Galvanizing Structural Steel

[structSU10]

Currently one of our details shows galvanizing the bottom 4' of a steel column which is to be encased in concrete. The Column is exterior, and we want to ensure protection from deicing salts and such.

The steel fabricator has been fighting to have us paint the column with a coal tar epoxy. We told them we wanted what we showed on the drawings.

They consulted with a paint guy, who says "Actually galvanized steel does not react well to exposure to either high or low ph environments. Fresh concrete has a very high ph and tends to break down the galvanizing". Is he just refering to A992 steel? Anyone have any issue with galvanizing A992 steel and embeding it in concrete? Any technical papers on the subject?

 

[JStephen]

It's awkward to galvanize part of something. It can be done, but I think the galvanizing guys are dunking 1,001 items and making sure they partially dunk just the 687th item upsets the flow.

Anchor bolts are commonly galvanized, so it must not be too big of a deal on the embed side of things.

 

[ishvaaag]

From

http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc47625/nrcc47625.pdf

"Zinc in galvanized form is another protective coating that can be used. It is applied to the rebar by hot-dipping. Galvanized rebar is superior to carbon steel rebar; however, its protection against pitting and localized rusting in the presence of high chloride concentrations is somewhat limited. This technology will only delay or postpone the onset of cracking and spalling; it will not prevent them. More research is required to assess its effectiveness for corrosion protection."

Embrittlement risk ...

http://www.daamgalvanizing.com/design/EmbrittlementWhitePaper.aspx

Distortion risk ...

http://elibrary.steel.org.au/shadom...mp;siteName=asi&CFID=1365197&CFTOKEN=48772034

"However, at galvanizing temperatures, the yield strength of steel
is lowered by approximately 50%. If the adjacent steel is not at
the same temperature and any stresses exist, the weaker area
will be subject to movement by the stronger area. There is a
responsibility on the designer, the fabricator and the galvanizer
to co-operate in ensuring that distortion risks are minimised or
eliminated."

A brochure on galvanization...

http://www.arcelormittal.com/sections/fileadmin/redaction/pdf/Brochures/Galvanisation_EN.pdf

I am not very confident that such small zone of galvanization be of any usefullness. One of the principles of impermeabilization or corrossion prevention is to be complete respect the exposure, and this looks to me more the introduction of some irregularity than protection itself.

 

[racookpe1978]

Above the concrete, how are you protecting the column now?

 

[dik]

If the item is long, then when they HDG the base, there will be an angular line for the galvanising because the object has to be tilted when dipped.

Coal tar epoxies should be avoided because they are carcinogenic. There are other coating systems, depending on the attack and degree of permanence. Attached, from my general notes for coatings.

Dik

 

[hokie66]

Just dip the whole column...done all the time. The "paint guy" is shooting a line of bull. Why would we use galvanized reinforcement if the concrete is going to break it down?