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Re: Slab on grade

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Phil
For what it is worth from field experience.
I am assuming that your are going to place the slab before erecting the
building.  Thus you run the risk of different ambient conditions for each
slab placement. I am also assuming the base and sub bases are properly
compacted.

We have had mixed results with cracking of a 6" slab if control joints were
cut in approximately 20ft x 20ft square. . (Fibermesh added concrete)  
We have had excellent results holding the slab to max 15ft x 15ft squares.  
Cut the joints ¼ slab thickness as soon as possible don't wait to long.

Be careful with fibermesh, pockets of it can form if not mixed correctly. 
Also if not properly finished fibers can be dragged to the surface. 
We have had to use weed burners to remove surface fibers. 

Good luck with your project and the toys your wife has collected.
Joe Murar



At 08:42 AM 10/8/98 -0700, you wrote:
>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?
>
>2) What about fibers?
>
>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?
>
>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
>
>
>