Corrosion of reinforcing steel in concrete leads to the premature failure of many structures exposed to harsh environments. Rust products form on the bar, expanding its volume and creating stress in the surrounding concrete. In this study we will present how metal acts into an aggressive environment and how we can adopt the best solutions to reduce the attack of corrosion. First we should understand how corrosion occurs. Corrosion occurs when two different metals, or metals in different environments, are electrically connected in a moist or damp concrete. This will occur when: steel reinforcement is in contact with an aluminium conduit; concrete pore water composition varies between adjacent or along reinforcing bars; where there is a variation in alloy composition between or along reinforcing bars; where there is a variation in residual/applied stress along or between reinforcing bars. Loss of alkalinity due to carbonation or chlorides, crack due to mechanical loading, stray currents, agents from atmospheric pollution, moisture pathways, low concrete tensile strength, electrical contact with dissimilar metals are some of the most important reasons of corrosion. Electro-chemical corrosion, which plays a subordinate role in air, is of greater significance in liquids. The extent of electro-chemical corrosion depends on the electrical conductivity of the liquid, which affects the protective influence of the zinc layer over greater or smaller areas. The pH value of the liquid is of most significance. The corrosion rate of zinc is normally low and stable in the pH range of 5,5—12,5, at temperatures between 0 and 20 °C. Corrosion outside this range is usually more rapid. Hard water, which contains lime and magnesium, is less aggressive than soft water. Together with carbon dioxide these substances form sparingly soluble carbonates on the zinc surface, protecting the zinc against further corrosion. Soft water often attacks zinc, since the absence of salts means that the protective layer cannot be formed. In some waters, polarity reversal can occur at about 70 °C so that the zinc coating becomes more electro-positive than the steel and pitting occurs. Oxygen, sulphates and chlorides counteract polarity reversal, which means that the problem may exist only in very clean water. Water temperature is of great significance to the rate of corrosion. Above approximately 55 °C, the layer-forming corrosion products acquire a coarse-grained structure and lose adhesion to the zinc surface. They are easily dislodged and expose new, fresh zinc for continued and rapid corrosion attack. The rate of corrosion reaches a maximum at about 70 °C, after which it declines so that at 100 °C it is about the same as at 50 °C. Keywords : composite materials, corrosion, reinforcement, water corrosion, reinforcement bars.

Concrete is a complex material of construction that enables the high compressive strength of natural stone to be sed in any configuration. In tension, however, concrete can be no stronger than the bond between the cured cement and the surfaces of the aggregate. This is generally much lower than the compressive strength of the concrete. Concrete is therefore frequently reinforced, usually with steel. When a system of steel bars or a steel mesh is incorporated in the concrete structure in such a way that the steel can support most of the tensile stresses and leave the immediately surrounding concrete comparatively free of tensile stress, then the complex is known as reinforced concrete. Corrosion of reinforcing steel in concrete leads to the premature failure of many structures exposed to harsh environments. Rust products form on the bar, expanding its volume and creating stress in the surrounding concrete. This leads to cracking and spalling, both of which can severely reduce the service life and strength of a member. Corrosion of reinforcing steel in concrete structures is one of the most expensive problems facing civil engineers in the world. The structural integrity of many bridges, overpasses, parking garages, and other concrete structures has been impaired by corrosion, and repairs are urgently required to ensure public safety. Corrosion-induced deterioration of reinforced concrete can be modelled in terms of three component steps: (1) time for corrosion initiation; (2) time, subsequent to corrosion initiation, for appearance of a crack on the external concrete surface (crack propagation); and (3) time for surface cracks to progress into further damage and develop into spalls, to the point where the functional service life, is reached. The two most common causes of reinforcement corrosion are: (i) localized breakdown of the passive film on the steel by chloride ions and (ii) general breakdown of passivity by neutralization of the concrete, predominantly by reaction with atmospheric carbon dioxide. Sound concrete is an ideal environment for steel but the increased use of deicing salts and the increased concentration of carbon dioxide in modern environments principally due to industrial pollution, has resulted in corrosion of the rebar becoming the primary cause of failure of this material. The scale of this problem has reached alarming proportions in various parts of the world. Corrosion in reinforced concrete structures is causing deterioration of our infrastructure. Structures in or near marine environments and transportation structures on which deicing salts are used are especially vulnerable. A widely promoted method for repairing damaged structures or for protecting structures in corrosive environments is the application of fiber-reinforced composite wraps over the surface of the structures elements.