> >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.
>
> A popular belief but not backed up with any evidence to my knowledge.
Where I work we have blown chunks out of concrete utility poles we were
testing with artificial lightning. And it is common for chimneys that are
hit to suffer damage. I have also heard of pieces being blown out of
concrete footings under high voltage power lines, but there is some question
of the cause... the energy dumped into the ground from the follow on current
after flashing over an insulator can be much higher than that from the
lightning that actually caused the flashover.
I don't have the conductivity figures handy but they are out on the web
somewhere, google for concrete conductivity and you should find it. But in
general it is better than poor soil or rock, enough so that it is not
uncommon to encase ground rods in concrete to improve conductivity in really
bad cases. There are also modified concrete formulas using carbon fiber or
fly ash that are used for improving grounds... and also for things like
resistively heated sidewalks and runways... just pour the concrete with some
electrodes in it and pump through a bunch of current, instant hot concrete
and bye bye ice and snow.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
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See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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