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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Plain cement concrete – Uses and formation method

The objective of plain cement concrete alias PCC is to arrange a firm impermeable bed to RCC in the foundation where the soil is soft and flexible. It is mostly applied over brick flat soling or devoid of brick flat soling.

It is also known as Cement Concrete (CC) or Blinding Concrete.

When, any reinforcement is not used inside the concrete, it is defined as the plain cement concrete. It’s just a blend of concrete ingredients.

Characteristics of Plain Cement Concrete - Given below, some vital characteristics of plain cement concrete:

• Compressive strength: 200 to 500 kilogram/square centimeter
• Tensile strength: 50 to 100 kilogram/square centimeter
• Density: 2200 to 2500 kilogram/cubic meter
• Stability: Outstanding

Applications of Plain Cement Concrete: PCC is mostly found in footings, grade slabs, and concrete roads. When the underlying soil is weak and flexible, brick flat soling is provided under PCC.

To form PCC, the following materials are utilized :-

Cement: Normally, the Portland cement is utilized as bonding material in PCC.

Fine Aggregate: Sand is employed as fine aggregate. The fineness modulus (FM) of sand should remain 1.2 to 1.5. FM stands for an index number that demonstrates the mean size of particles in sand. It is measured by carrying out sieve analysis.

Coarse Aggregate: Usually, the brick chips are utilized for developing PCC. It is also possible to utilize stone chips in these conditions. The size of the coarse aggregate remains 20mm downgrade.

Water: Pure drinkable water should be provided in PCC.

How to build up PPC?

With the following methods, plain cement concrete is formed.

The following tools are utilized for the production of PCC

• Wooden or Steel rammer
• Mixture machine (if any)

The Thickness of PCC: The thickness of PCC is normally 50mm over Brick Flat Soling (BFS). If you don’t use BFS below PCC then the thickness should be 75¬mm. When the PCC is used in car parking area then the thickness should be 75mmover BFS.

Ration of materials in PCC: The ratio of cement, sand and brick chips in foundation or basement should be 1:3:6. But, if it is applied in the car parking area, the ratio will be changed to 1:2:4.

The production method for PCC: If ready-mix concrete is applied, this step should be omitted. If PCC is produced through mixture machine then click “How to mix concrete by mixture machine”. If the concrete is mixed manually, get help by clicking on this link “how to mix concrete by hand”.

Placing and Compaction of PCC:

• Ensure that brick soling/sand bed level is perfect for PCC.
• Create formwork for PCC with wooden planks according to stipulated dimensions.
• There should be no dust and foreign materials in concreting area.
• The bed of PCC should be covered with polythene.
• Create level pillars of fresh concrete in the area at proper spacing but not in excess of 2m c/c both ways.
• Set the concrete softly from one side. Apply the mixed concrete within 45 minutes once the water is added.
• For compaction and finishing of PCC, wooden rammer should be used.
• The surface of PCC should be rough to combine future work prior to solidification of the concrete.

Curing of PCC: After PCC is placed for 24 hours, wet the concrete surface with water. Alternatively moist gunny bags can be used to cover the surface for minimum seven days.



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Published By
Rajib Dey
www.constructioncost.co
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