[Ferro List] Part 1/Tom's Crud/Passivisation

[Christopher Glasspool]

Tom,
I have been reading and studying all that I can find on galvanized material around the Internet, and I can not find even a single documented case of passivisation of galvanized reinforcement being a problem. I assume that because it isn't a known problem, little is documented about it, like would it a problem while the paste is very wet, or just damp and curing, or only after it is cured. Would it be worse in a low quality mix in a marine environment with some permeability? Or would it actually be worse in a quality mix where the passivisation could not find a way to dissipate into the mix? All good questions, but never answered because passivisation doesn't appear to have been a problem, therefore no studies, ASTM's, codes, or prescribed practices that I can find, other than Dr. Naaman, who suggests using Chromium Trioxide in the mix, but doesn't site much information, other than the amount he prescribes. I did try to email Dr. Naaman, with some
 specific questions, but didn't get a reply.
The information out there is kind of vague, and I think this like I said has something to do with the lack of actual problem. Many site photos, and descriptions of galvanized reinforcing bars that after many years in a marine environment have either been naturally exposed or forensically cut to show reinforcing material in excellent condition. As for the actual passivisation process, some seem to claim that the passivisation process actually increases the intimate bond, while others seem to say it decreases it but at a much lower rate than two to ten times in volume that corrosion on ordinary steel would eventually do, none seemed to mention an exact enlargement amount of zinc passivisation though. Many do however talk of a need for passivisation when the ph is over 13.5, but that isn't a normal mix design, so isn't much of a problem.
I did find one manufacturer - Z bar that coats the galvanized bars with a polymer, and I thought that this would be my chance to explore where someone was admitting to a problem, but no, I emailed their Representative, and what came back was that the polymer allowed them to use less zinc, while at the same time allowing the customer to retain more Zinc as less loss due to handling, bending and passivisation in the paste. They were not however admitting to any passivisation problems. 
NOW GO TO Part 2/Tom's Crud/Passivisation


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