[TowerTalk] Conductive Concrete and Grounding

[Randy]

At 09:43 AM 11/19/2004, Jim Brown wrote:
>Gentlemen,
>
>I'm doing some reasearch for an applications note I'm preparing on power and
>grounding for audio and video systems, and wanted to mention the use of a 
>Ufer as a
>ground electrode.  This got me into a google search on the resistivity of 
>concrete. It is
>clear that resistivity varies over at least four orders of magnitude, 
>depending on the
>formulation, the mix of concrete and water, and how the concrete is poured.
>
>I've come across an interesting webpage for what appears to be a small 
>company
>(garage?) selling specialty concrete.
>
>http://www.conductiveconcrete.com/
>
>There is now a lot of interest in the use of conductive concrete for snow 
>melting, EMP
>protection, and a variety of other uses. Here's a study of concrete for 
>use as railroad
>ties in electric railroads.
>
>http://www.cement.org/pdf_files/SN2457.pdf
>
>It seems logical that varying the formulation of concrete could 
>significantly impact its
>structural properties. But there would seem to be significant benefit from 
>tying the
>structural steel within a poured concrete foundation into the ground 
>system of a building.

<snip>

>Jim Brown  K9YC

Jim:
My personal, layman's point-of-view is that lightning is wicked, wicked 
stuff, and largely refuses
to do what is expected of it. It *will* cause concrete to explode exactly 
like wood, trees, etc., i.e.
the sudden vaporization of the moisture within causing a violent expansion 
thereof. It likes to jump
into and out of conductors, I suppose due to the inductance it "sees" as 
well as the electrolytic
charging of whatever (normally) non-conductors it's trying to drain into, 
and probably a host of
other variables I'm unaware of. I locate underground water leaks for a 
living, and I can tell you
that lightning wreaks havoc on copper systems, "almost" always from a 
strike to the AC mains,
the cold pipe generally being tied to the ground/neutral buss at the 
breaker panel (sometimes
the hot line is also bonded to the cold at the water heater, which is where 
the connection to the
panel is usually made, hereabouts anyway). Personally, I wouldn't want such 
a system in either
a residential setting for safety of persons and equipment, nor would I want 
it in a tower base
for structural considerations. I have no idea whether a potent, direct hit 
could cause such a failure,
but in any event I think you'd want to Cadweld each and every point where 
the rebars crossed,
and I wonder whether the flexing of the bars during the pour might crack 
the joint. Also, bear
in mind that concrete is caustic to such an extent that a copper pipe in 
direct contact with it
will, eventually, most likely leak, so I'd have to question the long-term 
viability of any copper conductor
passing into the concrete; I think you'd have to bring the steel outside of 
the concrete and bond
to it above ground, preferably.
I was under the impression that Ufer grounds were only in use as a last 
resort, i.e. desert conditions,
but I could be wrong...

73 de KZ4RV

Randy