Control joints in a large slab?

Originally Posted By: smcintire
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http://www.nachi.org/bbsystem/usrimages/P/PA240025.JPG ]


[ Image: http://www.nachi.org/bbsystem/usrimages/P/PA240029.JPG ]


[ Image: http://www.nachi.org/bbsystem/usrimages/P/PA260072.JPG ]


[ Image: http://www.nachi.org/bbsystem/usrimages/P/PA260073.JPG ]


Originally Posted By: clawrenson
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Typically in concrete ground slabs (slabs on grade) control joints should be in the range of 15-20 feet. Control joints are intended to induce controlled cracking that may result from tensile stresses to occur along predetermined lines. Additionally, they are also commonly used where irregular shapes occur.


http://www.concretenetwork.com/concrete/slabs/controljoints.htm


--
Ontario Home Inspections Inc.

Originally Posted By: mcyr
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icon_smile.gif icon_smile.gif


Steve’


In this type slab I would recommend cutting the slab control joints as close to a ten foot square as possible considering all the pipe penertrations and bond outs that I see.

Any time you create a bond out or a round penatration, the slab will relieve it's shinkage in those locations.

It can be possible to deviate from the ten foot parameter and locate the cuts under partion walls and aim as much as possible to pipes and/or bond outs. This way the cuts will be concealed and not be as visible to also impair floor coverings.

In my area it is also recommended to use 3000 PSI concrete with no air-entrainment. This seems to eleviate the slab curls normally seen at control joints and construction joints.

My concept of slab curl would be to seal the sawed control joints as soon as possible, because when the slab dose release, the air flows down under the slab and induces the slab curl syndrome. I have not proven this yet, but someone will eventually. When air flows to the underside of a concrete floor to meet the moist surface, it tends to dry like the surface and reacts like the dry surface, and tends to force upwards creating a curl and hump in the floor at the construction or control joint.
Remedial work for the flooring applications can be costly and time consumming.

Hope this helps.

Marcel


Originally Posted By: rcooke
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mcyr wrote:
![icon_smile.gif](upload://b6iczyK1ETUUqRUc4PAkX83GF2O.gif) ![icon_smile.gif](upload://b6iczyK1ETUUqRUc4PAkX83GF2O.gif)
Steve'

In this type slab I would recommend cutting the slab control joints as close to a ten foot square as possible considering all the pipe penertrations and bond outs that I see.

Any time you create a bond out or a round penatration, the slab will relieve it's shinkage in those locations.

It can be possible to deviate from the ten foot parameter and locate the cuts under partion walls and aim as much as possible to pipes and/or bond outs. This way the cuts will be concealed and not be as visible to also impair floor coverings.

In my area it is also recommended to use 3000 PSI concrete with no air-entrainment. This seems to eleviate the slab curls normally seen at control joints and construction joints.

My concept of slab curl would be to seal the sawed control joints as soon as possible, because when the slab dose release, the air flows down under the slab and induces the slab curl syndrome. I have not proven this yet, but someone will eventually. When air flows to the underside of a concrete floor to meet the moist surface, it tends to dry like the surface and reacts like the dry surface, and tends to force upwards creating a curl and hump in the floor at the construction or control joint.
Remedial work for the flooring applications can be costly and time consumming.

Hope this helps.

Marcel

It was always done when I was in large construction .
Never more then 20 ft..*20 ft.
Always had wire mesh in the pour and Plastic under the pour .
Plastic to slow down the drying as well as keep moisture
away from the floor at a later date .
Mesh to try and keep all sections at the same lever after shrinking.


--
Roy Cooke Sr.

http://Royshomeinspection.com

Originally Posted By: Jay Moge
This post was automatically imported from our archived forum.



relief cuts are neede. and i’ve always seen them in the blue prints and they line up with each unit shared wall, which was usualy about 17-20ft… icon_cool.gif


Originally Posted By: smcintire
This post was automatically imported from our archived forum.



Thanks everyone! That is what I was thinking and was hoping I would get comments that agreed with my thinking. I agree with the concrete curling comment. That is what happend to the crack in the last picture.


Thanks