Max free fall for ready-mix concrete

[Polecat]

Does anyone know of a code requirement that stipulates the maximum free fall that you can drop concrete from a ready-mix chute? I am aware of the possibility of segragation in this process, and feel sure that there must be a specific limit.

I have a pole to be direct buried in an augered hole and backfilled with concrete. I need to know the depth limit I can go to before requiring a treme or a concrete pump to be used.

Polecat

http://www.spiraleng.com

 

[Ron]

There is no code requirement for the maximum free-fall in the US. The code (ACI 318) and recommended practice (ACI 301)state that concrete shall be placed as near as practicable to its final point so as to prevent segregation. IBC 2000 has similar wording.

As a practical matter, concrete of moderate slump (4 to 6 inches) can be dropped 6 to 8 feet without significant issue.

 

[AseismicGuy]

As far as I know and implement, take this limit as 5'..
and also after concrete touch the wet surface, do not allow the concrete spread more than 10'(diameter!)..

 

[Jim6758]

I have this argument with Contractors all the time. The problem generally is not free falling the concrete, but free falling it through a rebar cage. The amount of segregation that can occur in a 20 ft. pier, especially using a square cage, is appalling. The problem is especially acute in small diameter piers(e.g. 12" and 18&quot. The problem generally lessens as the size of the pier increases and when circular rebar ties are used. The 5 ft. limit found in many specifications is necessary only in situations where rebar is involved.

 

[dirtsqueezer]

I agree with Jim. The problem with free fall and fresh concrete is not the fall, but anything along the way that causes segregation. I been part of engineer-overseen pours into steel piles 80 feet deep that did not require tremies, as the reinforcing steel did not extend through the depth of the pile. Best of luck.

 

[Ron]

dirtsqueezer...I'm interested to know how you confirmed there was no segregation of the concrete at 80 feet without a tremie.

A steel pipe pile works almost like a tremie, itself. If you were placing concrete for a drilled shaft of the same depth, I'm not sure you could get the same results.

I do; however, agree with you and Jim6758 about other things causing segregation besides the drop height.