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RE: SLAB ON GROUND CONTROL JOINT

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Rich,
I do not think the 1/4th d saw cut applies to slabs or mats greater than about 6" and I agree that it is better to cast the joint full depth for installation before the pour.  Depending on the concrete and steel strengths you need about 0.7% to completely eliminate cracking but 0.5% or even 0.4% should be okay with joints every 25'+/-.  The joint detail with filler (Homex, etc.) below backer rod and then adhesive filler is good but it is important that the depth of the filler is no greater than its width.  The reason for that is the volumetric change that occurs upon expansion.  With a greater depth the material has to bulge too far upward and it cannot return to its original shape.
Richard Hess
-----Original Message-----
From: Rich Lewis [mailto:seaint04(--nospam--at)lewisengineering.com]
Sent: Thursday, March 08, 2007 9:34 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: SLAB ON GROUND CONTROL JOINT

Paul,

 

Thanks for the feedback.  I appreciate it very much.

 

Did you reinforce it for the 0.5% steel to eliminate cracking?  If you use top & bottom steel do both layers count towards the 0.5% steel to eliminate joints, or just the top steel.

 

Thanks for your help.

 

Rich

 

 


From: Paul Blomberg [mailto:paul.blomberg(--nospam--at)gmail.com]
Sent: Thursday, March 08, 2007 10:16 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: SLAB ON GROUND CONTROL JOINT

 

Just ran into this same situation but took a little different approach.  We have a 14" SOG and reinforced it to eliminate the contraction joints and placed construction joints with dowels at the concrete pour limits.  We have significant forklift traffic and wanted to minimize joints.  We also didn't know if the contractor can cut the contraction joints to a 1/3 or 1/4 depth.

 

Paul.

Phoenix, AZ

 

On 3/8/07, Rich Lewis <seaint04(--nospam--at)lewisengineering.com> wrote:

I have a 12" thick slab on ground.  I'm wondering how deep the saw cut joints should be.  ACI 302.1R-04 "Guide to Concrete Floor & Slab Construction" does not have a recommended saw cut depth.  I have a 1989 version of the same standard where the recommended cut depth is 1/4 the slab thickness.  In this case the cut is 3" deep.  The joint then needs to be filled with a semi-rigid joint filler.  The tables I see for joint filler only go up to a joint depth of 1.75 inches.   Is anyone aware of other recommendations for shrinkage control joint depth for thick slab?   

Thanks for your help.

Rich