Anchor Bolts for Aluminum

[mattmlm]

I've got a project where Aluminum columns (and base plates) are being anchored to a concrete pier/footing. The contractor used your everyday common steel threaded anchor rods. In less than two weeks they are completely rusted over. The contract documents called for hot-dipped galvanized anchor bolts. (before judging, we did not provide the design or specifications, simply consulting on a separate portion of the larger project)

I'm thinking of having the contractor cut off and drill-in epoxy grout anchors.

Will the galvanized anchor bolts react to the aluminum? Should I use aluminum anchor bolts? If alum, what affect would the anchors have in steel reinforced concrete?

Thank you,

MLM

 

[Goahead]

Galvanized steel anchor bolts should be OK with aluminum.
As an extra precaution the contact areas could be painted with insulating paint.

http://www.welding-advisers.com/

 

[TVP]

Al bolts are unlikely to be strong enough if they were not specifically incorporated into the design. Zinc is the most compatible coating for steel bolts that is also relatively cost effective.

 

[Heckler]

Aluminum and Zinc are really close together on my Galvanic Corrosion Potential Chart.

 

[mattmlm]

Is that good thing or a bad thing?

MLM

 

[theonlynamenottaken]

Its a good thing... the farther apart two metals are on the galvanic series the greater potential between them, hence more aggressive attack.

Aluminum embedded in and in direct contact with concrete is not acceptable. A chemical reaction occurs and the concrete literally self destructs from the expansion (product of the reaction, just like rust on carbon steel that is allowed to corrode in concrete). I don't know about epoxy grouted aluminum in concrete but I've seen slabs with aluminum cast into it break themselves apart.

 

[UcfSE]

I have a question to go along with this. I have noticed in the past with aluminum panels that the manufacturer of the panels has recommended stainless steel screws with some kind of special washer between the steel and the aluminum. Does that line of thinking work also in this case, say with using stainless steel anchor bolts or epoxy bolts with an aluminum base plate?

 

[mattmlm]

How good is stainless in direct contact with Aluminum? When this issue first came up, the only thing that I thought of was stainless. Then came the comments about the specs calling for hot-dipped galvanized. I've always assumed that stainless was preferred, if not required. Is that assumption correct?

MLM

Also, thanks for the input.

 

[Heckler]

ASTM A-153 or ISO 1461 covers hot-dip galvanizing. I think it's more of a cost factor when considering Stainless verses galvanized steel.

 

[Goahead]

Stainless should not be in contact with aluminum. Stainless fasteners should be Cadmium or Zinc plated before
being inserted in aluminum bodies. Usual anodizing or conversion coating are not protective enough at the contact place.

http://www.welding-advisers.com/

 

[IFRs]

In my experience (27 years in the petrochemical industry), aluminum and stainless fasteners are acceptable in most environments. Althought they are far apart on the galvanic scale, the typically much larger area of the aluminum part compared to the fastener reduces to nearly nil the tendency of the aluminum to corrode. However, in this case, I'd definitly use galvanized anchors - they were specified, are compatible, are probably more available not to mention less costly. Note that the environment is a critical issue - If this is on the seashore, or exposed to wet atmosphere, or under water, or vibrating from machinery, etc then corrosion needs to be re-evaluated.