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RE: slab on grade

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I imagine that there are more than a few reasons for the excessive
shrinkage.  The concrete plant is no longer in business, and the records are
not that good.  And I imagine there was the standard spit on it and run
curing technique.  But the critical issue is that there was no steel in the
slab to hold any cracks together.  Once the cracks opened up the 2 slabs
curled differentially and now we have a tripping issue.

The cracks would have happened under the best of circumstances, but
reinforcing steel would have prevented them opening up and we probably would
not have lost granular interlock and the resulting tripper would not be

Harold Sprague
The Neenan Company

-----Original Message-----
From: Horning, Dick/CVO [mailto:dhorning(--nospam--at)]
Sent: Tuesday, January 05, 1999 10:51 AM
To: 'seaint(--nospam--at)'
Subject: RE: slab on grade

Could this have been partly due to a poor concrete mix (i.e., too high w/c )
or poor curing ?

	-----Original Message-----
	From:	Harold Sprague [SMTP:harold.sprague(--nospam--at)]
	Sent:	Tuesday, January 05, 1999 9:38 AM
	To:	'seaint(--nospam--at)'
	Subject:	RE: slab on grade

	I just inspected a project with the worst drying shrinkage cracks
that I have ever seen.  The cracks were 5/8" wide and there were many of
them.  It was a slab using polypropylene fibers.  I would not count on
fibers except for control of bleed water and plastic shrinkage cracks.
	You have already seen posts on post tensioning which is a good
	Consider also shrinkage compensating concrete.  
	Another thing is to eliminate as many restraints as possible.  Avoid
thickened areas.  Any penetrations by pipes, light standards, etc. should be
wrapped with a closed cell foam and sealed.  This allows the slab to shrink
without being restrained by the penetrating structures.  Add reinforcing
steel around any penetrations.  Try to create a good uniform slip plane and
eliminate restraints.
	Harold Sprague
	The Neenan Company
	harold.sprague(--nospam--at) <mailto:harold.sprague(--nospam--at)> 

	-----Original Message-----
	From:	jdcoombs(--nospam--at) <mailto:jdcoombs(--nospam--at)>
[mailto:jdcoombs(--nospam--at)] <mailto:[mailto:jdcoombs(--nospam--at)]> 
	Sent:	Monday, January 04, 1999 11:35 AM
	To:	'seaint(--nospam--at)'
	Subject:	slab on grade

	Happy New Year, y'all
	I need to put in a good slab for outdoor basketball courts.  The
client would like for them to be free of joints.  It will be an unloaded
slab, no traffic.  The slabs will be 100' x 65'.  I can spec a proper
subgrade spec.  How do I design for the slab thickness and reinforcing
required to keep cracking controlled.  I have reviewed  ACI 302 and 360, and
the PCA guide.  None really address the unloaded slab except fot the
"subgrade drag equation", which is not really a qualitative approach.  I'm
willing to add fibers to get a good crack control, but how does one balance
between that and steel?  How thick a slab?  How much steel?  How much
fibers?  Any comments are appreciated.
	Jerry D. Coombs, PE