Grade Beam Frost Void

[KevinValenta]

What would be a good way to get a frost void under a grade beam?

I'm building a post frame garage using 24"diameter x 36"deep concrete pier footings 8'OC (soil bearing capacity has been checked and pier footings can support 16,956 PSF vs. the load of 12,160 PSF) and Perma-Column's Sturdi-Wall Plus wet set moment resisting brackets to secure the glulam 3-ply 2x6 x 22' high posts.

I would like to connect the piers with a grade beam (vs. pressure treated splash boards on the exterior and interior) to avoid any surface water contacting the Sturdi-Column Plus steel brackets or the bottom of the glulam posts, and provide a concrete vs. wood break between the exterior & interior of the building by means of a min. 8" wide (Perma-Column spec)x 16" high grade beam/stem wall with two Grade 60 horizontal rebars (Perma-Column's spec) but need to protect against frost heave and saw the old thread about creating a void under the grade beam and wondering if there is a cost-effective way to create that.

One idea that comes to mind is corrugated solid wall drainage pipe in two rows of 4" diameter pipe conforming to ASTM F667 specifications that has a stiffness at 5% deflection of 30 psi and impact resistance of 27.5 ft.lbs. at 25 degrees F. With just the cured concrete weighing about 150 LB per cubic ft the 8"x 16" grade beam should weigh about 130 LB per LF not including the nominal weight of the rebar. Would the corrugated drainage pipe create a void effective at isolating the grade beam from frost? If not any other ideas? Thanks.

 

[dik]

I missed this... there are cardboard products made specially for this purpose. I prefer foam plastic ones, because I've done reports where the void formed by cardboard has filled with water and has frozen. The grade beam was then able to heave.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[SwinnyGG]

Google 'void form' and you'll get a long list of products designed exactly for this purpose.

As Dik stated, there are multiple options. The 'best' solutions are those which don't take on water, and have a compressive strength high enough to support concrete while it cures, but low enough that they will deform under the pressure of soil heave beneath without applying significant uplift to the concrete above. I agree with Dik that the foam plastic products are the cadillac solution, although the cardboard type options are more common in large construction because they are typically substantially less expensive.

I would not suggest using small diameter drainage pipe for this. Over time it will fill with water, soil, or both, and will wind up transferring the heave load directly to the slab.

For reference, in my area (mountain west, USA) void form is typically specified in depths of at least 12", sometimes larger, to avoid long-term damming of water or erosion spoils into the void and suddenly creating a path for heave load to reach the bottom of the slab 25 or 30 years down the road.