Exterior Equipment Concrete Pad

[CDG31]

I have an exterior concrete pad that is 14ft x 8ft. Frost Depth is 2ft. A 12" pad is enough to support the equipment. Can I provide a turndown only at the perimeter to account for the frost depth (2ft turndown) and keep the interior of the pad at 12"? Or do I need to thicken the entire concrete pad to 2ft?

Thank you,

 

[phamENG]

If it's exterior, what's going to keep the soil right under the slab inside the turn down from freezing and heaving?

 

[TRAK.Structural]

If it's exterior, what's going to keep the soil right under the slab inside the turn down from freezing and heaving?

Maybe the insulative quality of concrete? No idea if that actually checks out, but I've seen this approach taken.

Maybe use a layer of gravel under the pad to a depth beyond frost?

 

[ANE91]

Maybe the insulative quality of concrete? No idea if that actually checks out, but I've seen this approach taken.

The frost jacking happens due to ice lens formation at the boundary btwn cold enough and not cold enough.

 

[TRAK.Structural]

The frost jacking happens due to ice lens formation at the boundary btwn cold enough and not cold enough.

I don't know about ice lens formation, but I guess my thinking was that if the concrete is thick enough than this "boundary" you mention may occur within the concrete pad and therefore nullify any heave.

 

[jerseyshore]

Usually when we do a pad like this it's "floating". Rare that it needs to go down to frost depth.

Our frost depth in NJ varies from 30" and up so at only 2 ft I'd just make the whole thing 2 ft thick if frost is that much a concern.

 

[HTURKAK]

provide a turndown only at the perimeter to account for the frost depth (2ft turndown) and keep the interior of the pad at 12"? Or do I need to thicken the entire concrete pad to 2ft?

Inverted bowl foundation is OK and turndown slab edge 2 ft is reasonable to avoid erosion , but the soil below the slab down to frost depth 2ft should be frost free material ( sand, gravel etc).

 

[haynewp]

We put in non-frost heave susceptible granular fill to the frost depth. I usually ask the geotech for the recommended fill type in that area.

 

[gte447f]

If in-situ soil is replaced with non-frost heave susceptible material down to frost depth, then it seems to me that a turndown slab edge would not be needed for any frost related reason, and the entire slab could be just 12" thick if that satisfies all other considerations? Is this right?

 

[DaveAtkins]

If in-situ soil is replaced with non-frost heave susceptible material down to frost depth, then it seems to me that a turndown slab edge would not be needed for any frost related reason, and the entire slab could be just 12" thick if that satisfies all other considerations? Is this right?

Yes.

 

[GaStruct]

In my experience most housekeeping pads don't go down to frost. It's usually a non-critical design item.

 

[dik]

If the supporting equipment can tolerate movement, I usually let it float. If not I usually float it on hi load rigid insulation. If still a problem, I use real foundations.