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RE: 50' oc control joints for SOG ok?

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Rich,

I was please to see your rule of thumb of 2-3 times
the slab thickness.  I have stuck in my head that
control joint spacing should be 34t, and that's what I
use in design.

Recently I poured a patio along side my house, 4"
thick, exposed aggregate, no fibers, #4@24" centered
on chairs, no control joints.  Plan dimensions:  8' x
40'   No (visible) cracks after a month, and we've had
a severe dry spell here in the midwest.  I'm sure I'll
get a few cracks, but they won't open because of the
rebar (vs mesh, which would be at the bottom of slab).

IMHO, the critical aspect of concrete work is curing. 
My pour was wet for seven days.  Contractors can't or
won't do that, and I place little faith in the
spray-on compounds.

John Riley
   

--- Rich Lewis <seaint03(--nospam--at)lewisengineering.com> wrote:

> I suggest you consider the function of the slab and
> whether you can tolerate
> cracks in the slab.  As we all know, concrete will
> crack somewhere.  If you
> can tolerate cracks in the slab and you want to rely
> on the SF method then
> go ahead.  But if you can't tolerate them then put
> them in much more
> frequently.  Also, rebar placement plays a big part
> in crack control.  If
> the bars don't make it up to the top then you will
> get much more cracking.
> I recently did a 6 inch slab with joints at 25 ft.
> on center in one
> direction and about 15 ft. in the other.  It cracked
> at about 12.5 ft. in
> just about every panel.  The owner had serious
> concerns.  I didn't know of
> their crack concerns until after the concrete was
> poured.  Had I known
> before I would have put joints in more frequently
> than I did.
> 
>  
> 
> Personally, I don't trust the SF method.  I always
> get much higher spacing
> than the rule of thumb of 2-3 times slab thickness. 
> From my experience, in
> the real world the rule of thumb holds up much more
> than the SF method.
> 
>  
> 
> Rich
> 
>  
> 
>  
> 
>   _____  
> 
> From: Haan, Scott M POA
> [mailto:Scott.M.Haan(--nospam--at)poa02.usace.army.mil] 
> Sent: Tuesday, August 16, 2005 4:04 PM
> To: seaint(--nospam--at)seaint.org
> Subject: 50' oc control joints for SOG ok?
> 
>  
> 
>  
> 
> For a 6" slab on grade is it acceptable to have a
> 50' oc control joint
> spacing for no. 4 @ 18" oc ea way.  I am looking at
> a tensile stress based
> on subgrade friction formula that calculates out.
> 
>  
> 
> Thanks.
> 
>  
> 
> 



		
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