It’s a question that pops up from time to time: Why is only steel used in concrete?

Well, it’s not. Depending on use and application, other materials can be used as well. But when it comes to reinforcing and/or prestressing concrete, steel is by far the most popular option.

We’ve written before about the relative strengths inherent in precast concrete forms. In particular, we’ve discussed compressive strength and tensile strength. Now we’ll discuss why steel is so often used in concrete and what it has to do with those two measures of precast concrete strength.

But first, a brief review of compressive strength and tensile strength.

Compressive strength refers to concrete’s ability to withstand forces from above and below. Manufacturers of precast concrete often test its compressive strength by placing it between hydraulic cylinders and squeezing (compressing) it.

Concrete is exceptionally strong when it comes to compressive strength. It can resist many thousands of pounds per square inch (psi).

When it comes to tensile strength, however, concrete is less strong. Tensile strength refers to concrete’s ability to withstand being pulled apart. Since the tensile strength of concrete is relatively low, it is reinforced with steel rebar. (This makes reinforced steel a composite material.)

The name rebar is shorthand for reinforcing bar. Merriam-Webster calls it “a steel rod with ridges for use in reinforced concrete.”

But why steel?

Why Steel Is Used In Concrete

You can be sure that engineers have tried all sorts of metals and materials to determine which to use in order to reinforce or prestress concrete. There are a few reasons why they so often settle on steel. (Some of the reasons have to do with the coefficient of thermal expansion, which is a little beyond the scope of this particular blog piece.)

First, steel has high tensile strength. Thus, it already features something that the concrete in which it is embedded lacks. When it comes to building materials, it’s important to improve the tensile and shear strength of concrete. While concrete structures can handle compressive stresses, the tensile strength of steel reinforce otherwise plain concrete against tensile stress and shear forces.

Second, steel is extremely ductile, meaning it can be stretched without becoming weaker. This not only adds to the compressive strength of concrete but it also allows concrete to resist compression forces while adding to its tensile strength.

Third, steel is recyclable. (See our pieces on the energy efficiency of precast concrete for more info on this important topic.)

Fourth, steel bonds well with concrete and expands and contracts at similar rates when exposed to extremes of temperature. Thus there is an improvement in the fire resistance of steel bars when embedded in concrete beams and other forms.

And finally, steel is readily available and relatively inexpensive compared with other materials. And while it may be more expensive than the concrete itself, it’s not typically a burden to manufacturers.

Thus we can see that not only is steel extremely strong in and of itself but it also improves concrete’s tensile strength and ductility while remaining compatible in form and function with steel, which is easy to access and affordable for most producers.

Get in touch with Rogue Valley Precast with any questions.

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