rust on black steel

huangyhg

rust on black steel
c-floor systems is a new composite-action structural floor system using cold-formed steel.  one particular client wanted "black" steel to be exposed.  now, naturally, the steel is showing signs of rusting.  is there any advice that anyone can recommend for my client to minimize (or even eliminate) the rusting process without having to paint the steel? i mean, is there some kind of 'oil' or resin that protects the exposed steel while maintaining its "cold steel look"?
what you should do is look for an old article on the effects of mill scale on reinforcing steel and the design intent of the reinforced concrete.  i'd give you the name of the article but i can't recall off the top of my head which organization it was published by.  i want to say it was aci or concrete international but i don't recall.
at any rate, the article acknowledges that reinforcing steel is routinely shipped to the jobsite with such lead time that it sits on site for months before being used.  thus mill scale will develop.  the article notes when to clean and when to not to worry about it.
regards,
qshake
eng-tips forums:real solutions for real problems really quick.
my mistake to inform you properly... the purlins are modified to allow composite bonding to ±3½ -4" of concrete.  the whole of the purlin is exposed!  the rusting on the purlins is what the client wants to eliminate.
c-floor systems is comparable to canam's hambro... except, we use purlins instead of owsjs.
the rust on the purlins should be avoided.  i am not looking for the microscopic stress bonding between a rusted rebar and the concrete.  
you can clean the steel with a wire brush and immediately coat it with a urethane clear coat.  some peeling might occur, but it will protect the majority of it and maintain the uncoated steel look.
you can use a light oil, but eventually that will allow moisture penetration and will attract dust.
there's not a good solution that i know of.
you can oil it- works in motors and the like.  but the thing is, you'd have to keep oiling them, and it would be a mess.  you wouldn't just have a "dry" coating.
on the clear coatings- check with a coating manufacturer.  normally, they'd recommend the coatings on a bare steel surface (ie, sandblasted), not a "black" steel surface.
on the comment as to mill scale up above- i think the mill scale is just formed as the product cools.  what happens after that is rust, not mill scale.
steel gun parts are normally "blued".  this involves heating them (i forget, maybe 200 degrees f or so- not a metallurgical process) and applying some sort of solution.  but even then, the parts must be kept somewhat oiled, and you couldn't very well do this after a beam is attached to concrete.
you might consider just using an epoxy that is more or less the original color.
i think a whole thread or group on durability is worth starting.  after 20 years of design issues of temperature, creep, cracking etc., etc. seem to be causing us more problems than fe or any sort of 2nd. order elastic/plastic analysis method ever could...... we're ready.  lets go!
what about electrically reversing the rusting process?
i'm not sure how practical it would be, but it should be possible to use a zinc "sacrificial" electrode and use the steel joist as the other electrode (not sure which one is the anode/cathode).
i believe they use something similar to protect the goldengate bridge.
cfloor: i would like to "see" some information on the joists.

i'm not aware that you can cathodically protect a surface exposed to air- could make it a bit hazardous to walk in the area!