The impressive lifespan and durability of galvanized steel are responsible for its popularity. After shedding its brief experimental label in the early 1980s, the United States saw a resurgence of its use. Over time, galvanized steel has become a required standard for projects across the country.
Here’s a quick overview of the lifespan of galvanized steel, how it behaves within concrete, and why it is a solid choice for your construction project.
So, how long does it last? Galvanized steel has a decades-long lifespan. In various projects where galvanized rebar was re-exposed during repairs or upgrades, its condition surprised everyone. Often the protective coating had maintained like-new thickness or even became harder (more on that in the next section).
Proponents of galvanized steel believe its true longevity has yet to be seen. This is because the projects which use it often need to be repaired or replaced for reasons other than the state of the galvanized materials. One of the most powerful statements about the material’s lifespan and durability came after the construction of the Governor Mario M. Cuomo Bridge across the Hudson River. The report on the project states the bridge should not need “major maintenance for at least 100 years.”
The main conclusion is that galvanized steel can last for decades without showing signs of compromise to its integrity.
Galvanized steel has become the preferred material for construction and transportation infrastructure projects. This is for two reasons: one is because of how easy it is to work with and transport. The other is because of how well it behaves in concrete.
When galvanized steel is introduced to fresh or new concrete, it forms a strong bond with it. This is different from its inferior alternative, epoxy-coated materials. Epoxy-coated materials sit within the concrete without adhering to it. Alternately, the bond the zinc coating forms with the concrete creates a partnership, rather than a resistance. This allows it to adapt better to the environment the concrete is in as well.
This adherence of the zinc coating to the surrounding concrete also strengthens the concrete. The zinc will enter the pores of the concrete which it touches and change its chemical make-up for the better.
The self-healing property of the zinc coating makes it a good material to use within a concrete project. The properties of zinc allow it to build up extra rust resistance in compromised areas if they come into contact with water.
This is a major benefit for steel encased in concrete. It means that a compromised area will remain contained, rather than travel down the section of steel and cause greater damage. A small issue can remain a small issue without ruining the integrity of the total structure.
Whether a historic monument or essential portion of road, galvanized steel proves time and time again it is the best choice for structures that need to stand the test of time. It is a resilient problem-solver that will extend the life of any project that uses it.
If you need galvanized steel materials for your next construction project, we have a wide variety of the most common materials in stock. We have a simple ordering system with quick turnaround times.
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If rust is a concern either use a metal that doesn’t corrode, or coat one that does. Metals that don’t rust – looking at you, stainless steel – carry a cost penalty, and often a performance one too. Coating lets you use a metal that’s less expensive and often easier to work. Paint is the first coating that comes to mind when looking to protect mild steel, but it doesn’t last very long. So that leads us to galvanizing, and the million-dollar question: Does galvanized steel rust?
The short answer is, yes, and also no. Galvanization is a zinc coating applied over the top of steel. It prevents rust and corrosion far longer than paint will, often for 50 years or more, but eventually that brown rot will set in. Want to know why? Keep reading to find out.
Let’s start with some definitions. Corrosion is how metal breaks down as oxygen attacks the surface. Rust is the special type of corrosion experienced by iron. Oxygen creates iron oxide, which flakes away from the body of the metal, exposing fresh metal to oxygen.
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Metals that don’t rust, like aluminum and stainless, form an oxide layer on the surface. This resists further corrosion. Another metal that oxidizes without rusting is zinc, and zinc is interesting because it bonds well to steel.
So, if you want to give steel a coating that lasts longer than paint, cover it with a layer of zinc. And that’s galvanization.
Zinc prevents oxygen and water from reaching the steel beneath. It does this by first forming a zinc oxide layer on the surface. When there’s moisture present that turns into zinc carbonate. This gives the metal a dull gray patina that’s insoluble in water and stops any further chemical changes.
So why doesn’t galvanized steel last forever? Keep reading.
Having said that zinc carbonate is insoluble, that’s not completely true. It will break down slowly under certain conditions. These include:
Relative humidity above 60%. (Tropical environments, hothouses used for raising tropical plants)
Sodium chloride (salt) in water or air. (Marine or coastal environments.)
Situations where the coating is frequently wet or soaked. (A car wash would be an example.)
Sulfur dioxide pollution in urban atmospheres.
Exposure to hydrogen sulfide from volcanoes, hot springs, natural gas, and sewer gas.
Strong alkalis such as plaster and cement, (especially Portland cement,) as these contain chlorides and sulfates.
Acid rainwater runoff from roofs with wood shingles
Moss and lichen, which will hold moisture and create a high humidity micro-climate.
When you’re thinking about using galvanized steel it is important to consider what the local conditions will be like. More specifically, think about:
Air. High or low humidity, exposure to salt, acids or industrial pollutants. (Desert air: not a problem. Tropical city: potential problem.)
Soil. Burying galvanized steel in soil, (as the base of a fence post for example,) will expose it to more moisture. However, the size of the impact depends very much on the type of soil and overall conditions, (muddy and wet or sandy and dry.)
Temperature. High temperature alone won’t break down zinc, providing it’s below the melting point of 787°F (420°C). It is however an accelerating factor when combined with corrosive factors like humidity and industrial pollution. Low temperatures have no effect on a galvanized coating.
So does galvanized steel rust? The answer is yes, but very slowly. In fact, slow enough that it’s usually not a problem. This is why galvanized steel has been in use for the last 2,000 years, and why it’s probably going to be okay in your application.
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