How rebar is made

Concrete is strong when squeezed and weak when stretched, so steel bars with ridges do the stretching for it.

stations: 6
things upstream: 38
raw sources: 14
steps from the ground: 7

The short version

Rebar is rolled from steel billets that are heated until they are glowing and squeezed into round bars. The last roll stand presses ribs, or lugs, into the surface so concrete can grip the bar. The bars are cut to length, sometimes coated with zinc or epoxy to resist corrosion, and bundled for delivery to building sites.

Cast square billets

Molten steel is run through a continuous caster that produces billets, thick square bars under 200 millimeters across and up to 12 meters long. Billets are the usual feedstock for long products such as rebar, and rebar is often made entirely from recycled steel scrap.

Goes in
Steel Steel scrap
Reheat to rolling heat

Cold billets are heated in a furnace until they are soft enough to roll. Those coming straight from a caster can skip this and go in hot.
Roll the round bar

A train of roll stands squeezes the billet thinner and longer, step by step, until it is a round bar of the required diameter. Rolling above the recrystallization temperature keeps the steel from hardening as it is worked.
Emboss the ribs

In the final stand the rolls carry engraved patterns that press raised ribs into the bar. The height and spacing of those lugs are set by standards, because they are what lock the bar into the concrete and stop it sliding out.
Cut to length

Shears cut the cooled bars to lengths for shipping, or the bar is coiled if it is thin. Sizes are labeled by number, so a builder can ask for a standard bar by its size.
Coat against corrosion

Plain carbon steel bars are left uncoated for most buildings, because concrete itself protects them. Bars for bridges and seawater work can be galvanized with zinc or coated in epoxy resin instead.

Goes in
Zinc Epoxy

End of the lineRebar Next it goes into concrete, skyscraper.

Worth repeating

Steel and concrete expand and shrink with temperature by almost the same amount, so a reinforced beam does not tear itself apart on hot or cold days.
Epoxy-coated rebar went into over 70,000 US bridge decks, yet by 2005 it was being phased out in favor of stainless steel because it performed poorly.
Concrete keeps rebar from rusting because its chemistry is strongly alkaline, with a pH above 12, so cracks and thin cover let rust in.