A challenge to different mechanisms of inhibition in reinforced concrete structures

Carbon steel reinforcements in concrete structures are in passive conditions that is they are protected by a thin oxide layer promoted by the concrete alkalinity. Corrosion can initiate only when passivity is destroyed. This occurs in two ways: carbonation of concrete, the reaction of atmospheric ܱܥଶ with cement paste that lowers pH and causes general corrosion; the presence of chlorides at the steel surface in concentration higher than a critical threshold, generally considered in the range of 0.4–1% by cement weight. Chlorides may be added to concrete in the mix water or in the aggregates, even if nowadays it is restricted by standards; chlorides can also penetrate from outside, in highway viaducts where deicing salts are used, or in marine structures. Local passivity destruction by chlorides causes pitting corrosion. Among available methods, corrosion inhibitors offer a simple and cost effective prevention technique, primarily to prevent and stop chloride-induced corrosion.