[TowerTalk] Fwd: Screw Anchor Experience

[Hans Hammarquist]

What I have seen, it is only the portion closest to the surface that corrodes. I have found iron pieces buried for hundred of years with only slight corrosion. Scrap iron, stored laying on the ground, has almost disappeared in no time. I believe it is a combination of water, "dirt", and air that is causing this.


When installing fence with steel poles, a concrete "plate" is made around the pole just at the surface. It is sloped on the top to allow water run-off. If you don't do that the pole will corrode at the surface and eventually break there.


The rebar in concrete is "protected" by the concrete but will corrode if too close to the surface. In the same way the fence pole is "protected" by the concrete plate.


Maybe some concrete poured around anchor can extend the life-expectancy of the anchor.


Next: What method or how would you inspect an anchor for corrosion damages? Just digging around it?


Hans - N2JFS



-----Original Message-----
From: Mark Robinson <markrob at mindspring.com>
To: Jim Thomson <jim.thom at telus.net>; towertalk <towertalk at contesting.com>
Sent: Thu, Jun 20, 2013 11:36 am
Subject: Re: [TowerTalk] Screw Anchor Experience


Jim wrote


> ##  why mess with screw in anchors ?  Only power company’s + telco’s use 
> em. Even then
> they use eggs in the EHS guys.   A  40’ tall utlility pole is already 6 
> feet into the ground. No
> anodes used.
>
> ##  The rohn type rod anchors are in contact with the soil, where it is 
> trenched, so that portion
> of the rod needs to be coated with roofing tar pitch.  Those GAC series 
> anchor rods involve
> excavating a huge hole, that is then trenched.  The concrete slab needs to 
> be poured, then the
> entire mess is bakfilled with dirt.
>

I reply...

They weren't screw anchors. They were the Rohn supplied anchors set in 
concrete per the Rohn specifcations (as you describee) BUT they are still 
vulnerable to corrosion. I have read dubious accounts of using tar on the 
buried metal parts - the tar can fail and then the corrosion will be 
concentrated in the failed areas

My opinion/guess is that the sacrificial anodes are a better way to go but 
only time will prove me right or wrong.



Mark N1UK


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