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Concreting of pile foundations requires quality and workability of concrete to be maintained for durable construction of pile foundations with required strength. The grade of concrete, its workability, consistency and mixing for concreting of pile foundation is discussed in this article.
Materials and methods of manufacture of cement concrete piles should be in accordance with the method of concreting under the conditions of pile installation. The slump for concrete for pile foundation should be as follows:
|Sl. No.||Types of pile||Minimum Slump||Maximum Slump|
|1||Driven cast-in-situ piles||100||180|
|2||Cast-in-situ bored piles|
|a) Water free unlined bore with wide space reinforcement||100||180|
|b) Tremie concreting||150||180|
|3||Under reamed piles|
|a) Water free unlined holes||100||150|
|b) Tremie concreting||150||200|
Consistency of concrete to be used for the piles must be suitable to the method of installation of piles. Concrete is so designed or chosen as to have a homogeneous mix having a slump/workability consistent with the method of concreting under the given conditions of pile installation.
Fig: Concreting of pile foundation
The grade of concrete to be used for piling should be minimum M25 (or as as required at the site for load conditions) with the minimum cement content of 400 kg/m3. Mixing is carried out in mechanical mixer only.
In case of piles subsequently exposed to free water or in case of piles where concreting is done under water or drilling mud using method other than tremie, 10% extra cement over the design grade of concrete at the specified slump is used subject to a minimum quantity of cement specified above.
For the design purpose of bore cast-in-situ piles, the strength of concrete mix using above mentioned quantities of cement is taken as M20. Concreting for the piles is to be done with tremie of suitable diameter. Natural rounded shingle of appropriate size may be used as coarse aggregate. It helps to give high slump with less water cement ratio.
For tremie concreting aggregates having nominal size more than 20mm should not be used. Weigh Batching: The aggregate is always measured by weigh batching making due allowance for the water content in the aggregate. Volume batching of aggregate should not be used. Read more on Pile Foundations