He is not talking about gaps. The water used to form concrete is absorbed by
the cement and turns into a crystaline structure. It is that structure that
is conductive to some degree that is affected by the heat generated by a
stroke.
Exploding is too strong a term, it should be "fractured".
How many years or decades does it take a certain size mass of concrete to
completely cure and become a non conductor?
Personally, I have seen concrete that has been reportedly damaged by
lightning at several locations. However what the quality of the thru or
around ground rods that were installed decades before is anyones guess. I
have also witnessed a 6' high boulder at a mountaintop VHF contest site
split into several pieces while I was about 50' away.
Across the street from me is the site of a former fire tower. It was a 70' 4
legged galvanized steel tower with a wood observers room on top. The
irregular shaped granite area was leveled with concrete pads that were
anchored deep into the rock and the tower was attached to that. Each leg had
ground rods drilled an unknown depth into the rock and the cable looked to
be about 00 battery cable size. The tower was installed in the 30's and was
a favorite spot for VHF visitors.
When a storm approached the observer went down and sat in his vehicle 100'
or so away until it passed. On one of several walks over there he told me of
the many times that the structure was hit while he watched and showed me
several fractures in the concrete. It reached a point that the base was
considered unsafe by the state and the site was torn down as it wasnt worth
the money to rebuild in view of newer technologies.
After so many decades of strikes, the base encased in snow and ice in the
winter and all manner of rain and temperature cycling it is impossible to
determine the cause of any of the many cracks. However Im prety sure that
the lightning didnt help the matter.
Who here can predict what todays uber grounds will look like decades down
the road, especially in locations subject to all matter of weather and
temperature extremes as well as soil conditions. What works in a Southwest
desert may very well fail in Florida.
Carl
KM1H
----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
To: <Greenacres113@aol.com>
Cc: <towertalk@contesting.com>
Sent: Saturday, September 15, 2007 10:41 AM
Subject: Re: [TowerTalk] re; exploding concrete
> Greenacres113@aol.com wrote:
>> I believe it's entirely possible. When you are a novice learning arc
>> welding
>> & gas cutting the first lesson is to place the metal properly. If you
>> weld
>> or burn on concrete you can super heat the trapped water inside. It will
>> definitely explode. I have seen it happen. Lightning super heating
>> moisture as it
>> passes along a wire/pipe in concrete can cause this.
>>
>> k9il
>
> I don't think so.. Yes, it explodes or spalls, but the explanation is
> wrong. It's the thermal stresses (like pouring water on non-pyrex type
> hot glass). And, as Hank Lonberg pointed out, in well constructed
> concrete, there aren't any gaps for liquid water to accumulate in.
> _______________________________________________
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