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RE: Free-Fall of Concrete

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Code writers are often accused of trying to regulate everything in construction practice.  Although there is nothing in the code to preclude free-fall during placement, it is not considered a good practice.  The problem is not the fall, but hitting the reinforcing on the way down. 
A drop-chute can be used on caissons to keep the concrete from hitting the reinforcing cage.  This is allowed by the Bureau of Reclamation and by the US Army Corps of Engineers guide specs for caissons. 
If you allow a drop-chute, it should be monitored.  A drop chute is often available by a lot of ready mix suppliers.  The new ones are made from FRP.

Harold Sprague

Date: Tue, 29 Apr 2008 07:10:29 -0700
From: JCoombs(--nospam--at)
To: seaint(--nospam--at)
Subject: Free-Fall of Concrete

Howdy, Y'all.
I've seen many specs and General Notes that don't allow free-fall of concrete more than 5 ft (tremie or other means req'd).  There is nothing in any code documents that I'm aware of that nix free-fall.  Frankly, I don't see anything wrong w/ it and agree with the one article I've seen addressing it.  Maybe a very long drop and large aggregate may cause some of the aggregate to bounce off the concrete below separating it. 
I'd like to to hear what others are doing and any documented results or articles supporting either.

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