Galvanization of anchor bolts and embedded steel

[J1D]

In some environment hazardous to metal (like chemical attack, humid places, etc), we specify anchor bolts to be galvanized (hot-dipped), even for the steel items totally embedded in concrete. I wonder if the latter application is really necessary? I don’t know if any reinforcement rebar is ever galvanized for the same reason.

 

[SlideRuleEra]

Rebar is often galvanized, here are a few free .pdf documents on the the subject

http://www.galvanizeit.org/showContent,45,77.cfm

For items that are totally embedded, IMHO, galvanizing is a good idea if the concrete will be subjected to really a really "bad" environment, or if there is minimal (but acceptable) concrete cover (similar to rebar for salt water bridges, etc.)

Just high humidity... I would not consider galvanizing essential (for totally embedded objects).

http://www.SlideRuleEra.net

 

[J1D]

Thanks, SlideRuleEra. This is kind new to me.

 

[Gumpmaster]

I recently had a project in a location with a high soil chloride content. Our corrosion engineer recommended that all exterior rebar in contact with the ground should be galvanized. He said interior slabs were OK with ordinary rebar.

Plan ahead because galvanizing bent shapes has a pretty long lead time and any modifications during construction can cause a big delay.

 

[pba]

Is there any problem with galvanising high tensile steel bars? Do you loose strength or do the shapes deform?

I've never needed to do it so don't know the answers but Slide Rule is correct in that it is done quite often for agressive environments.

The alternatives (if they are practical) are increased cover, better concrete or external coatings - especially bituminous types...

 

[Dinosaur]

We coat steel products in a variety of locations and with a variety of products in the bridge industry.

All bar within the top 3 inches or more of a surface that will be exposed to runoff gets coated, either epoxy coating or galvanizing typically using the hot-dip process. All bar in the pier cap where an open joint is in the deck to accommodate expansion is coated with either epoxy or galv. All bar above the seat elevation in an abutment is usually coated. All structural steel is either weathering steel, painted steel, galvanized steel or even metalized steel. HS bolts are either galvanized or Type III for weathering steel.

Anchor rods are typically galvanized, but there are many more issues there. The galvanized anchor rods are A307 or F1554, Gr 36, or Gr 55. High strength anchor rods are vulnerable to hydrogen embrittlement when galvanized, so these are painted rather than galvanized. We avoid using high strength bars when corrosion is likely but can't avoid them 100%. Anchor rods supporting poles are often galvanized and then coated with asphalt. We even use stainless steel anchor rods to support smaller light poles.

Galvanizing reinforcing steel does not induce any problems that I am aware. When galzanizing causes problems, you probably already had a problem that the galvanizing uncovered, such as high residual stresses as a result of fabrication. Hot-dip galvanizing does require proper detailing to permit the molten zinc to get in and out again.

Good Luck.

 

[twinnell]

Dinosaur,

Do you know of a document that discussed the hydrogen embrittlement issue for the gr 105 anchor rod? I have seen some documentation on A490 bolts, but not f1554.

 

[kenvlach]

Hydrogen embrittlement is not usually a problem with hot dip galvanizing -- the heat drives out any hydrogen picked up in the acid pickling pretreatment (which should be minimized by use of a pickling inhibitor, anyway). As dinosaur said, embrittlement is usually due to preexisting problems [such as from heavy cold working or welding]. Rarely, embrittlement can result from contaminated galvanizing baths.
Of course, electroplating of zinc can cause hydrogen embrittlement, but that's another issue.

twinnell, I've given references to ASTM galvanizing specifications and several galvanizer associations at the finishing.com forum:

http://www.finishing.com/432/42.shtml

http://www.finishing.com/428/95.shtml