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RE: aggregate size in elevated structural slab

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David,
It is common to use mini conveyors for placing concrete these days.  That eliminates the whole pumping problem and you can have any aggregate you want.  But I will presume that you have broached that topic. 
 
The 3/8 aggregate is pretty small and the 3/4 might be too large.  Try a #6 which has a lot of 1/2" aggregate.  Heavy up your WWR to something like a 6 ga.  That will keep your cracks pretty tight. 
 
On a separate issue, you might want to consider using a heavier deck.  I will put my construction worker hat on.  That 26 ga is a pain.  Stepping on it will crush the flutes of the deck.  If you need to run a Georgia buggy, you are out of luck.  I wouldn't use anything less than 24 ga and I prefer a 22 ga.  Check out the costs.  It is minimal.  It will also allow you to use a Copperhead laser screed, which eliminates the need for screed bars.

Regards,
Harold Sprague




Subject: aggregate size in elevated structural slab
Date: Tue, 2 Sep 2008 00:14:16 -0400
From: Davids(--nospam--at)avantitampa.com
To: seaint-ad(--nospam--at)seaint.org
CC: seaint(--nospam--at)seaint.org; radams(--nospam--at)adams-engineers.com


I have another contractor requesting to use small rock (3/8" pump) mix for an elevated slab (3" concrete with WWM reinforcing over 0.6C 28 ga. decking over joists 24" o/c) mearly so it can be pumped. I've always been of the opinion 3/4" rock mix shall be used as pump mixes tend to present more shrinkage cracks and it's a "structural" slab. I know it's a durability issue for a slab on grade, but what about an elevated slab (walking traffic only)? I'm not finding any reference that helps one way or the other. After another round of research I'm thinking it shouldn't be a problem with WWM being used. Any thoughts?
 
Thank you.
 
David Schonacher Jr., P.E.
AvantiGroup
consulting engineers
1095 E. Brandon Blvd.
Brandon, FL 33511
Phone 813-655-2884, Ext. 301
Fax 813-655-2886
 


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