Short Answer

Methods of compaction are the different ways used to remove air voids from fresh concrete and make it dense and strong. Common methods include hand compaction and mechanical compaction using vibrators.

These methods are important because proper compaction improves strength, durability, and quality of concrete. The choice of method depends on the type of work, size of structure, and workability of concrete.

Detailed Explanation:

Methods of Compaction

Methods of compaction are the techniques used to make freshly placed concrete dense by removing trapped air and ensuring proper arrangement of particles. When concrete is placed in formwork, it contains air voids that reduce its strength and durability. Compaction methods help in eliminating these voids and produce strong and uniform concrete.

The selection of compaction method depends on the type of construction work, availability of equipment, and workability of concrete. For small works, simple methods are used, while for large and complex structures, advanced mechanical methods are preferred.

1. Hand Compaction
   Hand compaction is the simplest method of compacting concrete. It is done using tools like tamping rods, rammers, or spades. In this method, concrete is manually pressed and poked to remove air voids. It is suitable for small-scale construction works such as small foundations, pavements, or where mechanical equipment is not available. However, it is less effective compared to mechanical methods.
2. Mechanical Compaction
   Mechanical compaction is done using machines called vibrators. This method is more effective and widely used in modern construction. Vibrators produce vibrations that help concrete particles to move and settle into a dense arrangement, removing trapped air efficiently.
3. Needle Vibrator
   Needle vibrator, also known as internal vibrator, is commonly used for compacting concrete in columns, beams, and slabs. It is inserted into the fresh concrete, and vibrations are generated inside the mix. This helps in removing air voids and ensures proper compaction, especially around reinforcement.
4. Surface Vibrator
   Surface vibrator is used for compacting concrete in thin sections such as floors, roads, and slabs. It is placed on the surface of concrete and vibrates it from the top. This method is suitable for shallow concrete layers.
5. Table Vibrator
   Table vibrator is mainly used in laboratories and for precast concrete elements. In this method, molds are placed on a vibrating table, and vibrations help in compacting the concrete uniformly. It is useful for making small precast items like blocks and tiles.
6. External Vibrator
   External vibrators are attached to the outside of formwork. They are used where it is difficult to insert internal vibrators, such as in heavily reinforced sections. Vibrations are transferred through the formwork to compact the concrete.
7. Compaction by Rolling
   This method is used in road construction and large flat surfaces. Heavy rollers are used to compact the concrete surface. It is suitable for dry and stiff concrete mixes.

Conclusion

Methods of compaction are essential for removing air voids and improving the quality of concrete. Different methods like hand compaction and mechanical vibration are used depending on the type of work. Proper selection and use of these methods ensure strong, durable, and defect-free concrete structures.