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RE: Saw Cut joints in concrete walls

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Crack control requires the reinforcing be discontinuous at the joint.  Whether it is a wall or even a simple slab on grade.  The purist approach is to completely terminate the reinforcing each side of the control joint and use smooth slip dowels for the shear interlock.  The other option is to cut 50 percent of the reinforcing, but I have seen good and bad results with this.
 
For a wall I usually spec slip dowels and also use a chamfer strip on the forms.
 
If the reinforcing is continuous, the wall will not even realize the sawcuts are there and will crack where tension from shrinkage is greatest.  I have seen vertical shrinkage cracks 5 inches away from a sawcut.  The cracks micro-form long before the saw cut is applied, and the continuous bonded deformed reinforcement does not permit formation of a designated failure plane.
 
 
 
Paul Feather PE, SE
 
 


From: Gautam Manandhar [mailto:Gautam_Manandhar(--nospam--at)ci.richmond.ca.us]
Sent: Wednesday, February 11, 2009 10:37 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Saw Cut joints in concrete walls

Paul:

 

I do not believe the wall has been poured yet.  I do not know that the reinforcing is – I’d presume it would be two layers as it is 12 inch thick.  The architect would like to control the shrinkage cracks by hopefully directing it to the control joint.

 

Gautam Manandhar, SE

 


From: Paul Feather [mailto:PFeather(--nospam--at)se-solutions.net]
Sent: Wednesday, February 11, 2009 10:12 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Saw Cut joints in concrete walls

 

If the wall is already placed and the reinforcing is fully continuous in two layers, saw cuts will be completely ineffective and are a waste of time.  Crack control needs to be planned in the wall construction.

 

Paul Feather PE, SE

pfeather(--nospam--at)SE-Solutions.net

www.SE-Solutions.net

 

 

 


From: Gautam Manandhar [mailto:Gautam_Manandhar(--nospam--at)ci.richmond.ca.us]
Sent: Wednesday, February 11, 2009 10:08 AM
To: seaint(--nospam--at)seaint.org
Subject: Saw Cut joints in concrete walls

List members:

 

I was recently asked a question on how soon a contractor can saw cut a 12 in concrete wall (boundary wall) to install crack control joints.    The wall is free standing and varies from 5 to 10 feet in height.  No expansion joints were planned.  The rebar is in and concrete ready for pour.

 

Since a lot of the cracks are caused as the concrete dries and shrinks, it would seem appropriate to provide a saw cut as soon as possible.  ACI requires concrete to be cured for at least one week (regular concrete). 

 

I would appreciate your insight.

 

Gautam Manandhar, SE