High-content red mud-based engineering geopolymer composite material, preparation method and application thereof

Abstract

The application discloses a high-doped red mud-based engineering geological polymer composite material and a preparation method and application thereof. The engineering geological polymer composite material comprises the following components: red mud, fly ash, slag, river sand, water, sodium silicate and PE fibers, and further comprises nano-SiO2 dispersion liquid and nanocrystalline cellulose. The application takes high-doped Bayer red mud as a precursor main body, and obtains a high-performance EGC composite material through multi-component synergistic optimization and composite modification and enhancement, so that the mechanical properties, strain hardening capacity and durability are synergistically improved. The material is suitable for the fields of building structure reinforcement, infrastructure repair and industrial solid waste resource utilization.

Description

Technical Field

[0001] This invention relates to an engineering geological polymer composite material, particularly to a high-dosage red mud-based engineering geological polymer composite material, and also to a method for preparing and applying the above-mentioned engineering geological polymer composite material. Background Technology

[0002] Engineered Geopolymer Composite (EGC) is a novel inorganic cementitious material that uses industrial by-products as silicon-aluminum source precursors and generates a three-dimensional network structure under alkaline activation conditions. It has advantages such as high early strength, corrosion resistance, and low carbon emissions, and has received widespread attention in the fields of structural reinforcement and green building materials in recent years.

[0003] To improve the resource utilization level of industrial solid waste, the red mud-fly ash-slag ternary composite system has gradually become an important research direction for red mud-based EGC and geopolymer cementitious materials. Fly ash provides active silica-alumina components, slag provides a calcium source and promotes C-(A)-SH gel formation, while red mud contains both alkaline components and some active silica-alumina phases, which can partially replace fly ash and realize the resource utilization of large quantities of solid waste.

[0004] However, existing ternary systems based on red mud, fly ash, and slag still have many shortcomings. First, to ensure high mechanical properties, most studies typically control the red mud content at a low level (generally no more than 30%). Under high red mud content conditions, insufficient active silica-alumina components, high inert mineral content, and large particle specific surface area easily lead to decreased slurry fluidity, increased water demand, and incomplete cementation reaction, resulting in decreased material strength and toughness. Therefore, the application of high-red mud content in current technologies still has significant limitations, and the level of large-scale resource utilization of red mud needs to be improved. Second, the optimization methods of existing ternary composite systems mainly focus on adjusting the ratio between red mud, fly ash, and slag, lacking synergistic regulation of the system's microstructure and interfacial properties. Because high red mud content reduces gel formation and weakens the stress transfer capacity of the fiber-matrix interface, the material is prone to problems such as localized crack development, insufficient fiber bridging, and decreased tensile ductility. Currently, modification measures to address these problems are relatively limited, and an effective technical solution that balances strength, ductility, and crack control performance has not yet been formed.

[0005] Therefore, how to improve the microstructure, interfacial properties and crack evolution behavior of ternary geopolymer systems through multi-scale synergistic modification while maintaining a high red mud content, and achieve synergistic improvement in material strength, ductility and crack resistance, remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] Purpose of the invention: In view of the problems existing in the above-mentioned prior art, such as raw material supply bottlenecks, low utilization rate of red mud, and significant decrease in mechanical properties under high dosage, the purpose of this invention is to provide a high-dosage red mud-based engineering geological polymer composite material with excellent mechanical properties and significant strain hardening. It also provides a method for preparing the engineering geological polymer composite material and its application in engineering scenarios such as building structure reinforcement, crack repair, and impact protection.

[0007] Technical solution: The high-content red mud-based engineering geological polymer composite material of the present invention includes the following components: red mud, fly ash, slag, river sand, water, sodium silicate, PE fiber, and also contains nano-SiO2 dispersion and nanocrystalline cellulose (NCC).

[0008] The components, by mass parts, are as follows: red mud 300-360 parts, fly ash 50-65 parts, slag 160-180 parts, river sand 160-180 parts, water 200-230 parts, sodium silicate (by solid content) 60-75 parts, PE fiber 8-12 parts, nano-SiO2 dispersion 15-30 parts, and nano-crystalline cellulose 1-5 parts.

[0009] The red mud mentioned is Bayer process red mud with a specific surface area ≥450 m². 2 / kg;

[0010] The slag is S95 grade slag;

[0011] The fly ash is Grade F fly ash;

[0012] The PE fiber is ultra-high molecular weight polyethylene fiber, with a single filament length of 10-14 mm and a single filament diameter of 20-30 μm, preferably a single filament length of 12 mm and a diameter of 24 μm;

[0013] The river sand is natural river sand with a particle size ≤600 μm;

[0014] The nano-SiO2 is water-dispersible nano-silica with an average particle size of 20–50 nm, and the solid content of the nano-SiO2 dispersion is 20%–40%, preferably 30%.

[0015] The nanocrystalline cellulose was prepared by acid hydrolysis and has a diameter of 5–20 nm and a length of 100–300 nm.

[0016] The preparation method of the above-mentioned high-content red mud-based engineering geological polymer composite material includes the following steps:

[0017] (1) Mix sodium silicate powder with water, stir to dissolve, and obtain an alkaline activated solution. Cool and set aside.

[0018] (2) Weigh the red mud, fly ash, slag and river sand according to the proportion, put them into the mixer and dry mix at low speed until they are evenly mixed to obtain dry mixture;

[0019] (3) The nano-SiO2 dispersion was premixed with nanocrystalline cellulose and ultrasonically dispersed to obtain a composite modified suspension;

[0020] (4) Add the alkaline activation solution obtained in step (1) and the suspension obtained in step (3) to the dry mixture one after the other, stir at low speed, and then stir at high speed.

[0021] (5) During the high-speed mixing process, PE fibers are evenly sprinkled in batches. After the sprinkling is completed, high-speed mixing continues to obtain a uniform and stable red mud-based EGC slurry.

[0022] (6) Pour the slurry into shape, vibrate to compact it, cover and cure for 24 hours, then demold and cure under standard curing conditions until the set age.

[0023] In step (2), the low-speed dry mixing conditions are a mixing speed of 120-180 r / min and a mixing time of 1.5-3 min, preferably 2 min.

[0024] In step (4), the low-speed stirring conditions are a stirring speed of 120-180 r / min and a stirring time of 1.5-3 min, while the high-speed stirring conditions are a stirring speed of 250-320 r / min and a stirring time of 3-7 min.

[0025] In step (5), the high-speed stirring conditions are a stirring speed of 250-320 r / min and a stirring time of 1-2 min.

[0026] Invention principle: The high-red mud-based engineering geological polymer composite material of the present invention constructs a ternary synergistic cementitious system of "red mud-fly ash-slag" and introduces nano-SiO2 dispersion and organic-inorganic composite toughening components. Under the condition of high red mud content, it achieves synergistic improvement of mechanical properties, strain hardening ability and durability, which is significantly different from the simple substitution or proportion adjustment in the prior art.

[0027] Among them, nano-SiO2 has a high specific surface area and pozzolanic activity, which can promote the formation of gel products and improve the density of the matrix; nanocrystalline cellulose has excellent dispersibility and toughening effect, which can improve the microstructure of the slurry and promote the synergistic force of the fiber-matrix interface; nano-SiO2 dispersion can effectively fill the micro-nano pores between red mud particles, optimize the particle packing density, and its high specific surface activity can participate in the geopolymerization reaction, promote the nucleation and growth of C-(A)-SH gel, and compensate for the strength loss caused by insufficient red mud activity; nanocrystalline cellulose (NCC) as a bio-based toughening agent, its nano-size effect and abundant hydroxyl groups can form a hydrogen bond network with the geopolymer matrix, enhance the fiber-matrix interface bonding force, and synergize with PE fibers to form a "nano-micro" multi-level toughening structure, significantly improving the tensile strain capacity and multi-crack characteristics of the material;

[0028] The synergistic effect among the three (red mud, fly ash, and slag) is amplified with the assistance of nano-modifier nano-SiO2 dispersion and nanocrystalline cellulose. This not only overcomes the problems of poor fluidity and low strength caused by high red mud content, but also achieves a significant improvement in strain hardening behavior and crack dispersion ability.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0030] (1) High utilization rate of red mud: The amount of red mud can reach 300-360 parts, accounting for more than 50% of the total mass of cementitious materials, realizing the large-scale resource utilization of red mud and significantly reducing the environmental risk of stockpiling;

[0031] (2) Excellent mechanical properties: At the highest red mud content, the compressive strength at 28 days can still reach more than 50 MPa, the tensile strength is ≥3.0 MPa, and the tensile strain is ≥4.5%, which is better than the values ​​reported in most existing red mud-based EGC literature;

[0032] (3) Significant strain hardening: Through the multi-level synergy between nano-modifiers and PE fibers, multi-crack cracking and strain hardening behavior are achieved. The cracks are numerous, narrow, and closely spaced, and have good energy dissipation capabilities.

[0033] (4) Green and low carbon: This invention establishes a composite mechanism of alkaline activation, silicon and aluminum supply, enhanced reactivity and structural densification through the synergistic combination of three components: red mud, fly ash and slag. It completely replaces traditional cement. All components are derived from industrial solid waste or bio-based materials, and carbon emissions are significantly lower than those of traditional cement-based materials.

[0034] (5) Wide engineering applicability: The high-dosage red mud-based engineering geological polymer composite material prepared by the present invention has excellent engineering applicability and can be widely used in various engineering scenarios such as building structure reinforcement, crack repair, and impact protection. It helps to improve the performance of existing structures and extend the service life of buildings or structures. Detailed Implementation

[0035] The technical solution of the present invention will be further described below with reference to the embodiments. The test materials used in the embodiments can all be purchased through conventional means.

[0036] Example 1

[0037] The high-dosage red mud-based EGC material of the present invention, by mass parts:

[0038] Red mud: 340 parts, fly ash: 57 parts, slag: 170 parts, river sand: 170 parts, water: 215 parts, sodium silicate: 68 parts, PE fiber: 9 parts, nano-SiO2 dispersion (30% solid content): 20 parts, nano-crystalline cellulose: 3 parts.

[0039] The preparation method includes the following steps:

[0040] (1) Mix sodium silicate powder with water, stir to dissolve, and obtain an alkaline activated solution. Cool and set aside.

[0041] (2) Weigh the red mud, fly ash, slag and river sand according to the proportion, put them into the mixer, dry mix at low speed for 2 minutes, and mix evenly.

[0042] (3) The nano-SiO2 dispersion was premixed with nanocrystalline cellulose and ultrasonically dispersed for 10 min to obtain a composite modified suspension;

[0043] (4) Add the alkaline activation solution obtained in step (1) and the suspension obtained in step (3) to the dry mixture one after the other, stir at low speed for 2 min, and then stir at high speed for 2 min.

[0044] (5) During the high-speed mixing process, PE fibers are evenly sprinkled in batches. After the sprinkling is completed, high-speed mixing is continued for 1 minute to obtain a uniform and stable red mud-based EGC slurry.

[0045] (6) Pour the slurry into shape, vibrate and compact it, cover and cure for 24 hours, then demold. After demolding, place it in a constant temperature water bath at 60±2 ℃ for 24 hours. Then transfer it to standard curing conditions and continue curing until the set age. The standard curing conditions are a temperature of 20±2 ℃ and a relative humidity of 95% or higher.

[0046] Comparative Example 1

[0047] A composite material, which does not contain nano-modifiers compared to Example 1, comprises, by weight: 340 parts red mud, 57 parts fly ash, 170 parts slag, 170 parts river sand, 215 parts water, 68 parts sodium silicate, and 9 parts PE fiber.

[0048] Compared with Example 1, its preparation method does not involve nano-modification of red mud, fly ash, or slag.

[0049] Comparative Example 2

[0050] A composite material, compared with Example 1, with reduced red mud addition and no nano-modifier added, comprises, by mass parts: 255 parts red mud, 142 parts fly ash, 170 parts slag, 170 parts river sand, 215 parts water, 68 parts sodium silicate, and 9 parts PE fiber.

[0051] Compared with Example 1, its preparation method does not involve nano-modification of red mud, fly ash, or slag.

[0052] Comparative Example 3

[0053] A composite material, compared with Example 1 without the addition of nanocrystalline cellulose, comprises, by mass parts: 340 parts red mud, 57 parts fly ash, 170 parts slag, 170 parts river sand, 215 parts water, 68 parts sodium silicate, 9 parts PE fiber, and 20 parts nano-SiO2 dispersion (30% solid content).

[0054] Compared with Example 1, the preparation method of this method involves only dispersing nano-SiO2 in step (3) without adding NCC.

[0055] Comparative Example 4

[0056] A composite material, compared with Example 1, with reduced red mud addition and no nano-modifier added, comprises, by mass parts: 170 parts red mud, 227 parts fly ash, 170 parts slag, 170 parts river sand, 215 parts water, 68 parts sodium silicate, and 9 parts PE fiber.

[0057] Compared with Example 1, its preparation method does not involve nano-modification of red mud, fly ash, or slag.

[0058] The performance of the materials prepared in Example 1 and Comparative Examples 1-4 was tested, and the test results are as follows (28 days):

[0059] Table 1. Performance test results of the high-dosage red mud-based EGC material in Example 1 and the materials prepared in Comparative Examples 1-4.

[0060]

[0061] As can be seen from the table above, this invention significantly improves the mechanical properties and strain hardening behavior of materials by introducing nano-SiO2 and NCC under high red mud content. In particular, the performance does not decrease but increases under high red mud content, which reflects the advanced nature and non-obviousness of the technical solution.

[0062] In Example 1 of this invention, compared with Comparative Example 1, the compensation effect of nano-composite modification was verified: under the same high red mud content (340 parts), the present invention, by adding nano-SiO2+NCC, increased the compressive strength from 51.7 MPa to 58.3 MPa (+12.8%), the tensile strain from 3.92% to 5.03% (+28.3%), the number of cracks from 25 to 41, and the crack width from 125.4 μm to 98.2 μm. Conclusion: The nano-composite modifier effectively compensated for the loss of mechanical properties caused by high red mud content, achieving a simultaneous improvement in strength and ductility.

[0063] In Example 1 of this invention, compared with Comparative Example 2, the influence trend of changes in red mud content was verified: the red mud content of Comparative Example 2 was 255 parts (between 170 parts in Comparative Example 4 and 340 parts in Comparative Example 1). Without nano-modification, its compressive strength was 58.9 MPa and tensile strain was 4.52%. Compared with Comparative Example 1 (340 parts of red mud), it can be seen that as the red mud content increased from 255 parts to 340 parts, the compressive strength decreased from 58.9 MPa to 51.7 MPa (-12.2%), and the tensile strain decreased from 4.52% to 3.92% (crack control ability significantly deteriorated, the number of cracks decreased from 33 to 25, and the width increased from 109.6 μm to 125.4 μm). This indicates that without the addition of modifiers, increasing the red mud content will cause fluctuations in mechanical properties and deterioration in cracking modes. When the red mud content of this invention reaches 340 parts, the compressive strength (58.3 MPa) is basically the same as that of Comparative Example 2 (58.9 MPa), while the tensile strain (5.03%) exceeds that of Comparative Example 2 (4.52%), representing an improvement of 11.3%. Conclusion: This invention achieves performance superiority over conventional formulations with medium red mud content at high red mud content, proving that nano-composite modification can overcome the performance bottleneck caused by increasing red mud content.

[0064] Example 1 of this invention, compared with Comparative Example 3, verifies the irreplaceability of NCC: the only difference between Comparative Example 3 and Example 1 is the addition of NCC (both contain nano-SiO2, and both contain 340 parts of red mud). After adding NCC, the tensile strain increased from 4.74% to 5.03% (+6.1%), the number of cracks increased from 36 to 41, and the crack width decreased from 105.3 μm to 98.2 μm. Conclusion: Nano-SiO2 can provide filling and reinforcement; NCC, through interfacial bridging and hydrogen bond networks, provides toughening and dispersing functions that cannot be replaced by single nanoparticles, and the combination of the two has a significant synergistic effect.

[0065] Compared with Comparative Example 4, Example 1 of this invention verifies that the performance is improved against the trend under high red mud content:

[0066] Comparative Example 4, with a red mud content of only 170 parts (the lowest among conventional formulations), and no nano-modification, exhibited slightly higher compressive strength than the present invention (60.6 MPa vs. 58.3 MPa), but significantly lower tensile strain (4.51%) and crack count (29 cracks) compared to the present invention (5.03%, 41 cracks). Conclusion: Even with a red mud content doubled (340 vs. 170), the present invention not only maintained its tensile strain but actually increased it from 4.51% to 5.03%, and significantly enhanced crack dispersion. This strongly demonstrates that high red mud content is not necessarily a result of performance degradation. Through the "nano-SiO2 + NCC" compounding strategy of the present invention, the high alkalinity of red mud and the nano-modification effect can be synergistically transformed, achieving a counter-trend improvement through "toughening with waste," overturning the conventional technical understanding that high red mud content inevitably leads to performance degradation.

[0067] A comparison of Comparative Examples 1-4 with the embodiments of the present invention shows that, without the addition of nano-modifiers, the compressive strength continuously decreased (60.6→58.9→51.7 MPa) when the red mud content increased from 170 parts (Comparative Example 4) to 255 parts (Comparative Example 2) and then to 340 parts (Comparative Example 1). Furthermore, the crack control capability first increased and then decreased, demonstrating that conventional techniques are insufficient to simultaneously achieve high red mud utilization and excellent mechanical properties. The present invention, through the introduction of a composite modification of nano-SiO2 dispersion and nanocrystalline cellulose (NCC), achieved a compressive strength (58.3 MPa) close to that of Comparative Example 4 when the red mud content reached 340 parts (twice that of Comparative Example 4), while the tensile strain (5.03%) surpassed that of Comparative Example 4 (4.51%) by 11.5%, and the number of cracks (41) far exceeded that of Comparative Example 4 (29) by 41.4%. Meanwhile, compared with Comparative Example 3, which only added nano-SiO2, the introduction of NCC increased the tensile strain by 6.1% and the number of cracks by 13.9%, which fully demonstrates the synergistic effect and irreplaceability of the "nano-SiO2 + NCC" composite system.

[0068] Therefore, the high-dosage red mud-based engineering geological polymer composite material prepared by this invention can be widely used in building structure reinforcement, bridge deck repair, underground engineering seepage prevention, explosion protection and other fields. It is especially suitable for demonstration projects with clear requirements for green and low-carbon materials, and has good social and economic value and industrialization prospects.

Claims

1. A high-content red mud-based engineering geological polymer composite material, characterized in that, The engineering geological polymer composite material includes the following components: red mud, fly ash, slag, river sand, water, sodium silicate, PE fiber, and also contains nano-SiO2 dispersion and nanocrystalline cellulose.

2. The high-content red mud-based engineering geological polymer composite material according to claim 1, characterized in that, The components, by mass parts, are as follows: red mud 300-360 parts, fly ash 50-65 parts, slag 160-180 parts, river sand 160-180 parts, water 200-230 parts, sodium silicate 60-75 parts, PE fiber 8-12 parts, nano-SiO2 dispersion 15-30 parts, and nano-crystalline cellulose 1-5 parts.

3. The high-content red mud-based engineering geological polymer composite material according to claim 1, characterized in that, The red mud mentioned is Bayer process red mud with a specific surface area ≥450 m². 2 / kg; the slag is S95 grade slag; the fly ash is F grade fly ash.

4. The high-content red mud-based engineering geological polymer composite material according to claim 1, characterized in that, The PE fiber is ultra-high molecular weight polyethylene fiber, with a single filament length of 10-14 mm and a single filament diameter of 20-30 μm; the river sand is natural river sand with a particle size ≤600 μm.

5. The high-red-mud-based engineering geological polymer composite material according to claim 1, characterized in that, The nano-SiO2 is water-dispersible nano-silica with an average particle size of 20–50 nm and a solid content of 20%–40% in the nano-SiO2 dispersion; the nanocrystalline cellulose is prepared by acid hydrolysis and has a diameter of 5–20 nm and a length of 100–300 nm.

6. A method for preparing the high-content red mud-based engineering geological polymer composite material according to claim 1, characterized in that, Includes the following steps: (1) Mix sodium silicate powder with water, stir to dissolve, and obtain an alkaline activated solution. Cool and set aside. (2) Weigh the red mud, fly ash, slag and river sand according to the proportion, put them into the mixer and dry mix at low speed until they are evenly mixed to obtain dry mixture; (3) The nano-SiO2 dispersion was premixed with nanocrystalline cellulose and ultrasonically dispersed to obtain a composite modified suspension; (4) Add the alkaline activation solution obtained in step (1) and the suspension obtained in step (3) to the dry mixture one after the other, stir at low speed, and then stir at high speed. (5) During the high-speed mixing process, PE fibers are evenly sprinkled in batches. After the sprinkling is completed, high-speed mixing continues to obtain a uniform and stable red mud-based EGC slurry. (6) Pour the slurry into shape, vibrate to compact it, cover and cure for 24 hours, then demold and cure under standard curing conditions until the set age.

7. The preparation method according to claim 6, characterized in that, In step (2), the low-speed dry mixing conditions are a mixing speed of 120-180 r / min and a mixing time of 1.5-3 min.

8. The preparation method according to claim 6, characterized in that, In step (4), the low-speed stirring conditions are a stirring speed of 120-180 r / min and a stirring time of 1.5-3 min, while the high-speed stirring conditions are a stirring speed of 250-320 r / min and a stirring time of 3-7 min.

9. The preparation method according to claim 6, characterized in that, In step (5), the high-speed stirring conditions are a stirring speed of 250-320 r / min and a stirring time of 1-2 min.

10. The application of the high-content red mud-based engineering geological polymer composite material of claim 1 in engineering scenarios such as building structure reinforcement, crack repair, and impact protection.

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