; blend it with a solid, buttery consistency for quick application. Ready-made putty is accessible almost everywhere and it should be blended with water.
3. Apply a brush to moisten the surface or spray to the full depth of the unsealed crack. Ensure water arrives at the far end of crack. The surface should be moistened perfectly to make the bond better.
4. The patching material alias putty should be applied through a flexible putty knife to fill the opening totally. Finally, take away surplus putty and level it on the wall by a paint scrapper.
5. A fine grade sand paper should be applied to smooth the patch surface. The adjacent surface should also be leveled. If gap still exists among crack layer and adjacent, then apply second filling coat to keep it dry. As soon as, it becomes dry, again use sand paper. Dust the surface and check for any divergences.
6. As soon as repaired patch gets dried, use prime coat over the filled-in crack and surface adjacent area. It will conceal the repaired area and provides a fine smooth finishing.
7. To patch a big crack, then undercut it, take away all the loose plaster and moisten the surface like equivalent to small crack.
8. Blend a batch of plaster and fill the cavity. Keep it dry for 24hours. Shrinkage may take place throughout drying.
9. If shrinkage happens, moisten again the patch area and fill cavity with fresh filler. Let it gets dry. Sand smooth and finally use prime coat.



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Published By
Rajib Dey
www.constructioncost.co
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Common types of cracks in reinforced concrete column

Usually, Four types of cracks are found in reinforced concrete column which range from diagonal cracks, horizontal cracks, splitting cracks, corrosion cracks. The cracks happen in columns due to improper design, defective construction or overloading, erosion of reinforcement, isolated settlement of foundations, creep and shrinkage.

Cracking in reinforced concrete column may result in loosing of strength, consistency, longevity, and adversely impact aesthetics.

Types of cracks found in concrete columns:

1. Diagonal Cracks: If there are diagonal cracks in reinforced concrete columns, they encircle the whole face of column anywhere along its height. Because of insufficient load bearing strength of the columns, inadequate cross-section and inadequate reinforcement steel.

Diagonal Cracks significantly impact the structural soundness and therefore it should be monitored carefully.

2. Horizontal Cracks: Horizontal crack in reinforced concrete column is generally found at the beam-column joint, and on column face where tensile stress is massive. Columns with insufficient moment resistance strength, inadequate reinforcements, or disposition of installed reinforcement may lead to horizontal cracking owning to the effect of shear force and direct load and uniaxial bending.

Finally, horizontal cracks significantly decrease the shear strength of the column and as a result there is high risk of failure. So, it should be dealt with instantly and carefully.

3. Splitting Cracks: Splitting cracks in reinforced concrete column belong to short parallel vertical cracks having non-uniform width. These types of cracks may occur in columns with insufficient steel reinforcement, and low concrete quality. Splitting cracks in concrete columns originated because of attaining its maximum load bearing strength.

The ultimate Load bearing strength of the column is exceeded when concrete cross section is not enough or reinforcement ratio is inadequate or combination thereof.

4. Corrosion Cracks: Corrosion cracks in concrete columns are formed along the line of reinforcements. These types of cracks are usually homogeneous in width and expand as the column is ageing.

Probable reinforcement erosion and insufficient bond among the concrete and steel bars lead to erosion reinforcement in concrete columns. If these types of cracks are not dealt with properly, the erosion of reinforcement will be increased at a rapid rate.



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Published By
Rajib Dey
www.constructioncost.co
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