CN113024141B - Modified carbon fiber, preparation method thereof and modified carbon fiber reinforced cement-based material - Google Patents

Abstract

The invention discloses modified carbon fibers, a preparation method thereof and a modified carbon fiber reinforced cement-based material. The modified carbon fiber is carbon fiber with nano silicon dioxide and carbon nano tubes grown in situ on the surface. The preparation method of the modified carbon fiber comprises the following steps: (1) removing the epoxy coating on the surface of the carbon fiber; (2) surface oxidation of the carbon fibers; (3) growing nano silicon dioxide on the surface of the carbon fiber with oxidized surface in situ; (4) growing the carbon nano tube on the surface of the product obtained in the step (3) in situ. According to the invention, the nano-silica and the carbon nano-tube are simultaneously grown on the surface of the carbon fiber in situ, the modified carbon fiber combines the volcanic ash effect of the nano-silica with the bridging nucleation effect of the nano-carbon tube, and is doped into the cement-based material, so that the interface strength of the carbon fiber and the cement-based material can be obviously improved, and the modified carbon fiber fills the pores of the cement-based material, so that the structure is more compact, and the early shrinkage performance of the cement-based material is effectively improved.

Description

A kind of modified carbon fiber and its preparation method and modified carbon fiber reinforced cement-based material

technical field

The invention relates to a modified carbon fiber and a preparation method thereof, and the modified carbon fiber reinforced cement-based material, belonging to the technical field of carbon fiber modification.

Background technique

Cement-based materials are the most widely used traditional materials. They have the advantages of low price, good fire resistance, and can be cast into various shapes according to formwork. However, traditional cement-based materials are brittle materials. Due to early autogenous shrinkage, temperature drop shrinkage and drying shrinkage, micro-cracks will appear and develop into macro-cracks. For extra-long basement structures and roof structures, it is more likely to crack due to shrinkage. Once the cement-based material cracks, its durability is bound to deteriorate.

Nanomaterials have the characteristics of small particle size and large surface energy, which can make the microstructure of cement-based materials more compact and can improve the performance of cement-based materials. Among them, carbon fiber is used to improve cement-based materials due to its low density, high specific strength and specific modulus, and chemical corrosion resistance. Studies have shown that carbon fiber can effectively improve the strength of cement materials, especially the tensile strength, and thus can improve the shrinkage properties of cement-based materials and improve the durability of cement-based materials. However, whether carbon fiber can effectively improve the performance of cement-based materials mainly depends on the interface bond strength between carbon fiber and cement matrix. Good interfacial bonding can effectively transmit loads, thereby improving the mechanical properties of cement-based materials. However, the untreated carbon fiber has a smooth surface and low surface energy, weak interfacial adhesion with the cement matrix, and low interfacial slip resistance. Under the action of external force, the fiber is easily separated from the matrix, thus weakening the carbon fiber modification. The effect of cement-based materials. This defect severely limits the application of carbon fibers in modified cement-based materials. Therefore, it is necessary to modify the surface of carbon fiber to improve the interface bond strength between carbon fiber and cement matrix, thereby improving the effect of carbon fiber modified cement-based materials.

On the other hand, other nanomaterials can also effectively improve the properties of cement-based materials and are widely used in cement-based materials. At present, there are more applications of nano-silica and carbon nanotubes. Nano-silica not only has good particle filling effect, but also has pozzolanic activity, and in the early stage of cement hydration, it can be used as the nucleation site of cement hydration to promote cement hydration. Carbon nanotubes can significantly improve the mechanical properties of cement-based materials because of their excellent mechanical properties. However, due to the high ionic concentration of the cement slurry, nano-silica and carbon nanotubes are easy to agglomerate and are difficult to disperse uniformly. Therefore, it is difficult to give full play to its modification effect on cement-based materials.

In this regard, if the advantages of the above-mentioned cement-based reinforced nanomaterials can be exerted and the existing problems can be overcome, the performance of the cement-based materials will be effectively improved, and the effect of the modified cement-based materials will be fully exerted.

SUMMARY OF THE INVENTION

Purpose of the invention: Aiming at the problems of low interfacial bonding strength with the cement matrix or poor dispersibility in the cement matrix existing in the existing cement-based reinforcing materials, the present invention provides a method that can effectively enhance the interface bonding strength with the cement-based material. A modified carbon fiber is provided, and a preparation method of the modified carbon fiber is provided; in addition, the present invention also provides a cement-based material reinforced with the modified carbon fiber.

Technical solution: The modified carbon fiber described in the present invention is a carbon fiber with nano-silica and carbon nanotubes grown on the surface in situ.

The preparation method of a modified carbon fiber according to the present invention comprises the following steps:

(1) Removal of epoxy coating on carbon fiber surface;

(2) Surface oxidation of carbon fiber;

(3) In situ growth of nano-silica on the surface of the surface oxidized carbon fiber;

(4) In-situ growth of carbon nanotubes on the surface of the product obtained in step (3).

In the above-mentioned step (1), the method for removing the epoxy coating on the carbon fiber surface can be as follows: putting the carbon fiber into a container containing acetone, reacting at a temperature of 75 to 85 ° C, cooling to room temperature after the reaction, The carbon fibers are taken out, and then dried at 70-90° C. to obtain carbon fibers with the epoxy coating removed from the surface. Preferably, in this step, the reaction time is 20-48h, and the drying time is 1-3h.

In the above step (2), the method for surface oxidation can be as follows: first, the carbon fibers obtained in step (1) are immersed in concentrated nitric acid, heated to 70-80° C. for 2-3 hours, and then taken out; washed and dried to obtain dry carbon oxide fibers. Optionally, in this step, the washing is soaked in distilled water for 5-10 minutes, then taken out and then rinsed with ethanol for 3-5 times; the drying is drying at a temperature of 70-80° C. for 2-4 hours. Preferably, the dosage of concentrated nitric acid satisfies the following proportional relationship: the volume ratio of the mass of the original carbon fiber to the concentrated nitric acid is 1g:80-100ml.

In step (3), the method for in-situ growth of nano-silica on the surface of the oxidized carbon fiber surface is specifically:

① Immerse the oxidized carbon fiber in the silane coupling agent solution, soak it at a constant temperature of 70°C for 2-3 hours, then take it out, wash and dry;

② Put the carbon fibers obtained in step ① into an ethanol solvent, add the ionic surfactant CTAB, and stir evenly;

3. in step 2. the resulting mixture, add ammonia water as a catalyst, and ultrasonically treat it for 30 to 90 min;

④ Under stirring conditions, add ethyl orthosilicate dropwise to the mixture obtained in step ③, and stir and react at a constant temperature of 40°C to 50°C for 10 to 12 hours to obtain carbon fibers with in-situ growth of nano-silica on the surface;

⑤ The carbon fiber with in-situ nano-silica grown on the surface obtained in step ④ is taken out from the solution, washed and dried.

In step 1, preferably, the amount of the silane coupling agent solution satisfies the following proportional relationship: the volume ratio of the mass of the original carbon fiber to the silane coupling agent solution is 1g:200-300ml, wherein the silane coupling agent can be KH550 or the like; Preferably, washing is 2-3 times with ethanol, and drying is drying at 70-80° C. for 2-4 hours. In step (2), the amount of ethanol satisfies the following relationship: the volume ratio of the mass of the original carbon fiber to the ethanol is preferably 1g:400-600ml; preferably, the mass fraction of CTAB in the ethanol is 1-3%. In step ③, the volume ratio of ammonia water to ethanol is preferably 1:20 to 25, so as to provide an alkaline environment for the reaction. In step (4), the volume ratio of ethyl orthosilicate and ethanol is preferably 1:12～20. In step ⑤, preferably washing with methanol for 3 to 5 times, and then drying at 70 to 80° C. for 2 to 3 hours.

In the above-mentioned step (4), the method for further surface in-situ growth of carbon nanotubes is as follows: the surface in-situ growth of nano-silica carbon fibers and ferrocene are evenly mixed, the resulting mixture is poured into a container and placed in a microwave oven, and the microwave Irradiate for 10-30s, and then cool to room temperature to obtain carbon fibers with in-situ growth of nano-silica and carbon nanotubes on the surface. Ferrocene absorbs heat to generate carbon nanotubes, and the output of carbon nanotubes is controlled by controlling the duration of microwave irradiation. The length and number will increase; if the microwave irradiation time is less than 10s, the growth of carbon nanotubes is too small, and if the microwave irradiation time is higher than 30s, the growth of carbon nanotubes is too large, which may coat the nano-silica. , thereby deteriorating the properties of modified carbon fibers. Wherein, the mass ratio of the carbon fibers on the surface of the in-situ grown nano-silica to the ferrocene is preferably 1:1-3.

The modified carbon fiber reinforced cement-based material of the present invention includes cement cementitious material and the above-mentioned modified carbon fiber, and the content of the modified carbon fiber is 0.3-1.2% of the mass of the cement cementitious material.

Principle of the invention: The present invention uses in-situ growth of nano-silica and carbon nanotubes to modify carbon fibers. First, acetone is used to remove the hydrophobic coating-epoxy coating on the surface of the original carbon fiber, making it hydrophilic and facilitating subsequent reactions. After that, the surface of carbon fiber is oxidized with concentrated nitric acid. On the one hand, the surface of carbon fiber is roughened, which is convenient for the heterogeneous nucleation of nano-silica and carbon nanotubes. The adsorption capacity of nano-silica and carbon nanotubes promotes the in-situ growth of nano-silica and carbon nanotubes; and, because nano-silica and carbon nanotubes grow in-situ on the surface of carbon fibers, they are chemically bonded to carbon fibers and have strong adhesion. , difficult to fall off. Based on this, the modified carbon fiber of the present invention is obtained.

When the obtained modified carbon fiber is applied to a cement-based material, the nano-silica and carbon nanotubes grown on the surface of the carbon fiber in situ can significantly improve the surface roughness of the carbon fiber, thereby enhancing the bonding strength between the carbon fiber and the cement matrix. In addition, nano-silica can provide nucleation sites for cement hydration, so that cement hydration products can grow around it, which can also strengthen the bonding between carbon fibers and cement matrix; at the same time, nano-silica has pozzolanic activity and can interact with The calcium hydroxide produced by cement hydration reacts to form calcium silicate hydrate, which is also a process of improving the bonding strength of carbon fiber and cement matrix. In addition, carbon nanotubes themselves have excellent mechanical properties and bridging nucleation, and can strengthen cement-based materials. When they grow in situ on the surface of carbon fibers, they can effectively improve the strength of the transition zone between carbon fibers and cement matrix. Therefore, nano-silica and carbon nanotubes grown on the surface of carbon fibers in situ, as well as carbon fibers, synergistically improve the bonding strength of carbon fibers and cement matrix.

In addition, nano-silica and carbon nanotubes grow in situ on the surface of carbon fibers, which can hinder the agglomeration of nano-silica and carbon nanotubes during the preparation process by means of the steric hindrance effect of carbon fibers, thereby improving their performance. Dispersibility during preparation. In addition, in the cement matrix, the in-situ nano-silica and carbon nanotubes can be dispersed in the cement matrix along with the matrix carbon fibers, which can reduce the agglomeration, which is conducive to fully modifying the cement-based materials.

Beneficial effects: Compared with the prior art, the advantages of the present invention are: (1) The modified carbon fiber of the present invention simultaneously grows nano-silica and carbon nanotubes on the surface of the carbon fiber in situ, so that the crystals of nano-silica The combination of nucleation effect, pozzolan effect and carbon nanotube bridging and nucleation can significantly improve the bonding strength of carbon fiber and cement matrix, and improve the interface transition zone; (2) the modified carbon fiber of the present invention combines nano-silica and carbon nano- The tube grows on the surface of carbon fiber in situ, which can improve its dispersibility during preparation and use, and give full play to the role of nano-silica, carbon nanotube and carbon fiber. The three synergistically improve the density of cement-based materials more efficiently. , which can effectively improve the early shrinkage and mechanical properties of cement-based materials.

Description of drawings

Fig. 1 is the SEM image (a) and EDS image (b) of the CF@NS prepared in Example 1;

Fig. 2 is the XRD pattern (a) of the raw material CF in Example 1 and the XRD pattern (b) of the prepared CF@NS@CNT;

Fig. 3 is the SEM image of the CF@NS@CNT prepared by Example 1;

Fig. 4 is the TEM image of CF@NS@CNT prepared in Example 1;

Fig. 5 is the SEM image of the CF@NS@CNT prepared by Example 2;

Fig. 6 is the scanning picture of the original carbon fiber in the cement paste, wherein (b) is an enlarged view of the box area in (a);

Figure 7 is a scanning picture of modified carbon fibers in cement paste, wherein (b) is an enlarged view of the boxed area in (a).

Note: CF@NS@CNT is a carbon fiber with nano-silica and carbon nanotubes grown on the surface in situ.

Detailed ways

The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

A modified carbon fiber of the present invention is a carbon fiber with nano-silica and carbon nanotubes grown on the surface in situ. The modified carbon fiber combines the pozzolanic effect of nano-silica and the bridging and nucleating effect of carbon nanotubes. It can improve the interfacial bonding strength of carbon fiber and cement-based materials and also improve the early shrinkage properties of cement-based materials.

Example 1

The modified carbon fiber preparation process in the present embodiment is as follows:

(1) Removal of epoxy coating on carbon fiber surface

Take 1 g of carbon fiber and put it into a Soxhlet extractor equipped with acetone, and use acetone to clean and remove impurities on the surface of carbon fiber at a temperature of 75 °C. The cleaning time is 24h. After drying at 70 °C for 2 h, carbon fibers with epoxy coatings removed from the surface were obtained.

(2) Oxidation of carbon fiber

Step 21, immerse the carbon fiber obtained in step (1) in concentrated nitric acid, the mass ratio of the carbon fiber to the concentrated nitric acid is 1g: 100ml, heat to 80 ° C, react for 3h, and then take out the carbon fiber in the concentrated nitric acid;

In step 22, the carbon fibers obtained in step 21 were soaked in distilled water for 5 minutes, taken out and then rinsed with ethanol for 3 times, and dried at a temperature of 70° C. for 3 hours to obtain dry carbon oxide fibers.

(3) In situ growth of nano-silica on the surface of carbon fiber

Step 31, immerse the carbon fiber obtained in step 22 in a KH550 solution (the mass fraction is 3%, and the volume ratio of the mass of the carbon fiber to the KH550 solution is 1g:200ml), and soak it at a constant temperature of 70 ° C for 3h; then take out the carbon fiber and wash it with ethanol Dry 3 times at 70°C for 2h;

Step 32, put the carbon fiber obtained in step 31 into an analytically pure ethanol solvent (the volume ratio of the mass of the carbon fiber to the ethanol is 1g:500ml), then, the mass fraction is 1% (the mass fraction of CTAB in the ethanol solution) The ionic surfactant CTAB was added to the mixture and stirred well;

Step 33, in the mixture obtained in step 32, add ammoniacal liquor (ammonia: the volume ratio of ethanol is 1:25) as a catalyst, to provide an alkaline reaction environment and carry out the ultrasonic treatment of 30min;

Step 34, under the action of a magnetic stirrer, dropwise add ethyl orthosilicate (the volume ratio of ethyl orthosilicate: ethanol is 1:12.5) to the mixture obtained in step 33, and slowly at a constant temperature of 45°C. Stir for 10h;

In step 35, the carbon fiber with in-situ growth of nano-silica on the surface obtained in step 34 is taken out of the solution, washed with methanol for 3 times, and dried at 70° C. for 3 hours to obtain dry carbon fiber with in-situ growth of nano-silica on the surface. (CF@NS);

The SEM image and EDS image of CF@NS obtained after the above steps are shown in Figure 1. It can be seen from the SEM image that a layer of material has grown in situ on the surface of the carbon fiber, and it can be seen from the EDS that the in situ growth on the surface of the carbon fiber is silica.

(4) In situ growth of carbon nanotubes on the surface of carbon fibers

Step 41, according to the mass ratio of 1:1, the carbon fiber and ferrocene of the surface in-situ growth of nano-silica obtained in step 35 are evenly mixed;

In step 42, the mixture obtained in step 41 is poured into a crucible and placed in a microwave oven, microwaved for 30 s, and cooled to room temperature to obtain carbon fibers (CF@NS@CNT) with in-situ growth of nano-silica and carbon nanotubes on the surface.

2 (a) and (b) are the XRD patterns of untreated carbon fiber CF and CF@NS@CNT, respectively. It can be seen from Figure 2 that CF has a diffraction peak of graphite at 26°, and amorphous carbon at 20-25° and 40-45°. CF@NS@CNT was obtained by sol-gel method and microwave irradiation method, except In addition to the diffraction peak of graphite at 26°, there is also a diffraction peak of iron at 45°, amorphous carbon and amorphous silica between 20 and 25°, and amorphous carbon between 40 and 45°. , and there is no diffraction peak of crystalline silica. In conclusion, it can be concluded that the silica coated on the surface of carbon fiber after microwave irradiation is not crystallized.

The SEM picture of the CF@NS@CNT prepared in this example is shown in Figure 3. It can be seen that nano-silica and carbon nanotubes grow on the surface of CF@NS, and carbon nanotubes grow more; the prepared CF@NS The TEM image of @CNT is shown in Figure 4, where hollow tubular carbon nanotubes can be seen.

Example 2

The modified carbon fiber preparation process in the present embodiment is as follows:

(1) Removal of epoxy coating on carbon fiber surface

Take 1 g of carbon fiber and put it into a Soxhlet extractor equipped with acetone, and use acetone to clean and remove impurities on the surface of carbon fiber at a temperature of 75 °C. The cleaning time is 24h. After drying at 70 °C for 2 h, carbon fibers with epoxy coatings removed from the surface were obtained.

(2) Oxidation of carbon fiber

Step 21, immerse the carbon fiber obtained in step (1) in concentrated nitric acid, the mass ratio of the carbon fiber to the concentrated nitric acid is 1g: 100ml, heat to 80 ° C, react for 3h, and then take out the carbon fiber in the concentrated nitric acid;

In step 22, the carbon fibers obtained in step 21 were soaked in distilled water for 5 minutes, taken out and then rinsed with ethanol for 3 times, and dried at a temperature of 70° C. for 3 hours to obtain dry carbon oxide fibers.

(3) In situ growth of nano-silica on the surface of carbon fiber

Step 31, immerse the carbon fiber obtained in step 22 in a KH550 solution (the mass fraction is 3%, and the volume ratio of the mass of the carbon fiber to the KH550 solution is 1g:200ml), and soak it at a constant temperature of 70 ° C for 3h; then take out the carbon fiber and wash it with ethanol Dry 3 times at 70°C for 2h;

Step 32, put the carbon fiber obtained in step 31 into an analytically pure ethanol solvent, the mass ratio of the carbon fiber to the ethanol volume is 1g:500ml, and then, the mass fraction of ions with a mass fraction of 1% (the mass fraction of CTAB in the ethanol solution) is added. The surfactant CTAB was added to the mixture and stirred well;

Step 33, in the mixture that step 32 obtains, add ammoniacal liquor (ammonia: the volume ratio of ethanol is 1:25) as catalyzer, to provide alkaline reaction environment and carry out the ultrasonic treatment of 90min;

In step 34, under the action of a magnetic stirrer, ethyl orthosilicate (the volume ratio of ethyl orthosilicate: ethanol is 1:12.5) was added dropwise to the mixture obtained in step 33, and slowly at a constant temperature of 45°C. Stir for 10h;

In step 35, the carbon fiber with in-situ growth of nano-silica on the surface obtained in step 34 is taken out of the solution, washed with methanol for 3 times, and dried at 70° C. for 3 hours to obtain dry carbon fiber with in-situ growth of nano-silica on the surface. (CF@NS).

(4) In situ growth of carbon nanotubes on the surface of carbon fibers

Step 41, according to the two mass ratios of 1:1, the carbon fiber of the surface in-situ growth nano-silica obtained in step 35 and the ferrocene are evenly mixed;

In step 42, the mixture obtained in step 41 is poured into a crucible, placed in a microwave oven, irradiated with microwaves for 10 s, and cooled to room temperature to obtain carbon fibers (CF@NS@CNT) with in-situ growth of nano-silica and carbon nanotubes on the surface.

The SEM picture of the modified carbon fiber obtained after the above steps is shown in FIG. 5 . It can be seen from the figure that the surface of the carbon fiber is relatively uniformly coated with nano-silica and carbon nanotubes.

The CF@NS@CNTs prepared in Examples 1 and 2 were mixed into cement cementitious materials to prepare modified carbon fiber cement mortar specimens. In the test piece, the material mixing ratio of cement mortar is sand: cement: water = 4:2:1, the sand is river sand, the cement is PO42.5 cement, and the water is tap water. After the test piece was formed, it was demolded after standard curing for 24 hours. After demolding and measuring the initial length, it was sealed with polyethylene plastic film and paraffin wax, and then measured every other day until the 7th day. Forming and testing of the flexural strength of the mortar specimens were carried out according to the "Testing Method for Cement Mortar Strength GBT17671-1999". The test results are shown in Table 1 below.

Comparative Example 1

The carbon fiber cement mortar specimens were prepared with reference to the method in the examples by incorporating the untreated carbon fiber into the cement cementitious material. The self-shrinkage performance and flexural strength performance test of the test piece are carried out with reference to the method of the embodiment. The test results are shown in Table 1 below.

Comparative Example 2

With reference to the mixing ratio of cement mortar materials and the preparation method in the examples, the cement mortar specimens were formed, and carbon fibers were not doped. The self-shrinkage performance and flexural strength performance test of the test piece are carried out with reference to the method of the embodiment. The test results are shown in Table 1 below.

Table 1 Test results of autogenous shrinkage and flexural strength of the specimens

It can be seen from Table 1 that, compared with Comparative Example 1, the modified carbon fibers of the present invention can significantly improve the shrinkage reduction effect and flexural strength of mortar, and it can be seen from the examples that when the fiber content is 0.6% best effect. Comparing Figure 6 and Figure 7, it can be seen that the surface of the original carbon fiber is relatively smooth, and the interface with the cement-based material is not tightly combined; while the surface of the modified carbon fiber is rough, and the interface between the carbon fiber and the cement-based material is almost invisible. The calcium hydroxide produced by the hydration of cement reacts to form calcium silicate hydrate, and the carbon nanotubes act as a bridge and are tightly entangled with the hydration product, so that the interface strength between the modified carbon fiber and the cement-based material is improved, thereby reducing the mortar. Self-shrinkage increases the flexural strength of the mortar.

Claims (8)

1. a modified carbon fiber, it is characterized in that, described modified carbon fiber is the carbon fiber that has grown nano-silica and carbon nanotubes in situ on the surface, and wherein the method for in situ growth of carbon nanotubes on the surface of carbon fiber is: The carbon fibers of in-situ growth of nano-silica are evenly mixed with ferrocene, and the obtained mixture is poured into a container and placed in a microwave oven, irradiated by microwave for 10-30 s, and then cooled to room temperature to obtain in-situ growth of nano-silica and carbon nanotubes on the surface. of carbon fiber. 2. modified carbon fiber according to claim 1, is characterized in that, the mass ratio of the carbon fiber of described surface in-situ growth of nano-silica to ferrocene is 1:1～3. 3. a preparation method of modified carbon fiber according to claim 1, is characterized in that, comprises the steps: (1) Removal of epoxy coating on carbon fiber surface; (2) Surface oxidation of carbon fiber; (3) In situ growth of nano-silica on the surface of surface oxidized carbon fibers; (4) In-situ growth of carbon nanotubes on the surface of the product obtained in step (3). 4. The preparation method of modified carbon fiber according to claim 3, characterized in that, in step (1), the carbon fiber is put into a container containing acetone, and the reaction is carried out at a temperature of 75-85 °C. After cooling to room temperature, the carbon fibers were taken out, and then dried at 70-90° C. to obtain carbon fibers with epoxy coatings removed from the surface. 5 . The preparation method of modified carbon fiber according to claim 3 , wherein in step (2), the surface oxidation method is: immersing the carbon fiber obtained in step (1) with the surface epoxy coating removed in a concentrated In nitric acid, heated to 70~80°C, reacted for 2~3 hours, taken out; washed and dried to obtain dry surface-oxidized carbon fibers. 6 . The preparation method of modified carbon fiber according to claim 3 , wherein in step (3), the method for in-situ growth of nano-silica on the surface is: 6 . ① Immerse the oxidized carbon fiber in the silane coupling agent solution, soak it at a constant temperature of 70°C for 2~3 hours, then take it out, wash and dry; ② Put the carbon fibers obtained in step ① into an ethanol solvent, add the ionic surfactant CTAB, and stir evenly; 3. adding ammonia water as catalyst to step 2. the gained mixture, and ultrasonically treating for 30 to 90 min; 4. Under stirring conditions, add ethyl orthosilicate dropwise to the mixture obtained in step 3., and stir and react at a constant temperature of 40-50 ° C for 10-12 h to obtain carbon fibers with in-situ growth of nano-silica on the surface; ⑤ The carbon fiber with in-situ nano-silica grown on the surface obtained in step ④ is taken out from the solution, washed and dried. 7. The preparation method of modified carbon fiber according to claim 6, is characterized in that, the volume ratio of described CTAB and ethanol is 1:10～20; The volume ratio of described ammoniacal liquor and ethanol is 1:20～25; The volume ratio of the ethyl orthosilicate and ethanol is 1:12～20. 8. A modified carbon fiber reinforced cement-based material, characterized in that it comprises a cement cementitious material and the modified carbon fiber according to claim 1, and the content of the modified carbon fiber is 0.3 to 1.2 of the quality of the cement cementitious material. %.

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