Expanding Foam vs Concrete for Tower Base

[WeldGuy]

A local HAM has erected a 50 foot tower in his yard using expanding foam (for fence posts) instead of concrete for a secure base mounting. He recently guyed the tower, but it seems using foam instead of concrete could be a problem down the road.
Has anyone seen foam used this way???

 

[cavmedic]

The power companies have been using foam around the base of the poles when they set new ones.

I’m sure it’s of a higher quality than the fence post mix but hams gonna ham

 

[mmckenna]

Towers usually include plans for a foundation that is specifically designed for the height of the tower as well as wind load. Those plans are usually stamped by a Principal Engineer that is licensed in some fashion. Local building codes would want to see those plans.
If the plans included expanding foam as its base, then it should be just fine.

If the plans do not call for expanding foam, then they are kind of on their own. Might work just fine, as cavmedic said, some utilities use it for poles.

 

[RFI-EMI-GUY]

For a guided tower, the main concern would be the ability to support the weight of the tower, appurtenanes and guy tension. The base must be able to support the compressive load.

 

[buddrousa]

I am sorry but that is like using a baseball cap to replace a batting helmet.

 

[iMONITOR]

Foam is very light, how can that replace concrete?

 

[a417]

Foam is very light, how can that replace concrete?

here.

 

[iMONITOR]

Interesting, the use of foam! I wished I would have known that when I replaced my curb-side mail box, TWICE! I though the weight of concrete would add to the stability of the any vertical pole, post, ETC.

 

[GlobalNorth]

The anchoring foam is pretty popular around here for amateurs using those flagpole antennas in residential yards.

 

[eorange]

Ham-grade Great Stuff, done!

 

[Project25_MASTR]

I've seen flow-fill (flowable fill) used in some tower base designs to help provide a stable fill layer for lighter towers (still having a concreted base) to but I've not yet seen post setting foam used.

 

[paulears]

I suspect the ham with the tower has overlooked a few vital things here. Concrete is a material with specific properties. The vital ones for tower support, or in foundations, or things like lamp posts, electricity poles etc is that these all support tall structures that want to create turning moments when they are in motion - from things like wind, or rotating different top loads. The vertical can be set in concrete, or can have long studs or rebar like extensions that get set in concrete. What works for you is mass and weight and the resilience of the concrete where other materials are embedded in it. For a fence post, these turning moments are probably limited to wind - negligable with a wire fence, until animals or other things contact the wire. Otherwise the worst case is surface area of the solid fence style cladding vs wind.

For an antenna support, the other feature is the weight of the concrete. It's common for motorway construction firms to put the tall lights or CCTV gear on a tall tube - maybe 6m/20ft and put the bottom in a fabric 1m3 bag, fill it with concrete and that weight of concrete , sitting on grass/soil/more concrete is heavy enough to prevent that turning moment from wind or even accidental contact tipping them over. 1m3 of concrete is about 2.5 tons in weight. Foam in a 1m3 hole has virtually no weight by comparision, has little structral strength, and the bubbles mean the contact surface can deform with pressure. Fair enough, a long tube burried in it has the pressure diluted by the surface area in contact, but the resistance to toppling from 2.5 tons of weight is considerably more than using the physical contact area of the foma vs soil.

I found a few fencepost videos, but the revealing one was this one below, where the contact area only resistance clearly was insufficient for a 4 x 4" piece of timber, let alone a tall metal structure. In this video the problems with the foam are quite easy to translate to a mast scenario. when you look at typical 60ft antenna masts - a 1m3 lump of concrete would be classed as small!

 

[CcSkyEye]

I'm sure it will be fine, I guess time will tell.

 

[cg]

Found this. 65' tower set with foam, no tower load details though.

 

[AK9R]

Towers usually include plans for a foundation that is specifically designed for the height of the tower as well as wind load. Those plans are usually stamped by a Principal Engineer that is licensed in some fashion. Local building codes would want to see those plans.

How quaint that you think hams pull a building permit prior to putting up a tower.

Most don't even realize that a permit is required. Some think that if they don't pull a permit, they can fly their tower under the radar and avoid having that pesky building inspector tell them that they are doing it wrong. Some think that all those engineering drawings that were shipped with the tower are just suggestions. Some bought the tower second or third hand and have no engineering drawings.

A lot of folks don't realize that soil sometimes acts like a fluid. I believe that the concrete base that the tower manufacturer recommends acts like ballast in a sea of moving soil. Maybe guying the tower reduces the need for a concrete base, but I wouldn't do it unless the tower manufacturer signed off on it as in had their engineer put his PE stamp on drawings showing post-setting foam as an acceptable base.

 

[a417]

I've used it for a U-shaped cedar fence in a treeline that hides a propane tank. Great for things w/o appreciable wind loading or something which does not require the heavy counterweight properties of concrete.

One of the fence posts was misaligned, and it took me about 4 minutes to pull the post out, cut the foam off, and reset it.

 

[dave3825]

Wonder how well that holds up in moist environments over time. Many boats were built with closed cell high density foam that after years of exposure to water, mostly salt water, has broken down and became soft.

 

[iMONITOR]

I'd be concerned with the deep resessed hole collecting and holding water leading to premature corrosion of the tower. Concrete bases I've seen are usually well above ground level and domed so water runs off away from the tower itself.

 

[GlobalNorth]

Soils are not uniform geologic entities. Some soils are clay based, others are replete with botanical debris, clastic compositions range from microclasts to clasts that are several millimeters in diameter, moisture levels vary widely, soil stratigraphy/substrata is area/site specific, permeation of water, etc.

Yes, under very specific and limited conditions, some soils can act as liquid does, but more often then not, soils tend to behave as a plastic, a semisolid, or a solid material. The amount of water present/not present [along with shrinkage] determines the level of plasticity.

 

[RFI-EMI-GUY]

The anchoring foam is pretty popular around here for amateurs using those flagpole antennas in residential yards.

I wonder if use of that meets Florida building code. Uplift is a real problem with decks. A neighbors had a new deck, a storm pulled it up, flipped it onto his roof and wrecked the roof as well. If you don't have those set in concrete you have nothing anchoring them down.