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RE: Free-Fall of Concrete
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Free-Fall of Concrete
- From: <William.Sherman(--nospam--at)CH2M.com>
- Date: Tue, 29 Apr 2008 09:54:15 -0600
Do you know how much care was taken in the upper part of
the free fall? I've seen articles that say that free fall works as long as
the concrete does not impact any obstructions (rebar, sides of the hole,
If the concrete was not controlled to drop vertically in
the center of the hole, segregation due to impact with the rebar or sides of the
hole could have occurred.
Drop chutes are still the safest
CH2M HILL /
I worked for the
contractor in building New York
City's West Side Treatment Plant. We had 36"
diameter steel pipe caissons that were driven to rock and then socketed into
the rock. There was rebar only in the top of the caissons. We
filled the caissons with concrete, using free-fall. Everybody thought it
was working until the Resident Engineer had us make an exploratory boring
through the concrete in several of the caissons - DISASTER!! Voids were
found. More borings had to be made. More voids were found.
This one cost us large!
Sent: Tuesday, April 29, 2008 7:10
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
I'd like to to
hear what others are doing and any documented results or articles