06-09-2022, 11:29 AM
Concrete Compaction
After concrete is placed at the desired location concrete compaction is the next step in the process of concrete production. This step has a very significant contribution to the durability, strength, finish and appearance of the concrete structure.
We have in our earlier publications already covered various steps of concrete production. Even though concrete placing and compacting are done more or less simultaneously, it is felt that these should be treated separately specially because of their individual importance to the quality of concrete.
Concrete must be compacted at the same pace as it is being placed. Compacting process consolidates fresh concrete within the moulds or formworks and around embedded parts and reinforcement steel. Compaction is necessary to remove entrapped air which is present in concrete after it is mixed, transported and placed.
Compacting also helps eliminate stone pockets and thereby eliminate all types of voids that may possibly be left in the concrete, causing reduction in strength as well as durability.
Compaction of concrete is required to get rid of entrapped air and voids as much as possible, down to less than one percent in normal concrete. The amount of entrapped air is directly related to the workability of concrete. Lower the workability, higher is the percentage of entrapped air. In other words stiff concrete mix has high percentage of entrapped air and therefore would need higher compaction effort than highly workable mixes.
The importance of removal or entrapped air or voids from concrete can be best emphasized by the following :
Voids reduce the strength of concrete. With every one percent entrapped air the strength is reduced by about 5% to 6%. Five percent entrapped air mean 30% loss of strength.
Voids increase the permeability of concrete. Loss of impermeability creates easy passage of moisture, oxygen, chlorides, and other aggressive chemicals into the concrete. Th is causes rusting of steel and spalling (disintegration) of concrete i.e. loss of durability.
Easy entry of sulphate from the environment causes expansive reaction with the tricalcium aluminate (C3A) present in cement. This cause disintegration of concrete and loss of durability.
Entry of carbon dioxide causes carbonation of concrete i.e. loss of alkalinity of concrete or loss of the protective power that concrete gives to the reinforcement or concrete cover into the embedded steel, steel becomes vulnerable to the attack of moisture. This expedites rusting of steel as the protective concrete cover is no longer alkaline in nature.
Voids reduce the contact between embedded steel and concrete. This results in loss of bond strength of reinforced concrete member and thus the member loses strength.
Voids such as honeycombs and blowholes on the exposed surface produce visual blemish. Concrete surface is not good to look at with such blemishes. Concrete with smooth and perfect surface not only looks good but is also stronger and more durable.
For more details visit or download
After concrete is placed at the desired location concrete compaction is the next step in the process of concrete production. This step has a very significant contribution to the durability, strength, finish and appearance of the concrete structure.
We have in our earlier publications already covered various steps of concrete production. Even though concrete placing and compacting are done more or less simultaneously, it is felt that these should be treated separately specially because of their individual importance to the quality of concrete.
Concrete must be compacted at the same pace as it is being placed. Compacting process consolidates fresh concrete within the moulds or formworks and around embedded parts and reinforcement steel. Compaction is necessary to remove entrapped air which is present in concrete after it is mixed, transported and placed.
Compacting also helps eliminate stone pockets and thereby eliminate all types of voids that may possibly be left in the concrete, causing reduction in strength as well as durability.
Compaction of concrete is required to get rid of entrapped air and voids as much as possible, down to less than one percent in normal concrete. The amount of entrapped air is directly related to the workability of concrete. Lower the workability, higher is the percentage of entrapped air. In other words stiff concrete mix has high percentage of entrapped air and therefore would need higher compaction effort than highly workable mixes.
The importance of removal or entrapped air or voids from concrete can be best emphasized by the following :
Voids reduce the strength of concrete. With every one percent entrapped air the strength is reduced by about 5% to 6%. Five percent entrapped air mean 30% loss of strength.
Voids increase the permeability of concrete. Loss of impermeability creates easy passage of moisture, oxygen, chlorides, and other aggressive chemicals into the concrete. Th is causes rusting of steel and spalling (disintegration) of concrete i.e. loss of durability.
Easy entry of sulphate from the environment causes expansive reaction with the tricalcium aluminate (C3A) present in cement. This cause disintegration of concrete and loss of durability.
Entry of carbon dioxide causes carbonation of concrete i.e. loss of alkalinity of concrete or loss of the protective power that concrete gives to the reinforcement or concrete cover into the embedded steel, steel becomes vulnerable to the attack of moisture. This expedites rusting of steel as the protective concrete cover is no longer alkaline in nature.
Voids reduce the contact between embedded steel and concrete. This results in loss of bond strength of reinforced concrete member and thus the member loses strength.
Voids such as honeycombs and blowholes on the exposed surface produce visual blemish. Concrete surface is not good to look at with such blemishes. Concrete with smooth and perfect surface not only looks good but is also stronger and more durable.
For more details visit or download
