> -----Original Message-----
> From: email@example.com [mailto:towertalk-
> firstname.lastname@example.org] On Behalf Of James Wolf
> Sent: Monday, May 14, 2007 12:27 AM
> To: email@example.com
> Subject: Re: [TowerTalk] Rohn BPC25G
> >You don't want anything sticking out of the concrete either rebar or a
> ground rod. Not because it is a lightning path but because it will corrode
> >(rust) and the corrosion will work its way up into the concrete and that
> will crack the concrete.
> >It is fine to use the rebar inside the concrete as an auxiliary ground
> the tower but it should all be tied together in the concrete so that there
> is >no arcing from one piece to another in there.
> >It is just as important to build the concrete so that no water
> around any pier pin or j bolts sticking out of the top too. If they rust
> down >into the concrete you will have the same problem with the concrete
> >Gary K4FMX
> Can you expand on this. We have used usually two ground rods in a tower
> base (where the tower base is imbedded in concrete) for years. We angle
> them in opposite directions out the bottom and attach them to the base and
> rebar using brazing and tar to coat the weld. Only the tower base itself
> sticks out the top. Are you saying that using the ground rods the way we
> are, poses a potential base failure due to corrosion?
> Jim, KR9U
If I understand your setup right, you have ground rods coming out of the
bottom of the concrete. That is not a good idea for reasons stated above. It
is standard practice to not have any rebar or other metal that is inside of
concrete extending out into the earth. Anything that is exposed to the soil
will rust and that rust will move right into the concrete and as it rusts
inside the concrete it will expand and can crack the concrete.
A copper coated or galvanized ground rod will take longer to rust than raw
rebar but it will eventually rust.
The purpose of the copper coating on a ground rod is to retard corrosion but
any scratch in the coating is a place for rust to start.
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