06-10-2022, 10:23 AM
Initial Setting Time Of Concrete
The initial setting time of concrete is the time required for the mxi to stiffen after which compaction is not possible. The Initial setting time of concrete can depend on the following factors :
Initial setting time of cement used in concrete. Quantity and type of cement used in the mix.
Ambient temperature and wind conditions.
Temperature of water and other ingredients used in concrete.
Use of chemical additives such as retarders.
Workability and temperature of the concrete.
Absorption of water by aggregates in the concrete.
If a massive pour is required to be done it is essential to know the setting time of the mix in field conditions. This can be done by observing the compaction of a sample concrete of identical mix and in identical conditions. The poker is then inserted and withdrawn at different intervals of time say 15 to 30 minutes. If the poker is unable to ink into the concrete under its own weight or it leaves a hole when withdrawn slowly, it means that the initial setting of concrete has begun and the time when this happens is the initial setting time of concrete in the fields.
If this time is observed to be say one hour, then keeping a safety margin, the placing of concrete has to be planned in such a manner that the subsequent layers of concrete are placed within 30 minutes of each other, the other 30 minutes being the safety period for unforeseen stoppages and unknown problems. The safety period has to be suitably increased if standby equipment or other facilities are not planned or available.
The initial setting time of concrete is the time required for the mxi to stiffen after which compaction is not possible. The Initial setting time of concrete can depend on the following factors :
Initial setting time of cement used in concrete. Quantity and type of cement used in the mix.
Ambient temperature and wind conditions.
Temperature of water and other ingredients used in concrete.
Use of chemical additives such as retarders.
Workability and temperature of the concrete.
Absorption of water by aggregates in the concrete.
If a massive pour is required to be done it is essential to know the setting time of the mix in field conditions. This can be done by observing the compaction of a sample concrete of identical mix and in identical conditions. The poker is then inserted and withdrawn at different intervals of time say 15 to 30 minutes. If the poker is unable to ink into the concrete under its own weight or it leaves a hole when withdrawn slowly, it means that the initial setting of concrete has begun and the time when this happens is the initial setting time of concrete in the fields.
If this time is observed to be say one hour, then keeping a safety margin, the placing of concrete has to be planned in such a manner that the subsequent layers of concrete are placed within 30 minutes of each other, the other 30 minutes being the safety period for unforeseen stoppages and unknown problems. The safety period has to be suitably increased if standby equipment or other facilities are not planned or available.