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Chloride attack is one of the most important aspects for consideration when we deal with the durability of concrete. Statistics have indicated that over 40% of failure of structures is due to corrosion of reinforcement [a]. Chloride attack poses a significant threat to reinforced concrete especially for structures in marine environments or those that are likely to be exposed to high concentrations of salts. The net result of chloride attack is the corrosion of steel reinforcement, leading to cracking and spalling of concrete and in some cases catastrophic structural failure as the load bearing capacity of the concrete is compromised [b].

The mode of attack relies on salts and other corrosive substances, carried by moisture, being absorbed into the concrete via its pores and micropores through capillary action. Once absorbed, these substances act to reduce the PH value of the concrete thereby eliminating its passive oxide layer which would otherwise provide protection to the steel reinforcement. Corrosion takes place as the chloride ions meet with the steel and the surrounding passive material to produce a chemical process which forms hydrochloric acid. The hydrochloric acid eats away at the steel reinforcement [b].

Whilst cracking and spalling of concrete accompanied by rust staining is indicative of chloride attack, high strength dense concrete may suffer damage to reinforcement without exhibiting such obvious symptoms until substantial loss of steel has occurred. Where spalling has taken place, an inspection of the exposed reinforcement will typically reveal black colored rusting and pitting of the steel where the aggressive hydrochloric acid has ‘eaten’ the reinforcing material [b].

An engineer may employ several different methods or remedies to prevent corrosion induced by chloride intrusion. The simplest way to reduce corrosion is to increase the cover over rebar. Adding just an extra inch of concrete cover could double the life of a structure. Rebar modifications such as utilizing Epoxy coated rebar, stainless steel-clad rebar, or cathodic protection, can also serve to prevent the rate of deterioration. Another way to prevent chloride intrusion is to reduce the permeability of concrete [c]. Moreover, the addition of an anodic inhibitor to the concrete recipe for structures prone to chloride attack is one measure that may increase service life or time to necessary expensive repair [d].

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