A composition for geopolymers, a geopolymer and a preparation method thereof

Abstract

The present invention relates to the field of building materials, and discloses a composition for geopolymers, a geopolymer and a preparation method thereof. The composition contains a cementitious material and a fiber material; the cementitious material includes an alkali activator and a filler; the filler contains metakaolin and fly ash; the mass ratio of the cementitious material to the fiber material is 100:0.5-1.5; the fiber material contains aramid fiber and graphitized carbon fiber with a mass ratio of 1:0.3-3. The geopolymer of the present invention has excellent high temperature resistance.

Description

Technical Field

[0001] The present invention relates to the field of building materials, and particularly to a composition for geopolymers, a geopolymer and a preparation method thereof. Background Art

[0002] Geopolymers, as an environmentally friendly building material, have received extensive attention due to their excellent properties such as high temperature resistance, acid and alkali resistance, and corrosion resistance. Geopolymers are mainly synthesized by the reaction of aluminosilicate sources (such as metakaolin MK, fly ash FA) in a strong alkaline environment, and have chemical stability and mechanical properties that are incomparable to traditional cement. However, under extreme high temperature conditions, especially in a high temperature environment above 600 °C, the mechanical properties and structural stability of geopolymers will significantly decrease, limiting their application in high temperature engineering.

[0003] In recent years, incorporating fibers (inorganic or organic fibers) has become an effective means to improve the high temperature performance of geopolymers. Fibers can not only enhance the toughness and crack resistance of the matrix, but also effectively inhibit the propagation of cracks at high temperatures, thereby improving the overall thermal stability of the material.

[0004] Although fibers have certain advantages in improving the high temperature resistance of geopolymers, the synergistic effect of different types of fibers has not been fully explored. How to play their synergistic role and improve the comprehensive performance of geopolymers by reasonably designing the composite of fibers and inorganic polymers has become a current research hotspot.

[0005] CN110981295A discloses a geopolymer-based self-sensing anchoring mortar, which includes the following components: 100-120 parts of river sand, 30-40 parts of metakaolin, 10-20 parts of fly ash, 60-70 parts of alkali activator, 15 parts of expansive agent, 0.5-1 part of carbon fiber, and 0.2-0.5 part of carbon nanotube. However, this solution has problems such as the easy agglomeration of carbon fiber and carbon nanotube in the viscous geopolymer matrix and the high cost. In addition, the composite geopolymer synthesized in this solution does not show good high temperature resistance.

[0006] CN110255996A discloses a fly ash geopolymer concrete, which is prepared from fly ash and metakaolin as base materials, one or more combinations of sodium hydroxide, potassium hydroxide, potassium silicate and sodium silicate as an alkaline activator, adding modified ceramic microsphere particles, polymer fibers, coarse aggregate, fine aggregate and water; the modified ceramic microsphere particles are coated with a functional coating containing an anti-corrosion and rust inhibitor on the surface of ordinary ceramic microspheres, and the preparation raw materials include: 100-500 parts of ceramic microspheres, 20-60 parts of silica sol, 20-40 parts of anti-corrosion and rust inhibitor, and a total of 30-50 parts of acrylate emulsion and / or styrene-acrylic emulsion. However, this solution has problems such as complex preparation process, high cost, and the styrene-acrylic emulsion used contains volatile organic compounds (TVOC>50 μg / m³), which violates the green building material certification standard. Summary of the Invention

[0007] The object of the present invention is to overcome the technical problem of poor high-temperature resistance of geopolymers.

[0008] To achieve the above object, in the first aspect of the present invention, a composition for geopolymers is provided, which contains a gelling material and a fiber material; the gelling material includes an alkaline activator and a filler; the filler contains metakaolin and fly ash;

[0009] The mass ratio of the gelling material to the fiber material is 100:0.5-1.5;

[0010] The fiber material contains aramid fiber and graphitized carbon fiber with a mass ratio of 1:0.3-3;

[0011] The tensile modulus of the aramid fiber at 25°C is 100-150 GPa, and the tensile strength at 25°C is 3-6 GPa.

[0012] In the second aspect of the present invention, a method for preparing geopolymers is provided, which is carried out using the composition for geopolymers described in the first aspect. The method includes: mixing each component in the composition for geopolymers with water to obtain geopolymers.

[0013] In the third aspect of the present invention, geopolymers prepared by the method described in the second aspect are provided.

[0014] The present invention has at least the following advantages:

[0015] (1) The geopolymers of the present invention have excellent high-temperature resistance and stability, and show excellent mechanical properties and low mass loss rate in high-temperature environments.

[0016] (2) The preparation process of the present invention is simple and environmentally friendly. Detailed Embodiments

[0017] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values approaching these ranges or values. For numerical ranges, the values between the endpoints of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0018] It should be noted that in various aspects of the present invention, for the same components or terms in each aspect, the present invention is only described once in one aspect without repeated description. Those skilled in the art should not understand this as a limitation of the present invention.

[0019] As described above, the first aspect of the present invention provides a composition for geopolymers, which contains a cementitious material and a fiber material; the cementitious material includes an alkali activator and a filler; the filler contains metakaolin and fly ash;

[0020] The mass ratio of the cementitious material to the fiber material is 100:0.5 - 1.5;

[0021] The fiber material contains aramid fiber and graphitized carbon fiber with a mass ratio of 1:0.3 - 3;

[0022] The tensile modulus of the aramid fiber at 25°C is 100 - 150 GPa, and the tensile strength at 25°C is 3 - 6 GPa.

[0023] In the technical solution of the present invention, in an aqueous solution, specific proportions of aramid fiber and graphitized carbon fiber are used as reinforcing fibers, and are combined with a cementitious material containing an alkali activator and a filler. The geopolymers prepared exhibit excellent mechanical properties and low mass and volume loss rates under high-temperature environments, providing an excellent solution for engineering applications under high-temperature environments.

[0024] Preferably, the modulus of the alkali activator is 0.8 - 1.2.

[0025] It should be noted that the modulus of the alkali activator in the present invention refers to the molar ratio of silicon dioxide (SiO2) to total sodium oxide (Na2O) in the alkali activator system, where silicon dioxide and sodium oxide are obtained by chemical equivalent conversion of the actual components of the raw materials.

[0026] Preferably, the mass ratio of the alkali activator to the filler is 1:3 - 5.

[0027] Preferably, the mass ratio of the metakaolin to the fly ash is 1:0.1 - 1. The inventors of the present invention have found that under these preferred conditions, the overall performance of the material can be significantly improved. Specifically, this ratio can effectively enhance the mechanical strength of the material, endowing it with better compressive strength and flexural strength, thereby improving its durability and stability. At the same time, an appropriate mass ratio also optimizes the fluidity of the mixture, reducing the operation difficulty during the production process.

[0028] Preferably, the fly ash in the present invention is class I and / or class II fly ash specified in the standard of GB / T 1596 - 2017 Fly Ash Used in Cement and Concrete.

[0029] According to a preferred embodiment, the graphitized carbon fiber is a product prepared by the following steps:

[0030] Graphitize the carbon fiber to obtain the graphitized carbon fiber; the conditions for the graphitization treatment include: the temperature is 1200 - 1500 °C, and the time is 24 - 36 h. The inventors of the present invention have found that by preparing the graphitized carbon fiber material at 1200 - 1500 °C, it is beneficial to significantly improve the thermal stability and mechanical properties of the carbon fiber. Graphitization treatment within this high - temperature range helps the carbon atoms to be arranged more orderly, forming a more compact graphite layer structure, thereby increasing the density and rigidity of the material and enhancing its high - temperature resistance.

[0031] It should be noted that the present invention has no restrictions on the source of the carbon fiber, which may include carbon fibers from industrial production waste. Through graphitization treatment under specific conditions and in combination with the other components in the present invention, the geopolymers prepared have excellent high - temperature resistance; at the same time, using waste carbon fibers can effectively utilize waste resources, with the advantages of environmental protection and low cost.

[0032] More preferably, the length of the graphitized carbon fiber is 4 - 6 mm.

[0033] Preferably, the tensile modulus of the graphitized carbon fiber at 25 °C is 200 - 300 GPa, the tensile strength at 25 °C is 3 - 6 GPa, and the density is 1 - 3 g / cm³.

[0034] More preferably, the density of the aramid fiber is 1 - 3 g / cm³, and the length is 4 - 6 mm.

[0035] Preferably, the alkali activator is a combination of water glass and sodium hydroxide.

[0036] As described above, the second aspect of the present invention provides a method for preparing geopolymers, which is carried out using the geopolymer composition described in the first aspect. The method includes: mixing each component in the geopolymer composition with water to obtain a geopolymer.

[0037] Preferably, the amount of water used is controlled to satisfy a water-binder ratio of 0.35 - 0.45.

[0038] It should be specifically noted that the water-binder ratio in the present invention specifically refers to the ratio of the total mass of water in the material system to the total mass of the reactive cementitious components. The reactive cementitious components include two types of substances participating in the alkali activation reaction: the first type is aluminosilicate materials with pozzolanic activity, such as metakaolin with a chemical structure of Al2O3·2SiO2, fly ash with a component expression of mSiO2·nAl2O3, etc.; the second type is the functional components in the alkaline activation system, specifically referring to the reactive silica source (such as the SiO2 component in sodium silicate Na2O·nSiO2) that can dissociate to generate silicate ions (SiO3 2- ) and the alkaline oxides calculated according to equivalent oxides (such as the Na2O component in sodium silicate, and other alkali metal oxides such as K2O, CaO, etc.). The mass of the alkaline oxides needs to be chemically equivalent converted according to the actual components of the raw materials.

[0039] Preferably, the conditions for the mixing treatment include: a stirring speed of 100 - 1200 rpm, a stirring time of 2.5 - 6 h, and a reaction temperature of 20 - 50 °C.

[0040] According to a preferred embodiment, the operation of the mixing treatment includes:

[0041] (1) First mixing the solution 1 containing the alkali activator and water with the fiber material to obtain solution 2;

[0042] (2) Second mixing the solution 2 with the admixture to obtain a geopolymer.

[0043] In the present invention, by controlling the addition sequence of different raw materials, the reaction process is made more controllable, and the interaction between raw materials is more uniform, ensuring that the prepared geopolymer exhibits better mechanical properties and lower mass and volume loss rates under high-temperature environments.

[0044] Preferably, the temperatures of the first mixing and the second mixing are each independently selected from 20 - 50 °C, the stirring speeds are each independently selected from 100 - 1200 rpm, and the total mixing time is 2.5 - 6 h.

[0045] According to a preferred embodiment, the method further includes: subjecting the product obtained by the mixing treatment to injection molding and curing treatment in sequence to obtain the geopolymer.

[0046] Preferably, the conditions of the curing treatment include: temperature of 60 - 90 °C, time of 48 - 60 h, and relative humidity of 85 - 95%.

[0047] The present invention has no particular limitation on the operation of the injection molding. Those skilled in the art can select according to the known technical means in the art. The present invention exemplarily provides a preferred specific implementation manner hereinafter, which will not be elaborated herein. Those skilled in the art should not understand it as a limitation to the present invention.

[0048] As mentioned above, the third aspect of the present invention provides a geopolymer prepared by the method described in the second aspect.

[0049] In the following examples, unless otherwise specified, the raw materials are all ordinary commercially available products.

[0050] Aramid fiber 1: Tensile modulus at 25 °C is 150 GPa, tensile strength at 25 °C is 6 GPa, density is 2.8 g / cm³, length is 5 mm, purchased from Hubei Jiayuan Textile Co., Ltd.

[0051] Aramid fiber 2: Tensile modulus at 25 °C is 150 GPa, tensile strength at 25 °C is 1.5 GPa, density is 1.3 g / cm³, length is 5 mm, purchased from Hubei Jiayuan Textile Co., Ltd.

[0052] Aramid fiber 3: Tensile modulus at 25 °C is 100 GPa, tensile strength at 25 °C is 4.5 GPa, density is 1.25 g / cm³, length is 5 mm, purchased from DuPont.

[0053] Carbon fiber: Model STT49S, purchased from Hubei Jiayuan Textile Co., Ltd.

[0054] Sodium silicate: Modulus 3.3, CAS number: 1344 - 09 - 8, purchased from Jiashan Yourui Refractory Materials Co., Ltd.

[0055] In the present invention, the test method for tensile modulus refers to GB / T3362 - 2017.

[0056] In the present invention, the test method for tensile strength refers to GB / T3362 - 2017.

[0057] In the present invention, the test method for density is referred to GB / T30019 - 2013.

[0058] Preparation Example 1

[0059] The 5-mm carbon fiber was heated to 1200 °C at a rate of 10 °C / min and held at this temperature for 24 hours to obtain graphitized carbon fiber 1;

[0060] The tensile modulus of graphitized carbon fiber 1 at 25 °C is 220 GPa, the tensile strength at 25 °C is 4.9 GPa, and the density is 1.8 g / cm³.

[0061] Preparation Example 2

[0062] The 2-mm carbon fiber was heated to 1200 °C at a rate of 10 °C / min and held at this temperature for 24 hours to obtain graphitized carbon fiber 2;

[0063] The tensile modulus of graphitized carbon fiber 2 at 25 °C is 200 GPa, the tensile strength at 25 °C is 2.8 GPa, and the density is 1.4 g / cm³.

[0064] Example 1

[0065] (1) 54 g of sodium hydroxide and 212.7 g of water glass (modulus of the alkali activator is 1) were stirred and mixed in an aqueous solution to obtain Solution 1; and Solution 1 was allowed to stand for 24 hours; the stirring and mixing conditions were: stirring speed was 1200 rpm, time was 0.5 h, and temperature was 20 °C;

[0066] (2) 5 g of graphitized carbon fiber 1 and 5 g of aramid fiber 1 were first mixed with Solution 1 to obtain Solution 2; the conditions for the first mixing were: stirring speed was 1200 rpm, time was 2 h, and temperature was 45 °C;

[0067] (3) 750 g of metakaolin and 250 g of fly ash were stirred at 150 rpm for 2 min to obtain an admixture; the admixture and Solution 2 were secondarily mixed to obtain a geopolymer paste; the operation for the secondary mixing was: first stir at 150 rpm for 2 min, then stir at 750 rpm for 2 min, and the temperature was 20 °C;

[0068] The water-binder ratio in the geopolymer paste is 0.4; the mass ratio of the alkali activator (sodium hydroxide and water glass) to the admixture (metakaolin and fly ash) is 1:3.7; the mass ratio of metakaolin to fly ash is 1:0.33; the mass ratio of the cementitious material (alkali activator, metakaolin and fly ash) to the fiber material (graphitized carbon fiber and aramid fiber) is 100:0.79;

[0069] (4) Pour the geopolymer paste quickly into a triple steel mold with dimensions of 4 cm × 4 cm × 16 cm, and perform a sealing and molding treatment. After 24 hours, demold, and then place the demolded product in a steam curing box at 80 °C for 48 h (relative humidity is 90%). Then transfer it to a standard curing room (relative humidity is 90%) for 4 days to obtain the geopolymer.

[0070] Example 2

[0071] The same process as in Example 1 is adopted, with the difference that: in this example, the dosage of graphitized carbon fiber 1 is 6 g, and the dosage of aramid fiber 1 is 4 g, and the rest are the same as in Example 1 to obtain the geopolymer.

[0072] Example 3

[0073] The same process as in Example 1 is adopted, with the difference that: in this example, the dosage of graphitized carbon fiber 1 is 6.7 g, and the dosage of aramid fiber 1 is 3.3 g, and the rest are the same as in Example 1 to obtain the geopolymer.

[0074] Example 4

[0075] The same process as in Example 1 is adopted, with the difference that: in this example, the dosage of graphitized carbon fiber 1 is 4 g, and the dosage of aramid fiber 1 is 6 g, and the rest are the same as in Example 1 to obtain the geopolymer.

[0076] Example 5

[0077] The same process as in Example 1 is adopted, with the difference that: in this example, the dosage of graphitized carbon fiber 1 is 3.3 g, and the dosage of aramid fiber 1 is 6.7 g, and the rest are the same as in Example 1 to obtain the geopolymer.

[0078] Example 6

[0079] The same process as in Example 1 is adopted, with the difference that: on the premise of ensuring that the total amount of admixtures remains unchanged, the dosages of metakaolin and fly ash are adjusted to 1:1.5, and the rest are the same as in Example 1 to obtain the geopolymer.

[0080] Example 7

[0081] The same process as in Example 1 is adopted, with the difference that: graphitized carbon fiber 1 is replaced with graphitized carbon fiber 2 with the same mass dosage, and the rest are the same as in Example 1 to obtain the geopolymer.

[0082] Example 8

[0083] The same process as in Example 1 was adopted, with the difference that: in this example, while keeping the dosage of 266.7 g of the alkali activator unchanged, the dosages of sodium hydroxide and water glass were adjusted to make the modulus of the alkali activator 1.5, and the rest were the same as in Example 1, obtaining the geopolymer.

[0084] Example 9

[0085] (1) In an aqueous solution, 54 g of sodium hydroxide, 212.7 g of water glass (the modulus of the alkali activator was 1), 5 g of graphitized carbon fiber 1, 5 g of aramid fiber 1, 750 g of metakaolin, and 250 g of fly ash were mixed to obtain a geopolymer paste; the conditions for the mixing treatment were: the stirring speed was 750 rpm, the time was 2 h, and the temperature was 20 °C;

[0086] The water-binder ratio in the geopolymer paste was 0.4; the mass ratio of the alkali activator (sodium hydroxide and water glass) to the admixtures (metakaolin and fly ash) was 1:3.7; the mass ratio of metakaolin to fly ash was 1:0.33; the mass ratio of the cementitious materials (alkali activator, metakaolin, and fly ash) to the fiber materials (graphitized carbon fiber and aramid fiber) was 100:0.79;

[0087] (2) The geopolymer paste was quickly poured into a triple steel mold with dimensions of 4 cm × 4 cm × 16 cm and subjected to a sealing and forming treatment. After 24 hours, demolding was carried out, and then the demolded product was placed in a steam curing box at 80 °C for 48 h (relative humidity was 90%), and then transferred to a standard curing room (relative humidity was 90%) for curing for 4 days to obtain the geopolymer.

[0088] Example 10

[0089] The same process as in Example 1 was adopted, with the difference that: aramid fiber 1 was replaced with an equal mass dosage of aramid fiber 3, and the rest were the same as in Example 1, obtaining the geopolymer.

[0090] Comparative Example 1

[0091] This comparative example adopted the same process as in Example 1, with the difference that: in this comparative example, graphitized carbon fiber 1 and aramid fiber 1 were not added, and the solution 1 prepared in step (1) was directly mixed with the admixtures for the second time, and the rest were the same as in Example 1, obtaining the geopolymer.

[0092] Comparative Example 2

[0093] This comparative example adopted the same process as in Example 1, with the difference that: in this comparative example, graphitized carbon fiber 1 was not added, and the rest were the same as in Example 1, obtaining the geopolymer.

[0094] Comparative Example 3

[0095] This comparative example was carried out using the same process as in Example 1, with the difference that: in this comparative example, graphitized carbon fiber 1 was not added, and the amount of aramid fiber 1 was adjusted to 7.5 g, and the rest was the same as in Example 1, to obtain a geopolymer.

[0096] Comparative Example 4

[0097] This comparative example was carried out using the same process as in Example 1, with the difference that: in this comparative example, graphitized carbon fiber 1 was not added, and the amount of aramid fiber 1 was adjusted to 10 g, and the rest was the same as in Example 1, to obtain a geopolymer.

[0098] Comparative Example 5

[0099] This comparative example was carried out using the same process as in Example 1, with the difference that: in this comparative example, aramid fiber 1 was not added, and the rest was the same as in Example 1, to obtain a geopolymer.

[0100] Comparative Example 6

[0101] This comparative example was carried out using the same process as in Example 1, with the difference that: in this comparative example, aramid fiber 1 was not added, and the amount of graphitized carbon fiber 1 was adjusted to 7.5 g, and the rest was the same as in Example 1, to obtain a geopolymer.

[0102] Comparative Example 7

[0103] This comparative example was carried out using the same process as in Example 1, with the difference that: in this comparative example, aramid fiber 1 was not added, and the amount of graphitized carbon fiber 1 was adjusted to 10 g, and the rest was the same as in Example 1, to obtain a geopolymer.

[0104] Comparative Example 8

[0105] This comparative example was carried out using the same process as in Example 1, with the difference that: aramid fiber 1 was replaced with an equal mass of aramid fiber 2, and the rest was the same as in Example 1, to obtain a geopolymer.

[0106] Comparative Example 9

[0107] It was carried out using the same process as in Example 1, with the difference that: in this comparative example, the amount of metakaolin was adjusted to 1617 g, so that the mass ratio of the alkali activator to the admixture was 1:7, and at the same time the mass ratio of metakaolin to fly ash was 1:0.15, and the rest was the same as in Example 1, to obtain a geopolymer.

[0108] Test Example

[0109] The geopolymers prepared in the examples and comparative examples were calcined at 200 °C, 400 °C, 600 °C and 800 °C for 3 h respectively, and then their compressive strength and flexural strength were measured, and the retention rates of compressive strength and flexural strength were calculated:

[0110] Flexural strength retention rate = flexural strength after calcination treatment / flexural strength without calcination treatment;

[0111] Compressive strength retention rate = compressive strength after calcination treatment / compressive strength without calcination treatment.

[0112] The test methods for compressive strength and flexural strength refer to GB / T 17671-1999, and the specific parameters are shown in Tables 1 - 3.

[0113] Table 1

[0114]

[0115] Table 2

[0116]

[0117] Table 3

[0118]

[0119] From the data in Tables 1 - 3, it can be seen that compared with Example 1, the geopolymers prepared in Example 6 of the present invention, after being calcined at 200 °C, 400 °C, 600 °C and 800 °C respectively, the retention rate of their flexural strength decreases to a certain extent, but the retention rate of compressive strength and the mass loss rate are relatively good; that is, by adjusting the dosage of metakaolin and fly ash in a specific ratio, it helps to further improve the mechanical properties of geopolymers.

[0120] Compared with Example 1, the geopolymers prepared in Example 7 of the present invention still have good compressive retention rate and flexural retention rate after calcination treatment, but after being calcined at 600 °C for 3 h, their mass loss rate reaches 30.43%; that is, adopting the technical solution of the present invention with a specific type of graphitized carbon fiber helps to further reduce the mass loss of geopolymers in high-temperature environments.

[0121] Compared with Example 1, the geopolymers prepared in Example 8 of the present invention have a mass loss rate of 30.07% after being calcined at 800 °C for 3 h, but their compressive retention rate and flexural retention rate in high-temperature environments are still good; that is, by adjusting the modulus of the alkali activator, it helps to further reduce the mass loss of geopolymers in high-temperature environments.

[0122] Compared with Example 1, for the geopolymer prepared in Example 9 of the present invention, after calcination at 800 °C for 3 h, the flexural strength retention rate and the compressive strength retention rate slightly decrease, and its mass loss rate reaches 31.18%; that is, compared with the overall mixing treatment method, the step-by-step treatment helps the geopolymer to exhibit better mechanical properties and lower mass loss rate under high-temperature environments.

[0123] For the geopolymer prepared in Comparative Examples 1-9 of the present invention, its technical effect is significantly worse than that of the examples in the present invention; for the geopolymer prepared in the examples of the present invention, in order to ensure the practicability of the product, it is required that after calcination at 200 °C for 2 h, its mass loss rate should not be higher than 21%, the flexural strength retention rate should not be lower than 80%, and the compressive strength retention rate should not be lower than 90%. If these requirements are not met, it indicates that the prepared geopolymer has obvious thermal stability defects. In practical engineering applications, due to the insufficient heat resistance of the material at the initial stage of heating, it is easy to cause the deterioration of the structural performance; however, from the technical effects of Comparative Examples 1-9, its performance obviously does not meet the requirements.

[0124] It can be seen from the above that the geopolymer of the present invention obviously has better high-temperature resistance performance.

[0125] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A composition for geopolymers, characterized in that, The composition consists of a gelling material and a fiber material; the gelling material consists of an alkali activator and a filler; the filler consists of metakaolin and fly ash; the mass ratio of the alkali activator to the filler is 1:3 - 5; The mass ratio of the gelling material to the fiber material is 100:0.5 - 1.5; The fiber material contains aramid fiber and graphitized carbon fiber with a mass ratio of 1:0.3 - 3; The tensile modulus of the aramid fiber at 25 °C is 100 - 150 GPa, and the tensile strength at 25 °C is 3 - 6 GPa; The graphitized carbon fiber is a product prepared by the following steps: Graphitize the carbon fiber to obtain the graphitized carbon fiber; the conditions of the graphitization treatment include: temperature is 1200 - 1500 °C, time is 24 - 36 h; The length of the graphitized carbon fiber is 4 - 6 mm.

2. The composition according to claim 1, wherein The modulus of the alkali activator is 0.8 - 1.

2.

3. The composition according to claim 1 or 2, characterized in that, The mass ratio of the metakaolin to the fly ash is 1:0.1 - 1.

4. The composition according to claim 1 or 2, characterized in that, The tensile modulus of the graphitized carbon fiber at 25 °C is 200 - 300 GPa, the tensile strength at 25 °C is 3 - 6 GPa, and the density is 1 - 3 g / cm³; And / or, the density of the aramid fiber is 1 - 3 g / cm³, and the length is 4 - 6 mm; And / or, the alkali activator is a combination of water glass and sodium hydroxide.

5. A method for preparing geopolymers, characterized in that, This method is carried out using the geopolymer composition described in any one of claims 1 - 4. This method includes: mixing each component in the geopolymer composition with water to obtain a geopolymer.

6. The method according to claim 5, wherein Control the amount of water used to meet a water - binder ratio of 0.35 - 0.

45.

7. The method according to claim 5 or 6, characterized in that, The operations of the mixing treatment include: (1) First mix the solution 1 containing the alkali activator and water with the fiber material to obtain solution 2; (2) Second mix solution 2 with the filler to obtain the geopolymer.

8. The method according to claim 5 or 6, characterized in that This method further includes: sequentially carrying out injection molding and curing treatment on the product obtained by the mixing treatment to obtain the geopolymer.

9. A geopolymer prepared by the method described in any one of claims 5 - 8.

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