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[RFI] Conductive Concrete and Grounding

To: "RFI List" <rfi@contesting.com>,"Tower Talk List" <towertalk@contesting.com>
Subject: [RFI] Conductive Concrete and Grounding
From: "Jim Brown" <jim@audiosystemsgroup.com>
Reply-to: Jim Brown <jim@audiosystemsgroup.com>
Date: Fri, 19 Nov 2004 08:43:05 -0600
List-post: <mailto:rfi@contesting.com>
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.  

Several questions. Does anyone have experience with any of this?  Pros and 
cons?  
I've seen suggestions that there are corrosion issues for steel within the 
concrete. 
Would you want to use one of these specialty concretes to pour the base of your 
tower? 
Or would you use a more conventional concrete and mix it for lower resistivity? 
 

The key issues with respect to grounding for lightning protection seem to be 
inductance 
of interconnecting wiring and the impedance to earth of the ground electrodes. 
Putting 
the electrode in conductive concrete will greatly increase the surface area in 
contact 
with the earth, which should significantly reduce that portion of the impedance.

I would appreciate the collective wisdom of the assembled multitudes on these 
issues. 
While the thing that got me looking at this was this work-related project, the 
issue clearly 
is one of interest to all of us in our ham shacks.  

Jim Brown  K9YC


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