Precast Concrete

Precast concrete is a sustainable building system that provides slender, efficient structural elements.  Precast plants provide many advantages over concrete cast in the field.  Better control over conditions, materials, and workmanship gives a higher strength, higher quality product in a safer environment.  Repetitive forms can be reused.  The limitations of transportation, however, means widths over 14' can be problematic and expensive to move.


Testing is similar to that of site-cast concrete.

Precast concrete is often pre-stressed - prestressing allows a much more efficient distribution of compressive and tensile forces, thus it allows for smaller, cheaper concrete members.  Tensioned steel squeezes the concrete, putting the entire concrete section under compression, reducing cracking.  The strands can be shaped to more closely match the path of tensile forces through the beam, which tends to be at the top near the ends, but at the bottom near the center of the span.  T








Prestressing comes in two flavors:


PRE-TENSIONED:

Manufactured with steel cables or bars, called “tendons,” are pulled taut prior to the casting of the concrete, which bonds to the tendons and the force is transferred along the surface area of the rebar.  This site goes slightly further in depth.

POST-TENSIONED:
The tendons are not allowed to bond during curing by sheathing them.  After the concrete has cured, the tendons are jacked taut and anchored to the ends of the concrete, pulling the concrete section into compression.  Most commonly used in large building projects such as high-rises and bridges. Post-tensioned concrete slabs-on-grade also can be found where there are unusual soil conditions.

Precast pieces were used to reinforce the stage floor prior to Kirstie Alley's appearance on Dancing With The Stars.