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Durability, fire resistance, relatively low cost, and availability makes concrete a natural choice for wall construction. The insulating properties of concrete, however, greatly reduce its effectiveness. Concrete sandwich panels were developed in response to the need for more efficient concrete wall systems.
The first forms of sandwich walls used steel and/or concrete connections to hold two layers of concrete together with insulation sandwiched between. Steel and concrete traversing the insulation layer, however, can reduce the insulating value of a wall by 20 to 40% or more due to a phenomenon known as thermal bridging. A method for determining loss due to the thermal bridging has been developed by ASHRAE called the isothermal planes (series parallel) calculation method. A modern personal computer and spreadsheet can be used to easily perform these calculations.
Composite materials (reinforcing fibers and binding resins) developed for the aerospace industry have recently been adapted to take the place of steel and metal connections in concrete sandwich walls. The result is the ability to manufacture insulated concrete sandwich panels with no loss in thermal energy. The composite connections are stronger than steel, will not corrode, are flexible to withstand thermal cycling, and are cost competitive. Modern technology has provided concrete panel manufacturers with the ability to produce concrete panels that are almost 100% thermally efficient.
thermal bridge, fiber, composite(s), concrete, sandwich, insulation, precast, tilt-wall
President, Composite Technologies Corp., Ames, Iowa