A modified aramid III fiber multi-scale reinforced cement-based material and preparation method

Abstract

The present invention discloses a modified aramid III fiber multi-scale reinforced cement-based material and a preparation method, which relate to the field of cement-based composite materials. This is achieved by the following steps: desizing of aramid III fibers; surface modification of aramid III fibers; preparation of aramid III nano-scale reinforcement phase; wherein the aramid III fibers are subjected to oxygen low-temperature plasma to enhance surface activity and roughness, and glutaraldehyde cross-linked carbon quantum dots enhance fiber-matrix bonding. Millimeter-scale modified aramid III fibers (1-2 mm) bridge macro cracks, and nano-scale aramid III fibers (10-30 nm) and carbon quantum dots (average diameter 18 nm) fill micropores; a modified aramid III fiber multi-scale reinforced cement-based material has a fluidity of 190-196 mm, a 28-day compressive strength of 66.5-68 MPa, and a fracture toughness of 2.5-2.8 MPa·m 1 / 2 , porosity of 18.5%-18.8%, significantly better than traditional cement-based materials.

Description

Technical Field

[0001] The present invention relates to the field of cement-based composite materials, and in particular to a modified aramid III fiber multi-scale reinforced cement-based material and a preparation method thereof. Background Art

[0002] With the continued growth in infrastructure construction and demand for high-performance structural materials, cement-based materials are widely used due to their low cost and ease of construction. However, their inherent flaws, such as high brittleness, poor crack resistance, and insufficient impact toughness, are becoming increasingly prominent, limiting their application in high-performance scenarios.

[0003] To improve the mechanical properties of cement-based materials, especially their toughness, researchers often incorporate various fibers (such as glass fibers, carbon fibers, and synthetic polymer fibers) into the cement matrix for reinforcement. However, practice has shown that single-scale fiber reinforcement often faces problems such as fiber agglomeration, poor interfacial bonding with the cement matrix, and limited performance improvement, making it difficult to achieve the desired comprehensive reinforcement effect.

[0004] Aramid III fibers, with their high strength, high modulus, and excellent heat and corrosion resistance, are considered an ideal candidate for cement-based material reinforcement. However, directly incorporating aramid III fibers into the cement matrix results in poor interfacial adhesion due to their smooth surface and strong chemical inertness. This makes it difficult for the fibers to be effectively infiltrated, preventing them from fully utilizing the bridging and crack-resistance properties of their nanofibrils. Consequently, significant improvements in the overall mechanical properties of the composite material remain difficult to achieve.

[0005] To address the challenge of improving the performance of cement-based composites, multi-scale fiber synergistic reinforcement and nanomaterial modification are considered effective approaches. For example, prior art, such as patent CN 116874265 A, discloses a high-ductility multi-scale fiber-reinforced cement-based composite. By mixing carbon nanotubes (nanoscale), calcium sulfate whiskers / carbon fiber powder (micrometer scale), carbon fiber / modified polyethylene fiber (millimeter scale), and modified steel fiber (centimeter scale), the synergistic effect from nanometer to centimeter scales significantly improves the material's compressive strength, tensile strength, and ductility, imparting ultra-high strength and ductility, and extending its service life. Similarly, patent CN 118851679 A discloses a method for reinforcing and toughening concrete using specially treated natural bamboo fibers and nanomaterials, aiming to improve strength, toughness, and durability while overcoming the problem of low residual mechanical properties.

[0006] Therefore, addressing the key bottlenecks of weakened interfacial bonding and insufficient bridging crack resistance of aramid III fibers in cement matrices, there is an urgent need to develop effective surface modification technologies to strengthen their bonding with the matrix. This, combined with a multi-scale fiber synergistic reinforcement strategy, can optimize crack suppression and load transfer mechanisms from the nanoscale to the macroscale, thereby significantly improving the compressive toughness, fracture toughness, and overall service performance of aramid III fiber-reinforced cement-based composites. This is the core technical challenge that urgently needs to be overcome to achieve high performance of this type of material. Summary of the Invention

[0007] In response to the problems in the prior art of poor interfacial adhesion and limited effect of a single reinforcement scale in aramid III fiber cement-based composites, the purpose of the present invention is to provide a multi-step modification method of aramid III fiber through low-temperature plasma surface activation, glutaraldehyde cross-linking carbon quantum dot modification, nanofiber dispersion and blending, etc., to carry out multi-scale reinforcement design of aramid III fiber, thereby preparing modified aramid III fiber multi-scale reinforced cement-based materials with excellent fluidity, high compressive strength and high fracture toughness.

[0008] The method for preparing a modified aramid III fiber multi-scale reinforced cement-based material according to the present invention specifically comprises the following steps:

[0009] S1. Cut the aramid III fiber into 1-2 mm pieces, place it in ethanol for 30 minutes, rinse it with deionized water and dry it, then take it out and place it in acetone, Soxhlet extract it for 10 hours, take it out and wash it and dry it to obtain the desized aramid III fiber;

[0010] S2. Desized aramid III fibers were modified using low-temperature oxygen plasma to obtain surface-activated aramid III fibers. The activated aramid III fibers were immersed in a glutaraldehyde solution for 2 h, removed, washed, and dried, and then immersed in a glutaraldehyde solution. This process was repeated three times. The fibers were then immersed in a carbon quantum dot solution for 24 h, removed, washed, and dried to obtain carbon quantum dot-modified aramid III fibers.

[0011] S3, taking desized aramid III fibers, potassium hydroxide, and dimethyl sulfoxide and mixing and stirring for 4 days to prepare an aramid III nanofiber solution, replacing the dimethyl sulfoxide with deionized water to obtain an aramid III nanofiber aqueous dispersion, adding carbon quantum dots to the aramid III nanofiber aqueous dispersion, and mechanically stirring at 2000 rpm for 12 hours to obtain a carbon quantum dot / aramid III nanofiber mixed solution;

[0012] S4. Add water and water reducer to the carbon quantum dot / aramid III nanofiber mixed solution and stir at 1000 rpm for 5 minutes. Then, mix the modified aramid III fiber, cement, quartz sand, and fly ash evenly and add them. Then, stir at 5000 rpm for 5 minutes to obtain a cement mixture. Pour the mixture into a mold, form it, and then demold and cure it to obtain a modified aramid III fiber multi-scale reinforced cement-based material.

[0013] As a further improvement of the present invention, in step S1, the ultrasonic frequency is 50 kHz; the Soxhlet extraction temperature is 57 °C

[0014] As a further improvement of the present invention, in step S2, the oxygen low-temperature plasma modification parameters are set to an oxygen flow rate of 30 sccm, a processing power of 120 W, and a modification time of 400 s, so that the surface of the fiber is more active and the surface roughness is increased; the glutaraldehyde solution is a 25 wt% aqueous solution; the carbon quantum dots are prepared by mixing coffee grounds and ethanol (the mass volume ratio of coffee grounds to ethanol is 1 g:10 mL), placing the mixture in a hydrothermal reactor at 200°C for 8 hours, and then taking it out and filtering it with 2.2 μm filter paper to obtain a filtrate, which is dialyzed in deionized water for 48 hours using a dialysis bag with a molecular weight cutoff of 1000 Da (the water is changed every 6 hours), and then freeze-dried at -50°C and 10 Pa for 24 hours to obtain a carbon quantum dot solution of 0.5 g / L aqueous solution; the entire process is immersed in an environment of 70°C.

[0015] As a further improvement of the present invention, in step S3, the mass ratio of the desized aramid III fiber, potassium hydroxide, and dimethyl sulfoxide is 1:0.08:20; the mass ratio of the carbon quantum dots and the aramid III nanofiber is 1:100.

[0016] As a further improvement of the present invention, in step S4, the mass ratio of water, water reducer, carbon quantum dots / aramid III nanofibers, modified aramid III fibers, cement, quartz sand, and fly ash is 0.35:0.005:0.0005, 0.001, 0.0015, or 0.002:0.015:1:1:0.3, and the curing time is 28 d.

[0017] As a further improvement of the present invention, the modified aramid III fiber multi-scale reinforced cement-based material, the aramid III fiber has a diameter of 12-25 μm, the aramid III nanofiber has a diameter of 10-30 nm, the carbon quantum dots have an average diameter of 18 nm, the cement is ordinary Portland cement; the fly ash is first-grade fly ash; the quartz sand is 45-60 mesh; and the water reducer is a lignin sulfonate water reducer.

[0018] As a further improvement of the present invention, the modified aramid III fiber multi-scale reinforced cement-based material has a fluidity of 190-196 mm, a 28-day compressive strength of 66.5-68 MPa, and a fracture toughness of 2.5-2.8 MPa·m 1 / 2 , the total porosity is 18.5%-18.8%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) Multi-scale synergistic toughening mechanism:

[0021] Macroscale: Modified aramid III fibers (12–25 μm in diameter) effectively bridge cracks and prevent macroscopic crack propagation (compressive strength increased by 61% compared to a fiber-free system);

[0022] Nanoscale: Aramid III nanofibers refine cement hydration products and fill micropores; carbon quantum dots enhance interfacial chemical bonding and synergistically inhibit microcrack initiation (compared to single-scale enhancement, fracture toughness increases by 40%–55%).

[0023] (2) Breakthrough in interfacial bonding strength: Oxygen plasma modification roughens the fiber surface, and combined with glutaraldehyde cross-linking carbon quantum dots, the fiber-cement matrix interfacial bonding strength is significantly improved (compressive strength is increased by 18.0 MPa compared to unmodified fibers).

[0024] (3) Pore structure optimization: Nanofibers and carbon quantum dots fill the micropores, reducing the total porosity to 18.5% (compared to the system without nanophase, the porosity is reduced by 3.5%), improving the density and durability of the material.

[0025] (4) Performance balance: By optimizing the ratio (nanofiber content 0.2 wt%, macrofiber content 1.5 wt%), the fluidity (190 mm) and mechanical properties (compressive strength 68 MPa, fracture toughness 2.8 MPa·m 1 / 2 ), to solve the problem of fluidity loss caused by traditional fiber reinforcement.

[0026] (5) Resource recycling: Carbon quantum dots use waste coffee grounds as raw materials to achieve high-value utilization of biomass resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the preparation process and reinforcement mechanism of a modified aramid III fiber multi-scale reinforced cement-based material;

[0028] Figure 2 a is the diameter distribution histogram of the aramid III nanofibers prepared in Example 1;

[0029] Figure 2 b is the particle size distribution histogram of carbon quantum dots prepared in Example 1;

[0030] Figure 2 c is a digital photo of the aqueous dispersion of aramid III nanofibers prepared in Example 1;

[0031] Figure 2 d is a digital photo of the carbon quantum dots prepared in Example 1;

[0032] Figure 2 e is a digital photograph of the carbon quantum dot aqueous dispersion prepared in Example 1 under 365 nm ultraviolet light;

[0033] Figure 3 This is a scanning electron microscope image of unmodified aramid III fiber;

[0034] Figure 4 This is a scanning electron microscope image of carbon quantum dot modified aramid III fiber;

[0035] Figure 5 It is a dot-line graph of the fluidity of cement-based materials of Examples and Comparative Examples;

[0036] Figure 6 The compressive strength bar graph of cement-based materials of Examples and Comparative Examples is shown;

[0037] Figure 7 The fracture toughness histogram of cement-based materials in Examples and Comparative Examples;

[0038] Figure 8 It is a bar graph of the total porosity of cement-based materials in Examples and Comparative Examples. DETAILED DESCRIPTION

[0039] The present invention provides a method for preparing a modified aramid III fiber multi-scale reinforced cement-based material. In order to make the objectives, technical solutions and advantages of the present invention clearer and more specific, the present invention is further described in conjunction with specific embodiments and drawings.

[0040] Example 1

[0041] like Figure 1 As shown, a modified aramid III fiber multi-scale reinforced cement-based material of the present invention is prepared by the following steps:

[0042] Step 1: The aramid III fiber was cut into 1-2 mm pieces, placed in ethanol and ultrasonicated at 50 kHz for 30 min, then rinsed with deionized water and dried, then taken out and placed in acetone, Soxhlet extracted at 57 °C for 10 h, taken out, washed and dried to obtain desized aramid III fiber;

[0043] Step 2: Take the desized aramid III fiber and modify it with oxygen low-temperature plasma at an oxygen flow rate of 30 sccm and a processing power of 120 W for 400 s to obtain surface-activated aramid III fiber. The activated aramid III fiber is immersed in a 25 wt% glutaraldehyde aqueous solution at 70 ° C for 2 h, taken out, washed and dried, and then immersed in a glutaraldehyde solution. This is repeated 3 times, and then immersed in a carbon quantum dot solution at 70 ° C for 24 h, taken out, washed and dried to obtain carbon quantum dot-modified aramid III fiber; carbon quantum dots are prepared by mixing coffee grounds and ethanol (the mass volume ratio of coffee grounds to ethanol is 1 g: 10 mL), placing it in a hydrothermal reactor at 200 ° C for 8 h, taking it out and filtering it with 2.2 μm filter paper to obtain a filtrate, using a dialysis bag with a molecular weight cutoff of 1000 Da to dialyze in deionized water for 48 h (changing the water every 6 h), and then freeze-drying it at -50 ° C and 10 Pa for 24 h. The carbon quantum dot solution is 0.5 g / L aqueous solution;

[0044] Step 3: Desized aramid III fiber, potassium hydroxide, and dimethyl sulfoxide were mixed and stirred at a mass ratio of 1:0.08:20 for 4 days to prepare an aramid III nanofiber solution, and dimethyl sulfoxide was replaced with deionized water to obtain an aramid III nanofiber aqueous dispersion. Carbon quantum dots were added to the aramid III nanofiber aqueous dispersion and mechanically stirred at 2000 rpm for 12 hours to obtain a carbon quantum dot / aramid III nanofiber mixed solution. The mass ratio of carbon quantum dots to aramid III nanofiber was 1:100.

[0045] Step 4: Add water and water reducer to the carbon quantum dot / aramid III nanofiber mixed solution and stir at 1000 rpm for 5 minutes. Then, the modified aramid III fiber, cement, quartz sand, and fly ash are mixed evenly and added, and then stirred at 5000 rpm for 5 minutes to obtain a cement mixture. The mass ratio of water, lignin sulfonate water reducer, carbon quantum dot / aramid III nanofiber, modified aramid III fiber, ordinary Portland cement, 45-60 mesh quartz sand, and first-class fly ash is 0.35:0.005:0.002:0.015:1:1:0.3. The mixture is poured into a mold for molding and then demolded and cured for 28 days to obtain a modified aramid III fiber multi-scale reinforced cement-based material.

[0046] The diameter distribution of the aramid III nanofibers prepared in Example 1 is as follows: Figure 2 As shown in a, the diameter of aramid III nanofibers is 10-30 nm; the aramid III nanofiber aqueous dispersion was observed, and the results are shown in Figure 2 c; the particle size distribution of carbon quantum dots is shown in Figure 2 As shown in b, the average diameter of carbon quantum dots is 18 nm; the carbon quantum dots were observed in real life, and the results are as follows Figure 2d; The carbon quantum dot aqueous dispersion was observed under 365nm ultraviolet light. Figure 2 As shown in e, it has bright blue fluorescence.

[0047] The untreated aramid III fibers were observed using a scanning electron microscope. Figure 3 As shown, the fiber surface is very smooth and the diameter is in the range of 12-25 μm.

[0048] The carbon quantum dot modified aramid III fiber was observed using a scanning electron microscope. Figure 4 As shown, the fiber surface roughness increases;

[0049] Examples 2-4

[0050] Example 2-4 provides a method for preparing a modified aramid III fiber multi-scale reinforced cement-based material. Compared with Example 1, the difference is that the mass ratios of water, water reducer, carbon quantum dot / aramid III nanofiber, modified aramid III fiber, cement, quartz sand, and fly ash in the cement mixture in step four are 0.35:0.005:0.0005:0.015:1:1:0.3 (Example 2), 0.35:0.005:0.001:0.015:1:1:0.3 (Example 3), and 0.35:0.005:0.0015:0.015:1:1:0.3 (Example 4).

[0051] Comparative Example 1

[0052] Comparative Example 1 provides a method for preparing a modified aramid III fiber multi-scale reinforced cement-based material. Compared with Example 1, the difference is that the cement mixture in step 4 does not contain carbon quantum dots / aramid III nanofibers and modified aramid III fibers.

[0053] Comparative Example 2

[0054] Comparative Example 2 provides a method for preparing a modified aramid III fiber multi-scale reinforced cement-based material. Compared with Example 1, the difference is that the aramid III nanofibers and aramid III fibers in the cement mixture in step 4 are unmodified.

[0055] Comparative Example 3

[0056] Comparative Example 3 provides a method for preparing a modified aramid III fiber multi-scale reinforced cement-based material. Compared with Example 1, the difference is that the cement mixture in step 4 does not contain carbon quantum dots / aramid III nanofibers.

[0057] Comparative Example 4

[0058] Comparative Example 4 provides a method for preparing a modified aramid III fiber multi-scale reinforced cement-based material. Compared with Example 1, the difference is that the cement mixture in step 4 does not contain modified aramid III fiber.

[0059] The fluidity of the samples was measured using the microslump test specified in GB / T 8077-2012. Figure 5 As shown, Example 1 decreases by 20 mm compared with Comparative Example 1; the change is less than 20 mm compared with other comparative examples and examples.

[0060] The compressive strength of the samples was evaluated using a pressure testing machine, and the results were as follows: Figure 6 As shown, the compressive strength is increased by 25.7 MPa (61%) compared with Comparative Example 1 (no fiber); 18.0 MPa compared with Comparative Example 2 (unmodified fiber); 13.0 MPa compared with Comparative Example 3 (only modified aramid III fiber); and 2.0 MPa compared with Comparative Example 4 (only modified aramid III nanofiber). When the mass ratio of carbon quantum dots to aramid III nanofiber is 0.0005 (Example 2), the 28d compressive strength is 66.5 MPa; when the mass ratio is 0.002 (Example 1), the compressive strength is 68 MPa. When the mass ratio is in the range of 0.0005 to 0.002, the compressive strength increases linearly with increasing ratio.

[0061] The fracture toughness of the samples was evaluated using a compression testing machine, and the results were as follows: Figure 7 As shown, the performance is improved by 1.00 MPa·m compared with Comparative Example 1. 1 / 2 ; Compared with comparative examples 2 and 3, the 1 / 2 Compared with Comparative Example 4, it increased slightly by 0.20 MPa·m 1 / 2 Compared with Examples 2-4, the improvement range is 0.10 to 0.30 MPa·m 1 / 2 .

[0062] The total porosity of the sample was measured by mercury intrusion porosimetry. Figure 8 As shown, it is 3.5% lower than that of Comparative Example 1; it is 0.3-2.0% lower than that of Comparative Examples 2-4 and Examples 2-4, and the pore structure is denser.

[0063] The improved performance may be attributed to the macro-modified aramid III fibers acting as bridges during the crack propagation phase, effectively suppressing macrocracks. The aramid III nanofibers refine the crystal nuclei at the microscale, strengthening the interface between the cement matrix and the fiber, and pinning microcracks. The dual-scale combination hinders crack propagation, significantly improving strength and toughness. Oxygen plasma and glutaraldehyde treatment enhance fiber surface activity, strengthening chemical crosslinking with carbon quantum dots and enhancing the bond between the aramid III fibers and the matrix. The aramid III nanofibers and carbon quantum dots fill micropores, further reducing porosity and improving compressive resistance. Example 1 (0.20 wt% aramid III nanofibers per cement mass and 1.5 wt% aramid III fibers per cement mass) meets the optimal reinforcement window, balancing flowability and mechanical properties. The fiber-free system (Comparative Example 1) lacks crack pinning and bridging, resulting in a significant decrease in strength and toughness. The unmodified macrofiber interface (Comparative Example 2) exhibits weak bonding, resulting in limited macrocrack bridging. While single-scale reinforcement (Comparative Examples 3 / 4) shows some improvement, it fails to achieve both macro- and microcrack suppression, resulting in lower performance than the multi-scale system.

[0064] In summary, the present invention successfully breaks through the bottleneck of interfacial bonding of aramid III fibers in cement matrix through the innovation of multi-scale fiber collaborative design and surface modification technology. The modification process of plasma activation and glutaraldehyde cross-linking carbon quantum dots gives the fiber a highly active surface. The composite of aramid III nanofibers and carbon quantum dots achieves nano-scale dispersion and interface strengthening. The macro / nano dual-scale crack suppression mechanism makes the compressive strength (68 MPa) and fracture toughness (2.8 MPa·m 1 / 2 ) simultaneously improved; porosity reduced to 18.5%, significantly extending the material's service life. This provides an industrially feasible solution for high-performance cement-based composites, suitable for demanding scenarios such as earthquake-resistant structures and military engineering.

Claims

1. A method for preparing a modified aramid III fiber multi-scale reinforced cement-based material, characterized in that: The following steps are involved: S1. Cut the aramid III fiber into 1-2 mm pieces, place it in ethanol for 30 minutes, rinse it with deionized water and dry it, then take it out and place it in acetone, Soxhlet extract it for 10 hours, take it out and wash it and dry it to obtain the desized aramid III fiber; S2. Desized aramid III fibers were modified using low-temperature oxygen plasma to obtain surface-activated aramid III fibers. The activated aramid III fibers were immersed in a glutaraldehyde solution for 2 h, removed, washed, and dried, and then immersed in a glutaraldehyde solution. This process was repeated three times. The fibers were then immersed in a carbon quantum dot solution for 24 h, removed, washed, and dried to obtain carbon quantum dot-modified aramid III fibers. S3, taking desized aramid III fibers, potassium hydroxide, and dimethyl sulfoxide and mixing and stirring for 4 days to prepare an aramid III nanofiber solution, replacing the dimethyl sulfoxide with deionized water to obtain an aramid III nanofiber aqueous dispersion, adding carbon quantum dots to the aramid III nanofiber aqueous dispersion, and mechanically stirring at 2000 rpm for 12 hours to obtain a carbon quantum dot / aramid III nanofiber mixed solution; S4. Add water and water reducer to the carbon quantum dot / aramid III nanofiber mixed solution and stir at 1000 rpm for 5 min. Then, mix the modified aramid III fiber, cement, quartz sand, and fly ash evenly and add them. Then, stir at 5000 rpm for 5 min to obtain a cement mixture. Pour the mixture into a mold, form it, and then demold and cure it to obtain a modified aramid III fiber multi-scale reinforced cement-based material.

2. The method for preparing a modified aramid III fiber multi-scale reinforced cement-based material according to claim 1, characterized in that: The ultrasonic frequency in S1 is 50 kHz; and the Soxhlet extraction temperature is 57°C.

3. The method for preparing a modified aramid III fiber multi-scale reinforced cement-based material according to claim 1, characterized in that: The S2 is modified by oxygen low-temperature plasma with parameters set as an oxygen flow rate of 30 sccm, a processing power of 120 W, and a modification time of 400 s, which makes the surface of the fiber more active and improves the surface roughness. The glutaraldehyde solution is a 25 wt% aqueous solution. The carbon quantum dots are prepared by mixing coffee grounds and ethanol with a mass volume ratio of coffee grounds to ethanol of 1 g:10 mL. The mixture is placed in a hydrothermal reactor at 200°C for 8 hours, then taken out and filtered with 2.2 μm filter paper to obtain a filtrate. The filtrate is dialyzed in deionized water for 48 hours using a dialysis bag with a molecular weight cutoff of 1000 Da, and the water is changed every 6 hours. The mixture is then freeze-dried at -50°C and 10 Pa for 24 hours to obtain a carbon quantum dot solution of 0.5 g / L aqueous solution. The entire immersion process is carried out at 70°C.

4. The method for preparing a modified aramid III fiber multi-scale reinforced cement-based material according to claim 1, characterized in that: The mass ratio of the desized aramid III fiber, potassium hydroxide, and dimethyl sulfoxide in S3 is 1:0.08:20; the mass ratio of the carbon quantum dots and the aramid III nanofiber is 1:

100.

5. The method for preparing a modified aramid III fiber multi-scale reinforced cement-based material according to claim 1, characterized in that: The mass ratio of water, water reducing agent, carbon quantum dots / aramid III nanofiber, modified aramid III fiber, cement, quartz sand and fly ash in the S4 is 0.35:0.005:0.0005, 0.001, 0.0015 or 0.002:0.015:1:1:0.3, and the curing time is 28 days.

6. A modified aramid III fiber multi-scale reinforced cement-based material, characterized in that: The modified aramid III fiber multi-scale reinforced cement-based material is obtained by the preparation method according to any one of claims 1 to 5.

7. The modified aramid III fiber multi-scale reinforced cement-based material according to claim 6, characterized in that: The modified aramid III fiber has a diameter of 12-25 μm; the aramid III nanofiber has a diameter of 10-30 nm; the carbon quantum dots have an average diameter of 18 nm; the cement is ordinary Portland cement; the fly ash is first-grade fly ash; the quartz sand is 45-60 mesh; and the water reducer is a lignin sulfonate water reducer.

8. The modified aramid III fiber multi-scale reinforced cement-based material according to claim 6, characterized in that: The cement-based material has a fluidity of 190-196 mm, a 28-day compressive strength of 66.5-68 MPa, and a fracture toughness of 2.5-2.8 MPa·m 1 / 2 , the total porosity is 18.5%-18.8%.

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