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[TowerTalk] concrete

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Subject: [TowerTalk] concrete
From: gdaught6@leland.Stanford.EDU (George T. Daughters)
Date: Mon, 8 Nov 1999 09:49:27 +0008

Gary wrote...

> I'd like to hear comment on something the concrete people told me when I
> put in my base.  I think it might be important for those who haven't
> done it before.
> I was told that the use of the vibrator is a good idea, but that
> over-using it can cause problems with the concrete.  If you vibrate it
> beyond what it takes to get it to fill in the gaps, it begins to
> separate the components of the concrete.  I noticed some of that when I
> was playing with it in my pour.  Keep use of the vibrator to just what
> it takes.  Don't over-do it.

My concrete contractor consultant and the pumper-dude both told me:

1.  Concrete ordered to be pumped is usually delivered pretty "dry", 
with a small slump.  The mixer can adjust it as it's delivered to the 

2.  If it's pumped correctly, it doesn't need the vibrator, at least 
in the smallish hole I had.  (Gee, it seemed really big when I dug it 
by hand!)  The hose is put very near the surface, and the flow sets 
up a standing wave which will wet the sides of the hole, the rebar 
cage, and NOT incorporate any air bubbles.  They seemed convincing, 

The 2.5 cubic yard pour took under 3 minutes!


George T. Daughters, K6GT

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