MCI QUESTIONS & ANSWERS

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1 MCI QUESTIONS & ANSWERS Q. Are Migrating Corrosion Inhibitors (MCI) similar to Vapor phase Corrosion Inhibitors (VpCI)? A. MCI technologies are chemically similar to VpCI. The protection mechanism is identical. Q. What is the chemistry of MCI or VpCI protection? A. MCI and VpCIs are called mixed inhibitors because they work on both anodic and cathodic regions of a corrosion cell. A paper (#308, NACE CORROSION 83, "Use of Vapor Phase Inhibitors for Corrosion Protection of Metal Products") explains the detailed chemistry of this type of inhibitor, and is available on request from Cortec Corporation. MCI (and VpCI) are organic, amine based products which can volatilize under normal conditions, and move through the atmosphere in a gaseous state. They are attracted to metals and form a protective molecular layer on metallic structures. The latest generation of products consists of a blend of contact and vapor phase corrosion inhibitors formulated for the best performance in their specific application. For example, because MCI admixtures are blended into the concrete mix, they do not have to migrate as far. Therefore, they would contain less volatile corrosion inhibitors, while MCI that is applied to the concrete surface would contain more volatile corrosion inhibitors, ensuring its migration into the concrete and towards metallic reinforcement. This is also why our admixtures last much longer (25+ years) than our surface applied materials (7-10 years). Q. What does MCI protect? A. Cortec s MCI products help to mitigate corrosion of steel and other ferrous metals in concrete exposed to many different environments including carbonation, chloride exposure, polluted air, acid rain and other contaminants. By lowering the corrosion rate of the embedded metal, MCI increases the service life of the structure. Q. How does MCI migrate or penetrate into a structure? A. MCI migrates in three different ways simultaneously. Firstly, MCI acts through capillary action. The porous substrate (concrete, masonry, limestone, etc) acts like a sponge, drawing MCI inside. Secondly, MCI diffuses through the substrate as a vapor due to its volatility. It will move from areas of high concentration to areas of low concentration (Fick s 2nd Law). Finally, when MCI comes into contact with embedded metals, it adsorbs onto the metal surface, forming a protective molecular layer. The nitrogen (amine) in the MCI molecule is responsible for its strong bond with the metal surface, while the hydrocarbon 1

2 (carboxylate) tail of the MCI molecule creates a hydrophobic (water hating) layer that helps repel moisture away from the steel. Q. Are there other inhibitors on the market? A. Yes, there are several other types of inhibitors on the market. Corrosion inhibitors can be broken down into three categories: anodic, cathodic, and mixed. Calcium Nitrite (trade names include Grace's DCI 1 & Rheocrete 2 CNI) is an example of an anodic inhibitor. Anodic inhibitors affect the anodic portion of the corrosion cell, and can have a dangerous concentration level where not all anodic sites are treated, leading to pitting corrosion. Calcium Nitrite (CNI) is typically used for chloride induced corrosion, and its dosage rate is based upon expected future exposure to chlorides. Because CNI does not have a vapor phase at ambient temperatures (meaning it only moves as a liquid through concrete), it is typically used as an admixture for new construction. Cathodic inhibitors, on the other hand, affect the cathodic portions of a corrosion reaction. Usually they bond the electrons necessary for the cathodic reaction. An electric current is usually needed to facilitate cathodic protection. Such inhibitors do not have a dangerous concentration level where they would promote localized (pitting) corrosion. Cortec s Migrating Corrosion Inhibitors are an example of a mixed inhibitor, meaning they can affect both the anodic and cathodic portions of the corrosion cell. The amine in the MCI molecule adsorbs onto metal, and at the same time, the hydrophobic carboxylate group repels moisture and creates a barrier, increasing the effectiveness of the corrosion inhibitor. Competitor comparisons can be found on the MCI CD-ROM, or obtained from Cortec. Q. What is the difference between calcium nitrite and MCI? A. MCI is an organic mixed (anodic/cathodic) inhibitor, whereas calcium nitrite (CNI) is an anodic inhibitor. Calcium nitrite only affects the anodic portions of the corrosion cell. CNI requires high dosage rates to ensure that all anodic areas are treated or pitting corrosion could occur, and the dosage rate is dependent upon future expected exposure to chlorides. When chloride concentrations reach a critical level, they may accelerate the corrosion process. The dosage rate of MCI is independent of expected exposure to chloride levels. MCI admixtures are effective in mitigating corrosion in both new construction and repair applications, at much lower dosage rates than calcium nitrite (1-1.5 pints/cubic yard [0.6-1 liters/cubic meter] vs. 2-6 gallons/cubic yard [5-30 liters/cubic meter]). MCIs do not accelerate setting times, have shown up to 30% less shrinkage than calcium nitrite in the same mix designs, do not affect rapid 1 DCI is a registered trademark of W.R. Grace & Co. 2 Rheocete is a registered trademark of BASF Construction Chemicals. 2

3 chloride permeability testing, and can be used in conjunction with other types of corrosion inhibitors including cathodic protection. Q. What is the maximum chloride level CNI should be used at? A. The maximum design criteria is 7.8 Kg/m 3 (13 lbs/yd 3 ). This translates into the 2-6 gallons/ yd 3 (5-30 liters/ m 3 ) dosage rate listed above. The amount of calcium nitrite depends on the expected amount of chlorides in the concrete. Adding more than 6 gallons/cubic yard (30 liters/cubic meter) can not be done without significantly changing the concrete quality/characteristics. Q. Does MCI have a "critical" chloride problem? A. No. MCI will protect across a wide range of chloride levels. This is extremely important, as prediction of chloride levels is almost impossible. Field measurements have shown vastly different levels only a few feet or meters apart. Q. Is the MCI layer damaged by the current flow of Cathodic Protection? Over what time? A. MCI is not damaged by cathodic current flow over time. Q. Does the reduced current caused by the MCI layer reduce the effectiveness of Cathodic Protection or improve it by enabling it to function at a lower current for a given potential? A. Such a low concentration of MCIs are used and adsorb directly onto the metal, therefore, they are not participating in the current flow and, thus, not adversely affecting Cathodic Protection. For example, you can use Cathodic Protection on the columns of a bridge structure, and then use surface applied MCI and/or Cathodic Protection to protect the arch, beams, and deck. Q. What is the application procedure for use of MCI with Cathodic Protection? A. The procedure should follow these steps: 1. Clean the concrete surface, removing any dirt, laitance, as well as any coatings or sealers. 2. Immediately apply surface applied MCI 3. Apply Cathodic Protection In this scenario, MCI provides protection to the rebar, but also provides protection to the metal components in the Cathodic Protection. Q. Is MCI a sealer or surface conditioner? A. While the MCI product line includes sealers (water repellants) containing MCI, the migrating corrosion inhibitors themselves do not act as water repellants or surface conditioners. MCI molecules penetrate deep into concrete, adsorbing onto metal surfaces to mitigate corrosion. As MCI molecules migrate into the concrete, some of them may react with calcium, forming an insoluble salt. This reaction can effectively block some of the pores, reducing future ingress of chlorides and other contaminants, but does not seal the structure or act as a water repellant. 3

4 Q. What is the proof MCI penetrates deeply into concrete? Conventional sealers penetrate only a few mm (1/8-1/4"). A. Radioactive tagging of MCI has shown penetration of up to 4 cm (1.6") in only 24 days. X-ray Photoelectron Spectroscopy (XPS) shows the actual molecular film formed on embedded metals as well as displacement of chlorides with the use of MCI. Quaternary Ammonium Compounds (QAC) testing shows that surface applied MCI can migrate up to 3 inches (7.5 cm). Copies of test results are available. Q. What other tests show the effectiveness of MCI? A. Many, including internal tests performed by Cortec and independent testing: 1986 Wiss, Janey, Elstner ASTM G109 Salt Ponding 1993 SHRP S 666, Corrosion Inhibitors 1993 SHRP S 658, Bridges, Field Validation MN-DOT, Randolph Bridge over I35E, St. Paul 2002 MCI-2006 NS Migration from Repair into Existing Structure 2003 Cracked Beam Testing vs. Competitors 2004 Efficacy of MCI in Reinforced Concrete Dr. Bavarian 2004 MCI-2006 in Carbonation Induced Corrosion Q. How is MCI used? A. Cortec has a wide range of products for virtually every situation including: admixtures for new construction and addition to repair mortars, grouts, and shotcrete; surface applied products for existing structures; repair mortars, sealers and coatings containing MCI as well as other specialty products. Contact Cortec for further information on products for your specific applications. Q. Is MCI toxic? A. MCI-2020 has an oral LD-50 (Rat) of about 2450 mg/kg. In comparison, the oral LD-50 of table salt is 3000 mg/kg. The toxicity of MCI is much lower than its main competitor, calcium nitrite, which has an LD-50 (Rat) of about 283 mg/kg. Many MCI products have approval from Underwriter s Laboratories to meet NSF Standard 61 for use on structures containing potable water, which is not ture of most competitor products. MCI is also not carcinogenic (cancer causing). Q. Who has used MCI? A. MCI's have been used by many State Departments of Transportation and private companies around the world. Several case histories are published on Cortec Corporation s website and on the MCI CD-ROM, such as their use in the Pentagon, Burj Dubai, Wells Fargo Parking Garage, NASA Launch Platform, and many more. Q. What "approvals" does MCI have? 4

5 A. State DOTs who have approved Cortec admixtures include: Colorado, Florida, Iowa, Kentucky, North Carolina, Nebraska, Ohio, Pennsylvania (pending, but using MCI 2006 NS with shotcrete on specific bridge projects now), South Carolina, Utah, and Wyoming. Many other agencies have recognized the benefits of MCI's and have granted approval on a case by case basis until standard specifications are developed. That would include Alabama and Minnesota (our oldest case history for admixtures is the Randolph Avenue Bridge over 35 E in St. Paul, MN). Many independent testing laboratories have also found MCI to be effective. Q. How is MCI supplied? A. MCI liquids are sold in 5 gallon pails, 55 gallon drums, 275 gallon liquid totes and bulk. MCI powders come in 5, 50, and 100 pound drums. Specialty products list sizes supplied on their product data sheets. Q. How is MCI distributed? A. Cortec has representatives and distributors around the world. Cortec can give you the name of someone close almost anywhere in the world. 5