Building Materials, Third Edition

PSV f   





2w—

—

x


2†˜—X These are also knows as immersion, internal, or poker vibrator. Needle vibrator
can be used for any type of concrete work. This consists of a steel tube, called poker, having an
eccentric vibrating element inside it, a flexible shaft and a power unit. The needle diameter
varies from 20 to 75 mm and its length from 250 to 900 mm. In places where the reinforcement
is congested blades are used instead of needle. An average frequency of vibration used is 3,500
to 5,000 cycles per minute. The vibrator is immersed into concrete at a spacing of not more than
600 mm or 8 to 10 times the diameter of the poker. The vibrator is immersed at a place for about
30 seconds to 2 minutes. Location of the poker insertion should be staggered to ensure that
every bit of concrete is compacted (Fig. 10.9). The vibrator should be allowed to penetrate the
concrete vertically (inclination^3 10°) under its own weight. A needle vibrator is shown in
Plate 2. For proper compaction in a heaped concrete the poker position should be changed
gradually from the side of the heap and moving away from the heap all around
(Fig. 10.10(a)). Poker should not be introduced in the center of the heap (Fig. 10.10(b)).

p " 2 †˜—X These are also known as external or shutter vibrators. These are generally
used under the following circumstances:

p2IHIH w'22€12s2x—2—2r—

p2IHW w'22€12s22p"2g—™

Poorly compacted area

INCORRECT

Well compacted area

Linear vibrator needle position

CORRECT

Well compacted concrete areas

Staggered vibrator needle position

Poorly compacted area

INCORRECT

Well compacted area

Linear vibrator needle position

CORRECT

Well compacted concrete areas

Staggered vibrator needle position