Concrete is one of the most popular choices for material in construction. This is due to its strength, durability, and flexibility.
However, sometimes even concrete needs a little reinforcement to sustain the loads placed upon it. This can come in various materials, the most popular being rebar.
What is rebar, and why is it used? This article will answer those questions. We’ll also discuss the different types of rebar and when to use which.
Rebar is a construction term short for reinforcement bar. It is a rod made from steel that is placed into wet concrete before it dries.
These steel bars have bumps or ridges that bond with the concrete as it dries to create a stronger, more durable structure.
Rebar offers concrete structures many benefits, including:
Yes, concrete is strong, but concrete with rebar is stronger.
Rebar especially adds tensile strength to concrete, which naturally has excellent compressive strength but poor tensile strength:
Rebar practically doubles the tensile strength of concrete.
Because rebar improves the breaking point of concrete, it also reduces the number of cracks in a concrete structure.
Cracks are usually caused by greater pressure than the concrete can sustain. Rebar increases this ability. It also reduces the expansion and shrinking of a concrete slab due to temperature changes.
Cracks are a problem whether they are structural or not. Non-structural cracks can allow water or damaging minerals, such as chloride, carbon, or sulfate, to penetrate into the concrete. This compromises the bearing capacity and durability.
Generally, a thicker pour of concrete mix is needed for slabs requiring extra strength. However, sometimes you don’t have the space for it.
Adding rebar to the concrete reduces the necessary thickness while maintaining its ability to sustain the load.
This reduction in concrete needs translates into greater flexibility and cost savings for your construction project.
Rebar adds years of life to the concrete structure. Structural integrity is maintained over time by:
The inclusion of rebar in concrete construction reduces the chances of structural failure. One of the significant concerns that engineers are trying to address is the increase in structural damage due to natural disasters.
Concrete reinforced by steel bars has proven to reduce a building’s chance of collapse due to natural disasters. This includes earthquakes, hurricanes, and floods.
Maintaining structural integrity at these critical times can reduce the risk of injuries and fatalities. Reinforced concrete structures save lives.
Rebar comes in many different forms, shapes, types, and sizes. Rebar can also be shaped, bent, and cut to meet the needs of a project. Tying or joining rebar can add length or stability to the rebar placement for extra-large jobs. There really are very few situations in which rebar is not an option.
Mesh is a welded wire fabric placed into concrete as a reinforcing construction material. It’s an alternative to rebar but isn’t as strong. One upside to wire mesh is that it is easier to install and requires fewer man hours.
However, the cost you’ll save on labor won’t count for much since wire mesh is typically more expensive than rebar.
Mesh should only be used in concrete projects when the concrete is thinner than average and doesn’t have room for rebar. Otherwise, use rebar.
Some examples of projects that would require wire mesh include driveways, walkways, and thin-shell concrete.
Rebar can be used for just about any project, but not all types of rebar.
Rebar has evolved to include special materials that expand its abilities. Here are the seven main types of rebar that have been created:
Also known as carbon steel rebar, black bar is the most common version used in construction projects. It is cheap but corrodes easily.
Black bar coated with epoxy is another option. This rebar has the same strength as regular rebar but is more corrosion-resistant.
One downfall of this type of rebar is that the epoxy coating is delicate and easily damaged, so extra care must be taken during transportation and use.
Black bar with a zinc coating is known as galvanized rebar.
Similar to epoxy-coated rebar, it has a higher corrosion resistance. However, unlike epoxy-coated, galvanized is more expensive and less susceptible to damage.
Made with manganese, this rebar is cheap to buy and bends and shapes easily. However, it is weak in regards to added tensile strength, so it isn’t suitable for heavy industrial jobs.
Stainless steel rebar is very expensive because it’s resistant to corrosion and can still be bent if needed.
These “bars” are more like corrugated sheet metal with holes to bond to concrete. Typically used for thinner concrete, they are often utilized in floor slabs, stairs, and roofing.
GFRP simply will not corrode, but it is also very expensive. It should only be used for projects that have a large humidity factor. This rebar cannot be bent, but it is lightweight and durable.
Even within the different types of rebar above, more variables exist in terms of grades and sizes. These will determine its compressive and tensile strength, bending ability, and fatigue.
Bar sizes are grouped by weight, diameter, and area of the metal. When choosing rebar, you must consider a balance between strength and space.
The larger the rebar size, the stronger it is, but the more space it will take up in a concrete beam or slab.
#3 rebar is usually reserved for smaller projects like a patio because it provides the lowest tensile strength. Columns, piers, and walls typically require a #4 rebar. For concrete elements that will bear heavier loads, like footings and foundations, a #5 or higher rebar is used.
The grade given to the rebar is determined by its tensile strength. Common grades are 40, 60, 75, 80, and 100. The higher the grade, the more tensile strength it has — and the more expensive it will be.
Since there are so many different types, sizes, and grades of rebar, what determines the type that should be used for each project?
The answer is dependent on the following factors:
Just as the amount of concrete needed is calculated with the load it must support, the proper rebar for each project also considers the anticipated loads.
There are dead loads, which include the weight of the structure itself, and there are live loads, which are ever-changing (such as people and environmental factors).
The tensile stress, or force per area unit creating tension, must also be calculated. As discussed, rebar is a critical element in improving the tensile strength of concrete. Projects with a higher anticipated load and tensile stress will need a stronger rebar.
Rebar is made from steel, which will corrode if it comes into contact with water.
However, we’ve already discussed that special types of rebar are resistant to corrosion. There are levels of corrosion resistance within those types of rebar. The amount of corrosion resistance needed depends on how much humidity the structural concrete will be subjected to.
The structure’s location will determine the type of environmental factors the rebar will be exposed to.
Some areas are more prone to natural disasters such as earthquakes, tornadoes, floods, and hurricanes. These place a large amount of stress on the structure. Flooding and hurricanes also subject the concrete to extreme amounts of water.
Temperatures can also place the concrete under more stress than normal. Northern areas will see freezes, which can cause the concrete to expand and shrink, leading to cracks. Coastal regions will have much more humidity with saltwater in the air.
The cost of reinforcing materials based on the type of rebar can vary widely. There is no point in using the highest quality and most expensive rebar if it is unnecessary. The cost of the rebar should be balanced between the needs of the project and the project’s budget.
Rebar won’t be any help to strengthen the concrete unless it is properly installed.
It is imperative that you follow the engineer’s instructions to a tee. They have specialized training to calculate the necessary reinforcement needed. They also know and follow all local building codes.
One inch off of the proper rebar placement, and you’ll reduce the strength of the structure significantly. Of course, you should also use the specified grade, size, and type of rebar, laid out in the engineer’s specs. If you need shorter bars, cutting thinner rebar can be done with a hacksaw or bolt cutter. Thicker rebar is cut with a cutting wheel.
Bending rebar can be done with a hickey bar or a portable rebar bending machine. Although it may be quicker to bend it by hand, a bending machine is much more precise.
Before installing rebar, it must be clean and debris-free to ensure solid bonding with the concrete.
Following the proper splicing and tying protocol using steel wires is also important.
The rebar must be fully covered by concrete. If any rebar can still be seen through the concrete, more should be poured to cover it.
Using rebar with concrete will increase its tensile strength, reduce the concrete needed, provide versatility, and improve the safety and longevity of the structure.
FMP Construction is well aware of these benefits and the tactics to use to install the right rebar, the right way, for the strongest, most economical build.
Contact us today to build your next reinforced concrete structure.