Aluminum wire is mentioned in some of the recent posts about radial wire.
Here in northern Indiana, my soil is very acidic. Freshman chemistry was
almost 50 years ago, but if I remember it correctly, a metal immersed in
acid will displace the hydrogen in the acid, forming a salt. Aluminum
chloride probably isn't a very desirable radial material. Neither is
aluminum sulfate. So I'd go with those who say copper is the best bet.
As for attachment: I have a three leg tower (Rohn 45) which I shunt feed. I
got some bare #10 copper and some pipe clamps (make sure they are copper,
bronze, or stainless, including the bolts) and three ground bus strips of
the type that's used in breaker panels. These are available at Lowes, Home
Depot, etc. for about $3.00 for the ones with about a dozen holes. I put
the pipe clamps on the legs, and used the #10 bare copper (solid) to connect
both ends of the strips to the adjacent legs. Thus there's a terminal strip
between each pair of tower legs, and each strip has two connections to the
tower. There's a lot to be said for redundancy, especially when it comes to
outdoor connections. The remaining holes are for the radials. With #14
wire, the holes will accomodate about four radials each. Use
copper/aluminum joint compound such as No-ox on all connections, or cover
them all with roofing tar.
Incidentally, after putting the pipe clamps on the tower legs, I checked for
continuity and found there wasn't any. I had to sand the tower legs to
remove the invisible gunk. I painted the sanded spots with Rustoleum and
installed the clamps while the Rustoleum was still wet. Finally, each
ground clamp also has a #10 jumper to an adjacent ground rod.
All this was done this spring so I'm anxiously awaiting the fall
improvement in conditions to see how it performs.