Abstract:
A unitized fibrous construct for providing reinforcement to castable structures, such as cementitious structures is claimed. The construct includes a bundle of reinforcing fibers or filaments that are held in place prior to addition to the cementitious mixture by a retaining element. The retaining element is of such a composition that upon release into the cementitious mixture it provides reinforcing capability to the cement structure. As such, the construct adds additional reinforcing capability and diminishes the likelihood of detrimental side-effects attributed to retaining elements that otherwise dissolve or disperse in the cementitious mixture.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims benefit of U.S. provisional application No. 60/603,091, filed on Aug. 20, 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention is directed to unitized fibrous constructs for reinforcing castable mixtures, such as cementitious matrices or mixtures and, more particularly a unitized fibrous construct in which the circumferential retaining element that retains a bundle of reinforcing fibers or filaments also serves as a reinforcing element upon mixture into the castable mixture.  
       BACKGROUND OF THE INVENTION  
       [0003]     Many proposals have been made to reinforce, strengthen, and/or reduce cracking during curing or otherwise beneficially alter the properties of castable mixtures, such as cementitious mixtures, by applying and/or incorporating various types of fibrous components, including asbestos, glass, steel, as well as synthetic polymer fibers to aqueous based concrete mixes prior to the curing of the concrete. The types of polymer fibers in use or proposed for use include those composed of natural and synthetic composition. As is evident in the prior art, individual fibrous components are well known in terms of their performance modifying attributes. Relatively large diameter fibers, for example, in excess of 40 to 60 microns in diameter, can be added to a cementitious mixture such as a wet concrete blend, dispersed in the blend by mechanical agitation, followed by pouring and curing of the concrete. Large diameter fibers serve to reinforce the concrete after it has been cured, by providing additional tensile strength and minimizing impact damage and crack propagation. Small diameter fibers, typically less than 30 to 40 microns in diameter, and having a relatively high surface area, are commonly added to concrete mixes in order to reduce the development of small elastic shrinkage cracks in the concrete during the curing period. The problem of crack development is known to occur as a result of uneven curing of the concrete. The fibrous components used typically in the practice of reinforcing cementitious mixtures include specifically thermoplastic synthetic fibers of finite staple length, such as polypropylene staple fibers.  
         [0004]     Due to the variable and unpredictable form conventional reinforcing fibrous components have heretofore been provided for end-use consumption, such as at a construction work-site, the accurate and reproducible dosing of reinforcing fibrous component into sequential batches of cementitious mixtures has been dubious at best. Further complicating the actual utilization of the reinforcing fibrous components, numerous synthetic thermoplastic polymers used in the formation of suitable staple fibers are inherently hydrophobic in nature. As a result, difficulties can arise in obtaining a uniform dispersion and blending of the reinforcing fibrous component throughout hydrous cementitious mixtures using conventional mixing equipment.  
         [0005]     Prior attempts to address the issue described have focused on the use of binding agents. U.S. Pat. No. 5,399,195, entitled, “Fibres and material comprising the same”, issued on Mar. 21, 1995, in the name of inventors Hansen et al., discloses the addition of small amounts of fine (less than 30 microns) polymer fibers to concrete. During production, the filaments are treated with a topical wetting agent. After the filaments are chopped into staple-length fibers, the wetting agent holds or binds the staple fibers together in the form of micro-bundles. The micro-bundles remain relatively stable during handling, and when the fibers are added to the concrete mix, the wetting agent promotes dispersion of the fibers. U.S. Pat. No. 6,258,159, entitled, “Product and method for incorporating synthetic polymer fibers into cement mixtures”, issued on Jul. 10, 2001, in the name of inventor Pyle, attempts to address the forming of micro-bundles of fibers by incorporation of binding agents into the staple fibers themselves during the melt-extrusion process.  
         [0006]     The use of binding agents, whether internal or externally applied, while improving in-part issues inherent of individual staple fibers, such practices have not obviated such problems as random agglomerate size, and further, the use of binding agents has introduced additional problems. Most notably, the corresponding performance of the binding agent is based upon application of the binding agent to the reinforcement fibrous components such that the binding agent is both uniformly applied to the majority of the fibers so as to obtain equivalency within the batch, and that no excess binding agent is introduced as such will adversely effect the ability of the reinforcement fibrous components to disengage and distribute homogeneously. One other determent encountered in the use of binding agents is that air is often entrained within the micro-bundles upon application and agglomeration of the staple fibers. When such micro-bundles are subjected to mechanical mixing, the entrained air is released as a foam, which reasonably compromises the ability of the cementitious mixture to cure uniformly.  
         [0007]     Cellulosic tapes have also been utilized to retain reinforcement fibers; however, such tapes can become problematic for a cementitious matrix or mixture as well. See for example U.S. Pat. No. 5,807,458, entitled, “Reinforcing Elements for Castable Compositions”, issued Sep. 15, 1998, in the name of inventors Sanders et al. The cellulose tape is prone to degradation in the alkaline environment of the mixture. Degradation of the tapes may introduce void spaces within the mixture which can negatively impact uniform curing of the cement. Further, the wet cellulose tapes can promote mold growth within the mixture that can lead to cracks in the setting mix.  
         [0008]     More recently, circumferential binding elements have been utilized to provide temporary retention of fibrous constructs, as disclosed in commonly assigned U.S. Patent Publication 2004/0244653, entitled “Unitized Fibrous Concrete Reinforcement”, filed on Dec. 9, 2004, in the name of inventors Schmidt et al, which is herein incorporated by reference as if set forth fully herein. Heretofore, the circumferential binding element was purposeful as a retaining element, but did not contribute incremental functionality within the cementitious matrix.  
         [0009]     As is evident in the industry, an unmet need exists for a means of introducing reinforcing fibrous components into a cementitious mixture such that the reinforcing fibrous components exhibit the attributes of uniform and predictable presentation for use, while the circumferential retaining elements, which temporarily bind the oriented fibrous components, further provide an advantageous and incremental performance within the cementitious matrix.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention is directed to unitized fibrous constructs for reinforcement in a castable compound, such as a cementitious matrices or mixtures. The invention provides for a construct that includes a bundle of reinforcing fibers or filaments surround, at least partially, by a retaining element, which also serves the dual purpose, upon addition to the cementitious mixture, of acting as a reinforcing element. In this regard, the retaining element does not need to dissolve or otherwise be dispersible upon addition to the cementitious mixture. As such, degradation issues with dispersible materials are eliminated, such as issues related to void spaces in the mixture and possible mold issues leading to crack propagation. In addition, by creating a construct in which the retaining element serves as a reinforcing element further strengthening and stability of the overall cementitious mixture is imparted from a single unitized fibrous construct.  
         [0011]     In one embodiment of the invention a unitized fibrous construct for reinforcing a cementitious mixture includes a plurality of reinforcing filaments or fibers oriented in a generally parallel relationship such that the plurality of reinforcing filaments or fibers form a unit having a circumferential exterior surface. The unit will those typically form the geometry of a cylindrical bundle of filaments or fibers, although other geometries of the unit are herein contemplated and within the bounds of the present invention. The construct also includes a retaining element that serves as a reinforcing element in the cementitious mixture. The retaining element surrounds at least a portion of the circumferential exterior surface and retains the plurality of reinforcing filaments or fibers prior to adding the construct to the cementitious mixture. Thus, once the construct is formed, the circumferential retaining element aids in maintaining the integrity of the unitized fibrous construct, and the fibrous component therein, for purposes of shipment, measurement, and dosing into a cementitious mixture. Typically the retaining element will be spirally wound around the plurality of fibers or filaments, such that the retaining element provides temporal retention of the bundle of fibers or filaments prior to immersion in the cementitious mixture. In most instances, minimal spiral winding is required, less than about 30% coverage of the surface area of the circumferential exterior surface of the unit, so as to insure that the fibers and filaments become free from containment upon agitation in the cementitious mixture. Upon mechanical agitation of the unitized fibrous construct in a cementitious mixture, the circumferential retaining element is disrupted, allowing for the homogenous release, distribution, and dispersion of the reinforcing filaments and fibers into the overall cementitious mixture and release of the circumferential retaining element itself into the mixture, which also serves as a reinforcing element.  
         [0012]     Typically, the retaining element will be formed of a similar material, and in some embodiments the identical material, as is used to form the reinforcing fibers or filaments. The circumferential retaining element may be selected from suitable materials that are considered structurally beneficial to a cementitious matrix by providing additional reinforcement, minimize impact damage, and crack propagation. Such fibrous or filamentary material at least partially or may entirely include super absorbent polymers, splittable fiber or filaments, and fiber or filaments with three-dimensionality, such as coiled or crimped. Further, such materials may consist of thermoplastic, thermoset and partially soluble resins, which are subject to mechanical failure when a corresponding stress and/or solvency threshold is exceeded. The material selected may also be mechanically modified, as exemplified by fibrillation, drawing, perforation, crimping, embossing or molding, so as to exhibit performance attributes in the cementitious matrix such as a reinforcement or elastic shrinkage crack reduction.  
         [0013]     Various geometries may be employed in the application of the circumferential retaining element, including without limitation, continuous or discontinuous filaments, ribbons, or sheets, which circumscribe the combined, essentially parallel reinforcing fibrous components. It is within the purview of the present invention that the composition of the circumferential retaining elements and of one or more of the reinforcing fibrous components need not necessarily be the same.  
         [0014]     It is further within the purview of the present invention that the retaining element may be placed under additional tension by means of twisting the retaining element. Placing additional tension on the retaining element facilitates the mechanical removal of the retaining element upon mechanical agitation, which then enhances the fiber distribution within a cementitious mixture.  
         [0015]     It is also noted that while the present embodiment includes a single retaining element it is possible, and within the inventive concepts herein disclosed, for more than one retaining element to be used in connection with a single unitized reinforcing construct. For example, two reinforcing elements may be spirally wound around the unit of fibers or filaments in a double-helix type arrangement.  
         [0016]     The reinforcing filaments are continuous filaments and in fiber embodiments the fibers are finite staple-length fibers. Additionally, the reinforcing filaments may be characterized as fibrillated reinforcing filaments. The reinforcing filaments or fibers may be imparted with tension during processing to insure that the degree of dispersion necessary occurs once the bundle of filaments or fibers are free from retention within the cementitious mixture. In alternate embodiments the reinforcing filaments or fibers may be splittable filaments or fibers or may be formed from a super absorbent polymer composition.  
         [0017]     In another embodiment the unitized fibrous construct for reinforcing a cementitious mixture includes a plurality of reinforcing filaments or fibers oriented in a generally parallel relationship such that the plurality of reinforcing filaments or fibers form a unit having a circumferential exterior surface. The construct also includes a retaining element formed of one or more splittable filaments that surround at least a portion of the circumferential exterior surface and retains the plurality of reinforcing filaments or fibers prior to adding the construct to the cementitious mixture. Typically, the splittable filaments will provide reinforcing capabilities once they have been added to the cementitious mixture  
         [0018]     The reinforcing filaments or fibers may have a composition similar to or identical to the composition of the splittable filament retaining element. Additionally, the plurality of reinforcing filaments or fibers may be defined as fibrillated reinforcing filaments, which may be imparted with tension to further encourage dispersion upon release from the retaining element. The reinforcing filaments or fibers may further be defined as being formed from a super absorbent polymer composition.  
         [0019]     In yet another embodiment the unitized fibrous construct for reinforcing a cementitious mixture includes a plurality of reinforcing filaments or fibers oriented in a generally parallel relationship such that the plurality of reinforcing filaments or fibers form a unit having a circumferential exterior surface. The construct also includes a retaining element formed of a super absorbent polymer composition that surrounds at least a portion of the circumferential exterior surface and retains the plurality of reinforcing filaments or fibers prior to adding the construct to the cementitious mixture. Typically, the super absorbent polymer composition retaining elements will provide reinforcing capabilities once they have been added to the cementitious mixture.  
         [0020]     The reinforcing filaments or fibers may have a composition similar to or identical to the composition of the super absorbent polymer composition retaining element. Additionally, the plurality of reinforcing filaments or fibers may be defined as fibrillated reinforcing filaments, which may be imparted with tension to further encourage dispersion upon release from the retaining element. The reinforcing filaments or fibers may further be defined as being formed from a super absorbent polymer composition.  
         [0021]     Thus, the present invention is able to provide for a cementitious reinforcing construct that includes a retaining element that imparts reinforcing structure into the cementitious mixture. Such a construct benefits from not having a retaining structure that disperses or otherwise dissolves in the aqueous cementitious mixture and imparts possible negative side-effects to the cementitious mixture, such as voids, strength reducing mold and the like. Additionally, the reinforcing aspect of the retaining element provides for a construct that is able to provide additional per unit reinforcement of the cement mixture. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0022]      FIG. 1  is an illustrative embodiment of the unitized fibrous construct of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     While the present invention is susceptible of embodiments in various forms, hereinafter the present invention is described by presently preferred embodiments with the understanding that the present disclosure is to be considered as an exemplification of the invention, and is not intended to limit the invention to the specific embodiment illustrated.  
         [0024]     Referring to  FIG. 1 , therein is illustrated an embodiment of a unitized fibrous construct of the present invention. The unitized fibrous construct is added to a castable mixture, such as a cementitious mixture to provide added reinforcement, resulting in greater strength, stability and crack-resistance. The unitized fibrous construct  10  is defined herein as a construct including a plurality of oriented reinforcing continuous filaments or finite staple length fibers  12 . The filaments or fibers  12  are arranged in a general parallel relationship such that the filaments or fibers form a bundle. While the bundle will typically have a general cylindrical shape, the bundle may also have any other shape, for example oval, square, triangular, etc. The plurality of filaments or fibers  12  will be bundled such that they form a circumferential exterior surface  14 .  
         [0025]     The construct further includes one or more retaining elements  16  that surround at least a portion of the circumferential exterior surface  14  and serve to retain the reinforcing filaments or fibers  12  prior to adding the construct  10  to a castable mixture, such as a cementitious mixture. The retaining element will serve as a reinforcing element upon once added to the castable mixture, such as a cementitious mixture.  
         [0026]     In order for the retaining element  16  to serve as a reinforcing element upon addition to the castable mixture the retaining element will typically be formed of a similar, and in some embodiments identical, fibrous or filamentary material, denier, and length as the reinforcing fibers or filaments  12 . Further still, in alternate embodiment the retaining element  16  may be of a dissimilar fibrous or filamentary material, denier, and length as the reinforcing fibers or filaments  12 . In those embodiments in which the retaining element is a dissimilar fibrous or filamentary material compared to the reinforcing fibers or filaments, the retaining element will be formed of a material that allows for the retaining element to provide reinforcing characteristics upon addition to the castable mixture.  
         [0027]     Typically, the unitized fibrous construct of the present invention is formed from a plurality of reinforcing fibrous or filamentary components and one or more circumferential retaining elements. The composition of such reinforcing fibers and circumferential retaining element may be formed from any suitable synthetic polymers, including, but not limited to, thermoplastic and thermoset polymers, including polyesters, polyolefins, such as polypropylene and polypropylene copolymers, polyethylene and polyethylene copolymers, polyamides, polyimides, polylactic acid, polyhydroxyalkanoate, polyvinyl alcohol, ethylene vinyl alcohol, polyacrylates, copolymers thereof, and the combinations thereof. Additionally the reinforcing fibers or filaments and the circumferential retaining element may be formed from any suitable natural fibers, including, but not limited to rayon, cotton, pulp, flax, and hemp and the combinations thereof. A particularly preferred embodiment of the present invention is directed to reinforcing fibers or filaments including polyolefin thermoplastic resins.  
         [0028]     In one embodiment of the invention the retaining element that surrounds a portion of the exterior surface includes splittable filaments, which may be of similar or dissimilar polymeric composition in relation to the reinforcing fibers or filaments. Suitable splittable fibers are taught in U.S. Pat. No. 6,838,402, issued on Jan. 4, 2005, in the name of inventors Harris, et al.; U.S. Pat. No. 6,746,766, issued on Jun. 18, 2004, in the name of inventors Bond, et al.; U.S. Pat. No. 6,743,506, issued on Jun. 1, 2004, in the name of inventors Bond et al.; and U.S. Pat. No. 6,444,312, issued on Sep. 9, 2002, in the name of inventor Dugan, all of which are herein incorporated by reference as if set forth fully herein.  
         [0029]     In embodiments in which the retaining element is splittable filaments, the plurality of reinforcing filaments may be fibrillated, wherein the filaments may be fibrillated by any conventional fibrillation technique, such as by mechanical fibrillation described in U.S. Pat. No. 3,302,501, issued on Feb. 7, 1967, in the name of inventor Greene; U.S. Pat. No. 3,496,260, issued Feb. 17, 1970, in the name of inventors Guenther et al.; U.S. Pat. No. 3,550,826, issued Dec. 29, 1970; in the name of inventor Salmela; and U.S. Pat. No. 3,756,484, issued Sep. 4, 1973, in the name of inventor Guenther, or by fluid and sonic fibrillation as disclosed in U.S. Pat. No. 3,345,242, issued Oct. 3, 1967, in the name of inventor Rasmussen, all of which are hereby incorporated by reference as if set forth fully herein. In addition, the reinforcing filaments may be imparted with tension by way of twisting the filaments as well. Tension imparted in the reinforcing filaments will cause greater dispersion of the filaments once the retaining element has been removed from the construct/bundle of filaments.  
         [0030]     Additionally, in embodiments in which the retaining element is splittable filaments, the plurality of reinforcing fibers or filaments may be formed from a super absorbent polymer composition. Exemplary super absorbent polymers are disclosed in U.S. Pat. No. 5,145,609, issued Sep. 8, 1992, in the name of inventor Chambers; U.S. Pat. No. 4,820,773; issued Apr. 11, 1989, in the name to inventors Alexander et al.; and U.S. Pat. No. 4,645,039, issued Mar. 31, 1997; in the name of inventor Brandt et al., all of which are herein incorporated by reference as if set forth fully herein.  
         [0031]     In another embodiment of the invention the retaining element that surrounds a portion of the exterior surface may include a super absorbent polymer composition. Exemplary super absorbent polymers are disclosed in the previously referenced and incorporated patents.  
         [0032]     In those embodiments in which the retaining element is formed of a super absorbent polymer composition, the reinforcing fibers may include splittable fibers. Suitable splittable fibers are taught in the previously referenced and incorporated patents.  
         [0033]     According to the present invention, the retaining element surrounds at least a portion of the circumferential exterior surface of the construct. Once formed, the retaining element aids in maintaining the integrity of the unitized fibrous construct, and the reinforcing fibrous component therein, for the purposes of shipment, measurement, and dosing into a cementitious mixture. Upon mechanical agitation, and optionally exposure to appropriate solvents, the unitized fibrous construct in a cementitious mixture, the retaining element are disrupted, allowing for the homogenous release, distribution, and disbursement of the reinforcing fibrous component into the overall cementitious mixture. The unitized fibrous construct of the present invention is believe to reduce plastic shrinkage cracking by at least 10% per ASTM 1399, Obtaining Average Residual Strength of Fiber Reinforced Concrete.  
         [0034]     A number of suitable methodologies exist for the formation of unitized fibrous constructs in accordance with the present invention. A preferred, though non-limiting, method is taught in part by U.S. Pat. No. 4,228,641, issued on Oct. 1, 1980, in the name of inventors O&#39;Neil, this patent is herein incorporated by reference as if set forth fully herein. The &#39;641 O&#39;Neil patent teaches a twine including a core bundle of synthetic monofilaments circumscribed by a synthetic material in a thin band form spirally wound about the monofilaments. It has been found by the inventors of the present invention that by practice of the method taught in the &#39;641 O&#39;Neil patent, with subsequent and repeated scission of the continuous twine construct at or between each iteration of the spiral winding that finite length unitized fibrous constructs are formed which are suitable for practice in light of the present invention.  
         [0035]     The dimensions of the retaining element is defined in terms of the overall circumference of the exterior surface formed by the reinforcing fibers or filaments, as based on the quantity and relative denier of the individual reinforcing fibrous components, and of length, as based on the greatest finite staple length of the cumulative combination of reinforcing fibrous components. Suitable overall circumferences and lengths of the circumferential retaining elements formed in accordance with the present invention may reasonably range from 3 mm to 150 mm and from 8 mm to 100 mm, respectively. In a presently preferred embodiment for standard practices, circumferential retaining elements exhibit an overall diameter of between 3 mm and 30 mm and lengths of between 12 mm and 50 mm may be utilized. Further, the circumferential retaining elements may exhibit a width preferably about 1%-50% of the total diameter of the unitized fibrous construct, more preferably about 3%-40% of the total diameter of the unitized fibrous construct, and most preferably about 5%-30% of the total diameter of the unitized fibrous construct. Further still, the circumferential retaining element is preferably about 2%-50% by weight of the unitized construct including parallelized reinforcement fibers, more preferably of about 6%-40% by weight of the unitized construct, and most preferably of about 8%-30% weight of the unitized construct.  
         [0036]     The circumferential retaining element may include one or more continuous or discontinuous filaments, ribbons, or sheets of varying thicknesses that retain the reinforcing fibrous components by a plurality of wrapping techniques so as to expose more or less fiber to the external environment. For instance, two thin circumferential retaining elements may be used in a double helix wrapping technique, whereby two circumferential retaining elements criss-cross back and forth about the circumference of the fibrous components.  
         [0037]     Thus, the present invention is able to provide for a cementitious reinforcing construct that includes a retaining element that imparts reinforcing structure into the cementitious mixture. Such a construct benefits from not having a retaining structure that disperses or otherwise dissolves in the aqueous cementitious mixture and imparts possible negative side-effects to the cementitious mixture, such as voids, strength reducing mold and the like. Additionally, the reinforcing aspect of the retaining element provides for a construct that is able to provide additional per unit reinforcement of the cement mixture.  
         [0038]     From the foregoing, it will be observed that numerous modifications and variations can be affected without departing from the true spirit and scope of the novel concept of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated herein is intended or should be inferred. The disclosure is intended to cover, by the appended claims, all such modifications as fall within the scope of the claims.