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RE: Slab on grade

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See below.

Harold Sprague, P.E.
The Neenan Company
harold.sprague(--nospam--at)neenan.com


-----Original Message-----
From: Phil Hodge [mailto:phil(--nospam--at)joistdesign.com]
Sent: Thursday, October 08, 1998 9:43 AM
To: SEAOC
Subject: Slab on grade


I am writing this not as an engineer, but as an owner/contractor.  My
experience, both as SE and contractor, is exclusively with steel.  All I
know about concrete is that it cracks.

I am acting as
engineer/contractor/owner/banker/inspector/anything-else-anyone-can-think-of
on a 54'x105' hangar.  (I've always heard that anyone who acts as their own
attorney is employing a fool, does the same apply to engineers?  It's fun
wearing all the hats!)  

I plan the SOG to be 6" 3000 psi concrete with #4@12" both ways in the
middle, and a 12"x12" thickened edge, tapered to normal slab thickness
at 2:1, on 4" clean gravel.  The footings are not cast integrally with
the slab.  Soil is well compacted red clay common to eastern  Tennessee. 
Use will be for planes less than 3200#, plus dump trucks, backhoes, and any
other toys my wife acquires.  The finisher is just that, a
finisher.  He knows nothing about the stuff we're supposed to worry
about - rebar placement, crack spacing, mix, etc.  Three questions:

1)  How often should I cut control joints.  I will form and pour the
slab in two pours on seperate days, each 27'x105'.  I want the minimum
number of joints, but I also don't want any random cracks.  Suggestions?

	There are several publications regarding slabs on grade for design
and for construction that are published by the ACI.  Get em, read em.  You
can reduce your joints by adding rebar and providing a good slip surface for
the concrete to slide on from joint to joint.  Use PNA dowels and pocket
formers 800-542-0214.

2) What about fibers.

	When in doubt, use them.  They are cheap and offer good protection
from plastic shrinkage cracks, and they afford an increase in resistance to
cracking.  Do not use them in lieu of your rebar!

3)  Is there anything in the above that jumps out at those experienced
with concrete and shouts "This guy is an idiot"?  Anything I should do
different?  Again, suggestions?

	Just read the ACI stuff, and have fun.

By the way, if there are any pilots out there comfortable on 1900' of
grass, The 100 Aker Wood private field is at N85d46' W84o46'.  Drop in
someday.

TIA

Phil Hodge
phil(--nospam--at)joistdesign.com