[TowerTalk] From the perspective of a concrete technician

[N7DF]

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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