Low-temperature-rise, high-impermeability, low-carbon concrete nanofluid admixture and its preparation method and application

Abstract

The present invention discloses a low-temperature-rise, high-impermeability, low-carbon concrete nanofluid admixture, and its preparation method and application, which relate to the technical field of graphene materials. The nanofluid admixture includes water, graphene dispersed in water, and a dispersant, the dispersant includes polyvinyl alcohol and / or sodium carboxymethyl cellulose, and its preparation method includes the following steps: adding graphite powder to a dispersant solution, and then performing shear exfoliation and emulsification exfoliation in sequence to obtain a mixed solution; after centrifuging the mixed solution, collecting the supernatant to obtain the nanofluid admixture. Graphene nanofluid is added to cement-based materials as an admixture, which can effectively absorb and disperse the hydration heat released during the cement hydration process, slow down the hydration reaction rate, and thus reduce the overall hydration heat. At the same time, the high surface area and two-dimensional structure of graphene help to fill the microscopic pores of cement-based materials, improve their impermeability, durability and mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of graphene materials, and in particular to a low-temperature-rise, high-impermeability, low-carbon concrete nanofluid admixture, and a preparation method and application thereof. Background Art

[0002] Cement-based materials such as concrete are widely used in construction projects, but they often face challenges such as rapid hydration heat release, poor permeability, and insufficient mechanical properties. Traditional additives such as silicate admixtures or modifiers can address these issues to some extent, but their effectiveness remains limited, particularly when it comes to improving mechanical properties while meeting multiple other requirements.

[0003] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0004] Based on the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a low-temperature-rise, high-impermeability, low-carbon concrete nanofluid admixture and its preparation method and application, aiming to solve the problems of existing cement-based materials such as concrete hydration heat release too fast, poor impermeability and insufficient mechanical properties.

[0005] The technical solutions of the present invention are as follows:

[0006] A first aspect of the present invention provides a method for preparing a nanofluid admixture, wherein the nanofluid admixture comprises water, graphene dispersed in the water, and a dispersant, wherein the dispersant comprises polyvinyl alcohol and / or sodium carboxymethyl cellulose. The method for preparing the nanofluid admixture comprises the following steps:

[0007] Provide graphite powder and dispersant;

[0008] adding the dispersant into water and stirring to obtain a dispersant solution;

[0009] Adding the graphite powder to the dispersant solution, and then sequentially performing shear exfoliation and emulsification exfoliation to obtain a mixed solution;

[0010] After the mixed solution is centrifuged, the supernatant is collected to obtain the nanofluid admixture.

[0011] In this invention, graphene nanofluid, known for its excellent thermal conductivity and mechanical strength, is added as an admixture to cementitious materials. It effectively disperses within the cementitious system, absorbing and dispersing the heat released during cement hydration, slowing the hydration reaction rate and thus reducing the overall heat of hydration. Furthermore, graphene's high surface area and two-dimensional structure help fill the microscopic pores of the cementitious material, improving its impermeability and durability, and significantly enhancing its mechanical properties (including compressive and flexural strength).

[0012] In addition, graphene often faces the following problems in civil engineering applications: 1. Cost issue: Currently, the production of high-quality graphene is still an expensive process, which limits its application in large-scale civil engineering projects. 2. Production scale: Large-scale production of high-quality graphene remains a challenge. Current production methods can usually only obtain a limited amount of graphene, and the inability to expand the scale limits its application in the field of civil engineering. 3. Interface compatibility: The interface compatibility of graphene with traditional building materials is an important issue. The binding performance of graphene with building materials such as cement and concrete needs to be improved to ensure its effective application in civil engineering. However, the present invention uses graphite powder (which can be industrial grade) as raw material to prepare nanofluid admixtures, which replaces the more expensive commercial graphene and effectively reduces costs. Utilizing liquid phase exfoliation method, specifically a combination of shear exfoliation and emulsification exfoliation, the preparation of nanofluid admixtures is not only efficient and suitable for expansion to large-scale production, but also the graphene in the nanofluid admixture can be stably dispersed and can be directly used for cement mixing, thereby enhancing the feasibility of industrial application. By introducing water-soluble polymers (vinyl alcohol and / or sodium carboxymethyl cellulose), which can act as surfactants, the interfacial compatibility of graphene with cement-based materials is enhanced, and its dispersibility and performance are improved, thereby effectively solving the difficulties in the application of graphene in civil engineering and enhancing its feasibility and practicality in this field.

[0013] In the present invention, shear exfoliation triggers relative sliding between graphite layers, which in turn introduces initial exfoliation between graphite sheets, reducing the van der Waals forces between the graphite sheets, thereby providing graphite sheets that are easier to exfoliate during the subsequent emulsion exfoliation process. Furthermore, shear exfoliation helps break down the strong interactions between graphite sheets, increasing the graphene's exfoliable surface area and allowing the shear forces during the emulsion exfoliation stage to act more efficiently on the graphene exfoliation process. Therefore, the two-step process strategy of shear exfoliation combined with emulsion exfoliation significantly improves the release and yield of graphene.

[0014] Specifically, shear exfoliation relies on the turbulence generated by the high-speed rotating blades. The significant increase in local shear force and improved fluid mixing efficiency in the turbulent state enhances the interaction and shear effect between graphene sheets, promoting the effective separation of graphene sheets. Furthermore, microscopic vortices and high shear regions in the turbulent flow help overcome the van der Waals attraction between graphene sheets, further improving the exfoliation efficiency and dispersion of graphene.

[0015] In some embodiments, the concentration of the dispersant in the dispersant solution is 5 to 25 g / L. As the concentration of the dispersant (i.e., surfactant) increases, the surface tension decreases, resulting in more dispersant molecules being adsorbed onto the liquid-gas interface. The adsorption of dispersant molecules can significantly reduce surface tension, so the adsorption capacity per unit area will increase with the increase in concentration. However, once a certain concentration (i.e., critical micelle concentration) is reached, the surface is already saturated, and the surface tension will not change significantly due to the increase in concentration, or even no longer increase. Therefore, the final graphene concentration in the nanofluid admixture shows an upward trend as the dispersant concentration increases, and will no longer rise after reaching a certain concentration. However, too much dispersant will affect the performance of cement-based materials. Within this concentration range, it is possible to ensure that the graphene concentration in the prepared nanofluid admixture remains at a high level without affecting the performance of cement-based materials too much.

[0016] In some embodiments, the shear stripping is performed at a rotation speed of 10,000 rpm, and the shear stripping time is 3 to 21 minutes (for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or 21 minutes, etc.).

[0017] In some embodiments, the rotation speed of the emulsification peeling is 6000 rpm, and the time of the emulsification peeling is 20 to 180 min (for example, it can be 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170 or 180 min, etc.).

[0018] In some embodiments, the centrifugation speed is 10,000 rpm, and the centrifugation time is 30 to 80 min (eg, 30, 40, 50, 60, 70, or 80 min, etc.).

[0019] In some embodiments, the shear peeling is performed for 12 minutes, the emulsification peeling is performed for 120 to 140 minutes, and the centrifugation is performed for 30 minutes.

[0020] The second aspect of the present invention provides a nanofluid admixture, which is prepared using the preparation method of the present invention as described above.

[0021] A third aspect of the present invention provides an application of the nanofluid admixture of the present invention as described above, wherein the nanofluid admixture is applied to a cement-based material, and the cement-based material includes one of cement paste, cement mortar, and concrete.

[0022] A fourth aspect of the present invention provides a modified cement-based material, wherein the modified cement-based material comprises one of modified cement paste, modified cement mortar, and modified concrete;

[0023] The modified cement paste comprises cement, water and the nanofluid admixture of the present invention as described above;

[0024] The modified cement mortar comprises cement, sand, water and the nanofluid admixture of the present invention as described above;

[0025] The modified concrete is prepared from the modified cement paste or the modified cement mortar.

[0026] In some embodiments, in the modified cement paste, the mass ratio of the cement, water, and graphene in the nanofluid admixture is 1:(0.45-0.55):(0-0.002); in the modified cement mortar, the mass ratio of the cement, sand, water, and graphene in the nanofluid admixture is 1:(2-4):(0.45-0.55):(0-0.002); and in the modified cement paste and the modified cement mortar, the mass of the graphene in the nanofluid admixture is not zero. That is, the mass of the graphene in the nanofluid admixture accounts for 0% to 0.2% of the mass of the cement, but not 0%.

[0027] Beneficial effect: In the present invention, graphene nanofluid with excellent thermal conductivity and mechanical strength is added to cement-based materials as an admixture, which can be effectively dispersed in the cement-based system, can effectively absorb and disperse the release of hydration heat during the cement hydration process, slow down the hydration reaction rate, and thus reduce the overall hydration heat. At the same time, the high surface area and two-dimensional structure of graphene help to fill the microscopic pores of cement-based materials, improve their impermeability and durability, and significantly enhance the mechanical properties of cement-based materials, including compressive strength and flexural strength. In addition, the present invention uses graphite powder (which can be industrial grade) as a raw material to prepare nanofluid admixtures to replace commercial graphene with higher costs, effectively reducing costs. The use of liquid phase exfoliation method, specifically the combination of shear exfoliation and emulsification exfoliation, to prepare nanofluid admixtures is not only efficient and suitable for expansion to large-scale production, but also the graphene in the nanofluid admixture can be stably dispersed and can be directly used for cement mixing, thereby enhancing the feasibility of industrial applications. By introducing water-soluble polymers (vinyl alcohol and / or sodium carboxymethyl cellulose), which can act as surfactants, the interfacial compatibility of graphene with cement-based materials is enhanced, and its dispersibility and performance are improved, thereby effectively solving the difficulties in the application of graphene in civil engineering and enhancing its feasibility and practicality in this field. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1(a) is the appearance of the first nanofluid admixture prepared in Example 1 on the first day and after standing for 180 days; (b) is the appearance of the nanofluid admixture prepared in Example 2 under the conditions of 350 mL of CMC solution, shear stripping for 12 minutes, and emulsification stripping for 40 minutes on the first day and after standing for 180 days.

[0029] Figure 2 (a) is a TEM image of the third nanofluid admixture prepared in Example 1, (b) is a TEM image of the nanofluid admixture prepared in Example 2 under the conditions of 350 mL of CMC solution, shear stripping for 12 min, and emulsification stripping for 40 min, (c) is an enlarged view of a certain area in Figure (a), (d) is an enlarged view of a certain area in Figure (b), (e) is a diffraction spot pattern of the third nanofluid admixture prepared in Example 1, and (f) is a diffraction spot pattern of the nanofluid admixture prepared in Example 2 under the conditions of 350 mL of CMC solution, shear stripping for 12 min, and emulsification stripping for 40 min.

[0030] Figure 3 The AFM results of the second nanofluid admixture prepared in Example 1 are shown, where (a) is the AFM topography at one position, (b) is the AFM topography at another position, (c) is the height curve corresponding to (a), and (d) is the height curve corresponding to (b).

[0031] Figure 4 These are the XPS results of the second nanofluid admixture prepared in Example 1, where (a) is the overall spectrum, (b) is the C1s spectrum, and (c) is the O1s spectrum.

[0032] Figure 5 Graphene concentration is a linear relationship diagram showing the absorbance obtained in Example 1.

[0033] Figure 6 This is a graph showing the graphene concentration results in the four nanofluid admixtures prepared in Example 1.

[0034] Figure 7 This is a graph showing the change in graphene concentration with emulsification stripping time in Example 1.

[0035] Figure 8 This is a graph showing the change in the yield of graphene by emulsification exfoliation as a function of the emulsification exfoliation time in Example 1.

[0036] Figure 9 This is a graph showing the graphene concentration results in 30 nanofluid admixtures in Example 2.

[0037] Figure 10(a) is a graph showing the change of graphene concentration in PVA-GNAs with centrifugation time in Example 3, and (b) is a graph showing the change of graphene concentration in CMC-GNAs with centrifugation time in Example 3.

[0038] Figure 11 This is a graph showing the effects of nanofluid admixtures prepared with PVA on the strength of cement mortar without centrifugation and after 30 minutes of centrifugation.

[0039] Figure 12 This is a graph showing the initial setting time and final setting time of PVA-GNAs modified cement paste with different graphene mass contents in Example 4.

[0040] Figure 13 This is a graph showing the initial setting time and final setting time results of CMC-GNAs modified cement paste with different graphene mass contents in Example 5.

[0041] Figure 14 This is a hydration heat release rate curve of PVA-GNAs modified cement slurry with different graphene mass contents in Example 6.

[0042] Figure 15 This is the hydration heat release rate curve of cement paste when PVA is added alone.

[0043] Figure 16 This is the cumulative hydration exotherm curve of the PVA-GNAs modified cement paste in Example 6.

[0044] Figure 17 (a) is the hydration heat release rate curve of the CMC-GNA modified cement in Example 6, and (b) is the cumulative hydration heat release curve of the CMC-GNA modified cement in Example 6.

[0045] Figure 18 (a) is the flow velocity test result diagram of the PVA-GNAs modified cement mortar in Example 7, and (b) is the flow velocity test result diagram of the CMC-GNAs modified cement mortar in Example 7.

[0046] Figure 19 (a) is the compressive strength test result of PVA-GNAs modified cement mortar in Example 8, and (b) is the compressive strength test result of CMC-GNAs modified cement mortar in Example 8.

[0047] Figure 20 (a) is the flexural strength test result of PVA-GNAs modified cement mortar in Example 8, and (b) is the flexural strength test result of CMC-GNAs modified cement mortar in Example 8.

[0048] Figure 21 These are SEM images of PVA-GNAs modified cement mortars with different graphene mass contents after curing in Example 9, where (a) is 0.02%, (b) is 0.04%, (c) is 0.06% and (d) is 0.08%.

[0049] Figure 22 These are SEM images of CMC-GNAs modified cement mortars with different graphene mass contents after curing in Example 9, where (a) is 0.02% and (b) is 0.04%.

[0050] Figure 23 These are SEM images of the CMC-GNAs modified cement mortar with different graphene mass contents after curing in Example 9 under backscattering mode at a scale of 100 μm, where (a) is 0%, (b) is 0.02%, (c) is 0.04%, (d) is 0.06%, (e) is 0.08%, and (f) is 0.10%.

[0051] Figure 24 These are SEM images of the CMC-GNAs modified cement mortar with different graphene mass contents after curing in Example 9 under backscattering mode at a scale of 500 μm, where (a) is 0%, (b) is 0.02%, (c) is 0.04%, (d) is 0.06%, (e) is 0.08%, and (f) is 0.10%.

[0052] Figure 25 (a) is a graph showing the relationship between the cumulative pore volume and pore size (adsorption branch) of the CMC-GNAs modified cement mortar in Example 10, and (b) is a graph showing the pore size distribution (adsorption branch) of the CMC-GNAs modified cement paste in Example 10.

[0053] Figure 26 (a) is a curve showing the relationship between the chloride ion concentration in the test block and the corresponding depth after 60 days of salt water immersion in Example 11, and (b) is a curve showing the relationship between the chloride ion concentration in the test block and the corresponding depth after 120 days of salt water immersion in Example 11. DETAILED DESCRIPTION

[0054] The present invention provides a nanofluid admixture and its preparation method and application. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only for the purpose of explaining the present invention and are not intended to limit the present invention.

[0055] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0056] The present invention will be further described below with reference to specific examples.

[0057] The information of some of the equipment and raw materials used in the following examples is as follows:

[0058] Graphene powder: 100 mesh, industrial grade; polyvinyl alcohol (PVA) powder: Mw = 90,000, industrial grade; sodium carboxymethyl cellulose (CMC) powder: Mw = 90,000.

[0059] Blender: Philips HR2096 household blender. Emulsifier: Silverson L5 series emulsifier. Centrifuge: Xiangli TG16-WS desktop high-speed centrifuge.

[0060] Example 1

[0061] The preparation method of the first nanofluid admixture comprises the following steps:

[0062] (1) PVA powder was added to water, which was then heated and stirred continuously for 24 h on a constant temperature magnetic stirrer at 80 °C to ensure that the powder was completely dissolved to form a uniform PVA solution (wherein the concentration of PVA was 14.3 g / L).

[0063] (2) 21.4 g of graphite powder was added to 350 mL of PVA solution, followed by shear exfoliation at 10,000 rpm in a blender for 6 min, and then emulsification exfoliation at 6,000 rpm in an emulsifier for 60 min to obtain a mixed solution;

[0064] (3) The mixed solution was placed in a centrifuge and centrifuged at 10,000 rpm for 30 minutes, and the supernatant was collected to obtain the nanofluid admixture.

[0065] The preparation method of the second nanofluid admixture differs from that of the first nanofluid admixture only in that the shear stripping time in step (2) is 12 minutes.

[0066] The preparation method of the third nanofluid admixture differs from that of the first nanofluid admixture only in that the volume of the PVA solution in step (2) is 1600 mL and the shear stripping time is 12 min;

[0067] The preparation method of the fourth nanofluid admixture differs from that of the first nanofluid admixture only in that the shear stripping time in step (2) is 0 min, for comparison.

[0068] test:

[0069] (1) The dispersion stability of the nanofluid admixture was tested by the static observation method as follows:

[0070] The above nanofluid admixtures were placed in sample bottles, and then left to stand at room temperature. The appearance changes at different time points were recorded and observed. After 180 days, there was no significant change in the appearance of the first, second and third nanofluid admixtures. This indicates that the graphene in the nanofluid admixture prepared by the preparation method provided by the present invention has good dispersion stability. Taking the first nanofluid admixture as an example, its appearance on the first day and on the 180th day is as follows: Figure 1 As shown in (a).

[0071] (2) The third nanofluid admixture was tested by transmission electron microscopy (TEM). The results are as follows: Figure 2 As shown. Figure 2 As shown in (a), the graphene nanosheet has a wrinkled transparent layered structure with clearly visible edges, reflecting its layered two-dimensional nanomaterial characteristics. Figure 2 As shown in (c), the magnified view shows the obvious edge of the single-layer graphene, which further proves that the number of graphene layers in the nanofluid admixture is controlled at a low level. Figure 2 As shown in (e), the diffraction pattern of graphene shows its hexagonal lattice structure, indicating that the prepared graphene has good crystal quality.

[0072] (3) Atomic force microscopy (AFM) test was performed on the second nanofluid admixture. The results are as follows: Figure 3 As shown, the linear size of the graphene is distributed between 1 and 5 μm. The height curve and topography indicate that the graphene nanosheets are folded. The graphene interlayer spacing is 0.335 nm. The flake heights measured in the AFM topography in this example are 0.352 nm and 0.682 nm, respectively. This indicates that the AFM captured both single-layer and double-layer graphene in the nanofluid admixture.

[0073] (4) X-ray photoelectron spectroscopy (XPS) test was performed on the second nanofluid admixture, and the results were as follows: Figure 4 As shown. Figure 4 The total spectrum in (a) of the sample was analyzed, which showed C1s and O1s peaks, indicating that the sample contained PVA, because PVA itself contains a large amount of carbon and oxygen elements. Figure 4The C1s peak in (b) is analyzed and located at about 284.5 eV, which is the sp 2 The sign of hybridized carbon indicates that a large amount of graphene structure exists in the sample being tested. A CO bond appears at a binding energy of 286eV and a CC bond appears at 284eV. These bonds are chemical bonds in the PVA molecule, indicating that no new chemical bonds appear between graphene and PVA, and the connection between graphene and PVA is a non-covalent bond. Therefore, during the centrifugal stripping and emulsification stripping process, PVA did not change the structure of graphene and did not introduce other structural defects to graphene. Figure 4 The O1s peak in (c) is analyzed. The presence of the O1s peak generally indicates the presence of oxides or functional groups with high oxygen content, such as hydroxyl groups, on the sample surface. The hydroxyl groups in PVA produce an O1s peak in the XPS spectrum at 531-533 eV.

[0074] (5) The graphene concentration of the four nanofluid admixtures was tested as follows:

[0075] a. Preparation of graphene powder: Add 120 mL of the second nanofluid additive to a crucible, then place it in a high-temperature furnace for high-temperature treatment to remove moisture and PVA. The high-temperature treatment program is set as follows: the temperature is raised from room temperature (25°C) to 250°C within 1 hour; maintained at 250°C for 3 hours; then heated to 500°C within 30 minutes; maintained at 500°C for 2 hours; and finally allowed to return to room temperature. After the temperature returns to room temperature, remove the crucible and the black powder inside is the graphene powder. The detailed reaction process is as follows:

[0076] Water evaporation (initial, close to 100°C):

[0077] H2O(l)→H2O(g) (Equation 1)

[0078] PVA dehydration reaction (200-300℃):

[0079] [-CH2CH(OH)-] n →[-CH=CH-] n +nH2O (Formula 2)

[0080] The main chain of PVA breaks (further heated to 300-400℃):

[0081] [-CH2CH(OH)-] n →CH3COOH+CH3OH+…(Formula 3)

[0082] Further pyrolysis and cracking reactions (400-500 °C), as the temperature further increases, PVA and its cracking products may undergo more complex chemical changes, including further cracking, condensation and cyclization reactions, and may form more different types of small molecular compounds, such as alkenes, alkynes, aromatic compounds, etc.

[0083] Carbonization reaction (approaching 500°C or higher): At higher temperatures, especially in the presence of oxygen, residual organic matter is converted into gas:

[0084] Organic matter → H2O(g) + CO + CO2 + ... (Formula 4)

[0085] b. Preparation of graphene aqueous dispersions of different concentrations: 0.01 g, 0.025 g, 0.05 g, 0.075 g, and 0.1 g of the graphene powder prepared above were weighed, respectively, mixed with 100 mL of deionized water, and ultrasonicated for 10 min to obtain graphene aqueous dispersions with concentrations of 0.1 g / L, 0.25 g / L, 0.5 g / L, 0.75 g / L, and 1.0 g / L, respectively.

[0086] c. Establish a linear relationship between graphene concentration and absorbance: Use a UV-visible spectrometer to measure the absorbance of the above-mentioned graphene aqueous dispersions with different concentrations at a wavelength of 660nm. Based on this, a standard curve of concentration and absorbance is drawn, which shows that there is a linear relationship between the two. The results are as follows: Figure 5 The linear regression equation is A=0.506C+0.04, where A represents absorbance and C represents graphene concentration.

[0087] d. By measuring the absorbance of the four nanofluid admixtures at a wavelength of 660 nm and then inserting it into the above linear regression equation, the concentration of graphene in the four nanofluid admixtures can be measured. The results are as follows: Figure 6 shown.

[0088] The results show that under the same solution volume (350mL), pre-shear exfoliation for 6 minutes followed by emulsion exfoliation can significantly improve the yield of graphene. Compared with the sample that was directly emulsion exfoliated without pre-shear exfoliation, the graphene yield produced by pre-shear exfoliation + emulsion exfoliation was more than twice as high. This shows that because the pre-shear exfoliation process introduced initial exfoliation between graphite sheets, it reduced the van der Waals force between graphite sheets, thereby providing graphite sheets that are easier to peel for the subsequent emulsion exfoliation process. In addition, pre-shear exfoliation also helps to break the strong interactions between graphite sheets, increase the exfoliable surface area of ​​graphene, and make the shear force in the emulsion exfoliation stage act more efficiently on graphene. Therefore, the two-step treatment of shear exfoliation combined with emulsion exfoliation significantly improved the release and yield of graphene.

[0089] In addition, this embodiment also studies the graphene concentration in the nanofluid admixture and the emulsification exfoliation graphene yield after 350 mL of PVA solution was subjected to shear exfoliation for 6 min and then emulsification exfoliation for different times (0, 20, 40, 60, 80, 100, 120, 140, 160, 180 min); the graphene concentration in the nanofluid admixture and the emulsification exfoliation graphene yield after 350 mL of PVA solution was subjected to shear exfoliation for 12 min and then emulsification exfoliation for different times (0, 20, 40, 6 The graphene concentration in the nanofluid admixture and the yield of graphene by emulsification exfoliation were obtained after 12 minutes of shear exfoliation and then emulsification exfoliation of 1600 mL of PVA solution for different time periods (0, 20, 40, 60, 80, 100, 120, 140, 160, 180 min). The graphene concentration in the nanofluid admixture and the yield of graphene by emulsification exfoliation were obtained after 12 minutes of shear exfoliation and then emulsification exfoliation of 1600 mL of PVA solution. Figure 7 As shown in Figure 3, when the shear stripping time is fixed, the graphene concentration obtained by the smaller solution volume (350 mL) used in the single preparation process generally exceeds that of the larger solution volume (1600 mL) before the emulsification stripping time reaches 120 min.

[0090] The high-speed rotation of the instrument probe during the shear emulsification process introduces higher fluid velocities when the solution volume is low, leading to an increase in the Reynolds number. When the Reynolds number reaches a certain threshold, the flow transitions from laminar to turbulent. The significantly enhanced local shear forces and improved fluid mixing efficiency in the turbulent state enhance the interactions and shear effects between graphene sheets, promoting the effective separation of graphene sheets. Furthermore, microscopic vortices and high-shear regions in the turbulent flow help overcome the van der Waals attractive forces between graphene sheets, further improving the efficiency and dispersion of graphene exfoliation. Therefore, by adjusting the shear and emulsification conditions to achieve an appropriate Reynolds number, transitioning from laminar flow to turbulent flow, the graphene production process can be optimized, achieving efficient graphene exfoliation and dispersion. At this stage, extending the emulsification exfoliation time significantly increased the graphene concentration, indicating that graphene concentration increases with emulsification exfoliation time. However, once the emulsification exfoliation time is extended to 120 minutes, the graphene concentration increases slowly but continuously with larger solution volumes, while the concentration stabilizes or even slightly decreases with smaller solution volumes. This suggests that extending the emulsification time to more than 120 minutes is more conducive to obtaining higher graphene concentrations in the case of larger solution volumes, while for smaller solution volumes, the optimal emulsification time does not need to be so long. Therefore, when the goal is to prepare high-concentration, large-volume nanofluid admixtures, the appropriate emulsification time should be set to more than 120 minutes to achieve high graphene concentration and yield.

[0091] Although a higher unit concentration of graphene can be achieved in a smaller solution volume used in a single preparation process, from the perspective of total yield, that is, the product of concentration and solution volume, the total yield when a larger solution volume is used in a single preparation is not necessarily lower than the output when the solution volume is smaller. Therefore, it is important to further evaluate the overall yield of graphene. Figure 8 As shown, this yield is obtained by removing the initial concentration increment caused by shear exfoliation from the overall graphene concentration. The results show that shear exfoliation can effectively improve the subsequent emulsification exfoliation yield. In the early stage of the emulsification exfoliation process, although the initial concentration was low, a relatively high yield was observed when a larger solution volume (1600 mL) was used in a single preparation process, which reflects the positive role of shear exfoliation pretreatment in promoting emulsification efficiency. In addition, Figure 8 The results also revealed a yield peak at the end of the emulsification exfoliation process, occurring at 120 minutes (350 mL) and 140 minutes (1600 mL), respectively, depending on the amount of solution used in a single preparation. The time of the yield peak was delayed as the amount of solution increased. This finding suggests that using a larger solution amount can achieve a better yield than using a smaller solution amount when preparing nanofluid admixtures.

[0092] Example 2

[0093] The preparation method of the nanofluid admixture comprises the following steps:

[0094] (1) CMC powder was added to water, and then heated on a constant temperature magnetic stirrer at 80°C and stirred continuously for 24 h to ensure that the powder was completely dissolved to form a uniform CMC solution (wherein the concentration of CMC was 14.3 g / L).

[0095] (2) Take 10 portions (350 mL) of CMC solution, add 21.4 g of graphite powder to each portion, and then shear and peel for 6 min in a blender at a speed of 10,000 rpm, and then emulsify and peel for 0, 20, 40, 60, 80, 100, 120, 140, 160, and 180 min in an emulsifier at a speed of 6,000 rpm to obtain 10 portions of mixed solution;

[0096] (3) The 10 mixed solutions were centrifuged at 10,000 rpm for 30 min, and the supernatant was collected to obtain 10 nanofluid admixtures.

[0097] At the same time, 10 portions of 350 mL of CMC solution were taken to prepare 10 nanofluid admixtures. The only difference from the above steps was that the shear stripping time was 12 min. Then 10 portions of 1600 mL of CMC solution were taken to prepare 10 nanofluid admixtures. The only difference from the above steps was that the shear stripping time was 12 min.

[0098] test:

[0099] (1) The dispersion stability of the nanofluid admixture was tested by static observation method, the method was the same as that in Example 1. After 180 days, the appearance of the nanofluid admixture (except the nanofluid admixture prepared when the shear stripping time was 0) still did not change significantly, indicating that the graphene in the nanofluid admixture prepared by the preparation method provided by the present invention had good dispersion stability. Taking the nanofluid admixture prepared by 350mL of CMC solution, shear stripping for 12min, and emulsification stripping for 40min as an example, the appearance of the nanofluid admixture on the 1st day and the 180th day was as follows: Figure 1 As shown in (b).

[0100] (2) The TEM results of the nanofluid admixture prepared under the conditions of 350 mL of CMC solution, shear stripping for 12 min, and emulsification stripping for 40 min are as follows: Figure 2 As shown in (b), (d) and (f), it has a morphology and diffraction spot similar to the third nanofluid admixture in Example 1.

[0101] (3) The graphene concentration in the above 30 nanofluid additives was tested using the same method as in Example 1. The results are as follows: Figure 9 As shown in the figure, high graphene concentrations can be obtained under different conditions, and under the same conditions, the graphene concentration prepared using CMC is higher than that prepared using PVA in Example 1. In addition, when a large solution volume (1600 mL) is selected for a single preparation, the emulsification and stripping time is selected to be 120 minutes, which can ensure high yield while optimizing the total graphene yield.

[0102] Example 3

[0103] Preparation of nanofluid admixture using PVA includes the following steps:

[0104] (1) Provide a PVA solution, the preparation method of which is the same as that of Example 1.

[0105] (2) 6 portions (350 mL) of PVA solution were taken, 21.4 g of graphite powder was added to each portion, and then sheared and peeled in a blender at a speed of 10,000 rpm for 12 min, and then emulsified and peeled in an emulsifier at a speed of 6,000 rpm for 120 min to obtain 6 portions of mixed solution;

[0106] (3) The six mixed solutions were centrifuged at 10,000 rpm for 30, 40, 50, 60, 70, and 80 min, respectively, and the supernatant was collected to obtain six nanofluid admixtures, which were recorded as six PVA-GNAs.

[0107] The preparation method of nanofluid admixtures using CMC is as follows: repeat the above steps, except that the PVA is replaced by CMC in step (1), to obtain 6 nanofluid admixtures, which are recorded as 6 CMC-GNAs.

[0108] The graphene concentration in PVA-GNAs and CMC-GNAs was tested, and the results were as follows: Figure 10 As shown in the figure, the length of centrifugation time directly affects the separation efficiency of graphene sheets from other components in the solution, thereby affecting the final graphene concentration. After 50 minutes of centrifugation, the graphene concentration in the nanofluid admixture remains almost constant, indicating that the graphene sedimentation velocity is close to zero. The density of the graphene particles and the medium is very close, so the downward gravitational force on the particles and the upward buoyancy force are essentially offset, indicating that the nanofluid admixture has been completely centrifuged. Using Stokes' law, it is known that higher medium viscosity will lead to slower sedimentation velocity. Therefore, it can be shown that PVA and CMC can sufficiently increase the viscosity of the medium, thereby slowing the sedimentation velocity of graphene, causing it to reach equilibrium after 50 minutes. In addition, since the sedimentation velocity approaches 0 after 50 minutes, it shows that both PVA-GNAs and CMC-GNAs can form stable graphene dispersions. Even under the influence of centrifugal force at a speed of 10,000 rpm, the graphene particles can remain suspended without sedimentation. The present invention fully considers the large-scale application of nanofluid admixtures, so the graphite powder raw materials selected are all industrial grade, which requires the stability and reproducibility of the process. The trade-off between efficiency and cost is crucial, and the selection of a centrifugation time of 30 minutes is more in line with the actual conditions of industrial production. A shorter centrifugation time can significantly reduce energy consumption and operation time, which can reduce costs in mass production. The nanofluid admixture prepared with PVA, the effect of the nanofluid admixture obtained without centrifugation and after 30 minutes of centrifugation on the strength of cement mortar is shown in the following figure. Figure 11As shown in the results, in the 28-day strength test of cement mortar, a 30-minute centrifugation time had little effect on the compressive strength, but significantly improved the flexural strength. This suggests a good balance between performance and cost. Furthermore, in cement-based materials, graphene not only improves mechanical properties but also provides multiple potential functions, such as electrical and thermal conductivity. Excessive centrifugation may disrupt the overlap and interconnection between graphene sheets, hindering the formation of an effective conductive network or enhancing the mechanical properties of the composite. Moderate centrifugation time helps preserve these structural features. Uniform dispersion of graphene in cement-based materials is critical, but marginal effects are not necessary. Moderately centrifuged graphene is more easily dispersed in cement-based materials, while excessive centrifugation may cause it to reaggregate within the cement-based material, affecting the final material properties. Furthermore, cement-based materials generally do not require ultra-high-purity graphene. Graphene aggregates or multilayer structures may, to a certain extent, enhance the material's performance. Excessive centrifugation time may also negatively impact graphene quality, such as oxidation or structural damage.

[0109] The results of Examples 1, 2, and 3 above demonstrate that the bond between graphene and PVA (or CMC) is non-covalent, and the use of a dispersant does not introduce additional structural defects. A combined shear exfoliation process of 12 minutes and emulsification exfoliation of 120-140 minutes yields the most efficient graphene production. Considering practical applications and cost-effectiveness, a centrifugation time of 30 minutes was selected as the optimal parameter.

[0110] Example 4 Application of Nanofluid Admixture (PVA-GNAs) in Increasing the Final Setting Time of Cement Paste

[0111] (1) Nanofluid admixtures (PVA-GNAs) with different graphene mass concentrations (0.025%, 0.050%, 0.075%, 0.100%, 0.125%, 0.150%, 0.175%, and 0.200%) were prepared using PVA solution. The preparation method is described above.

[0112] (2) PVA-GNAs were added to cement paste to prepare modified cement paste (referred to as PVA-GNAs modified cement paste): the modified cement paste included cement, water, defoamer TBP (tributyl phosphate), and nanofluid admixtures with different graphene mass concentrations; the mass ratios of cement, water, defoamer TBP, and graphene in the nanofluid admixture were 1:0.45:0.006:0. 025%, 1:0.45:0.006:0.050%, 1:0.45:0.006:0.075%, 1:0.45:0.006:0.100%, 1:0.45:0.006:0.125%, 1:0.45:0.006:0.150%, 1:0.45:0.006:0.175%, 1:0.45:0.006:0.200%.

[0113] The mixing process of PVA-GNAs modified cement paste is as follows: low speed stirring for 60s → stop stirring for 60s → high speed stirring for 60s → stop stirring → vibrate for 60s. After completing the stirring process of PVA-GNAs modified cement paste, the PVA-GNAs modified cement paste is immediately sent to the automatic Vicat instrument for setting time measurement, so as to accurately determine the initial setting time and final setting time. The results are as follows Figure 12As shown (the 0.000 group is also the blank control group, which means that no nanofluid admixture is added), it can be seen that the nanofluid admixture helps to slow the setting of cement paste. Specifically, with the increase of graphene dosage, the initial setting and final setting time of cement paste are significantly extended. Specifically, the initial setting time of the blank control group is 210min and the final setting time is 555min, which is extended to the initial setting time of 300min and the final setting time of the group with the highest graphene dosage (0.200%) is 735min. PVA plays a key retarding role in cement paste. PVA not only increases the viscosity of cement paste by interacting with the surface of cement particles, but also "captures" water molecules and cement particles by forming a network structure, thereby slowing down the rate of hydration reaction. This retarding effect is due to the fact that the PVA molecular chain can form a physical barrier in the cement paste that hinders the free movement and reaction of water molecules and cement particles, resulting in an extension of the setting time. The addition of graphene promotes a nucleating effect. Due to its extremely high surface area, it provides numerous nucleation sites, theoretically accelerating the hydration reaction. The high-energy sites on the graphene surface adsorb water molecules, creating an optimized local environment for the formation of hydration products. This should theoretically accelerate the setting process. However, in the modified cement paste, the retarding effect of PVA and the nucleating effect of graphene form a complex competitive relationship. On the one hand, the retarding effect of PVA slows the hydration reaction rate and prolongs the setting time; on the other hand, the nucleating effect of graphene attempts to accelerate the process. With increasing graphene content, this competitive relationship leads to longer initial and final setting times, with the final setting time being particularly prolonged. This phenomenon occurs primarily because, while graphene may promote the hydration reaction in the early stages, the retarding effect of PVA gradually becomes dominant as the reaction progresses. In the later stages of the hydration reaction, the influence of PVA becomes more pronounced, resulting in a significant increase in the final setting time.

[0114] Example 5 Application of Nanofluid Admixture (CMC-GNAs) in Increasing the Final Setting Time of Cement Paste

[0115] (1) Nanofluid admixtures with different graphene mass concentrations (0.02%, 0.04%, 0.06%, 0.080%, and 0.10%) were prepared using CMC solution. The preparation method is described above.

[0116] (2) Adding a nanofluid admixture (CMC-GNAs) to a cement paste to prepare a modified cement paste (referred to as CMC-GNAs modified cement paste): the modified cement paste comprises cement, water, a defoamer TBP, and nanofluid admixtures having different graphene mass concentrations; the mass ratios of the cement, water, defoamer TBP, and graphene in the nanofluid admixture are 1:0.5:0.006:0.02%, 1:0.5:0.006:0.04%, 1:0.5:0.006:0.06%, 1:0.5:0.006:0.08%, and 1:0.5:0.006:0.10%, respectively. The stirring process of the CMC-GNAs modified cement paste is the same as that of Example 3.

[0117] After the mixing process of CMC-GNAs modified cement paste is completed, the CMC-GNAs modified cement paste is immediately sent to the automatic Vicat instrument to measure the setting time, so as to accurately determine the initial setting time and final setting time. Figure 13 As shown in the figure (the 0.00 group, also known as the blank control group, refers to the group without the nanofluid admixture), the results show that increasing the graphene content significantly increases the initial and final setting times of the cement paste, from 450 minutes and 705 minutes in the blank control group to 810 minutes and 1080 minutes in the group with the highest graphene content (0.10%). CMC acts as a retarding agent in cement paste. This is primarily because, as a surfactant, CMC forms an adsorption film on the surface of cement particles. This film not only increases the viscosity of the cement paste but also reduces the rate of hydration. By adsorbing on the cement particle surface, CMC molecules reduce direct contact between water molecules and cement particles, thereby slowing the hydration process. Similarly, in cement paste, the retarding effect of CMC competes with the nucleation effect of graphene. Despite graphene's potential to promote hydration, the presence of CMC significantly slows the overall hydration rate, resulting in an overall increase in setting time. This competitive relationship results in almost identical increments in the initial and final setting times, 360 min and 375 min, respectively, indicating that the effect of CMC maintains a consistent influence throughout the hydration process.

[0118] Example 6 Application of Nanofluid Admixtures (PVA-GNAs) in Delaying the Hydration Reaction and Reducing the Heat Release Rate

[0119] (1) Nanofluid admixtures with different graphene mass concentrations (0.07%, 0.14%, 0.21%, and 0.28%) were prepared using PVA solution. The preparation method is described above.

[0120] (2) Adding a nanofluid admixture (PVA-GNAs) to a cement paste to prepare a modified cement paste (referred to as PVA-GNAs modified cement paste): the modified cement paste comprises cement, water, a defoamer TBP, and nanofluid admixtures having different graphene mass concentrations, wherein the mass ratios of the cement, water, defoamer TBP, and graphene in the nanofluid admixture are 1:0.45:0.006:0.07%, 1:0.45:0.006:0.14%, 1:0.45:0.006:0.21%, and 1:0.45:0.006:0.28%, respectively. The stirring process of the PVA-GNAs modified cement paste is the same as that of Example 4.

[0121] The hydration heat release rate curves of PVA-GNAs modified cement paste under different graphene content are as follows: Figure 14 As shown in the graphite graphite graphite admixture data, during the accelerated hydration phase (III) of the PVA-GNAs-modified cement paste, the silicate exothermic peak intensity decreases and the peak onset is delayed with increasing graphene content. This phenomenon indicates that the nanofluid admixture inhibits the hydration reaction of calcium trisilicate (CS), one of the primary reactions in cement setting and hardening. Due to the slower hydration rate of CS, the heat released by the hydration reaction decreases during the initial and accelerated phases of cement setting, resulting in a lower and delayed peak heat flux. The high surface area and adsorption properties of graphene can weaken the interaction between water molecules and cement particles, thereby reducing the reaction rate. Furthermore, the physical barrier formed by the graphene and PVA in the nanofluid admixture on the cement particle surface, as well as their possible chemical interactions, may slow the dissolution of CS and the subsequent formation of calcium silicate hydrate (CSH) and calcium hydroxide (CH).

[0122] During the deceleration period (IV), the sulfate depletion peak intensity decreased and its onset was delayed with increasing graphene content. This suggests that the incorporation of PVA-GNAs also delayed the solute reaction of tricalcium silicate (CA) to form ettringite, and that PVA-GNAs affected the interaction between CA and sulfate. The reformation of ettringite increased significantly, while the rapid formation of monosulfate was completed in a shorter time. This is because the nucleation effect of graphene plays a more complex role in the sulfate hydration reaction. Graphene provides additional nucleation sites, promoting ettringite formation in the early stages. However, with increasing graphene content, the retarding effect of acetate in PVA may become more pronounced, affecting the availability of water and sulfate, thereby reducing the intensity of the sulfate depletion peak in the later stages. This is also the period when the effect of different graphene content on the hydration heat is most pronounced. Therefore, the effect of the nanofluid admixture on hydration during this period primarily affects the formation of two hydration products: ettringite and monosulfate.

[0123]

[0124] (-CH[OOC-CH3]-CH2-CH[OH]-CH2-) n +nH2O→(-CH[OH]-CH2-CH[OH]-CH2-) n +nCH3-COOH (Formula 7)

[0125] 2CH3-COOH+Ca(OH)2→Ca(OOC-CH3)2+H2O (Formula 8)

[0126] Among them, formula 7 is the main reaction and formula 8 is the side reaction.

[0127] Figure 14 It was observed that the peak intensity of the sulfate depletion peak in the PVA-GNAs modified cement paste was higher than that in the blank group (without PVA-GNAs), which was due to the fact that the acetate produced by the presence of PVA had a blocking effect on the sulfate in the cement paste.

[0128] In addition, if Figure 15 As shown in the test results, PVA forms a film on the surface of cement particles, which restricts the reaction of sulfate. This blocking effect causes incomplete sulfate reaction in the early hydration stage, resulting in an increase in the intensity of the sulfate depletion peak in the later stage.

[0129] The cumulative hydration exothermic curve of PVA-GNAs modified cement paste is as follows Figure 16 As shown in the figure, the total heat release of cement pastes incorporating PVA-GNAs is generally lower than that of the blank paste during the initial hydration phase. This is because the addition of PVA-GNAs slows the initial rate of cement hydration, particularly affecting the hydration reactions of C3S and C3A, which are the primary sources of cement hydration heat. When examining the final cumulative heat release, it can be seen that the total heat release decreases significantly with increasing graphene content. This is because higher graphene content enhances its influence on the hydration reaction, especially in the later stages of hydration. This is because higher graphene content not only affects the dissolution of C3S in the initial hydration phase but also influences the hydration of C3A and its reaction with sulfate in the middle and late stages, thereby reducing heat release throughout the hydration process. Furthermore, analysis reveals that PVA and graphene exhibit a competitive effect on the heat of cement hydration. PVA primarily slows the hydration rate, while graphene promotes the hydration process to a certain extent by providing nucleation sites. With increasing graphene content, these two effects either enhance or antagonize to varying degrees, resulting in a complex, nonlinear relationship.

[0130] In conclusion, the incorporation of PVA-GNAs has a significant effect on the cumulative heat release of cement hydration heat, which demonstrates the potential of PVA-GNAs as cement admixtures in regulating cement hydration heat and optimizing cement paste properties.

[0131] Similarly, this embodiment also uses CMC to prepare nanofluid admixtures (CMC-GNAs) with different graphene mass concentrations (0.07%, 0.14%, 0.28%, 0.42%, 0.64%, and 0.98%), and uses CMC-GNAs with different graphene mass concentrations to prepare CMC-GNAs modified cement pastes, and then provides the hydration exothermic rate curve and cumulative hydration exothermic curve of the CMC-GNAs modified cement paste, as shown in FIG. Figure 17 shown. Figure 17 The results show that, for both PVA-GNAs and CMC-GNAs, increasing the graphene content delayed the onset of the first and second exothermic peaks in the cement paste and reduced their intensities. This indicates that the addition of the nanofluid admixture significantly affects the cement hydration kinetics, slowing the hydration reaction and reducing the rate of heat release. However, in the PVA-GNAs modified process, although the intensity of the second exothermic peak decreased with increasing graphene content, it remained higher than that of the blank control without the nanofluid admixture. This reflects a competitive relationship between PVA and graphene, namely, a dynamic balance between the retarding effect of PVA and the nucleation sites provided by graphene. At certain dosages, although PVA reduces the hydration rate, the high specific surface area and nucleation capacity of graphene are sufficient to maintain a high exothermic intensity. CMC-GNAs exhibited different behavior from PVA-GNAs. The exothermic peak of the cement paste containing CMC-GNAs was lower than that of the blank group at all dosages, and the rate and intensity of hydration heat release were generally delayed as the graphene dosage increased. This is because CMC, as a surfactant, provides stronger adsorption capacity and a more stable hydration reaction barrier compared to PVA. CMC-GNAs did not show a significant competitive relationship with graphene, but instead displayed a more synergistic effect between graphene and CMC, which makes CMC-GNAs potentially more ideal for controlling hydration heat.

[0132] This synergistic effect is due to the following two reactions: On the one hand, the carboxyl groups in CMC can increase the viscosity of the cement paste by adsorbing on the surface of cement particles, thereby physically hindering the hydration reaction. On the other hand, the carboxyl groups in CMC form complexes with calcium ions. The formation of the complex reduces the concentration of free calcium ions, thereby affecting the hydration rate, but does not significantly change the pH value. The reaction is:

[0133] (-CH2COONa-) (CMC) +Ca2+ →(-CH2COO-) (CMC) Ca+Na + (Equation 9)

[0134] Figure 17 Figure (b) shows that the upward trend in the total hydration heat release slows down with increasing graphene addition. This indicates that CMC-GNAs effectively slow the cement hydration reaction, particularly at higher additions, where the rate of increase in heat release is lower, demonstrating their potential in controlling the development of hydration heat. Specifically, compared to the blank control without CMC-GNAs, even at the lowest graphene addition (0.07 wt%), CMC-GNAs exhibited the ability to reduce the rate of hydration heat release. This slowing effect increased with increasing addition, being particularly pronounced at high additions of 0.64 wt% and 0.92 wt%. The slope of the cumulative heat release curve in the high-addition group was significantly lower than that in the blank control, indicating that CMC-GNAs played a key role in slowing the early and middle stages of the hydration reaction. It is important to note that the hydration heat test was conducted for 72 hours. Therefore, while the curve in the figure shows an exothermic trend within 72 hours, the actual total cement hydration heat release may still be increasing after the test period. The incorporation of CMC-GNAs showed a significant effect in reducing the total amount of cement hydration heat in the 72-h hydration heat test, which not only slowed down the cement hydration reaction rate but also helped reduce the internal stress and crack risk caused by hydration heat.

[0135] In summary, while both PVA-GNAs and CMC-GNAs can effectively control the exotherm of cement hydration, CMC-GNAs provide a more balanced and comprehensive control effect. With increasing graphene content, CMC-GNAs can more consistently delay all stages of the hydration reaction and reduce heat development.

[0136] Example 7 Application of Nanofluid Admixture in Increasing the Fluidity and Water Retention of Cement Mortar

[0137] (1) Nanofluid admixtures (PVA-GNAs) with different graphene mass concentrations (0.02%, 0.04%, 0.06%, 0.08%, and 0.10%) were prepared using PVA solution. The preparation method is described above.

[0138] (2) PVA-GNAs were added to cement mortar to prepare modified cement mortar (referred to as PVA-GNAs modified cement mortar).

[0139] The modified cement mortar comprises, by mass, cement, sand, water, defoamer TBP and nanofluid admixtures (PVA-GNAs) with different graphene concentrations;

[0140] The mass ratios of the cement, sand, water, defoamer TBP and graphene in the nanofluid admixture are 1:3:0.45:0.006:0.02%, 1:3:0.45:0.006:0.04%, 1:3:0.45:0.06:0.075%, 1:3:0.45:0.006:0.08% and 1:3:0.45:0.006:0.10%, respectively.

[0141] The mixing process of PVA-GNAs modified cement mortar is as follows: cement and water are stirred at low speed for 60 seconds → stirring is stopped for 60 seconds → nanofluid admixture, defoamer and standard sand are added → stirring at low speed for 30 seconds → stirring at high speed for 90 seconds → stirring is stopped → vibration is performed for 60 seconds.

[0142] The same method as above was used to prepare nanofluid admixtures (CMC-GNAs) with different graphene concentrations using CMC solution, and then to prepare CMC-GNAs modified cement mortar. The only difference from the above method was that PVA was replaced by CMC.

[0143] The flow rate of PVA-GNAs modified cement mortar and CMC-GNAs modified cement mortar was tested, and the results are as follows: Figure 18 As shown. Figure 18 As shown in (a), after the graphene production exceeds a certain concentration, the fluidity of the PVA-GNAs modified cement mortar gradually decreases as the graphene content increases. This phenomenon can be attributed to the high specific surface area of ​​graphene, which can absorb more water at the microscopic level, resulting in an increase in the water demand of the cement mortar. Although the micro-filling effect of graphene can theoretically reduce the water consumption of the cement mortar by filling the gaps between cement particles and replacing the water therein, the specific surface area of ​​graphene is so large that its effect on increasing water demand far exceeds the possible water reduction effect. This leads to the observation on a macroscopic scale that the fluidity of the cement mortar decreases significantly with increasing graphene content.

[0144] like Figure 18As shown in (b), the overall fluidity of the CMC-GNAs-modified cement mortar increases with increasing graphene content, reaching a plateau at 0.04% addition. Thereafter, the fluidity shows little significant change with further increases in addition. This characteristic is due to the inherent water-retention properties of CMC, which forms a water-absorbing film within the cement mortar that locks in moisture and reduces evaporation and loss. Therefore, the addition of CMC helps maintain moisture in the cement mortar, maintaining good fluidity even with the high surface area of ​​graphene. Therefore, while CMC-GNAs-modified cement mortar optimizes fluidity, it may also improve water retention, which is highly beneficial during construction because it helps reduce defects caused by rapid water evaporation, such as cracking and shrinkage.

[0145] Example 8 Application of Nanofluid Admixture in Increasing the Strength of Cement Mortar

[0146] In this embodiment, the PVA-GNAs modified cement mortar and CMC-GNAss modified cement mortar prepared in Example 7 are cured (including two ages of 7 days and 28 days), and then the PVA-GNAs modified cement mortar and CMC-GNAs modified cement mortar are poured into molds respectively, and plastic wrap is covered on the surface. Subsequently, they are placed in a constant temperature and humidity curing room with a curing temperature of 20°C and a curing humidity greater than 95%. After waiting for 24 hours, the molded test blocks can be demoulded to obtain the formed test blocks. After the test blocks are cured to the test age (such as 7 days and 28 days), the test blocks are taken out for testing (the curing in the present invention is carried out according to this method), and are made into 160mm×40mm×40mm prism parallel specimens, and then the compressive strength is tested. According to the provisions of GB-T17671-1999 "Test Method for Strength of Cement Mortar", when conducting the compressive strength test, the loading rate should be set to 2.4kN / s. The results are as follows Figure 19 As shown. Figure 19As can be observed in Figure (a), after 7 days of curing, the strength improvement of the PVA-GNAs-modified cement mortar at various dosages was not very significant compared to the blank control (maximum 23.00%). This is partly attributed to the retarding and air-entraining effects of PVA, the latter of which increases the void content of the mixture. These voids hinder the potential role of graphene as a microfiller in improving density and strength during the initial hydration period. As the curing time extends to 28 days, the hydration of the cement mortar becomes more mature, and the microfilling effect of graphene is more fully realized, resulting in a significant improvement in compressive strength. At dosages of 0.02%, 0.04%, and 0.06%, the compressive strength shows similar levels, forming a plateau. This is because at these dosages, the interaction between graphene and PVA reaches a dynamic equilibrium, with their effects offsetting each other, resulting in little change in compressive strength. On the one hand, the retarding and air-entraining effects of PVA limit the hydration rate, while on the other hand, the microfilling effect of graphene and the nucleation sites it provides promote the formation of a denser structure. When the addition amount was increased to 0.1%, a significant increase in compressive strength (59.17%) was observed, indicating that at higher addition amounts, the micro-filling effect of graphene dominated, specifically due to the formation of a more uniformly dispersed network structure in the cement matrix, which effectively improved the compressive strength. This distribution improved the quality of the interfacial transition zone (ITZ), thereby enhancing the overall performance.

[0147] like Figure 19 As shown in (b), for CMC-GNAs modified cement mortar, at low dosages, the compressive strength improvement after 7 days of curing is higher than that of PVA-GNAs modified cement mortar. This is because CMC does not have the air-entraining effect of PVA. Air-entraining introduces tiny bubbles into the concrete, increasing its porosity, which may reduce the compressive strength at an early stage. Because CMC does not introduce additional gas, CMC-GNAs modified cement mortar can maintain a high initial compressive strength even at low dosages. At a curing age of 28 days, the compressive strength of CMC-GNAs modified cement mortars at all dosages was significantly improved compared to the blank control.

[0148] Therefore, it can be seen from the above results that the nanofluid admixture provided by the present invention can improve the compressive strength of cement mortar.

[0149] In this embodiment, the PVA-GNAs modified cement mortar and CMC-GNAs modified cement mortar prepared in Example 7 were cured (including two periods of 7 days and 28 days) and then made into 160mm×40mm×40mm prism parallel specimens. Then, the flexural strength was tested. According to the provisions of GB-T17671-1999 "Test Method for Strength of Cement Mortar", the loading rate should be set to 50N / s. The results are as follows: Figure 20As shown in FIG, the nanofluid admixture provided by the present invention can significantly improve the flexural strength of cement mortar. Specifically, as Figure 20 As shown in Figures (a) and (b), at a 7-day curing age, the flexural strength of cement mortars incorporating nanofluid admixtures was generally higher than that of the blank control (no nanofluid admixture). This phenomenon is due to the relatively small retarding effect at low dosages, resulting in a less pronounced delay in the hydration reaction. PVA, as a polymer, can enhance the connectivity of cement mortars through its film-forming properties. This is because PVA forms a polymer film between cement particles, which helps transfer stress and improve the toughness of the mortar. At the same time, CMC, due to its polymer chain structure, acts as a "bridge" in the cement matrix, connecting cement particles and improving the stability of the overall structure. Because the concentration of PVA is higher than that of CMC at the same graphene dosage, the improvement in flexural strength of PVA-GNAs is more significant after 7 days of curing. When the curing age is 28 days, the cement hydration is more complete. At this time, the synergistic effect of PVA, CMC and graphene is more prominent in improving strength. The peak values ​​of flexural strength appear at dosages of 0.08% and 0.04%, respectively (increased by 30.64% and 25.83%, respectively). This is because as the hydration reaction proceeds, the amount of CSH gel and other hydration products formed in the cement matrix increases, which, combined with the micro-filling effect of graphene, further improves the toughness and crack resistance of the cement mortar. However, at higher dosages, graphene is prone to agglomeration, which will destroy the uniformity at the microscopic level and affect the material properties. Relatively speaking, CMC-GNAs show the advantage of improving flexural strength at low dosages. This is because the special molecular configuration of CMC has a more obvious dispersion effect on graphene than PVA. Therefore, CMC-GNAs can play a good role at low dosages and show the advantage of improving flexural strength.

[0150] Example 9 Application of Nanofluid Admixture in Promoting the Formation of Interwoven Fibrous Hydration Products, Needle-Shaped Hydration Products, and Flake-Shaped Hydration Products in Cement Mortar

[0151] In this embodiment, the PVA-GNAs modified cement mortar in Example 7 was subjected to SEM testing after a curing period of 28 days. The SEM images are shown in FIG. Figure 21As shown in Figure 2, with increasing graphene content, the flake-like hydration products (such as calcium hydroxide [CH]) in the cement mortar become smaller and denser. This change suggests that the addition of graphene affects the morphology of the hydration products, promoting the formation of more compact hydration products. At a graphene content of 0.08%, SEM images reveal a large number of fibrous and needle-like hydration products, such as calcium silicate hydrate (CSH) and ettringite (AFt) or monosulfate (AFm). These fibrous and needle-like products intertwine and form a composite structure around the flake-like CH. In addition, some blocky hydration crystals were observed attached to these fibrous and needle-like products. This "template effect" suggests that graphene can guide the growth of hydration products, thereby improving the density and mechanical properties of the cement mortar. Combined with previous hydration heat test results, it is speculated that in the graphene-doped samples, the hydration reaction generates some CSH and CH during the acceleration phase, while the dissolution of CA and its reaction with sulfate are delayed until the deceleration phase. This delay leads to the formation of more intertwined hydration products, resulting in a stronger microstructure.

[0152] The SEM images of CMC-GNAs modified cement mortar after 28 days of curing are shown in Figure 2. Figure 22 As shown, similarly, interwoven fibrous and needle-like hydration products were formed.

[0153] The SEM test of CMC-GNAs modified cement mortar with a curing age of 7 days was carried out in the backscattered (BSE) mode at a scale of 100 μm. The results are shown in Figure 2. Figure 23 As shown, in the samples with intermediate doping amounts (e.g., Figure (c), 0.06%), a large number of flake-like calcium hydroxide (CH) hydration products are displayed. These flake-like products form an interwoven composite structure with needle-rod-like hydration products, which may be calcium aluminate (AFt) or monosulfate (AFm). This structure shows that the addition of CMC-GNAs not only promotes the formation of flake-like CH, but also may affect the morphology and distribution of other hydration products. These interwoven hydration products in the intermediate doping amount samples help to improve the structural density and mechanical properties of the material. The formation of flake-like CH fills the micropores of the material, while the needle-rod-like hydration products increase the anchoring effect of the structure at the microscopic level, thereby improving the overall structural stability and load-bearing capacity of the material. As the graphene doping amount increases further, as shown in Figures (e) and (f), flake-like and needle-rod-like hydration products can still be observed.

[0154] The SEM test of CMC-GNAs modified cement mortar with a curing age of 7 days was carried out in backscattering mode at a scale of 500 μm. The results are as follows: Figure 24 As shown, in the sample with intermediate graphene content, Figure 24As shown in (c) in the figure, the fibrous calcium silicate hydrate (CSH) and needle-shaped calcium aluminoferrite (AFt) or monosulfate (AFm) hydration products are more obvious. These slender fibrous CSH products are crucial to the strength and toughness of cement-based materials because they are intertwined to form a dense network structure, which helps to improve the crack resistance and tensile strength of the material. At the same time, the needle-shaped AFt or AFm products will be interspersed between the CSH fibers, further strengthening this microscopic network and improving the overall structural stability of the material. As the graphene content increases further, as shown in Figure 24 As shown in (e) and (f), the distribution density of fibrous and needle-like hydration products seems to be reduced.

[0155] Example 10 Application of Nanofluid Admixture in Reducing the Cumulative Pore Volume of Cement Mortar After Curing

[0156] After the CMC-GNAs modified cement mortar in Example 7 was cured for 7 days, a BET (Brunauer-Emmett-Teller) test was performed.

[0157] The relationship between the cumulative pore volume and pore size (adsorption branch) of CMC-GNAs modified cement mortar at 7 days of age is shown in the figure below: Figure 25 As shown in (a), the cumulative pore volume of the cement mortar sample is lowest at a graphene content of 0.04%, indicating that graphene effectively fills the pores at this content, maximizing the density of the cement mortar. This is consistent with the aforementioned results, which show that the sample with 0.04% graphene content exhibits the highest flexural strength. These results are consistent with the aforementioned research conclusions and further confirm the influence of graphene content on the pore structure and mechanical properties of cement-based materials.

[0158] In cement-based materials, pores can be divided into the following categories according to pore size:

[0159] Micropores: Pores with a diameter of less than 2 nanometers. These pores are commonly found in adsorption materials such as activated carbon.

[0160] Mesopores: Pores with diameters between 2 and 50 nanometers. These pores have a significant impact on the mechanical properties and durability of materials, as they determine the hydration and strength growth of cement-based materials.

[0161] Macropores: Pores with a diameter greater than 50 nanometers. They generally reduce the strength of a material but can increase its thermal and acoustic insulation properties.

[0162] Harmful pores: generally refer to pores larger than 200 nanometers. They are usually considered harmful because their large size may weaken the mechanical properties of the material.

[0163] The pore size distribution curve (adsorption branch) of CMC-GNAs modified cement paste after 7 days of curing is as follows: Figure 25 As shown in (b), 0.02% graphene shows a higher number of micropores smaller than 4nm. The distribution and connectivity of micropores and mesopores in the material determine the transport capacity of water, solutes and reaction products during the hydration process, which directly affects the strength and durability of cement paste. This is consistent with the test results that 0.02% graphene yield shows the highest compressive strength ( Figure 18 (b) is consistent with the graphene content in Figure 2. At a graphene content of 0.10%, there are fewer small-volume mesopores, indicating that at higher content, excessive graphene aggregation leads to agglomeration, hindering the pore filling process. Graphene agglomeration can form larger aggregates, which may form macropores at the microscopic level, which are detrimental to improving the mechanical properties of the material. Therefore, high graphene content may lead to a deterioration of the pore structure, thereby affecting the macroscopic properties of the material.

[0164] Example 11 Application of graphene nanofluid in reducing chloride ion penetration in cured cement mortar

[0165] After curing the PVA-GNAs modified cement mortar in Example 7 for 28 days, a test block with a volume of 160 mm × 40 mm × 40 mm was obtained. The test block was then placed in a 5% NaCl solution. After immersion in salt water for 60 and 120 days, the relationship between the chloride ion concentration in the test block and the corresponding depth was shown in the following curve: Figure 26 As shown. Figure 26 As can be seen from (a) in the figure, with the increase of graphene content, the diffusion trend of chloride ion concentration in the test block shows a downward trend. Specifically, with the increase of depth, the chloride ion concentration of all test blocks gradually decreases, which indicates that chloride ions gradually diffuse into the interior of the test block. Moreover, with the increase of graphene content, the initial concentration of chloride ions also decreases, indicating that PVA-GNAs enhance the resistance of cement mortar to chloride ions. Figure 26 As can be seen in (b), the chloride ion concentration also decreases significantly at deeper measurement points. In addition, the rate of decrease in chloride ion concentration slows down with the increase in graphene content, which is related to the dispersed network structure formed by graphene in cement mortar.

[0166] The measured chloride ion diffusion coefficient is as follows:

[0167] Table 1. Chloride ion diffusion coefficient of PVA-GNAs modified cement mortar tested by salt water immersion method

[0168]

[0169] During the 60-day and 120-day test periods, the diffusion coefficient of chloride ions decreased significantly with the increase in the dosage of PVA-GNAs (also known as graphene), indicating that the addition of nanofluid admixtures significantly increased the density of cement mortar and reduced the permeability of chloride ions. Specifically, the layered structure of graphene increases the path length of chloride ions through cement mortar and improves the barrier performance. This effect becomes more obvious over time, specifically due to the further hardening of the cement mortar. In addition, the decrease in surface chloride ion concentration (Cs) with increasing dosage also indicates that graphene has a strong adsorption effect on chloride ions, thereby reducing the accumulation of chloride ions on the surface. R 2 A value close to 1 indicates a good fit to the experimental data.

[0170] Based on the above test results, we can know that:

[0171] (1) PVA and CMC, as dispersants for graphene, significantly affected the setting time of cement paste after their introduction. The introduction of PVA prolonged the setting time, especially in the PVA-GNAs modified cement paste, where the final setting time was significantly prolonged. This indicates that although the nucleation effect of graphene helps to accelerate the hydration reaction, the retarding effect of PVA dominates in the later stages of the hydration reaction, especially with the increase in graphene content, this effect becomes more pronounced.

[0172] (2) Regarding the influence of hydration heat, PVA-GNAs and CMC-GNAs modified cement pastes showed different control effects. PVA-GNAs modified cement significantly reduced the hydration heat release at high dosage, slowed down the hydration reaction rate, and especially affected the hydration of C3S and C3A. CMC-GNAs modified cement also showed that the increasing trend of the total hydration heat release was effectively slowed down with the increase of dosage. In particular, at higher dosages, the rate of increase of heat release was relatively low, demonstrating its significant role in slowing down the hydration reaction.

[0173] (3) In terms of fluidity and mechanical properties, nanofluid admixtures improve the fluidity and mechanical properties of cement mortar, and the interaction between the micro-filling effect of graphene and the cement matrix enhances the toughness and crack resistance of the material.

[0174] (4) Effect on the microscopic hydration products of cement mortar. The results show that with the increase of graphene content, the structure of hydration products in cement mortar becomes smaller and denser, and fibrous (AFt) and needle-like hydration products (such as calcium silicate hydrate [CSH] and ettringite [AFt] or monosulfate [AFm]) are intertwined, which enhances the density and mechanical properties of the material.

[0175] (5) The introduction of nanofluid admixture significantly changed the pore structure of cement mortar, especially promoting the development of micropores and mesopores. When the admixture amount was 0.02% and 0.04%, the pore structure of the sample was obviously refined and filled.

[0176] (6) The introduction of nanofluid admixtures significantly reduces the chloride ion diffusion coefficient, which indicates that nanofluid admixtures have the potential to improve the durability of cement mortar, especially to reduce the penetration of chloride ions into the interior through the microscopic pore network.

[0177] The above shows that the nanofluid admixture provided by the present invention has the effectiveness and potential as a nanofluid admixture for cement-based materials in improving setting time, controlling hydration heat, optimizing pore structure, and enhancing mechanical and durability properties.

[0178] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing a nanofluid admixture, characterized in that: The nanofluid admixture includes water, graphene dispersed in the water, and a dispersant, wherein the dispersant includes sodium carboxymethyl cellulose, and the sodium carboxymethyl cellulose is connected to the graphene via a non-covalent bond. The preparation method of the nanofluid admixture includes the following steps: Provide graphite powder and dispersant; adding the dispersant into water and stirring to obtain a dispersant solution; Adding the graphite powder to the dispersant solution, and then sequentially performing shear exfoliation and emulsification exfoliation to obtain a mixed solution; After centrifuging the mixed solution, collecting the supernatant to obtain the nanofluid admixture; The concentration of the dispersant in the dispersant solution is 5 to 25 g / L; The rotation speed used in the shear stripping is 10000 rpm, the rotation speed used in the emulsification stripping is 6000 rpm, the rotation speed used in the centrifugation is 10000 rpm, the time used in the shear stripping is 12 min, the time used in the emulsification stripping is 120~140 min, and the time used in the centrifugation is 30 min.

2. A nanofluid admixture, characterized in that: The preparation method according to claim 1 is used for preparation.

3. An application of the nanofluid admixture according to claim 2, characterized in that: The nanofluid admixture is applied to cement-based materials, and the cement-based materials include one of cement paste, cement mortar and concrete.

4. A modified cement-based material, characterized in that: The modified cement-based material includes one of modified cement paste, modified cement mortar, and modified concrete; The modified cement paste comprises cement, water and the nanofluid admixture according to claim 2; The modified cement mortar comprises cement, sand, water and the nanofluid admixture according to claim 2; The modified concrete is prepared from the modified cement paste or the modified cement mortar.

5. The modified cement-based material according to claim 4, characterized in that In the modified cement paste, the mass ratio of the cement, water, and graphene in the nanofluid admixture is 1:(0.45-0.55):(0-0.002); In the modified cement mortar, the mass ratio of the cement, sand, water and graphene in the nanofluid admixture is 1:(2-4):(0.45-0.55):(0-0.002); In the modified cement paste and the modified cement mortar, the mass of the graphene in the nanofluid admixture is not 0.

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