Who needs rebar? Exploring its vital role in concrete reinforcement!
Rebar, aka concrete reinforcement is deformed steel bar embedded in the middle of concrete to add strength. Concrete naturally has extremely high compressive strength. In simple terms, that means that if the concrete is squeezed between 2 extremely hard surfaces at a very high pressure it has a strong resistance to cracking and breaking.
A picture of a formed concrete foundation stem wall follows below. Before the concrete is poured, you can see all of the rebar. Once the concrete is poured, all of that rebar will be embedded inside of the concrete and you will not be able to see it. The rebar in the picture below is bent and formed into a unified cage. The the long uninterrupted bars of rebar create the strength axis. The rectangular shaped bent bars that wrap-around the straight bars are called ligatures or stirrups depending on the exact configuration and shape.
Concrete has innately high compressive strength; however, concrete has a relatively low tensile strength. In simple terms that means that concrete can easily snap if forces try to bend it. To understand this concept, think of concrete like a giant dry spaghetti noodle. If you press down on a dry spaghetti noodle, on a hard surface with your fingertip, you can press hard enough to hurt your fingers without breaking the dry noodle. One the other hand though, imagine taking that same spaghetti noodle and extending it off the edge of the same countertop and then lightly pressing down on each end of the spaghetti noodle, the noodle will break with hardly any force.
This example over simplifies a complex subject, but concrete would be very similar in the same principle ways. Pressing the noodle down against a hard surface would be similar to how concrete works with compressive strength. It can withstand thousands of pounds of per square inch of compressive force. Concrete’s tensile, however, is very weak.
On the other hand, steel has extremely high tensile strength and has even more functional tensile strength when embedded in concrete.
The rebar we use in modern construction is generally a type called deformed reinforcement bar. The word deformed, in this context, means that the surface of the rebar has a texture. In most cases that texture looks like a woven net around the outside of the rebar, but it’s an integral part of the steel. That deformed surface allows rebar to have a greater surface area, creating a better bond between the steel and concrete.
Rebar is available in 1/8″ increments. Common sizes are #4 (1/2″), #5 (5/8″), #6 (3/4″). From there, rebar can get much larger for heavy construction, following the same increment and nominal system.
The picture below shows a stack of rebar, upclose where you can get a clear view of the deformation in the texture. Also, you can see there are markings to indicate the size and details of specification of the rebar.
The picture below shows a double mat of rebar in a future or work in process concrete slab. This is a thick heavy slab set on a gradebeam foundation with a vapor barrier and sacrificial void former below.
A similar slab preparation with reinforcement is shown below in a photo taken from a different angle.
In the picture below you can see a stockpile of rebar laid on the ground. That stockpile will be distributed and then installed inside of a slab like the one shown above.