Galvanized Steel Reinforcement Bars...

Galvanized Steel Reinforcement Bars  Galvanized steel reinforcement bars (also called galvanized steel rebars) are the normal reinforcement steel bars which are coated with a protective layer of zinc (Zn) metal. Zn coating is usually carried out by hot dip galvanizing process. The Zn coating serves as a barrier to the corrosive environment which the rebars are exposed to when embedded in concrete. In addition to the barrier protection, Zn also provides cathodic protection where Zn corrodes preferentially when in contact with unprotected steel. This means that in case of any gap in Zn coating the surface of bare steel is protected by the surrounding Zn. The reaction between steel and molten Zn produces a coating on the steel made up of a series of iron -zinc alloy layers (gamma, delta and zeta) which grow from the steel-zinc interface with a layer of essentially pure Zn (eta) at the outer surface. What distinguishes galvanizing from other types of coatings is that the coating is metallurgically bonded to the steel. It actually becomes an integral part of the steel, as compared to the paints and epoxy coatings which are simply attached to the steel surface by physical bonding. The alloy layers in the coating are harder than the base steel resulting in a coating that is not only firmly adhered to the steel but is tough and hard and can resist abrasion and fairly heavy handling. It also allows the galvanized rebar to be handled, transported and fabricated in the same manner as ordinary steel. A typical galvanized coating structure is shown in Fig 1.  Fig 1 Galvanized coating structure  The first regular use of galvanized coating was done in USA during 1930s. Since then, and especially during the last 25 -30 years, it is being...