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 enhance the longevity of concrete piles

If concrete is mixed perfectly and compacted to a solid impervious, the longevity of all the construction materials is significantly increased in a non aggressive atmosphere.

The strength of concrete is influenced by sulphate and sulfuric acid that takes place normally in soils, erosive chemicals existent in industrial waste in fill materials and organic acids and carbon dioxide existent in ground water.

A solid, properly compacted concrete can efficiently safeguard the concrete piles, pile cap and ground beams against the attack by sulphates. The low penetrability of dense concrete resists or significantly controls the ingress of the sulphates into the pore spaces of the concrete.

That's why high strength precast concrete piles are mostly recommended for application. Although these are not acceptable for all the site conditions and bored cast in situ / driven cast in situ piles, so, at the time of application, these should be designed perfectly to attain necessary degree of impenetrability and defiance to aggressive action.

Both high alumina cement and super sulphated cement are not suitable for piling work. As an alternative, reliance is provided on the resistance of solid impervious concrete that is formed with a low water cement ratio. Coating of tar or bitumen on the surface, metal sheeting or glass fibre wrapping filled with bitumen may be chosen.

A layer of heavy gauge polythene sheeting provided on a sand carpet or on blinding concrete is arranged to safeguard pile caps and ground beams on the underside. The vertical sides are safeguarded once the formwork is eliminated with the use of hot bitumen spray coats, bituminous paint, trowelled on mastic asphalt or adhesive plastic sheeting.

Preventative measures against the aggressive action caused by sea water on concrete should only be taken into consideration with regard to precast concrete piles. Cast in situ concrete is utilized only as a centering to steel tubes or cylindrical precast concrete shell pills. The precast concrete piles for marine condition, a minimum ordinary portland cement content of 360 kg/m3 and a maximum water cement ratio of 0.45 by weight should be chosen.



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Published By
Rajib Dey
www.constructioncost.co
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