Letter 19051

Passivation of hot dip galvanized steel [Finland]

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The problem in using hot dip galvanized steel in reinforcing of concrete is the reaction of zinc with wet unset concrete. Zinc reacts with wet concrete (high pH) forming hydrogen gas and there is a danger that the hydrogen bubbles can weaken the strength of concrete. Is there any good chromate free passivation chemical for hot dip galvanized surface to inhibit the reaction of zinc and wet concrete until the concrete is hard. The treatment should be easily carried out e.g. by dipping just after galvanizing and the treatment should not be too expensive.

Second use for the passivation is prevention of white rust formation during storage and transport. It is quite probable that if the passivation layer prevents reaction with concrete it protects also again white rust. In order to be suitable in general use, protection again white rust, it should be almost invisible and the surface should be suitable for painting. Big part of hot dip galvanized steel will be painted.

Is there any passivation chemical which fulfills all the requirements: - prevents reaction of zinc with wet concrete - prevents formation of white rust - chromate free - easy one step treatment - not expensive - practically invisible - easily paintable surface. I will appreciate if you can suggest any passivation treatment for this purpose or give any information (articles etc.) concerning of this problem. Also information of the passivation chemicals suitable only for prevention of white rust (one step processes just after hot dip galvanizing) are interesting. Kauko Jyrkas - Hameenlinna, Finland

I'm interested in reading the responses to question 19051.

O. Picozzi
- Albany, NY USA

Unfortunately, it appears that no one has yet offered hope, O. However, some of our advertisers, including Sanchem, and International Chemicals have non-chromate conversion chemistries that may be worth inquiring about.

Ted Mooney, P.E.  finishing.com Brick, NJ

 

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