Humans are imperfect, which can be a serious problem when pouring concrete. Concrete contractors have one chance to make the slab or structure turn out right in order to avoid expensive repairs and the possibility of tearing it all up and doing it over again. Fortunately, several concrete application errors can be solved or at least mitigated using Cortec® Migrating Corrosion Inhibitor™ (MCI®) Technology. Some common application errors and their MCI® solutions are outlined here.

Forgot to Add Corrosion Inhibitor

One of the easiest application errors to fix is the failure to add a corrosion inhibiting admixture to the readymix. Although it is ideal to include an MCI® admixture in a concrete structure from the start, MCI® can also be added as a surface applied corrosion inhibitor (SACI) to concrete that has already hardened. Two great versions of MCI® SACI to start with are MCI®-2020 and MCI®-2018. MCI®-2020 contains a high concentration of Migrating Corrosion Inhibitors that penetrate through the concrete pore structure to form a protective molecular layer on the rebar surface. This protective layer delays time to corrosion and reduces the rate of corrosion once started. Wherever high humidity environments or other conditions call for water repellency, MCI®-2018 can introduce Migrating Corrosion Inhibitors along with a 100% silane water repellent. More options exist for different budgets and circumstances.

Insufficient Concrete Cover

Another common worker error is to not apply enough concrete cover and only realize later that it is too thin (e.g., 1 inch [2.54 cm] instead of 2 inches [5.08 cm] as specified). When this issue occurs, it is difficult or impossible to change without destroying the structure. However, a great alternative to protect against the higher risk of early corrosion is to apply an MCI® SACI on top. This type of scenario took place at a desalination plant, where MCI®-2020 was consequently applied to desalinated water reservoirs to help compensate for a concrete cover that was too thin.

Honeycombing

A third problem is honeycombing, a situation where the ready-mix has not been able to thoroughly work its way through the rebar network and fill the concrete forms as one consolidated substance. This leaves behind small air pockets and is known as honeycombing. Usually, MCI®-2020 or MCI®-2018 can be applied to account for the higher risk of corrosion. However, honeycombing is sometimes so bad that it leaves behind exposed rebar and voids large enough to threaten structural integrity. In these cases, CorrVerter® MCI® Rust Primer should be applied directly to the rebar to passivate and protect the metal from further rusting before completing the repair. From there, a product such as MCI®-2044 Self-Consolidating Concrete Mix is a great way to fill void spaces while adding Migrating Corrosion Inhibitors to actively protect against chlorides or other corrosives that may have entered the concrete. Another option is to add an MCI® admixture or MCI® Grenades to the ready-mix or repair mortar. For smaller repairs, Cortec® also offers two MCI® enhanced high performance repair mortars: MCI®-2039 for horizontal repairs and MCI®-2040 for vertical and overhead repairs.

Rebar Shifting

Rebar shifting also causes problems. This happens when rebar chairs fall over before or during the concrete pour, causing rebar to sink down in one area and forcing it up toward the surface in another. Sometimes, the error is so bad that the rebar actually protrudes out of the concrete surface. In less drastic cases, the only concern may be a thinner concrete cover, which raises the risk of early corrosion and can, again, be addressed by the application of MCI®-2020, MCI®-2018, or other MCI® SACIs.

If All Else Fails

It is a fact of life that mistakes happen. When it comes to construction projects, the best that can be done is to prevent problems whenever possible, follow up with proper inspection, and correct application errors that do occur. The last step can be much easier thanks to the versatile forms of MCI® that allow Migrating Corrosion Inhibitors to be applied to the structure even after it is completed. Contact Cortec® for further help correcting application errors with MCI®: https://www.cortecmci.com/contact-us/

Keywords: honeycombing, rebar shifting, insufficient concrete cover, MCI, corrosion protection, forgot to add corrosion inhibitor, common concrete application errors, Migrating Corrosion Inhibitors, From Grey to Green, Cortec

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The famous Zagreb Cathedral is the tallest and one of the most beautiful buildings in Croatia that attracts thousands of tourists worldwide. As the most impressive gothic-style sacral building southeast of the Alps, it is characterized by great architectural and historical value. Its construction dates back to 1093 with continued enrichment of the cathedral by famous architects during the following centuries.

Reconstruction of the cathedral in the late 1800s was led by Hermann Bollé, who brought the cathedral to its most recent architectural form in which it stood until the earthquake of March 22^nd, 2020, damaged the cathedral’s southern spire. Over the last 30 years, extensive restoration work has been undertaken on the cathedral, with ongoing repairs to this day. During reconstruction work on the south tower of the cathedral in 2012, damaged steel joints were found surrounding the tower 10 cm (4 in) below the surface at approximately every 3 m (1.1 yd) between the first and 25^th rows. Most of the joints were only partially exposed in order to replace the surface layer of stone on the bell tower, while the back of the joints remained embedded in stone and lime mortar. The joints were covered with a layer of rust and in drainage areas corroded all the way through the cross-section. In order to define the optimal solution for maintaining or improving the mechanical resistance and structural stability of the tower, the Faculty of Mechanical Engineering and Naval Architecture of Zagreb was called in to examine the joints. At their laboratory, they performed experiments on steel joints removed from the cathedral. They recommended doing the following:

• Remove corrosion from accessible joint connections
• Apply corrosion protection to accessible joint connections
• Strengthen the joint connections where damage had occurred

It was suggested that a minimal range of intrusion be used to keep the mechanical resistance and stability of the tower structure at their existing level while keeping costs at a minimum. Cortec’s CorrVerter® MCI® Rust Primer was recommended for cor­rosion protection. CorrVerter® is a water-based product that quick­ly converts rust into a protective layer and is capable of penetrat­ing into corroded surfaces. It contains a novel chemical chelating agent that modifies surface rust into a hydrophobic passive layer. A metal brush was used to remove loose rust from the joints. Then, two layers of CorrVerter® MCI® Rust Primer coating were ap­plied directly onto the metal. A brush was used for CorrVerter® MCI® application on smaller metal joint surfaces, while spray ap­plication was used for larger areas. The first coat was applied at a thickness of 100 microns (4 mils). A second coat was applied at a thickness of 75 microns (3 mils). During application, the coating temperature was 13 °C (55 °F). The joints were then reinforced with steel fishplates that were welded onto the joints and also pro­tected with CorrVerter® MCI® Rust Primer. The final step was to replace the stones around the joints. With the help of a skilled team and good project management, the entire project was completed successfully with minimal cost and intrusion as specified. The coating penetrated into the metal and stopped further advancement of the corrosion process.

Renovation of Medieval City Walls

The town of Ilok, Croatia, is a place of rich history and cultural heritage. The medieval long fortress and royal castle of Ilok are protected historical and cultural treasures of the highest degree, enabling visitors to step into ages long past. The tower walls have a square floor plan and rest on foundations made of broken stone. These walls are exposed to damaging atmospheric influences, and the binding material between the bricks has washed away, leading to brick deterioration. Renovation work on “tower three” includes strengthening of the foundations, restoration of collapsed parts, and injection of cracks. The project involves the use of corrosion inhibitors to prolong the life of the structure. Cortec’s corrosion inhibitor, MCI®-2005 is added into concrete being used to reinforce the foundation. This amine-carboxylate based corrosion inhibitor additive will be used to protect embedded metallic reinforcement from corrosion in order to extend the lifetime of the walls. MCI®-2005 is a water-based, organic corrosion inhibiting admixture with set-retarding effects. When incorporated into concrete, it migrates towards reinforcement to form a molecular layer that inhibits the corrosion reaction on both anodic and  cathodic components of the corrosion cell. In new construction, this protection is quantified by subsequent reduction in corrosion rates when corrosion does initiate. When used with repair mortars and grouts, MCI®-2005 not only protects rebar within the patch, but can also help protect embedded reinforcement already in place in undisturbed concrete adjacent to the repair. MCI®-2005 is a USDA Certified Biobased Product.

You can learn more about Migrating Corrosion Inhibitors (MCI^®) here: https://www.cortecmci.com/

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