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Glass fiber reinforced concrete ( GFRC ) is a proven engineered composite building material consisting of Portland cement, aggregate, water, glass fiber reinforcement and additives. The glass fibers reinforce the concrete, much as steel reinforcing bars do in conventional construction. The glass fiber reinforcement results in a product with much higher flexural strength than normal concrete, allowing its use in thin-wall casting applications. Because of its low shrinkage rate, GFRC is ideal for replication of historic designs, whether in terra cotta, cast stone, or other materials. By making molds directly from the existing pieces, the exact shape and appearance of the originals can be faithfully replicated. Nova-Cotta® is ARC's trade name for its replacement terra cotta castings. These faithful replications have won the approval of Historic Commissions in many jurisdictions. The surface finish and coloration make the replacements indistinguishable from the original material. For building panel construction, GFRC castings are manufactured by spraying a series of layers of polymer-concrete material with glass fiber reinforcement in a female mold. A steel frame is bonded to the casting, allowing the panels to be installed by bolting or welding the frame to the building's structural steel. The flex-anchors, which connect the skin to the frame, allow movement of the skin relative to the supporting structure. By using pigments and finishing techniques, a wide variety of colors and surface finishes can be obtained, either to suit the Architect's vision, or to recreate historical building elements. HISTORY In the late 1960's, GFRC was first successfully produced in England. The key to success was the development of alkali-resistant glass fibers, capable of resisting the alkali attack that occurs when the fibers are mixed with normal hydrating Portland cement. In 1980 the product began to be used in the USA. During the 1980's and 1990's, GFRC became widely accepted, and the industry has grown dramatically. HISTORIC REPLICATION OF EXISTING DESIGNS GFRC has made a major contribution to historical restoration because of it’s fine texture, allowing almost perfect replication of building ornaments and terra-cotta. Its very low shrinkage allows molds to be made from existing structural ornamentation, then cast in GFRC to replicate the original designs. GFRC is also used for wall panels, spandrels, column covers, soffits, and architectural ornaments. Photos of some such installations are shown in the Historic Replication section. DURABILITY In freeze-thaw tests, samples showed only slight flaking after 300 cycles, compared to severe deterioration of un--reinforced mortar after 200 cycles. Laboratory tests show no surface deterioration after the equivalent of fifty years service in weather typical of the northern U.S. GFRC's permeability compares favorably to other cementitious materials. In laboratory tests, GFRC panels subjected to water blown wind of 75 miles per hour. Moisture absorption tests indicate an absorption rate in the 8 to 16 percent by weight range. ADVANTAGES For historic replication, GFRC can provide the look of terra cotta, carved stone, or ornate cast iron building elements. With its high flexural strength and high strength to weight ratio, GFRC can provide the appearance of precast concrete with a weight of only one-quarter that of precast concrete. The casting process allows very ornate shapes to be produced, with a very high degree of detail.
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