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RE: Maximum Aggregate Size

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Depends on how densely packed your reinforcing is.  If you specify a 1"max
rock, not much of it is actually 1", perhaps 10%. It depends on the ASTM C33
grading being provided.  If the reinforcing is reasonably spaced, say 3" or
4", the rock won't "pile up" or if it does it will get settled into the
concrete when you vibrate the form. If you have a slab where the reinforcing
is that closely spaced you are probably going to have lots of other problems
anyway.  In my experience, we have never had rock pockets in slabs except
very occasionally around a PT anchor. (got to keep those iron workers on
their toes!)

Nick Blackburn


-----Original Message-----
From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
Sent: Monday, June 16, 2003 1:57 PM
To: seaint(--nospam--at)seaint.org
Subject: Maximum Aggregate Size


Yes!

The aggregate will pile up on the reinforcing and, block any concrete from
passing the reinforcing.  In general, you will have voids up the wazoo.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Michael Bryson wrote:

. > ACI 211.1-91 gives the maximum aggregate size as 3/4 of the clear
spacing
. > between reinforcing bars and between reinforcement and formwork.

. > California practice commonly uses 1" max aggregate size. This means you
. > would need to space reinforcing bars and have clear cover of at least
. > 1.33" (say 1.5"). Slabs typically require 3/4" minimum (or 1" minimum
for
. > a higher fire rating).

. > Is there a problem with allowing a 1" max aggregate size but keeping a
. > 3/4" cover? This seems to be the standard practice and I am not aware of
. > any problems with it.

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