Reinforcement Concrete Cover for Slab in Ground - Plastic Vapor Barrier? 2

[JoelTXCive]

I have a question regarding the concrete cover requirements for a slab in ground.

Does having a plastic vapor barrier (6 mil to 10 mil) change the 3" cover requirement for concrete 'cast against & permanently in contact with ground?'

Could the cover requirements be reduced? Personally, I don't think it is a great idea to reduce them, but I wanted to get other opinions.

Below is the ACI table...

Thank for input!

 

[hokie66]

If just a slab on ground, it would not be structural, so I don’t think the ACI code would apply.

 

[thaidavid40]

A vapor barrier is just that, and is not a water-tight seal (as typically installed and used). I don't think that using one would change the ACI classification of being in contact with earth.
Dave

Thaidavid

 

[JoelTXCive]

Hokie- you are correct. ACI 318 section 1.4.7 specifically says that 318 does not apply to slabs in ground.

But.....I think that 318 might still apply. Here is my argument...

I should state that I am talking about cover for conventional or post-tensioned ribbed slabs where you get 24"-36" beams and 4"-6" thick pad areas.

As mentioned, ACI 318 does not apply to slabs in ground. So, I went to ACI 360, which covers Slabs on Ground.

To the best of my knowledge, ACI 360 does not provide any guidance on concrete cover. Also, if you have a slab supporting building code loads, then ACI 360 refers you back to ACI 318. See below excerpt from ACI 360.

My reading is that If we follow ACI 360, then I think we should apply the ACI 318 cover provisions.

I'm confused and open to input?

 

[hokie66]

For ribbed foundation slabs, I would treat them as footings, so the cover provisions would apply. A vapor barrier would not change the requirement, but a membrane would.

 

[dik]

Rebar should be approx 2" from the top of the slab, so, 3" cover to soil shouldn't even be an issue.

Dik

 

[sswan60]

IMO no, I believe the common 3" requirement deals with the variations in the subsurface elevation and stability during a pour. I say keep it at 3".

Depending on the size of the job. We have found it beneficial to pour a mud slab using lean concrete to form a stable level base to build off of. In this case 2" of cover would be acceptable.