Hello, This article is about compaction of concrete. However everyone in civil engineering field will be aware of this term but majority of them will not be knowing some of the important things of compaction. In this article all the necessary points are covered.
Once the concrete has been placed, it is ready to be compacted. The purpose of compaction is to get rid of the air voids that are trapped in loose concrete.
Why is compaction of concrete necessary?
It is important to compact the concrete fully because:
Air voids reduce the strength of the concrete. For every 1% of entrapped air, the strength falls by somewhere between 5 and 7%. This means that concrete containing a mere 5% air voids due to incomplete compaction can lose as much as one third of
its strength.
Air voids increase concrete's permeability. That in turn reduces its durability. If the concrete is not dense and impermeable, it will not be watertight. It will be less able to withstand aggressive iquids and its exposed surfaces will weather badly.
Moisture and air are more likely to penetrate to the reinforcement causing it to rust.
Air voids impair contact between the mix and reinforcement (and, indeed, any other embedded metals). The required bond will not be achieved and the reinforced member will not be as strong as it should be.
Air voids produce blemishes on struck surfaces. For instance, blowholes and honeycombing might occur.
Summing up, fully compacted concrete is dense, strong and durable; badly compacted concrete will be porous, weak and prone to rapid deterioration. Sooner or later it will have to be repaired or replaced. It pays, therefore, to do the job properly in the first place. Stiff mixes contain far more air than workable ones. That is one of the reasons why a low-slump concrete requires more compactive effort than one with a higher slump - the compaction needs to continue for a longer time, or more equipment has to be used.
Even air-entrained concrete needs to be compacted to get rid of entrapped air voids. The difference between air voids and entrained air bubbles should be noted at this stage. The air bubbles that are entrained are relatively small and spherical in shape, increase the workability of the mix, reduce bleeding, and increase frost resistance. Entrapped air on the other hand tends to be irregular in shape and is detrimental to the strength of the mix. It is to remove this air that the concrete must be properly compacted. There is little danger that compaction will remove the minute air bubbles that have been deliberately entrained, since they are so stable.
Methods of Compaction of concrete
Vibration:
To compact concrete you apply energy to it so that the mix becomes more fluid. Air trapped in it can then rise to the top and escape. As a result, the concrete becomes consolidated, and you are left with a good dense material that will, after proper curing, develop its full strength and durability.
Vibration is the next and quickest method of supplying the energy. Manual techniques such as rodding are only suitable for smaller projects. Various types of vibrator are available for use on site.
There are two types of vibrators
· Internal vibrators
· External vibrators
Poker Vibrators
The poker, or immersion, vibrator is the most popular of the appliances used for compacting concrete. This is because it works directly in the concrete and can be moved around easily.
Plate vibrator
vibrator is the most popular of the appliances used for compacting concrete. This is because it works directly on the surface of concrete and can be moved around easily.
Once the concrete has been placed, it is ready to be compacted. The purpose of compaction is to get rid of the air voids that are trapped in loose concrete.
It is important to compact the concrete fully because:
Air voids reduce the strength of the concrete. For every 1% of entrapped air, the strength falls by somewhere between 5 and 7%. This means that concrete containing a mere 5% air voids due to incomplete compaction can lose as much as one third of
its strength.
Air voids increase concrete's permeability. That in turn reduces its durability. If the concrete is not dense and impermeable, it will not be watertight. It will be less able to withstand aggressive iquids and its exposed surfaces will weather badly.
Moisture and air are more likely to penetrate to the reinforcement causing it to rust.
Air voids impair contact between the mix and reinforcement (and, indeed, any other embedded metals). The required bond will not be achieved and the reinforced member will not be as strong as it should be.
Air voids produce blemishes on struck surfaces. For instance, blowholes and honeycombing might occur.
Summing up, fully compacted concrete is dense, strong and durable; badly compacted concrete will be porous, weak and prone to rapid deterioration. Sooner or later it will have to be repaired or replaced. It pays, therefore, to do the job properly in the first place. Stiff mixes contain far more air than workable ones. That is one of the reasons why a low-slump concrete requires more compactive effort than one with a higher slump - the compaction needs to continue for a longer time, or more equipment has to be used.
Even air-entrained concrete needs to be compacted to get rid of entrapped air voids. The difference between air voids and entrained air bubbles should be noted at this stage. The air bubbles that are entrained are relatively small and spherical in shape, increase the workability of the mix, reduce bleeding, and increase frost resistance. Entrapped air on the other hand tends to be irregular in shape and is detrimental to the strength of the mix. It is to remove this air that the concrete must be properly compacted. There is little danger that compaction will remove the minute air bubbles that have been deliberately entrained, since they are so stable.
Methods of Compaction of concrete
Vibration:
To compact concrete you apply energy to it so that the mix becomes more fluid. Air trapped in it can then rise to the top and escape. As a result, the concrete becomes consolidated, and you are left with a good dense material that will, after proper curing, develop its full strength and durability.
Vibration is the next and quickest method of supplying the energy. Manual techniques such as rodding are only suitable for smaller projects. Various types of vibrator are available for use on site.
There are two types of vibrators
· Internal vibrators
· External vibrators
Poker Vibrators
The poker, or immersion, vibrator is the most popular of the appliances used for compacting concrete. This is because it works directly in the concrete and can be moved around easily.
Plate vibrator
vibrator is the most popular of the appliances used for compacting concrete. This is because it works directly on the surface of concrete and can be moved around easily.
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