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RE: Slab-on-grade control joint question

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All things being equal, yes. The movements/shrinkage that cause cracking
will occurs at the path of least resistance, in this case, the location
where there is less concrete. The rebar or WWF does not do a whole lot
in the first day or so to prevent cracking, you need the joints to
relieve the internal stresses that build up from the heating and cooling
as the concrete cures.

-----Original Message-----
From: Cliff Schwinger [mailto:clifford234(--nospam--at)comcast.net] 
Sent: Sunday, August 04, 2002 11:20 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Slab-on-grade control joint question

Since the reinforcing steel is providing the "real" resistance to
cracking, will a weakened plane (created via a Soff-Cut machine) really
create enough weakening in the slab (with continuous reinforcing across
the control joint) to ensure that the crack will occur at the joint and
not at some other location.

I have a feeling that if the reinforcing is laying on the bottom of the
slab it will not be as effective in restraining cracks and the
"soff-cut" joint will be sufficiently weak to cause the shrinkage crack
to occur there. But if the reinforcing is properly chaired to within 1"
clear of the top of the slab, I have a feeling that the "soff-cut" joint
not that much more of a "weakened plane" than anywhere else on the slab.

Cliff

> cracking and are not deep into the slab. In a weakened plane joint,
the
> main requirement is to not soff-cut the slab too late. The reinforcing
> is the same as everywhere else in the slab - no cutting is necessary.



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