Concrete Rebar: Everything You Need To Know [plus 8 Main Types]
Concrete is used all over the world as one of the most common construction materials. And it should be - it’s durable, low maintenance, fire-resistant, and easy to use.
But concrete has a potentially fatal flaw. If a particular force is placed on concrete, it will break - quickly.
Thankfully, there’s a way to combat that fatal flaw.
By using reinforcement.
In this article, we’re going to learn all about reinforcing concrete by using rebar.
Let’s get started!
Why Does Concrete Require Rebar?
Most concrete requires some type of reinforcement.
To know why, we have to understand the different stresses that can be placed on objects.
First, there is compressive stress. Compressive stress is a force that is placed upon an object that shortens or compresses the object. For example, if an elephant steps on your toe, you would experience compressive stress.
Second is shear stress. Shear stress occurs when forces are applied perpendicularly to one another. If you lock your fingers together and pull against yourself, you are experiencing shear stress.
Finally, there is tensile stress. Tensile stress is a force that is exerted upon an object that lengthens or stretches that object. When you jump into a swimming hole using a rope swing, you exert tensile stress on the rope.
Concrete handles compressive stress and shear stress well, but it performs poorly when it comes to tensile strength. In fact, the tensile strength of concrete is only about 10-15% of its compressive strength.
That’s where rebar comes in.
Rebar is used primarily to increase the tensile strength of concrete.
What Is Concrete Rebar?
Rebar (short for reinforcing bar) is a steel rod that is used to strengthen concrete.
The rods come in various lengths and thicknesses, and usually have ridges or bumps, so they bond well with the concrete.
Rebar is made from steel because steel is very strong, and because steel expands and shrinks at nearly the same rate as concrete in hot and cold weather.
What Does Rebar Do For Concrete?
Like we already mentioned, concrete handles compressive stress well but does poorly under tensile strength.
This is a problem because almost every structure experiences more than one force acting on it.
Take, for example, the classic beam.
When a beam experiences compressive stress on the top, it bends. Think about it - when a beam bends from compressive stress on the top, the beam's bottom stretches.
That means the bottom of the beam experiences tensile stress.
So, concrete on its own does not make a good structural material.
But, when we add rebar, two things happen.
1 - When rebar is placed in concrete, the two combine to make a composite material. The concrete protects against compressive stress, and the rebar protects against tensile stress. This composite material is extremely strong.
In fact, concrete that includes rebar has a breaking point that is almost double that of concrete without rebar.
2 - When rebar is placed in concrete, a warning is given before the concrete breaks. Concrete that does not include rebar is considered brittle.
As the amount of pressure increases on concrete without rebar, it suddenly breaks without warning.
On the other hand, concrete that includes rebar is considered ductile. That means that as pressure increases, small fissures and cracks can be seen forming in the concrete.
This is positive in two ways:
Concrete that contains rebar remains strong even with small cracks
A warning is given before the concrete completely fails.
When is Rebar Necessary?
Does every single concrete job need rebar?
Concrete surfaces required to uphold large trucks, heavy machinery, or steady traffic need concrete rebar reinforcement. Any structural concrete, like that used in walls, should definitely include rebar.
If you’re pouring a concrete driveway that won’t regularly hold more than the family minivan, you might not need rebar.
But when in doubt, use rebar. No matter how large or small the concrete pour is that you are doing, rebar will make your concrete stronger. At the very least, rebar dramatically decreases the number of cracks in the concrete.
Here’s a quick bonus tip: if you are doing a small residential concrete bar and steel rebar rods feel like overkill, you can use welded wire fabric. Mesh is thinner than rebar reinforcement, so it’s not as strong, but it’s cheaper.
8 Main Types of Rebar
We just talked about welded wire fabric as a type of rebar that may be ideal for certain applications.
Maybe you’re wondering: are there other types of rebar that are ideal for specific situations?
Yes, there is!
Carbon Steel Rebars: This is the most common type of rebar and is sometimes referred to as a "black bar." It's incredibly versatile, but it corrodes more easily than other types, making it less than ideal in areas that are subject to high humidity or in structures frequently exposed to water.
Welded Wire Fabric: Welded wire fabric (WWF) is made from a series of steel wires arranged at right angles and electrically welded at all steel wire crossings.
It is useful in slab-on-ground slabs where the ground has been well compacted. A heavier fabrication of welded wire fabric can be used in walls and structural floor slabs. This is commonly used in road pavement, box culverts, drainage structures, and small concrete canals.
Epoxy-Coated Rebars: Epoxy-coated rebars are simply rebars coated with a thin epoxy coat. This makes them up to 1,700 more times resistant to corrosion than standard carbon steel rebars. As a result, they are often used in areas in contact with saltwater or where a corrosion problem is imminent.
The only problem is that the coating can be very delicate, so bars should be ordered from a reputable supplier.
A particular concern with epoxy-coated rebars is that they can suffer severe corrosion where the epoxy is damaged since all the corrosion is concentrated at that one spot.
Galvanized Rebars: Galvanized rebars are 40 times more resistant to corrosion than carbon steel rebars, and they are much harder to damage than epoxy-coated rebars.
This makes it an excellent alternative to epoxy-coated rebars if you need something less likely to corrode.
Unfortunately, galvanized rebar is about 40% more expensive than epoxy-coated rebar.
Sheet-Metal Reinforcing Bars: Sheet-metal reinforcement is commonly used in floor slabs, stairs, and roof construction. Sheet-metal reinforcing is composed of annealed sheet steel pieces bent into corrugations of about one-sixteenth of an inch deep with holes punched at regular spacing.
European Rebars: The advantage of European rebar is its low cost. European rebar is made primarily of manganese, which makes it cheap and easy to bend.
This flexibility makes European rebar easy to work with in the field, but it is generally not recommended for use in areas that experience earthquakes nor for projects that require substantial structural integrity from its rebar.
Stainless Steel Rebars: Stainless steel rebar is quite expensive - about eight times the price of epoxy-coated rebar.
It is also the best rebar available for most projects. However, using stainless steel in all but the most unique of circumstances is often overkill.
But, for those who have a reason to use it, stainless steel rebars are 1,500 times more resistant to corrosion than black bars. Stainless steel rebars can also be bent in the field, which is very convenient.
Glass-Fiber-Reinforced-Polymer (GFRP) Rebars: Like carbon fiber, GFRP rebars will not corrode — ever, under any conditions. You'll pay dearly for that, however. These rebars can run ten times the cost of epoxy-coated rebars.
If you read over that list of rebar types and still feel confused about which one is best for you, that's ok. A good option is to reach out to a rebar manufacturer or local concrete provider to get advice on which kind of rebar you should be using.
Choosing the Right Size of Rebar
There aren't just different types of rebar - there are also different sizes of rebar!
The size of the rebar used in a particular job is dependent on the amount of strength that is needed. As you might guess, when more strength is needed, bigger rebar is used.
In the United States, rebar is categorized by a number reflecting the solid diameter of the rebar. The numbers range from #3 (smallest) to #18 (largest).
For example, The #3 bar size is 3/8″ diameter of the solid section, #4 bar size is 4/8″ diameter of the solid section, and #5 bar size is 5/8″ diameter of the solid section.
There are three different sizes of rebar which are needed for home projects are usually #3, #4, and #5.
The rebar size #3 is used for driveways and patios. For walls and columns, #4 rebar size should be used as they require more strength. It is better to use the #5 rebar size for footers and foundations.
How to Place Rebar in Concrete
Maybe you already know exactly what kind and size of rebar you need. If so, that’s great!
But what about placing the rebar in concrete?
Should you throw it in and let it lay how it lands? Should it be crisscrossed? How deep in the concrete should it be?
There is no formula when it comes to placing rebar.
Many variables affect how much rebar needs to be placed in a particular application, and exactly how it needs to be placed. For example, how much force will be exerted on the concrete? Will the concrete be freezing and thawing over the seasons?
If you are doing a simple pour around your home, your local concrete contractor will know how to place the rebar.
When it comes to bigger commercial pours, the rebar specifications should be detailed in the blueprints. An engineer has carefully figured out exactly how much rebar is needed and how it should be spaced, so follow the directions carefully.
The bottom line is that if thought and care are not put into how the rebar is placed, the concrete's structural integrity could be compromised.
For example, if the engineer calls for rebar spaced every 4 inches, three bars need to be placed for every 12 inches of the form.
If the steel placer is a little sloppy and places the bars at 5-inch spacing rather than 4-inch spacing, the product's strength will be reduced by 20%. Yes, concrete's structural integrity can be compromised just that easily!
Bending and Cutting Rebar
You may know precisely how far apart to place your rebar, but what if your bars are too long? Or what if the structure you are creating requires bends in the rebar?
Some rebar does come bent already, but in general, you’ll need to be prepared to cut and bend rebar so you can place it properly.
If you have the right tools, the process is easy.
Several tools can be used to cut rebar.
A hacksaw or bolt cutter is a good option if the rebar is thin enough, and if you aren’t cutting a large quantity. If you are doing a job of significant size, an angle cutter with a cutting wheel does a great job.
With all the tools listed, it’s important to note that you don’t need to cut through the entire rebar. You only need to cut through half of it, and you can break it in half easily. Use this little hack, and you’ll end up saving yourself a lot of time.
Bending rebar is usually pretty simple. If you can get sufficient leverage, you can bend thinner pieces of rebar by hand.
If you are using thicker rebar, or if you can’t get adequate leverage, you can purchase a rebar bender. There are plenty of options available, but as long as your job is only moderate in size, the cheaper models will work great.
Sometimes, rebar needs to be tied. That’s a whole topic in and of itself, but if you’d like to learn more about tying rebar, your local concrete contractor is a great place to start.
Concrete is an essential material in construction. But, without rebar, it loses a lot of its value.
Thankfully, you don’t need to be an engineering expert to be able to understand and use rebar. Next time you want to pour concrete, you can be confident in choosing the correct type and size of rebar. You can even feel good about installing the rebar.
To read more from the blog, read our other articles!
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