Poured concrete can contain large amounts of trapped air which reduce the density of the concrete making it weaker and more permeable. If the concrete is left in this state, it will lack durability in service and will need to be replaced before long. Concrete vibration plates are a common way of solving this problem by removing the air trapped in freshly poured concrete.
How is trapped air removed from poured concrete?
Traditionally concrete trowels were used to smooth out poured concrete and to release the air bubbles trapped within. Today, it is more common to employ vibration plates to consolidate newly poured concrete and release the excess water and trapped air so that the concrete will settle correctly into the required form. Using the vibration plates will smooth the concrete and remove blemishes, honeycombing and bug holes. The plates will do this more thoroughly than concrete trowels ever could.
Despite these advantages which vibration plates offer, it is still important that they are used correctly. One of the problems that can occur when employees are not trained in the correct use of vibration plates is that the plates are removed before the vibration effect has had time to do its work. Simply levelling the concrete is not enough as that will not remove the trapped air. Vibration works by liquefying the mortar and reducing the internal friction between the aggregate particles. The instability this creates causes the air to rise to the surface and increases the density of the concrete, this process takes time.
How long should you vibrate your concrete?
The poured concrete needs to be vibrated long enough for it to thoroughly liquefy. The amount of time this takes will depend on many factors including the amplitude of the vibrator and the workability of the concrete. It is important employees take the time to familiarise themselves with both the vibration plates being used and the particular concrete mix being employed by the plant before they start applying the vibration plate to the concrete. It should be possible to see the vibration having an effect on the concrete. The large air bubbles will come to the surface of the mix and as the vibration completes a creamy sheen will be seen at the top of the concrete.
Educating your workers in the correct method of vibrating concrete is vital if you want to create concrete structures that will be solidly constructed and will offer a long service life once construction is completed.