A rebar (short for reinforcing bar), also known as reinforcing steel, reinforcement steel, or a deformed bar, is a common steel bar, and is commonly used in reinforced concrete and reinforced masonry structures. It is usually formed from carbon steel , and is given ridges for better mechanical anchoring into the concrete. In Australia , it is colloquially known as reo. 

History 

Rebars were known in construction well before the era of the modern reinforced concrete . Some 150 years before its invention rebars were used to form the carcass of the Leaning Tower of Nevyansk in Russia , built on the orders of the industrialist Akinfiy Demidov . The purpose of such construction is one of the many mysteries of the tower. The cast iron used for rebars was of very high quality, and there is no corrosion on them up to this day. The carcass of the tower was connected to its cast iron tented roof , crowned with what might have been the first lightning rod in the Western world. This lightning rod was grounded through the carcass, though it is not clear whether the effect was intentional. 

Use in concrete and masonry 

Concrete is a material that is very strong in compression , but relatively weak in tension . To compensate for this imbalance in concrete's behavior, rebar is cast into it to carry the tensile loads . 

Masonry structures and the mortar holding them together have similar properties to concrete and also have a limited ability to carry tensile loads. Some standard masonry units like blocks and bricks are made with strategically placed voids to accommodate rebar, which is then secured in place with grout . This combination is known as reinforced masonry. 

While any material with sufficient tensile strength could conceivably be used to reinforce concrete, steel and concrete have similar coefficients of thermal expansion : a concrete structural member reinforced with steel will experience minimal stress as a result of differential expansions of the two interconnected materials caused by temperature changes. 

Physical characteristics 

Steel has an expansion coefficient nearly equal to that of modern concrete. If this were not so, it would cause problems through additional longitudinal and perpendicular stresses at temperatures different than the temperature of the setting. Although rebar has ribs that bind it mechanically to the concrete, it can still be pulled out of the concrete under high stresses, an occurrence that often precedes a larger-scale collapse of the structure. To prevent such a failure, rebar is either deeply embedded into adjacent structural members (40-60 times the diameter), or bent and hooked at the ends to lock it around the concrete and other rebar. This first approach increases the friction locking the bar into place, while the second makes use of the high compressive strength of concrete. 

Common rebar is made of unfinished tempered steel, making it susceptible to rusting . Normally the concrete cover is able to provide a pH value higher than 12 avoiding the corrosion reaction. Too little concrete cover can compromise this guard through carbonation from the surface. Too much concrete cover can cause bigger crack widths which also compromises the local guard. As rust takes up greater volume than the steel from which it was formed, it causes severe internal pressure on the surrounding concrete, leading to cracking, spalling , and ultimately, structural failure . This is a particular problem where the concrete is exposed to salt water, as in bridges built in areas where salt is applied to roadways in winter, or in marine applications. Epoxy -coated, galvanized or stainless steel rebars may be employed in these situations at greater initial expense, but significantly lower expense over the service life of the project. Especially epoxy-coated have to be installed with great care, because even small cracks and failures in the coating can lead to intensified local chemical reactions not visible at the surface. 

Fiber-reinforced polymer rebar is now also being used in high-corrosion environments. It is available in many forms, from spirals for reinforcing columns, to the common rod, to meshes and many other forms. Most commercially available rebars are made from unidirectional glassfibre reinforced thermoset resins. 

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