Slab-on-grade radiant heat

[ajk1]

Has anyone ever done a building basement slab-on-grade with embedded plastic pipes in the bottom half of the slab that provide radiant heating?

Can the slab-on-grade design be the same as if there were no pipes in it -- that is, unreinforced and early-entry sawcut to about 1/4 the slab depth at 4.5 m maximum centres each way? I am concerend about whether the plastic pipes kill some or much of the effectiveness of the sawcuts.

If they do interfere with the effectiveness of the sawcuts, what can be done, without making the slab-on-grade excessively expensive?

The slab is about 70 m square. The plastic pipes are about 16 mm diameter I believe.

 

[XR250]

I did my basement radiant slab by dividing it into 20x20 ft. squares with cold joints and made each area a separate zone for the radiant.
Do not saw cut as you will likely hit the tubing.

 

[ajk1]

To ExcelEngineering - in my case I suspect that it is too vast an area (> 200 feet square, or 40,000 sq.ft) to be economical to zone into 20 foot square segments, although perhaps not. The sawcuting ought not be a problem because the mechanical engineer proposes a 150 mm (6") deep slab with the piping in the bottom half of the slab; the the piping will be well below the the bottom of the sawcut.

But what I am really interested in, is whether anyone has done large area slab-on-grade with the radant heating piping crossing the sawcuts. Or does anyone have any advice for how this should perform, if the palstic piping crosses the sawcuts?

 

[Canuck67]

I would expect that the plastic piping may provide some restraint at the control joint locations. How much restraint is difficult to quantify. As long as all parties are informed of the possibility of cracking and willing to accept the possibility of cracking within the panels, it should not be a problem.

 

[KootK]

I haven't done this but my gut feel is that it shouldn't be a problem. The radiant tubing should be much less stiff than the concrete and, therefore, shouldn't affect the cracking behaviour materially.

Are you concerned more with the performance of the slab or potential damage to the radiant tubing?

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[jayrod12]

In my experience the radiant heat tubing has the ability to elongate much more than your concrete crack width will be. Due to this I cannot see it providing enough resistance to change where the concrete will crack.

I would go ahead with your sawcutting as if the heat lines weren't there.

 

[KootK]

It's also not that different from the situation with topping slab systems which we deal with regularly.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[ajk1]

Thanks for your comments. Would you agree that we do not have to put any mesh or rebar in the slab-on-grade, as that would be our standard practice for slab-on-grade on sound soil and not loaded to greater than 100 psf? Thinking of 150 mm thick slab of 25 MPa concrete.

 

[XR250]

The tubing has a tendency to float to the top if not secured properly or often enough.

 

[ajk1]

Yes right. That requires only a mesh to tie it down to, but we do not need rebar over the piping to control cracking - right?

 

[DBronson]

ajk1:

See the attached for typical details. These are Viega's (from their Concrete Systems Manual"). Uponor (another major supplier) uses similar details.

Regards,

DB

 

[ajk1]

To Dbronson - this deals directly with my question and is very helpful indeed. Thank you very much. Much appreciated.

 

[ajk1]

Do you also happen to know how the pipes are held down against flotation?

And do we need to specify "expansion joints" at some given centres to avoid the possibility that the thermal effect from the embedded pipe heating will exceed the concrete shrinkage, and cause the slab to buckle?

 

[RFreund]

In regards to the details -> I have no experience here but from what I recall those tubes are pretty flexible (maybe there are different types of tubing?). I mean more flexible than pvc, but I suppose there is basically no adhesion from pvc to concrete(?). I suppose better safe than sorry (?). But atleast there is a publication to back you up.

EIT

http://www.HowToEngineer.com

 

[ajk1]

I expect that the sleeves are needed or they would not have shown them in their typical detail. But on a project 200 feet sqaure, it is a heck of a lot of sleeves to install.

 

[jayrod12]

I don't believe the radiant heating ever causes enough thermal expansion of the concrete to risk buckling. I have seen these installed in an 8 plex thickened edge slab (roughly 200'x50') using only sawcuts and there was no issues with either cracking outside of the sawcuts nor thermal expansion. And these were installed in an area where the heat is cranked all the time and the outside temperature is well below freezing for the majority of the year (Northern Canada).

 

[jayrod12]

There's always the danger of vertical movement causing issues in a building. you need to prepare the base material appropriately to limit the amount of movement seen. if you are concerned you could always put in a rebar mat (or mesh but I rarely allow the use of mesh in any of my projects as more often than not it gets trampled during the concrete pour and ends up at the very bottom of the slab removing any effectiveness).

The benefit to adding the mat is you can then tie the radiant heat lines to the mat which will keep them in the bottom of the slab instead of floating to the surface.

 

[StructuralEd]

And back to his original question about the integrity of the slab....