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[TowerTalk] From the perspective of a concrete technician

Subject: [TowerTalk] From the perspective of a concrete technician
From: N7DF <>
Date: Fri, 14 Sep 2007 23:41:30 -0700 (PDT)
List-post: <>
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

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