Secure 6061 Aluminum to Concrete 2

[dik]

What is the best post-applied fastener to secure an aluminum 6061 frame to concrete to minimise galvanic corrosion. or is it an issue? I know the aluminum has to be isolated from the concrete for alkalinity reasons.

Thanks, in advance...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik

 

[JedClampett]

We use stainless steel concrete anchors (which I believe we define as expansion anchors). There should be a galvanic corrosion issue, but I've never seen it once, and we work in high humidity environments. Maybe the passivating layer on the stainless steel and the anodic coating on the aluminum provide enough of a barrier. Beats me.

 

[dik]

That's what I was suspecting... they are close enough that there is no issue... thanks very much for the information... will use SS rather than HDG.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik

 

[r13]

Dik,

I am not very knowledgeable on this matter. Just assembled a few excerptions from the web FYI. Note that there are quite a few concerns on galvanic reaction when aluminum and stainless steel are put together, I think you can find out more by yourself.

"Aluminum and galvanized steel are both compatible with each other, and adjacent to each other in the galvanic scale. There are many aluminum under structures with galvanized steel exteriors built over the past half century."

"Aluminum and Stainless Steel. Under atmospheric conditions of moderate to mild humidity, contact between a galvanized surface and aluminum or stainless steel is unlikely to cause substantial incremental corrosion. However, under very humid conditions, the galvanized surface may require electrical isolation from the aluminum or stainless steel."

"When aluminum and stainless steel are used in an assembly together, the electrons from the aluminum will begin to transfer into the stainless steel. This results in the aluminum weakening. This weakened aluminum causes it to deteriorate at a much faster rate. This can lead to an extended life of the stainless steel."

 

[dik]

Thanks...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik

 

[Ron]

dik....have done hundreds of aluminum structures. As you noted, you isolate the aluminum from concrete. Fasteners should be stainless steel, preferably 304 or 316. 400 series stainless fasteners are not very corrosion resistant. I would not use galvanized steel. The nobility charts are a little whacked out with regard to connecting aluminum, as compared to field observation. As an example, look at the galvanized hardware on a chain link fence that fastens the aluminum castings at gates and accessories. According to the nobility charts, the galvanized steel should not corrode and the surrounding aluminum should corrode. It is just the opposite. The fasteners corrode and that aluminum is fine. I believe it has to do with initial general corrosion of the aluminum over its entire area which then passivates it to further corrosion and the corrosion is reversed.

As for the aluminum structures I've done, where we used other than direct embedment of columns into concrete and we had to use base plates and anchor bolts, we used stainless expansion anchors or stainless chemical anchors. No issues with other than normal light corrosion and this goes back to over 35 years of observation.

 

[dik]

Exactly what I've done... use 304 and cautioned about HDG. Also an 80 mil EPDM sheet between base and concrete. Concrete surface is smooth and not rough. Interior application, but near to door. Thanks for the confirmation.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik

 

[r13]

Quote below seems a fare assessment. Most of the articles also seem to agree that galvanic reaction between aluminum and galvanized steel, or stainless steel, can be avoid by separating the contact surface using non-metallic materials.

Under atmospheric conditions of moderate to mild humidity, contact between a galvanized surface and aluminum or stainless steel is unlikely to cause substantial incremental corrosion. However, under very humid conditions, the galvanized surface may require electrical isolation from the aluminum or stainless steel.

 

[dik]

Thanks...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik

 

[dik]

Some additional information in thread338-475300 and have revised the separator to a smooth neoprene material... EPDM often has a surface texture.


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik

 

[r13]

Interesting. I came across an article mentioned it too, along with plastic/rubber washer/gasket, also painting. I guess problem with galvanized steel lies in preexist defects, or damages during installation/erection.

 

[r13]

A closing note.

"There are three conditions must exist for galvanic corrosion to occur. First there must be two electrochemically dissimilar metals present. Second, there must be an electrically conductive path between the two metals. And third, there must a conductor for the metal ions to move from the more anodic metal to the more cathodic metal. If any one of these three conditions does not exist, the galvanic corrosion will not occur." The galvanic corrosion is most likely to occur under outdoor harsh environment, that has high humidity, salty air, and prolonged exposure to sufficient amount of water, or moisture. In design, the galvanic compatibility is managed by "finishes and plating".