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Fighting the Danger of Overprotection on Concrete Repairs

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Reading Time: 3 minutes
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Is it possible to give concrete too much protection against reinforcement corrosion? Research indicates that this is so, although no consensus exists on the exact mechanisms and how to avoid it. However, following logical reasoning, Cortec® recommends applying Migrating Corrosion Inhibitors to mitigate the problem.

What is overprotection?

Overprotection occurs when metal reinforcement in one part of the concrete is more protected than in another. This can happen when a new concrete patch is laid, replacing contaminated or carbonated concrete with uncontaminated concrete that has a high pH and therefore a naturally protective alkaline environment. The resulting difference in corrosion potential between the patch and the adjacent concrete eventually leads to corrosion in surrounding areas, thus transferring the original problem elsewhere. This is known as the ring anode/halo effect.

Examples of overprotection

Overprotection can also happen in a variety of other ways. One is through the common practice of cathodic protection (CP). The challenge of calculating the appropriate number of anodes for an area and removing concrete to install them is compounded by the fact that it is not possible to gain access to and treat all parts of the rebar equally.

 

This leaves some portions of the metal reinforcement with more protection than others, an imbalance that could show itself over time by corrosion in areas with less protection. A similar effect may happen with the application of an epoxy coating to one part of a rebar and not to another. Using other corrosion protection measures may cause a similar imbalance when over-applied.

 

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Even Out the Corrosion Potential

The use of MCI® Surface Applied Corrosion Inhibitors (SACIs) makes it easier to balance out the corrosion potential. Rather than leaving a well-protected patch surrounded by chloride-contaminated concrete, contractors can apply MCI® SACIs to the undisturbed concrete to reduce the difference in corrosion potential between the two portions.

 

Fortunately, MCI® SACIs are easy to apply by spraying onto the concrete like a standard surface treatment. As time progresses, Migrating Corrosion Inhibitors in the MCI® SACI work their way deeper in through the concrete pores toward the metal reinforcement. Their metal affinity allows them to form a protective molecular layer on the embedded rebar when they encounter it.

 

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MCI® SACI Options

MCI®-2020 contains the highest concentration of surface applied Migrating Corrosion Inhibitors on the market and is therefore the number one recommended SACI for this purpose. Typically, a coating or water repellent should be applied on top of this to keep moisture out and MCI® in.

 

Two-in-one MCI®/ water repellents are also available for greater convenience, albeit with smaller doses of Migrating Corrosion Inhibitors (MCI®-2018 combines MCI® with a 100% silane water repellent, and MCI®-2019 combines MCI® with a 40% silane water repellent).

Take a Balanced Approach to Corrosion Protection

Concrete repairs are too labour-intensive to make the mistake of overprotection. By being sure to protect the concrete around the patch area with Migrating Corrosion Inhibitors, contractors can take one step ahead of the chain reaction of corrosion that is common in less protected areas. Contact Cortec® to learn more about the advantages of mitigating corrosion in reinforced concrete with MCI®.

 

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Getting the Most Out of Dual SACI and Concrete Sealer Systems

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Reading Time: 3 minutes
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When performing a concrete repair or routine sealer application, is there any benefit to adding a surface-applied corrosion inhibitor (SACI) underneath? Will the combination enhance protection or undermine the whole system? Cortec ® looks at these issues and suggests how contractors can get the most out of their dual SACI waterproofing system.

Why use concrete waterproofing?

Sealers, waterproofing membranes, and other moisture barrier coatings are a common part of concrete maintenance and repair. Their chief purpose is to block or seal the surface so that moisture, chlorides, and carbonation cannot seep into concrete pores. This slows down the deterioration process and helps the concrete last longer. Common places to find epoxy or urethane coatings, methyl methacrylate sealers, or other waterproofing membranes on concrete are parking ramps and industrial buildings—especially those in the chemical processing industry.

What are the benefits of SACIs?

Treating concrete with SACIs before applying a coating, sealer, or traffic membrane adds an additional level of corrosion protection. MCI ® -2020 contains the highest corrosion inhibitor concentration among SACIs on the market and is therefore the most efficient choice for this application.

 

Migrating corrosion inhibitors in MCI ® -2020 penetrate concrete pores and are attracted to metal surfaces to form a molecular layer that actively inhibits the corrosion reaction. This second line of defence is especially important if the physical barrier or coating fails, allowing water and corrosives to seep in and be trapped on the concrete surface. The presence of SACIs in the concrete can help mitigate the corrosion reaction.

 

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How to ensure proper adhesion

While both sealers and SACIs can play a role in concrete protection, there is sometimes a concern for adhesion between layers when applying multiple products to a concrete substrate. If adhesion fails, the effectiveness of the applied system is jeopardized, leaving concrete exposed to water and other contaminants.

 

Fortunately, the solution is as simple as proper application. Waiting 24 hours after applying MCI® -2020 gives more time for the corrosion inhibitors to work their way into the concrete pores, away from the surface. Subsequent rinsing with water removes any residual and leaves behind a clean surface for coating or waterproofing application.

 

Testing according to ASTM D7234 has confirmed the compatibility of several traffic coatings and membranes with MCI ® -2020, and in some cases, a water rinse was not needed to maintain adhesion.

Get the most out of your surface-applied system

The application of water repellents, coatings, and waterproofing membranes will remain a common practice as long as parking garages and other concrete structures remain vulnerable to corrosion. Using MCI ® SACIs is a great way to enhance routine maintenance or repairs by fortifying the concrete with Migrating Corrosion Inhibitors. Simple steps such as rinsing the surface prior to waterproofing application help contractors and building owners get the most out of their dual water-repelling, corrosion-inhibiting system to extend concrete service life.