Rod-shaped modified nano silica sol, preparation method and application thereof

Abstract

The invention belongs to the technical field of nano silica sol, and particularly relates to rod-like modified nano silica sol as well as a preparation method and application thereof. The method comprises the following steps: (1) adding alkaline nano silica sol into an ethanol-water mixed solvent, and carrying out ultrasonic dispersion; (2) adding CTAB (Cetyltrimethyl Ammonium Bromide) accounting for 0.1-0.5 wt% of the mass of the silica sol into the mixed solution obtained in the step (1), and stirring to form a micelle template; (3) carrying out gradient heating on the micelle template obtained in the step (2) to 60-80 DEG C, and adding a silane modifier by adopting a pulse dripping method; and (4) centrifuging and drying the reaction liquid obtained in the step (3) to obtain the rod-like M-CNS powder. According to the invention, CTAB is adopted to form rodlike micelles, rodlike structure silica sol is adopted to realize physical barrier, M-CNS with high length-diameter ratio is alternately filled in a concrete matrix to block a Cl <-> transmission channel, and silica sol is adopted to modify, enhance interface bonding force and block Ca < 2 + > adsorption, so that the durability of the concrete is improved.

Description

Technical Field

[0001] This invention belongs to the field of nano-silica sol technology, specifically a rod-shaped modified nano-silica sol, its preparation method, and its application. Background Technology

[0002] Marine concrete is used extensively and is an indispensable key material in major marine engineering projects such as offshore military engineering, artificial islands, cross-sea bridges, and subsea tunnels. (From Cl) - The resulting steel corrosion is considered a key factor contributing to the degradation of the durability of marine concrete. The presence of regular or irregular pores, interface transition zones, and cracks in heterogeneous cement concrete creates a loose and porous structure, which is conducive to the corrosion of reinforcing steel. - The transport of chlorine within the concrete matrix provides a pathway and represents a bottleneck in improving the durability of marine concrete. In recent years, methods for solidifying Cl- through chemical bonding to form Friedel's salt (FS) and Kuzel's salt (KS) have been employed. - The effect was good, providing a new approach to problem-solving; however, the solidification of Cl... - The main components are silicate cement and alumina-rich auxiliary cementitious materials. Its chlorine-fixing capacity is only a few mg / g. Furthermore, the excessive addition of auxiliary cementitious materials will lead to a decrease in the early strength and density of the matrix, thereby weakening the rust-inhibiting ability of the concrete.

[0003] Nano-sized silica (NS) powder has become a popular nano-additive for cement concrete due to its nanoscale particle characteristics and high pozzolanic activity. Numerous studies have verified the effectiveness of NS in improving the mechanical properties and density of cement-based materials, as well as their impermeability and erosion resistance. However, due to its large specific surface area and high surface energy, NS is prone to agglomeration, affecting its effectiveness in cement-based materials. To better leverage the advantages of NS in cement-based materials, researchers have tried various dispersion techniques, such as mechanical dispersion, chemical additive dispersion, and dispersion in different media. However, these methods are energy-intensive, increasing the production cost of cement concrete and hindering large-scale application. Therefore, researchers have changed the preparation method to directly prepare monodispersible silica sol (CNS). Based on the presence of a large number of active groups (-Si-OH) on the surface of silica sol, CNS, like NS, has a theoretical basis for improving the mechanical properties and durability of cement-based materials. It can also undergo a pozzolanic reaction with Ca(OH)2, a cement hydration product, to transform the weak Ca(OH)2 in cement-based materials into CSH gel, which contributes to strength. This optimizes the pore structure of concrete and gives full play to the potential to improve the mechanical properties and durability of cement-based materials.

[0004] However, similar to NS, in cement systems, CNS will react with Ca in the pore solution due to the presence of surface silanol groups.2+ The formation of loose aggregates by these aggregates prevents further dispersion of nanoparticles within the CNS. Therefore, the question arises as to how to prepare modified silica sol (M-CNS) to improve the interfacial properties of CNS, thereby reducing or delaying the reaction between surface hydroxyl groups and Ca. 2+ The combination of these factors, along with surface modification, effectively resists the damage of external corrosive media to cement-based materials, and improving the overall durability of the structure has become an urgent problem to be solved. Summary of the Invention

[0005] To address the poor performance caused by silica sol agglomeration and to optimize porosity and reduce Cl - To address the corrosion problem, this invention provides a rod-shaped modified nano-silica sol, its preparation method, and its application.

[0006] This invention is achieved through the following technical solution: A method for preparing rod-shaped modified nano-silica sol includes the following steps: (1) adding alkaline nano-silica sol to an ethanol-water mixed solvent and dispersing it by ultrasonication; (2) Add 0.1-0.5 wt% of CTAB (hexadecyltrimethylammonium bromide) by weight of silica sol to the mixture obtained in step 1 and stir to form a micelle template; (3) The micelle template obtained in step 2 is heated to 60-80℃ using a gradient heating method, and the silane modifier is added using a pulse dropping method: (4) The reaction solution from step 3 was centrifuged and dried to obtain rod-shaped M-CNS powder.

[0007] A further improvement of this invention is that, in step 1, the mass-to-volume ratio of alkaline nano-silica sol to ethanol-water is 1:2 to 1:4 (g / mL). Choosing an appropriate range for the solvent volume balances morphology control and safety, avoiding excessively low ratios (e.g., 1:1) which would lead to excessive viscosity, causing localized overheating and gelation during ultrasonic dispersion, and ensuring that CTAB micelles fully adsorb particles, thus improving the rod-shaped morphology formation rate. Preferably, the mass-to-volume ratio of alkaline nano-silica sol to ethanol-water is 1:3.

[0008] The silane modifier in step 3 is 1.8~3.0 wt% of the silica sol mass, which satisfies the minimum effective grafting and avoids exceeding the saturation adsorption capacity of silane on the silica sol surface. Excessive silane will trigger a self-condensation side reaction, which will increase the particle size.

[0009] A further improvement of the present invention is that the pulsed dropping in step 3 is alternating between fast and slow speeds. Specifically, the silane modifier is dissolved in ethanol, and the volume ratio of the silane modifier to ethanol is 1:8-10. The high-speed dropping is 5-8 mL / min, and the low-speed dropping is 1-2 mL / min, alternating between the two.

[0010] A further improvement of the present invention is that, in step 3, the silane modifier is one or more of KH560 and / or C12-C16 alkyl phosphate silanes, and when they are added together, the molar ratio of KH560 to C12-C16 alkyl phosphate silanes is 1-3:1.

[0011] A further improvement of the present invention is that the C12-C16 alkyl phosphate silane is prepared by the following method: by condensation reaction of aminopropyltriethoxysilane (preferably KH-550) with a monoalkyl phosphate ester.

[0012] Preferably, the preparation method includes the following steps: (1) Add alkaline nano silica sol to an ethanol-water mixed solvent (volume ratio 1:1) and ultrasonically disperse for 10-20 min; (2) Add 0.1-0.5 wt% of CTAB to silica sol and stir at 30-40℃ for 20-30 min to form a micelle template; (3) Gradually increase the temperature to 60-80℃ at a rate of 3-6℃ / min, and add the bissilane modifier using a pulse dropping method: (4) The reaction solution from step 3 was centrifuged, washed, and dried to obtain rod-shaped M-CNS powder.

[0013] A further improvement of the present invention is that the gradient temperature is increased to 60°C at a rate of 3°C / min, held at 60°C for 20 min, increased to 80°C at a rate of 5°C / min, and held at 80°C for 4 h.

[0014] On the other hand, the present invention provides a rod-shaped modified nano-silica sol with an aspect ratio of 3-6 and a surface grafting rate of ≥8 wt% obtained by the above preparation method.

[0015] Furthermore, this invention provides the application of the above-mentioned rod-shaped modified nano silica sol, incorporating rod-shaped M-CNS into concrete at 1-5 wt% of cement mass.

[0016] As can be seen from the above technical solutions, the beneficial effects of the present invention are: (1) To address the poor performance caused by silica sol agglomeration, Cl - To address the corrosion problem, this invention utilizes CTAB to form rod-shaped micelles in an ethanol-water system, guiding the oriented alignment of nano-silica particles and preventing random aggregation. Furthermore, gradient heating stabilizes the morphology, achieving stability of the rod-shaped structure. The rod-shaped silica sol provides physical barrier properties, while the high aspect ratio M-CNS penetrates and fills the cement matrix, refining pores and blocking Cl-. - Transmission channel.

[0017] Precise grafting using pulsed dripping: high-speed dripping prevents excessive local concentration from causing aggregation, while low-speed dripping promotes directional grafting of silanes, thus improving the grafting effect. The grafting rate can reach 8.7 wt%.

[0018] Simultaneously, silica sol is used for modification. Preferably, the epoxy groups of KH560 bond with cement hydration products to enhance interfacial adhesion. A hydrophobic layer is formed by the long-chain alkyl groups of C12–C16 alkyl phosphate silanes, and the phosphate groups passivate the surface, blocking Ca2+. 2+ Adsorption.

[0019] (2) This invention improves the durability of concrete. The rod-shaped M-CNS accelerates cement hydration and nucleation, and the pozzolanic reaction consumes Ca(OH)2 to convert it into CSH gel, which refines the pores and thus improves the strength. The rod-shaped particles block the pores, and the hydrophobic alkyl chains block Cl. - Penetration and synergistic optimization of concrete density. Attached Figure Description

[0020] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 These are transmission electron microscope (TEM) images of Embodiments 1 and 2 of the present invention. Detailed Implementation

[0022] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the specific embodiments. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this patent, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this patent.

[0023] Alkaline silica sol: pH=10.5, solid content 30%, particle size 10-15 nm, purchased from Linyi Kehan ​​Silicon Products Co., Ltd.; CTAB, KH56, xylene, and 4-dimethylaminopyridine were purchased from Maclean's; C12-C16 alkyl phosphates were purchased from Hubei Longfei Biotechnology Co., Ltd. and Maclean's; ethanol was purchased from Sinopharm Reagent.

[0024] The preparation method of C12-C16 alkyl phosphate silane is as follows: The corresponding C12-C16 alkyl phosphate and aminopropyltriethoxysilane (KH550) are added to a reaction vessel, along with xylene and 4-dimethylaminopyridine (DMAP) catalyst. The reaction is carried out at 60-80℃ for 10-12 h under nitrogen protection. The solvent is removed by vacuum distillation to obtain the product. The molar ratio of C12-C16 alkyl phosphate, KH550, and DMAP is 1:1:0.1, and the molar volume ratio of C12-C16 alkyl phosphate to xylene is 0.5:200-400 (mol:mL).

[0025] Taking the synthesis of C14 alkyl phosphate silane as an example: monotetradecyl phosphate (0.5 mol) and aminopropyltriethoxysilane (KH550, 0.5 mol) were added to a reaction vessel, along with 300 mL of xylene and DMAP catalyst (0.05 mol). The reaction was carried out at 80 °C for 12 h under nitrogen protection, and the solvent was removed by vacuum distillation to obtain the product.

[0026] (I) Influence of process parameters on morphology and grafting effect Example 1 (1) Take 100 g of silica sol and add it to 300 mL of ethanol-water (volume ratio 1:1), and sonicate for 15 min; (2) Add 0.3 g CTAB and stir at 35°C for 25 min; (3) Gradual heating to 80℃ (heating to 60℃ at 3℃ / min, holding at 60℃ for 20 min, heating to 80℃ at 5℃ / min, holding at 80℃ for 4 h), pulse-dropping 2.5g of mixed silane (molar ratio of tetradecyl phosphate silane and KH560 = 1.5:1, mixed silane dissolved in ethanol, volume ratio of silane modifier to ethanol 1:10), dropping program: 7mL / min × 1 min, then 1.5mL / min × 1 min, and so on. (4) Centrifuge (10000 rpm, 15 min), wash, and vacuum dry at 60℃ to obtain the product.

[0027] Example 2 The difference from Example 1 is that the temperature is kept constant at 80°C, no gradient temperature increase is used, and the pulse dropping program is a uniform dropping (2 mL / min).

[0028] Example 3 Unlike Example 1, the temperature was kept constant at 80°C, and no gradient heating was used.

[0029] The grafting rates of Examples 1-3 were measured. The residual carbon content at 600°C was calculated using TGA (nitrogen atmosphere, 10°C / min).

[0030] The grafting rate (wt%) of Example 2 was 6.2 ± 0.5, the grafting rate (wt%) of Example 3 was 7.8 ± 0.3, and the grafting rate (wt%) of Example 1 was 8.7 ± 0.2.

[0031] Simultaneously, the products were observed, and in Example 2, spherical aggregates coexisted with a small number of short rods. Figure 1 a), Example 3 mainly consists of short rods mixed with irregularly shaped particles, while Example 1 consists of uniform long rods ( Figure 1 b).

[0032] It can be seen that gradient heating is irreplaceable. The orderly transformation of CTAB micelles is achieved during the 40-60℃ window, turning spherical micelles into rod-like shapes, and silane cross-linking and curing are completed in the 80℃ high-temperature section. At the same time, precise control of pulsed droplet addition is achieved: the high-speed stage prevents agglomeration, the low-speed stage promotes directional grafting, and the alternating cycle ensures grafting uniformity and grafting amount.

[0033] (II) Effect of different components on dispersion effect Example 4: (1) Take 100 g of silica sol and add it to 300 mL of ethanol-water (volume ratio 1:1), and sonicate for 15 min; (2) Gradual heating to 80℃ (heating to 60℃ at 3℃ / min, holding at 60℃ for 20 min, heating to 80℃ at 5℃ / min, holding at 80℃ for 4 h), pulse-dropping 2.5g of mixed silane (molar ratio of tetradecyl phosphate silane and KH560 = 1.5:1, mixed silane dissolved in ethanol, volume ratio of silane modifier to ethanol 1:10), dropping program: 7mL / min × 1 min, then 1.5mL / min × 1 min, and so on. (3) Centrifuge (10000 rpm, 15 min), wash, and vacuum dry at 60℃ to obtain the product.

[0034] Example 5: (1) Take 100 g of silica sol and add it to 300 mL of ethanol-water (volume ratio 1:1), and sonicate for 15 min; (2) Add 0.3 g CTAB and stir at 35°C for 25 min; (3) Centrifuge (10000 rpm, 15 min), wash, and vacuum dry at 60℃ to obtain the product.

[0035] Example 6: The difference from Example 1 is that 2.5g of mixed silane tetradecyl phosphate silane was added dropwise in a pulse, and KH560 was not added dropwise.

[0036] Example 7: The difference from Example 1 is that 2.5g of mixed silane KH560 was added dropwise in a pulse, and tetradecyl phosphate silane was not added dropwise.

[0037] Example 8: Take unmodified silica sol.

[0038] Example 9: Dispersion Test 1. Dispersion stability: Add 0.1 g M-CNS to 100 mL of saturated Ca(OH)2 solution and ultrasonically disperse at 25℃ for 10 min.

[0039] 2. Particle size / Zeta potential: Measured after standing for 24 h.

[0040] The test results are shown in Table 1 below: Table 1. Dispersion stability and Zeta potential Example <![CDATA[Particle size (nm) in saturated Ca(OH)2]]> Zeta potential (mV) 1 188±25 -37.5±1.1 4 430±65 -33.2±2.2 5 810±100 -15.7±3.2 6 220±35 -36.1±1.9 7 330±40 -29.7±2.1 8 1000±200 -10.9±2.4 By comparison, it can be found that in Example 1, the phosphate ester passivation layer + KH560 interfacial bonding synergistically resists calcium; in Example 4, template deficiency leads to spherical aggregates; and in Example 5, unmodified silanol groups adsorb a large amount of Ca. 2+ Severe aggregation failure; Example 6 has excellent calcium resistance, but is worse than Example 1; Example 7 KH560 alkyl chain provides steric hindrance, but the lack of phosphate ester leads to the failure of passivation layer formation and insufficient calcium resistance.

[0041] (III) Comparison of Concrete Durability Example 10: The original concrete had the following raw material ratio: cement (P·O 42.5) 460 kg / m³ 3 Fly ash (Grade I) 92 kg / m³ 3 Mineral powder (S95) 138 kg / m³ 3 Fine aggregate (medium sand) 750 kg / m³ 3 Coarse aggregate (5-25 mm) 1050 kg / m³ 3 Water-reducing agent (polycarboxylate) 4.95 kg / m 3 Entraining agent 0.01 kg / m³ 3 The water-to-binder ratio is 0.38.

[0042] The product of Example 1 was added at 0 wt%, 1 wt%, 2 wt%, and 5 wt% of cement mass based on Example 10.

[0043] First, the strength was tested according to the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019), and the test data are shown in Table 2.

[0044] Table 2 Concrete Strength Group 3D strength (MPa) 28-day strength (MPa) 0% M-CNS 27.5±0.7 49.3±1.3 1% M-CNS 29.3±0.6 51.7±1.4 2% M-CNS 32.4±0.8 56.8±1.7 5% M-CNS 29.9±1.1 54.1±1.3 Comparison reveals that the addition of M-CNS improves both the 7-day and 28-day strengths compared to the original concrete. Early-stage M-CNS promotes the nucleation effect of rod-shaped M-CNS, accelerating hydration, while later-stage pozzolanic reaction and pore refinement lead to sustained strength growth. However, when the M-CNS content reaches 5%, a certain degree of strength decreases, which is attributed to localized agglomeration caused by excessive addition.

[0045] The chloride ion diffusion coefficient was then measured using the NT Build 492 standard, and the test data are shown in Table 3.

[0046] Table 3 Cl - diffusion coefficient Group <![CDATA[28d diffusion coefficient (×10 -12 m 2 / s)]]> <![CDATA[Diffusion coefficient at 90d (×10 -12 m 2 / s)]]> 0% M-CNS 10.3±0.3 7.8±0.3 1% M-CNS 7.6±0.3 3.9.±0.2 2% M-CNS 5.1±0.2 2.6±0.1 5% M-CNS 6.3±0.3 3.8±0.2 Comparative analysis revealed that the addition of M-CNS reduced both the 28-day and 90-day diffusion coefficients compared to the original concrete. The rod-shaped M-CNS physically fills the capillary pores, and the surface alkyl chains form a hydrophobic barrier, blocking Cl-. - Diffusion pathway. The diffusion coefficient is lowest at a doping level of 2% (5.2 × 10⁻⁶). -12 m 2 At 5%, local defects arise due to aggregation, and the diffusion coefficient rebounds.

[0047] Example 11: (1) Take 100 g of silica sol and add it to 200 mL of ethanol-water (volume ratio 1:1), and sonicate for 10 min; (2) Add 0.1 g CTAB and stir at 30°C for 20 min; (3) Gradual heating to 60℃ (heat to 60℃ at 3℃ / min, hold at 60℃ for 20 min, heat to 80℃ at 5℃ / min, hold at 80℃ for 4 h), pulse-drop 1.8g of mixed silane (molar ratio of tetradecyl phosphate silane and KH560 = 1:1, mixed silane dissolved in ethanol, volume ratio of silane modifier to ethanol 1:8), drop program: 5mL / min × 1 min, then 1mL / min × 1 min, and repeat in this cycle; (4) Centrifuge (10000 rpm, 15 min), wash, and vacuum dry at 60℃ to obtain the product.

[0048] The modified silica sol obtained by adding 2 wt% of cement was the same as in Example 10. The 28-day concrete strength was measured to be 56.1 MPa, and the 28-day diffusion coefficient was 5.8 × 10⁻⁶. -12 m 2 / s.

[0049] Example 12: (1) Take 100 g of silica sol and add it to 400 mL of ethanol-water (volume ratio 1:1), and sonicate for 20 min; (2) Add 0.5 g CTAB and stir at 40℃ for 30 min; (3) Gradual heating to 80℃ (heat to 60℃ at 3℃ / min, hold at 60℃ for 20 min, heat to 80℃ at 6℃ / min, hold at 80℃ for 4 h), pulse-drop 3.0 g of mixed silane (molar ratio of tetradecyl phosphate silane and KH560 = 3:1, mixed silane dissolved in ethanol, volume ratio of silane modifier to ethanol 1:9), drop program: 8 mL / min × 1 min, then 2 mL / min × 1 min, and so on. (4) Centrifuge (10000 rpm, 15 min), wash, and vacuum dry at 60℃ to obtain the product.

[0050] The modified silica sol obtained by adding 2 wt% of cement was the same as in Example 10. The 28-day concrete strength was measured to be 56.7 MPa, and the 28-day diffusion coefficient was 5.4 × 10⁻⁶. -12 m 2 / s.

[0051] Example 13: The difference from Example 1 is that 2.5g of mixed silane (molar ratio of dodecyl phosphate silane and KH560 = 1.5:1, mixed silane dissolved in ethanol, and volume ratio of silane modifier to ethanol 1:10) was pulsedly added.

[0052] The modified silica sol obtained by adding 2 wt% of cement was the same as in Example 10. The 28-day concrete strength was measured to be 57.2 MPa, and the 28-day diffusion coefficient was 4.6 × 10⁻⁶. -12 m 2 / s.

[0053] Example 14: The difference from Example 1 is that 2.5 g of a mixed silane (hexadecyl phosphate silane and KH560 molar ratio = 1.5:1, the mixed silane dissolved in ethanol, and the volume ratio of silane modifier to ethanol 1:10) was pulsedly added. The 28-day strength was 56.1 MPa, and the 90-day diffusion coefficient was 3.0 × 10⁻⁶. -12 m 2 / s.

[0054] The modified silica sol obtained by adding 2 wt% of cement was the same as in Example 10. The 28-day concrete strength was measured to be 55.3 MPa, and the 28-day diffusion coefficient was 6.5 × 10⁻⁶. -12 m 2 / s.

[0055] Example 15: 2 wt% of the modified silica sol from Example 6 (based on the cement content) was added, with other parameters the same as in Example 10. The 28-day concrete strength was measured to be 54.1 MPa, and the 28-day diffusion coefficient was 7.1 × 10⁻⁶. -12 m 2 / s.

[0056] Example 16: 2 wt% of the modified silica sol from Example 7 (based on the cement content) was added, with other parameters the same as in Example 10. The 28-day concrete strength was measured to be 53.7 MPa, and the 28-day diffusion coefficient was 7.5 × 10⁻⁶. -12 m 2 / s.

[0057] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing rod-shaped modified nano-silica sol, characterized in that, Includes the following steps: (1) Add alkaline nano silica sol to an ethanol-water mixed solvent and disperse by ultrasonication; (2) Add 0.1-0.5 wt% CTAB by weight of silica sol to the mixture obtained in step 1 and stir to form a micelle template; (3) The micelle template obtained in step 2 is heated to 60-80℃ using a gradient heating method, and the silane modifier is added using a pulse dropping method: (4) The reaction solution from step 3 was centrifuged and dried to obtain rod-shaped M-CNS powder.

2. The preparation method according to claim 1, characterized in that: In step 1, the mass-to-volume ratio of alkaline nano-silica sol to ethanol-water is 1:2 to 1:4 (g / mL). The silane modifier in step 3 is 1.8 to 3.0 wt% of the silica sol.

3. The preparation method according to claim 1, characterized in that: In step 3, the pulsed dropping is alternating between fast and slow speeds. Specifically, the silane modifier is dissolved in ethanol, with a volume ratio of silane modifier to ethanol of 1:8-10. The high-speed dropping is 5-8 mL / min, and the low-speed dropping is 1-2 mL / min, alternating between the two.

4. The preparation method according to claim 1, characterized in that: In step 3, the silane modifier is one or more of KH560 and / or C12-C16 alkyl phosphate silanes. When added together, the molar ratio of KH560 to C12-C16 alkyl phosphate silane is 1-3:

1.

5. The preparation method according to claim 1, characterized in that: The C12-C16 alkyl phosphate silane is prepared by reacting aminopropyltriethoxysilane with a monoalkyl phosphate ester.

6. The preparation method according to claim 1, characterized in that, Includes the following steps: (1) Add alkaline nano silica sol to an ethanol-water mixed solvent and ultrasonically disperse for 10-20 min; (2) Add 0.1-0.5 wt% of CTAB to silica sol and stir at 30-40℃ for 20-30 min to form a micelle template; (3) Gradual heating to 60-80℃, heating rate 3-6℃ / min, and adding bissilane modifier by pulse dropping method; (4) The reaction solution from step 3 was centrifuged, washed, and dried to obtain rod-shaped M-CNS powder.

7. The preparation method according to claim 1, characterized in that, The gradient temperature increase is as follows: increase the temperature at 3℃ / min to 60℃, hold at 60℃ for 20 min, increase the temperature at 5℃ / min to 80℃, and hold at 80℃ for 4 h.

8. The rod-shaped modified nano-silica sol obtained by the preparation method according to claim 1, characterized in that: Aspect ratio of 3-6, surface grafting rate ≥8 wt%.

9. The application of the rod-shaped modified nano-silica sol according to claim 8, characterized in that: Add rod-shaped M-CNS to concrete at 1-5 wt% of cement mass.

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