Concrete repair specialist, Hindle Mason Projects, provides a total concrete corrosion management solution.
These safeguard against carbonation and chloride-induced corrosion. Carbonation-induced corrosion occurs when carbon comes into contact with hydrated lime that is present in non-carbonated concrete. The highly alkaline lime transforms into low alkaline calcium carbonate. Typically occurring in structures with low concrete cover, it is rather slow and typically affects large areas of reinforcement. Concrete spalling usually occurs before loss of reinforcement cross section which threatens structural integrity. Meanwhile, chloride-induced corrosion is significantly faster and can even occur in high alkaline concrete. It is very localised and produces no external signs of degradation until the concrete cover delaminates. Thus, sudden collapses of structures due to local loss of reinforcement cross section without prior signs is a real risk.
Quality concrete corrosion management solution
Our quality corrosion management solution comprises tried-and-tested methods.
These include:
- Concrete repair mortars
- Corrosion inhibitors
- Hydrophobic impregnations
- Protection coatings
- Concrete re-alkalisation
- Concrete chloride extraction
- Impressed current cathodic protection
- Galvanic protection, for example, embedded galvanic anodes
Mortars for concrete corrosion management
Repair mortars are widely used by our teams for effective concrete corrosion management.
They include hand-placed concrete repair mortars. Damaged concrete is first removed with hydro demolition systems or jack hammers. After the exposed steel reinforcement is cleaned, the damaged area is restored with a repair mortar. This results in a passive repair area. However, sometimes, corrosion-induced corrosion occurs in the parent concrete around the patch. This usually happens shortly after the repair has been completed. This phenomenon is known as the incipient or ring-node formation or the halo effect. It is caused by natural cathodic protection losses of corroding steel in the parent concrete adjacent to the patch repair. After repairs are undertaken with proprietary cement-based repair mortars that are highly alkaline, the repaired area becomes a cathodic zone. In turn, the cathodic zones surrounding the patch become anodic areas. This is because they are less alkaline than the freshly applied repair mortar. They are also more likely to contain some chlorides. Therefore, the reinforcing steel is no longer in a passive environment. Refer to Diagnosing the cause of incipient anodes in repaired reinforced concrete structures – ScienceDirect. For this reason, a concrete repair mortar, alone, will seldom provide the desired long-term results. They have to be used together with suitable corrosion control systems.
Inhibitors – effective concrete corrosion management
By delaying the rate of chemical reaction, inhibitors are also effective concrete corrosion management solutions.
These admixtures are mixed with repair mortars or concrete or used on their own as surface applied systems.
Hindle Mason Projects is experienced working with all types of corrosion inhibitors. These include those nitrite-based types that suppress the anodic reaction. Anodic inhibitors effectively suppress anodic reactions. However, if used in insufficient concentrations, they can accelerate corrosion and are, thus, considered risky.
Cathodic inhibitors either slow the cathodic reaction or selectively precipitate on cathodic areas. This action increases surface impedance and limits the diffusion of reducible species to these areas. Typical systems are zinc-compound or sodium-sulphate based. Zinc compound-based products form a protective film on rebar and sodium sulphate-based systems scavenge oxygen. They are safer than anodic inhibitors but less effective.
Ambiodic or “mixed” inhibitors act simultaneously on both anodic and cathodic zones. By combining the benefits of anodic and cathodic types even at low dosages, this inhibitor has a synergy effect. It is also safe to use in low dosages. A good example of such a systems is the surface applied and admixed Sika FerroGard. Refer to [Sika® FerroGard®-903 Plus | Corrosion Inhibitor]. The product is based on mixed amino alcohol. Amino alcohol comprises small particles [Amino Alcohol – an overview | ScienceDirect Topics]. These do not react with cement and are available to migrate freely within its matrix.
Innovative concrete-corrosion management system
This innovative concrete-corrosion management system penetrates concrete as liquid and vapour. It displaces hydroxides on the steel surface in carbonated concrete and chlorides on steel surfaces. Thereafter, it forms a 100 to 1 000-angstrom-thick absorbed chemical layer on steel reinforcement surfaces. This, in turn, reduces iron dissolution at the anode and oxygen access at the cathode.
However, surface-applied inhibitors still have their limitations. The first is their inability to migrate in a quantity sufficient to be effective. This is a challenge when concrete is of a high quality or its cover relatively thick. Inhibitor modules of the surface-applied inhibitors will not migrate deep enough in sufficient quantities to reach the reinforcement bars. This is a typical challenge that is encountered on civil engineering structures.
These inhibitors are also not effective when a certain quantity of chlorides is already present at the reinforcing bar.
Our teams have found that this technology is suited to protecting against carbonation-induced corrosion. This is because carbonation-induced corrosion is often associated with low concrete cover. Therefore, it is easier for the inhibitor to reach the reinforcement steel. Furthermore, carbonation mainly occurs in concrete of a lower quality. The inhibitor can penetrate concrete of a lower density more easily. In addition, the corrosion speed associated with carbonation is rather slow.
Impregnations for concrete corrosion management
Hindle Mason Projects continues to successfully deploy hydrophobic impregnations for concrete corrosion management.
Extensive research has demonstrated the efficacy of hydrophobic impregnations in terms of reducing water penetration. Refer to https://www.sciencedirect.com/science/article/abs/pii/S0950061813006521. According to Christian Christodoulou, 20-year-old hydrophobic impregnations can still offer residual protective effects.
https://icaarconcrete.org/wp-content/uploads/2024/05/16ICAAR-RodumE-1.pdf also demonstrates the efficacy of impregnations in terms of preventing chloride migration in concrete. Notably, Eva Rodum’s research shows that the technology can prevent chloride migration 10 years after application. However, its ability to completely mitigate corrosion is debatable as this is dependent on the level of corrosion.
Coatings in concrete-corrosion management
Protective coatings play a unique role in concrete-corrosion management by halting the progress of carbonation. They can also be formulated to bridge cracks – even at temperatures of below 20oC.
The protective coatings that we use have a track record of long performance. Our flexible coatings (Sikagard®-550 W Elastic | Concrete Protection) have a lifespan of between 10 and 15 years. Impressively, coatings such as Sikagard®-680 S Betoncolor | Surface Protection of Concrete can perform for up to 20 years. After the repair has been completed, they are also used to further stop the ingress of deleterious elements. These include chlorides and CO2. We also use them to provide a homogenous aspect by hiding the difference in colour of the patched areas.
Effective concrete-corrosion management methods
There are other effective concrete-corrosion management methods. These include concrete re-alkalisation and chloride extraction, both of which entail introducing a current to concrete for a limited period.
Re-alkalisation entails generating hydroxides which increase the alkalinity of the concrete pore solution. Chloride extraction involves generating a current that draws the chlorides towards an anode placed provisionally at the concrete surface.
These systems are effective, but they can damage the concrete surface if undertaken incorrectly. In addition, they cannot be used on pre-stressed concrete due to the very high current generated over a long period. This can lead to hydrogen embrittlement.
Furthermore, they are costly and labour-intensive techniques.
Impressed current cathodic protection entails placing an anode at the concrete surface and connecting it to the reinforcement network. A current is then drawn in the area to maintain the rebar in cathodic zones. This prevents corrosion from occurring in these areas even if high chloride is present. It is the only method that completely prevents corrosion. However, sophisticated skills are needed to design and install the system. Furthermore, current alimentation and continuous monitoring over the entire service life are essential. If the system does not operate correctly, it can damage the structure due to the induced current.
Similar concrete corrosion management technique
A similar concrete corrosion management technique entails connecting a galvanic anode to the reinforcing bar, which serves as a cathode. The galvanic anode is less noble than steel. Thus, reinforcement is protected from corrosion as long as sufficient galvanic current flows between the anode and the reinforcement. The efficiency of this technique depends on the lasting activity of the zinc anode. Passivation of the zinc anode occurs through the deposition of anodic products on zinc surfaces. It also happens when contact is made with calcium hydroxide in the concrete pore solution.
Research has shown that the technique can continue adding value for at least 20 years. Hindle Mason Projects is an expert in all types of galvanic anode systems. These include anodes that have been embedded inside and outside patch repair areas. This is in addition to embedded hybrid and surface applied anodes.
Galvanic systems offer an array of benefits over impressed current cathodic protection. For example, they do away with the need for anode wiring which eliminates the risk of copper wire theft. It can also be installed at a relatively low cost. This while eliminating the risk of hydrogen embrittlement in prestressed or post-tensioned tendons. Current density is also self-adjusting and there is no need for servicing or monitoring.
Learn more about Hindle Mason Projects. www.hindlemason.co.za