reo

Reo is reinforcing steel, typically in the form of bars or mesh, embedded in concrete to carry tensile loads that the concrete itself cannot handle. Concrete is strong in compression but weak in tension, so when a beam bends or a slab flexes, the bottom face experiences pulling forces that would cause cracking and failure without steel reinforcement. The reo transfers that stress across the crack and keeps the concrete from splitting apart.

The most common form is deformed bar, or rebar, with raised ribs running along its length to grip the concrete mechanically. Sizes range from 10 mm diameter up to 50 mm or more, graded by yield strength, typically 300 MPa or 500 MPa in modern supply. Welded wire fabric and rolled mesh are also used, especially in slabs. The cover, the thickness of concrete between the reo and the exposed surface, must meet code requirements to protect against corrosion and fire.

Where the term comes from

Reo is an acronym or abbreviation, short for reinforcement, and the word stuck in the trades, especially in Australia and New Zealand where it originated. In North America, rebar is the dominant term; in the UK, reinforcement or simply steel is more common. All three labels refer to the same material and function.

Corrosion is the main failure mode in wet or coastal climates. Even microscopic cracks let water and oxygen reach the steel, triggering rust that expands and spalls the concrete cover. Placement matters too: reo that sits too close to the surface, or too deep, or out of position, cannot do its job properly and may not be caught on visual inspection. Concrete cover, bar spacing, and lap length are specified in design and must be verified during setting and pouring.