FIBER STRUCTURAL REINFORCEMENT WITH FRICTIONAL SURFACE COATING

Abstract

The present invention is directed to fiber composite structures, including one or more composite fibers or igneous rock fibers, such as basalt fibers and/or andesite fibers, that are impregnated with a polymer resin and subsequently coated with a frictional additive, such as aluminum oxide. The frictional additive provides for improved frictional engagement when the fiber composite structures are included in concrete or other structural materials and reduces alkaline degradation of the composite structures within the concrete over time. A process for manufacturing the fiber composite structures is also described herein. The process includes inductive heating of the fiber composite structures in order to cure the polymer resin, so as to affectively apply heat without being impeding by the external layer of frictional additive.

Claims

1. A fiber composite structural reinforcement, comprising: a plurality of composite fibers disposed within a polymer resin matrix; wherein the polymer resin matrix includes at least one electroconductive additive; wherein the fiber composite structural reinforcement is coated with a plurality of ultrafine aggregates; and wherein the fiber composite structural reinforcement is coated with a plurality of fine aggregates.

2. The fiber composite reinforcement of claim 1, wherein the fiber composite structural reinforcement is between approximately 1 inch and approximately 2.5 inches.

3. The fiber composite reinforcement of claim 1, wherein the at least one electroconductive additive includes graphene.

4. The fiber composite reinforcement of claim 1, wherein the plurality of ultrafine aggregates include calcium hydroxide, calcium silicate hydrate, tricalcium aluminate, and/or gypsum.

5. The fiber composite reinforcement of claim 1, wherein the one or more ultrafine aggregates have diameters less than 40 microns.

6. The fiber composite reinforcement of claim 1, wherein the plurality of fine aggregates include aluminum oxide.

7. The fiber composite reinforcement of claim 1, wherein the plurality of fine aggregates have diameters between about 100 microns and about 200 microns.

8. The fiber composite reinforcement of claim 1, wherein the plurality of composite fibers includes basalt and/or andesite fibers.

9. A method for producing a fiber composite structural reinforcement, comprising: melting at least one resin to form a resin melt; adding at least one electroconductive additive to the resin melt; a resin impregnator receives a plurality of composite fibers and impregnating the composite fibers with the resin melt to form one or more composite structures; coating the one or more composite structures with one or more ultrafine aggregates; curing the one or more coated composite structures via a first inductive heating step, forming one or more cured composite structures; coating the one or more cured composite structures with one or more fine aggregates; curing again the one or more cured composite structures via a second inductive heating step; slicing the one or more cured composite structures into a plurality of composite reinforcement bars.

10. The method of claim 9, wherein the at least one electroconductive additive includes graphene.

11. The method of claim 9, wherein the resin melt includes at least one thermosetting polymer.

12. The method of claim 9, wherein one or more ultrafine aggregates include calcium hydroxide, calcium silicate hydrate, tricalcium aluminate, and/or gypsum.

13. The method of claim 9, wherein the one or more ultrafine aggregates have diameters less than 40 microns.

14. The method of claim 9, wherein the one or more fine aggregates include aluminum oxide.

15. The method of claim 9, wherein the one or more fine aggregates have diameters between about 100 microns and about 200 microns.

16. The method of claim 9, wherein the first inductive heating step is performed in a first chamber and the second inductive heating step is performed in a second, additional chamber.

17. A fiber composite structural reinforcement, comprising: a plurality of igneous rock fibers disposed within a thermoset polymer resin matrix; wherein the polymer resin matrix includes at least one electroconductive additive; wherein the at least one electroconductive additive includes graphene; wherein the fiber composite structural reinforcement is coated with a plurality of ultrafine aggregates; wherein the fiber composite structural reinforcement is coated with a plurality of fine aggregates; and wherein the fiber composite structural reinforcement is between approximately 1 inch and approximately 2.5 inches.

18. The fiber composite reinforcement of claim 17, wherein the one or more ultrafine aggregates have diameters less than 40 microns.

19. The fiber composite reinforcement of claim 17, wherein the one or more fine aggregates have diameters between about 100 microns and about 200 microns.

20. The fiber composite reinforcement of claim 17, wherein the plurality of igneous rock fibers includes basalt and/or andesite fibers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 illustrates a diagram of a system for producing fiber composite structures according to one embodiment of the present invention.

[0029] FIG. 2 illustrates a flow diagram of a process for producing fiber composite structures according to one embodiment of the present invention.

[0030] FIG. 3 illustrates a flow diagram of a process for producing fiber composite structures according to one embodiment of the present invention.

[0031] FIG. 4 illustrates a flow diagram of a process for producing fiber composite structures according to one embodiment of the present invention.

[0032] FIG. 5 illustrates a cross-sectional view of a fiber composite structure according to one embodiment of the present invention.

DETAILED DESCRIPTION

[0033] The present invention is generally directed to fiber composites including improved surface coatings and more specifically to fiber composites for strengthening of concrete or other structural materials.

[0034] In one embodiment, the present invention is directed to a fiber composite structural reinforcement, including one or more igneous rock filaments impregnated with at least one plastic resin and coated with at least one frictional coating as described herein.

[0035] In another embodiment, the present invention is directed to a method for producing a fiber composite structural reinforcement, including impregnating a bundle of igneous rock filaments with at least one plastic resin and coating the impregnated bundle with at least one frictional coating as described herein.

[0036] None of the prior art discloses composite fiber-reinforced minibars with applied frictional coatings to improve retention of the minibars within concrete or other structural materials.

[0037] Many common structural materials, most notably concrete, are chosen for their ability to withstand high compressive loads, which is the predominant loading regime for most construction materials, due to the force of gravity. However, materials such as concrete tend to perform notably poorly in tension, having a relatively low ultimate tensile strength and a brittle failure mode that lends itself easily to catastrophic failure. While concrete is generally under predominately compressive stress, concrete used in specific types of structures, including bridges and arches, is also under almost constant tensile stress. Furthermore, disturbances to structures where the concrete is generally under compressive stresses (e.g., buildings) often still impose tensile stresses that the concrete needs to withstand. For example, phenomena such as earthquakes often apply unusual tensile loads to structures normally in compression, leading these structures to fail if they lack ability to perform in tension.

[0038] Steel fibers have been added to concrete to improve mechanical properties since the 1970s. These steel fibers are intended to improve properties such as ductility, toughness, energy absorption, and crack prevention. Many of these properties arise from steel fibers' far greater tensile strength relative to concrete. However, even as steel fibers provide improved mechanical properties in reinforced concrete, still greater improvements are needed to better prevent cracks and absorb energy in the concrete. One solution, proposed inventions such as those described in U.S. Pat. No. 10,369,754 and U.S. Patent Pub. No. 2021/0245456, utilizes composite fibers to provide increased strength to concrete. While the composite fiber structures described in these inventions do demonstrate greatly improved properties relative to steel, the cured external polymer resin in the composite fiber structures tends to react with the concrete, creating a small liquid boundary layer between the composite fiber structures and the surrounding concrete. This liquid boundary layer further tends to be alkaline in nature, causing potential degradation to basalt fibers within the composite fiber structures, due to the alkali-silica reaction. Not only does this tend to degrade some of the thickness of the composite fiber structures, thereby reducing their mechanical performance, but this also causes the composite fiber structures to less readily engage when the concrete is in tension. By not engaging as readily when the concrete is in tension, the concrete tends to fail quicker than is optimal given the enhanced properties of the fibers, and some of the fibers tend to slip out, unbroken, after the concrete has failed. Therefore, a method of increasing the frictional contact between the fiber composite structures and the surrounding concrete is needed.

[0039] The present invention includes using frictional additives to coat the composite structures to improve performance. Prior art documents, including U.S. Pat. No. 10,369,754, describe applying sizing agents as coatings to fibers in order to protect and lubricate the fibers. However, applying sizing agents to the fibers themselves is not sufficient in cases where a fiber composite structure (i.e., a fiber impregnated with resin) is inserted into a concrete block, as the sizing agent in that case is not external to the fiber composite structure, but is largely between the fibers and the impregnated resin and therefore not substantially in contact with the concrete. Elsewhere, prior art documents, such as U.S. Pat. No. 7,790,284 and U.S. Patent Publication Nos. 2021/0245455 and 2019/0092686, describe coating composite fibers, but use the term coating in reference to the impregnated resin itself, and not in reference to any external frictional coating applied over the impregnated resin. Therefore, what is needed are new composite fiber structures, having improved compatibility with the concrete and which therefore more readily engage in tension than previous structures.

[0040] Referring now to the drawings in general, the illustrations are for the purpose of describing one or more preferred embodiments of the invention and are not intended to limit the invention thereto.

[0041] The present invention describes a method for creating minibars, defined as short resin impregnated composite fiber structures, for inclusion into structural materials (e.g., concrete) in order to provide improved structural properties for the concrete. Preferably, the inclusion of minibars obviates the need for steel fibers in the concrete or even for large rebar included in the concrete due to the improved properties of the composite fibers relative to steel. Importantly, the minibars described herein are coated with frictional additives to improve the frictional interface between the minibars and the surrounding structural material.

[0042] FIG. 1 illustrates a diagram of a system for producing fiber composite structures according to one embodiment of the present invention. In one embodiment, one or more roving bobbins 102 are unwound and the fibers 106 are fed through one or more air blower texturizers 106 into a resin impregnator 108. In one embodiment, the fibers include composite fibers, preferably including igneous rock fibers, such as basalt fibers and/or andesite fibers. In another embodiment, the fibers include carbon fiber and/or fiberglass. Resin is fed into the resin impregnator 108 through at least one viscosity stabilizer 110 from at least one resin melting chamber 116. In one embodiment, the resin is a polyurethane resin. In one embodiment, the resin includes a thermosetting polymer, including but not limited to epoxy, polyester, polyvinyl ester, thermoset polyurethane, and/or other thermosetting polymers. In another embodiment, the resin includes a thermoplastic polymer, including polyurethane, thermoplastic polyurethane (TPU), polyethylene (e.g., low-density polyethylene (LDPE), high-density polyethylene (HDPE), ultra-high molecular weight polyethylene (UHMWPE), etc.), polypropylene, polycarbonate, polyvinyl chloride (PVC), polystyrene, polytetrafluoroethylene, and/or any other suitable polymer. One of ordinary skill in the art will understand that the resin is able to include a pure polymer resin (i.e., including only a single polymer), or a mixed polymer resin (i.e., including a mixture of a plurality of different polymers). In one embodiment, the polymer resin includes at least one conductivity additive for increasing the electrical conductivity of the polymer resin. In one embodiment, the at least one conductivity additive includes at least one metal powder (e.g., copper powder) and/or at least one carbon allotrope (e.g., graphite, graphene, etc.). In the case of graphene being used for the at least one conductivity additive, the graphene is able to be added in a variety of forms, including as graphene nanoplatelets.

[0043] The now resin-coated fibers 112 exit the resin impregnator 116 and pass toward a first curing station 118. In one embodiment, before the resin-coated fibers 112 enter the first curing station 118, at least one frictional coating is applied to the fibers 112 via a frictional applicator 114. In one embodiment, the frictional applicator 114 applies the at least one frictional coating via a spray mechanism. In another embodiment, as the resin-coated fibers 112 move toward the first curing chamber 118, the fibers 112 contact a surface of the frictional applicator 114 including the at least one frictional coating, such that the at least one frictional coating is rubbed off on the fibers 112. The present invention is not limited to a single frictional applicator 114 but is able to include any number of frictional applicators 114 having the same or different mechanisms that are described herein. In one embodiment, the at least one frictional coating includes aluminum oxide (i.e., alumina). One of ordinary skill in the art will understand that the at least one frictional coating is able to include any substance that does not react with the polymer resin or the composite fibers used in the composite fiber structures (or minibars), such that the composite fiber structures do not degrade. Furthermore, in a preferred embodiment, the at least one frictional coating does not react with concrete, preventing or reducing the formation of a liquid layer between the composite fiber structures and the surrounding concrete.

[0044] The addition of at least one frictional coating, such as alumina, is beneficial for improving the concrete-fiber structure interface, but presents its own challenges. For example, the process used in documents such as U.S. Pat. No. 10,369,754 and U.S. Patent Pub. No. 2021/0245456, utilizes external heat in a plurality of curing chambers to cure the polymer resin and stabilize the composite fiber structure. However, the at least one frictional coating renders these existing processes practically unusable, as the at least one frictional coating prevents the external heat from adequately reaching the polymer resin, thereby preventing, or at least greatly increasing the time for, the curing process. For this reason, significant changes must be made to the curing process used in order to adapt to the usage of a frictional additive coating. Importantly, these adaptations were not previously needed for cases where the coating is merely applied as a sizing agent to the fibers themselves, as that coating is not external to the impregnated resin and therefore does not prevent application of external heat.

[0045] The fibers 112 enter the first curing chamber 118. In one embodiment, the first curing chamber 118 includes one or more induction coils 120. The one or more induction coils 120 inductively heat the at least one polymer resin, such that the curing process is able to continue without external heat needing to be transported through the at least one frictional coating. In one embodiment, the inclusion of the at least one conductivity additive increases the effectiveness of the inductive heating process. In one embodiment, the at least one frictional coating is not added to the fibers until after the fibers have exited the first curing chamber 112. In this embodiment, the first curing chamber 118 is capable of utilizing direct heating or inductive heating, as the at least one frictional coating is not yet impeding the transport of external heat into the polymer resin.

[0046] In one embodiment, after exiting the first curing chamber 118, the fiber composite structures 112 pass through one or more shaping gears 122, which shape the fiber composite structures 112 into a non-linear shape (e.g., a square wave structure as shown in FIG. 1, a wave structure, etc.). However, in another embodiment, no shaping gears are used and the fiber composite structures 112 passes straight from the first curing chamber 112 to the second curing chamber 124. Unexpectedly, the benefits of providing surface ridges or non-linear structure to the fiber composite structures are relatively low. Instead, due to the fluid interface between the composite structures and the surrounding concrete, during tension, the fiber composite structures are pulled into a straight linear pattern and then begin slipping, still without substantially engaging in tension. As this is an unexpected outcome, one of ordinary skill in the art is unlikely to have modified the processes described in U.S. Pat. No. 10,369,754 and U.S. Patent Pub. No. 2021/0245456 to remove the one or more shaping gears 122. Therefore, the at least one frictional coating instead provides a benefit previously expected to have been provided by the shaping of the fiber composite structures.

[0047] The fiber composite structures then enter the second curing chamber 124. In one embodiment, the second curing chamber 124 includes one or more induction coils 126. The one or more induction coils 126 inductively heat the at least one polymer resin, such that the curing process is able to continue without external heat needing to be transported through the at least one frictional coating. In one embodiment, the inclusion of the at least one conductivity additive increases the effectiveness of the inductive heating process.

[0048] One of ordinary skill in the art will understand that the system and method of the present invention are not limited to two curing chambers. Any number of curing chambers are able to be included to ensure that the polymer resin fully cures. Additionally, one of ordinary skill in the art will understand that, in one embodiment wherein the resin is a thermoplastic polymer, the curing chambers cool, rather than heat, the composite fiber structure, while those embodiments utilizing thermosetting resins have curing chambers that heat the composite fiber structure as previously mentioned.

[0049] After curing in the second curing chamber 124, the cured composite fiber structure 128 exits the chamber 124. In one embodiment, the cured composite fiber structures passes over at least one support roller 130 and is cut into individual short composite fiber structures (or minibars) 134 by at least one cutting tool 132. In one embodiment, each minibar 134 has a length of approximately 2 inches. In one embodiment, each minibar 134 has a length between approximately 1 inch and approximately 2 inches. In another embodiment, each minibar 134 has a length between approximately 1 inch and approximately 2.5 inches. In one embodiment, each minibar 134 has a diameter of between approximately 0.5 mm and about 2 mm. However, one of ordinary skill in the art will understand that the length and diameter of the minibars 134 described herein are not intended to be limited.

[0050] FIGS. 2-3 illustrate flow diagrams of a process for producing fiber composite structures according to one embodiment of the present invention. As discussed with reference to FIG. 1, composite fiber (e.g., basalt fiber, andesite fiber, etc.) roving is unwound and passed through a texturizer before entering a resin impregnator. In another embodiment, the composite fibers are twisted and impregnated simultaneously in the resin impregnator. The resin is melted and mixed in a separate chamber, passed through a viscosity stabilizer, and then injected into the resin impregnator in order to impregnate the composite fibers with at least one polymer resin (e.g., polyurethane, polypropylene, high-density polyethylene, etc.).

[0051] In one embodiment, when the resin-coated fibers exit the resin impregnator, the resin coated fibers are coated with at least one frictional additive (e.g., aluminum oxide, etc.). After exiting the resin impregnator, the resin-coated fibers enter a first curing chamber, which applies heat in order to cure the resin and thereby solidify the composite structure. If the resin-coated fibers are already coated with the at least one frictional additive, then the first curing chamber uses inductive heating coils to indirectly heat the composite structure, such that external heat does not need to penetrate the frictional additive coating in order to cure the resin.

[0052] In one embodiment, after exiting the first curing chamber, the composite structure passes over at least one shaping gear, which provides a 2D or a 3D structure to the composite structure. In another embodiment, the composite structure does not pass over at least one shaping gear. In one embodiment, at least one frictional additive is coated onto the composite structure after the composite structure exits the first curing chamber. The composite structure then enters the second curing chamber. The second curing chamber includes at least one inductive coil, operable to inductively heat the composite structure so as to cure the resin and further solidify the composite structure. Finally, the composite structure is cut into individual minibars, which are then able to be added to concrete.

[0053] FIG. 4 illustrates a flow diagram of a process for producing fiber composite structures according to one embodiment of the present invention. In one embodiment, fibers and polymer resin are added to a resin impregnator. In one embodiment, the polymer resin added to the resin impregnator includes thermosetting polymer components, such as epoxy, polyester, vinyl ester, and/or polyurethane. In one embodiment, one or more electroconductive additives are also added to the resin impregnator. In another embodiment, the one or more electroconductive additives are added to the resin melt before the resin is added to the resin impregnator. In one embodiment, the one or more electroconductive additives are nano sized particles, including a carbon allotrope, such as graphite or graphene, one or more metal additives, such as aluminum, silver, cobalt, lithium, copper, iron, zinc, platinum, tin, titanium, or other metals, and/or salts thereof. In one embodiment, after the fibers are twisted and impregnated with the polymer resin to form fiber composites, the fiber composites are coated with one or more ultrafine aggregates (i.e., particle sizes not larger than approximately 40 microns in diameter). In one embodiment, the ultrafine aggregates include calcium hydroxide, calcium silicate hydrate, tricalcium aluminate, gypsum, alumina-silicates, ferro-silicates, and/or other cementitious materials. The cementitious materials prevent or reduce the formation of a gel-like paste between reacted components along the surface of the fiber composite and therefore improve adhesion of the fiber composites within the concrete. Cementitious composites are characterized by an interfacial transition zone (ITZ) in the vicinity of the reinforcing inclusion, in which the microstructure of the paste matrix is considerably different from that of the bulk paste, away from the interface. The nature and size of this transition zone depends on the type of fiber and the production technology; in some instances, it changes considerably with time. These characteristics of the fiber-matrix interface exert several effects which should be taken into consideration, especially with respect to the fiber-matrix bond, and the debonding process across the interface.

[0054] The special microstructure of the transition zone in cementitious composites is closely related to the particulate nature of the matrix. The matrix consists of discrete cement particles ranging in diameter from ?1 to ?100 ?m (average size of ?10 ?m) in the fresh mix, which, on hydration, react to form mainly colloidal calcium silicate hydrate (CSH) particles and larger crystals of calcium hydroxide (CH). The particulate nature of the fresh mix exerts an important influence on the transition zone, since it leads to the formation of water-filled spaces around the fibers due to two related effects: 1. bleeding and entrapment of water around the reinforcing inclusion, and 2. inefficient packing of the ?10 ?m cement grains in the 20-40 ?m zone around the fiber surface.

[0055] After coating with the ultrafine aggregates, the coated fiber composites are then inductively heated in order to cure the fiber composites. In one embodiment, after inductively heating the fiber composites in a first chamber, the fiber composites are then coated again. In one embodiment, the second coating utilizes fine aggregates (i.e., particles sizes with diameters between about 100 microns and about 200 microns). In one embodiment, the fine aggregates include aluminum oxide and/or one or more ceramic materials. In one embodiment, the fine aggregates are frictional additives designed to improve frictional contact between the fiber composites and the surrounding concrete, reducing chances that the fiber composites slip out of engaging with the concrete. The coated fiber composites are then inductively heated in a second chamber before being pulled and cut into individual minibars. The matrix in the vicinity of the fiber is much more porous than the bulk paste matrix, and this is reflected in the development of the microstructure as hydration proceeds. The initially water-filled transition zone does not develop the dense microstructure typical of the bulk matrix in existing, prior art materials, and it contains a considerable volume of CH crystals, which tend to deposit in large cavities. Based on above mentioned information, the reinforcement fibers have to have very advanced surface topographies with irregularities more than 40 microns. Experimentally it has been found that 80 grit alumina oxides particles provide both very good friction and alkalinity attack protection and thus, in one embodiment, such 80 grit alumina oxide particles are utilized for the fine aggregates. However, the present invention is not limited to 80 grit particles, and both 100 and 120 grit particles are also able to be used.

[0056] FIG. 5 illustrates a cross-sectional view of a fiber composite structure according to one embodiment of the present invention. A fiber composite structure, or a minibar 200, includes one or more composite fibers, such as igneous rock fibers (e.g., basalt fibers, andesite fibers, etc.) 202, impregnated with at least one polymer resin (e.g., polyurethane, polypropylene, etc.) 204. In one embodiment, the one or more composite fibers and the least one polymer resin are in a core sheath configuration (with the fibers as the core, and the polymer resin as the sheath). In another embodiment, the one or more composite fibers are in an eccentric core sheath and/or a side-by-side core sheath configuration. The combination of the composite fibers 202 and the polymer resin 204 is coated with a first cementitious additive 208 and/or a second frictional additive 206. For example, in one embodiment, the first cementitious additive 208 and/or a second frictional additive 206 nucleate to form small crystal-like structures along the length and circumference of the minibar 200. Importantly, even if the first cementitious additive 208 and/or a second frictional additive 206 does not entirely cover the length and circumference of the minibar 200, any addition provides frictional engagement with the concrete that improves performance and prevents at least some percentage of the degradation of the fiber composites within the concrete to improve performance. In one embodiment, the second frictional additives 206 include particles having diameters between approximately 100 ?m and approximately 200 ?m. In one embodiment, the first cementitious additives 208 include particles having diameters less than approximately 40 ?m.

[0057] Experimental results including the minibars of the present invention in concrete demonstrate a pull-out load force (i.e., the amount of force need to rip the fibers out of the concrete) at least two times greater than the pull-out load force needed for existing fiber composites of a similar nature on the market. This means that the minibars' flexural strength and residual strength are demonstrably higher than those of existing fibers previously available on the market.

[0058] One of ordinary skill in the art will understand that the structural materials to which the minibars are able to be added are not limited to forms of concrete. By way of example and not limitation, the minibars are able to be added to concrete, asphalt, wood, granite, brick, and/or any form of thermoplastic or thermoset structural material (e.g., polyvinyl chloride (PVC), polyurethane, etc.).

[0059] Certain modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. The above-mentioned examples are provided to serve the purpose of clarifying the aspects of the invention and it will be apparent to one skilled in the art that they do not serve to limit the scope of the invention. All modifications and improvements have been deleted herein for the sake of conciseness and readability but are properly within the scope of the present invention.