WO2006138224A1

WO2006138224A1 - Fabric reinforced concrete

Info

Publication number: WO2006138224A1
Application number: PCT/US2006/022836
Authority: WO
Inventors: Lancelot Coar
Original assignee: Lancelot Coar
Priority date: 2005-06-14
Filing date: 2006-06-13
Publication date: 2006-12-28

Abstract

A reinforced concrete structure utilizing a woven structural fabric acting as the primary tensile reinforcing component. The reinforcing fabric is embedded in the concrete structure to follow the general or specific anticipated stress patterns in order to provide efficient tensile support. Made of a light material the fabric reinforcing will ease installation, provide increased efficiency in reinforcement and improved performance with environmental conditions over typical steel reinforcing construction.

Description

Fabric Reinforced Concrete

BACKGROUND OF THE INVENTION

The present invention relates to the field of fabricating reinforced concrete structures. These structures are load bearing and require additional tensile reinforcing to assist the concrete to resist anticipated loads. Common reinforced concrete applications may be for building construction, support structures, bridge design or the like.

Prior art in forming reinforced concrete structures uses reusable pr temporary panels usually made of wood, metal or plastic to make the concrete forms. Steel reinforcing (rebar) is usually used for the primary tensile reinforcing in such structures., Rebar is shaped and installed into these forms as designed in order to provide tensile support in the concrete. Upon completion of the "tying" (connecting) and forming of the rebar, the concrete is poured into the formwork. Once the concrete cures (hardens) the mold is disassembled and the desired structure is obtained. The method of using rebar (simply textured steel bars of varying gauges) is labor intensive to fabricate, transport, move on site, arrange, shape and install. Because of the manpower required to transport, shape and install, the use of steel in reinforcing is a slow and labor intensive process which controls the speed of many phases of a construction project.

The stiff properties of steel inhibit rebar to be shaped with reasonable effort to follow the actual stress patterns anticipated for concrete structures. Those stress patterns in concrete structures are curvilinear in nature, however the rebar used to reinforce is straight. Because of this, a simplified reinforcing pattern is generally adopted and the steel then is formed to follow this simplified, straighter but less accurate pattern, which is easier to form with the stiff steel bars. However this representation of the reinforcing design is inherently redundant in order to compensate for the shapes the steel cannot easily be made to follow. This redundancy forces more reinforcing to be used than is necessary, thereby increasing the mass, weight and material used in a reinforced concrete structure.

In the curing process of concrete, and because of the load cycles experience during the lifetime of a structure, a concrete structure forms cracks. These cracks are necessary for the reinforcing material in the concrete to be fully utilized. The cracks allow the rebar (when properly placed) to hold the concrete together and distribute the loads to the rest of the structure. Additionally environmental moisture absorbed by concrete is subjected to freeze thaw cycles in colder climates. This causes an expansion and contraction of the water in the concrete, also forcing cracks to form. These cracks allow rainwater and environmental moisture to penetrate the concrete.

Water when it inevitably reaches the steel rebar causes a reaction of oxidation to occur. In the process of oxidation, the steel corrodes and expands which releases the bond to the concrete. The mass added as a result of the chemical reaction between the water and steel often causes the thin layer of concrete between the steel reinforcing and the exterior to become dislodged or break off. This reaction is called 'spalling'. The spalling of concrete further exposes the reinforcing which in turn allows for expanded decaying of the steel tensile reinforcing, further weakening the structure. It is the object of this invention to ease the construction process through reduced labor in fabrication and assembly. An additional object of this invention is to increase the efficiency of tensile reinforcing in concrete structures both for resisting the design loads as well as enhanced performance for withstanding moisture problems commonly plaguing steel reinforcing.

DESCRIPTION OF PRIOR ART

Concrete is generally reinforced to withstand greater tensile and ductile stresses than concrete can bear by itself. There are two primary methods of reinforcing. One method uses mesh (usually steel) and the other rebar (usually steel), which are placed in the areas where the highest tensile stresses are experienced. The concrete in the composition receives and resists the compressive forces of the loads experienced, the reinforcing material acts to receive and transfer the tensile stress along the axis of the reinforcing material.

The mesh that is used in concrete slabs which are formed are used for many purposes including but not limited to road decks, floor slabs, sidewalks and architectural elements. The tensile capacity of the mesh reinforcing is a function of the gauge (sectional area) of the steel used in the mesh. Because the mesh's primary purpose is to resist cracking of the slab by general loads experienced on the structure, the gauge of the steel used does not require a large capacity for reinforcing. The mesh is not necessarily intended to provide a great load-bearing capacity like that of rebar. It is an economical, fast and less labor intensive method of installation of reinforcing when great loads are not experienced. Concrete structures using a mesh as reinforcing are generally already supported by the aid of other thicker metal rebar in the design or by the support of ground or other structure beneath it.

Rebar is used in concrete structures as the entity intended to resists the primary

1 tensile forces in the structure, Rebar is much stronger than steel mesh due to it's increased gauge and texture. Steel rebar is very labor intensive to fabricate, transport, . shape, tie together and slow to install.

By a great margin, the principal reinforcing material used by the field of construction is steel. However some materials have recently been invented and are used in similar fashions to that of standard steel reinforcing. These composite materials have been inspired by their non-corrosive qualities under environmental conditions, their lightness, and increased strength to weight ratio than that of typical steel used in rebar and metal mesh.

The inventions described in U.S. Pat. No. 5,218,810, U.S. Pat. No. 6,846,537 B2 and U.S. Pat. No. 6,790,518 B2 are each comprised of a non metallic structural fabric which is intended to aid in the reinforcing of masonry or concrete structures. However each of them is designed for external applications on the structure needing reinforcement and supplement an already steel reinforced concrete or masonry structure.

U.S. Pat. No. 5,218,810 "is a reinforced concrete column wherein the exterior surface of the concrete is wrapped with a composite reinforcement layer". This layer wrapped around the concrete column adds greater load bearing capacity of the column by resisting buckling or bending forces experienced during an earthquake or asymmetric loading. Being located on the outside of the column, the reinforcing material does not increase the tensile capacity of the concrete itself. It is intended to be a supplemental reinforcing system to an existing concrete or masonry column. Additionally its exterior application exposes it to the elements of it's environment making it susceptible to damage caused by external factors such as weather, people or traffic.

U.S. Pat. No. 6,790,518 is a structural fabric that is intended to increase the load- bearing capacity of a concrete beam already reinforced by traditional steel rebar. The capacity of the structural member is added only by the superficial exterior application of the structural woven fabric that has similar deficiencies to the exterior application of U.S. Pat. No. 5,218,810. The steel reinforcing in the concrete structure still contributes a great portion of the tensile reinforcing.

U.S. Pat. No. 6,846,537 is a structural system that is applied to existing masonry or concrete structures (generally walls) in order to increase its loading capacity. The applications when applied aid generally in the lateral bearing capacity of the structures. They are not changing the inherent properties of the concrete or masonry of the structure itself. Additionally its exterior application has similar deficiencies as is noted in the description of U.S. Pat. No. 5,218,810.

Other efforts have been made to explore the use of a non-metal rigid rebar in reinforced concrete structures. U.S. Pat. No. 6,800,164 is a composite reinforcing bar (rebar) which is made of woven fiber strands which are set with a resin bath and fabricated to form the final rod similar to steel rebar including texture and size. U.S. Pat. No. 5,613,334 teaches "a non-metallic laminated composite reinforcing rod for use in reinforced or prestressed concrete." This invention is made up of multiple layers of composite materials which are formed, shaped, hardened and are then cut to size to be used as reinforcing rods. The purpose of both of these inventions are that they are to be used in a similar fashion to that of standard steel reinforcing bars (rebar) in reinforced concrete construction. Their greater strength to weight ratio increases the capacity of the structural members they are used in, however their capacity to support the concrete structure they are imbedded in is limited to the surface area they have in contact with in the concrete.

The total surface area the composite rebar comes in contact with is a function of their distribution in the concrete structure. The distribution in standard rebar design is intended to be used as minimally as possible in order to support the desired load. Steel mesh on the other had has a broad distribution throughout the concrete structure and is able to reinforce a wider area of the concrete. The steel mesh is however limited, as previously described, by the capacity of the gauge of steel used. Rebar, having a thicker gauge, may be and is often laid in a similar pattern to that of mesh in order to gain broader distribution as is often done. This design pattern however is very labor intensive to install and uses a great amount of material to cover such a wide distribution as is achieved by metal mesh. This complex design for rebar (steel or composite) slows the construction process as well as makes the structure heavier and thus less efficient. .

In U.S. Pat. No. 4,617,219 a non-woven three-dimensional spatial fabric intended to reinforce a concrete structure in panel form. Its non-woven core is used in conjunction with a woven or non-woven fabric in order to complete a sandwiched composition when combined with concrete. This invention uses a distribution of reinforcing to aid the concrete in its capability of resisting tensile stresses, however it's design does not reflect a method of designing specific reinforcing patterns to follow more known stress which are expected in a concrete structure. Because "...the non- woven fabric has fibers which are not oriented and in fact are disposed in random fashion in all directions..." the reinforcing described does not attempt to follow specific stress patterns, even though the larger resulting member may be intended to be positioned within a structure that would provide optimal tensile reinforcement. Additionally, it is important to note that the three- dimensional fabric being used is non-woven which is what distinguishes it from previous inventions and the preferred embodiment of this invention.

Although the above mentioned inventions are well suited for their intended purpose, a need still exists to combine the strength, weight and weather resistance characteristics of composite materials, the distribution qualities of mesh reinforcing and the efficiency of specific reinforcing patterns as intended for use with rebar.

SUMMARY OF THE INVENTION

The present invention uses a structural fabric (preferably a woven fabric) embedded within a concrete structure in order to give it tensile reinforcement. The fabric may be a non-corrosive composite woven material with a strength to weight ratio comparable with that of common steel used in rebar. This lighter reinforcing material will ease the installation process of reinforcing in concrete structures as compared to conventional rebar reinforcing design. Once embedded in a concrete structure the fabric would provide extremely efficient tensile reinforcing design as well as improve the performance of the concrete structure with the environmental elements such as moisture and pollution. A reinforced concrete structure utilizing the preferred embodiment may be formed by traditional methods in prior art. Because of the weight and flexibility of the fabric reinforcing, the transportability and installation on the site of the forming is greatly eased. Instead of individual steel bars being transported, shaped, installed, and tied, the fabric may be designed and fabricated off site, folded and brought to the site and installed in large sections, not a piece at a time. The reinforcing material would be positioned to best resist the tensile forces in the structure. The fabric reinforcing would be then stretched into shape in order to be engage the tensile strength of the fabric. Concrete then would be poured into the form, completely enveloping the reinforcing fabric. The poured form is then allowed to set and cure which will then give the concrete the chance to bond to the reinforcing material. Because of the reduced labor, the construction time of reinforced concrete structures that use this invention is greatly reduced when compared to current states of technology using rebar.

Concrete structures experience very complex force patterns throughout the structure. There are commonly known and used methods of calculating these stresses in a desired structure. Diagrams such as moment diagrams are often used as a template for determining where tensile reinforcing is needed most. Because of the inherent properties of steel including heavy massing and stiffness, considerable labor is needed to overcome these restrictions in order to manipulate the straight bars into various shapes. This . understanding of the material properties and labor involved with its forming is considered in designing the reinforcing design. Steel rebar therefore is designed to respond to greatly simplified stress patterns that basically represent the realities of the stresses not truly following the actual stress patterns. The redundancy in the steel reinforcing creates added massing and weight to the overall structure.

In a preferred embodiment of the invention the reinforcing material would be a woven fabric that is both lightweight (as compared to the unit weight of the steel members used) and flexible enough to be formed to follow more accurate stress patterns predicted to occur in new concrete structures. This more accurate design for reinforcing would provide a more efficient support system within the structure than the simplified steel reinforcing patterns. The more efficient use of the reinforcing material reduces the overall material needed to support the structure thus reducing the overall weight of the structure. Additionally, because of the comparable strength to weight ratio of the preferred embodiment as compared to steel, and the more efficient use of reinforcing material, the structural fabric would also be inherently a lighter reinforcing system than steel. This lightened product would allow for greater spans using less material for reinforcing.

In a preferred embodiment of the invention the reinforcing fabric is a woven fabric that is light, flexible and able to be worked with under normal building construction site conditions. The fabric may be of many different types of materials that are readily available which are flexible enough to be shaped to follow the stress patterns in the proposed concrete structure. A preferred material is a composite fabric having non- corrosive reaction to water or common airborne environmental elements such as pollution or typical air compositions. This quality would enable the fabric to reinforce the concrete structure but not become susceptible to decomposition or corrosion because of environmental factors like water or pollution. These two factors are a major contributor to steel reinforced concrete structure ruin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE l is a cut away isometric of a beam using a reinforcing system according 5 to the invention.

FIGURE 2 is a cut away isometric of a floor slab using a reinforcing system according to the invention.

FIGURE 3 is a cut away isometric of a column using a reinforcing system according to the invention.

10

FIGURE 4 is a cut away isometric of a combination of a column and a floor slab each using a reinforcing system according to the invention.

FIGURE 5 is an isometric of a combination of a column and a floor slab each using a reinforcing system according to the invention.

, , FIGURE 6 is a diagram showing the typical arrangement of steel rebar in a continuous slab as well as the ideal path for reinforcing.

FIGURE 7 is a diagram showing the reinforcing system of the invention following the ideal path for reinforcing in a continuous slab.

FIGURE 8 is a diagram showing a section of a pre-stressed concrete beam using the reinforcing system of the invention immediately following the pouring of the concrete with the preferred embodiment pre-stressed.. FIGURE 9 is a diagram showing a section of a pre-stressed concrete beam using the reinforcing system of the invention after the tension has been released from the preferred embodiment at the appropriate curing state of the concrete in order to achieve the desired deformation. , i

FIGURE 10 is a section of a fabric forfnwork used in conjunction with the reinforcing system of the invention as the reinforcing element in the slab of the. framework.

FIGURE 11 shows a method of shaping the woven fabric reinforcing material of the invention.

FIGURE 12 shows another method of shaping the woven fabric reinforcing material of the invention.

DETAILED DESCRIPTION

The present invention may be used to reinforce a wide variety of concrete structures. The invention is intended to increase the bearing capacity and performance of concrete structures by providing greater tensile reinforcement at a lesser weight than that of commonly used steel reinforcing. Additionally it is the intended purpose of this invention to be easier to install and perform better over the life of the structure than the previous art of steel reinforcing.

"Concrete" as described in this patent refers to the cementitious composition that is most commonly used in the field of this invention. This concrete is most often made of Portland cement, aggregates (sand and gravel) and water. However this is one example of a concrete composition and should not imply that the preferred embodiment be limited to use with only this type of concrete. There are other types of concrete compositions which may also serve as a reasonable material to use in conjunction with the preferred embodiment. Varying mixtures and compositions may be used including performance enhancing additives and other types of cement.

The preferred embodiment of this invention uses a structural fabric being called so because it has the capacity of providing structural support to loads placed upon it. The embodiment would be created using a woven technology that is already available. The woven characteristic of the fabric would enable fibrous material to carry stresses along the length of their axis while distributing loads throughout the fabric plane. A "woven" fabric is described herein as a cloth made by interlacing the threads of the weft and the warp on a loom or similar device as is commonly done in the field.

A wide variety of known structural fabrics may be employed and are readily available. Preferred fabrics would be fiberglass, carbon fiber, Fiber Reinforced Plastic (FRP), Kevlar®canvas, linen, hemp fabric, or other types of man-made or natural materials. The woven fabrics would preferably be non-corrosive when exposed to water or environmental conditions that are experience on a typical construction or factory site. Additionally the fabric is preferably resilient to the Alkaline conditions which are present in some forms of concrete construction. If this is the case, materials such as those that are susceptible to a corrosive reaction to alkali must be protected prior to the introduction of the concrete in the structure. The use of an epoxyresin, plastic, rubber or other protective coatings (which are readily used in the field) could protect the fabric from degenerative reactions with the concrete. The fabric may be woven in a wide variety of patterns. It is preferred that the fabric pattern be constructed in such a way that is compatible with the properties of the concrete in order to create a mechanical bond between the two materials.. For this to happen there must be a texture to the weave whereby the concrete may adhere to the surface of the fabric, or the fabric must have a porosity that can allow concrete to pass through the fabric material in order for the concrete on both sides of the fabric layer to create a mechanical bond with each other and the fabric. This bond is necessary in order to utilize the strength of the fabric material to act as an integral structural component in the composition.

If the weave is to allow for concrete to pass through it, it should be chosen to be , compatible with the aggregate size and composition of the particular concrete being used. For larger aggregates it would be preferred to have larger holes so that no spacing be blocked by aggregate components of the concrete. Preferably, the weave of the fabric will also have a pattern that does not allow for stretching or distortion beyond the material's properties, unless is designed to do so. This might apply when using the fabric reinforcing in a process similar to that of pre-stressed concrete construction in which some degree of stretching is necessary in order to create the desired forms. The preferred embodiment will also have negligible elastic properties (comparable to that of steel's length to elastic deformation ratio) so as to act as a useful reinforcing material that gives ample support for the tensile stresses without noticeable deformation. Some deformation may be possible so as to allow the preferred embodiment to support a pre-stressed condition as it commonly done in the field. Reinforced concrete structures embodying the present invention may be formed by a wide variety of methods. These include those that are readily used in common construction as well as those that may not be very common. Individμal structural components may be prefabricated and transported to a site for installation. Or alternatively entire structural systems may be formed on site at once setting up a formwork upon which other building components may be added. Various techniques and combinations of the like may be used to create the reinforced concrete structures.

Common structural members may be formed using the preferred embodiment. Figure 1 shows a reinforced concrete beam 2 using a woven fabric 1 as the reinforcing material. The shape and position of woven fabric 1 would vary based on the size, span and load of the beam. It is important to note the various shapes that are possible within a form. Figure 2 shows woven fabric 3 being used in a typical floor slab 4. Similarly Figure 3 shows woven fabric 5 being used to reinforce a round column. It is important to I c note that the concrete forms around the preferred embodiment may vary in any shape that is determined to be the most efficient. The Figures only show examples and should not be considered the limitation of the invention.

The woven fabric may be used to reinforce singular components to a structural system or several pieces that would tie together. For example Figure 4 shows how a _jr. column 7 may utilize woven fabric 8 for its reinforcing, and then the fabric could then tie into the fabric reinforcing 9 in the floor slab. The reinforcing for these separate structural elements may be stitched together or fabricated as a single reinforcing element. Because of the flexible nature of the reinforcing material, continuous reinforcing from one element to the next would provide extremely efficient reinforcing to transfer stress as shown in Figure 5 from one 10 structural element to the next 11:

Figure 6 shows a diagram of a conventionally reinforced continuous slab 12 using rebar 13. Through conventional analysis as is presently done in the field, one would find the ideal reinforcing pattern 15 would generally follow this simplified reinforcing design. However because of the stiff nature of the reinforcing material 13 the design must include extra reinforcing material 14 that compensates for the inability to follow the idealized stress pattern 15. Figure 7 shows a similar continuous slab that is reinforced with the woven fabric of the invention 17 which follows the idealized stress patterns much more closely.

A preferred fabric will be a fabric with high stiffness for cast in place and preformed reinforcing patterns. However if a structural fabric is used which has a very minor elastic quality comparable to that of the length to elastic deformation ratio of steel, the fabric may be used in a common technique called pre-stressing. Figure 8 shows how the reinforcing fabric 18 in the form would be pre-stressed 19 before the concrete is added. Once the concrete is applied into the form and hardens to an appropriate amount, the fabric tension is released 20 causing the structure to deform 21 in a desirable way as is previously practiced in the art, as shown in Figure 9.

Another fabrication method which may be employed with the invention is that of shotcrete. This method is commonly used in the current art where it employs the use of a concrete composition that is suitable for 'shooting' onto a surface that has reinforcing already set in place. The shotcreted concrete then covers the surface and area behind the reinforcing in order to encapsulate the reinforcing layer. This method is often used to create vertical, sloping or complex surfaces as it does not need to be poured to a level plane. This method also allows for the concrete to be sculpted to it's desired form. This method may be used in combination with other methods of forming to achieve an appropriate bond or form as desired;

Because of the composition and flexible nature of the preferred embodiment, the fabric has a unique ability to be stitched or integrated with other fabrics.. Because of this, the structural fabric may be used in conjunction with a fabric formwork that is impermeable by the concrete in order to create a novel method of forming reinforced concrete structures. In this case, the concrete may encapsulate the reinforcing fabric as shown in Figure 10. Fabric formwork 23 may be constructed and erected to enclose the shape of the desired concrete form. The fabric 24 may be positioned within the formwork and the concrete 22 introduced would encapsulate the reinforcing material. The reinforcing layer that is contained within the flexible formwork may be used throughout or in parts of the concrete structure. In this example the reinforcing layer is only used in the reinforcing of the floor slabs where as the column may use the fabric formwork as sufficient reinforcing for the columns themselves.

The forming of the fabric within a concrete formwork may be done using several techniques including but not limited to those described in this document. One of the primary advantages of using a flexible reinforcing material such as the preferred embodiment is that it may be formed in a variety of simple and complex shapes. Because of this, flexible reinforcing has the ability to follow primary stress patterns that are determined to be the most efficient to follow in order to achieve optimal reinforcing results. Conventional stiff reinforcing materials like steel or epoxy based composite rebar or mesh cannot achieve these curvilinear forms without considerable labor.

The woven fabric can be shaped in a preferred pattern by various ways. One method to place the fabric reinforcing within the formwork would be that the fabric be woven, stitched or formed in such a way that when pulled in tension, it creates the desired shape. Another way is that the fabric be shaped by mechanical means and then coated with an epoxy resin or the like which would harden the reinforcing in the preferred shape. Once in its final form, it may then be mixed with the concrete by having the concrete poured, prayed, shot or any other way introduced into the formwork.

Another method for shaping the woven fabric within a concrete formwork may be with the help of guides, either imposed on a formwork or built into the formwork itself. Figure 11 shows how a rectangular concrete beam may have a series of metal rods or tubes 25 inserted through the formwork in order to guide the woven fabric, when pulled in tension along line 26, in order to create the ideal shape for the reinforcing to follow.

The other method of guiding the preferred embodiment to achieve the ideal shape within a concrete structure is by using the formwork to shape the reinforcing fabric. Figure 12 shows how the formwork built in two pieces 27 and 29 for a simple rectangular beam for example may assemble and guide the reinforcing fabric 28 along the ideal shape desired.

Both methods described here use existing techniques for creating reinforced concrete structures. However with simple modifications, these standard techniques allow for the preferred embodiment to be introduced without seeking new methods of fabrication to be introduced.

The above description constitutes the preferred embodiment of the present invention, however it will be .appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the , accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. An article for use in reinforcing a load bearing concrete structure wherein a structural fabric is the primary tensile reinforcing component.

2. The article of claim 1 wherein the structural fabric comprises woven fibers.

3. The article of claim 1 wherein the reinforcing component is entirely enclosed within the concrete structure.

4. The article of claim 1 wherein the structural fabric is used entirely or partially on the exterior of the concrete structure.

5. The article of claim 1 wherein the structural fabric embedded in the concrete structure is used in conjunction with an impermeable fabric formwork that remains on the exterior of the entire or partial part of the concrete structure.