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Re: [TowerTalk] Exploding Foundations

To: Jim Lux <>
Subject: Re: [TowerTalk] Exploding Foundations
From: David Gilbert <>
Date: Fri, 14 Sep 2007 11:55:43 -0700
List-post: <>
Hi, Jim.

I think we mostly agree here.  You make a good devil's advocate, though ;)

Regarding copper corrosion, if the ground environment was as extreme as 
you say, my guess is that any ground rods (copper plated steel) would 
disappear long before the wires do.  Alkaline soil looks very much like 
concrete for ph, and strongly acidic soil will probably attack copper no 
matter what.

I've heard the concern about dissimilar expansion/contraction of a 
copper wire versus the concrete before, and that doesn't make any sense 
to me either.  Concrete is typically loaded with micro-cracks (and many 
not-so-micro-cracks).  Shrinkage cracks that occur while curing are 
going to generate far more and larger ingress paths into the bulk 
concrete than whatever might form around the wire, but you also have the 
stress over time caused by the tower itself.  Imagine what kind of 
forces (vibration and flexural) are imparted to the foundation by a tall 
tower in a wind storm.  Concrete is phenomenally strong in compression, 
reasonably strong in shear, but is unreliably weak in tension.  That's 
why rebar is required to hold it together.  But if you want to focus on 
expansion/contraction differences, the larger tower legs will create 
larger gaps to the concrete than the smaller wire, even taking into 
account the volumetric differences in expansion coefficients between 
steel and copper.

Dave   AB7E

Jim Lux wrote:
> David Gilbert wrote:
>> Third question ... why would a solid copper wire that can exist 
>> forever within concrete without corroding, and exist virtually 
>> forever in normal soil without corroding, corrode when leaving the 
>> concrete to enter the soil?
> The latter first..Different chemistry inside and outside the concrete? 
> But, copper is pretty resistant to corrosion in general.. I doubt it's 
> a concern.
> But, for wild speculation's sake.. what if the soil chemistry and 
> concrete chemistry were such that you have a galvanic action causing a 
> current flow in the copper (or, perhaps, something like a DC potential 
> gradient.. maybe your tower is right next to that 3 GW HVDC line?)
> Of course, we also assume that your concrete footing is in the middle 
> of a huge saltwater marsh, just to make the situation worse.
> My only concern (and it's not a big one) would be my general aversion 
> (possibly not well founded in theory OR practice) to having metal 
> penetrate the concrete below grade, because of the possibility of 
> capillary cracks resulting from different coefficients of thermal 
> expansion.  In reality though, I'd bet this isn't a real concern.

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