On 7 Jul 2006 at 8:50, JC Smith wrote:
> Also, I have heard
> from enough others that I am now fairly convinced that the "exploding"
> concrete is not a myth. It probably doesn't happen very often, and it may
> be more of a crack than an explosion, but it's something to avoid in any
> case.
> 73 - JC, K0HPS
There was a thread some months back about conductive concrete,
i.e. such as is used in cold climates to allow passing current
through to melt ice.
I expressed some dismay at the thought of having such stuff as
a home's slab and using it as a ground...
A gentleman whose call I forget joined in the thread to state that
he had lost a tower from a lightning strike, due to the failure of a
concrete guy anchoring system.
While I haven't personally seen *structural* damage from lightning,
to slabs, I've seen several examples of chunks blown out of slabs
by lightning that caused no structural problems.
It was mentioned that such structural damage might be due to
voids around the rebar allowing corrosion or water accumlation,
etc., but how often do hams feel the need to vibrate the concrete
with proper equipment when pouring a tower base? IOW, there's
no satisfaction in knowing some anomaly destroyed the tower if
there's generally no attempt to prevent the anomaly.
While I lack the wherewithal to figure it all out, surely one of the
TT list members could calculate a "worst-case" of how many
joules of lightning-juice could heat a given mass of concrete,
containing X percent moisture to heat up by N degrees over
how-ever-many milliseconds, creating outward forces of
blah blah blah...
Somebody *must* have IEEE papers covering the subject,
I'd guess....
73
Randy
KZ4ZZ
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