Last edited 25 Feb 2021

Concrete compaction


[edit] Introduction

Compaction is a process of expelling entrapped air. If we don’t expel this air, it will result into honeycombing and reduced strength. It has been found from the experimental studies that 1% air in concrete reduces the strength by approximately 6%.

There are two methods of compaction:

  • Hand compaction.
  • Mechanical compaction i.e vibration method
  • Compaction by pressure and jolting method
  • Compaction by a spinning method

[edit] Hand compaction

Hand compaction is used for simple, small structures. Workability should be decided in such a way that the chances of honeycombing is minimised.

Methods of hand compaction include:

  • Rodding: 'Poking' with a 2m long, 16 mm dia rod at sharp corners and edges. The thickness of layers for rodding should be 15 to 20 cm.
  • Ramming: Generally used for compaction on ground in plain concrete. It is not used either in RCC or on upper floors.
  • Tamping: The top surface is beaten by a wooden cross beam of cross section 10 cm x 10 cm. Both compaction and levelling are achieved simultaneously. It is mainly used for roof slabs and road pavements.

[edit] Mechanical compation

Vibration is imparted to the concrete by mechanical means. This causes temporary liquefaction so that air bubbles come to the top and are expelled.

Mechanical vibration techniques include:

[edit] Compaction by pressure and jolting method

[edit] Compaction by a spinning method

  • Compaction by Spinning is also called centrifugation
  • This method Compaction by Spinning is used in the manufacture of concrete pipes, concrete lamp posts etc
  • The initial w/c ratio of 0.35 to 0.40 reduced to about 0.30 after spinning

[edit] Related articles on Designing Buildings Wiki.

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