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COMPOSITE BUILDING MATERIAL
CROSS-REFERENCE TO RELATED
APPLICATION
This application claims the benefit of U.S. Provisional Application No. 60/239,155, filed Oct. 10,2000, the entirety of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
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1. Field of the Invention
This invention relates to a composite building material, and more particularly to a building material incorporating a lightweight core and one or more fiber cement skins formed on opposite sides of the core. :5
2. Description of the Related Art
Fiber-reinforced cement products such as water-resistant building sheets have been used for building since 1895. In recent history, reinforcing fibers used in such products have 2Q included not only asbestos fibers, but also cellulose (wood) fibers (see Australian Patent No. AU 515151), metal fibers, glass fibers and other natural fibers. Typically the density of such building sheets is from 1.2-1.7 g/cm3, the variation in density typically being achievable by compression and 2J dewatering of the fiber cement slurries used in manufacture, and by varying the amount of fiber used.
The densities of fiber cement described above mean the products are heavier than timber-based products of equal dimension and are more difficult to cut, machine and nail 30 than timber and timber-based products. The density of lumber typically ranges from 0.7-0.9 g/cm3 for dry hardwoods and from 0.38-0.6 g/cm3 for dry softwoods. Thus, a fiber cement material of density similar to lumber would enable products to be manufactured that were lighter, more 35 nailable, easier to cut, and easier to machine, while retaining the durability, fire-resistant, rot-resistant, and water-resistant properties of fiber cement.
SUMMARY OF THE INVENTION 40
Fiber cement building materials are commonly installed to external surfaces of building envelopes. The outside surface of the fiber cement product is exposed to local weather conditions and is subjected to stresses brought about by changes in temperature and humidity, UV exposure, and 45 exposure to pollutants and carbon dioxide in the atmosphere. A building product that has the exterior durability, planar strength, and the resistance to moisture degradation of fiber cement on the outside surfaces, along with a modified core to provide one or more special properties to the composite, 50 is desired. The special properties may include, but are not limited to:
Lighter weight for ease of handling of full sheets and long lengths of product,
Ease of cutting similar to gypsum wallboard to ensure quick and easy installation of the product by score-andsnap cutting with a utility knife,
Low thermal conductivity for insulation of walls in building structures from the outside environmental g0 conditions,
Thermal fire insulation and low thermal shrinkage to provide resistance to the progression of heat and fire through building walls and ceilings,
Low moisture transmission to control and direct moisture 65 flow and permeation of water and moisture into building walls, ceilings and roofs, and
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Low acoustic transmission and high acoustic absorption to reduce noise transmission throughout rooms in a building.
The desired properties can be achieved with a sandwich composite design using fiber cement facing on a core having a composition tailored for the specific properties.
This invention in one embodiment generally pertains to a composite building material comprising a lightweight core with a thin fiber cement facing material or fiber cement skin bonded to one side of the core and a second facing material bonded to the other side. The fiber cement facing that is used on at least one of the faces of the building material is preferably less than about 3/i6" thick, more preferably less than about Vs" thick. Thinner skins provide an overall light composite because the skin material is of higher density than the core material. The fiber cement facing is preferably in a preformed green (uncured) state at the time of assembly of the skins and the core into the sandwich composite.
It is an object of this invention to produce composite building materials that can be designed specifically for applications such as but not limited to tile backer, wallboard, wall panel, siding, trim, sheathing, decking, flooring, structural members, fencing, roofing, roof decking, or substrates thereof. The bulk of the physical properties (strength, durability, etc.) can be tailored by varying the composition of the facing material and/or the core. The fabrication of composites with a particular set of mechanical properties can be done with the proper choice of facing material and thickness. The density of the composite can be reduced by foaming the core slurry and/or by adding low-density filler materials. The uncured fiber cement facings are preformed and preferably continuous in length. The use of continuous, preformed fiber cement facing sheets simplifies the manufacture of the composite since only the core composition is cast, instead of casting one each for the core and for the facing. Also, the use of continuous, preformed fiber cement facing sheets eliminates the need for separate carrier sheets.
It is a further object to produce composites with improved properties by co-curing the core and facings. Manufacturing with uncured fiber cement sheet offers greater flexibility in the surface texture, surface profile, corner profile, and composite properties. Penetration of the core slurry into the uncured fiber cement facing and subsequent co-curing of the core and skins produces superior interlayer bonding, resulting from mutually interpenetrating mechanical and chemical bonding. The bonding can be further improved with a cementitious bonding layer applied to the core side of the facing. Controlling the water content and/or degree of precure of the green sheets to enable sufficient penetration of the core slurry into the void network of the sheet enhances interlayer bonding. This leads to stronger mechanical interlock and chemical bonding after curing. Also, antifoaming agents, thickening agents, or other additives in the uncured facing can be used to collapse the foam at the facing-core interface. This leads to the formation of a dense interlayer that enhances bonding by increasing the surface area of contact between the core and facing. This prevents the occurrence of delaminations that would greatly reduce the strength and durability of the composites.
In one aspect of the present invention, a building material is provided comprising at least a first component and a second component provided adjacent the first component. The first component is provided as pre-formed, uncured fiber cement, wherein the fiber cement is reinforced with individualized fibers. The uncured fiber cement is cured after providing the first component adjacent to the second component.
