Control joint corner to corner.

[Cannonball]

Hi all.

Getting ready to pour a monolithic slab 18'X24' for my back yard workshop/storage garage.
In order to avoid having control joints near the post location for a future two post lift I am thinking on placing the control joints from corner to corner.
There will be a 6"X6" floor drain in the centre of the slab.
The slab will be 6" thick with the outer 2' being 10" thick. 1/2" rebar at 12" centres.
Will also be insulating under the slab and installing I-Pex for future radiant heat.

Do you see any problem going corner to corner with the cuts?
I know this is not ideal as the long side of one triangular piece is 24' but my thought is this is better than no cuts and will leave the lift posts on the largest possible piece.

Your thoughts and input are appreciated.

 

[ConCretin]

I wouldn't recommend the diagonal CJ pattern. The 'panels' created by CJs should be as square as possible to avoid random cracks.

Personally, I wouldn't bother with CJs at all in a 18 x 24 mono slab especially one as heavily reinforced as yours. Keep the mix water to a minimum with a mid range and cure the slab properly and you should be fine. I've got a 28 x32 with no CJs and no cracks.

 

[Cannonball]

No control joints was also a consideration.
My house garage (20'x22') was done with out CJs and even has a protruding corner into it. Only a few hairline cracks which I filled and covered with an epoxy coating. Never showed up after three years. Knock on wood!!

If I did this, then I would go to a 6" round floor drain to lessen corners where cracks could occur.

 

[GYPSY400]

My building engineer is calling for control joints in an H pattern, so im installing the hoist posts just outside the cuts.. Also, be sure to let the guy know where the hoist posts are going so he can avoid running pex in these areas

My slab is 36 x 24, fully reinforced with rebar and mesh

 

[Gary S]

My experience with concrete tells me that any time you have a piece of concrete (or control joint) that comes to a point, it will be weak as it gets narrower and you can expect cracks across the narrow ends.
The H pattern suggested here sounds good to me.

 

[Shea]

My experience with concrete tells me that any time you have a piece of concrete (or control joint) that comes to a point, it will be weak as it gets narrower and you can expect cracks across the narrow ends.

I've witnessed this many times.