Plain Concrete Grade Wall - Slab Detail

[waytsh]

Client would like to replace my 2' wide X 1' thick concrete footing and my 8" thick x 22" tall concrete grade wall with a solid rectangular plain concrete grade wall 2' wide x 34" tall. They would also like to try to pour the slab at the same time and use bent dowels at the slab to grade wall transition.

I am not so concerened about the grade wall as there is virtually no load on it because of the metal wall sheeting above and it is serving mainly as a frost break but I am concerened about the transition to the slab and it being one continuous pour. Even with the dowels I am concerned about cracking as the slab wants to shrink and is restrained by the grade wall.

Has anyone used a detail like this and have any thoughts or recommendations?

Thanks!

 

[hokie66]

The slab will certainly shrink and crack. In order to prevent this cracking, there must be provision for separation of the two or a way for the slab to slide relative to the footing.

 

[waytsh]

Here is a detail showing what they would like to do.

 

[ToadJones]

The grade wall potion of the sketch seems mighty hefty.

 

[waytsh]

Oh it is. I wouldn't have a problem going thinner for the reasons I mentioned earlier and I will tell them this before they construct but this is the description they gave me.

 

[waytsh]

I had them change the detail (see attached). Unfortunately they had already dug the trench for the grade beam at 24" wide so they are stuck with that width.

 

[hokie66]

Their detail was terrible. Not only for causing shrinkage cracks in the slab, but those bars around the corners violate good practice, as if they straighten, they break out the corners.

Suggest rather than just a cold joint, a layer or two of plastic would help to allow the slab to slide and reduce restraint cracking. However, if it is necessary to provide tiedown to the footing, crack control would be a secondary consideration.

 

[ToadJones]

Are there concerns with cold penetrating the slab as have been expressed in other similar posts?

 

[msquared48]

They were trying to save money by limiting forming and the number of pours, saying the extra cost of the concrete was less expensive.

Personally, I would limit possible water intrusion at the exterior here by setting the edge of the slab in by the width of the exterior wall above. This will require extra formwork. Otherwise, depending on your locale, you could be looking at frost heave between the bottom of the slab and the strip footing. Just a thought...

Mike McCann
MMC Engineering
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