Aluminum Guardrail Post Embedded in Concrete 2

[JDV22]

Hello Everyone!

We're looking at a job where the client would like an aluminum guardrail core drilled into a concrete curb. I've always heard that aluminum in contact with concrete is not good.. Could anyone explain to me what exactly is going on when aluminum comes into contact with concrete? Is it that you don't want aluminum in contact with the concrete during the curing process because of the chemical reaction or is it throughout the entire life of the concrete? If it is throughout the entire life of the concrete, does the grout in a core drilled hole act as enough of a barrier to where it is not a concern?

Thanks so much for all the wisdom and insight!

 

[jayrod12]

Aluminum in contact with only concrete isn't the end of the world. I believe more people don't like the embedded detail regardless of material for the railing. Embedding the posts may look "nice" but it really just invites corrosion to happen below the top of concrete surface that causes issues not only with the guardrail but with the concrete itself as the corrosion byproducts cause spalling and breaking of the concrete. Not to mention the potential for water freezing to expand and break stuff as well depending on the local climate.

 

[EdStainless]

If you live someplace where it snows, and there is salt used, then corrosion is assured.
There not really a good long term way to prevent water down in the hole.

The wide flange has been cut, the smoother potion is fracture face.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dik]

The alkali from the concrete 'dissolves' aluminum... back in university I studied torsion in concrete and was looking for a means to determine crack propagation... carefully place aluminum foil strip conductors and checked for continuity when I cast the first ones... was good until 28 days later...

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

-Dik

 

[la belle vie]

I once designed repairs for a switchyard pothead foundation that had aluminum anchor bolts. No idea why this was done some 70 years ago. The concrete surface had radiating cracks all around the each bolt, some as wide as 1/2". Somehow the concrete reaction with the aluminum caused something to expand.

 

[JDV22]

Thanks for all the replies!

Dik, that sounds like a very interesting experiment!

La Belle, did they anchors look like post installed anchors? Maybe my ignorance in material sciences is becoming blatantly obvious, but I wonder if there is a difference between casting aluminum in concrete while it is curing vs. post installing some aluminum component. If the anchors you are describing are post installed, then it looks like it doesn't matter at what point during the process the concrete comes in contact with the aluminum - it could always be potentially harmful.

Thanks again for all the insight! just trying to learn!

 

[la belle vie]

JDV22- The aluminum anchor bolts were CIP. I have often seen standard general notes saying to apply two coats of bituminous paint to the aluminum when contact between concrete and aluminum can't be avoided.

 

[JedClampett]

Here's a picture of some aluminum vs. concrete damage. It might be thermal, but is more likely a galvanic issue.

 

[dik]

I was a kid back then, and very little was available about torsion in concrete... I think in the west, the ACI at the time noted that it should be accommodated... other than that, nothing. The Russians had done a fair amount of work on it and they had methods of analysis. The beginning of my thesis had the ACI requirements as the initial statement.

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

-Dik

 

[Ingenuity]

Back in the day, aluminum electric conduit was embedded in concrete - with devastating results.

 

[dik]

I always spec that biutuminous coatings be non-carcinogenic... and that cadmium coatings not be used. I have for over a decade. I wouldn't be using bituminous coatings on anchor rods... maybe epoxy with increased development length... I don't recall ever spec'cing an aluminum anchor... even bolts.

-EOR SHALL CONFIRM ALL BITUMINOUS COATINGS ARE NON-CARCINOGENIC.

-CADMIUM PLATED FASTENERS SHALL NOT BE USED.


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

-Dik