Compaction:

Compaction of concrete is the procedure adopted for expelling the entrapped air from the concrete. In the procedure of placing and mixing of concrete, air is likely to get entrapped within the concrete. If this air is not erased fully, the concrete losses strength considerably. 5 % voids decrease the strength of concrete through about 30 % and 10 % voids reduce the strength through over 50 %. Thus, it is imperative that 100 % compaction of concrete is one of the most significant aim to be kept in mind in good concrete-making practices.

In sequence to achieve full compaction and maximum density, along with reasonable compacting efforts available at site, it is essential to use a mix with adequate workability. It is also of general knowledge that the mix should not be too wet for simple compaction, which also decreases the strength of concrete. For maximum strength driest probable concrete should be compacted 100 %. The whole economy demands 100 % compaction along with a reasonable compacting effort available in the field.

The subsequent methods are adopted for compacting the concrete:

Hand Compaction

(a)        Rodding

(b)       Ramming

(c)        Tamping

Compaction by Vibration

(a)        Internal vibrator (Needle vibrator) - example. Column, slab, beam, footing.

(b)       External vibrator (Formwork vibrator) - example. column, thin sections.

(c)        Table vibrator - e.g. cube testing.

(d)       Platform vibrator - e.g. pre-cast units.

(e)        Surface vibrator (Screed vibrator) - e.g. concrete roads, industrial flooring.

Compaction by Pressure and Jolting - e.g. blocks, tiles, etc.

Compaction by Spinning - e.g. cement pipes.