September 1, 2022
The ubiquitous problem of rebar rust is hard to escape in the construction industry, but there is a practical answer. As part of Cortec’s High Performance Repair System (HPRS®), CorrVerter® MCI® Rust Primer simplifies surface prep by passivating corrosion on steel surfaces. It is an exciting tool to help the construction industry tackle a recurring challenge.
The Problem of Rebar Rust
Rebar and other reinforcing metals play an integral role in providing the strength necessary to make concrete a viable building material. It is also one of the major causes of concrete deterioration. Although the high initial pH of concrete creates a naturally passive environment that protects metal reinforcement in new concrete, carbonation and cracking can lead to the formation of corrosion products on embedded reinforcement. As rebar rusts, it expands, putting pressure on the concrete cover. This causes more cracking and concrete spalling, deteriorating the structure and eventually requiring repair.
Effective Concrete Repair
For a repair to be effective, exposed reinforcement is typically sandblasted to remove corrosion and promote good surface adhesion to the new repair material. The ICRI 310.1R-2008 “Guide for Surface Preparation for Repair of Deteriorated Concrete Resulting from Reinforcing Steel Corrosion,” states that exposed reinforcing steel should be free of any materials such as concrete, dirt, and corrosion products that could interfere with repair material adhesion, although tightly bonded light rust is usually not detrimental to the bond of patch materials. This opens the door to a completely different level of surface prep convenience using CorrVerter® MCI® Rust Primer.
How CorrVerter® MCI® Works
CorrVerter® MCI® is a unique formulation of chelating agents combined with a high-solids waterborne latex with extremely low water vapor permeability. This fast drying, single-component primer converts surface rust into a hydrophobic passive layer and offers excellent protection against re-rusting of metal surfaces. These characteristics are ideal for repairs, making surface prep extremely simple. When using CorrVerter® MCI, the first step is to wire brush loose rust off the metal surface. This requires much less labor than blasting and no special equipment. The next step is to remove the excess salt, dust, and contamination by rinsing with water. CorrVerter® MCI® can then be applied by spray or brush and left to cure for 12 hours before applying repair products. CorrVerter® will turn visibly black by the time it dries to touch in about two to three hours.
A Convenient Solution for the Construction Industry
CorrVerter® MCI® is an exciting labor- and time-saving tool for contractors and engineers to be aware of. In addition to increasing the convenience of concrete repairs, CorrVerter® MCI® is also useful for construction delays where some concrete was already poured, leaving rebar partially exposed to the elements until the project can resume. When the project starts again, CorrVerter® MCI® is a good way to passivate any rust that has begun in the meantime, thus forestalling additional corrosion problems that could develop as a result. Contact Cortec® to learn more about these great alternatives to sandblasting during concrete repair and rusty surface prep: https://www.cortecmci.com/contact-us/
Keywords: rusted rebar in concrete, surface prep, rebar rust, construction industry, concrete deterioration, concrete repair, Cortec, MCI, concrete spalling, alternative to sandblasting
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A medical center parking garage in Ohio had corrosion problems in its top precast slab, requiring partial to full repair. MCI®-2005 NS was added to new parts of the slab to mitigate corrosion of existing steel and protect against the ring anode effect. Areas with heavy reinforcing mats were treated with MCI®-2020 surface applied corrosion inhibitor. These Cortec® products provided a superior method of restoration and corrosion prevention that was efficient, cost-effective, and easy to apply.
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Construction delays are common and often unpredictable. Winter weather, budget constraints, material delays, and leadership changes are all factors that can interrupt the original timeline of a construction project. Unfortunately, delaying a project does not mean the elements of nature stand still. One of the serious problems of construction delays is that materials left out in the open may begin to deteriorate through corrosion. Cortec® suggests the following guidelines to avoid some of these common corrosion problems.
Post Tensioning Grouting Delays
When the weather gets too cold to grout PT (post-tension) ducts, or when other interruptions halt the process for two weeks or more, it is important to protect against corrosion on PT strands. Fogging PT ducts with MCI®-309 is one of the most logical options to do so. This powder-based Migrating Corrosion Inhibitor™ vaporizes and forms a protective molecular layer on metal surfaces within the enclosed space. Better yet, MCI®-309 does not have to be flushed out before grouting, making this method of PT strand protection extremely efficient and convenient.
Construction Materials Left Out in the Open
When a construction delay hits, some building materials and tools are almost inevitably left out in the open. Piles of unprotected rebar are a common sight. Even worse, half-finished concrete structures with partially installed, partially exposed rebar present a special challenge for structural preservation. Tools and various other steel building materials may also be left sitting outside at risk for weathering.
MCI® CorShield® is an outstanding protective coating for new and partially installed reinforcing metal. It can be sprayed on and left to cure into a soft non-tacky film that eventually hardens and provides short- to medium-term protection against corrosion in unsheltered outdoor environments. For ultimate convenience, MCI® CorShield® has been tested for steel bond strength in accordance with ASTM A944-99 and does not have to be removed prior to embedding in concrete.
Other steel building materials lying out in the open can be wrapped in MCI® Construction Film for protection. The advantages of MCI® Construction Film go beyond the simple physical barrier benefits of using a tarp, because the film creates a molecular corrosion inhibiting layer on enclosed metal surfaces. MCI® Construction Film is good for protecting tools or equipment, especially those sitting in harsh coastal environments at higher risk for attack from airborne chlorides.
Damage Control at the End of a Delay
Anything can happen during a construction delay. Even a site left perfectly pristine and orderly may be disheveled and dirty when the job starts up again. Oil may have leaked or spilled onto new concrete surfaces and need to be cleaned up before applying a coating system or a waterproofing membrane to finish the project. If this is the case, MCI®-2061 or MCI®– 2062 are two excellent cleaners/degreasers that make use of biodegradable surfactants and good bacteria to tackle grease stains. The longer these products are left to sit, the more time microorganisms in the cleaning solutions will have to digest the grease compounds in the stain. Theoretically, this means the stain will get cleaner as time goes on (the product can be left to sit for one hour or overnight if needed). The components work in synergy: cleaning agents lift and disperse the waste while enzymes and microorganisms from MCI®– 2061 and MCI®-2062 digest hydrocarbons and other organic wastes, respectively.
When the issue is rebar rust from lack of protection during the delay, CorrVerter® MCI® Rust Primer should be used to passivate any visible corrosion on unused or partially exposed steel reinforcement. Workers should also examine partially built reinforced concrete structures for signs of corrosion, and, if any are found, should seek to mitigate the problem by treating the concrete with a surface applied corrosion inhibitor such as MCI®-2020 or MCI®-2018 to slow the rate of any corrosion that has begun.
Be Prepared for the Inevitable
Whatever the reason, construction delays are sure to happen. However, they should not be allowed to destroy sound construction materials or deteriorate partially finished structures. Following the preceding guidelines can go a long way toward preventing corrosion and minimizing damage and loss that could otherwise occur during a construction delay. Contact Cortec® to discuss these options further: https://www.cortecmci.com/contact-us/
Keywords: rebar rust, concrete surface, corrosion protection, construction delays, MCI, From Grey to Green, grouting delays, surface applied corrosion inhibitor, concrete oil stains, Cortec
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