Abstract:
The present invention relates to an improved concrete additive product comprising synthetic concrete reinforcing fibers packaged in a closed paper package, whereby under the influence of mechanical action in a concrete mixer, the packaging material disintegrates and the fibers are uniformly distributed throughout the fresh concrete mixture. The synthetic fibers may additionally be coated with a dispersant. The present invention also relates to the methods of using the above improved concrete additive product.

Description:
TECHNICAL FIELD 
     This invention relates to an improvement in the field of concrete additives useful in decreasing the potential for early drying cracking of concrete. Specifically, this invention relates to a concrete-ready bag containing reinforcing fibers which is added directly to a concrete mixer, or similar apparatus, during a concrete mixing operation. 
     BACKGROUND 
     It is well known in the construction industry to add fibers to fresh concrete to improve the characteristics of the resulting hardened concrete structure. Fibers, such as steel, glass or synthetic materials are typically added to the mixture. See for example, U.S. Pat. No. 4,665,109 to Pedersen, et al., issued May 12, 1987; U.S. Pat. No. 4,426,458 to Woodhams, issued Jan. 17, 1984; and U.S. Pat. No. 4,210,009 to Farfor, et al., issued Jul. 1, 1980. Fiber-reinforced concretes are said to have improved fracture toughness as well as a retarded degree of crack propagation. 
     These concrete-reinforcing fibers are packaged and sold in polyethylene bags and the fibers are added to the concrete mixture by opening the package and shoveling or dumping the fibers directly into a concrete mixer, or similar apparatus, during the concrete mixing operation. This labor intensive task is often messy and can also result in a non-uniform dispersion of fibers when clumps of fibers become encased in the fresh concrete mixture and resist wetting due to their hydrophobic nature. Accordingly, it is desirable to have a means of dispersing concrete reinforcing fibers which is less labor intensive, less messy and more effective at uniformly distributing the fibers through out the mixture. 
     It is an objective of the present invention to provide a concrete additive product in the form of a fiber-containing package which is easier to administer to a concrete mixing operation and which also imparts improved fiber distribution throughout the fresh concrete mixture. 
     It is also an object of the present invention to provide a method for uniformly distributing fibers throughout fresh concrete. 
     These and other objects will be made apparent from the following: 
     SUMMARY OF THE INVENTION 
     In the construction field, many methods of strengthening concrete have been developed through the years. One modern method involves distributing fibers throughout a fresh concrete mixture. Upon hardening, this concrete is referred to as fiber-reinforced concrete. Fibers can be made of steel, glass, or synthetic materials, e.g., polypropylene, nylon, polyethylene, polyester, rayon, high-strength aramid, (i.e. Kevlar®), or mixtures thereof. Preferred fibers of the present invention are synthetic fibers. Preferred synthetic fibers, according to the present invention, are manufactured from 100% virgin polypropylene in collated, fibrillated form. Preferred fibers are about 1/2 to about 3/4 inch in length. Fibers, in general, are further discussed in ASTM designation C116, &#34;Standard Specification for Fiber-Reinforced Concrete and Shotcrete&#34;, incorporated herein by reference. 
     In commercial applications, the fibers are typically added to a concrete mixer by shoveling the fibers from a shipping bag or merely opening the bag and dumping the contents directly into the concrete mixer during the concrete mixing operation. This process is very labor intensive, very messy, and often results in a non-uniform dispersion of fibers, since hydrophobic fibers, like polypropylene, resist wetting and can clump together into slow dispersing balls. Surprisingly, it has been discovered that improved dispersion of fibers can be achieved by packaging the fibers in a bag or pouch which disintegrates during the concrete mixing operation. Thus, the fibers are gradually dispersed as the concrete mixes. It has also been found that this distribution, as well as concrete strength, can be enhanced by including a dispersant in the packaging of the fibers. 
     Specifically, the present invention relates to a method for providing a relatively uniform distribution of fibers throughout a fresh concrete mixture by placing one or more closed packages containing a cumulatively effective amount of fibers directly into the fresh concrete mixture under sufficient agitation so as to cause the packaging material to disintegrate and dispense the fibers. 
     The present invention also relates to an improved concrete additive product in the form of synthetic fibers suitable for preventing early cracking of concrete, wherein the improvement comprises containing the fibers within a closed paper bag, whereby under the influence of mechanical action in a concrete mixer, the fibers are uniformly distributed throughout the fresh concrete. Preferably the improved concrete additive product further comprises an effective amount of dispersant packaged with the fibers. 
     The present invention also relates to a method for uniformly distributing synthetic fibers throughout a fresh concrete comprised of the steps of: (a) placing a closed package containing an effective amount of said fibers directly into said fresh concrete, and (b) mixing the fresh concrete in a batch type concrete mixer for sufficient time to cause the packaging material to disintegrate and dispense said fibers, wherein the package material is paper. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is an illustrative representation of an exemplary concrete admixture package of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a concrete admixture package 10 of the invention which comprises synthetic fibers 12 operative to dispense throughout a volume of fresh concrete upon agitation of the concrete and to reinforce the concrete when set; and a closed non-soluble paper bag 14 enclosing the fibers 12, the bag operative to disintegrate in agitated fresh concrete and uniformly distribute the fibers throughout the fresh concrete. 
     As used herein, the term &#34;effective amount&#34; of reinforcing fibers means an adequate quantity of fibers per cubic meters of hardened concrete to impart an improvement in the early crack resistance of the resulting material. In most concrete operations, this means from about 0.1 lbs. to about 300 lbs. of fibers per cubic meter of concrete. For synthetic fibers, the effective amount is from about 0.2 lbs. to about 20.0 lbs. per cubic meter of concrete, preferably from about 3/4 to about 3 lb. per cubic meter. Often, more than one bag of fiber material is added to a commercial concrete mixer. As a result, the total amount of fibers from the bags must &#34;cumulatively&#34; result in an effective amount. Typically, one bag containing about 1.5 lb. of fibers is added to each cubic meters of concrete (dry weight). 
     As used herein, the term &#34;uniform distribution &#34; or &#34;relatively uniform distribution&#34; means that the fibers are distributed in such a manner as that no clumps of fiber larger than 0.5 inches (1.27 centimeters) in diameter can be detected in the mixture. 
     As used herein the term &#34;batch type concrete mixer&#34; means any batch mixer suitable for thoroughly mixing cement and aggregates so as to obtain a homogeneous mass and coat all particles with cement paste. Preferred concrete mixers are: (1) rotating mixers, consisting of a revolving drum or a square box revolving about its diagonal axis and usually provided with deflectors and blades to improve the mixing; or (2) paddle mixers, consisting of a stationary box with movable paddles which perform the mixing. Rotating mixers are most preferred for use in the present invention. 
     Many manufacturers have developed water soluble papers. For example, Gilbreth Company, Philadelphia Pa., markets &#34;Dissolve&#34;, which is a water soluble paper prepared by coating synthetic paper with polyvinyl alcohol. The resoluble papers comprise carboxy methyl cellulose and the sodium or potassium salt of carboxy methyl cellulose. (See U.S. Pat. No. 3,859,125 issued Jan. 7, 1975 to Miller, et al.) These specialized papers would surely dissolve in the aqueous environment of a concrete mixing operation. However, these papers are very expensive and, without being bound by theory, it is believed that these papers would dissolve too rapidly and could produce a large clump of fibers within the mix which might resist distribution. Furthermore, the alcohol coatings of the soluble paper have a detrimental effect on the resulting concrete as they tend to detrain air in the wet mix. 
     Applicants have discovered that a packaged material prepared from paper of a non-soluble, traditional variety abrades more slowly and, surprisingly, distributes the fibers very uniformly throughout the fresh concrete mixture. These non-soluble papers tend to disintegrate upon the wet abrasion found in the concrete mixer, they do not dissolve, because the cellulosic materials found within the paper are insoluble in water. The abrasion of the sand, gravel and other concrete components causes the paper to disintegrate, i.e. fragment into pieces which are unnoticeable to the human eye and have no detrimental effect on the properties of the finished concrete. Preferred papers contemplated in the present invention include repulpable and beater paper, shopping bag kraft paper, and multiwall kraft paper. The most preferred papers are repulpable, beater papers. Flexible paper container material are further described in Kirk-Othmer, Encyclopedia of Chemical Techonolgy, 3rd ed. (1981), vol. 16, page 801, incorporated herein by reference. 
     One paper which is particularly effective in the present invention is a 50 lb. white beater paper. This paper is fabricated from 100% pine pulp, has a basis weight of about 50 lb., a machine direction tear of about 109, a machine direction tensile of about 16, sizing of about 0, a brightness (TAPPI) of about 80.0, and a moistron moisture of about 5.6%. These paper specification determinations are further described in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd ed., (1981), Vol. 1b, pp. 771-780, incorporated herein by reference. This paper can be fabricated into a bag or pouch. Union Camp Corporation, Wayne, N.J., fabricates a 50 lb. white multi-wall beater paper bag which is most preferred in the present invention. 
     Bags or pouches can be fabricated in any shape, provided that they fit into the fill opening of a standard concrete mixture. A preferred embodiment of the present invention includes 1.5 lb. of a polypropylene fiber contained in a 15&#34;×14&#34; flat pillow pouch fabricated from the 50 lb. white multiwall beater paper bag described above. 
     The bag or pouch is typically placed inside the concrete mixer drum via the drum opening. This may be done before introducing the other concrete components, during the introduction of the concrete components, after the introduction of the concrete components, or any combination of the three. Mixing times should be at least about 5 minutes. 
     Applicants have discovered that it is also helpful to seal bags of the present invention with a water soluble adhesive. These adhesives can be any water soluble or water miscible adhesive which imparts sufficient bond strength to prevent premature opening of the bag in transit. It is also important that the adhesive does not impart any deliterious qualities to the resulting concrete. A typical water soluble adhesive suitable for use in the present invention is a one-part acrylic copolymer emulsion adhesive. 
     It has also been discovered that distribution of fibers can be improved by including a dispersant in the package along with the fibers. These dispersants can be water-reducing and high-range water-reducing dispersants selected from the group consisting of lignosulfonates (e.g., sodium lignosulfonate), naphthlene sulfonate, malemine sulfonate, &#34;superplasticizers&#34; (like those described in U.S. Pat. Nos. 4,518,725 to Arfaei on Mar. 21, 1989; 4,657,593 to Aignesberger et al. on Apr. 4, 1987; and 4,814,014 to Guicquero on May 21, 1985, incorporated herein by reference), and mixtures thereof. Preferred dispersants are lignosulfonate and naphthlene sulfonate. Liquid dispersants are added to the fibers by spraying or any other acceptable coating means. Dry dispersants, in powder form, may be added directly to the bag containing the fibers. The ratio of dispersant to fibers is typically from about 1:1 to about 1:15 w/w. The preferred ratio of dispersant of fibers is from about 1:6 to about 1:9 w/w. The level of dispersant can vary based on the dispersant itself. 
     The following examples depict typical embodiments of the present invention: 
     EXAMPLE I 
     Method of Preparing the Improved Concrete Additive Product of the Present Invention 
     A quantity of 1.5 lb. of collated, fibrillated polypropylene fibers which are 3/4&#34; in length and are weighed. The fibers are distributed by W. R. Grace &amp; Co.-Conn. under the name GRACE FIBERS™. These fibers have the following typical properties: 
     
         ______________________________________Specific Gravity         0.91Absorption               NoneModulus of Elasticity    500 ksiMelt Point               160° C.Ignition Point           590° C.Alkali, Acid + Salt Resistance                    High______________________________________ 
    
     The fibers are spray coated with naphthlene sulfonate dispersant solution, wherein the fibers are coated with 90 gm of dispersant. 
     The coated fibers are manually packaged in a 14&#34;×15&#34; 50 lb. white multi-wall beater paper flat pillow-type bag, manufactured by Union Camp Corp., Wayne, N.J. The bag comprises one open end which has a lip coated with a water soluble pressure sensitive adhesive. The adhesive is protected by a cover strip to prevent contamination of the adhesive surface. 
     After the bag is full, the cover strip is removed from the lip at the open end of the bag, exposing the adhesive. The adhesive lip is folded so that the bag is closed and the adhesive is contacting the bag fully. Manual pressure is then applied to seal the bag firmly. Finally, the bag is placed in a cardboard box for shipping. 
     EXAMPLE II 
     Alternative Method of Preparing the Improved Concrete Additive Product of the Present Invention 
     A quantity of 1.5 lb. of collated, fibrillated polypropylene fibers which are 1/2&#34; in length are weighed. The fibers are distributed by W. R. Grace &amp; Co.-Conn., Cambridge, Mass. under the name GRACE FIBERS™. These fibers have the following typical properties: 
     
         ______________________________________Specific Gravity         0.91Absorption               NoneModulus of Elasticity    500 ksiMelt Point               160° C.Ignition Point           590° C.Alkali, Acid + Salt Resistance                    High______________________________________ 
    
     The fibers are manually packaged in a 14&#34;×15&#34; 50 lb. white multi-wall beater paper flat, pillow-type bag, manufactured by Union-Camp Corp., Wayne, N.J. The bag comprises one open end which has a lip coated with a water soluble, pressure-sensitive adhesive. The adhesive is protected by a cover strip to prevent contamination of the adhesive surface. 
     90 gm. of sodium lignosulfonate (lignosite 458. manufactured by Georgia-Pacific Corp.) are added directly into the bag through the opening. 
     The bag is fed into an automatic sealing/folding machine. The machine then removes the cover from the lip, folds the adhesive lip to close the bag, and applies enough pressure to seal the bag. The bag is then put into a cardboard box for shipping. 
     EXAMPLE III 
     Method of Using the Improved Dispersant-Free Concrete Additive Products of the Present Invention. 
     A quantity of 1.5 lb. of collated, fibrillated polypropylene fibers which are 1/2&#34; in length are weighed. The fibers are distributed by W. R. Grace &amp; Co.-Conn., Cambridge, Mass. under the name GRACE FIBERS™. These fibers have the following typical properties: 
     
         ______________________________________Specific Gravity         0.91Absorption               NoneModulus of Elasticity    500 ksiMelt Point               160° C.Ignition Point           590° C.Alkali, Acid + Salt Resistance                    High______________________________________ 
    
     The fibers are manually packaged in a 14&#34;×15&#34; 50 lb. white multi-wall beater paper flat, pillow-type bag, manufactured by Union-Camp Corp., Wayne, N.J. The bag comprises one open end which has a lip. 
     The bag is fed into an automatic sealing/folding machine. The machine then applies the adhesive to the bag lip, folds the bag to close the bag, and applies enough pressure to seal the bag. The bag is then put into a cardboard box for shipping. 
     EXAMPLE IV 
     Method of Using the Improved Concrete Additive Products of the Present Invention. 
     The concrete additive product of Example I is removed from the cardboard box. The bag is placed in a revolving drum-type rotating concrete mixer containing 1 m 3  of fresh ready-mix concrete mixture through the drum opening. The fresh concrete and bag are mixed for 5 minutes. No lumps of fibers greater that 1/2 inch (1.27 cm) in diameter are observed in the resulting fresh concrete. 
     EXAMPLE V 
     Alternative Method of Using the Improved Concrete Additive Products of the Present Invention 
     The concrete additive product of Example II is removed from the cardboard box. The bag is placed in a revolving drum-type rotating concrete mixer via an automated magazine feed dispenser which introduces the bag to the other concrete components at a rate of one bag per 1 m 3  of concrete. Water is added to the dry mix and the fresh concrete slurry is mixed by rotating the drum for 5 minutes. No lumps of fibers greater and 1/2 inch (1.27 cm.) are observed in the resulting fresh concrete.