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Re: [TowerTalk] From the perspective of a concrete technician

To: <>
Subject: Re: [TowerTalk] From the perspective of a concrete technician
From: "David Robbins K1TTT" <>
Date: Sat, 15 Sep 2007 18:57:01 +0000
List-post: <>
Concrete is generally more conductive than the earth it is in so the fields
would not concentrate in the concrete.  The only times I have known
lightning, or artificial lightning where I used to work, to damage concrete
was when a conductor that was not bonded to the rebar was too close outside
the concrete, in air, not under ground.  Then you could draw an arc through
the concrete and cause spalling.  Note that because concrete is often a
better conductor than soil it is often specified to encase ground rods in
concrete to improve their effectiveness.  

David Robbins K1TTT
AR-Cluster node: 145.69MHz or telnet://

> -----Original Message-----
> From: [mailto:towertalk-
>] On Behalf Of David Gilbert
> Sent: Saturday, September 15, 2007 17:29
> To: N7DF
> Cc:
> Subject: Re: [TowerTalk] From the perspective of a concrete technician
> The only problem with that is that the tower base already represents a
> very low impedance conductor embedded in the concrete. It is THE lowest
> impedance conductor in the system. In the case of many towers (such as
> the self-supporting one I will be installing), that low impedance
> conductor goes almost to the bottom of the foundation. A significant
> field will almost certainly be there inside the concrete during a
> lightning strike. I'm not sure what kind of shunt grounding system would
> be required to prevent any portion of the lightning strike from imposing
> a major electric field within the concrete, but I'll bet it would be
> impressive.
> So in my mind, the question becomes how do you most benignly get the
> resulting current out of the concrete. The Ufer seems to be an accepted
> practice with good theory and decades of history behind it, and I still
> don't understand why an assist from a few copper wires to ground is not
> also a reasonable tactic.
> 73,
> Dave AB7E
> N7DF wrote:
> > I guess I might as well jump in here on the subject of concrete
> exploding under lightning stresses.
> >
> >   First of all I am a certified concrete technician with nearly 30 years
> experience and have designed numerous concrete structures, including tower
> bases and water tank foundations.
> >
> >   Concrete is a hydrated crystalline material.  The crystal structure
> combines several inorganic elements with water molecules.  When concrete
> hardens it does not "dry" it becomes rigid as the crystal structure forms.
> None of the water in the concrete mixture is lost. The crystallization
> process is very slow.  About 60% will be completed in a week and nearly
> 90% in a month.  Theoretically it never reaches completion.
> >
> >   The point is, concrete contains water; a lot of it, in the crystal
> structure.  It also contains metallic elements.  When a sufficiently
> powerful electric field is imposed on the crystal structure it begins to
> break down and becomes conductive.  The water molecules in its structure
> begin to be released and will flash into water vapor.  As one person
> stated, this can happen in 40 year old concrete that is as dry as a bone.
> >
> >   The final analysis is that you must not, under any circumstance,
> permit an electric current to run through the concrete.  Even if a good
> conductor is embedded in the concrete, a lightning strike will cause
> current to flow in the concrete immediately in contact with the conductor
> and the degradation process will take place.
> >
> >   Ground rods and conductors should always be placed outside the
> concrete foundation. QED
> >
> >
> > ---------------------------------
> > Moody friends. Drama queens. Your life? Nope! - their life, your story.
> >  Play Sims Stories at Yahoo! Games.
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