Corrosion Inhibitors in Concrete: Reinforced concrete is an established combination of steel and concrete that has been commonly used for over a century. Steel gives tensile strength to the set, whereas concrete acts as a physical barrier to protect the steel from corrosion. The alkalinity of the concrete, which ranges between pH 12 and 14, creates the ideal conditions for the development of a passive film that protects the steel bars from corrosion.
However, the protection offered by the concrete is inadequate in some cases because it is porous and has fissures, which enable aggressive agents such as chloride ions to penetrate, resulting in reinforcement corrosion. Additionally, the reaction between carbon dioxide (CO2) and the cement hydration materials, referred to as carbonation, lead to the formation of calcium carbonate and a pH drop, destabilizing the reinforcement passivating film and exposing it to corrosion.
Corrosion of steel bars is a major cause of reinforced concrete premature decay, resulting in substantial economic losses. Rapid deterioration can occur as a result of chloride ions in a marine zone, or as a result of the use of thaw salts or as a result of carbonation in urban areas.
Several corrosion inhibitors were used in recent years to provide extra protection and extend the life of reinforced concrete buildings. Corrosion inhibitors have gained increased interest in recent years due to the benefits they provide. The use of inhibitors to improve the resilience of concrete systems exposed to chloride ions and carbonation is a promising process.
Inhibitors are chemicals that, when present in specific quantities, dramatically reduce the rate of corrosion without drastically changing the concentration of any corrosion agent. Due to its low cost and ease of use, corrosion inhibitors can be a viable alternative to more traditional methods of safety and repair. Additionally, inhibitors may be used as a preventative measure or even as a corrective measure.
Corrosion Process in Concrete Structures
Steel’s corrosion product (iron oxides or hydroxides) takes up a far larger amount than steel itself (4-12 times the volume). This volume increase places a significant amount of expansive stress on the concrete, which results in cracking.
Corrosion process in concrete involves an electrolyte, since it is an electrochemical reaction. Concrete is porous and therefore a good electrolyte since it contains moisture. In between anode and the cathode, a minor electrical current flows, with the anode undergoing corrosion (rust formation).
Role of Corrosion Inhibitors
Corrosion inhibitors can interfere in the corrosive phase in one of two ways: by delaying reinforcement depassivation, by improving the passivating film, or by slowing the rate of corrosion following depassivation. Thus, when used in sufficient amounts, corrosion inhibitors retard the corrosive mechanism, thereby extending the life of reinforced concrete buildings. Nowadays, as concern about the longevity of reinforced concrete buildings grows, the use of corrosion inhibitor compounds has been increasingly growing in order to increase the structure’s life span.
The inhibitor has little effect on the strength or setting time of concrete, but prolongs its lifespan. The inhibitor’s chemical composition does not change over time. This property contributes to the concrete’s increased life.
Different materials are used to safeguard new and established reinforced concrete buildings. In the case of new buildings, inhibitors should be applied to the fresh concrete to eliminate or postpone the initiation of the corrosive process. For pre-existing structures, inhibitors may be inserted to repair mortars or repair concrete, applied to the concrete base, or incorporated through holes or grooves in the surface.
The liquid products, which are typically phosphate substances like monofluorophosphate, are among the inhibitors used in existing concrete structures. It is critical for this class of inhibitors to have absorptive capacity in order to enter the concrete structure thru the interstitial pores and reach the reinforcement.
Inhibitors, particularly when mixed with concrete, may alter the properties of the material in both the fresh and hardened states, affecting the setting time, the rate of strength gain, and other properties. Thus, it is important to consider how it works and potential side effects in order to avoid unintended consequences.
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