Fabric-reinforced concrete: Fid-Bau Portal

Fabric-reinforced concrete

In US Patent 6 960 394, Milliken & Co describes a cement panel reinforced by a fabric made of nucleated polypropylene (PP) fibres. The company from Spartanburg, South Carolina, describes a panel that includes a core made from lightweight cement. This is covered by a layer of the reinforcing fabric, top and bottom, each bonded to the cement. On the edges, the fabric layers are overlapped. Using nucleated polypropylene monofilaments enhances the performance, according to the Patent, when compared with glass reinforcements that are currently widely used. For instance, the new fabric has improved resistance to alkalis. Such yarns also have the advantages of breaking at higher elongations and are less likely to fail due to brittleness. Overall, Milliken claims its development offers better lightweight cement compositions. The nucleated polypropylene is high modulus and, in a simple weave, an adhesive may be used to bond the intersections of warp and weft. It is also possible to create tri-directional fabrics for this use, the company notes. Nucleated yarns have a lower shrinkage than nonnucleated ones and they perform better at elevated temperatures such as those often used in curing. Because of their nature, cement panels have a tendency to be brittle at their edges, which are often used as points of attachment. By overlaying the fabric at these regions the strength of the edges is increased and the boards retain sufficient integrity to stabilize the reinforcement and so remain attached. In one specific version of the reinforcement the fabric was a bi-directional scrim and included a layer of parallel wefts that are arranged between two convergent layers of warp ends. These may be held together by an adhesive such as polyvinyl alcohol (PVOH), acrylic, polyvinyl acetate, polyvinyl chloride. This adhesive may be dried on application and so stabilizes the fabric. In a preferred construction, the warp ends are arranged at about 1.6-10 ends.cm -1 (4-25 ends an inch). The yarns used should be 55.6-88.9 tex (500-800 denier), although this may be varied depending on the strength and modulus requirements of the final cement panel. The use of nucleated polypropylene eliminates the need for a protective coating over the reinforcement fabric and offers advantages such as higher strength, improved temperature shrinkage characteristics and less degradation during curing of the panels. In making such yarns at least one nucleator compound is used to create a fibre with a shrinkage rate of at most 10 % at 135 deg C, a 3 % secant modulus of at least 8.83 N.tex -1 (100 g a denier) and optionally a tenacity of at least 0.35 N.tex -1 (4 g a denier). The cross-section of fibres for this use may be circular or highly elongated rectangular, such as those used when making slit film monofilaments (tapes).