FIBER REINFORCED BUILDING MATERIALS

Abstract: In accordance with the present invention, there are provided novel fiber reinforced building material formulations, comprised of an inorganic binding agent and synthetic fibers. The fibrous material employed in invention formulations is capable of undergoing progressive fibrillation upon agitation. As a result, tougher building materials, due to higher fiber addition rates than previously possible, are produced. Formulations containing Portland cement-based compositions and fibrillating synthetic fibers are also contemplated. In addition, there are provided methods of producing fiber reinforced building materials, including Portland cement-based compositions, and articles produced therefrom.

Description: FTBER REINFORCED BUILDING MATERIALS FIELD OF THE TNNE TTON The present invention relates to fiber reinforced building m.aterials. In a p.articu r aspect, tiie invention relates to methods for the production of building materials reinforced with synthetic fiber that, under agitation, progressively fibrillates, to produce building materials with enhanced perfoimance properties. In .another .aspect of the present invention, there are provided articles prepared from the .above-described fiber reinforced materi.als. BACKGROUND OF THE TNVENTTON Concrete has the largest production of .all man made lralerials. Comp.ared with other construction materials, it possesses many advantages including low cost, general availability of raw m^eriak, adaptability and utilώation under different environmental conditions, Therefore, concrete will most probably continue to be the dointπant construction materi.il in the foreseeable future. Unfortunately, pl-ain concrete is also a brittle τasteάal with very low tensile strength .and ^ain capacity, generally requiring reinforcement before it can be used extensively as a construction material. The idea of using another material to reinforce a low tensile strength material is an age-old concept. For example, straw and horsehair have been used for thous.ands of years to improve the properties of clay bricks. Bentur, A., Mindess, S., "Fiber Reinforced Cementitious Composites," (Elsevier Applied Science, 1990). In more recent years, fibers have been incorporated into a wide range of engineering materials (including ceramics, plastics, cement, and gypsum products) to enhance the perform.ance properties of the renting composite. American Concrete In^tute ACl 544.1R-96, "Fiber Reinforced Concrete," 1996, IntrOiduction of fibers into concrete results in post-el.astic property changes that range from subtle to substantial, depending upon a number of factors, including matrix .strength, fiber type, fiber modulus, fiber aspect ratio, fiber strength, fiber .surface bonding characteristics, fiber content, fiber orientation, aggregate size effects, and the like. The enhanced properties include tensile strength, compressive strength, elastic modulus, crack resistance, crack control, durability, fatigue life, resi.st.ance to imp-act .and abrasion, shrink-age, expansion, theπωl characteristics, a . nd fire re stance. Id. Although fiber reinforcement is known to be more effective than conventional reinforcement in the control of local cracking, unlike reinforcing bars, it does not, in most cases, provide any increase in the load bearing c . apacity of concrete. Convention^ reinforcing b.ars .are strategically located in the .structure to carry tensile stresses while fibers arc distributed randomly in the concrete mixture. Fibers, therefore, .are not used in design as a .substitute for conventional reinforcement. Although not currently addressed by ACl Committee 318, fibers are .sometimes used in structural .applications with conventional re . inforcement .American Concrete Institute, ACl 318 Building Code Requirements for Reinforced Concrete, 1995. The practice of adding steel fibers to concrete to overcome its drawb.ac5ks was firet introduced early in this century. Between 1920 and 1935 several patents ps- rtaining to steel fiber reinforced concrete (SFRC) were granted. See, e.g., Kleinl-agel, A., German Patent No. 388.959; Scailles, J.C, French Patent No. 514.186; Martin, G.C., US Patent No. 1,633,219; and Etheπidge, H., US Patent No. 1,913,707. Use of gla- ss fibers in concrete was firat attempted in the USSR in the kite 1 50s. Biiyukovich, .L., .and Yu, D.L., "Glass Fiber Reinforced Cement," (translated by G.L. Cairns, CERA Translation, No.12, Civil Eng. Res. Assoc, London, 1965). Initial attempts at using synthetic fibers (nylon, polypropylene) were made in the 1960s. Monforc, G.E., "A review of Fiber Reinforced Portland Cement Paste, Mortar and Concrete," J. Res. Dev. Labs, Vol. 10, No. 3, Sept. 1968, pp. 36-42; Goldfein, S., "Plastic Fibrous Reinforcement for Portland Cement," Technical Report No. 1757-TR, U.S. Army Rese∑irch Development Laboratories, Fort Belvoir, Oct 1963, pp. 1-16. hen steel fibers first were used, only .straight steel fibers were employed. The use of steel fibers resulted in improved characteristics for ductility and fracture toughness; flexural strength increases were .also reported, For straight steel fibers, the primary factors that controlled the properties of the composite were fiber volume fraction and length/diameter, or aspect ratio of the fibers. The amount of fibers ranged from 90 to 120 kg/m (1.1 to 1.5% by volume) of concrete. The aspect ratios were in the range of 60 to 100. The major probl-sms encountered in the early stages were difficulty in mixing .and workability. At higher volume fractions, fibers were found to b.all up during the mixing process. This process, called balling, was found to occur frequently for longer fibers. This tends to .affect the qu.ality of concrete in place, especially for higher fiber volume fractions. Furthermore, there w-as always a reduction in workability of the concrete as a re^t of the addition of fibers. The advent of deformed steel fibers in the late 1970's resulted in increased use of fiber reinforced concrete in the field. Ramakrishnan established that fibers with hooked ends can be used at much lower volume fr-actions than straight steel fibers, producing the same results in terms of product ductility and toughness. Ram∑ύcrishnan, V., Brandshaug, T., Coyie, W.V., and Schrader, EJL, "A Comparative Evalu^on of Concrete Reinforced with Straight Steel Fibers and Deformed End Fibers Glued Together in Bundles," ACl Journal, Vol. 77, No.3, May-June 1980, pp. 135-143. These fibers were glued together at the edges with water soluble glue .such that, when added to the concrete, the fibers bad a much lower (.apparent) aspect ratio. During muting, the fibers were separated and dispersed as individual fibers. The gluing .and .sub-sequent disperse, in combination with a lower volume fraction of fibers, resulted in virtual elimination of balling. Later, a number of other fiber shapes such as crimped, paddled, and enlarged ends were also developed. The ACl 544 Committee Report on Fiber Reinforced Concrete, published in 1996, reports that the first significant use of synthetic fibers in concrete was done in 1965, by the US Army Corps of Engineers Research and Development Section. Ameήcaα Concrete Institute ACl 544.1R-96, 'Tiber Reinforced Concrete," 1996. Synthetic monofilament fibers were used for construction of blast-resistant concrete structures. The fibers used were 13 to 25 mm long and had an aspect ratio of between 50 to 100, i.e. geometry not too different from the steel fibers being used in concrete at that time. With these fibers it waε found that addition rates of up to 0.5% by volume of the concrete rented in significant increases in ductility .and impact resistance. There was, however, very little commercial exploitation of fiber reinforcement technology and it was not until the 1980's that large scale development and use of synthetic fibers in concrete started to take place. This work was predominantly done with much lower denier fibers (i.e. small diameter fibers with high aspect ratios) at lower fiber .addition rates. Morgan, D.R., and Rich, L., "High Volume Synthetic Fiber Reinforced Shotcrete," The First International Conference on Synthetic Fiber Reinforced Concrete, Orlando, Florida, USA, January 16, 1998. Most work was performed with collated, fibrillated polypropylene fibers at 0,1 to 0.2 % by volume addition rates. At these lower fiber volume addition rates, the prim.ary benefits of the fibers are for plastic shrinkage crack control -and provision of green strength to extruded .and certain green-cast, precast concrete products. Enhancement of ductility and impact resistance, and resirtance to long term restrained drying .shrink-age cracking is limited at such low fiber volume .addition rates. It should be noted that even at these low fiber addition rates, the fiber count (number of fibers in a unit volume of matrix) and .specific surface (surface area of fibers per unit volume of matrix) is very high. Consequently, it is currently very difficult to introduce in concrete more ttøn 0.4% by volume of conventional fibrillating polypropylene fibers without making significant changes to the concrete mixture design, As a result, the majority of .synthetic fibers used today are incorporated in concrete at very low fiber addition rates to simply control plastic shrinkage. With the emergence of new zteas of .application, research interest has moved to higher fib-sr contents where toughness index .and other factors are design considerations. Toughneβs index is an indication of the lo.ad-canying capabilities of the fibers within the concrete matrix after first crack. As previously mentioned, cast-in-place concrete will accommodate up to 0.4% by volume of .synthetic fibers with minimal mix proportion adjustments. Wet mix shotcrete with fibers added at a rate of up to 0.75% by volume will provide major increases in toughness index values. Morgan, D.R., McAskill, N., Richardson, B.W., -and Zellers, R.C., "A Comparative Evaluation of Plain, Polypropylene Fibers, Steel Fibers, and Wire Mesh Reinforced Shotcrete," Transportation Research Board, Washington D.C., Jan. 1989. Fiber length .and fiber configuration are important factors at mis fiber content, In slab-on-grade applications, the use of collated fibrillated polypropylene fiber at contents up to 0.3% by volume has dramatically increased the fatigue .strength. American Concrete Institute ACl 544.1R-96, 'Tiber Reinforced Concrete," 1996. A few years ago, a new monofilament, polyolefin fiber, with a unique dispensing system, was developed, which has now been used at fiber addition rates in the 1.0 to 2.0% by volume range (i.e. values up to 10 times greater than the conventional use of fibrillated polypropylene fibers). The fiber has been used in a range of different concrete fiatwork and other cast-in-place concrete apphcations, e.g. full-depth concrete pavement, bridge deck overlays, whitetopping, etc. Rarnakrislu , V., and MacDonald, C.N., "Durability Evaluation and Performance Hirtories of Projects Using Polyolefin Fiber Reinforced Concrete," ACl Bri.ti.sh Columbia Chapter, High Performance Concrete Seminar, Vancouver BC, April 1997, p. 15. The fibers used range in length from 25 to 50mm and have aspect ratios in the range of 66 to 80. At these much higher fiber addition rates, ductility, impact resistance and toughness in the concrete -composites are substantially increased and are much more comparable to values achieved with steel fiber reinforced concretes, with 0.5 to 0.7 % (40 to 55 kg m 3 ) fiber addition by volume. Ap∑ut from demonstrating excellent .reinforcing characteristics the polyolefin fiber has the advantage over its .steel counterpart in that it would never rust Following the same philosophy (use of polymeric fiber at high addition rates), Synthetic Industrie hias just released a new polymer fiber for shotcrete applications. The new fiber, called S-152 High Perfoπnmce Polymer (HPP), is mmufactur.ed as a -coarse filament with .an engineered contoured profile. Synthetic Industries, product literature, 1998. The wave-like sh-ape of the fibers is designed to anchor the fibers in the shotcrete. Additionally, the ccarseness of the fiber allows it to be blended at much higher rate per unit volume than conventional fibers, thereby giving the shotcreted application enhanced structural performance. Polyolefin fiber is, however, of limited utility because it is a monofilament fiber that will remain in its original form after mixing. It has a relatively low surface area and hence has correspondingly poor bonding characteristics. Therefor, one must introduce a relatively large percent by volume (1.5% .and higher) in order to achieve beneficial results, Addition of fibers to concrete will generally result in loss of slump and handling characteristics of the mixture. This loss is magnified as the aspect ratio (length/ diameter) of the fiber or the addition rate of fibers increases. For conventionally mixed fiber reinforced concrete, high aspect ratio fibers are more effective in improving the po.3t-pe.ak perfoπn.ance because of their high reastance to pullout from the matrix. A detrimental effect of using high aspect ratio fibers is the potential for balling of the fibers during mixing. Most synthetic fibers used today are fibrill^ed fibers having very high surface are.as and aspect ratios. The very high surface areas of these fibers make it very difficult to produce a worlcable concrete mixture at higher fiber addition rates than 0.5% by volume, without causing severe workability and fiber balling problems. For this re.ason, synthetic fibers axe mostly used at 0.1% by volume fiber .addition rates, and are added mostly for the control of shrinkage cracking in concrete. Thus, there is still a need in the art for fiber reinforced concrete formulations that overcome the disadvantages noted above, while still m.aintaining superior shrinkage and handling characteristics. More particularly it would be desirable to be able to employ fiber of a type that is less sensitive to balling and can therefor be .added at higher volume fractions. Higher volume fractions will result in increased reinforcing characteristics, previously unattainable with fiber-reinforced building materials such as concrete, BRIEF DESCRIPTION OF THE INVENTION The present invention addresses the .above-described needs in the .art by providing fiber reinforced building materi.als, such a . s concrete, having improved performance properties such as reduc- ed plastic shrinkage, reduced drying shrinkage, improved fire resistance, improved fatigue life, improved resistance to thermal expansion and conn-action, higher toughness index, improved workability and h∑mdling, and the like. Invention reinforced building materi.als -are prepared using fibrous material having defined initial properties and the .specific ability to fibrillate resulting in substantially increased surface area upon mixing. The initial low surface area of fibrous material contemplated for use acco.rding to the invention .allows the addition of a relatively high fiber content without making any changes to the concrete mixture design or using -any time rele- ase bonding agent to avoid balling of the fibere. The ability of fibrous material employ^ herein to undergo progressive fibrillation enables one to .achieve a uniform distribution of fibers throughout the concrete mix in the early .stages of mixing, while the fibers are still relatively intact. Subsequently, when the fibers start to fibrill^e, they do not, at that stage, tend to ball since they have already been well dispe- rsed in the concrete mix. PRIEF DESCRIPTION OF THE FIGURE Figure 1 graphically illustrates the flexural toughness curve of a ".shotcrete" formulation containing 1.5% by volume of monofilament fibers having perfoπnance/physical properties as described for use in the practice of the present invention. O 99/46214 DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, there a . re provided building product formulations comprising a mixture containing inorganic binding agent and in the range of about 0, 1 up to about 3.0 percent by volume of a fibrous material, wherein said fibrous m^erial is characterized by having: (a) a low initial aspect ratio, (b) an initial .surface area of no greater than about 200mm ; wherein said fibrous material is capable of, and undergoes, progressive fibrillation under agitation of said formulation, reciting in .an average increase in surface area of at least about 20 percent, preferably at least about 50 percent. Also provided herein .are methods of producing the above-described building product formulation as well as articles comprising the formulation. As employed herein, "building product formulation" refers to a variety of construction materials and matrices including, Portland cement-biased formulations and articles produced therefrom, such as concrete, shotcrete, bricks, mortar, plaster, white-top, synthetic composites, carbon-based composites, .and the like, In a preferred embodiment of the invention, the Portl.and cement-based formulation is concrete comprised of Portlmd cement, stone (such as gravel or .crushed rock) and sand. Those of skill in the art can r.eadily identify inorganic binding materials suitable for use in the practice of the present invention. As used herein, the term "inorganic binding materials" refers to predominantly non-carbon containing materials that serve to hold together the v-mous solid constituents of an aggregate. Examples of materials .contemplated for use herein include poitl-and cement, clay, stucco, plaster of pads, and the like. Such materials, including those currently available and those developed in the future, jure contemplated for use in compositions and methods of the present invention. As used herein, "fibrous material" refers to a synthetic monofilament tending to bre.ak up by progressive splitting of the fibers, typically from the ends of the fibers inwards (i.e., "fibrillate"), under appropriate conditions, into a plurality of various length filaments, from full length to microscopically small, each of much smaller cross-sectional area and higher aspect ratio than the original monofilament. It is, of course, recognized by those of skill in the .art thzit the fibrous material may not completely split or break apart, but may remain one unit composed of a plurality of fibrils (i.e., may be partially fibrillated). In one aspect of the present invention, a population of long, short, attached and detached fibrils may be expected under the appropriate conditions. Conditions suitable for generating the fully and parti-ally fibrillated fibers include agitation, mixing, vibrating, -spraying, and the like. The resulting variety in fiber size and aspect ratios of fibrillated fibers will contribute to a range of enhanced characteristics such as workability, toughness .and resistance to shrinkage. The fibrous material contempl-ated for use herein typically has such desirable performance properties as resilience, tensile strength, toughness, resistance to changes in pH, and resistance to moisture, sufficient to render such materials useful for reinforcing building product formulations under standard loads and conditions. In a specific embodiment, fibrous material contemplated for use herein is comprised of flat, crimped and or embossed fiber articles. In mother aspect of the present invention the initial cross sectional dimensions of the original .synthetic monofilament are about 1.1mm x 0.37mm. In •accordance with another .specific -aspect of the invention, fibrillated or partially-fibrillated fibrous material comprises a fine network structure of fibers of a synthetic polymer blend. As used herein, the phrase "network .structure" conforms to the noπn.al us.age of the term, i.e, the fibrillated and partially-fibrillated fibers form a relatively disordered mesh or tangled net-like structure. The modifier "fine", as used in the phrase "fine network structure", denotes the inherently srn.all nature of the network due to the size of the fibers described herein for use in invention compositions and methods. 10 Examples of suitable synthetic polymer blends contemplated for use herein include polymer blends of polypropylene and polyethylene. Preferably, the polyethylene/polypropylene blend employed herein will have a mass of about 7.5 grams per denier, a specific gravity of about 0.94 and a stretch elongation at bre.ak in the range of about 16% up to about 18%. In this preferred embodiment the polymer blend is comprised of in the range of about 70 up to about 90% polypropylene resin having a melt flow rate in the range of about 1.2 up to about 4 g/10 min. and a specific gravity in the range of about 0,88 up to about 0.90 g/ cm 3 . The other component of the presently preferred polymer-blend is in the range of about 10 up to about 30% high density polyethylene resin with a melt flow rate of in the range of about 0.6 up to about 1,1 g/10 min and a specific gravity of in the range of about 0.94 up to about 0,96g/ cm 3 . In a preferred aspect of the invention, the fibrous network conasts of the .above-described polyethylene polypropylene polymer blend exclusively and is not held together by any type of adhesive agent. Exemplary fibers of this type are made under the name of "Polysteel™" and are available in rope form from East Coast Rope Ltd., of Sydney, Nova Scotia, Canada. Fibers contemplated for use in accordance with invention compositions find methods may be produced by my method known in the ar In one aspect of the present invention, fibers contemplated for use in the practice of the invention are m.anufactured by individually extruding a filament which is subsequently quenched .and then stretched in a stretching oven. The filament is then reheated in an annealing oven to relax the filament and lock in the "memory" of the filament. The filament may then be embossed to create flexibility and enhance grip ability of the filament. Finally, the filament is cut to the specified length (application dependent) using, for example, a rotatory cutting wheel, Of course, as readily recognized by those of skill in the art, other suitable methods for producing fibers meeting the fiber specifications set forth herein may also be employed. As employed herein, "aspect ratio" means the length of a fiber divided by the di.ameter of a cylindrical fiber having a similar cross-sectional area. In accordance with the 11 present invention the fibrous material employed has a low initial aspect ratio. Suitable aspect ratios can be readily determined by those of skill in the .art, Typically, the initial aspect ratio will fall in the range of about 30 up to about 80. As will be readily understood by those of .skill in the art, any value in the above-described range may be employed in the practice of the present invention, depending on the particular formulation of invention compositions, the intended use, the desired property(ies) of invention compositions, .and the like. For example, in one aspect of the invention, when preparing formulations useful for pumped concrete (eg. "shotcrete"), the initial aspect ratio should be at the lower end of the range, typically be about 50, In another aspect of the invention, when preparing formulations useful for poured or cast in place concrete (such as slabs) the initial aspect ratio should be at the higher end of the range, typically be about 70. As readily recognized by those of skill in the art, a wide range of fiber lengths are suitable for use in the practice of the present invention. As will be understood by those of skill in the art, the length of fibers to be employed in the practice of the present invention willl vary depending on the paτticul.ar formulation of invention compositions, the intended use, the desired property(ies) of inv-ention compositions, .and the like. For example, in one .aspect of the invention, whenprep.aring formulations useful for pumped concrete, the initial fiber length for fibrous material contemplated for use herein will be relatively short, typically about 38mm. In another aspect of the invention, when p.reparing formulations useful for poured or cast in place concrete, fiber length will be somewhat longer, typically about 50mm. As used herein, the "low iπitia. l surface area" contemplacted for the fibrous material employed herein is no greater than .about 200mm . It is presently preferred that the initial surface area be no greater than about 150mm . In a specific embodiment for use in the prep.aration of Port nd cement-based compositions that are to be pumped (eg. "s.hotcrete" and the like), an initial surface .area of about 110 mm 2 is preferred. In a .specific embodiment for use in the preparation of Portland cement-based compositions th.at .are to be cast or poured in-place, the preferred initial surface area is about 150mm . 12 As employed herein, "agitation" refers to any means of blending/mixing the contents of the inv-ention formulations, All such me∑tns are contemplated for use in the practice of the present invention. Agitation may be accomplished by any mechanical means, such as, for example, by mixing, rotating, stirring, shaking, pouring, kneading, vibrating, pumping, and the like. Additional means of agitation contemplated for use in the present invention include ultrasonic vibration tod thermally induced mixing or turbulence. In a presently preferred embodiment, the agitation will occur through the mechanical action of a cement mixer. Use of the term "fibrillation" in the present claims and specification, refers to the progressive separation or splitting of the initial low-surface-area fibrous material into individu memb-ers of the component fibrous network. In a given population of fibrous material that h.as undergone fibrillation, some of the initial low-surface-area fibrous material may remain substantially intact and unseparated, while others of the starting fibers may substantially completely separate. According to the present invention, following fibrillation, a range of separated fibers will exist, resulting in an average increase in surface area of the population of fibrous material of in the range of at least about 20 percent, preferably at least about 50 percent, hi a particularly preferred embodiment, the fibrous material will have undergone an average increase in surface area of at least 100 percent. In an especially preferred embodiment the population of fibers will represent an average increase in surface area of the fibrous material of at least 200 percent. In a preferred embodiment of the present invention, the progressive fibrillation of the fibers allows one to achieve a near uniform distribution of the fibers throughout the concrete mix in the early stages of the mixing while the fibers are still relatively intact (i.e., prior to the fibrillation thereof), As will readily be understood by those of skill in the .art, even the slightest increase in surface area of the fiber (e.g., 5% and up), caused by a minimal level of fibrillation, will lead to improvements in the overall performance properties (e.g., flexural toughn.ess, ptastic 13 shrinkage, drying shrinkage, fire resistance, fatigue life, resist-ance to theπn.al expansion .and contraction, impact resistance, workability, pumping tod handling, and the like) of the fiber reinforced building materials over that .achieved with the original (i.e., non-fibrillated) monofilament fiber. More substanti.al increases (e.g., in the range of at least about 50 percent) in surface area of the fiber will le^ to significant improvements in performtoce properties. Fibrillation of fibers contemplated for use in accord ce with the present invention will lead to average incre.ases in the surface area of the fibrous material anywhere up to about 20,000% or higher. In spite of these average values, those of skill in the art will readily recognize that even at high percentage increases in the surface area, some fibers will remain intact and show no visible increase in surface area after mixing .and placing, In accordance with one aspect of the present invention, there are provided building product formulations comprising the herein-descaibed fibrous matcήal in the range of about 0.1 up to about 3.0 percent by volume. Such buikiing product formulations show improved characteristics, when compared to other fiber reinforced building formulations, such as reduced plastic shrinkage, reduced drying shrinkage, improved fire resi.stance, improved fatigue life, improve. d resi4Stance to thermal expansion a . nd contraction, improved impact resistance, increased flexural toughness, improved workability, pumping .and handling, tod the like. In accordance with another aspect of the present invention, there are provided building product foπnulations comprising in the range of about 0.1 up to about 0.3 percent by volume of the herein-described fibrous material. At these lower rates of fiber addition, such foπnulations demonstrate improved characteristics such as plastic shrinkage, drying shrinkage, improved fire resistance, improved fatigue life, improved resistance to thermal expansion tod contraction, improved workability, pumping and htodling, as well as some improvment in impact resistance .and flexural touglmess. In yet another aspect of the present invention, there are provided building product formulations comprising in the range of about 0.3 up to about 3.0 percent by volume of 14 the herein-described fibrous materi.al. At these relatively higher rates of fiber addition such foπnulations also demonstrate improved characteristics such as plastic shrinkage, drying slirinkage, improved fire resistance, improved fatigue life, improvisd resistance to thermal expansion and contraction, improved workability, pumping and handling, as well as substantial improvements in impact resistance and flexural toughness, In .accordance with another embodiment of the present invention, there are provided methods of producing building product foπnulations by adding the above- described fibrous material to inorganic binding materials wherein the formulation is subjected to agitation .sufficient to achieve an average increase in surface area of the fibers of at least about 20 percent, preferably at le.ast about 50 percent. These methods yield building materials having, when compared with other synthetic fiber reinforcement systems, improved characteristics such as reduced plastic shrinkage, reduced drying shrinkage, improved fire resistance, improved fatigue life, improved resistance to thermal expansion and contraction, improved impact resistance, increωed flexural toughness, improved workability, pumping and handling, tod the like. In one aspect of invention methods, in the range of about 0.1 up to about 0.3 percent by volume of fibrous material is added to a Portland cement-based composition which is then subjected to agitation as above, thereby providing building product fonmύatioris with improved ch.aracteristics such as plastic shrinkage, drying shrink-age, improved fire resi.stance, improved fatigue life, improved resistance to theπr l exp.ansion and contraction, improved work-ability, improved pumping and handling, as well as some improvment in impact resistance .and flexural toughness. In another aspect of invention methods, in the range of about 0.3 up to -about 3.0 percent by volume of a fibrous material is added to a Portland cement-based composition which is then subjected to agitation as above, thereby providing building product formulations with pl.astic shrinlrage, (hying shrinkage, improved fire resistance, improved fatigue life, improved resistance to thermal expansion and contraction, improved 15 W Orkability, pumping tod handling, as well as substantial improvements in impact resistance and flexural toughness. In accordance with another embodiment of the present invention, there are provided .articles comprising the building product formulations described above. In a preferred .aspect of the invention there .are provided articles comprising the Portland cement-based formulations described above. The invention will now be described in greater detail by reference to the following, non-limiting examples. EXAM ES In a recent experiment, it was demonstrated that 3000 denier Poly-steel™ fiber (available from E-ast Ccast Rope, Ltd., North Sydney, Nova Scotia), comprised of polyethylene polypropylene polymer blend with a mass of about 7.5 grams per denier, a .specific gravity of .about 0.94 and a stretch elongtoon at break in the range of about 16% up to about 18%, wlien added at a volume a<idition rate of 1% outperformed polyolefin fiber at 1.67% by volume (fiber of similar initi-al specific surface area, and identical tensile strenght tod modulus of elasticity) in both flexural toughness and plastic shrinkage performance. Similar tests were conducted on a series of steel fibers at fiber addition rates of 0.5 and 0.75 %; results show that the fibrillating fiber, when added at a volume addition rate of 1%, easily outperformed the steel fibers in the control of plastic shrinkage and drying shrinkage. Shotcrete tests conducted on fiber, having performance and physical properties described herein, reveals that the fiber is easily pumped and shot at fiber volume fractions up to 1.5%. A slight change in the concrete mixture design allowed the fiber to be pumped and shot at a very high percent addition rate of 2% by volume. One should note that it is almost impossible to pump .and shoot most fibrillated synthetic fibers available on the market at fiber .addition rates in excess of 0.5% by volume. Again, the initial low fiber 16 surface area of the monofilament fiber allowed the .addition of a very high .amount of fibers in the shotcrete. In the case of shotcrete, the fibrillating action was produced both by the mixing action of the concrete mixer and by the impact of the fibers onto the projected surface, The results, as illustrated in Figure 1, indicate that the fibrillating fiber has achieved a Toughness Performance Level V at 1.5% addition, a perform-ance never reached by any synthetic fiber before. Fiber .addition rates of 1% in shotcrete of the fibrillating fiber achieved Toughness Performance Level IV, which is .again, substantially higher that other synthetic fiber. While the invention .has been described in detail with reference to certain prefeπed embodiments thereof it will be understood that modifications and variations are within the scope and spirit of that which is described and claimed.

Claims: 17 That which is claimed: 1. A building product formulation comprising a mixture containing inorganic binding agent and in the range of about 0.1 up to about 3.0 percent by volume of a fibrous material, wherein said fibrous material is characterized by having: (a) a low initial aspect ratio, (b) an initial surface area of no greater than about 200mm 2 ; wherein said fibrous material is capable of, and undergoes, progressive fibrillation under agitation of said formulation, resulting in an average increase in surface area of at least about 20 percent. 2. A Portland cement-based formulation comprising Portland cement and in the range of about 0.1 up to about 3.0 percent by volume of a fibrous material, wherein said fibrous material is characterized by having: (a) a low initial aspect ratio, (b) an initial surface area of no greater than about 200mm 2 ; wherein said fibrous material is capable of, and undergoes, progressive fibrillation under agitation of said formulation, resulting in an average increase in surface area of at least about 20 percent. 3. A Portland cement-based formulation according to claim 2, wherein said initial aspect ratio falls in the range of about 30 up to about 80. 4. A Portland cement-based formulation according to claim 2, wherein said fibrous material consists essentially of integrated, flat, crimped fibers. 5. A Portland cement-based formulation according to claim 2, wherein said fibrous material is comprised of a fine network structure of filaments from a synthetic resin. 18 6. A Portland cement-based formulation according to claim 5, wherein said synthetic resin comprises a blend of polypropylene and polyethylene. 7. A Portland cement-based formulation according to claim 6, wherein said fibrous material has a mass of about 7.5 grams per denier, a specific gravity of about 0.94 and a stretch elongation of about 16% to about 18%. 8. A building product formulation according to claim 1, comprising in the range of about 0.1 up to about 0.3 volume percent of said fibrous material. 9. A building product formulation according to claim 1, comprising in the range of about 0.3 up to about 3.0 volume percent of said fibrous material . 10. A method for the production of a Portland cement-based formulation with improved plastic shrinkage and/or drying shrinkage characteristics, said method comprising adding in the range of about 0.1 up to about 3.0 percent by volume of a fibrous material to a Portland cement-based composition, wherein said fibrous material is characterized by having: (a) a low initial aspect ratio, (b) an initial surface area of no greater than about 200mm 2 ; wherein said fibrous material is capable of, and undergoes, progressive fibrillation under agitation of said formulation, resulting in an average increase in surface area of at least about 20 percent . 11. A method for the production of a Portland cement-based formulation with improved flexural toughness characteristics, said method comprising adding in the range of about 0.1 up to about 3.0 percent by volume of a fibrous material to a Portland cement-based composition, wherein said fibrous material is characterized by having: 19 (a) a low initial aspect ratio, (b) an initial surface area of no greater than about 200mm 2 ; wherein said fibrous material is capable of, and undergoes, progressive fibrillation under agitation of said formulation, resulting in an average increase in surface area of at least about 20 percent. 12. A method for the production of a Portland cement-based formulation with improved crack resistance and crack control, said method comprising adding in the range of about 0.1 up to about 3.0 percent by volume of a fibrous material to a Portland cement-based composition, wherein said fibrous material is characterized by having: (a) a low initial aspect ratio, (b) an initial surface area of no greater than about 200mm 2 ; wherein said fibrous material is capable of, and undergoes, progressive fibrillation under agitation of said formulation, resulting in an average increase in surface area of at least about 20 percent. 13. A method for the production of a Portland cement-based formulation with improved fatigue life, said method comprising adding in the range of about 0.1 up to about 3.0 percent by volume of a fibrous material to a Portland cement -based composition, wherein said fibrous material is characterized by having: (a) a low initial aspect ratio, (b) an initial surface area of no greater than about 200mm 2 ; wherein said fibrous material is capable of, and undergoes, progressive fibrillation under agitation of said formulation, resulting in an average increase in surface of at least about 20 percent .

Inventors: MAHONEY MICHAEL, TROTTIER JEAN-FRANCOIS, MAHONEY, MICHAEL, TROTTIER, JEAN-FRANCOIS
Applicants: MAHONEY MICHAEL, TROTTIER JEAN FRANCOIS, UNIV DALHOUSIE, DALHOUSIE UNIVERSITY, MAHONEY, MICHAEL, TROTTIER, JEAN-FRANCOIS
Application year: 1999
Main classification: C04B16
IPC codes: C04B16, C04B28, E04C5