Concrete Compaction and Points to Be Considered in Compaction
There is entrapped air inside the plastic concrete, and in order to make the concrete impervious and attain its maximum strength, compaction is done. The concrete loses a lot of strength if the air isn't completely removed. This article discusses the types of compacting of concrete and important points to be considered during concrete compaction.
1. Different Methods of Compaction of Concrete :
The strength of concrete is reduced by around 30% if there are 5% voids, so concrete compaction is quite critical. Concrete can be compacted either manually or mechanically.
1.1 Hand Compaction
When the compaction of concrete is done manually (with steel rods), it is called hand compaction or manual compaction. Hand compaction is used on site when the construction work involves minor quantities of concrete. There are numerous hand compaction methods, which are listed below :
It's a process of poking sharp corners and edges with a 2 m long, 16 mm diameter rod. For rodding, the layers should be 15 to 20 cm thick.
It is commonly used in plain concrete for ground compaction. It's not allowed in RCC or on the top levels.
It's a method in which a wooden cross beam with a cross-section of 10 cm x 10 cm is used to beat the top surface. Both compaction and leveling are accomplished at the same time.
1.2 Machine Compaction :
Machine compaction is what occurs when mechanical vibrators are utilized. Different types of vibrators are used for concrete compaction which is as follows :
Internal vibrators are the most common type of vibrator and are generally used for compaction. Internal vibrators are made up of a metal rod-type vibrating head that houses an eccentric shaft.
External Vibrators or Formwork Vibrators
In situations where internal vibration cannot be used due to thin sections or substantial reinforcing, external vibrators are used. External vibrators are connected to the concrete formwork, and the vibrating force is transmitted to the concrete via the formwork. When external vibration is utilized, the formwork must also be made extremely sturdy. A nice finish on the concrete surface may be achieved by using a formwork vibrator. Because the vibration is transmitted to the concrete via the formwork, it consumes more energy.
These vibrators are also known as screed board vibrators. Vibration is applied to the surface by placing the vibrator on the screed board. The majority of floor and roof slabs are so thin that using a vibrator or any other sort of vibrator is difficult. In such situations, a surface vibrator can be quite useful. However, it is ineffective beyond a depth of 15 cm.
This kind of vibrator is fastened to the table or the table is supported by springs that vibrate, imparting the vibration to the table. They're frequently used to shake concrete cubes. Any item placed on the table vibrates.
A platform vibrator is a type of table vibrator that is relatively large. This is used to make massive prefabricated concrete components like electric poles, railroad sleepers, and prefabricated roofing elements.
2. Points to be Remembered while Compacting the Concrete
The points to be considered and remembered while compacting the concrete are :
The water content of the mix shall be reduced when vibration is adopted.
The vibrators shall be used by skilled and experienced workmen only.
Hand compaction shall be done by tamping or rodding using rods.
Concrete must not be over-tamped, as this will not only bring the water to the surface but also the cement paste which is required to act as the matrix.
Both excessive compaction and under compaction are harmful to concrete.
3. Points to Remember when using Vibrators
1. It is important to avoid contacting the vibrating head with hard things such as hardened concrete, steel, or timber.
2. When the introduction space is limited, the vibrator should only be turned on once the vibrator head has been introduced into the concrete.
3. The formation of watery grout on the surface of the concrete as a result of vibration indicates that the concrete was made too gently and is not suited for vibration; nevertheless, a close-textured layer of viscous grout may be allowed.
4. The formwork used for vibrated concrete should be stronger than that used for hand-compacted concrete, and it must be assembled with greater care.
5. The vibrator may be used vertically, horizontally, or at an angle depending upon the nature of the work. But needle vibrators should be immersed vertically in beams and other thick sections at regular intervals.
Concrete compaction is a critical site procedure that permits fresh concrete to achieve its maximum design strength. It also has a significant effect on getting the specific desired finish. This article has emphasized the necessity of compaction of concrete as well as the things to keep in mind while performing it.
Visit the following links for more information on construction details:
Concrete Mixing Methods and Points to Remember While Concreting