What is Prestressed Concrete?
Prestressed concrete is a type of building material that was created to counteract the inherit weakness of concrete – tension. While concrete is great in compression, it is weak in tension. The prestressing process forces the pre-compression of concrete to counteract this weakness. This type of concrete is best used in structures that will bear a lot of weight or that require a longer lifespan.
Prestressing tendons, such as tensile steel cables or rods, are tensioned like stretching a rubber band. As the tension force is released into the concrete, the member experiences compressive forces that now must be overcome before the concrete member ever experiences any tension. Not only does the prestressed steel compress the concrete, but it also serves as the reinforcement within the member.
Prestressed cable or rods are first tensioned within a steel form or mold after which fresh concrete is poured around the prestressing steel. Once the concrete has cured, the tension within the steel is released usually by flame cutting the cable or rod. Prestressed concrete members can be found in roadway bridge girders, parking garages, and even railroad ties just to name a few.
Benefits of Prestressed Concrete
The most recognized benefit of prestressed concrete is the dramatically increased holding capacity and longevity of the structures it is used in. With prestressed concrete, materials are less likely to crack and are therefore less expensive to keep up than other forms of concrete. The initial construction costs for this type of concrete are also lower, as it is generally precast and costs less to produce. Creating using this material costs less, as does its upkeep. Moreover, the concrete style offers thinner slabs, which are necessary in tall structures that need a solid yet lighter support system. Often, the thin prestressed slabs will be used to construct high-rise buildings.
Prestressed concrete also significantly increases the length the structure is able to span by allowing it to hold weight while spread over a long distance. The fact that this material gets stronger with age, rather than weaker, is one less worry a building’s construction.
This type of concrete also diminishes the number of joints necessary for a project and enables a more rapid construction. Part of the reason the construction is able to be so streamlined with this material is that it is generally precast and can be deployed to a site when necessary. Additionally, since the material is produced in a very deliberate and regulated environment, prestressed concrete has a very high level of quality control and few variables that could bring unpleasant surprises for users down the line. It may also be used in repetitive construction, as the molds are able to be filled multiple times to replicate the initial structure.