concrete strength 2

[DNBEA]

the contractor violated the max drop criteria when pour the piling. they dropped about 20ft. we specified 4000psi concrete. what is the minimum strength of the concrete it can achieve. any idea?

 

[civilperson]

There is no maximum drop criteria for falling concrete as long as the placement does not impact the reinforcement cage with damage to the bar location. The cylinders will adequately match the in place concrete.

 

[PEinc]

According to M.L. Tomlinson's Pile Design and Construction Practice, Fourth Edition, Section 3.4.4, Page 90, "Concrete placed in 'dry' shell piles is merely dumped in by barrow or chute. It should be reasonably workable with a slump of 100 to 150 mm to avoid arching as it drops down a tapered shell or onto a reinforcing cage." Tomlinson does not give a maximum fall distance for the concrete. If there is water in the pile, it should be pumped out befour pouring the concrete. If water is seeping into the pile and you do not or cannot dewater, then you should allow the pile to fill to a stabilized water level and then tremie pour the concrete as Tomlinson describes in Section 3.4.7 on Page 93. I believe that there have been one or more studies done on caissons (drilled shafts, bored piles) which indicate it is acceptable to dump concrete into dry shafts. Most piles, caissons, drilled shafts, bored piles are at least 20 feet deep. Unless your concrete mix was very stiff, I would not expect that you would have a problem.

 

[DNBEA]

thanks

 

[BigH]

I think that one more thought might be considered. What is the purpose of the concrete? Is it being relied on for the geotechnical or structural design? - or is it just filler? (e.g., filling a steel tube pile.)

 

[Zambo]

The risk when dropping concrete for any form of construction is segregation, this is particularly the case when there is dense reinforcement and the concrete is falling through the rebar cage.

For this reason I belive most codes would limit dropping concrete to about 3m, beyond that a tremie should be used. Having said that I expect that the pile was reinforced by a cage on the circumference and that the rebar would not be considered dense, in this case 6m does not seem excessive.

As mentioned in other replies this is only in the case that the pile is "dry". For future castings a tremie is adviseable.