Abstract:
An initial process for preparing material to use in manufacturing fiber-reinforced structures. One embodiment envisions a method of manufacturing a cement board. The initial process includes providing an open mat of recycled carpet fibers in a container, placing a mortar mixture directly over the fiber mat, distributing the mortar through the fiber mat by moving a comb having bent tines through the mortar-fiber mixture, and vibrating the mortar-fiber mixture substantially simultaneously with the distribution of mortar through the fiber. Also provided is a method for making the final product.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a process for making fiber-reinforced structure, and more particularly to a method of manufacturing a cement board incorporating recycled carpet fiber. 
     BACKGROUND 
     Various techniques are presently available for making cement boards, as illustrated in U.S. Pat. Nos. Re. 271,109; 3,972,972; 4,668,548; 4,856,754; 5,787,597; 5,078,937; 5,724,783; 5,139,722; and 5,729,936. In particular, U.S. Re. Pat. No. 27,109 to Viden discloses a method and apparatus for producing special surfaces on panel board wherein the surface layer is simultaneously doctored onto a lower carrying layer and provided with an irregular top surface by a rotating roll arranged at an angle to the movement of the carrier material. 
     U.S. Pat. No. 3,972,972 to Yano et al. discloses a process of continuously producing a board of cement-like material reinforced by fibrous material wherein a granular mixture of the cement-like material and fibrous material is formed into a board under compression, and optionally with the addition of water. 
     U.S. Pat. No. 4,668,548 to Lankard discloses a method of producing a concrete overlay by drilling anchor holes in the concrete and placing a layer of fibers on the exposed surface and infiltrating a flowable cement slurry throughout the fibers and into the integral holes. Curing the slurry procedures an overlay with integral fiber-reinforced anchor portions. 
     U.S. Pat. No. 4,856,754 to Yokota et al. discloses a shuttering for forming concrete which includes a plate with a plurality of through holes openings on both its face and reverse, and double woven fabric consisting of a face tissue that permits passages of water, but prevents concrete from passing in the reverse tissue opposed to the face of the plate. 
     U.S. Pat. No. 4,787,597 to Yokota et al. discloses concrete forms including a first cloth sheet permitting surplus water and air contained in concrete cast in the form to pass therethrough but capable of blocking the passage of concrete, a second cloth sheet permeably secured to the first sheet permitting the surplus water and air to pass between and through the first and second sheets and to be absorbed into the second sheet as well as the first sheet and a support plate. 
     U.S. Pat. No. 5,078,927 to Eela discloses a method and system for producing a slab-like product in which a fibrous material is mixed with a settable material. The blank shaping units of the system are provided with stud-like material dispersing members. 
     U.S. Pat. No. 5,724,783 to Mandish discloses a panel manufactured by using Portland cement and waste aggregate materials, including used fiberglass insulation, recycled polystyrene, rubber tires, and old carpet material. 
     U.S. Pat. No. 5,139,722 to Lawton discloses pressing wet concrete between a ram and a mold to compact the concrete and express water from it so as to produce a molded slab. A layer of filter material is provided between the ram or the base of the mold and the concrete, and the filter material is secured by a discontinuous coat of adhesive applied as a transfer to the ram and/or to the base of the mold. 
     U.S. Pat. No. 5,729,936 to Maxwell discloses forming prefabricated panels by compressing a fiber slurry which may be composed of waste fiber products such as waste paper, cardboard, straw, leaves and grass clippings. 
     In conventional techniques, an attempt is made to add the fiber to the mortar during the final stages of the preparation of the mortar, i.e., after all of the constituents of the mortar have been worked into a fine paste. However, the fiber “balls-up” to some extent as it is wetted by the mortar. These fiber balls appear in varying amounts making it impossible to incorporate the fiber into the mixture and making it impossible to ensure that the fiber is uniformly distributed throughout the mortar mixture. Any blade or whisk system used after the fiber is added, ends up matted with fibers that may have wrapped around the mixing elements, such as the blade or wire, when the mixture is rotated. Drum mixing typically rolls the fiber into clumps, in much the same way as a rotary pelletizer operates to make pellets or balls. The rotating drum mixer cannot consistently produce uniform blending of the fiber and mortar. 
     In summary, the present techniques are not satisfactory in that they do not properly mix the fluid mortar into a tangled mat of fiber to thereby produce a board that does not have air-filled voids or have an irregular or rough surface. 
     In view of the above, there is a need in the industry for a technique that produces a strong cement board using recycled carpet fiber as a reinforcement material. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method of manufacturing a cement board incorporating recycled carpet fiber which produces a strong cement board even with a fluid mortar because the process specifies the use of a high-range water reducing agent to minimize the amount of water that is used, and further includes a step in which the fiber-mortar mixture is pressed between layers of filter fabric to assure that any problem of excess water is eliminated. 
     Another object of the present invention is to provide a method of manufacturing a cement board incorporating recycled carpet fiber in which the problem of air-filled voids or “bugholes”, that might produce an irregular, rough surface on the finished cement board, is eliminated. 
     Yet another object of the present invention is to provide a method of manufacturing a cement board incorporating recycled carpet fiber which produces a cement board with smooth surface. 
     Still yet another object of the present invention is to provide a method of manufacturing a cement board incorporating recycled carpet fiber which produces a uniform mixture of mortar and fiber from tangled recycled fibers, such as processed post-consumer carpet materials. 
     A further object of the present invention is to provide a method of manufacturing a cement board incorporating recycled carpet fiber wherein the use of tangled fibers produces a cement board in which the fiber has high pull-out resistance compared to the conventional short discrete fiber materials used in most concrete reinforcement applications. 
     Yet a further object of the present invention is to provide a method of manufacturing a cement board incorporating recycled carpet fiber in which the mixed fiber and mortar can be placed as a discrete layer thereby making it possible to make a cement board that has two exterior layers containing fiber and a central layer containing only mortar. This construction places the fiber reinforcement in a location in the cement board where it is needed to resist flexure. 
     Still yet a further object of the present invention is to provide a method of manufacturing a cement board incorporating recycled carpet fiber which utilizes comb-type mixing to incorporate a Portland cement-based mortar into a tangled mass of fiber. 
     In accordance with the present invention, a method of manufacturing a cement board includes providing an open mat of recycled carpet fibers in a container, placing the mortar mixture directly over the fiber mat, distributing the mortar through the fiber mat by moving a comb through the mortar-fiber mixture, and vibrating the mortar-fiber substantially simultaneously with the distribution of mortar through the fiber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and novel features of the present invention will become apparent from the following description of the invention, illustrated in the drawings, in which: 
     FIG. 1 is a schematic illustration of a mixing comb used in the method of the present invention; 
     FIG. 2 is a schematic illustration of the mixing motion of the comb in the mortar; and 
     FIG. 3 is a schematic cross-sectional illustration of a mold, showing the fiber-mortar mixture placed therein for forming a board. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the method of the invention, the carpet fiber is initially processed by cutting the used carpet into strips. The strips are shredded, chopped and hammered and screened to separate the components of the carpet. For instance, the latex and the calcium carbonate are removed by sieving. The process produces a tangled mass of fibers that varies with the type of fiber in the carpet. Typically, the mass of fiber is a mixture of nylon, polyester and polypropylene fibers. The tangled mass is then carded or combed to create an open mat of fibers. 
     Next, a low-viscosity mortar mixture is prepared by mixing Portland cement, sand, water, a dispersing agent and a high-range water reducer. An example of the proportions needed for such a mortar is as follows: 
     
       
         
               
               
               
             
           
               
                   
               
             
             
               
                 Type I-II Portland Cement 
                 500 
                 grams 
               
               
                 Fine aggregate 
                 1000 
                 grams 
               
               
                 (quartz sand meeting the specifications 
               
               
                 set out in ASTM C778) 
               
               
                 Water 
                 230 
                 grams (cc) 
               
               
                 Dispersing Agent 
                 1 to 2 
                 grams 
               
               
                 (METHOCEL K-1000 ® from 
               
               
                 Dow Chemical Co., Midland, MI) 
               
               
                 High-range Water Reducer 
                 4 
                 ml 
               
               
                 (SIKAMENT 300 ® or SIKAMENT S-10 ® from 
               
               
                 Sika Corp. Lyndhurst NJ) 
               
               
                 w/c = 0.46 
               
               
                   
               
             
          
         
       
     
     As best shown in FIG. 2, the fiber mat  10  is arranged in a layer on the bottom of a container  12  and the mortar mixture  14  is placed as a layer directly over the mat. The container with the fiber mat and mortar is placed on a vibratory table (not shown). The vibrator is switched on and a metal comb  16  (FIG. 1) with multiple bent wire-teeth  18  (in the style of a curry comb) is moved across and in-and-out of the fiber and mortar layers (see arrows x and y). The teeth  18  of the comb  16  transmit the motion of the vibrating mold into the mortar mixture  14 , and the motion of the comb  16  separates the fibers  10  so that the mortar  14  can move into the mat  10 . The angled teeth  18  of the comb  16  pull the fibers  10  up into the mortar mixture  14  distributing the mortar evenly through the fiber mat  10  (FIG.  2 ). Care is taken to lift the comb  16  frequently so that the fiber mat  10  remains as a continuous layer from one side of the container  12  to the other (FIG.  2 ). 
     After the mat  10  containing the mixture of fiber and mortar  14  has been prepared, it is transferred from the container  12  to a box-like mold  20  (FIG.  3 ). Drain holes (not shown) are drilled through the bottom of the mold  20  to allow water to escape, and the bottom of the mold  22  is covered with a layer  24  of fabric that will act as a filter which will allow water to escape through the drain holes, but retain the cement and sand. The non-woven form liner material, ZEMDRAIN® (DuPont Non-wovens, Old Hickory, Tenn.) is an example of a suitable material. The mortar-fiber mixture  26  is placed as an even layer over the liner filter material  24 . The thickness of the fiber-mortar layer  26  is adjusted so that it is slightly thicker, preferably 1 to 5% thicker, than the thickness of the finished cement board. Another fabric filter layer  28 , preferably a piece of ZEMDRAIN®, is placed over the mortar-fiber mat  26  and a lid  30 , that has been drilled through with drain holes (not shown), is placed over the filter fabric (ZEMDRAIN®)  28  and pressed down evenly. Pressure is maintained on the top  30  of the mold  20  while the mold  20  is vibrated. After the mortar-fiber mixture  26  has consolidated and the thickness of the mortar-fiber layer  26  is reduced to that desired for the finished panel, vibration is stopped. The mold  20  and its contents are then transferred to a warm, moist storage area to allow the mortar-fiber mixture  26  to set and cure. 
     When the cement board (hardened mortar-fiber layer  26 ) has achieved sufficient strength so that it will not crack when it is de-molded (typically this takes 3 to 4 days); the cement board is removed from the mold  20 . The filter fabric  24 ,  28  is removed and the “green” (not completely cured) cement board is maintained in a moist condition until it cures and achieves a strength that approaches its ultimate strength. Typically, this takes about 28 days at 23° C. The rate of strength gain can be accelerated by exposing the curing board to steam or moist heat. After curing, the finished cement board can be trimmed with a diamond saw, if desired, and packed for transportation and use in construction. 
     The method of vibrating and combing the mortar mixture  14  into a mat  10  of fibers is the desired way to disperse the fibers through the mixture  26  without first separating and chopping the fibers to a convenient size, i.e., 20 to 25 mm length. A steel fiber-reinforced concrete has been known to be manufactured by placing a layer of mortar over a layer of fibers and vibrating the layers to mix them (Josifek, C. and Lankard, D. 1987. “SIFCON: Slurry infiltrated fiber concrete.” Proc. Fiber Reinforced Concrete Int. Symp., 7.15-7.23). This works with dense fibers such as steel fibers, but will not work with light fibers. It is therefore necessary to use a combing action to mix the low-density fibers like nylon or polypropylene with mortar. 
     The use of filter fabric layers  28  and  24 , and drainage holes above and below the mortar-fiber layer  26 , during molding, results in a stronger panel than could be produced by simple casting. The increased cement/water ratio and the lack of surface “bugholes” produced by air bubbles results in a more architecturally acceptable panel than simple casting would produce. 
     The ability of the technique of the present invention to use tangled or matted fiber  10  makes it much more economical in manufacturing cement board than the methods that require the use of virgin fiber or recycled fiber which has been chopped, cleaned and separated. The use of a tangled mass of fibers also increases the pull-out resistance of the individual fibers over the pull-out resistance of conventional short, 20-25 mm long, fibers. 
     The invention can be used in any mixture system where a slurry material must be mixed with a fiber-reinforcement. This would include operations, such as: 
     1) Manufacture of wall board or plasterboard; 
     2) Production of fiber-reinforced molded plastic panels, such as fiber-reinforced epoxy; 
     3) Manufacture of fiber-reinforced paper board; and 
     4) Fiber reinforcement of soil embankments, or embankments stabilized with soil-Portland cement mixtures. 
     While this invention has been described as having preferred ranges, steps, materials, or designs, it is understood that it is capable of further modifications, uses and/or adaptations of the invention following in general the principle of the invention, and including such departures from the present disclosure, as those come within the known or customary practice in the art to which the invention pertains and as may be applied to the central features hereinbefore set forth, and fall within the scope of the invention and of the appended claims.