What is the main application of a table vibrator?

They are used for compacting concrete in moulds for precast elements like blocks, joists, pipes, and railway sleepers (Clause 1.1).

What frequency should be used for concrete with 20mm aggregate?

For aggregate sizes from 10 to 40 mm, a frequency of 3000 vibrations per minute (vpm) is recommended (Table 1).

How do you determine when compaction is complete?

Compaction is considered complete when the concrete mass flattens, air bubbles stop emerging, and a thin film of cement paste appears on the top surface (Clause 6.3).

Are table vibrators suitable for all concrete mixes?

They are particularly effective for stiff and harsh concrete mixes that are otherwise difficult to compact by hand rodding (Clause 1.2).

IS 7246

: 1974

Recommendations for the use of table vibrators for consolidating concrete

CurrentSpecializedCode of PracticeMaterials Science · Cement, Concrete, Aggregates and RCC

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This Indian Standard provides recommendations for the selection, operation, and maintenance of table vibrators used for consolidating concrete. It is primarily intended for the production of precast concrete elements, ensuring dense and uniform compaction by specifying vibration characteristics like frequency and amplitude for different concrete mixes.

Recommendations for the use of table vibrators for consolidating concrete

Quick Reference Values

Recommended frequency for normal concrete (<40mm aggregate)3000 vibrations per minute (vpm)

Recommended frequency for fine particle concrete (<10mm aggregate)6000 vibrations per minute (vpm)

Typical acceleration for effective compaction4g to 7g

Typical amplitude range0.25 to 1.25 mm

Maximum concrete depth for effective table vibration60 cm

Practical Notes

Ensure moulds are clamped rigidly to the table to allow for efficient and uniform transfer of vibration energy.

Over-vibration should be avoided as it can lead to segregation of aggregates and bleeding of the cement paste, weakening the concrete.

The effectiveness of vibration depends heavily on the consistency of the concrete mix; stiff mixes generally require higher frequency or amplitude.