Galvanized Rebar Specs: ASTM A767, Grades and Bending

Galvanized rebar is specified with two separate standards: one for the bar and one for the zinc coating. The coating is either ASTM A767/A767M (batch hot-dip galvanizing, with bars normally cut and bent before they are dipped) or ASTM A1094/A1094M (continuous galvanizing, with bars designed to be bent after coating). The bar underneath keeps its own grade, which in Canada is normally CSA G30.18 400W or 500W. Galvanizing does not change the bar's grade, and under Canadian practice it does not lengthen laps the way epoxy coating does.

This post is a specifier's and buyer's view of galvanized rebar. For how it compares with epoxy, see galvanized vs epoxy-coated rebar. For what drives the cost, see galvanized rebar price in Canada.

The two galvanized rebar standards

ASTM A767 is the traditional route and the one most specifications name. Because the bars are shaped before dipping, the bar list has to be final before the steel leaves for the galvanizer, and any later change means new bars. A767 also requires a treatment after galvanizing that limits the reaction between fresh zinc and wet concrete and helps prevent storage stain on bundles.

ASTM A1094 came later and works more like ordinary rebar: coat the straight stock, then fabricate. Availability depends on finding a supplier with a continuous line, so check before designing around it.

The RSIC Manual of Standard Practice, which follows ASTM A767/A767M-19, lists the minimum zinc coating mass for each class:

The specification should name one of these standards, plus the coating class where A767 is used. "Galvanized" on its own leaves the important choices to whoever quotes the job.

Which bar grade goes under the zinc

Galvanizing is a coating, not a grade. The grade on the drawings applies to the bar before it is coated:

• In Canada, that is normally CSA G30.18 Grade 400W, or 500W where the engineer has designed for it. See rebar grades in Canada.
• On US-designed work, the base bar is typically to an ASTM bar standard such as A615 or A706, and the ASTM galvanizing standards are written with those bars in mind.

The industry research summarized by the galvanized rebar sector is that the tensile, yield and elongation properties of reinforcing steel are substantially unaffected by hot-dip galvanizing when the steel and process are chosen correctly. The concern is with bending after batch galvanizing: the alloy layers are hard and brittle, and they can crack and flake at a tight bend. That is the main reason A767 bars are bent first.

Write it on the order as two lines: the bar standard and grade, then the coating standard and class. For example, "CSA G30.18 400W, galvanized to ASTM A767 Class I, fabricated before galvanizing."

Can you bend galvanized rebar?

It depends on the standard and the timing.

A767 bars: usually bent first. Most batch-galvanized bar is cut and bent, then sent to the galvanizer, so the brittle alloy layers are never bent. A767 includes a table of minimum finished bend diameters by bar size; compare it with the hooks and bends on the bar list and use the larger where they differ. Our rebar bending chart lists both the CSA A23.1 black bar values and the galvanized values.

The RSIC manual notes that fabrication can be done before or after galvanizing, using the same fabricating standards as black bar, with approved touch-up to ASTM A780 wherever the zinc flakes. Bending after batch galvanizing is still the riskier route for the coating, so treat it as something to agree in advance:

• Get the engineer's approval first.
• Expect cracking or flaking of the coating on the outside of the bend.
• Repair the damaged area to ASTM A780 before it is cast in.
• Never heat a galvanized bar to bend it.

A1094 bars: bend after coating. Continuous galvanized bar is designed to be formed after galvanizing much like uncoated bar. Its industry guidance notes that some cracking or flaking at the bend may occur and is not, on its own, a reason for rejection, and that slower bend speeds help keep the coating intact.

On site: field bending of any coated bar is a last resort. A bar list that is right the first time is cheaper than a pile of repaired bends.

Galvanized rebar in concrete: bond, laps and contact

Bond and laps. Industry testing reports that galvanized and black deformed bars reach the same fully developed bond strength, although galvanized bar can take longer to get there. In CSA A23.3, the coating factor that increases development and lap lengths applies to epoxy-coated bar, not zinc. The RSIC Manual of Standard Practice says lap lengths for galvanized bar are the same as for black bar because of their equivalent bond strength, and points users to its black bar tables. So on a like-for-like design, galvanized bar laps match black bar laps. See Class A vs Class B lap splices for how those lengths are set. Your engineer confirms the laps on the drawings.

Contact with uncoated steel. Zinc and bare steel in contact, in wet concrete, is a mixed-metal situation, and electrolytic action can occur. The RSIC manual calls for some form of separation to electrically isolate galvanized bars from dissimilar metals. Where galvanized bars meet black bar or existing reinforcement, the engineer decides how that separation is achieved. Do not improvise it on site.

Tie wire and supports. RSIC practice is to support galvanized bar on non-corrosive chairs and spacers and to tie it with zinc-coated or dielectric (non-conductive) wire. Plain black wire on galvanized bar creates small points of dissimilar metal. See rebar tie wire.

Cover still matters. Galvanizing extends the time to corrosion. It does not replace the cover, concrete quality and curing that CSA A23.1 requires.

Couplers, cut ends and repairs

Cut ends. Any bar cut after galvanizing has bare steel at the cut. Cut ends are repaired to ASTM A780, which covers three methods: zinc-rich paint, zinc-based solder and sprayed zinc (metallizing). Zinc-rich paint is the usual choice on site.

Mechanical couplers. Threaded, swaged and other coupler systems are proprietary. Before ordering galvanized bar with couplers, confirm with the coupler manufacturer:

• whether the bar ends are threaded or prepared before or after galvanizing,
• whether the coupler itself is galvanized or otherwise protected,
• and how exposed threads or bare steel at the joint are to be treated.

The coupler system still has to meet the splice performance the design calls for. Our post on rebar couplers vs lap splices explains those requirements.

Welding. Welding galvanized bar burns off the zinc at the weld and gives off zinc fumes, which need proper ventilation and controls. The weld area then needs repair. Rebar welding in Canada follows CSA W186 and needs weldable bar and the engineer's approval.

Handling and storage. Galvanized bar can be handled much like black bar and can be stored outdoors without losing its protection, though care is still needed to avoid chipping the zinc, and tightly packed wet bundles can develop white storage stain. Store bundles off the ground and ventilated.

Tags. Paper bar tags do not survive the acid pickling step before galvanizing, so the fabricator and galvanizer need a system to re-tag the bars afterwards. Ask how your bundles will be identified on delivery.

What to put in the specification and order

A complete galvanized rebar specification or purchase order covers:

1. Bar standard and grade (for example CSA G30.18 400W).
2. Coating standard: ASTM A767 or ASTM A1094, and the coating class where applicable.
3. Fabrication sequence: bent before or after galvanizing, and the bend diameters to use.
4. Which bars are galvanized. Often only the outer layer, the exposed face or one element is coated, and the rest is black bar.
5. Repair method for cut ends and damage (ASTM A780).
6. Accessories: galvanized tie wire, coated or plastic supports, compatible couplers.
7. Laps and splices as shown by the engineer.

If the drawings only say "galvanized rebar", ask the engineer to complete the list before pricing. A fabricator quoting without it has to guess at the coating route, and that changes schedule and cost.

Ordering galvanized rebar

We detail, cut and bend rebar from 10M to 55M to your bar lists, and we offer galvanizing, so fabricated bar can be galvanized to suit your specification. Tell us the bar grade, coating standard and class when you request a quote, and we will confirm how we can meet it.

Send your drawings and specification for a free take-off and quote, or see our rebar products.