Of every material that arrives on a site, reinforcement steel is the easiest to substitute and the hardest to inspect once concrete has been poured. It is worth knowing what you ordered and how to confirm it turned up

Reading the designation

Bars are commonly written as a letter followed by a number: Y12 means a high-yield deformed bar of 12 mm nominal diameter. R denotes plain round mild steel. The number is always the diameter in millimetres, so Y16 is 16 mm.

Common sizes and typical use

  • 8 mm and 10 mm — links and stirrups, slab distribution steel, light lintels

  • 12 mm — slab main reinforcement, lintels, light beams.

  • 16 mm — beams and columns in typical residential frames.

  • 20 mm and 25 mm — heavily loaded columns, transfer beams, raft and pad foundations.

These are conventions, not rules. The bar schedule prepared by your engineer governs, and it accounts for spans, loads and cover that a general guide cannot.

Weight is the honest check

Diameter can be eyeballed; mass cannot be faked. Steel has a consistent density, so a bar of a given diameter has a predictable mass per metre — roughly 0.395 kg/m for 8 mm, 0.617 for 10 mm, 0.888 for 12 mm, 1.58 for 16 mm, 2.47 for 20 mm and 3.85 for 25 mm.

Weigh a measured length from a delivery and compare. An underweight bar is an under-diameter bar, whatever the label says, and it will not deliver the capacity the design assumed.

Rolling margin allows small variation. A shortfall of several per cent, repeated across a delivery, is not variation — it is a different product.

What else to inspect

Look for consistent rib pattern along the length, since ribs are what develop bond with the concrete. Light surface rust is normal and even helps bond; flaking scale that comes away in sheets does not. Reject bars with sharp kinks, as bending and re-straightening work-hardens steel and leaves it brittle at exactly the point you cannot see.

Keep the mill certificate for the delivery. If a structural question is raised later, that document is the difference between an inspection and an argument.