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RE: aggregate size in elevated structural slab

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I would not permit 3/8 aggregate mix for structural concrete.
3/8 mix will experience around 30% greater shrinkage, so even with the WWM you will have cracking problems.  If they insist on 3/8 mix for pumping etc (which is really bulls**t) have them provide a performance guarantee; you will be amazed how fast the larger pump becomes feasible.
Paul Feather PE, SE

From: David Schonacher [mailto:Davids(--nospam--at)]
Sent: Monday, September 01, 2008 9:14 PM
To: seaint-ad(--nospam--at)
Cc: seaint(--nospam--at); radams(--nospam--at)
Subject: aggregate size in elevated structural slab

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.
consulting engineers
1095 E. Brandon Blvd.
Brandon, FL 33511
Phone 813-655-2884, Ext. 301
Fax 813-655-2886
Email: davids(--nospam--at)