How To Reinforce Concrete
As one of the strongest building materials on earth, concrete has been a staple in building for centuries. Many aqueducts, bridges, and other structures of the Roman Empire still stand today. Today, concrete is used in foundations for high-rises, buried infrastructure, water storage, and much more. But how to reinforce concrete?
Obviously, the strains on concrete are much more involved than they were in ancient Rome. However, some of the marvels that are built today just wouldn’t be possible without a patent filed by a French gardener in the mid 19th century. Jean Monier added steel wire mesh to concrete to make his pots more durable.
Through the years, the type of reinforcements have improved and the use of reinforced concrete has grown. Today, concrete has surpassed steel as the most-used construction industry material in the world. In fact, when comparing tonnage, concrete doubles the use of steel, wood, plastic, and aluminum combined.
Sure, concrete, as a matter of fact, is heavier than those other materials. But it’s also more durable, can be cheaper, and is easy to work with. The advent of precast concrete makes working with the material that much better as you don’t have to wait for pour-in-place concrete to harden before continuing work.
Why does concrete need to be reinforced?
The most widely used form is Portland Concrete, which is a very durable substance once mixed. What makes concrete buildings so attractive in areas that could be affected by earthquakes is its ability to handle different kinds of stresses. It allows the building to sway to and from without crumbling.
By itself, concrete already has impressive compressive strength. This means it stands up very well to forces pushing on the material, which is important when it comes to the concrete flooring of your facility. If concrete is rated with a strength of 4,000 psi, that means it can withstand a pressure of up to two tons per inch.
Concrete doesn’t fare as well when it comes to tensile strength. This the ability of the concrete to be stretched to a point of breaking. If we use the same concrete example from above, the unenforced concrete only has a tensile strength of around 400 psi.
There’s where the rebar comes into play. Steel handles the stretching much better, so rebar can absorb those stresses at a higher rate. With rebar in place, concrete is able to stretch and contract more consistently, making for a more dependable material.
But that’s only if the rebar is placed at the proper intervals, obviously. Engineers are responsible for calculating the strengths needed to meet building codes for each structure. Let’s say it’s been determined that a specific type of rebar (length, width, etc.) needs to be placed at every four inches. If that rebar is placed every five inches, the strength is reduced by 20 percent.
To increase the strength even more, the bars can be placed in tension before the concrete is poured. Once the concrete has hardened around the steel, the tension is released. The concrete, referred to as prestressed concrete, is under constant compression, adding to the strength.
This method actually allows engineers or architects to design smaller concrete spans used in bridges, roofs, and walls. That means spans can be longer and use less concrete without sacrificing strength.
However, these reinforcing bars can also hurt the structure from the inside. If the rebar is treated with anti-corrosive additives or improperly installed, the building can start exhibiting concrete cancer. As the rebar rusts, it expands, affecting the concrete.
Pieces can begin to break, allowing in more water, more rust, and more expansion. In addition to affecting the integrity of the building, large pieces of concrete suddenly falling from a hundred feet up could injure people below. When even the smallest cracks begin to appear in the facade, it’s important to seal them up as soon as possible.
Obviously, there’s more to concrete that just shoving a bunch of material into a mixer and then pouring it. It is a highly engineered building material that must be created just so to make sure it’s able to handle the job being asked of it. This testing can be affected by how the concrete is created.
For the most part, there are two ways to create concrete pieces: pour in place and precast. With pour in place concrete, the concrete is mixed, put in a concrete truck, and poured when the forms are ready at the location. The forms are usually made of steel or wood depending on the size of the job.
Once the forms are in place, rebar is placed in the middle of the form at the proper intervals. These steel reinforcing bar “cages” are configured outside of the from and then lowered in. Then the concrete is poured in as crews work the concrete to release any air pockets.
After an appropriate amount of time to allow for strengthening, and after testing the strength, the forms are removed and backfilling can begin. It’s the same process whether you’re building the foundation walls for a two-bedroom bungalow or a 50,000 square foot warehouse.
While forms are a popular choice for foundations or concrete slabs, precast concrete has advantages when it comes to buried infrastructure. These could be utility vaults for powerlines running underground or wells to help with water drainage at a facility. Because of the sizes of these pieces depend on building codes, precast companies work with adjustable forms.
The rebar is added to the forms, the concrete is mixed and then poured into the forms. This usually takes place in a controlled environment, it’s much easier to manage the mixture and test the strength of these reinforced concrete structures. This means the pieces are ready for installation at a specific time and backfilling can begin after being placed.
The kind of concrete work is being done determines which method makes the most sense. If 20 vaults are needed to handle water runoff are needed, precast makes sense. If it’s just a 10×20 patio with a slab thickness of 6-inches, throwing up some forms is a less expensive way to complete the job.
No matter what major industrial or commercial concrete job you have coming up on the horizon, call Storee Construction. We’ll make sure your concrete foundations, walls, ceilings, and other structural materials are engineered to proper specifications. Give us a call today.