HK1111947A - Lightweight, fiber-reinforced cementitious panels - Google Patents

Abstract

Lightweight, fiber reinforced, cementitious panels possessing exceptional toughness for use as building components in applications such as roofing elements, siding elements, framing and sheathing elements, and substrate elements for installation of floor finishes in residential and other building construction types. The panels employ a continuous phase resulting from the curing of an aqueous mixture of inorganic binder, PVA fibers and lightweight filler. The inorganic binder may be, for example, hydraulic cement alone, or a combination of hydraulic cement and pozzolan/s, or a combination of hydraulic cement, alpha hemihydrate, active pozzolan and optionally lime. The PVA fibers reinforce the continuous phase and are randomly distributed throughout the composite. Typical panels of the invention have a density of 60 - 85 pcf.

Description

Lightweight, fiber reinforced cement board

Technical Field

The present invention relates generally to lightweight panels suitable for the following applications: roof members, framing and cladding members, exterior wall panel members and underlayment members for installing floor finishes in homes and other types of housing structures, the panels having significantly improved flexural toughness due to the use of polyvinyl alcohol (PVA) fibers having selected characteristics such as reinforcement. More particularly, the present invention relates to panels capable of resisting impact loads applied by hail or other objects.

Background

Cementitious panels are used in the construction industry to form interior and exterior walls in residential and/or commercial buildings. Advantages of the board include moisture resistance compared to standard gypsum-based wallboard. However, a disadvantage of the conventional panels is that they are not sufficiently flexible to the extent that they are comparable, if not more flexible, to wood panels such as plywood or Oriented Strand Board (OSB).

Building structures are subjected to a variety of impact loads over their useful life (e.g., hail damage, or damage from objects thrown onto the building by tornados or hurricanes). Not all building sheathing panels are tough enough to withstand such impact loads. Where it is necessary to demonstrate impact load resistance, the sheathing panels were measured to determine the impact that the substrate could resist without failure.

Flexural toughness, as characterized in this specification, is measured as being equal to the total area under the flexural load versus deflection curve of the sample loaded in a four-point bend.

Flexural toughness is measured as the total area under the load versus deflection curve of a flexural sample loaded in a four point bend according to ASTM (american society for testing and materials) C947 test method.

Wood panels that achieve significant flexural toughness are typically plywood or Oriented Strand Board (OSB) made up of wood chips glued together. These panels can provide flexural toughness, but each is flammable and also not durable when exposed to water. Boards made from hydraulic cement resist water, but are much heavier and do not have sufficient flexural toughness compared to wood boards. It is believed that no panel is yet available that can provide the flexural toughness of the present invention while avoiding the drawbacks of plywood or OSB panels.

Furthermore, the need for cementitious panels configured to behave in a building environment similar to plywood or OSB panels means that the panels can be nailed and cut or worked using conventional saws and other conventional woodworking tools. It is also desirable that the cementitious structural panels have a low density to facilitate handling.

The board should be capable of being cut with a circular saw used to cut wood.

The plates should be capable of being fixed to the frame with nails or screws.

The panel should remain dimensionally stable when exposed to water, meaning that it should swell as little as possible, preferably less than 0.1% as measured by ASTM C1185.

The panels should not be biodegradable or susceptible to attack by insects or corrosion.

The panel should provide a bondable substrate for exterior finishing systems.

After 28 days of cure treatment, the density was 60lb/ft as measured by ASTM C947 test³(961kg/m³) To 75lb/ft³(1200kg/m³) The 0.5 inch (12.7mm) thick plate flexural strength of (a) is at least 750psi (5.2MPa), and preferably greater than 1000psi (6.9 MPa).

It is clear that the currently available cement-based and wood-based products and composites can only meet some, but not all, of the above performance characteristics. In particular, there is a need for improved lightweight cementitious substrates having improved flexural toughness and which exceed the performance of currently used cementitious and wood based panels by providing non-flammability and water resistance.

Although glass fibers are used to reinforce cement, it is known that strength will be lost over time as the glass is attacked by the lime present in the set cement. This phenomenon can be compensated to some extent by coating the glass fibers or using special alkali-resistant glass. Other fibers have been proposed for reinforcing cement, such as metal fibers, wood or other cellulosic fibers, carbon fibers or polymeric fibers. Column 10, lines 1-6, states that "although they do not provide comparable strength to glass fibers, it is possible to include certain polymer fibers in the panels of the invention. Such as polypropylene, polyethylene, polyacrylonitrile and polyvinyl alcohol fibers, which are less expensive and less susceptible to attack by lime than alkali-resistant glass fibers. "

U.S. patent No. 6,241,815 to Bonen, which is incorporated herein by reference, discloses a composition for use in building materials that can replace high performance concrete, repair materials, joint compounds (joints compounds), and the like, such as backer boards or boards comprising settable calcium sulfate (preferably hemihydrate), Portland cement (Portland cement), fine pozzolanic materials, lime, and aggregates optionally other additives. The aggregate to combined calcium sulfate, portland cement, pozzolanic material, and lime (cement binder) volume ratio is equal to or greater than 2/1. Boards made from this composition are available for good dimensional stability, especially when exposed to water.

US 4,199,366 a to Schaefer et al discloses a fiber reinforced cementitious material having short polyvinyl alcohol fibers in an amount of at least 2 volume percent based on the total volume of the material. These fibers have an elongation at break of between about 4% and 8% and a modulus of greater than 130 grams per dtex (g/dtex). A method of making the material is also disclosed. US 4,306,911 a to Gordon et al discloses a method of manufacturing a fibre-reinforced hydraulically setting material. US 4,339,273 a to Meier et al discloses a method of making a fiber-reinforced, hydraulically setting composition, the composition produced and its use. U.S. Pat. No. 5,298,071A to Vondran discloses a fiber hydratable cement composition comprising uniformly dispersed broken fibers in a hydratable cement powder. US 6,528,151B 1 to Shah et al discloses an extruded fiber reinforced cement matrix composite made by mixing cement, water, a water soluble binder, and relatively short discontinuous reinforcing fibers, preferably short polyvinyl alcohol fibers, to provide an extrudable mixture, then extruding the mixture into shape, and allowing the cement to set. US 6,723,162B 1 to Cheyrezy et al discloses a concrete comprising organic fibers dispersed in a cement matrix, a concrete cement matrix, and a premix. Some examples of the concrete use polyvinyl alcohol fibers. US 2002/0019465 a1 to Li et al discloses short fiber reinforced cement composites that are self-filling and can be prepared by adding hydrophilic polymer fibers to a cement composition containing a polymeric thickener and a superplasticizer. Nelson et al, J.Mat.Civil.Eng.2002, 9/10, of "Fracture Toughness of Microfiber Reinforced Composites" disclose the results of Fracture Toughness tests performed on sheet Cement Composites Reinforced with polypropylene (PP), polyvinyl alcohol (PVA) and refined cellulose fibers under air-drying conditions. However, the cement products in these references have high densities. In other words, the current state of the art of PVA fiber reinforced cement substrates presented in these references relates to high density boards rather than lightweight boards.

U.S. patent application No. 10/666,294, which is incorporated herein by reference, discloses a multi-layer process for making structural cement panels (SCP panels), and SCPs made by the process. After an initial deposition of loosely distributed chopped fibers or a layer of slurry on a moving web, the fibers are deposited on the slurry layer. It also discloses a Structural Cementitious Panel (SCP) produced by the method, and an apparatus suitable for producing a structural cementitious panel according to the method.

Disclosure of Invention

The present invention relates to a polyvinyl alcohol (PVA) fiber reinforced cement composition for making extremely tough, lightweight cement-based composites. The composition is a mixture of inorganic binder, lightweight filler and a variety of preferred PVA fibers. The material combination of the present invention has been found to be suitable for lightweight cement-based composites possessing significant toughness (energy absorption capacity). For the composites of the present invention, several orders of magnitude higher toughness is achieved than composites reinforced with other fibers such as alkali-resistant glass, carbon, or steel. The PVA fibers are selected to have preferred characteristics and parameters that result in good composite performance. These various preferred PVA fibers may be used in combination with other types of fibers such as alkali resistant glass, carbon, steel or other polymer fibers. Cement-based composites made using the disclosed formulations may be directed to a variety of applications in building construction. The disclosed formulations and resulting composites are particularly useful in applications where damage due to impact loads, such as hail damage, is highly valued. Examples of some potential applications include house roof tiles and exterior wall panels for buildings.

Typical compositions of embodiments of the inventive panel that achieve a combination of low density, improved flexural strength and nailability comprise an inorganic binder (examples: gypsum cement, portland cement, or other hydraulic cement) with selected PVA fibers, lightweight fillers (examples: uniform hollow glass microspheres, hollow ceramic microspheres, plastic microspheres, and/or perlite), and superplasticizer/high proportion water reducing admixtures (examples: polynaphthalenesulfonates, polyacrylates, etc.) distributed throughout the thickness of the panel.

The board may be a single layer board or a multilayer board. If desired, the single-layer or multilayer sheet can also have a screen, for example a glass fiber screen. A typical panel is made of a mixture of water and inorganic binder with selected PVA fibers, lightweight ceramic and/or polymer microspheres and a superplasticizer throughout the mixture. Other additives such as accelerating and retarding impurities, viscosity control additives may optionally be added to the mixture to meet the requirements of the manufacturing process involved.

A key feature of the cementitious panel of the present invention is that the panel is lightweight. Preferably, the density of the cement boards of the present invention is less than 85pcf, or more preferably, the density of the cement boards of the present invention is less than 70 pcf. The present invention employs selected PVA fibers in lightweight cementitious panels to achieve panels with advantageous properties.

Preferred fibers may be used alone or in combination with other types of fibers such as alkali resistant glass, carbon fibers, steel fibers, or other polymer fibers.

The flexural toughness of the composite is typically greater than 2.25 joules according to the flexural toughness characterization method described in this specification. Furthermore the panel may act as a shear panel when the fiber volume fraction is at least 2%.

Drawings

Fig. 1 is a schematic side view of a single-ply board of the present invention.

The data provided in fig. 2 shows the effect of fiber type and fiber volume fraction on the flexural toughness of lightweight, fiber reinforced cement-based composites.

The data provided in fig. 3 shows the effect of fiber type (at a fiber volume fraction of 2%) on flexural toughness of lightweight, fiber reinforced cement-based composites.

The data provided in fig. 4 shows the effect of fiber type and fiber volume fraction on the flexural strength of lightweight, fiber reinforced cement-based composites.

The data provided in fig. 5 shows the effect of fiber type and fiber volume fraction on the lateral fastening resistance of lightweight, fiber reinforced cement-based composites.

The data provided in fig. 6 shows the effect of fiber type and fiber volume fraction on the maximum deflection of lightweight, fiber reinforced cement-based composites.

The data provided in fig. 7 shows the effect of fiber type on the maximum deflection of a lightweight, fiber-reinforced cement-based composite.

The data provided in fig. 8 shows the effect of fiber type on the toughness of lightweight, fiber-reinforced cement-based composites.

The data provided in fig. 9 shows the effect of fiber type on the flexural strength of lightweight, fiber-reinforced cement-based composites.

Detailed Description

As previously mentioned, there is a need in the art for building panels that are lightweight and can replace currently available cement-based and wood-based panels to provide improved toughness against damage due to impact from hail or other objects carried by high winds. Wood-based panels and products generally provide adequate flexural toughness properties, but they are dimensionally unstable when exposed to water and can be subject to corrosion or insect attack. Currently available cement substrates and products have the following drawbacks: high product density, poor toughness properties, instability under freeze-thaw conditions leading to delamination of the board, poor mold and termite resistance of the board reinforced with cellulose fibers, and poor moisture resistance of the board reinforced with cellulose fibers.

Furthermore, when using wood-based panels or cement-based panels reinforced with cellulose fibers, it is necessary to spend considerable additional costs to apply a water-repellent coating or an additional water-repellent panel thereon to protect the panels from moisture. In contrast, the panels of the present invention are waterproof and dimensionally stable. The board may be cut with the tools used for wood boards and fixed to the frame with nails or screws. If necessary, a tongue and groove structure is possible.

The main raw materials used to make the panels of the invention are inorganic binders (e.g., calcium sulfate alpha hemihydrate, hydraulic cement, and pozzolanic materials), selected PVA fibers, lightweight fillers (e.g., perlite, ceramic microspheres, and/or polymer microspheres), superplasticizers (e.g., polynaphthalenesulfonates and/or polyacrylates), water, and optional additives.

Calcium sulfate hemihydrate

Calcium sulfate hemihydrate useful in the panels of the invention is made from naturally occurring mineral gypsum ore (calcium sulfate dihydrate CaSO)₄·2H₂O) is prepared. Unless otherwise indicated, "gypsum" will refer to the dihydrate form of calcium sulfate. After production, the gypsum is heat treated to form settable calcium sulfate, which may be anhydrous, but more typically is hemihydrate CaSO₄·1/2H₂And O. For familiar end uses, the settable calcium sulfate is reacted with water to pass throughDihydrate (gypsum) is formed to cure. The hemihydrate has two recognized forms, known as alpha hemihydrate and beta hemihydrate. These morphologies are selected for use in a variety of applications based on their physical characteristics and cost. Both forms react with water to form calcium sulfate dihydrate. Upon hydration, alpha hemihydrate is characterized as producing rectangular-faced gypsum crystals, while beta 0 hemihydrate is characterized as hydration producing acicular gypsum crystals, typically with a high aspect ratio. Either the alpha or beta form, or both, may be used in the present invention depending on the desired mechanical properties. Beta hemihydrate forms a lower density microstructure and is preferred for low density products. The higher density microstructure formed by alpha hemihydrate has a higher strength and density than the microstructure formed by beta hemihydrate. Thus, alpha hemihydrate can replace beta hemihydrate to increase strength and density or combine the hemihydrate to adjust properties.

Typical examples of inorganic binders used to make the panels of the present invention comprise hydraulic cement, such as portland cement, high alumina cement, pozzolan-blended portland cement, or mixtures thereof.

Another exemplary embodiment of an inorganic binder for use in making the panels of the present invention comprises a blend comprising alpha calcium sulfate hemihydrate, a hydraulic cement, a pozzolan, and lime.

Hydraulic cement(hvdraulic cement)

ASTM defines "hydraulic cement" as follows: a cement which sets and hardens by chemical interaction with water and which is capable of doing so in water. There are several hydraulic cements used in the construction and construction industries. Examples of hydraulic cements include: portland cement, slag cement, such as blast furnace slag cement and sulfate-rich slag cement, calcium sulfoaluminate cement, high alumina cement, expansive cement, white cement, and quick setting and quick hardening cement. Although calcium sulfate hemihydrate sets and hardens through chemical interaction with water, it is not included within the broad definition of hydraulic cement in the context of the present invention. All of the aforementioned hydraulic cements can be used to make the panels of the present invention.

The most common and widely used family of closely related hydraulic cements is known as portland cement. ASTM defines "portland cement" as a hydraulic cement obtained by grinding a clinker consisting essentially of hydraulic calcium silicates, usually containing one or more forms of calcium sulfate as a broken-up aggregate, into a powder. To produce portland cement, a homogeneous mixture of limestone, angalicous stone and clay is ignited in a kiln to produce clinker, which is subsequently further processed. As a result, the following four main phases of portland cement are generated: tricalcium silicate (3 CaO. SiO)₂Also known as C₃S), dicalcium silicate (2 CaO. SiO)₂Called C₂S), tricalcium aluminate (3 CaO. Al)₂O₃Or C₃A) And tetracalcium aluminoferrite (4 CaO. Al)₂O₃·Fe₂O₃Or C₄AF). Other compounds present in the portland cement in trace amounts include calcium sulfate and other double salts of basic sulfuric acid, calcium oxide and magnesium oxide. Of the various cognitive classes of portland cement, type III portland cement (ASTM classification) is preferred for making the panels of the present invention, found to provide greater strength due to its fineness. Other cognitive classes of hydraulic cements include: slag cements such as blast furnace slag cement and sulfate rich slag cement, calcium sulfoaluminate (calcium sulfoaluminate) cement, aluminous cement, expansive cement, white cement, fast setting and fast hardening cements such as set-setting cement and VHE cement, and other portland cement types can also be successfully used to make the panels of the present invention. Slag cement and calcium sulfoaluminate cement have low alkalinity and are also suitable for making the panels of the present invention.

PVA fiber

Substantial differences in the mechanical properties of the composite occur with the use of different types of PVA fibers. Thus, the present invention selects PVA fibers having characteristics believed to result in good composite performance. Table 1 lists the properties.

TABLE 1

Characteristics of the fibres	Numerical value
		Preferred diameter	10-400 microns
More preferable diameter	10-100 microns
		Optimum diameter	10-50 microns
Preferred fiber length	0.1 to 1.0 inch
		Better fiber length	0.20 to 0.75 inch
Optimum fiber length	0.20 to 0.5 inch (e.g., 0.25 inch)
		Preferred modulus of elasticity of the fiber	20 to 50GPa
Better modulus of elasticity of fiber	30 to 50GPa

The polyvinyl alcohol (PVA) fiber has the general formula of (-CH)₂-CH(OH)-)_nHaving a molecular weight of, for example, 13,000 to 100,000 and a density of, for example, 1.23 to 1.30gm/cc and can generally be prepared as is known in the art.

Preferred commercially available PVA fibers are listed in table 2.

TABLE 2

Preferred commercially available PVA fibers	KURALON REC15KURALON REC100LKURALON RM182KURALON RE182KURALON RBW203KURALON RKW1502KURALON RMS182KURALON RMH182KURALON RKW182KURALON RFS602KURALON RF350
		More preferred commercially available PVA fibers	KURALON REC15KURALON REC100LKURALON RMS182KURALON RFS602KURALON RKW1502
KURALON polyvinyl alcohol fibers are available from japan poultice (Kurashiki) kuraray co.

The PVA fibers are added to the cementitious substrate to provide such fibers in an amount of at least 0.50 volume percent, preferably 0.50 to 3.00 volume percent, in the resulting product. Fiber blends below 0.50% do not provide materials with the desired characteristics. Fiber mixtures above 3.00% by volume make the production of the desired product very expensive without any significant improvement in the flexural or impact strength. The individual fibers may be uniform in length or may vary.

The PVA fibers are uniformly distributed in the cement material. The fibers may be PVA monofilaments or PVA multifilament yarns. The cross-section of the fibers can have a variety of shapes, particularly shapes caused by physical and chemical changes in the manufacturing process. For example, the spinning solution material, precipitation bath and spinneret nozzles may be different. In this way, the production of round fibers, multilobal fibers, hollow fibers, porous fibers, etc. can be facilitated. The outer surface of the fibers may be roughened, split or bonded by physical post-treatment methods.

PVA fibers can be easily chemically modified due to their high chemical reactivity. Various functional groups such as carboxyl group, amide group, nitrile group, phosphoric acid group, sulfuric acid group, etc. can be introduced by addition reaction or radical reaction. Brighteners or binders can be introduced onto or into the fibers by purely physical means and can assist in the anchorage of the PVA fibers in the cementitious material. By the above method, the PVA fiber can be made to have inflammability, hydrophobicity or crosslinkability. All PVA fibers modified in this way are suitable as fillers in the present invention.

The polyvinyl alcohol fibers may be added to the cementitious material alone or in combination with glass or other synthetic or natural fibers, according to the method of the present invention. In addition to reinforcing fibers, adjuvants such as cellulose waste, wood chips, "fibrids" (e.g., polypropylene fibrids), and other fillers may be added to the reinforced material.

Other optional fibers

Glass fibers are commonly used as insulating materials, but have also been used as reinforcing materials with a variety of substrates. The fibers themselves provide tensile strength to the material susceptible to brittle failure. The fibers break upon loading, but the common failure mode of composites containing glass fibers arises from the breakdown and destruction of the bonds between the fibers and the continuous phase material. Thus, the bonding is very important if the reinforcing fibers are to maintain their ability to increase the ductility and strengthen the composite over time. It has been found that glass fibre reinforced cement does lose strength over time due to attack on the glass by the lime generated when the cement sets. One possible way to overcome the erosion is to cover the glass fibers with a protective layer, for example a polymer layer. Generally, the protective layer is resistant to attack by lime, but it has been found that the strength is reduced in the panels of the invention and therefore the protective layer is not preferred. A more expensive way to limit lime erosion is to use special alkali resistant Glass fibers (AR Glass fibers), such as Nippon Electric Glass (NEG) 350Y. The fibers have been found to provide superior bond strength to the matrix and are therefore preferred for the panels of the present invention. The glass fibers are monofilaments having a diameter of about 5 to 25 microns, and typically about 10 to 15 microns. The filaments are typically combined into fiber bundles of 100 filaments, which may be bundled into rovings containing about 50 fiber bundles. The fiber bundles or rovings may generally be chopped into suitable filaments and filament bundles of, for example, about 0.25 to 3 inches (6.3 to 76mm) in length, preferably 1 to 2 inches (25 to 50 mm).

Other polymer fibers may also be included in the panels of the present invention. Such as polypropylene, polyethylene, high density polyethylene, polyacrylonitrile, polyamide, polyimide and/or aramid fibers, which are less expensive and less susceptible to attack by lime than alkali-resistant glass. Carbon or steel fibers are also potential additives.

Pozzolanic materials(pozzolanic material)

As previously mentioned, most portland cement and other hydraulic cements produce lime during hydration (curing). It is desirable to react the lime to reduce the attack on the glass fibers. It is also known that when calcium sulfate hemihydrate is present, it reacts with tricalcium aluminate in the cement to form ettringite which can lead to undesirable cracking of the cured product. This phenomenon is commonly referred to in the art as "sulfate attack". The reaction can be prevented by the addition of a "pozzolanic" material, defined in ASTM C618-97 as "… … silicic acid or alumino silicate material, which has little or no cementitious value by itself, but which, in finely divided form in the presence of moisture, will react chemically with calcium hydroxide at conventional temperatures to form compounds having cementitious properties. "A common pozzolanic material is silica fume, a fine amorphous silica that is the product of a silicon metal and iron-silicon alloy product. Characterized by a high silica content and a low alumina content. A variety of natural and man-made materials are known to have pozzolanic properties, including pumice, perlite, diatomaceous earth, tuff, volcanic earth, metakaolin, microsilica, ground blast furnace slag powder and fly ash. While silica fume is a particularly convenient pozzolan for use in the panels of the present invention, other pozzolanic materials can be used. In contrast to silica fume, metakaolin, granulated blast furnace slag powder, and pulverized fly ash have much lower silica content and a significant amount of alumina, but can be effective pozzolanic materials. When silica fume is used, it will constitute about 5 to 20% by weight, preferably 10 to 15% by weight, of reactive powder (examples of reactive powders: hydraulic cement alone; a blend of hydraulic cement and pozzolan; or a blend of hydraulic cement, calcium sulfate alpha hemihydrate, pozzolan and lime). If substituted for other pozzolans, the amount should be selected to provide a chemical performance similar to silica fume.

Lightweight filler/microspheres

The lightweight cementitious panels of the present invention typically have a density of 60 to 85 pounds per cubic foot, preferably 60 to 75 pounds per cubic foot. In contrast, typical cement boards have densities of, for example, 90 to 145 pounds per cubic foot.

To assist in achieving these low densities, the panels are provided with lightweight filler particles. The particles typically have an average particle size of 50 to 250 microns and/or fall within a particle size range of 10 to 500 microns. The particles also typically have a particle density (specific gravity) in the range of 0.02 to 1.00. Microspheres play an important role in the panels of the invention which would otherwise be heavier than required for building panels. The microspheres act as lightweight fillers to help reduce the average density of the product. When the microspheres are hollow, they are sometimes referred to as microspheres (microbeads).

Typical lightweight fillers included in the mixture used to make the panels of the present invention are selected from the group consisting of: ceramic microspheres, polymer microspheres, perlite, glass microspheres, and/or fly ash cenospheres (cenospheres).

Ceramic microspheres can be made from a variety of materials and using different manufacturing methods. Although a variety of ceramic microspheres may be utilized as the filler component in the panels of the present invention, the preferred ceramic microsphere systems of the present invention are generated as a by-product of coal combustion and are a fly ash component found in coal burning applications, such as Extendpospheres-SG manufactured by Kish Company Inc. (Mentor, Ohio) or FILLITE  brand ceramic microspheres manufactured by Trelleberg Fillite Inc. (Norcross, Georgia USA). The chemical composition of the preferred ceramic microspheres of the present invention is primarily Silica (SiO) in the range of about 50 to 75 weight percent₂) And alumina (Al) in the range of about 15 to 40 wt%₂O₃) And up to 35 wt% of other materials. Preferred embodiments of the inventionCeramic microspheres are hollow spherical particles having a diameter in the range of 10 to 500 microns, a spherical shell thickness of typically about 10% of the sphere diameter, and a particle density of preferably about 0.50 to 0.80 g/mL. Preferred ceramic microspheres of the invention have a crush strength of greater than 1500psi (10.3MPa) and preferably greater than 2500psi (17.2 MPa).

The preferred ceramic microspheres in the panels of the invention are primarily due to the fact that they are about three to ten times stronger than most organic glass (synthetic glass) microspheres. In addition, the preferred ceramic microspheres of the present invention are thermally stable and provide enhanced dimensional stability to the panels of the present invention. Ceramic microspheres can be used in a range of other applications such as adhesives, sealants, caulks, roofing composites (rooming composites), PVC flooring, paints, industrial coatings and high temperature resistant plastic composites. It should be understood that the microspheres need not be hollow and spherical, although it is preferred because it is the particle density and compressive strength that provide the board of the present invention with its light weight and important physical properties. Alternatively, porous irregular particles may be substituted as long as the resulting panel meets the desired properties.

The polymeric microspheres are also preferably hollow spheres having a shell made of a polymeric material such as polyacrylonitrile, polymethacrylonitrile, polyvinyl chloride or polyvinylidene chloride or mixtures thereof. The shell may be filled with a gas that is used to expand the polymeric shell during the manufacturing process. The outer surfaces of the polymer microspheres may have some type of inert coating such as calcium carbonate, titanium oxide, mica, silica and talc. The polymeric microspheres have a particle density of preferably about 0.02 to 0.15g/mL and have a diameter in the range of 10 to 350 microns. The presence of the polymeric microspheres helps to achieve the dual goals of low board density and enhanced cuttability and nailability simultaneously. Although all of the panels of the present invention can be cut using conventional woodworking tools, the inclusion of polymeric microspheres reduces nail resistance. This is a valuable feature when nailing manually. When a pneumatic nailing apparatus is used, the nail resistance of the board is less important, and therefore the strength of the board can be higher than that of a board to be manually nailed. Furthermore, when a blend of ceramic microspheres and polymer microspheres is used in a specific ratio, a synergistic effect will be achieved in terms of improved rheology of the slurry and increased dry flexural strength of the panel.

Other lightweight fillers such as glass microspheres, perlite or hollow alumina silicate cenospheres or fly ash derived microspheres are also suitable for inclusion in the mixture in combination with, or replacement of, the ceramic microspheres employed in making the panels of the invention.

The glass microspheres are typically made of alkali resistant glass materials and may be hollow. Typical glass microspheres are available from GYPTEK INC (Suite 135, 16 Midlake Blvd SE, Calgary, AB, T2X 2X7, CANADA).

In a first embodiment of the invention, only ceramic microspheres are used throughout the thickness of the panel. The panel preferably contains about 35 to 42 wt% ceramic microspheres uniformly distributed through the thickness of the panel.

In a second embodiment of the invention, a blend of lightweight ceramic microspheres and polymer microspheres is used throughout the thickness of the panel. To achieve the desired properties, the volume fraction of polymer microspheres in the panel of the second embodiment of the invention will preferably be in the range of 7 to 15% of the total volume of the dry ingredients, wherein the dry ingredients of the composition are reactive powders (examples of reactive powders: hydraulic cement alone; a blend of hydraulic cement and pozzolan; or a blend of hydraulic cement, calcium sulfate alpha hemihydrate, pozzolan and lime), ceramic microspheres, polymer microspheres and alkali resistant glass fibers. The amount of polymeric microspheres can be varied by adjusting the ratio of water to reactive powder to achieve similar effects as desired. Typical aqueous mixtures have a ratio of water to reactive powder of greater than 0.3/1 to 0.7/1.

Formulations

The components used to make the shear resistant panels of the present invention are PVA fibers, hydraulic cement, calcium sulfate alpha hemihydrate, active pozzolans (e.g., silica fume), lime, ceramic microspheres, polymer microspheres, superplasticizers (e.g., sodium polynaphthalenesulfonate), and water. Small amounts of set accelerators and/or set retarders may be added to the composition to control the setting characteristics of the green (i.e., uncured) material. Typical non-limiting additives include: accelerators for hydraulic cement, such as calcium chloride; set accelerators for alpha calcium sulfate hemihydrate, such as gypsum; retarders, such as DTPA (diethylenetriaminepentaacetic acid), tartaric acid or alkali metal salts of tartaric acid (e.g., potassium tartrate); shrinkage reducing agents, such as glycols) and entrained air.

The panels of the invention comprise a continuous phase with uniformly distributed PVA fibers and microspheres. The continuous phase results from the curing of an aqueous mixture of reactive powders (examples of reactive powders: hydraulic cement alone; a blend of hydraulic cement and pozzolan; or a blend of hydraulic cement, calcium sulfate alpha hemihydrate, pozzolan and lime), which preferably includes a superplasticizer and/or other additives.

Typical generalized weight proportions of such reactive powder (inorganic binder) examples of the present invention based on dry weight of the reactive powder are shown in tables 3 and 4. Table 5 lists typical ranges for reactive powders (inorganic binders), lightweight fillers, superplasticizers, and water in the compositions of the invention.

TABLE 3

Reactive powder	Weight ratio (%)
				Generalized sense	Typical of
Hydraulic cement	70-100	100
			Volcanic ash	0-30	0

TABLE 4

Reactive powder	Weight ratio (%)
				Generalized sense	Typical of
Hydraulic cement	20-55	25-40
			Alpha calcium sulfate hemihydrate	35-75	45-65
Volcanic ash	5-25	10-15
			Lime	At most 3.5	0.75-1.25

TABLE 5

Typical lightweight cement admixture composition
		Composition (I)	Minimum-maximum range (wt%)
Inorganic binder	30-60
		Light weight filler	10-40
Superplasticizer	0.5-4.0
		Water (W)	15-40

TABLE 5A

Typical Cement admixture composition (dry basis)	Weight ratio (%)	Weight ratio (%)
			Reactive powder	35-70	35-68
Light weight filler	20-50	23-49
			Glass fiber	0-20	0-17
PVA fiber	0.5-5.0	0.75-3.0

Lime is not necessary for all formulations of the present invention, but the addition of lime provides superior panels. Typical lime content in the reactive powder is about 0.2 to 3.5% by weight.

In a first embodiment of the invention, the dry ingredients of the composition will be reactive powders (examples of reactive powders: hydraulic cement only; a blend of hydraulic cement and pozzolan; or a blend of hydraulic cement, calcium sulphate alpha hemihydrate, pozzolan and lime), PVA fibers, ceramic microspheres and optionally alkali-resistant glass fibers, while the wet ingredients of the composition will be water and superplasticizer. The dry ingredients and wet ingredients are combined to produce the board of the present invention. The PVA fibers and ceramic microspheres are uniformly distributed within a matrix throughout the thickness of the panel. The panels of the present invention are formed from about 49 to 56 weight percent reactive powder, 0.75 to 3.0 weight percent PVA fibers, 35 to 42 weight percent ceramic microspheres, and 0 to 12 weight percent alkali resistant glass fibers, based on the total weight of the dry ingredients. In a broad scope, the panels of the invention are formed from 35 to 58 wt% reactive powder, 0.5 to 5.0 wt% PVA fibers, 34 to 49 wt% ceramic microspheres and 0 to 17 wt% alkali resistant glass fibers based on total dry ingredients. The amount of water and superplasticizer added to the dry ingredients should be sufficient to provide the desired slurry fluidity needed to meet the processing considerations for any particular manufacturing process. Typical addition rates of water are in the range of 35 to 60% by weight of the reactive powder and typical addition rates of superplasticizers are in the range of 1 to 8% by weight of the reactive powder.

The optional glass fibers are monofilaments having a diameter of about 5 to 25 microns, preferably about 10 to 15 microns. The monofilaments are typically combined into fiber bundles of 100 filaments, which can be bundled into rovings containing about 50 fiber bundles. The glass fibers should preferably be about 1 to 2 inches (25 to 50mm) in length and about 0.25 to 3 inches (6.3 to 76mm) in a broad sense. The glass fibers and PVA fibers have a random orientation providing isotropic mechanical features in the plane of the sheet.

A second embodiment of the invention contains PVA fibers and a blend of ceramic and polymer microspheres uniformly distributed throughout the thickness of the panel. The incorporation of polymer microspheres in the board helps to achieve the combination of low density and ductility needed to enable the board to be cut or secured (with nails or screws) with conventional woodworking tools. Furthermore, when a combination of hollow ceramic and polymeric microspheres is utilized as part of the composition, the rheological properties of the slurry are substantially improved. Thus, in a second embodiment of the invention, the dry ingredients of the composition are reactive powders (hydraulic cement, calcium sulfate alpha hemihydrate, pozzolan and lime), ceramic microspheres, polymeric microspheres and optionally alkali-resistant glass fibers, while the wet ingredients of the composition will be water and superplasticizer. The dry ingredients and wet ingredients are combined to produce the board of the present invention. For good fastening and cutting ability, the volume fraction of the polymeric microspheres in the panel should preferably be in the range of 7 to 15% of the total volume of the dry ingredients. The panels of the present invention are formed from about 54 to 65 wt% reactive powder, 0.75 to 3.00 wt% PVA fibers, 25 to 35 wt% ceramic microspheres, 0.5 to 0.8 wt% polymer microspheres, and 0 to 10 wt% alkali resistant glass fibers, based on the total weight of the dry ingredients. In a broad scope, the panels of the invention are formed from about 42 to 68 wt% reactive powder, 0.5 to 5.00 wt% PVA fibers, 23 to 43 wt% ceramic microspheres, 0.2 to 1.0 wt% polymer microspheres, and 0 to 15 wt% (e.g., 5 wt%) alkali resistant glass fibers, based on the total dry ingredients. The amounts of water and superplasticizer added to the dry ingredients are adjusted to provide the desired slurry fluidity needed to meet the processing considerations for any particular manufacturing process. Typical rates of water addition range from 35 to 70% by weight of the reactive powder, but can be greater than 60% up to 70%, preferably 65% to 75%, when it is desired to utilize the ratio of water to reactive powder to reduce board density and improve nailability. Because the ratio of water to reactive powder can be adjusted to provide a similar effect to that of the polymeric microspheres, one or a combination of the two methods can be used. The amount of superplasticizer is in the range of 1 to 8% by weight of the reactive powder.

The optional glass fibers are monofilaments having a diameter of about 5 to 25 microns, preferably about 10 to 15 microns. They are typically bundled into fiber bundles and rovings as described above. The glass fibers preferably have a length of about 1 to 2 inches (25 to 50mm), in a broad sense, about 0.25 to 3 inches (6.3 to 76 mm). The fibers have a random orientation with isotropic mechanical features in the plane of the sheet.

In a second embodiment of the invention, the incorporation of polymeric microspheres in the above amounts to partially replace ceramic microspheres helps to improve the dry flexural strength of the composite. In addition, partial replacement of the ceramic microspheres by polymer microspheres can reduce the ratio of water to reactive powder required to achieve a given slurry fluidity. Slurries containing a blend of ceramic and polymeric microspheres will have superior flow characteristics (processability) compared to slurries containing only ceramic microspheres. This is particularly important when the industrial processing of the panels of the invention requires the use of a slurry with superior flow characteristics.

Manufacture of the boards of the invention

Reactive powders (examples of reactive powders: hydraulic cement alone; a blend of hydraulic cement and pozzolan; or a blend of hydraulic cement, calcium sulfate alpha hemihydrate, pozzolan and lime), chopped PVA fibers and lightweight fillers (e.g. microspheres) are blended in the dry state in a suitable mixer. PVA fibers are typically provided in chopped form and added in chopped form directly to the dry ingredients or to the wet slurry. Typically, the PVA fibers are not chopped from the roving as is the case with glass fibers.

The water, superplasticizer (e.g., sodium polynaphthalenesulfonate), and pozzolan (e.g., silica fume or metakaolin) are then mixed in another mixer for 1 to 5 minutes. If necessary, a retarder (e.g., potassium tartrate) is added at this stage to control the setting characteristics of the slurry. The dry ingredients are added to the mixer containing the wet ingredients and mixed for 2 to 10 minutes to form a lump-free homogeneous slurry.

The slurry containing PVA fibers may then be combined with glass or other fibers as appropriate in several ways in order to obtain a homogeneous slurry mixture. The cementitious panel is then formed by pouring the slurry containing the fibers into a suitable mold having the desired shape and size. If desired, the mold may be vibrated to provide better compaction of the material within the mold. The plates are given the desired surface finish characteristics using suitable blades or trowels.

Other methods of depositing a mixture of the slurry, PVA fibers and optionally glass fibers or other fibers will occur to those familiar with board making techniques. For example, rather than using a batch process to make each panel, a continuous sheet can be prepared in a similar manner that can be cut into panels of desired dimensions when the material is sufficiently set.

In many applications (e.g., siding), the panels are nailed or screwed to a vertical frame. In some applications, such as where the panels are used as structural sub-floor or floor underlayments, it will be preferred to make tongue and groove structures, which can be made by shaping the edges of the panels during casting or cutting a tongue and groove with a router prior to use.

It is another feature of the present invention to construct the resulting cementitious panel so that the PVA fibers and optionally the glass fibers or other fibers are uniformly distributed throughout the panel. The percentage of fibers relative to the volume of the slurry is preferably in the range of about 0.5% to 3%, for example 1.5%.

The panels of the invention generally have one or more of the following characteristics:

the flexural strength is typically at least 750psi (5.2MPa), and preferably greater than 1000psi (6.9 MPa).

The flexural toughness is typically at least 2.25 joules, which represents the total area under the load versus deflection curve in a 4 point bend according to ASTM C947 test method for a 4 inch (102mm) wide, 12 inch (305mm) long, 0.5 inch (12.7mm) thick sample loaded at a 10 inch (254mm) span.

The transverse fastening resistance of a 0.5 inch (12.7mm) thick panel is typically at least 300 pounds, measured according to ASTM D1761 modified version described by r.tuomi and w.mccutcheon in 1978, asci Structural Division Journal of 7.

Examples of the invention

Table 6 summarizes the properties of the six fibers studied.

TABLE 6 fibers studied

Fibrous material	Name of fibre trade mark	Manufacturer(s)	Fiber length (inches)	Fiber diameter (micron)	Specific gravity of fiber
						Polyvinyl alcohol	KURALONRF350×12	KurarayCo.，Ltd.	0.50	200.0	1.30
Polyvinyl alcohol	KURALONREC15×12	KurarayCo.，Ltd.	0.50	40.0	1.30
						Alkali-resistant glass fiber	NEG ACS13H-350Y	NipponElectricGlass Co.	0.50	13.0	2.76
Carbon fiber	FORTAFIL143	FortafilFibers	0.25	7.0	1.80
						Steel microfiber	CW2-3750U	InternationalSteel Wool	0.38	125.0	7.85
Acrylic fiber (Polymer)	Dolainit 18 type	FisipeBarcelona，S.A.	0.24	27	1.18
						Polypropylene fibre (Polymer)	STEALTH	SyntheticIndustries	0.50	20	0.91

All of the fibers studied had a length equal to or less than 0.5 inch (12.7mm) and a diameter equal to or less than 200 microns. The mixture composition studied was generated by combining the following ingredients: reinforcing fibers, inorganic binders, lightweight fillers, superplasticizers and water. A total of 19 mixtures were studied. The design slurry density for the mixture studied was 70 pounds per cubic foot (pcf). The fiber volume fractions in the blends were different and the various fibers studied ranged from 0.5% to 2.0%.

Mixture composition of the invention

Table 7 provides a description of the target mixture compositions for the examples. The weight fractions of the different ingredients are wet pulps used to exclude fibers as shown in the table. Tables 8 and 8A show the actual compositions of the wet slurries combined with the PVA fibers of these examples.

Table 7: example target lightweight cementitious mixture compositions

Composition (I)	(wt%)
		Inorganic binder1，2	43.3
Light weight filler3，4	26.2
		Superplasticizer5	1.9
Water (W)	28.6
		Total of	100％
Fiber	As described elsewhere in this specification
		1. Inorganic binders used in the examples: a gypsum-cement composition having the following composition: calcium sulfate hemihydrate-58%; 29 percent of Portland cement; 12 percent of silicon powder; lime content of 1 percent
2. Other inorganic binders, such as those mentioned below, may be used as part of the present invention: a. portland cement only

b. Portland cement and pozzolanic material combinations (examples: clinker, silica fume, metakaolin)
	3. The lightweight fillers used in the examples: hollow ceramic microspheres
4. Other lightweight fillers, such as those mentioned below, may be used as part of the present invention: a. expanded perlite b. hollow plastic microspheres c. expanded polystyrene beads
	5. The superplasticizers used in the examples: polynaphthalenesulfonates
Other additives (e.g., set accelerators and retarder mixtures, viscosity control additives) may optionally be added to meet the requirements of the relevant manufacturing process.

The panels are manufactured as described above in the section entitled "manufacture panels of this invention".

TABLE 8

Composition (I)	Mixture composition (percentage by weight)
						Example 2A (0.5% fiber volume fraction)	Example 2B (1.0% fiber volume fraction)	Example 2C (1.5% fiber volume fraction)	Example 2D (2.0% fiber volume fraction)
PVA fiber	0.6	1.2	1.7	2.3
					Inorganic binder	43.9	43.6	43.4	43.1
Light ceramic ball	26.5	26.4	26.2	26.1
					Superplasticizer	2.0	2.0	2.0	1.9
Water (W)	27.0	26.8	26.7	26.5
					Total of	100.0	100.0	100.0	100.0

TABLE 8A

Composition (I)	Mixture composition (percentage by weight)
							Example 1A (0.5% fiber volume fraction)	Example 1B (1.0% fiber volume fraction)	Example 1C (1.5% fiber volume fraction)	Example 1D (2.0% fiber volume fraction)	Example 1F (3.0% fiber volume fraction)
Inorganic binder	43.9	43.6	43.4	43.1	42.6
						Light ceramic ball	26.5	26.4	26.2	26.1	25.8
Superplasticizer	2.0	2.0	2.0	1.9	1.9
						Water (W)	27.0	26.8	26.7	26.5	26.2
PVA fiber	0.6	1.2	1.7	2.3	3.5
						Total of	100.0	100.0	100.0	100.0	100.0

Results

Table 9 summarizes the results for the compositions studied. Table 9 shows the performance data for the fiber reinforced lightweight cementitious formulations. The data for examples 2A-2D are for composites of the invention using PVA fiber KURALON REC 15X 12 (also labeled PVA-2). One-half inch thick composite panels were made by mixing the ingredients in a Hobart (Hobart) mixer and casting the resulting mixture into a mold. For all of the blend compositions evaluated, the fiber orientation in the panel was three-dimensionally random. The results of the study are also illustrated in figures 2 to 5. The following is a discussion of the results.

TABLE 9

Examples of the invention	Fiber	Fiber volume fraction (%)	Design paste Density (pcf)	Toughness (Joule)	Flexural Strength (psi)	Maximum deflection (inches)	Transverse fastening resistance (pound)
								1A	PVA fiber KURALONNRF 350X 12(PVA-1)	0.50	70.0	0.1	561	0.028	80
1B	″	1.00	70.0	0.1	687	0.030	111
								1C	″	1.50	70.0	2.4	812	0.057	184
1D	″	2.00	70.0	3.6	827	0.104	191
								1E	″	2.50	70.0	5.6	891	0.241	282
1F	″	3.00	70.0	6.7	1035	0.201	292
								2A	PVA fiber KURALANREC 15X 12(PVA-2)	0.50	70.0	1.8	665	0.048	145
2B	″	1.00	70.0	4.3	850	0.160	335
								2C	″	1.50	70.0	7.8	1050	0.197	382
2D	″	2.00	70.0	11.6	1181	0.342	533
								3A	AR glass fiber NEGACS13H-350Y	0.50	70.0	0.7	447	0.035	-
3B	″	1.00	70.0	0.8	610	0.092	-
								3C	″	2.00	70.0	2.2	1065	0.108	-
4A	Carbon fiber	0.50	70.0	0.3	847	0.043	246
								4B	″	1.00	70.0	0.3	790	0.057	328
4C	″	1.50	70.0	0.3	899	0.066	337
								4D	″	2.00	70.0	0.3	874	0.045	422
5A	Steel microfiber	0.50	70.0	0.1	484	0.031	-
								5B	″	1.00	70.0	0.1	629	0.028	-
5C	″	1.50	70.0	0.2	838	0.051	-
								5D	″	2.00	70.0	0.3	952	0.052	-

Flexural toughness of composites

Flexural plate samples 4 inches (102mm) wide and 12 inches (305mm) long were loaded in four-point bending according to ASTM C947 test method at a span of 10 inches (254 mm). The load was applied at a constant displacement rate of 0.5 inches/minute (12.7 mm/minute). The response curve of flexural load versus displacement is recorded. The composite toughness was calculated as the total area under load and deflection until failure of the sample.

Table 9 and figures 2 and 3 show the resulting flexural toughness for the different composites studied. The following important observations can be made.

Composites reinforced with carbon fibers and steel microfibers are extremely brittle as indicated by their low toughness values.

Composites reinforced with alkali-resistant glass fibers and PVARF350 fibers have slightly better toughness than composites reinforced with carbon fibers and steel microfibers.

The toughness properties of composites reinforced with KURALON REC15 × 12(PVA2) PVA fibers are particularly attractive. It can be observed that the PVA REC15 fiber reinforced composites have toughness values that are several orders of magnitude greater than those of composites reinforced with other types of fibers.

In detail, at 2% fiber volume fraction, the PVA REC15 fiber reinforced composite absorbed about 5 times more energy than the alkali resistant glass fiber reinforced composite, about 35 times more energy than the carbon fiber reinforced composite and about 40 times more energy than the steel microfiber reinforced composite (fig. 3).

Flexural Strength

Flexural plate samples 4 inches (102mm) wide and 12 inches (305mm) long were loaded in four-point bending according to ASTM C947 test method at a span of 10 inches (254 mm). The load was applied at a constant displacement rate of 0.5 inches/minute (12.7 mm/minute). The response curve of flexural load versus displacement is recorded. Flexural strength of the composite was calculated according to ASTM C947 test method.

Table 9 and fig. 4 show the flexural strength data obtained for the different mixture compositions studied. The PVA REC15 fiber reinforced composite had the best flexural strength properties.

Groove direction fastening male power

The transverse fastening resistance of the composite was measured according to ASTM D1761 modified version described by r.tuomi and w.mccutcheon in the ascie Structural Division Journal of 7 months 1978. By a length ofAn inch (41.3mm) screw was used as a fastener to perform the test.

Table 9 and fig. 5 show the lateral fastener pull-out resistance for the different composites tested. The lateral tightening resistance quantifies the lateral pull-out resistance provided by the plate to the fastener. By a length equal toInch (41.3mm) screws were used to determine the lateral tightening resistance of the composite. The figure shows that the composite reinforced with PVAREC15 fibers has the best lateral fastening resistance. The differences in composite performance reinforced with two different types of PVA fibers (PVA REC15 and PVA RF350) are particularly noticeable. On the one hand, composites fiber reinforced with PVA REC15 performed very well. The performance of the composites reinforced with PVA RF350 fibers is not satisfactory.

Maximum deflection

The data provided in table 9 and fig. 6 and 7 show the effect of fiber type and fiber volume fraction on the maximum deflection of lightweight, fiber reinforced cement substrates. The maximum deflection values shown in table 9 were measured using the deflection test performed according to ASTM C947 standard, and these values represent the deflection deformation of the sample at the point of application of the load corresponding to the peak of the load observed during the test protocol.

It is apparent from fig. 6 and 7 that the PVA fiber-reinforced composite has a higher maximum deflection. This observation and the mechanical characteristics of the composite indicate that the composite reinforced with PVA fibers has a stronger deformability (i.e. a stronger ductility) and therefore a stronger toughness. From these results, it can be readily understood that even an increase in the volume fraction of fibers in the composite does not improve the ductility of the composite for composites reinforced with carbon fibers and steel microfibers. Composites reinforced with carbon and steel microfibers at even 2% fiber volume fraction have only maximum deflection values of less than 0.07 inch. These results, along with the composite toughness values, indicate that composites reinforced with carbon and steel microfibers are extremely brittle in their mechanical response compared to composites reinforced with PVA fibers.

Comparison of selected PVA fibers with acrylic and polypropylene fibers

Using the materials and procedures described above but replacing the fibers in the examples above with acrylic and polypropylene fibers, the use of the selected PVA fibers in the composite was compared to the use of acrylic and polypropylene fibers.

The data provided in table 10 and fig. 8 show the effect of fiber type on the toughness of fiber-reinforced lightweight cement-based composites. It is apparent from the results given in table 10 and fig. 8 that other types of polymer fibers do not produce a reinforcement comparable to the toughness reinforcement of composites produced by PVA fibers.

The data provided in table 11 and fig. 9 show the effect of fiber type on the flexural strength of lightweight, fiber reinforced cement-based composites. From the results given in table 11 and fig. 9, it can be observed that other types of polymer fibers do not produce reinforcement comparable to the composite flexural strength reinforcement produced by PVA fibers.

Watch 10

Example number	Fiber	Fiber volume fraction (%)	Design paste Density (pcf)	Toughness (Joule)
					2D	PVA fiber KURALANREC 15X 12(PVA-2)	2.00	70.0	11.6
6	Acrylic fiber Dolanit 18 type	2.00	70.0	3.0
					7	Stealth Polypropylene fiber	2.00	70.0	2.6

TABLE 11

Example number	Fiber	Fiber volume fraction (%)	Design paste Density (pcf)	Flexural Strength (psi)
					2D	PVA fiber KURALANREC 15X 12(PVA-2)	2.00	70.0	1181
6	Acrylic fiber Dolanit 18 type	2.00	70.0	464
					7	Stealth Polypropylene fiber	2.00	70.0	432

Preferred characteristics of the PVA fibers of the present invention

Based on this data, it is clear that the use of different PVA fibers can have substantial differences in the mechanical properties of the composite. Thus, preferred parameters and characteristics of PVA fibers that produce good composite performance are identified and highlighted in table 1. Table 2 in turn lists several commercially available fibers that are preferred fibers of the present invention. These preferred types of fibers may be used in combination with other types of fibers such as alkali resistant glass fibers, carbon fibers, steel fibers, or other polymer fibers.

While particular embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the invention in its broader aspects and as set forth in the following claims.

Claims (26)

1. A reinforced, lightweight, dimensionally stable panel having a density of 60-85pcf (961-1360 kg/m)³) A density of (a), comprising: a continuous phase resulting from curing of an aqueous mixture of reactive powders, the reactive powders comprising, on a dry basis, 35-70 wt% reactive powders, 20-50 wt% lightweight fillers, 0-20 wt% glass fibers, and 0.5-5.0 wt% PVA fibers, the continuous phase being reinforced with and containing the PVA fibers, the lightweight fillers having a particle specific gravity of 0.02 to 1.00 and an average particle size of 50 to 250 microns and/or being in the range of 10 to 5A particle size range of 00 microns, wherein the PVA fibers have a diameter of about 10 to 400 microns and a length of about 0.1 to 1 inch (2.5 to 25.4mm), and a fiber elastic modulus of 20-50 GPa.

2. The panel of claim 1 wherein the continuous phase is uniformly reinforced with the PVA fibers, the lightweight filler is uniformly distributed and the panel has a flexural strength of at least 750psi (5.2 MPa).

3. The panel of claim 1, wherein the panel has a flexural strength of at least 1000psi (6.9 MPa).

4. The panel of claim 1, wherein the panel has a flexural toughness of at least 2.25 joules, representing the total area under the load versus deflection curve in four-point bending according to ASTM C947 test method for a 4 inch (102mm) wide, 12 inch (305mm) long, 0.5 inch (12.7mm) thick sample loaded at a 10 inch (254mm) span.

5. The panel of claim 1, wherein the panel has a lateral fastening resistance of at least 300 pounds for a 0.5 inch (12.7mm) thick panel.

6. The panel of claim 1, wherein the aqueous mixture of reactive powders comprises, on a dry basis, 35 to 75 weight percent calcium sulfate alpha hemihydrate, 20 to 55 weight percent hydraulic cement, 0.0 to 3.5 weight percent lime, and 5 to 25 weight percent active pozzolan, the continuous phase being uniformly reinforced with the PVA fibers and containing uniformly distributed ceramic microspheres, the spheres having an average diameter of about 10 to 500 microns.

7. The panel of claim 1, wherein the aqueous mixture of reactive powders comprises a hydraulic cement.

8. The panel of claim 1, wherein the aqueous mixture of reactive powders comprises 70 to 100 weight percent hydraulic cement and 0 to 30 weight percent of at least one pozzolan on a dry basis.

9. The panel of claim 1, wherein the panel has a thickness of about 1/4 to 1 inch (6.3 to 25.4 mm).

10. The panel of claim 1, wherein the 0.5 inch (12.7mm) thick panel has a flexural toughness of at least about 2.25 joules, which represents the total area under the load versus deflection curve in four-point bending according to ASTM C947 test method for a 4 inch (102mm) wide, 12 inch (305mm) long, 0.5 inch (12.7mm) thick sample loaded at a 10 inch (254mm) span.

11. The panel of claim 1 wherein the lightweight filler comprises hollow ceramic spheres comprising about 50 to 75 weight percent silica, about 15 to 40 weight percent alumina, and up to 35 weight percent of other materials.

12. The panel of claim 1, wherein the lightweight filler comprises polymer microspheres comprising at least one member of the group consisting of polyacrylonitrile, polymethacrylonitrile, polyvinyl chloride, and polyvinylidene chloride, and optionally coated with at least one powder selected from the group consisting of calcium carbonate, titanium oxide, mica, silica, and talc.

13. The panel of claim 1 wherein said PVA fibers have a diameter of about 10 to 100 microns and a length of about 0.2 to 0.5 inches (5.1 to 12.7mm), and a fiber elastic modulus of 30-50 GPa.

14. The panel of claim 1 wherein the density is 60lb/ft³(961kg/m³) To 75lb/ft³(1200kg/m³) The flexural strength of the sheet of (a) is at least 750psi (5.2 MPa).

15. The panel of claim 1 wherein the density is 60lb/ft³(961kg/m³) To 75lb/ft³(1200kg/m³) The flexural strength of the sheet of (a) is at least 1000psi (6.9 MPa).

16. The panel of claim 1, wherein edges are shaped to provide a tongue and groove structure for adjacent panels.

17. The panel of claim 1, wherein the hydraulic cement is portland cement.

18. The panel of claim 1 wherein the PVA fibers comprise at least 0.5 volume percent of the aqueous mixture on a wet weight basis.

19. The panel of claim 1 wherein the PVA fibers comprise about 1-3 volume percent of the aqueous mixture on a wet weight basis.

20. The panel of claim 1 wherein the PVA fibers comprise about 1-2 volume percent of the aqueous mixture on a wet weight basis.

21. A method of manufacturing the panel of claim 1, comprising: placing an aqueous mixture of reactive powders on a board mold and curing the aqueous mixture to form the board, the mixture comprising 40 to 95 weight percent cement on a dry weight basis, the continuous phase being uniformly reinforced with PVA fibers and containing a uniform distribution of lightweight filler having a particle specific gravity of 0.02 to 1.00, wherein the PVA fibers have a diameter of about 10 to 400 microns and a length of about 0.1 to 1 inch (2.5 to 25.4mm), and a fiber elastic modulus measured at 20-50 GPa.

22. The method of claim 21, wherein the lightweight filler comprises uniformly distributed polymer spheres,

it has an average diameter of about 10 to 350 μm.

23. The method of claim 21, wherein the lightweight filler comprises hollow polymer microspheres comprising at least one of the group consisting of polyacrylonitrile, polymethacrylonitrile, polyvinyl chloride, and polyvinylidene chloride, and optionally coated with a powder selected from the group consisting of calcium carbonate, titanium oxide, mica, silica, and talc.

24. The method of claim 21, wherein the PVA fibers are monofilaments having a diameter of about 5 to 25 microns and a length of about 0.25 to 1 inch (6 to 25.4 mm).

25. The method of claim 21, wherein the PVA fibers are monofilaments.

26. The method of claim 21, wherein the aqueous mixture has a ratio of water to reactive powder of greater than 0.3/1 to 0.7/1.