Precast concrete consists of concrete (a mixture of cement, water, aggregate and often admixtures) that is cast into specific shapes at a location other than its final in-service position. The concrete is placed into a form, or mold typically made of wood or steel, and cured before being stripped from the form, typically the following day. These components are then transported to the construction site for erection into place.
Precast concrete is reinforced with either conventional reinforcing bars, strands with high-tensile strength, or a combination of both. Prestressing is a method of reinforcement where the steel strands are pretensioned in the form before the concrete is cast. Once the concrete is cured to a specific strength, the strands are cut (detensioned). As the strands, having bonded to the concrete, attempt to regain their original untensioned length, they bond to the concrete and apply a compressive force. This compressive force allows precast elements to span greater distances, carry more load, or a combination of both. Prestressing also reduces cracks as the members are in compression. Often it, allows precast members to be reduced in size and weight relative to a similar conventional reinforced, cast-in place concrete member.
Precast Components
A variety of components can be fabricated from precast concrete, meeting a range of project needs. Listed here are the most common components that precast producers manufacture and that designers incorporate into their projects. Customized pieces, sizes and shapes can be created in most cases to meet specific needs.
Floors and Roofs
Walls
Building Structural Components (beams, columns, etc.)
Piles
Transportation Components
Modular Components
Miscellaneous Components
The designer should consult with a producer early in the design phase to determine what components will work most efficiently and review specific sizes, joint locations, and other details that can create cost efficient options.