Guide to concrete compaction and vibration
20th Sep 2008 by Admin
Many thanks to George Lee for producing this guide to concrete compaction. George is our sales representitive for Back Pack Pokers. Any queries regarding this or concrete compaction please contact George 01670 590777 Compacting / Vibrating Concrete. What is compaction ? Compaction is shaking or vibrating the concrete, this liquefies it allowing the trapped air to rise out then the concrete settles filling in all the available space. When to compact ? Compaction MUST be done as the concrete is being placed , whilst it is still plastic. Once it starts to dry out it will stiffen and be to hard to compact. Why compact ? Concrete becomes more dense, stronger and more durable when compacted. Also the moulded finish off the former is very much improved. How to Compact ? There are two methods to compact concrete. 1). External vibration is when the vibration device is clamped to the outside of the concrete former causing it to transmit vibration to the concrete. 2).Internal vibration is when the vibration device is plunged into the concrete, directly vibrating the concrete. External (clamp on or limpet) vibrators Usually an eccentric weight supported on bearing blocks and powered by a motor to spin it at high speed. The motive force for the motor can be air, electric or hydraulic but is usually air. The vibration force can be varied by altering the speed of the motor but the area affected is fixed so more than one vibrator unit is usually required to cover a large mould surface. Method As the concrete is placed into the mould the vibrators are started slowly at first then the speed / vibration is built up to max as the mould is filled. Internal (poker) vibrators Usually an eccentric weight supported on bearings and built into a sealed tube, (poker head) this is fixed to a long sealed flexible drive connected to the motor, this could be an engine, electric, air or hydraulic motor. The tube is plunged directly into the plastic concrete applying the vibration force directly to the concrete, because of the portability of this method a large area can be compacted with one unit. Method As the concrete is placed into the form the poker is plunged quickly into the concrete, then pulled slowly out. The effective area compacted can be seen by the ring of air bubbles rising around the poker, a pattern should be developed so the rings of bubbles overlap indicating full compaction. The poker and flexi should be able to reach the lowest layer of concrete but should not touch the formers or any reinforcing rods in the concrete.