Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-04-18
2003-07-29
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S297400, C428S300400, C428S423100, C428S521000, C428S522000, C427S369000, C156S071000, C052S309100, C052S309130, C052S309160
Reexamination Certificate
active
06599632
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to composites for structure reinforcement, particularly to fiber reinforced polymer systems for retrofit reinforcement of existing structures, particularly concrete structures.
BACKGROUND OF THE INVENTION
With the advent of composite materials such as fiberglass, carbon fiber, Kevlar and similar materials there became a need for resins which are capable of utilizing the strengths of the composite materials. The development of resins for use with composite materials has greatly expanded due to the increased popularity of composite materials. For example, composite materials retained within a resin are utilized in sporting goods, aircraft, automobiles and thousands of other products.
In each application it is necessary to select an appropriate resin. For example, in some applications it is desirable to include a pre-determined amount of flexibility in the overall design, therefore a resin must be chosen that is capable of providing strength and stiffness to the composite fibers as well as retain a pre-determined amount of flexibility suitable for the desired end use. In other applications a resin may be chosen for its strength and hardness for resistance to mechanical impacts. Epoxy resins are conventionally used in both molding and laminating techniques to make fiber-reinforced articles with various desired mechanical strengths, chemical resistance and electrical insulating properties.
As a result of these needs, thousands of resins have been developed for use with composite fibers. Each of the resins having different mechanical properties, thereby allowing a manufacturer to chose a resin that is appropriate for the end use of the product.
One type of resin commonly used to retain the composite fibers is a thermosetting resin. Thermosetting resins are usually used because when they “set” they are irreversibly solidified. Other types of resin commonly used include thermoplastic resins, which have different properties compared to thermoset resins and can soften at elevated temperatures, even after they are cured.
Composite fibers disposed within a curable polymer matrix may be utilized to strengthen, support, and/or repair damaged building structures, or to prevent damage or collapse. For example, as described in U.S. Pat. No. 5,043,033 to Fyfe, incorporated herein by reference in its entirety, a concrete column supporting an overhead load may be strengthened by wrapping the work area of the column with at least one layer of high-strength, stretchable fibers. After wrapping the column a hardenable material, having a modules at least as great as that of the fibers overlaying the structure, is applied to the fibers and allowed to cure, thereby forming a hard outer shell. U.S. Pat. No. 5,218,810 to Isley, incorporated herein by reference in its entirety, contains a similar disclosure of fabric-resin matrix reinforced concrete columns.
In U.S. Pat. No. 5,505,030 to Michalcewiz et al., incorporated herein by reference in its entirety, there is described a method of reinforcing concrete, wood, or steel support columns, beams or other structures. The method includes disposing pre-formed reinforcing layers constructed of engineering materials having a high tensile strength and a high modulus that are attached, via an adhesive, thereby increasing the compressive, shear, bending, ductility, and/or seismic load carrying capability. U.S. Pat. No. 5,633,057 to Fowley, incorporated herein by reference in its entirety, contains a similar disclosure of fabric-resin matrix reinforced concrete columns.
In U.S. Pat. No. 6,003,276, to Hegemier et al., incorporated herein by reference in its entirety, there is described a method of reinforcing walls with composite materials, wherein the walls are covered with composite materials disposed within a curable matrix and aligned in a pre-determined direction to externally reinforce the wall against in-plane horizontal forces as well as out-of plane forces.
U.S. Pat. No. 5,680,739 to Cercone et al., U.S. Pat. No. 6,108,998 to Dumlao and U.S. Pat. No. 6,123,485 to Mirmiran et al., all incorporated herein by reference in their entirety, disclose additional approaches to composite reinforcement of existing structures.
In the references above, the composite materials are retained in a curable matrix, typically an epoxy matrix. The curable epoxy matrix may be further disposed upon the structure to which the composite materials are to be attached, thereby increasing the adhesion of the composite fibers to the structures.
One of the problems encountered in the conventional systems for composite reinforcement of structural elements, including those systems disclosed in the above patents, is that when the structural elements are stressed beyond their structural limits and cracks develop in the structure, those cracks are then propagated into the composite reinforcement which has been adhered to the surface of the structural element. The conventional approach to prevent propagation of the cracks and structural failure through the composite reinforcement system has been to use stronger fibers or matrix materials to provide increased strength for the overall reinforcement system.
It is an object of this invention to provide an improved composite reinforcement system for existing structural elements to provide increased resistance to crack propagation and increased resistance to structural failure.
It is a further object of this invention to provide an improved polymer system for improved performance of the composite reinforcement of structures.
SUMMARY OF THE INVENTION
In one aspect, this invention provides a method of reinforcing an external surface of a structural member comprising: applying to said surface a fiber reinforced polymer system; and curing or hardening the polymer system, wherein the polymer system is characterized by comprising a single phase homogeneous system before curing or hardening and by becoming a two phase system during curing, thereby resulting in, when cured, a structural polymer continuous phase and elastomeric polymer discontinuous phase.
In another aspect, this invention provides a reinforced structure comprising a structural member having an external surface and a fiber reinforced polymer system adhered to said surface, wherein the polymer system is characterized by a cured two-phase system comprising a structural polymer continuous phase and an elastomeric polymer discontinuous phase.
In another aspect, this invention provides a reinforced structure comprising a structural member having an external surface and a fiber reinforced polymer system adhered to said surface, wherein the polymer system is characterized by comprising a single phase homogenous system capable of becoming during curing a two-phase system comprising a structural polymer continuous phase and an elastomeric polymer discontinuous phase.
In another aspect, this invention provides a liquid polymer system that is easy to use in conventional fiber reinforcement of existing structural elements either through layup or prepreg applications. The present system is provided in a two part liquid polymer system which is mixed at the time of use. The first part of the polymer system comprises a structural polymer, typically an epoxy resin or other thermoset resin used for structural reinforcement applications, which is a “toughened” resin. Such “two phase” or “second phase” polymers are typically but not limited to epoxies containing a toughener, like a butadiene rubber or elastomer resin. During curing an immiscible phase forms whereby the epoxy cures as the continuous structural polymer, and a portion of the elastomer separates out and cures as isolated domains of cured elastomer. The second part of the liquid system is an elastomeric polymer, such as a urethane or butadiene polymer. The first and second liquid parts are miscible when mixed and form a single phase liquid at the time of mixing with sufficient work time to allow applications to desired structures by the worker in a conventional method. When the two part liquid po
Dixon Doyle G.
Gillette Karl
Martin Richard
Molton Richard J.
Burns Doane Swecker & Mathis L.L.P.
Dawson Robert
Edge Structural Composites, LLC
Feely Michael J
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