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Corrosion
Inhibitors Raise the Chloride Threshold for Corrosion in Concrete.
A Good Bond between Concrete and Steel in Reinforced Concrete is Important for Maintaining Strength.
Salt Easily Penetrates Poor Quality Concrete
because It Is Porous.
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| Condominium
in Washington, DC has Corrosion Problems |
Balconies Repaired on the
St. NicholasParking garages, bridge decks and coastal structures
are not the only places where a corrosion inhibitor should be used. The St. Nicholas
Condominium, located in the Northwest section of Washington, DC, had balconies with
corroding rebars. This was due to insufficient concrete cover over the embedded rebars and
water infiltration of soluble deicing salts. Corrosion problems can occur almost anywhere
that concrete is used.
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| The
Corrosion Process |
Understanding what causes corrosion can
lead to care and treatments that will eliminate it. Corrosion is an electrochemical
process. A simple example is the flashlight that never seems to work when you need it
most. When a flashlight is turned on, the chemicals in the batteries interact causing
reaction products to build up, and eventually the batteries die.
When salt enters
concrete, corrosion proceeds in a similar way just like the loss of battery power. Without
a corrosion inhibitor, the corrosion products move into the concrete and destroy the
concrete before the process is turned off. With the use of a corrosion inhibitor, the
reaction products build up at the steel surface and the corrosion process stops much like
the flashlight battery that goes dead.
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| Corrosion
Control |
In addition to using a corrosion
inhibitor, the following should be considered to block the ability of salt making contact
with the steel and to retard the progression of carbonation. 1. Reduce the permeability of
the concrete. 2. Use at least 2 inches of concrete cover over the rebars. 3. Keep the
concrete dry. 4. Cure the concrete properly.The permeability of concrete can be reduced as much as 1,000
fold with the correct use of a supplemental cementing material such as fly ash, slag or
silica fume, and a superplasticizer to reduce the water to cement ratio.
The most common cause of staining on
concrete surfaces is poor placement of the rebars. It is important to place the rebars
well within the concrete.
Keeping the concrete dry will work,
but, it is almost impossible to accomplish this in the real world. Salt will not be able
to diffuse into the concrete.
What is possible, but rarely done,
is to properly cure the concrete.
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| Boris Miksic
Named 2000 Entrepreneur of the Year |
Boris Miksic, President/CEO of Cortec
Corporation in St. Paul, MN, was named Master in the local Entrepreneur of the Year
program in Minnesota and the Dakotas. Boris had great vision and few resources when he
founded Cortec Corporation back in 1977. Cortec is now a global supplier of corrosion
control systems. VCI (Vapor Corrosion Inhibitors) use non-hazardous chemistry to prevent
corrosion in concrete. |
| Does a
Corrosion Inhibitor Work in Cracked Concrete? |
This question is always raised when discussing
the use of a corrosion inhibitor in concrete. Peter Schiessl at the University of Munich
has done much research in this field. His answer is YES, provided that the cracks are
small. With good quality concrete he found that a corrosion inhibitor was effective even
in regions with cracks as wide as 0.30 mm. |
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