Galvanized steel: a) bond of concrete b) white rust
Galvanized steel: a) bond of concrete b) white rust
(OP)
We are designing a steel stair with concrete infill to the stair tread pans. It is open and exposed to the exterior and will have an electrical snow melting system in each tread. We are considering galvanized steel (we think it is superior to a zinc-rich paint or epoxy paint, in this type of situation). There are several flights of the stair; it goes up to the roof of a hospital and the helicopter pad on the roof.
Questions:
1. We would like the concrete to bond to the the galvanized steel, so that water cannot collect at the concrete to steel interface (and freeze and crack the concrete if the snow melting system fails). Many materials will not bond or bond poorly to galvanized steel. Will concrete bond to galvanized steel the same as to black steel?
2. Is white rust on galvanized steel only an issue of how the steel is stored before erection, or can white rust be formed on the galvanized steel after it is erected?
3. Is there any treatment that should be specified to prevent formation of white rust?
4. Does the galvanized steel routinely receive a passivating chromate treatment, or does that have to be specifically specified in addition to the galvanizing?
Questions:
1. We would like the concrete to bond to the the galvanized steel, so that water cannot collect at the concrete to steel interface (and freeze and crack the concrete if the snow melting system fails). Many materials will not bond or bond poorly to galvanized steel. Will concrete bond to galvanized steel the same as to black steel?
2. Is white rust on galvanized steel only an issue of how the steel is stored before erection, or can white rust be formed on the galvanized steel after it is erected?
3. Is there any treatment that should be specified to prevent formation of white rust?
4. Does the galvanized steel routinely receive a passivating chromate treatment, or does that have to be specifically specified in addition to the galvanizing?






RE: Galvanized steel: a) bond of concrete b) white rust
Why concrete-filled pans for exterior?
Why not open-grate treads?
RE: Galvanized steel: a) bond of concrete b) white rust
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Galvanized steel: a) bond of concrete b) white rust
White "rust" is the oxidation of the zinc in the galvanizing. It can occur at any time after galvanizing is done, whether in storage or in exposed applications.
RE: Galvanized steel: a) bond of concrete b) white rust
Thanks everyone for the responses.
This is a hospital stair up to a helicopter pad on the roof. Where I have seen open tread stairs, is seems to me to have been in industrial type buildings. I am not sure about its use in a hospital, and its acceptability as an emergency exit. It would solve the issue of water collecting in the bottom of the tread, but the open treads would be subject to icing up and I don't think that there is any way to install snow melting cables on such a stair.
If the open tread turns out not to be acceptable to our client, then we could perhaps use a bonding agent, except that may be difficult to apply with the electric heating cables there.
Ron - the literature that I see on the internet seem to say white rust is only an issue with respect to the "young" age of the zinc when the steel is stored prior to shipping, and that as the zinc coating ages it becomes resistant to formation of white rust. Is there any publication on which you rely in noting that the white rust also forms at later ages?
No one yet has responded to questions 3 and 4...
RE: Galvanized steel: a) bond of concrete b) white rust
3. Sometimes either chromate passivation or a light mineral oil coating is used to prevent the formation of "white rust" during storage. As I noted, the white rust is oxidation of the zinc. This can occur at any time before the zinc carbonate layer forms on the surface of the galvanizing. This layer is the dull appearance of galvanizing after weathering uniformly.
4. No. Chromate passivation is usually not done prior to galvanizing but can be done as a protection for storage conditions. It does not last long when done post-galvanizing.
If for any reason the zinc carbonate layer is removed or compromised during the life of the galvanizing, white rust can again form until the zinc carbonate is re-formed.
RE: Galvanized steel: a) bond of concrete b) white rust
RE: Galvanized steel: a) bond of concrete b) white rust
RE: Galvanized steel: a) bond of concrete b) white rust
RE: Galvanized steel: a) bond of concrete b) white rust
Looks like everyone is advising against steel stair with concrete filled treads. Interesting.
RE: Galvanized steel: a) bond of concrete b) white rust
Dave
Thaidavid
RE: Galvanized steel: a) bond of concrete b) white rust
- Have you done a stair as you describe? In a deicing chemical environment like Canada or the north-east U.S.?
- How does the cost roughly compare to that of a galvanized steel stair with concrete fill in the treads?