Continuous Galvanized Rebar vs Hot Dip Galvanized Rebar - Further reading 3

[Sosipater]

thread507-478297

Much like the OP in the referenced thread, I have had a GC ask to substitute in a Continuous Galvanized Rebar (ASTM A1094) product.

The literature online appears to be very passionate about the success of Continuous Galvanized Rebar (CGR), but it feels somewhat biased. Most articles seem to source from a particular supplier. However, they are still interesting:

https://www.structuremag.org/?p=11305

https://www.azz.com/featured_storie...rrosion-and-materials-reliability-laboratory/

Then there is the white paper discussed in the above thread, "Continuously Galvanized Reinforcing Steel":

https://www.researchgate.net/publication/301609328_Continuously_Galvanized_Reinforcing_Steel

One of the upshots of this report is the differences in thickness of the zinc.
ASTM A1094 (Continuously Galvanized rebar) - 2 mils zinc thickness specified. Thinner, but is a purer zinc coating than HDG.
ASTM A767 (HDG rebar) - Class 1 coating is 3.0 ounces/ft2 of zinc works out to 5.9 mil coating. Thicker, but the zinc has more iron in it.

I eventually came across a test performed at the University of Waterloo, "Evaluation of the Corrosion Behaviour of Continuously Galvanized Rebar"

https://uwspace.uwaterloo.ca/handle/10012/10943

This is a corrosion test comparing Continuously Galvanized to HDG rebar.
The Continuously Galvanized Rebar (CGB) did not perform as well as the HDG, for a few reasons: inconsistent coating thickness and presence of aluminum were the big issues.
"As a result, the author recommends to the producer of the bars that thicker and more uniform coating should be added to the CGR, to at least stand a chance to show similar performance as the conventionally hot-dipped galvanized steels."

This is new to me. So, I thought I'd put it out there, see if anybody had any thoughts.

 

[BridgeSmith]

I guess the big question is whether the supposedly lesser performance of the CGR would still provide adequate protection for the service life of the structure.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Sosipater]

I agree.

Also, there are other excellent reasons for considering CGR. Cost and formability being two of the big ones.

I think, because it's new to me, I'm pushing back against the it's-the-greatest-thing-ever nature of some of the literature. And the suggestion, at least one supplier makes, that it can outright replace HDG.

CGR absolutely has it's place, and is a tool I'll reach for in the future. Just somewhere between pig steel and HDG rebar.