Concrete, Metal and Salt Interaction

[kxa]

What is the best refernce for finding out the effects of concrete and salt including calcium chloride on steel?

I have looked at some stairs that the thin metal was used as risers and as formwork for the slate steps (thread). This metal appeared to be galvanized steel or tin. It was silvery color, at least the little areas that weren't heavily rusted. Anyway, looking from under the stairs and almost all the risers, there were severe rusting. In fact, I was told that the rusting started almost a year after the construction.

Any idea what could have caused it. Would limestone cause excessive rusting of the metal as well?

 

[Dinosaur]

Many maintenance workers will heavily salt stairways in the winter. If you live in one of the regions where this is common, I would say this is the problem. Metal treads in this application will experience a high degree of wear. Coatings will be hard pressed to withstand the loads. Most well built stairways I have noticed had a substantial piece of steel scribed with a gripping pattern of diamonds laid into the concrete covering the four inches of the leading top surface of the treadways. There was corrosion, but the steel was substantial and the wear rubbed it off before it became unreasonably thick. Good Luck.

 

[EdStainless]

The basic environment from the concrete will help protect the steel. The two factors trying to hasten the corrosion are the salt and moisture.
If these stairs are in a place that will see salt you need to take two precautions.
You need to make extra sure that they will drain well.
And you need to use a lot heavier steel than you normally would. You can't really prevent the corrosion. If you are concerned about the apperance you might look at using coated steel. Epoxy over galvanizing will at least stand up for a while.

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Rust never sleeps
Neither should your protection

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[swall]

During my youth, I spent summers working for a company that made and erected these types of stairs. The riser/tread piece (the "pan") was nothing more than a formed angle of hot rolled 16 ga. steel. We applied a dipped black laquer paint, no cleaning or pre-treatment. These "pans" would get field welded to the stair stringer channels and then the tread portion of the pan would get poured with concrete to form the tread surface. Both sides of the riser and the bottom side of the tread pan are exposed to the elements and would be relatively accessible for cleaning and painting. The tread pan under the concrete would not corrode until water wicked along the pan/concrete interface. In a high salt usage/low maintenance enviroments, I would expect the riser to be the weak link.