GALVANIZED STEEL CONTACTING CONCRETE

[wynn]

Currently, we are having our fabricators mask the underside of baseplates before galvanizing our columns in order to prevent any reaction between the zinc and the grout. Since we erect quite a number of columns, this is an expensive approach. Can anyone advise:

- is it advisable/compulsory that we prevent contact between the grout and the galvanizing.

- if they must be kept from contact, is there some simple, inexpensive way to do so.

 

[dickwilber]

In over thirty years dealing with galvanized components attached directly to concrete structures, this is the first time I have ever heard of this approach. Can you tell me why? My instincts tell me the rusting of the ungalvanized steel against the concrete would be a greater problem than any galvanic action between concrete and zinc.

With aluminum, which does have a strong detrimental reaction with concrete, we used to coat the contacting surfaces with an asphaltic material. This may not work for you because of the compressive forces being exerted at the interface.

 

[wynn]

Perhaps I should explain myself more clearly. Your comment about ungalvanized steel may not apply here. In fact, steel is commonly used without protection (e.g. rebar, embedded plates) in direct contact with concrete, and is fine unless some outside agent (e.g. road salt on bridge decks) kills the alkalinity. After that, steel will oxidize leading to spalling.

In our situation, we have structural steel which is galvanized for use in an industrial environment. Our engineers are concerned that galvanizing under the base plate will react when it contacts the grout bed, causing expansive zinc salts. To prevent this, we are masking off the underside of baseplate prior to dipping so there is not galvanizing on this surface. We would prefer a more convenient solution.

That brings us back to the original questions. First, do we even need to worry about galvanizing in contact with concrete? Second, if it is a problem, is there some easy way to interrupt this interface?

Thanks for your original comments, and I look forward to your response.

 

[dickwilber]

WYNN,

You misunderstood my comments - I was talking about galvanized steel components in contact with concrete. Designing and selling concrete structures with galvanized steel attachments used in moderately corrosive environments for over thirty years, I never came across any information regarding a reaction between the concrete and the zinc surface. Equipment constructed in this way nearly half a century ago is still serving well.

I have also seen galvanized steel pieces imbedded in the cocrete, and, again, there has not been a problem. (Because of the protective effect of the concrete for the steel, this has always seemed to me to be a case of overkill.)

I would NOT BE CONCERNED about GALVANIZED STEEL IN DIRECT CONTACT WITH CONCRETE.

 

[dickwilber]

wynn,

I followed up on this with the American Galvanizers Association (

http://www.galvanizeit.org)

and received the following:

"There is typically not a problem with galvanized surfaces in contact with concrete for many decades. There may be some reactions between the galvanized steel and the concrete during the curing stages if there is an absence of chromate either in the concrete itself or on the galvanized steel. Galvanized steel is used sometimes as reinforcement bar for concrete. The only special requirement that the ASTM specification regarding galvanized rebar is that either the concrete contain a small amount of chromate (~ 100 ppm) and/or the rebar actually be post-treated after galvanizing with a chromate passivation. The presence of chromate eliminates reactions during the curing stages. After the curing stages there are no detrimental reactions that proceed between the galvanized coating and the concrete. If you have any other questions or concerns please feel free to contact me. Sorry for the delay in reply."

The question is then whether there is any chromate in either the grout you are using or the galvanized surface. I would employ the chromate passivation treatment on the surface of the base plate before placing it on the grout. (In our case, the concrete had cured some before we had placed the galvanized materials on it.

Good Luck
dickwilber