<P> 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 voids to accommodate rebar, which is then secured in place with grout . This combination is known as reinforced masonry . </P> <P> Steel has a thermal 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 from 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 accompanies 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 . </P> <P> 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, and salt penetration . 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 phenomenon is known as oxide jacking . This is a particular problem where the concrete is exposed to salt water, as in bridges where salt is applied to roadways in winter, or in marine applications . Uncoated, corrosion - resistant low carbon / chromium (microcomposite), 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 . Extra care is taken during the transport, fabrication, handling, installation, and concrete placement process when working with epoxy - coated rebar, because damage will reduce the long - term corrosion resistance of these bars . Even damaged bars have shown better performance than uncoated reinforcing bars, though issues from debonding of the epoxy coating from the bars and corrosion under the epoxy film have been reported . These bars are used in over 70,000 bridge decks in the USA . </P> <P> Fibre - reinforced plastic rebar is also used in high - corrosion environments . It is available in many forms, such as spirals for reinforcing columns, common rods, and meshes . Most commercially available rebar is made from unidirectional glass fibre reinforced thermoset resins . </P>

What type of steel is used in rebar