Aluminum rivets in steel structure

[Sparweb]

I’m repairing a free-standing antenna tower (Wade DMX). Replacing the mast support brackets. Removing the rivets was surprisingly easy… so it seems the original manufacturer used aluminum rivets. That was a bit of a surprise, since I would expect bare aluminum rivets in steel to cause a corrosion problem.

I can go on and on about aluminum rivets in aluminum structure (aerospace stuff) but for a structure like this, I'd like to check my assumptions. Should I have expected steel rivets here?

In the pictures below, no sign of corrosion at the rivet holes. There was plenty of corrosion elsewhere on the tower (hence the repairs). The original structure is galvanized, but somehow the galvanized finish was worn off in many places. But all the rivet joints are fine. Is that due to a particular aluminum rivet type that was used? This tower is about 20 years old.

I have lots of “aircraft” style rivets here of many aluminum alloys and have nice coatings, but they're all intended for aluminum structure. Is there a particular aluminum alloy type to be used in steel? By reworking some of these holes, I expect the zinc to be gone.

 

[GC_Hopi]

Try contacting WADE to see if they will supply new rivets. Otherwise replace with HDG bolts. WADE recommends replacing loose/damaged rivets with bolts. Also dont forget to repair the existing coating where needed. Either coating select areas or the entire structure depending of expected lifetime and % of the existing coating that is worn away.