Admixtures for use in concrete compositions, and processes for producing the same

Abstract

The present document relates to a concrete admixture comprising a dispersant such as a polysaccharide comprising mannose and galactose units, or a derivative thereof, or a combination thereof, and a carbon material comprising graphene, graphite, a derivative of graphene or graphite, or a combination of at least two thereof, where the weight ratio of carbon material to the dispersant is between 3 : 1 and 20 : 1.

Description

[0001] ADMIXTURES FOR USE IN CONCRETE COMPOSITIONS, AND PROCESSES FOR PRODUCING THE SAME

[0002] RELATED APPLICATION

[0003] The present application claims priority under applicable law to United States provisional application No. 63 / 567,089 filed on March 19, 2024, the content of which is incorporated herein by reference in its entirety and for all purposes.

[0004] TECHNICAL FIELD

[0005] This technology generally relates to concrete additives comprising at least a dispersant and a carbon material such as graphene and / or graphite or their derivatives, for modulating concrete properties, to the concrete produced therefrom and to the use thereof.

[0006] BACKGROUND

[0007] The accelerated demand of concrete increases with the urbanization process. Throughout the globe, developed and developing countries seek alternatives that can reduce the cost of construction and reduce the waste of natural resources.

[0008] Cement is one of the most important components of concrete. Cement is classified as a soft, fine, powdered binder material that sets to a hard mass when combined with water. Therefore, cement in concrete is the binding agent that generates the uniform mass between the concrete aggregates (e.g. sand, gravel, silica fumes, fly ash, etc.) in the presence of water. Some admixtures reported, for example in WO2023 / 209386, include the application of graphene that had the surface modified with functional groups such as sulfones, amines, amides, etc. Such surface modification increases the final cost of the admixture and it’s mostly recommended to graphene oxides derived from graphite. Other graphene admixtures reported use graphene oxide or modified graphene oxide together with surfactants.

[0009] There thus remains a need for the development of alternative admixtures that increase the strength of concrete while reducing the amount of cement. SUMMARY

[0010] This technology generally relates to concrete additives or admixtures enhanced by carbon materials together with a specific type of dispersant for modulating concrete properties. In this technology, an admixture was developed that uses natural products and / or a combination of natural products with carbon materials and which works with or without surfactants. More specifically, the following embodiments are provided:

[0011] Embodiment 1 . A concrete admixture comprising: a carbon material; and a dispersant selected from a polysaccharide comprising mannose and galactose units, or a derivative thereof, or a combination thereof; wherein said carbon material comprises graphene, graphite, a derivative of graphene or graphite, or a combination of at least two thereof; wherein the weight ratio of carbon material to the dispersant is between 3 : 1 and 20 : 1 ; and wherein said carbon material is stabilized by the dispersant.

[0012] Embodiment 2. The concrete admixture of embodiment 1 , wherein said dispersant is a polysaccharide comprising mannose and galactose units.

[0013] Embodiment 3. The concrete admixture of embodiment 2, wherein said polysaccharide comprising mannose and galactose units is a galactomannan.

[0014] Embodiment 4. The concrete admixture of any one of embodiments 1 to 3, wherein said polysaccharide has a molar ratio of mannose to galactose within the range of about 0.5:1 to about 6:1.

[0015] Embodiment 5. The concrete admixture of embodiment 3, wherein said galactomannan is selected from guar gum, fenugreek gum, tara gum, locust bean gum, and cassia gum.

[0016] Embodiment 6. The concrete admixture of embodiment 5, wherein said galactomannan is guar gum.

[0017] Embodiment ?. The concrete admixture of any one of embodiments 1 to 6, further comprising a lignin or derivative thereof. Embodiment 8. The concrete admixture of embodiment 7, wherein said lignin derivative is an anionic lignin derivative.

[0018] Embodiment 9. The concrete admixture of embodiment 7, wherein said lignin derivative is a lignosulfonate.

[0019] Embodiment 10. The concrete admixture of any one of embodiments 1 to 9, wherein said carbon material is a carbon nanomaterial.

[0020] Embodiment 11. The concrete admixture of any one of embodiments 1 to 10, wherein said carbon material comprises graphene.

[0021] Embodiment 12. The concrete admixture of embodiment 11 , wherein said graphene comprises monolayer graphene, few-layer graphene (2 to 20 layers), or a combination thereof.

[0022] Embodiment 13. The concrete admixture of embodiment 11 or 12, wherein said graphene has a structure comprising flakes (e.g. nanoflakes), platelets (e.g. nanoplatelets), carbon shells, or a combination thereof, preferably comprising flakes and / or platelets.

[0023] Embodiment 14. The concrete admixture of embodiment 11 or 12, wherein said graphene has a structure comprising nanocones, nanohorns, nanodandelions, nanoribbons, nanopetals, or a combination thereof.

[0024] Embodiment 15. The concrete admixture of any one of embodiments 1 to 14, wherein said carbon material comprises graphite.

[0025] Embodiment 16. The concrete admixture of embodiment 15, wherein said graphite is synthetic graphite having a structure comprising synthetic graphite platelets or nanoplatelets.

[0026] Embodiment 17. The concrete admixture of any one of embodiments 1 to 16, wherein said carbon material has an average particle size or flake length between about 1 nm and about 200 pm, or between about 1 nm and about 100 pm, or between about 5 nm and about 50 pm, or between about 5 nm and about 5 pm.

[0027] Embodiment 18. The concrete admixture of any one of embodiments 1 to 17, further comprising at least one surfactant. Embodiment 19. The concrete admixture of embodiment 18, wherein the surfactant is an anionic or cationic surfactant or a non-ionic surfactant, e.g. selected from long chain alkyl or alkenyl sulfate salts (e.g. sodium dodecyl sulfate, sodium lauryl sulfate, long chain alkylphenyl or alkenylphenyl sulfonate salts (e.g. sodium dodecyl benzene sulfonate (SDBS)), polyethylenepolypropylene glycol block copolymers or pegylated esters and alkoxylates (e.g. poloxamers, pegylated sorbitan long chain carboxylic acid esters, etc.), cholate and deoxycholate salts (e.g. sodium cholate or deoxycholate (SDOC)), alkylphenol derivatives of polyethylene and / or polypropylene glycols (e.g. Triton X-100), polyols, long chain alkyl or alkenyl quaternary ammoniums (e.g. cetyltrimethylammonium bromide (CTAB)), and the like.

[0028] Embodiment 20. The concrete admixture of embodiment 18 or 19, wherein the weight ratio of surfactant to carbon material is within the range of from about 1 :100 or 1 :10 000.

[0029] Embodiment 21. The concrete admixture of any one of embodiments 1 to 20, further comprising at least one acid selected from organic acids (e.g. acetic acid, gluconic acid), inorganic acids, and salts thereof.

[0030] Embodiment 22. The concrete admixture of embodiment 21 , wherein said acid is phosphoric acid and / or acetic acid.

[0031] Embodiment 23. The concrete admixture of any one of embodiments 1 to 22, further comprising at least one crystallized carbohydrate, sugar, oligosaccharide or polysaccharide other than the polysaccharide comprising mannose and galactose units.

[0032] Embodiment 24. The concrete admixture of any one of embodiments 1 to 23, further comprising at least one defoamer (e.g. a silicon-glycol emulsion).

[0033] Embodiment 25. The concrete admixture of any one of embodiments 1 to 24, further comprising at least one water reducer (e.g. a polycarbonate, polysaccharide, lignosulfonate) in addition to the dispersant.

[0034] Embodiment 26. The concrete admixture of any one of embodiments 1 to 25, further comprising a surface modifier (e.g. a silicate or titanate coupling agent, preferably a titanate coupling agent).

[0035] Embodiment 27. The concrete admixture of any one of embodiments 1 to 26, further comprising water. Embodiment 28. Process for the preparation of the concrete admixture of any one of embodiments 1 to 27, comprising at least a step of mixing the carbon material together with the dispersant.

[0036] Embodiment 29. The process of embodiment 28, wherein said mixing step further comprises addition of water.

[0037] Embodiment 30. A concrete composition comprising the concrete admixture as defined in any one of embodiments 1 to 27, together with cement, sand, and aggregates.

[0038] Embodiment 31. The concrete composition of embodiment 29, further comprising silica fumes and / or fly ash.

[0039] Additional objects and features of the present compositions, methods and uses will become more apparent upon reading of the following non-restrictive description of exemplary embodiments and examples section, which should not be interpreted as limiting the scope of the invention.

[0040] DETAILED DESCRIPTION

[0041] All technical and scientific terms and expressions used herein have the same definitions as those commonly understood by a person skilled in the art to which the present technology pertains. The definition of some terms and expressions used is nevertheless provided below. To the extent the definitions of terms in the publications, patents, and patent applications incorporated herein by reference are contrary to the definitions set forth in this specification, the definitions in this specification will control. The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter disclosed.

[0042] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. It should be noted that, the singular forms "a", "an", and "the" include plural forms as well, unless the content clearly dictates otherwise. Thus, for example, reference to a composition containing "a dispersant" also contemplates a mixture of two or more dispersants. It should also be noted that the term "or" is generally employed in its sense including "and / or" unless the context clearly dictates otherwise. Furthermore, to the extent that the terms “including”, "includes", "having", "has", "with", or variants thereof are used in either the detailed description and / or the claims, such terms are intended to be inclusive in a manner similar to the term "comprising”. The term "about" or "approximately" means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e. , the limitations of the measurement system. For example, "about" can mean within one or more than one standard deviation, as per the practice in the art. Alternatively, "about" can mean a range of up to 20%, preferably up to 10%, more preferably up to 5%, and more preferably still up to 1% of a given value. Where particular values are described in the application and claims, unless otherwise stated the term "about" meaning within an acceptable error range for the particular value should be assumed.

[0043] The terms “graphene”, “graphite”, and “graphene and / or graphite” as used herein refers to synthetic materials generally recognized as being composed of layers of trigonal planar carbon in the form of a honeycomb lattice. Graphite includes multiple layers of this lattice, whereas graphene is generally understood to include fewer layers (e.g. 20 or less, or 10 or less). It should be understood that these terms also encompass graphene and / or graphite derivatives such as surface functionalized graphene and / or graphite, graphene and / or graphite oxides, reduced graphene and / or graphite oxides, and / or as including other carbon forms in combination with the graphene and / or graphite or derivatives thereof provided that these other carbon forms form less than half of the carbon material’s weight, preferably less than 40%, less than 30%, less than 20% or less than 10%.

[0044] The term “galactomannan” used herein designates a member of a family of polysaccharides which comprise a mannose backbone and galactose side groups, more specifically, a (1 -4)-linked beta- D-mannopyranose backbone with branchpoints from their 6-positions linked to alpha-D- galactose, (i.e. 1-6-linked alpha-D-galactopyranose). Non-limiting examples of galactomannans and their mannose to galactose molar ratio include without limitation fenugreek gum (about 1 :1), guar gum (about 2:1), tara gum (about 3:1), locust bean gum (about 4:1), cassia gum (about 5:1), and the like.

[0045] The present technology reports the development of an admixture that uses natural products and / or a combination of natural products with a carbon material such as graphene and / or graphite or a derivative of graphene and / or graphite with or without surfactants. The admixture is particularly useful in the preparation of concrete compositions. Preferably, the present admixture allows for a reduction of the cement content in the concrete while preserving its strength or enhancing it. The present admixture and process do not require the pre-functionalization or surface modification of the carbon material (e.g. of the graphene, graphene oxide or reduced graphene oxide, or graphene fibers). However, it allows the optional application of small amounts of surfactants, water reducer components, anti-aging compounds or a combination thereof in some variations of the process.

[0046] While, as mentioned above, other admixtures require either an additional functionalization of carbon materials like graphene, or depend on a certain lateral size, the present process does not require any of these surface modifications or flake size control. In fact, the admixtures are prepared with natural products classified as natural surfactants, stabilizers, or water reducers.

[0047] Furthermore, the admixtures generally do not require further treatment such as a chemical pretreatment of the carbon material and / or a chemical post-treatment of the obtained admixture. Accordingly, since the admixtures do not generally apply any harsh chemical conditions such as bases, or organic solvents during the synthesis or to pre-treat the carbon source or its final product, the present method may be considered as being eco-friendly and a clean technology. The method is also applicable to a one-pot synthesis setting.

[0048] More specifically, the present document therefore relates to the development of carbon materialcontaining concrete admixtures said admixtures comprising at least the one combination of carbon material or nanomaterial such as graphene, graphite or a derivative or a combination thereof, stabilized in a liquid by a natural product acting as a dispersant, for instance a polysaccharide (e.g. a polysaccharide comprising mannose and galactose units such as a galactomannan), or a derivative thereof. The admixture can be prepared in a mixer, such as a high shear mixer or any other equipment that promotes the interactions between the carbon material and the dispersant as described above.

[0049] The admixture may further contain small amounts of commercially available surfactants or surfactants mixtures, for instance where the volume ratios between surfactants and the admixture are between 1 :100 or 1 :10 000. The admixture may further contain diluted acids such as phosphoric acid, gluconic acid, and / or acetic acid, crystalized carbohydrates, and / or defoamers.

[0050] For instance, the present concrete admixture comprises: a carbon material; and a dispersant selected from a polysaccharide comprising mannose and galactose units, or a derivative thereof, or a combination thereof; wherein said carbon material comprises graphene, graphite, a derivative of graphene or graphite, or a combination of at least two thereof; wherein the weight ratio of carbon material to the dispersant is between 3 : 1 and 20 : 1 ; and wherein said carbon material is stabilized by the dispersant.

[0051] In some preferred embodiments, the dispersant is a polysaccharide comprising mannose and galactose units, such as a galactomannan. For instance, the molar ratio of mannose to galactose in the polysaccharide is within the range of about 0.5:1 to about 6:1. Non-limiting examples of galactomannan include guar gum, fenugreek gum, tara gum, locust bean gum, and cassia gum.

[0052] In other embodiments, the admixture further comprises a lignin or derivative thereof, such as an anionic lignin derivative (e.g. a lignosulfonate).

[0053] In some examples, the carbon material may be a carbon nanomaterial. The carbon material or nanomaterial may comprise graphene, graphite, or an oxide or reduced form thereof, or a combination thereof.

[0054] For instance, when the carbon material comprises graphene, the graphene may comprise monolayer graphene, few-layer graphene (2 to 20 layers), or a combination thereof. Graphene may be of any known structure, for instance comprising flakes, platelets, shells, cones, horns, dandelions, ribbons, petals, fibers, or their nanometric equivalents, or any combination of two or more thereof.

[0055] When the carbon material comprises graphite, the graphite may be in any known graphite form, for instance, the graphite may be synthetic graphite having a structure comprising synthetic graphite platelets or nanoplatelets.

[0056] The carbon material preferably has an average particle size or flake length between about 1 nm and about 200 pm, or between about 1 nm and about 100 pm, or between about 5 nm and about 50 pm, or between about 5 nm and about 5 pm.

[0057] As mentioned above, the admixture may further comprise a surfactant which may serve to further promote the stabilization of the carbon material in the admixture. The surfactant may be an anionic, cationic or non-ionic surfactant. Non-limiting examples of surfactants comprise long chain alkyl or alkenyl sulfate salts (e.g. sodium dodecyl sulfate, sodium lauryl sulfate, long chain alkylphenyl or alkenylphenyl sulfonate salts (e.g. sodium dodecyl benzene sulfonate (SDBS)), polyethylene-polypropylene glycol block copolymers or pegylated esters and alkoxylates (e.g. poloxamers including Pluronic™ poloxamer surfactants, pegylated sorbitan long chain carboxylic acid esters including Tween™ surfactants, etc.), cholate and deoxycholate salts (e.g. sodium cholate or deoxycholate (SDOC)), alkylphenol derivatives of polyethylene and / or polypropylene glycols (e.g. Triton X-100), polyols, long chain alkyl or alkenyl quaternary ammoniums (e.g. cetyltrimethylammonium bromide (CTAB)), and the like. The weight ratio of surfactant to carbon material may be within the range of from about 1 :100 or 1 :10 000.

[0058] In some cases, the admixture may also further comprise at least one acid selected from organic acids (e.g. acetic acid, gluconic acid), inorganic acids, (e.g. phosphoric acid), and salts thereof. For instance, the acid may be phosphoric acid and / or acetic acid.

[0059] Additional components may also be included in the admixture, such as crystallized carbohydrates, sugars, oligosaccharides or polysaccharides other than the polysaccharide comprising mannose and galactose units, defoamers (e.g. a silicon-glycol emulsion), water reducers (e.g. a polycarbonate, polysaccharide, lignosulfonate) in addition to the dispersant, and / or a surface modifier (e.g. a silicate or titanate coupling agent, preferably a titanate coupling agent).

[0060] In a preferred embodiment, the concrete admixture also further contains water, where the carbon material is at a concentration in water between about 0.1 g / L and about 5 g / L and the dispersant a concentration of between about 0.02 g / L and about 1 g / L.

[0061] The present technology also relates to a process for preparing a concrete admixture as defined herein, comprising at least a step of mixing the carbon material together with the dispersant, preferably as a water suspension. Additional steps may be included comprising the mixing of the carbon material and dispersant with other components, such as surfactant, water reducer, etc.

[0062] This technology also further relates to a concrete composition comprising the concrete admixture as defined herein, together with cement and aggregates (e.g. sand, gravel, silica fumes and / or fly ash).

[0063] The recitation of an embodiment or example for a variable herein includes that embodiment or example as a single embodiment or example or in combination with any other embodiments, examples or portions thereof. The recitation of an embodiment herein includes that embodiment as any single embodiment or in combination with any other embodiments or portions thereof. EXAMPLES

[0064] The following non-limiting examples are illustrative embodiments and should not be construed as further limiting the scope of the present invention.

[0065] Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, concentrations, properties, stabilities, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the present specification and attached claims are approximations that may vary depending upon the properties sought to be obtained. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the embodiments are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors resulting from variations in experiments, testing measurements, statistical analyses and such.

[0066] Example 1 - General method - base admixture

[0067] The base admixture was obtained by the interaction between graphene materials and a galactomannan (e.g. gaur gum) and a commercially available surfactant or mixture of surfactants.

[0068] The guar gum (or other galactomannan) was first dispersed into water at concentrations between 0.007 wt.% and 0.04 wt.% with some dispersions using 0.025 wt.% of guar gum.

[0069] The amount of graphene used is at a concentration between 0.035 wt.% to 0.2 wt.% with some dispersions using 0.125 wt.% of graphene in water.

[0070] The ratio graphene galactomannan (guar gum) is usually between 3 : 1 and 20 : 1 , ideally 5:1 or may be higher.

[0071] For instance, a 1 wt.% graphene dispersion is prepared by adding 100 g of graphene powder to 10 litres of distilled water with 7 g of guar gum and 0.3 g of a 0.13g / 100 ml Dawn™ soap regular strength solution (hereafter the Base admixture). The dispersion is treated in a high shear mixer for 40 hours at 3500 RPM and removed. Any water lost to evaporation during the mixing step is replaced with distilled water to maintain the components concentration. The concentration of the graphene dispersion directly influences the volume of graphene admixture used to replace the tail-water of the concrete.

[0072] Example 2 - Admixtures with Zyla™ (commercial water reducer)

[0073] Admixtures were prepared as indicated in Example 1 and the water reducer Zyla™ was further added. Mixing with a 40 MPa concrete mix was performed. Quantities and results are described in Table 1 and compared with equivalent compositions without graphene and guar gum.

[0074] Table 1. Concrete with concrete admixtures further comprising Zyla™

[0075] Example 3 - Admixtures with lignosulfonate (natural water reducer)

[0076] Admixtures using the Base admixture described in Example 1 and a lignosulfonate were also prepared. Quantities and results are described in Table 2 and compared with equivalent compositions without the graphene and guar components and without lignosulfonate.

[0077] Table 2. Concrete with concrete admixtures further comprising a lignosulfonate

[0078] Example 4 - Admixtures that evaluate the effect of the concentration of the graphene material in the concrete

[0079] Admixtures were prepared as indicated in example 1 and the water reducer Eucon™ and Plastol™ are further added. Mixing with a 40 MPa concrete mix was performed. Quantities and results are described in Table 1 and compared with equivalent compositions without graphene and guar gum.

[0080] Table 3. Concrete with concrete admixtures varying graphene concentrations

[0081] As can be seen from the results obtained in Examples 2 to 4, the addition of an admixture comprising a carbon material such as graphene and a polysaccharide such as guar gum allows for a reduction in cement in the final concrete as well as in increase in strength in the early stage of concrete formation.

[0082] Numerous modifications could be made to any of the embodiments described above without departing from the scope of the present invention. Any references, patents or scientific literature documents referred to in the present document are incorporated herein by reference in their entirety for all purposes.

Claims

CLAIMS1. A concrete admixture comprising: a carbon material; and a dispersant selected from a polysaccharide comprising mannose and galactose units, or a derivative thereof, or a combination thereof; wherein said carbon material comprises graphene, graphite, a derivative of graphene or graphite, or a combination of at least two thereof; wherein the weight ratio of carbon material to the dispersant is between 3 : 1 and 20 : 1 ; and wherein said carbon material is stabilized by the dispersant.

2. The concrete admixture of claim 1, wherein said dispersant is a polysaccharide comprising mannose and galactose units.

3. The concrete admixture of claim 2, wherein said polysaccharide comprising mannose and galactose units is a galactomannan.

4. The concrete admixture of any one of claims 1 to 3, wherein said polysaccharide has a molar ratio of mannose to galactose within the range of about 0.5:1 to about 6:1.

5. The concrete admixture of claim 3, wherein said galactomannan is selected from guar gum, fenugreek gum, tara gum, locust bean gum, and cassia gum.

6. The concrete admixture of claim 5, wherein said galactomannan is guar gum.

7. The concrete admixture of any one of claims 1 to 6, further comprising a lignin or derivative thereof.

8. The concrete admixture of claim 7, wherein said lignin derivative is an anionic lignin derivative.

9. The concrete admixture of claim 7, wherein said lignin derivative is a lignosulfonate.

10. The concrete admixture of any one of claims 1 to 9, wherein said carbon material is a carbon nanomaterial.

11. The concrete admixture of any one of claims 1 to 10, wherein said carbon material comprises graphene.

12. The concrete admixture of claim 11 , wherein said graphene comprises monolayer graphene, few-layer graphene (2 to 20 layers), or a combination thereof.

13. The concrete admixture of claim 11 or 12, wherein said graphene has a structure comprising flakes (e.g. nanoflakes), platelets (e.g. nanoplatelets), carbon shells, or a combination thereof, preferably comprising flakes and / or platelets.

14. The concrete admixture of claim 11 or 12, wherein said graphene has a structure comprising nanocones, nanohorns, nanodandelions, nanoribbons, nanopetals, or a combination thereof.

15. The concrete admixture of any one of claims 1 to 14, wherein said carbon material comprises graphite.

16. The concrete admixture of claim 15, wherein said graphite is synthetic graphite having a structure comprising synthetic graphite platelets or nanoplatelets.

17. The concrete admixture of any one of claims 1 to 16, wherein said carbon material has an average particle size or flake length between about 1 nm and about 200 pm, or between about 1 nm and about 100 pm, or between about 5 nm and about 50 pm, or between about 5 nm and about 5 pm.

18. The concrete admixture of any one of claims 1 to 17, further comprising at least one surfactant.

19. The concrete admixture of claim 18, wherein the surfactant is an anionic or cationic surfactant or a non-ionic surfactant, e.g. selected from long chain alkyl or alkenyl sulfate salts (e.g. sodium dodecyl sulfate, sodium lauryl sulfate, long chain alkylphenyl or alkenylphenyl sulfonate salts (e.g. sodium dodecyl benzene sulfonate (SDBS)), polyethylene-polypropylene glycol block copolymers or pegylated esters and alkoxylates (e.g. poloxamers, pegylated sorbitan long chain carboxylic acid esters, etc.), cholate and deoxycholate salts (e.g. sodium cholate or deoxycholate (SDOC)), alkylphenol derivatives of polyethylene and / or polypropylene glycols (e.g. Triton X-100), polyols, long chain alkyl oralkenyl quaternary ammoniums (e.g. cetyltrimethylammonium bromide (CTAB)), and the like.

20. The concrete admixture of claim 18 or 19, wherein the weight ratio of surfactant to carbon material is within the range of from about 1 :100 or 1 :10 000.

21. The concrete admixture of any one of claims 1 to 20, further comprising at least one acid selected from organic acids (e.g. acetic acid, gluconic acid), inorganic acids, and salts thereof.

22. The concrete admixture of claim 21 , wherein said acid is phosphoric acid and / or acetic acid.

23. The concrete admixture of any one of claims 1 to 22, further comprising at least one crystallized carbohydrate, sugar, oligosaccharide or polysaccharide other than the polysaccharide comprising mannose and galactose units.

24. The concrete admixture of any one of claims 1 to 23, further comprising at least one defoamer (e.g. a silicon-glycol emulsion).

25. The concrete admixture of any one of claims 1 to 24, further comprising at least one water reducer (e.g. a polycarbonate, polysaccharide, lignosulfonate) in addition to the dispersant.

26. The concrete admixture of any one of claims 1 to 25, further comprising a surface modifier (e.g. a silicate or titanate coupling agent, preferably a titanate coupling agent).

27. The concrete admixture of any one of claims 1 to 26, further comprising water.

28. Process for the preparation of the concrete admixture of any one of claims 1 to 27, comprising at least a step of mixing the carbon material together with the dispersant.

29. The process of claim 28, wherein said mixing step further comprises addition of water.

30. A concrete composition comprising the concrete admixture as defined in any one of claims 1 to 27, together with cement, sand, and aggregates.

31. The concrete composition of claim 29, further comprising silica fumes and / or fly ash.

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