Remedial Measures to Rehabilitate Affected Structures

The following types of remedial measures are used for controlling the corrosion of steel on the existing structures. 

1. By insulating  the concrete surfaces from the corrosive environment. 
2. By modifying the environment to make it less corrosive. 
3. By actively controlling the electron flow within the environment so that no metal is lost from the structure. 
4. By applying a combination of the above techniques. 

The reinforced concrete structure may be insulated from the corrosive environment through application of an impermeable, dielectric barrier between the structure and the corrosive environment. The barrier may be a coating or membrane applied to the surface of the concrete, may be formed as an integral part of the concrete matrix through polymer impregnation, or may be an overlay of polymer concrete, low slump concrete, latex-modified concrete, or internally-sealed concrete. 

The environment may be altered to reduce corrosion either by removing detrimental constituents (such as chloride ion), or by removing or neutralizing stray current sources. Cathodic protection can be used to control the direction of electron flow within the steel-environment electro chemical circuit to stop corrosion of the reinforcing steel. 

Applicability 

All reinforced concrete structures are susceptible to corrosion. Although bridge decks are perhaps the most notorious examples today, these include buildings, caissons, foundations. parking garages, piers, piles, pipes, silos, tower footings, and water tanks. Some of these structures may be totally or partially berried in soil.  Others, such as offshore platforms, water tanks, and the internal surfaces of pipe, are exposed to aqueous solutions.  Bridge decks, parking garages, and buildings are exposed to the atmosphere. 

If the structure is burried or permanently underwater such that the concrete surfaces are not accessible for treatment, and it is impractical to expose them, treatment of the surfaces with surface coatings or membranes or by application of overlays is not applicable. Similarly, if the structure to be maintained is a burried pipeline or an offshore platform exposed in a large body of water, modifying the environment to make it less corrosive would not be a practical solution. Thus, not all the remedies discussed here are applicable to all types of reinforced concrete structures in the various environments. Hence a judicious,  cautious assessment of the situation is required before employing any method. 

Cathodic protection is by far the most versatile method of corrosion control since it is applicable to any electrically continuous structure within a suitable electrolyte. In as much as the steel embedded in concrete, and not the concrete, requires the protection from metallic corrosion, damp concrete serves as a suitable electrolyte and even structures exposed to the atmosphere, such as bridge decks, can be protected cathodically.