Prestressed concrete is a way to improve the tensile strength of precast concrete. Tensile strength measures concrete’s ability to withstand the pressure of being pulled apart. (Compressive strength, as the name indicates, is concrete’s ability to withstand compression.)
The higher the tensile strength, the more pressure concrete can withstand before stretching or breaking apart. Tensile strength in concrete is typically much lower than compressive strength. Producers use rebar and/or reinforcing mesh to keep concrete from being stretched or spread to the breaking point.
In short, we can say that prestressed concrete is the method we use to precompress concrete beams using highly tensioned steel tendons (strand), wires, cables, and rods. This steel reinforcement is pulled to meet engineering specs. The concrete is then cast over the tendons.
Details of Prestressed Concrete Processes
The process of prestressing concrete improves its tensile strength and allows it to handle greater weight. These days, concrete is prestressed as a matter of routine.
A piece from the National Precast Concrete Association provides a good general definition that adds to our initial overview.
“Prestressing means the intentional creation of permanent stresses in a structure or assembly to improve its behavior and strength under various service conditions,” they write.
The Portland Cement Association (PCA) goes into greater and more helpful detail.
“In conventional reinforced concrete,” they explain, “the high tensile strength of steel is combined with concrete’s great compressive strength to form a structural material that is strong in both compression and tension.”
In practice, the PCA continues, “compressive stresses induced by high-strength steel tendons in a concrete member before loads are applied will balance the tensile stresses imposed in the member during service.”
Prestressed concrete has been around in theory since the late 1800s. Manufacturers used to limit prestressing procedures to pre-tensioning. Now, however, it is common practice to utilize pre-tensioning and then to continue the manufacturing of prestressed concrete structures using post-tensioned concrete — i.e., after the concrete has been cast.
Tendons can be inside the concrete (internal prestressing) or outside of it (external pre stressing). When combined with steel reinforcement (tensioned tendons), the concrete hardens into a product designed to last multiple lifetimes.
Either of these methods ensures a precast concrete product of ultimate strength and endurance for a wide variety of applications.
You’ll find prestressed and precast, high-strength concrete just about everywhere. In both public and civil engineering realms. In buildings, bridges, silos, dams, pavement. Even within nuclear and blast-containment structures.
Questions? Get in touch with Columbia Precast Products today!