Category: Press Release

October 30, 2023

Winter weather and freezing temperatures will soon mean that construction projects are delayed in many parts of the Northern Hemisphere. For concrete PT (post-tensioning) structures such as bridges or parking ramps, this delays the grouting that should be done as quickly as possible after the placement of bonded PT strands. Cortec^® MCI^®-309 is an outstanding solution to counteract corrosion during this critical period of grouting delays.

Corrosion and Grouting Delays

Grouting delays may range from a few days to several months depending on site conditions and circumstances, the severity of the temperatures, and weather. During delays, metal tendons that have been placed inside the PT duct but not enveloped in grout are exposed to oxygen, the potential ingress of moisture, and (depending on proximity to the sea) even chlorides. In the US, state and federal requirements typically call for corrosion inhibitor application if the waiting period is seven to 20 days or longer (each DOT has different requirements). While oil-based corrosion inhibitors offer some protection, they can have a negative impact on bond strength once tendons are grouted.

The Migrating Corrosion Inhibitor™ Advantage

The best option on the market for corrosion protection of PT tendons that have been installed but not grouted is MCI^®-309. This Migrating Corrosion Inhibitor™ powder is easily fogged through ducts using a low-pressure air hose and sandblast cup—no special equipment required. MCI^®-309 releases corrosion inhibiting vapors that diffuse throughout the entire void space. An attraction to metal allows the corrosion inhibitors to adsorb onto tendons, forming a protective molecular layer. When better weather comes, grout can be applied as normal without flushing the corrosion inhibitor out of the duct.\

MCI^®-309 ‘Claims to Fame’

MCI^®-309 has been used in a wide variety of construction projects, ranging from the Samuel De Champlain Bridge in Quebec to the extradosed St. Croix River Crossing bridge near Cortec^® World Headquarters in Minnesota. It has been used in Washington, DC, for the Frederick Douglass Memorial Bridge Project and in the Middle East and Hawaii for non-winter-related grouting delays. Due to its migrating ability, MCI^®-309 can also be and has been used for corrosion protection in other void space applications, such as flex-float structures at the Round Butte Reservoir where painting hard-to-reach internals of the ballast areas was impractical and MCI^®-309 provided a much better alternative.

Get Ready for Winter Construction Delays

By planning now for possible construction delays this winter, contractors can be prepared with a stock of MCI^®-309 to protect PT strands that must be placed but cannot be immediately grouted. To learn more about MCI^®-309 specifics and how they apply to your PT project, contact Cortec^® today.

Keywords: winter construction, grouting delays, corrosion inhibitors, bridge construction, post-tensioning structures, Cortec, MCI, prevent corrosion in PT ducts, bridge contractors, corrosion inhibitor bond strength

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Commodities such as molybdate or sodium nitrate/borate dominate the market for corrosion protection inside closed loop systems. However, that does not mean the status quo should remain the same. For example, the VpCI® chemistry of the S-69 Series from Cortec® offers a variety of advantages in terms of effectiveness, user-friendliness, and cost. These features make the S-69 Series highly attractive as a corrosion inhibiting building block for closed loop water treatments.

Challenges of Sodium Nitrate/Borate and Molybdate

Sodium nitrate/borate and molybdate are anodic corrosion inhibitors that work by passivating the metal surface against which they flow. Unfortunately, when the water slows down or stagnates, the energy needed to continue passivation diminishes and the passive layer eventually breaks down, making corrosion protection during layup a frustrating endeavor. This method also leaves unfilled areas of the closed loop (such as the headspace above the water) unprotected, even though water condensation may put these areas at risk for corrosion. Furthermore, sodium nitrate/borate will lose effectiveness in the presence of oxygen, whereas molybdate will not be effective in the absence of O2. Sodium nitrate/borate and molybdate also tend to have more restrictions on disposal.

Advantages of the S-69 Series as a Corrosion Inhibitor Building Block

Rather than being a commodity that is tossed into the water with the faint hope that it will protect the system during layup, the S-69 Series is a specialty chemistry with a wide range of benefits. Much of the advantage lies in its capacity to adsorb onto metal surfaces, forming a protective molecular layer that inhibits both anodic and cathodic reactions. This not only occurs on metals with which the treated water is in direct contact (contact-phase protection); it also occurs in air pockets above the water level (vapor-phase protection) when the molecules vaporize and migrate through the air. This action continues to work whether the water is moving or stagnant, allowing formulators to use the S-69 Series as a building block in water treatment formulations for either operational or layup conditions. It works in both the presence or absence of O2 and typically has fewer disposal restrictions.

Cost and Availability Comparisons

The current economy has seen all prices on the rise, making affordability more difficult in practically every area. Interestingly, though, the prices for sodium nitrite/borate and molybdate have seen a much steeper increase than for the S-69 Series in the last few years. Access to these raw material commodities has also become more difficult, while S-69 Series availability remains strong. The S-69 Series offers protection at a much lower dosage than nitrite/borate and molybdate, so cost comparisons must look at estimated cost of use. Since the S-69 Series is estimated to be 1.2 times the cost of nitrite and molybdate is estimated to be 1.3 times the cost of nitrite,* the S-69 Series is highly attractive considering its advantages over standard commodities at a comparable price.

Now Is the Time to Challenge the Status Quo

With traditional water treatment commodity prices rising, availability decreasing, and disposal restrictions tightening, now is the time to consider enhancing closed loop water treatments with corrosion inhibitors that challenge the status quo in practicality and effectiveness. Contact Cortec® today to discuss upgrading your current water treatment formulations.

Keywords: closed loops, corrosion inhibitors, closed loop layup, sodium nitrite corrosion inhibitors, sodium borate corrosion inhibitors, molybdate corrosion inhibitors, Vapor phase Corrosion Inhibitors, Cortec, water treatment, water treatment building blocks

*Based on recent comparison of MSRP for equivalent water treatments.

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