Below is good information, but only applies to electrical systems'
grounding... not commercial radio vault lightning ground systems. Also,
the aluminum system I came across certainly had crimp or other mechanical
bonding methods which avoids the connection issues discussed in the NEC.

I have no control or great concern on this, but was surprised to see
aluminum for my first time. I just wondered if it was common.

Ed K7AAT


..

The National Electric Code has some fairly specific requirements for
how grounding system connections must be made. Soldering is not
permitted, as the high temperatures which can occur at such
connections during a lighting strike can blow the soldered connection
apart. Strong mechanical connections, or welding (e.g. "CadWeld"
thermite-type welding) is required.

I just ran across the following:

http://www.homeinspector.org/resourc...lectrical-Grou
nding.pdf

It indicates that the NEC forbids the use of aluminum conductors for
grounding "where in direct contact with masonry or earth. Aluminum
conductors require 18 inches of clearance from earth." (NEC
paragraphs 250-91a and 250-92a are cited).

There's also a note on the citation: "ATJ note: we have field
reports of complete failure of uninsulated bare aluminum grounding
conductor wire when it was not properly protected from corrosion - for
example where left touching a masonry foundation wall."

It sounds to me as using aluminum wire as a lightning ground system
is a poor idea.