Prestressed industrial concrete floors represent a relatively new technology (gaining ground only in the last 50 years or so) that offers high tensile strength to concrete without requiring mesh or rebar to be embedded within the concrete.
What Does It Mean to Prestress Concrete?
By itself, concrete has high compressive strength and low tensile strength. This means it can easily withstand weight on top of it but cannot necessarily withstand the pull of gravity. For tall buildings and bridges, adding tensile strength is absolutely necessary or else the structure will collapse.
Even for concrete floors, adding tensile strength helps to prevent cracks by increasing the concrete’s ability to withstand tensile pressure – the pressure that threatens to pull material apart rather than compress it together. When a heavy machine rolls over top of concrete, it compresses the concrete in the area directly below it (compression force), which pulls on the concrete surrounding it (tensile force). Concrete with low tensile strength will crack in those areas.
In many cases, concrete is reinforced with rebar or wire mesh in order to provide the necessary tensile strength. But another way to add tensile strength is to add external compression to either side of the concrete. This is prestressed concrete.
Think about how you might pick up a row of three cardboard boxes while only putting your hands on the outer two. If you apply no inward pressure onto the middle box, you will simply lift up the two outer boxes. But if you press the two boxes onto the middle one, you can successfully lift all three. This is the theory behind prestressed concrete: it stays strong and “lifted” thanks to that external pressure.
It’s easy to see how this would come in handy for building bridges, but even in terms of concrete floors, the concrete’s tensile strength increases.
How Is Concrete Prestressed?
Before the concrete is poured, steel cables are run through the mold and held taught. After the concrete is cast and dried, the cables are attached to plates on either side of the concrete. Pressure is then applied to the cables to pull the plates inward. The amount of pressure applied depends on how much tensile strength is required.
Once the pressure is applied, it is retained / maintained within the cables themselves. The ends of the cables can be cut and the plates removed.
Advantages of Prestressed Concrete Floors
As mentioned previously, one of the main advantages of prestressed concrete floors is less cracking. This means that the floor needs to be repaired less often, saving money not only from the material and labor costs, but also from a factory or company’s potential shutdown time to redo the floor.
Cracking also allows water to enter the concrete, which can lead to further cracking problems if the water freezes. However, the main issue with water inside concrete is that if it reaches the steel mesh, rebar or cables, it can cause corrosion. Corroded steel is weak steel and no longer provides the correct tensile strength. Avoiding cracks in the first place ensures the integrity of the steel and therefore the stability of the entire structure.
There are other savings to take into account, such as the significantly reduced amount of rebar needed to provide comparable tensile strength. The prestressed concrete technique eliminates the need for large amounts of rebar, instead using the relatively small amount of steel in the cables. Sometimes less concrete is required because the overall strength increases so much, a greater thickness is no longer required.
Disadvantages of Prestressed Industrial Concrete Floors
Of course, if there were no drawbacks to this technique, it would be used for every project everywhere. However, the equipment necessary to prestress concrete can sometimes be expensive or difficult to maneuver into tight spaces. The technique itself also requires training that many concrete professionals have not yet had the opportunity to attend. Therefore, it may not be available in all areas, nor may it provide enough benefits over traditional reinforced concrete to warrant its use. It all depends on the project’s specifications, the location of installation, and the ability of the concrete team.