TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field of graphite, and more particularly, to compositions and methods of graphite oxide entrainment in cement and asphalt composites.

BACKGROUND OF THE INVENTION

Without limiting the scope of the invention, its background is described in connection with composite materials.

Graphene is one of the strongest materials ever tested. Various research institutes have loaded hosts with carbon allotropes such as carbon nanotubes (CNT), graphene flakes (GF), graphene oxide (GO), and graphite oxide and have seen up to a 200% increase in tensile strength in the loaded host, but with inconsistent results. Measurements have shown that graphene has a breaking strength 200 times greater than steel, with a tensile modulus (stiffness) of 1 TPa (150,000,000 psi). An atomic Force Microscope (AFM) has been used to measure the mechanical properties of a suspended graphene sheet. Graphene sheets held together by van der Waals forces were suspended over S1O ₂ cavities where an AFM tip was probed to test its mechanical properties. Its spring constant was in the range 1-5 N/m and the Young's modulus was 0.5 TPa (500GPa) thereby demonstrating that graphene can be mechanically very strong and rigid.

Nano-silica's spherical shape, carbon nanotubes (CNTs) and Hummers' based GO that has both surface oxidation, epoxy groups and surface distortion have high-aspect-ratio. CNTs and Hummers' based graphene/graphite oxide are suspended and dispersed in water then combined with Ordinary Portland Cement and or other materials reacted to form a cementitious composite.

Depending on whether they are single walled CNTs (SWCNTs) or multi-walled CNTs (MWCNTs), CNTs generally have the diameter of 1-3 nm or 5-50 nm, respectively. The length of CNTs can be up to centimeters, which gives an aspect ratio exceeding 1000. CNTs also exhibit extraordinary strength with moduli of elasticity on the order of TPa and tensile strength in the range of GPa, With the concurrent benefits of high aspect ratio and excellent mechanical performance, CNTs have been found to improve the toughness and strength of cementitious matrix materials. Incorporation of CNTs in cement composites has proven to be complex, yielding inconsistent results. Researchers have found that, the addition of CNTs results in little change in strength or even deterioration of the composite in some cases. Poor dispersion of CNTs in the water based cement matrix is due to the weak bonding between the CNTs and the cement matrix. Owing to strong Van der Waal's attractive forces between particles, CNTs tend to form agglomerates or self -attraction/assembly similar to that seen in carbon black creating defect sites in the composites. CNTs without a dispersing agent had worse mechanical properties than the plain cement paste. Non-uniform distribution/dispersion of CNT bundles are responsible for the deterioration of the mechanical properties. Attempts have been made to incorporate CNTs into Bitumen. The Bitumen was either heated or modified the pH while being stirred in a vessel to incorporate the CNTs. The resulting suspension was then combined with the dry portions constituents of the asphalt. Although non- optimally dispersed the resulting composite had reasonable enhanced performance.

Hummers' based graphite/graphene oxide (HGGO) is produced by using concentrated acids and oxidants and often required significant purification of the HGGO product. HGGO is more readily suspendable/dispersible in a polar solvent (ultra pure water) because the high level of oxidation making it hydrophilic. The HGGO can also irreversibly precipitate from the suspension in the polar solvent as a function of pH or exposure to mobile ions in a short period of time. This forces the suspension/dispersion of the HGGO to be done on site using tap water, done at a remote facility using ultra pure (Dl) water or done at a remote facility and continuously mixed until it is used. If the HGGO suspension is improperly handled it will result in aggregation of the HGGO resulting in defects and damaging the physical properties in the composite. Additionally, strongly oxidized HGGO has mechanical distortions on the surface of the flake and epoxy groups due to the oxidation process. The physical distortions prevent optimal improvement of the physical properties in a cementations material. In addition to the physical damage to the graphene/graphite oxide flake the creation of epoxy groups prevent the formation of chemical reaction in the cementitious material.

In order to mix bitumen with road-building aggregates, you first need to considerably reduce the viscosity of the cold hard binder. Traditionally, this was done by heating the bitumen and mixing it with heated aggregates to produce hot-mix asphalt. Other methods of reducing the bitumen viscosity include dissolving the bitumen in solvents and emulsification. Foamed asphalt was developed as a technology to uniformly incorporate Bitumen with the aggregates in asphalt.

FIG. 1 shows a foamed asphalt 10 of the prior art that is based on a process that heats Bitumen 12, the binder for asphalt, between 135°C to 180°C, and is injected with a small quantity of cold water 14 and compressed air 16. The water achieves a sudden temperature increase and becomes steam. The water expands on contact with the hot asphalt expanding (or foaming) the asphalt to 5-40 times its initial volume. The three ingredients are combined in a small chamber optimized to create the foaming of the material. The percentage of cool water to the Bitumen is 1% to 5% by mass. D. Csanyi at Iowa State University first demonstrated foam Bitumen/Asphalt. The foamed asphalt, or asphalt bubbles, can be dispersed into the mix fairly uniformly with a variety of solids to improve their properties and produce superior asphalt-based products. This can be compared to a traditional liquid asphalt binder at high temperature without foaming would immediately become globules when it contact cold aggregates and as such poorly dispersed. In general, if the ambient air temperature is greater than 10°C (50°F) or the road surface temperature is greater than 15°C (60°F) for uniform dispersion of the foamed asphalt in the aggregate.

SUMMARY OF THE INVENTION

The present invention can create foamed asphalt reinforced with graphene oxide (GO) by incorporated into the GO into the Bitumen foam. The aggregate can comprise aggregate pieces of at least one of asphalt, concrete, and stone (e.g. rough stone or gravel).

To reduce cost of the aggregate material and shipping, foamed asphalt has often uses recycled road material in conjunction with 10% to 20% new limestone (mainly calcium carbonate and a small percent of quartz/silicon dioxide) and sand. The specific composition of the aggregate changes based on the geographic region where the aggregate is mined.

This can use the application of a relatively small amount of GO by weight to the aggregate prior to mixing in the foamed Bitumen. The GO functionalization of COOH can react with calcium and silicon components found in limestone (mainly calcium carbonate and a small percent of quartz/silicon dioxide) sand to catalyze C-S-H (Calcium Silicate Hydrate) crystal formation and growth in the aggregate dramatically enhancing the strength of the final foamed bitumen product. In one embodiment, after dispersing the GO in the aggregate, the aggregate can then be combined with the foamed Bitumen where the foamed bitumen is produced in the normal method.

The present inventors' flat- flake reduced-oxygen GO (r-GO) material can be suspended in water or suspended for a long period of time in hot bitumen. When the suspended GO is injected into the foaming chamber 28 it becomes thoroughly mix during in addition the Bitumen 22 becoming less viscous and easier to incorporate with the aggregate. Bitumen is a thermoplastic such that the r-GO will react chemically with it, to strengthen the final foamed asphalt product.

In some embodiments the present invention also includes a method of making a foamed-bitumen reinforced asphalt structure comprising: preparing an asphalt aggregate; mixing said asphalt aggregate with hot bitumen, graphene oxide and cool water; and forming said mixture into an expansion-confining volume within a structure, wherein the graphene oxide flakes strengthen the structure. In some embodiments the graphene oxide flakes are mixed with the hot bitumen before the cool water is added. In other embodiments, compressed air is added along with the cool water. In some embodiments the mixture of asphalt aggregates, hot bitumen, graphene oxide and cool water also contains at least one of calcium carbonate and sand. In some embodiments the structure becomes at least part of a roadway.

In one aspect, the aggregates contain at least 50% recycled asphalt. In one aspect, the graphene oxide flakes have less than 20 layers, and at least 50% graphene oxide flakes are substantially flat and are made by stirred ball milling and have an oxidization of from 0.1% to 30%.

This can also be a method of making an improved a bitumen-foam reinforced structure. The invention uses an aggregate containing pieces of at least one of asphalt, concrete, and stone. Mixing the aggregate, hot bitumen and graphene oxide, cool water and compressed air causes foaming of said hot bitumen and produces a graphene oxide-containing foam. Inserting the foaming mixture into a restraining volume forms a foamed bitumen structure, wherein the graphene oxide strengthens the structure.

In one aspect, the foamed bitumen also contains at least one of calcium carbonate and sand. Preferably the graphene oxide flakes have less than 20 layers and at least 50% graphene oxide flakes are substantially flat and are made by stirred ball milling and have an oxidization of from 0.1% to 30%.

This can also be method of making foamed-bitumen comprising: mixing graphene oxide flakes with hot bitumen, and cool water, wherein said graphene oxide flakes are added to at least one of the hot bitumen and/or the cool water and wherein compressed air is added along with the cool water; and Inserting said mixture into an expansion-confining volume, wherein the graphene oxide flakes strengthen the structure. In one aspect, the bitumen also contains at least one of calcium carbonate and sand. In one aspect, the graphene oxide flakes have less than 20 layers, and at least 50% graphene oxide flakes are substantially flat and are made by stirred ball milling and have an oxidization of from 0.1% to 30%. The graphite oxide flakes can be hydrophobic and be mixed with other hydrophobic powders.

The graphite oxide flakes generally have a surface area to thickness ratio greater than 300 Angstroms, and thickness of less than 160 Angstroms, wherein the graphene flakes have no significant physical surface distortions, having no significant epoxy functionalization and has an oxidation level less than 1.5% by mass. In one aspect, 95% of the graphene oxide flakes are from about 0.8 to 16 nanometers in thickness. In some embodiments the maximum dimension of the graphene/graphite oxide flakes between 220 Angstroms and 100 microns. In another aspect, the graphene/graphite oxide flake has primarily edge oxidation, the flakes have the same hydrophobicity as the aggregate pieces, and/or the stirred media mill is an Attrition mill or ball mill.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which:

FIG. 1 shows the making of a foamed asphalt of the prior art;

FIG 2 shows one embodiment of the modified foamed asphalt of the present invention; and

FIG. 3 shows another embodiment of the modified foamed asphalt of the present invention

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Obtaining consistent size and thickness can require controlled pre-processing (e.g., milling and separation) of the crystalline graphite mechanochemical process that use crystalline graphite with a mild oxidizing agent in conjunction with mechanical energy (milling) for synthesis of graphene/graphite oxide flakes.

The mechanical energy in conjunction with a mild oxidizing environment can produce edge oxidation of the graphene minimizing the strong surface oxidation, formation of epoxy groups and mechanical defects generated in a Hummers' based process.

Graphite (30g) can be used as the starting material for the graphene/graphite oxide flakes mechanochemical process. The mechanochemical process can be done in what is generically referred to as a "stirred ball mill." Milling in a closed chamber for 360 minutes at 2,000 RPM or less. When grinding in the ball mill, the balls (media) in their random movement are spinning in different rotation and therefore are exerting shearing forces on the crystalline graphite. The resulting graphene/graphite oxide preferably has edge-only oxidization flakes with a pristine surface primarily free of distortions, epoxy groups or corrugations with low surface energies allowing for easier incorporation and entrainment in a host through powder mixing resulting in enhance physical properties.

If the suspension application requires a narrow size distribution the edge oxidized graphene/graphite flake can be chemically separated via acidic precipitation by titrating hydrochloric acid into the bath, which causes the larger (thicker/heavier) material comes out of suspension first creating a narrow graphene oxide flake distribution. The particle size can be monitored during this process by a Dynamic Light Scattering (DLS) measurement tool. Dynamic Light Scattering tools can resolve particle sizes down to 30A.

In one example, the surface area to thickness ratio should be greater than about 300 to have a positive impact on the host as a suspension. The pH of the water containing the oxidized graphite/graphene oxide can range from 5 to 9 while maintaining the suspension of the media the pH of the resulting water/ graphene/graphite oxide mixture is typically is about 7. A mechanochemical process can be controlled to process graphene/graphite with oxidization from 0.1% to 30%. Unless otherwise indicated or produced by the Hummers' process (which produces more-highly oxidized non-flat flakes), the term "graphene" as used herein means graphene oxide with oxidization of from 0.1% to 30%. The functionalization can be COOH on the edge carbons preserving the graphene structure with substantially no epoxy groups.

Oxidized graphene/graphite produced by this milling method is typically hydrophilic and easily suspended in a neutral aqueous solution. The oxidized graphite can be kept in suspension until varying the pH of the solution.

A ball mill operating with less than or equal to 2000 RPM can be generally sufficient to prevent agglomeration of the graphene adhering to the milling balls or tank.

The present invention can be a composite with a foamed asphalt reinforced with reduced graphene oxide (r-GO) by incorporating the r-GO into the aggregate or into the Bitumen foam. The GO oxidation, of COOH, can be from 2% to 30%. The COOH functional group will react with calcium and silicon components in limestone and sand to catalyze C-S-H (Calcium Silicate Hydrate) crystal formation and growth in the aggregate dramatically enhancing the strength of the final foamed asphalt product. After dispersing the GO in the aggregate it can then be combined with the foamed Bitumen where the foamed is produced in the normal method.

FIG. 2 shows the process of the present invention, in which GO is incorporated into the foamed GO-Bitumen 20 prior to combing the foamed Bitumen with the aggregate. This can be accomplished by two different insertion points. The first insertion point is relates to the GO suspended in the cool water 24 and injected into the hot Bitumen 22 and compressed air 26 in the foaming cavity 28. The second approach is to suspend GO in the hot Bitumen 22 before injection into the cool water 24 and compressed air foaming cavity 28.

FIG. 3 shows another embodiment in which GO can be incorporated in to the foamed Bitumen directly prior to combing the foamed Bitumen with the aggregate. This can be accomplished by injecting the GO in two different insertion points. The first insertion of GO into the foamed Bitumen 32 can be accomplished by suspending the r-GO or GO in the cool water 34 prior to injecting the water in the foaming chamber 38. Garmor's reduced GO (r-GO) material can be suspended, for a short time in water. The cool water is 1% to 5% by mass relative to the mass of Bitumen to achieve foaming. Although GO can be suspended in water in concentration from 0.0001% to 30% by mass. As the maximum percentage of water in the foaming process is 5%. The maximum mass GO that can be injected into the foamed Bitumen through this approach is 1.5% by mass relative to Bitumen. The second approach is to suspend GO in the hot Bitumen 32 before being injected into the cool water 34 and compressed air 36 foaming cavity. Garmor's r-GO can be suspended up to 30% by mass in the Bitumen.

The bitumen suspended GO 32 is injected into the foaming chamber 38 it becomes thoroughly mixed with the bitumen, and in addition the Bitumen becoming less viscous and easier to incorporate with the aggregate. Bitumen is a thermoplastic such that the r-GO will react chemically with it, to strengthen the final foamed asphalt product.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, kit, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

All publications and patent applications mentioned in the specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

The use of the word "a" or "an" when used in conjunction with the term "comprising" in the claims and/or the specification may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one." The use of the term "or" in the claims is used to mean "and/or" unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and "and/or." Throughout this application, the term "about" is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

As used in this specification and claim(s), the words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. In embodiments of any of the compositions and methods provided herein, "comprising" may be replaced with "consisting essentially of or "consisting of. As used herein, the phrase "consisting essentially of requires the specified integer(s) or steps as well as those that do not materially affect the character or function of the claimed invention. As used herein, the term "consisting" is used to indicate the presence of the recited integer (e.g., a feature, an element, a characteristic, a property, a method/process step or a limitation) or group of integers (e.g., feature(s), element(s), characteristic(s), propertie(s), method/process steps or limitation(s)) only.

The term "or combinations thereof as used herein refers to all permutations and combinations of the listed items preceding the term. For example, "A, B, C, or combinations thereof is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

As used herein, words of approximation such as, without limitation, "about", "substantial" or "substantially" refers to a condition that when so modified is understood to not necessarily be absolute or perfect but would be considered close enough to those of ordinary skill in the art to warrant designating the condition as being present. The extent to which the description may vary will depend on how great a change can be instituted and still have one of ordinary skilled in the art recognize the modified feature as still having the required characteristics and capabilities of the unmodified feature. In general, but subject to the preceding discussion, a numerical value herein that is modified by a word of approximation such as "about" may vary from the stated value by at least ±1, 2, 3, 4, 5, 6, 7, 10, 12 or 15%.

Additionally, the section headings herein are provided for consistency with the suggestions under 37 CFR 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings refer to a "Field of Invention," such claims should not be limited by the language under this heading to describe the so-called technical field. Further, a description of technology in the "Background of the Invention" section is not to be construed as an admission that technology is prior art to any invention(s) in this disclosure. Neither is the "Summary" to be considered a characterization of the invention(s) set forth in issued claims. Furthermore, any reference in this disclosure to "invention" in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of such claims shall be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein.

All of the compositions and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.