Precast concrete is a form of construction, where concrete is cast in a reusable mould or "form" which is then cured in a controlled environment, transported to the construction site and lifted into place. In contrast, standard concrete is poured into site specific forms and cured on site. Precast stone is distinguished from precast concrete by using a fine aggregate in the mixture so the final product approaches the appearance of naturally occurring rock or stone.
Ancient Roman builders made use of concrete and soon poured the material into molds to build their complex network of aqueducts, culverts and tunnels. Modern uses for precast technology include a variety of architectural and structural applications featuring parts of or an entire building system. Precast architectural panels are also used to clad all or part of a building facade free-standing walls used for landscaping, soundproofing and security walls. Stormwater drainage, water and sewage pipes and tunnels make use of precast concrete units. The advantages of using precast concrete is the increased quality of the material, when formed in controlled conditions, and the reduced cost of constructing large forms used with concrete poured on site.
There are many different types of precast concrete forming systems for architectural applications, differing in size, function and cost.
The double wall process has been in use in Europe for many years. The walls consist of 2 wythes of concrete separated by an insulated void.The most commonly specified thickness of the wall panels is 8 inches. The walls can also be built 10 and 12 inches thick if desired. A typical 8-inch wall panel consists of two wythes (layers) of reinforced concrete (each wythe is 2-3/8 inches thick) sandwiched around 3-1/4 inches of high R-value insulating foam. The two wythes of the interior and exterior concrete layers are held together with steel trusses. The insulation is continuous throughout the wall section. The composite sandwich wall section has an R-value exceeding R-22. The wall panels can be made to any height desired, up to a limit of 12 feet. Many owners prefer a 9-foot clearheight for the quality of look and feel it affords a building.
The walls can be produced with smooth surfaces on both sides because of the unique manufacturing process which form finishes both sides. The walls are simply painted or stained on the exterior surface to achieve the desired color or textured surface. When desired, the exterior surface can be manufactured to have a wide variety of brick, stone, wood or other formed and patterned appearances through the use of reusable, removable formliners. Interior surfaces of the double-wall panels are drywall quality in appearance right out of the plant, requiring only the same prime and paint procedure as is common when completing conventional interior walls made of drywall and studs.
Window and door openings are cast into the walls at the manufacturing plant as part of the fabrication process. Electrical and telecommunications conduit and boxes are flush mounted and cast directly in the panels in the specified locations. The carpenters, electricians and plumbers do need to make some slight adjustments when first becoming familiar with some of the unique aspects of the wall panels. However, they still perform most of their job duties in the manner to which they are accustomed.
Double-wall precast concrete sandwich panels can be used on most every type of building including but not limited to: Multi-family, Townhouses, Condominiums, Apartments, Hotels/Motels, Dormitories/Schools and Single Family homes. Depending upon building function and layout, the double-wall panels can be easily designed to handle both the structural requirements for strength and safety, as well as the aesthetic and sound attenuation qualities the owner desires. Speed of construction, durability of finished structure and energy-efficiency are all hallmarks of a building that utilizes the double-wall system.
This system seems to be the way of the future as more attention is being paid to fortified housing. Systems like these can save many lives in areas at risk of dangerous weather.