New Generation of Mortars with Migratory Corrosion Inhibitors

Corrosion inhibitors protect reinforced concrete structures to prolong their life. But do you know which one to choose when repairing concrete? We tell you in this article.

The concrete forms an external screen to protect the reinforcement against corrosion, providing durability to the structural element, both physically and chemically.

Therefore, in order to maintain their stability and functionality intact, concrete structures need certain care and a maintenance plan that will be conditioned by different aspects such as use, exposure environment and current regulations. We must not forget that concrete ages with the passage of time, losing part of the initial properties of protection against corrosion that it offers to the reinforcement.

It is our responsibility to make repairs to structures more corrosion resistant and therefore more durable. This is especially important in severely corrosive environments. Greater durability will mean fewer repairs, greater structural integrity and a longer service life, which also translates into greater sustainability.

Corrosion in reinforced concrete

Reinforced concrete structures deteriorate mainly due to attacks on the concrete itself or due to corrosion of its reinforcement, with deterioration of the reinforcement being the most common of all. The maintenance of reinforced concrete is an essential task throughout the life of the structure and, therefore, an additional cost that should not be ignored.

The presence of pollutants such as atmospheric carbon dioxide and chlorides promote the oxidation of reinforcement by their penetration into reinforced concrete structures. These two phenomena are known as Concrete Carbonation and Chloride Attack, respectively.

The electrochemical corrosion process of reinforced concrete is initiated by a combination of the following effects: the presence of oxygen, the presence of wet concrete (electrolyte), the depassivation of the steel or loss of the protective alkaline layer and/or the presence of aggressive agents such as chlorides.

The degradation of reinforcement due to corrosion represents a high percentage of the pathologies detected. In generic terms, the phenomenon of corrosion can be defined as a process of electrochemical destruction or deterioration of a metal due to the action and reaction of the metal with the surrounding medium (simultaneous oxidation and reduction reactions).

In order for electrochemical corrosion to start, a galvanic battery must be formed, therefore, there must be an anode, a cathode, an electrolyte (wet concrete) and oxygen. In this electrochemical system, the armour acts as anode and cathode, allowing the connection between the two electrodes and, consequently, the passage of electrons between them.

The anode (- pole) is the place where the steel corrodes, as this is where the metal loses electrons. The cathode (+ pole) is the part of the steel that is not oxidised.

In reinforced concrete, the main factors favouring corrosion of reinforcement within the concrete are mainly carbonation and the presence of chlorides, either independently or together as we have already seen.

• Carbonation: the phenomenon of corrosion of reinforcement by carbonation in concrete is due to a natural process that occurs when carbon dioxide in the atmosphere and present in the air reacts with the water or moisture retained inside the concrete, reducing its alkaline pH.

The reduction of the pH of the concrete due to the effect of carbonation implies a loss of this protective capacity and the consequent activation of the corrosion process of the reinforcement, always under the right conditions.

• On the other hand, chloride attack occurs when chlorides penetrate the concrete, dissolved in water, and gain access to the reinforcement. This corrosion process occurs even in concrete with an alkaline pH, as the chlorides act as catalysts for the oxidation reaction of the steel, reducing the diameter and the resistant section of the reinforcement, with the consequent risk of collapse of the structure.

The degradation of reinforcement due to corrosion represents a high percentage of the pathologies detected. In generic terms, the phenomenon of corrosion can be defined as a process of electrochemical destruction or deterioration of a metal due to the action and reaction of the metal with the surrounding medium (simultaneous oxidation and reduction reactions).

Consequences of corrosion in concrete

When corrosion starts, the concrete covering the reinforcement first cracks and then peels off because the corroded steel generates a larger volume than the original steel.

This increase in volume transmits stresses to the concrete, causing pathological processes and deterioration.

As these cracks in turn expose the reinforcement to the exterior, they facilitate new steel oxidation processes, the deterioration of the structure is accelerated due to the constant loss of protection of the reinforcement to which it is subjected, gradually compromising the reinforcement not affected by the initial source of corrosion.

How to choose corrosion inhibitors: New generation of mortars with migrating corrosion inhibitors

At Molins, we work to develop effective solutions for the comprehensive treatment of reinforced concrete structures, which ensure the quality and durability of conservation and maintenance work on buildings and infrastructures.

That is why on 5 October we launched a new generation of mortars with MCI® migratory corrosion inhibitors, a range of products with the most advanced technology to boost the maximum durability of reinforced concrete.

With this generation, a pioneer in the national market, Molins consolidates its commitment to innovation and sustainability, axes that will allow the useful life of concrete structures to be extended to the maximum.

Greater durability means fewer repairs, greater structural integrity and a longer service life, which also translates into greater sustainability and a reduced carbon footprint.

Reinforced concrete structures deteriorate due to attacks on the concrete itself or corrosion of its reinforcement. The presence of pollutants, such as atmospheric carbon dioxide and chlorides, cause this deterioration, as they promote the oxidation of the steel.

In particular, these two phenomena – carbonation of the concrete and chloride attack – make continuous maintenance work essential throughout the life of the structure and, therefore, an additional cost.

MCI mortars for maximum durability of concrete

To deal with all this, Molins uses migratory corrosion inhibitors, which offer additional protection to concrete against harmful external agents that can compromise the stability of its structure. These are the most advanced technical mortars on the market: PROPAM® REPAR TECHNO 40 MCI® and PROPAM® REPAR TECHNO FLUID MCI®.

With the use of migratory corrosion inhibitors, once the migratory inhibitor reaches the armour, by ionic attraction it forms a monomolecular layer that reacts with the metal surface, actively protecting it against corrosion.

These mortars – which meet the requirements of EN 1504-3 class R4, EN 1504-2 and EN 1504-7 – have been part of several accelerated corrosion tests. It has been proven that PROPAM® REPAR TECHNO 40 MCI and PROPAM® REPAR TECHNO FLUID MCI mortars delay the initiation of corrosion by carbonation by at least six times compared to traditional mortars and improve the critical concentration of chlorides to values much higher than those normally found in traditional mortars or concrete.

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