Air bubbles can be removed by decreasing the amount of required water, but it affects the workability of concrete. Therefore, the vibration of concrete is the only suitable method that helps without affecting the properties of fresh concrete. Vibration is only affected in a fresh mix concrete or one can say up to that time when concrete has the ability to flow. This stage exists before the start of the initial setting.
Compaction of concrete or Vibration of concrete can be performed in five different methods are:-
1- Vibrating the concrete internally by inserting an internal vibrator into the concrete mass.
2- Vibrating the concrete while fixing the shuttering using Shutter formwork vibrators
3- By Vibrating the entire mass of concrete using a vibrating table
4- Vibrating the concrete externally on the surface using surface vibrators
5- Vibrating the concrete using rebar shakers.
Concrete Vibrating Tips
1- Do not over vibrate the concrete as it lets the mixture break and separate. Also, do not under vibrate the concrete because air might still be trapped in the lower layers of the cement pour, which leads to a weak concrete structure that easily breaks with minimum pressure.
2- The most common technique with an internal vibrator is to withdraw the vibrator slowly, at a rate of around 25mm inch per second. If bubbles are still emerging as the concrete vibrator is withdrawn, more vibration is necessary.
3- To prevent cold joints from occurring to concrete layers as these are poured over with a new layer of cement mixture, make sure to penetrate the pour thoroughly with a vibrator and mix in the previously poured layer with the newly placed one.
4- For maximum efficiency, use only vertical movements when vibrating to have an even mixture of aggregate and concrete. Horizontal motion can lead to uneven distribution and increases the possibility of the vibrator tangling in the rebar or reinforcing steel.
5- Avoid using the vibrator as a concrete placement tool because it will not produce a consistent surface and it might even provide more problems in structural strength and form.
5- Use the appropriate type of concrete vibrator depending on the structure being built or the size of the working area. Consider using a compact lightweight concrete vibrator for smaller jobs for manageability and efficiency.
6- Consider having a back-up concrete vibrator on hand to have a second replacement tool instantly if the first one encounters any problems while on the job.
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