A fly ash based high density geological composition, its preparation method and application in road engineering

Abstract

The application belongs to the technical field of geological compositions, and particularly relates to a fly ash-based high-density geological composition, a preparation method thereof and application thereof in road engineering. The fly ash-based high-density geological composition comprises the following components in mass fractions: fly ash 50-60 parts; slag 20-30 parts; metakaolin 7-12 parts; modified nano Al2O3 2-4 parts; modified polypropylene fiber 1.0-2.0 parts; silica ash 3-8 parts; alkali activator 30-40 parts; and water 15-20 parts. The application provides a fly ash-based geological composition which has normal-temperature bending strength, compressive strength and excellent freeze-thaw resistance.

Description

Technical Field

[0001] This invention belongs to the field of geological composition technology, specifically relating to a fly ash-based high-density geological composition, its preparation method, and its application in road engineering. Background Technology

[0002] Geopolymers are a class of inorganic cementitious materials made from aluminosilicate industrial solid wastes such as fly ash and slag, which form a three-dimensional network structure through depolymerization-condensation reactions under the action of alkaline activators. Due to their advantages such as high early strength, good durability, and low carbon emissions, they are considered a potential alternative to ordinary silicate cement and show broad application prospects in the field of road engineering.

[0003] Previous studies have shown that the particle size distribution of fly ash has a significant impact on the mechanical properties of geopolymer materials. Patent document CN104803619B discloses a geopolymer composition and its preparation method, which divides fly ash into three components based on average particle size, and uses fly ash with two or three different particle size distributions for blending. By optimizing the particle bulk density of the fly ash, the compressive strength of the prepared geopolymer material after 28 days of curing at room temperature is significantly improved, showing a clear advantage compared to fly ash systems with a single particle size distribution.

[0004] However, the aforementioned existing technologies primarily focus on the static compressive strength of geopolymer materials under normal temperature conditions, and their comprehensive performance evaluation in the specific application scenario of road engineering is insufficient. Road engineering materials must withstand repeated vehicle loads, drastic changes in ambient temperature, and moisture erosion during actual service. Freeze-thaw cycles are a key factor leading to the deterioration and even destruction of pavement materials. In cold regions, the pore water inside pavement materials undergoes repeated phase change and volume expansion during freeze-thaw cycles, resulting in the continuous accumulation of frost heave stress, leading to the initiation, propagation, and eventual structural failure of microcracks within the material. Furthermore, there is room for improvement in the room-temperature strength of geopolymer materials in existing technologies.

[0005] Therefore, there is an urgent need to develop a fly ash-based geological composition that combines strength with excellent freeze-thaw resistance, so that it can not only meet the mechanical performance requirements at room temperature in road engineering applications, but also resist the deterioration effects of harsh environmental factors such as freeze-thaw cycles, thereby extending the service life of road structures and reducing the total life cycle maintenance cost. Summary of the Invention

[0006] The purpose of this invention is to provide a fly ash-based high-density geological composition, its preparation method, and its application in road engineering, which has both room temperature strength and excellent freeze-thaw resistance.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A high-density geological composition based on fly ash, comprising the following components by mass parts: 50-60 parts fly ash; 20-30 parts slag; 7-12 parts metakaolin; 2-4 parts modified nano-Al2O3; 1.0-2.0 parts modified polypropylene fiber; 3-8 parts silica fume; 30-40 parts alkali activator; and 15-20 parts water.

[0008] Preferably, the preparation method of the modified nano-Al2O3 includes the following steps: (1) Preparation of silane-modified nano-Al2O3 powder; (2) Add silane-modified nano Al2O3 powder to toluene and disperse it by ultrasonication to obtain a uniform dispersion; under a nitrogen atmosphere, add isopropyl tris(dioctyl pyrophosphate) titanate to the dispersion, heat up and reflux the reaction. After the reaction is completed, cool down to room temperature to obtain the reaction system. (3) Add PEG-4000 solution dropwise to the reaction system, heat up, keep the temperature for reaction, cool naturally to room temperature after the reaction is completed, separate by centrifugation, wash the solid, vacuum dry, pulverize, and obtain modified nano Al2O3.

[0009] Preferably, in step (2), the temperature is raised to 103-107℃ and refluxed for 4-6 hours; in step (3), the temperature is raised to 60-62℃ and kept at that temperature for 1-3 hours.

[0010] Nano-Al2O3 can improve the strength of geopolymer samples, but nanoparticles are prone to agglomeration and have weak interfacial bonding with the matrix. Existing technologies modify them with silane coupling agents, but the improvement in performance is limited. This invention improves the compressive and flexural strength of the geopolymer by first amidling the hydroxyl groups on the surface of nano-Al2O3 with a silane coupling agent, followed by titanate grafting and PEG coating. The present invention introduces -NH2 functional groups by first amylating the hydroxyl groups on the surface of nano-Al2O3 with a silane coupling agent; then grafting isopropyl tris(dioctylpyrophosphate)titanate (NDZ-201) to introduce pyrophosphate groups; and finally physically coating with PEG-4000. The resulting bifunctional chemical bonds are as follows: -NH2 forms hydrogen bonds or covalent bonds with the matrix, and the pyrophosphate anion forms ionic coordination bonds with metal ions. At the same time, the pyrophosphate ester structure of the titanate has hydrolysis resistance stability in an alkaline environment, and the PEG coating layer provides physical barriers and steric hindrance, synergistically achieving uniform dispersion, stable existence, and strong interfacial bonding of nano-Al2O3 in a strongly alkaline geopolymer system.

[0011] Preferably, the method for preparing the modified polypropylene fiber includes the following steps: (1) Polypropylene, PP-g-GMA and antioxidant are melt-mixed and then extruded and granulated to obtain modified polypropylene masterbatch; (2) Modified polypropylene masterbatch is melt-spun, wound and thermally drawn to obtain modified polypropylene fiber.

[0012] Polypropylene fiber, commonly known as polypropylene fiber, can improve the freeze-thaw resistance of geological compositions. However, polypropylene fibers have low surface energy, lack polar groups on their molecular chains, are hydrophobic, and have poor adhesion to other components, significantly affecting the performance of polypropylene fiber-reinforced geological compositions. Existing technologies use polypropylene grafted with maleic anhydride for modification, but the improvement effect is not ideal. This invention uses PP-g-GMA to melt-graft modify polypropylene, which can significantly improve freeze-thaw resistance. Analysis shows that existing technologies using polypropylene grafted with maleic anhydride, although the introduced anhydride groups can increase polarity, are easily hydrolyzed in the strongly alkaline environment of the geological polymer to generate carboxylate groups, resulting in limited interfacial bonding strength. This invention uses PP-g-GMA to introduce epoxy groups. Under alkaline conditions, the epoxy groups open the ring to generate hydroxyl groups, which can covalently bond with the matrix and the -NH2 on the surface of modified nano-Al2O3 to form a stable chemical cross-linking network. At the same time, the epoxy groups have higher reactivity and stronger hydrolysis resistance, making it difficult to pull out the fiber after freeze-thaw and significantly reducing the compressive strength loss rate.

[0013] Preferably, the grafting rate of PP-g-GMA is 0.8-1.2 wt%.

[0014] Preferably, 80-90 parts by weight of polypropylene, 7-12 parts by weight of PP-g-GMA, 0.1-0.3 parts by weight of antioxidant 1010 and 0.1-0.3 parts by weight of antioxidant 168 are melt-mixed and then extruded and granulated.

[0015] Preferably, the modified polypropylene fiber has a diameter of 15-25 μm and a length of 6-12 mm.

[0016] Preferably, the fly ash comprises the following components in parts by weight: 20-30 parts of particle size D 50 Fine components of 2-5 μm; 50-60 parts with a particle size D 50 Medium-sized components of 15-30 μm and 10-20 parts by particle size D 50 It is a coarse component with a size of 40-80 μm.

[0017] In existing technologies, the flexural strength loss rate of geological compositions due to freeze-thaw cycles is higher than that of their compressive strength loss rate. This is because, compared to pressure, bending stress more easily expands the cracks caused by freezing pressure in the sample, which is a major problem that urgently needs to be improved. This invention classifies fly ash into three grades to achieve the densest packing. Based on this, modified nano-Al2O3 fills the nanoscale pores and carries -NH2 / phosphate ester groups. The epoxy groups on the surface of modified polypropylene fibers are chemically cross-linked with it to form a three-dimensional anchoring network of fibers and nanoparticles. This network effectively bridges cracks and disperses stress under bending stress, while the dense matrix reduces the intrusion of freezeable water, fundamentally solving the problem of more severe flexural deterioration of geological polymers.

[0018] The preparation method of the fly ash-based high-density geological composition includes the following steps: weighing fly ash, slag, metakaolin, modified nano-Al2O3 and silica fume according to the ratio, putting them into a mixer and dry mixing for 3-5 minutes until uniformly mixed to obtain a mixed dry material; adding the alkali activator mixed with water to the mixed dry material and wet mixing for 2-4 minutes, then adding the modified polypropylene fiber and continuing wet mixing for 3-5 minutes to obtain the fly ash-based high-density geological composition.

[0019] Application of the fly ash-based high-density geological composition in road engineering.

[0020] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention improves the compressive and flexural strength of geological compositions by first amifying the hydroxyl groups on the surface of nano-Al2O3 with a silane coupling agent, followed by titanate grafting and PEG coating.

[0021] 2. The present invention uses PP-g-GMA to melt-graft modify polypropylene, which can significantly improve its freeze resistance.

[0022] 3. The invention uses 20-30 parts of fly ash with a particle size D 50 Fine components of 2-5 μm; 50-60 parts with a particle size D 50 Medium-sized components of 15-30 μm and 10-20 parts by particle size D 50 It is a specific ratio of coarse components with a diameter of 40-80μm, which works synergistically with other components in the system, fundamentally solving the problem of more severe deterioration of the flexural strength of geopolymers. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] All raw materials used in the following embodiments of the present invention are commercially available products: The particle size of nano-Al2O3 is 15-30 nm.

[0025] The chemical name of the titanate coupling agent NDZ-201 is isopropyl tris(dioctylpyrophosphate) titanate.

[0026] The slag is granulated blast furnace slag powder with a specific surface area of ​​450-500 m². 2 / kg.

[0027] The specific surface area of ​​metakaolin is 800-900 m². 2 / kg.

[0028] The specific surface area of ​​silica fume is 15-25 m². 2 / g.

[0029] The alkali activator is a composite solution of water glass and sodium hydroxide, with a modulus (SiO2 / Na2O molar ratio) of 1.5 and a solid content of 40 wt%. The preparation method of the alkali activator is as follows: commercially available sodium water glass (Foshan Zhongfa Water Glass Factory, model ZF27-45B) is selected. Based on the target modulus of 1.5, the required amount of sodium hydroxide is calculated. Sodium hydroxide is added to the water glass, the stirring speed is controlled at 300 rpm, stirring for 30 min, and then allowed to stand for aging for 12 h to obtain the alkali activator.

[0030] PP-g-GMA model: PPG-2321, grafting rate 1.0%, Guangzhou Dongjin Plastics Technology Co., Ltd. Example 1

[0031] This embodiment provides a fly ash-based high-density geological composition, which, by mass parts, includes the following components: 53 parts fly ash; 24 parts slag; 10 parts metakaolin; 3 parts modified nano-Al2O3; 1.5 parts modified polypropylene fiber; 6 parts silica fume; 36 parts alkali activator; and 17 parts water.

[0032] The preparation method of the modified nano-Al2O3 includes the following steps: by mass parts, (1) Add 2.0 parts of KH-550 to 30 parts of anhydrous ethanol, stir until completely dissolved, add 10 parts of deionized water, adjust the pH to 4.5 with glacial acetic acid, and stir and hydrolyze for 45 min at room temperature (25℃) to obtain a hydrolyzing coupling agent solution; add 10.0 parts of nano-Al2O3 to 50 parts of anhydrous ethanol and sonicate: power 300W, frequency 20kHz, sonication time 20 min, and use an ice-water bath to control the temperature at 30℃ during sonication to prevent overheating, to obtain a nano-Al2O3 dispersion; in 2 The hydrolytic coupling agent solution was added dropwise to the nano-Al2O3 dispersion at a stirring speed of 1 drop / second. After the addition was complete, the temperature was raised to 75℃ and the reaction was refluxed under nitrogen protection for 7 hours. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged, and the supernatant was discarded. The solid was washed with anhydrous ethanol twice. The washed product was then vacuum dried under the following conditions: temperature 60℃, vacuum degree -0.09MPa, time 12 hours. The product was then pulverized to pass through a 200-mesh sieve to obtain silane-modified nano-Al2O3 powder. (2) 9.6 parts of silane-modified nano Al2O3 powder were added to 120 parts of toluene and ultrasonically dispersed for 15 min to obtain a uniform dispersion. Under a nitrogen atmosphere, 1.8 parts of isopropyltris(dioctylpyrophosphate)titanate were added to the dispersion, the temperature was raised to 105℃, and the reaction was refluxed for 5 h. After the reaction was completed, the temperature was lowered to room temperature to obtain the reaction system. (3) Dissolve 1.0 part of PEG-4000 in 30 parts of toluene to obtain a PEG-4000 solution. Add the PEG-4000 solution dropwise to the reaction system. Heat to 60℃ at 200 rpm and keep warm for 2 h. After the reaction is completed, cool naturally to room temperature and separate by centrifugation. Wash the solid once with anhydrous toluene and then twice with anhydrous ethanol. Dry under vacuum. Drying conditions: temperature 60℃, vacuum degree -0.09MPa, time 24 h. After drying, pulverize to pass through a 200-mesh sieve to obtain modified nano Al2O3.

[0033] The method for preparing the modified polypropylene fiber includes the following steps: (1) Based on the mass fraction, 85 parts of polypropylene, 9 parts of PP-g-GMA, 0.2 parts of antioxidant 1010 and 0.1 parts of antioxidant 168 were melt-mixed at 200℃ and then extruded and granulated to obtain modified polypropylene masterbatch. (2) The modified polypropylene masterbatch is melt-spun, wound and hot-drawn. The spinning temperature is 220℃ and the hot drawing is two-stage drawing: the first stage drawing temperature is 100℃ and the drawing ratio is 4 times, the second stage drawing temperature is 140℃ and the drawing ratio is 1.5 times. The diameter of the modified polypropylene fiber is 15-25μm and the length is 6-12mm, thus obtaining the modified polypropylene fiber.

[0034] The fly ash comprises the following components in parts by weight: 23 parts particle size D50 Fine fractions of 2-5 μm; 52 parts with a particle size D 50 Medium-sized components of 15-30 μm and 14 parts with particle size D 50 It is a coarse component with a size of 40-80 μm.

[0035] The preparation method of the fly ash-based high-density geological composition includes the following steps: weighing fly ash, slag, metakaolin, modified nano-Al2O3 and silica fume according to the ratio, putting them into a mixer and dry mixing for 5 minutes until uniformly mixed to obtain a mixed dry material; adding the alkali activator mixed with water to the mixed dry material and wet mixing for 4 minutes, then adding the modified polypropylene fiber and continuing wet mixing for 5 minutes to obtain the fly ash-based high-density geological composition. Example 2

[0036] The difference between this embodiment and Example 1 is that this embodiment is a fly ash-based high-density geological composition, comprising the following components by mass: 60 parts fly ash; 20 parts slag; 12 parts metakaolin; 2 parts modified nano-Al2O3; 2.0 parts modified polypropylene fiber; 3 parts silica fume; 38 parts alkali activator; and 18 parts water. All other conditions are the same as in Example 1.

[0037] Comparative Example 1 The difference between this comparative example and Example 1 is that the preparation method of the modified nano-Al2O3 includes the following steps: by mass parts, 2.0 parts of KH-550 were added to 30 parts of anhydrous ethanol and stirred until completely dissolved. 10 parts of deionized water were added, and the pH was adjusted to 4.5 with glacial acetic acid. The mixture was then stirred and hydrolyzed at room temperature (25°C) for 45 minutes to obtain a hydrolyzed coupling agent solution. 10.0 parts of nano-Al₂O₃ were added to 50 parts of anhydrous ethanol and sonicated at 300W power, 20kHz frequency, and for 20 minutes. During sonication, an ice-water bath was used to control the temperature at 25°C to prevent overheating, resulting in a nano-Al₂O₃ dispersion. The hydrolytic coupling agent solution was added dropwise to the nano-Al2O3 dispersion at a stirring speed of 1 drop / second. After the addition was complete, the temperature was raised to 75℃ and refluxed under nitrogen protection for 7 hours. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged, and the supernatant was discarded. The solid was washed with anhydrous ethanol, and the washing was repeated twice. The washed product was then vacuum dried under the following conditions: temperature 60℃, vacuum degree -0.09MPa, time 12 hours. The product was then pulverized to pass through a 200-mesh sieve to obtain modified nano-Al2O3.

[0038] Comparative Example 2 The difference between this comparative example and Example 1 is that the preparation method of the modified nano-Al2O3 includes the following steps: by mass parts, (1) Add 2.0 parts of KH-550 to 30 parts of anhydrous ethanol, stir until completely dissolved, add 10 parts of deionized water, adjust the pH to 4.5 with glacial acetic acid, and stir and hydrolyze for 45 min at room temperature (25℃) to obtain a hydrolyzing coupling agent solution; add 10.0 parts of nano-Al2O3 to 50 parts of anhydrous ethanol and sonicate: power 300W, frequency 20kHz, sonication time 20 min, use an ice-water bath to control the temperature at 25℃ during sonication to prevent overheating, to obtain a nano-Al2O3 dispersion; in 2 The hydrolytic coupling agent solution was added dropwise to the nano-Al2O3 dispersion at a stirring speed of 1 drop / second. After the addition was complete, the temperature was raised to 75℃ and the reaction was refluxed under nitrogen protection for 7 hours. After the reaction was completed, the mixture was naturally cooled to room temperature, centrifuged, and the supernatant was discarded. The solid was washed with anhydrous ethanol twice. The washed product was then vacuum dried under the following conditions: temperature 60℃, vacuum degree -0.09MPa, time 12 hours. The product was then pulverized to pass through a 200-mesh sieve to obtain silane-modified nano-Al2O3 powder. (2) 9.6 parts of silane-modified nano Al2O3 powder were added to 120 parts of toluene and ultrasonically dispersed for 15 min to obtain a uniform dispersion. Under a nitrogen atmosphere, 1.8 parts of isopropyltris(dioctylpyrophosphate)titanate were added to the dispersion, the temperature was raised to 105℃, and the reaction was refluxed for 5 h. After the reaction was completed, the temperature was lowered to room temperature, centrifuged, and the solid was washed once with anhydrous toluene and then twice with anhydrous ethanol. The solid was then vacuum dried under the following conditions: temperature 60℃, vacuum degree -0.09MPa, time 24 h. After drying, the solid was pulverized to pass through a 200-mesh sieve to obtain modified nano Al2O3.

[0039] Comparative Example 3 The difference between this comparative example and Example 1 is that the preparation method of the modified polypropylene fiber includes the following steps: (1) Based on the mass fraction, 85 parts of polypropylene, 9 parts of polypropylene grafted with maleic anhydride (Arkema PP 18728), 0.2 parts of antioxidant 1010 and 0.1 parts of antioxidant 168 were melt-mixed at 200℃ and then extruded and granulated to obtain modified polypropylene masterbatch. (2) The modified polypropylene masterbatch is melt-spun, wound and hot-drawn. The spinning temperature is 220℃ and the hot drawing is two-stage drawing: the first stage drawing temperature is 100℃ and the drawing ratio is 4 times, the second stage drawing temperature is 140℃ and the drawing ratio is 1.5 times. The diameter of the modified polypropylene fiber is 15-25μm and the length is 6-12mm, thus obtaining the modified polypropylene fiber.

[0040] Comparative Example 4 The difference between this comparative example and Example 1 is that 9 parts of PP-g-GMA were replaced with 5 parts of PP-g-GMA.

[0041] Comparative Example 5 The difference between this comparative example and Example 1 is that 9 parts of PP-g-GMA were replaced with 15 parts of PP-g-GMA.

[0042] Comparative Example 6 The difference between this comparative example and Example 1 is that the fly ash comprises the following components in parts by mass: 15 parts particle size D 50 Fine components of 2-5 μm; 65 parts with a particle size D 50 Medium-sized components of 15-30 μm and 5 parts with particle size D 50 It is a coarse component with a size of 40-80 μm.

[0043] Comparative Example 7 The difference between this comparative example and Example 1 is that the fly ash comprises the following components in parts by mass: 35 parts particle size D 50 Fine components of 2-5 μm; 40 parts with a particle size D 50 Medium-sized components of 15-30 μm and 25 parts with a particle size D 50 It is a coarse component with a size of 40-80 μm.

[0044] Comparative Example 8 This comparative example is the product prepared in Example 7 of a geopolymer composition and its preparation method disclosed in CN104803619B.

[0045] Performance testing 1. Room temperature compressive strength: After the compositions of Examples 1-2 and Comparative Examples 1-8 were molded at a temperature of 25°C and a relative humidity of 55%, they were transferred to a standard curing chamber and placed under standard curing conditions of 20°C and 90% relative humidity for 28 days to obtain samples cured for 28 days. The 28-day compressive strength and compressive strength were determined in accordance with GB / T17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)".

[0046] 2. After 28 days of curing, the samples were immersed in water at 20℃ for 5 days. One freeze-thaw cycle consisted of freezing at -20℃ for 5 hours and thawing in water at 20℃ for 3 hours. After 100 freeze-thaw cycles, the samples were restored to room temperature. The compressive strength and flexural strength of the samples were measured. The strength loss rate of the samples after freeze-thaw cycles was calculated as follows: (Compressive strength at room temperature - Compressive strength after freeze-thaw cycles) ÷ Compressive strength at room temperature × 100%. The flexural strength loss rate of the samples after freeze-thaw cycles was calculated as follows: (Flexural strength at room temperature - Flexural strength after freeze-thaw cycles) ÷ Flexural strength at room temperature × 100%.

[0047] The test results are shown in Table 1.

[0048] Table 1 Test Results As shown in Table 1, the geological compositions of Examples 1-2 have excellent comprehensive properties, with compressive strength of 51.9-53.6 MPa, flexural strength of 8.3-8.5 MPa, freeze-thaw compressive strength loss rate of 18.0-18.3%, and freeze-thaw flexural strength loss rate of 20.3-20.6%.

[0049] Combining Example 1 and Comparative Examples 1-2, it can be seen that in Comparative Example 1, only silane modification was performed when preparing modified nano-Al2O3, without titanate grafting and PEG coating. In Comparative Example 2, only silane modification and titanate grafting were performed when preparing modified nano-Al2O3, without PEG coating. This shows that in the process of preparing fly ash-based high-density geological compositions, the three-step modification of nano-Al2O3 can significantly improve the mechanical properties and freeze-thaw durability of the prepared compositions.

[0050] Based on Examples 1 and Comparative Examples 3-5, and referring to Table 1, it can be seen that in Comparative Example 3, the modified polypropylene fiber prepared by grafting maleic anhydride onto polypropylene resulted in a decrease in the properties of the resulting composition. In Comparative Example 4, the amount of PP-g-GMA was reduced to 5 parts, while in Comparative Example 5, the amount of PP-g-GMA was increased to 15 parts. The mechanical properties and freeze-thaw durability of the compositions prepared in both examples deteriorated to varying degrees. The epoxy groups introduced by PP-g-GMA are polar functional groups. During melt blending and spinning, when the amount is increased to 15 parts, excessive epoxy groups may undergo hydrogen bonding or weak interactions, resulting in excessively high surface polarity of the fibers. Excessive surface polarity may cause the fibers to attract each other during dispersion, forming fiber bundles or fiber agglomerates, making it difficult to disperse uniformly in the matrix. This demonstrates that in the preparation of fly ash-based high-density geological compositions, the use of PP-g-GMA modified polypropylene fibers, and the control of the amount of PP-g-GMA and modified polypropylene fibers within a reasonable range, can significantly improve the interfacial bonding strength and freeze-thaw resistance of the composition, and reduce the strength loss rate after freeze-thaw cycles.

[0051] Based on Example 1 and Comparative Examples 6-7, and in conjunction with Table 1, it can be seen that by controlling the amount of fly ash and the three-stage gradation within a reasonable range during the preparation of fly ash-based high-density geological compositions, the densest packing of fly ash can be achieved, reducing matrix porosity and significantly improving the density, mechanical properties, and freeze-thaw durability of the composition.

[0052] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fly ash-based high-density geological composition, characterized in that, By weight, it includes the following components: 50-60 parts fly ash; 20-30 parts slag; 7-12 parts metakaolin; 2-4 parts modified nano-Al2O3; The modified polypropylene fiber comprises 1.0-2.0 parts; silica fume 3-8 parts; alkali activator 30-40 parts; and water 15-20 parts. The modified nano-Al2O3 is prepared by reacting nano-Al2O3 sequentially with silane coupling agent, isopropyltris(dioctylpyrophosphoryloxy)titanate and polyethylene glycol. The modified polypropylene fiber is prepared by extruding and granulating polypropylene, PP-g-GMA and antioxidant after melt mixing, followed by melt spinning, winding and thermal traction.

2. The fly ash-based high-density geological composition according to claim 1, characterized in that, The preparation method of the modified nano-Al2O3 includes the following steps: (1) Silane-modified nano-Al2O3 powder was prepared using silane coupling agent and nano-Al2O3; (2) Add silane-modified nano-Al2O3 powder to toluene to obtain a dispersion; under a nitrogen atmosphere, add isopropyl tris(dioctylpyrophosphate) titanate to the dispersion, heat up, reflux reaction, and after the reaction is completed, cool down to obtain the reaction system; (3) Add polyethylene glycol solution dropwise to the reaction system, heat up, keep the reaction at the temperature, cool after the reaction is completed, centrifuge, wash, vacuum dry, and pulverize to obtain modified nano Al2O3.

3. The fly ash-based high-density geological composition according to claim 2, characterized in that, In step (2), the temperature is raised to 103-107℃ and refluxed for 4-6 hours; in step (3), the temperature is raised to 60-62℃ and kept at that temperature for 1-3 hours.

4. The fly ash-based high-density geological composition according to claim 1, characterized in that, The method for preparing the modified polypropylene fiber includes the following steps: (1) Polypropylene, PP-g-GMA and antioxidant are melt-mixed and then extruded and granulated to obtain modified polypropylene masterbatch; (2) Modified polypropylene masterbatch is melt-spun, wound and thermally drawn to obtain modified polypropylene fiber.

5. The fly ash-based high-density geological composition according to claim 4, characterized in that, The grafting rate of PP-g-GMA is 0.8-1.2 wt%.

6. The fly ash-based high-density geological composition according to claim 4, characterized in that, By mass, 80-90 parts of polypropylene, 7-12 parts of PP-g-GMA, 0.1-0.3 parts of antioxidant 1010 and 0.1-0.3 parts of antioxidant 168 are melt-mixed and then extruded into granules.

7. The fly ash-based high-density geological composition according to claim 4, characterized in that, The modified polypropylene fibers have a diameter of 15-25μm and a length of 6-12mm.

8. The fly ash-based high-density geological composition according to claim 1, characterized in that, The fly ash comprises the following components in parts by weight: 20-30 parts particle size D 50 Fine components of 2-5 μm; 50-60 parts with a particle size D 50 Medium-sized components of 15-30 μm and 10-20 parts by particle size D 50 It is a coarse component with a size of 40-80 μm.

9. A method for preparing a fly ash-based high-density geological composition according to any one of claims 1-8, characterized in that, The process includes the following steps: Weigh fly ash, slag, metakaolin, modified nano-Al2O3, and silica fume according to the specified ratio and mix them evenly to obtain a mixed dry material; Add the alkali activator mixed with water to the mixed dry material and wet mix; then add the modified polypropylene fiber and continue wet mixing to obtain the fly ash-based high-density geological composition.

10. The application of the fly ash-based high-density geological composition according to any one of claims 1-9 in road engineering.

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