Prestressed concrete, such as post-tensioned slabs, can span longer distances than regular concrete. Steel tendons are laid in a grid before pouring the concrete, which is then allowed to cure partially before being tensioned using hydraulic jacks. Post-stressed concrete is useful for construction in areas with changing weather conditions and reduces construction costs due to its shallower depth and lighter weight.
Even though concrete is a very stiff material, it has a natural weakness when it comes to tension. It is limited compared to the length of a beam, floor or bridge that can be made from it. One way these structures can be built with longer spans than would be possible with ordinary concrete is through a technique called prestressing. A post-stressed slab is a concrete slab that has been prestressed using a specific method to increase the strength of the concrete.
There are several methods for prestressing concrete, and post-tensioning is very common. Before a post-tensioning slab is cast, high-strength steel strands or cables, called tendons, are laid in a tight grid. These help support and give strength to the slab once it has hardened. The tendons are covered in plastic so they don’t touch the cement directly. After the grid is made, the concrete is poured, taking special care to ensure that the cables remain at the correct depth.
The concrete is allowed to cure approximately 75% of the way through, at which point post-tensioning occurs. Each of the tendons of the post-tensioning slab is tensioned using a hydraulic jack. The tensioning of the cables takes place after the concrete has hardened more, hence the term “post-tensioning”. The tendons are usually pulled at a tension of 25,000 pounds per square inch (4503 kg per square cm). Once the cables have reached their designated tension, they are anchored in the concrete and the slab is allowed to fully cure.
Many modern homes are built on post-tension slab, which serves as an excellent foundation. This method of prestressing concrete is particularly useful in areas where the ground expands and contracts in relation to weather conditions. In addition to residential applications, post-stressed concrete opens up the possibility for many construction techniques that would otherwise be impossible. For example, car parks and stadiums are sturdier and cheaper to build with post-stressed concrete.
Using a post-stressed slab instead of ordinary concrete often makes good economic sense. Because a shallower depth of concrete is used to achieve the same end result, construction costs are reduced. This particular advantage has even greater implications for the construction of skyscrapers and office buildings.
When the floor thickness is reduced, so is the weight of the structure. A lighter building means that the cost of building the foundation is reduced. Thinner floors also result in a reduced building height, meaning exterior finishing costs, such as window glass, are reduced.
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