There are two main type of vibration elements used in the placement of concrete – external and internal. This post discusses the correct use of  “internal” or “insertion ” vibrators – so called because of because the vibrating head is “inserted” into the concrete.

Handheld concrete vibrators are used to consolidate concrete by forcing  the coarse aggregate in the mix down and away from the insertion point of vibrator.

Image of  a commercial grade gasoline powered internal vibrator.

When an operator is using an internal vibrator they should insert the head it at intervals of approx 18-inches apart for 5 to 10 seconds a few seconds longer into nonair-entrained concrete. However the exact period of time that you are required to “vibrate” for is dependant on the slump of the mix.

Try to overlap the previously vibrated area with each new insertion. Always lower the vibrator under gravity into the concrete vertically taking care that the vibrator not only pass through the concrete layer that has just been placed, but also penetrates down through several inches to create a good bond between the previous layers of placed concrete.

With normal use vibration will not damage the lower layers provided that the concrete that in these lower layers is plastic under vibration.

You will know that the concrete is properly vibrated when a line of mortar shows on the formwork near the vibrator head, all of the coarse aggregate disappears into the concrete, or a paste appears near the vibrator head.

When this happens you should withdraw the vibrator at a similar rate to the speed gravity descended.

Some degree of hand spading should accompany all use of vibration with concrete placement.

Do not vibrate mixes that you can consolidate easily by hand, this will result in segregation and do not use vibrators to move concrete around the formwork.

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