Green low-carbon cementitious material for roadbed and preparation method thereof

Abstract

The application discloses a kind of green low-carbon cementitious material for roadbed and a preparation method thereof, and belongs to the technical field of low-carbon cementitious material, and its composition is as follows by weight fraction, including: slag powder 40-50 parts, self-made functional fly ash 25-35 parts, steel slag powder 15-25 parts, desulfurization gypsum 8-15 parts, modified basalt fiber 2-4 parts.The self-made functional fly ash in the cementitious material of the present application breaks the surface inertness of fly ash through alkali activation, and a large amount of solid waste is used, which is widely used in roadbed materials, not only can solve the environmental problems caused by the accumulation of these solid wastes, but also conforms to the strategic development direction of green, recycling and sustainability, and has great market potential.

Description

Technical Field

[0001] This invention belongs to the field of low-carbon cementitious materials technology, specifically, it relates to a green low-carbon cementitious material for roadbeds and its preparation method. Background Technology

[0002] Traditional road concrete primarily uses silicate cement as the main cementitious material. The extensive use of silicate cement not only significantly increases the production cost of road concrete but also leads to substantial carbon emissions, hindering the green and sustainable development of the building materials industry. Furthermore, the accumulation of various industrial solid wastes also causes considerable environmental problems. Currently, efforts are underway to partially or completely replace natural soil and aggregate materials and cementitious materials used in road base courses with industrial solid waste, which has become an effective way to treat large quantities of solid waste on a large scale.

[0003] The prior art includes Chinese invention patent application number CN202510000303.1, which discloses a low-carbon cementitious material for preparing highway subgrade and its preparation method, comprising the following steps: Step S1: Weigh 100-120 parts by weight of mineral powder and add it to 450-500 parts by weight of anhydrous ethanol, and disperse it ultrasonically for 1-2 hours to obtain a suspension; add 20-25 parts by weight of DL-alanine to the suspension, heat it to 75-80℃ and stir for 0.5-1 hours, and obtain aminated mineral powder after filtration, washing and drying; Step S2: Add 40-70 parts by weight of aminated mineral powder, 10-30 parts by weight of fly ash and 5-20 parts by weight of gypsum to 100-140 parts by weight of deionized water for a first stirring treatment, and then add 2-15 parts by weight of red mud for a second stirring treatment to obtain the low-carbon cementitious material for preparing highway subgrade.

[0004] The aforementioned existing technologies utilize a significant amount of solid waste, aligning with the strategic development direction of green, circular, and sustainable development. Furthermore, under the basic mechanical performance evaluation system, namely compressive strength and flexural strength, they exhibit relatively excellent performance and can barely handle highway subgrades. However, when applied to more complex subgrade applications, the durability and impact resistance of these existing technologies have considerable room for improvement when facing subgrades with more complex comprehensive working conditions. Moreover, as a subgrade material, superior freeze-thaw resistance and impact resistance would allow for a longer service life.

[0005] Therefore, in order to fill the technological gap in the market, this application provides a green and low-carbon cementitious material for roadbeds and its preparation method to solve the above-mentioned technical problems. Summary of the Invention

[0006] To address the deficiencies in the aforementioned technical solutions, the present invention aims to provide a green and low-carbon cementitious material for roadbeds and its preparation method. This objective can be achieved through the following technical solution: A green and low-carbon cementitious material for roadbeds, by weight, comprises the following components: 40-50 parts slag powder, 25-35 parts self-made functionalized fly ash, 15-25 parts steel slag powder, 8-15 parts desulfurized gypsum, and 2-4 parts modified basalt fiber.

[0007] The slag powder is S95 grade granulated blast furnace slag powder;

[0008] The steel slag powder is a powder obtained by grinding steel slag using a ball mill, and the specific surface area of ​​the steel slag powder is 450-650 m². 2 / kg, alkalinity greater than 1.8;

[0009] The specific surface area of ​​the desulfurized gypsum is ≥450m². 2 / kg;

[0010] The P2O5 content of the desulfurized gypsum is 0.6–0.8 wt%.

[0011] The desulfurized gypsum meets the requirements of GB / T23456-2009 standard.

[0012] The modified basalt fiber is prepared as follows: Basalt fiber is placed in a reaction vessel; sodium hydroxide aqueous solution is added to completely submerge the fiber; the mixture is stirred at low speed and heated to 80°C, and reacted at a constant temperature for 2 hours; after the reaction is completed, heating is stopped, the alkaline solution is discharged, and the fiber is repeatedly rinsed with deionized water until the pH of the washing water is 7.0±0.2; the washed fiber is dried by forced air drying to obtain surface-activated dry basalt fiber; the dried activated basalt fiber is then immersed in sodium alginate aqueous solution; the mixture is stirred at low speed at room temperature. After stirring for 1 hour, the fibers were removed and centrifuged to remove excess sodium alginate solution, resulting in wet fibers containing sodium alginate solution. These fibers were then immersed in calcium chloride solution and stirred continuously at a constant temperature of 25°C for 4 hours. After the reaction was complete, the fibers were removed, preliminarily drained, and then thoroughly rinsed 3-5 times with a large amount of deionized water until no chloride ion precipitate was detected in the wash water using silver nitrate solution. Finally, the washed fibers were centrifuged to remove water and dried to obtain modified basalt fibers.

[0013] Furthermore, the concentration of the sodium hydroxide aqueous solution is 1.0 mol / L;

[0014] Furthermore, the concentration of the sodium alginate aqueous solution is 2.0% (w / v);

[0015] Furthermore, the concentration of the calcium chloride aqueous solution is 2.0% (w / v).

[0016] The method for preparing the self-made functionalized fly ash is as follows: Fly ash and sodium hydroxide particles are placed in a mortar and ground thoroughly. The mixture is then transferred to a crucible and placed in a muffle furnace for calcination for 1 hour. After cooling, the mixture is removed, ground finely, and passed through a 200-mesh sieve. It is then repeatedly washed with a large amount of deionized water until the pH of the filtrate is neutral. The final product is then dried in a 105°C oven for 12 hours to obtain alkali-activated fly ash. The prepared alkali-activated fly ash is placed in a reaction vessel, deionized water is added, and the mixture is stirred to form a uniform suspension. The temperature is maintained at 90°C. MgCl2 solution and NaOH solution are added dropwise. After the addition is complete, the temperature is maintained at 90°C for another 90 minutes. The product is then sieved. The mixture was filtered and washed with a large amount of deionized water until neutral, then dried at 105℃ for 12 hours to obtain Mg(OH)2-coated modified fly ash. The prepared Mg(OH)2-coated fly ash was placed in a high-speed heating mixer and preheated to 110℃ at 1000 rpm. N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane was uniformly sprayed into the high-speed rotating powder through an atomizing nozzle. High-speed mixing was continued at 110℃ for 20 minutes to allow the methoxy end of N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane to undergo a complete de-alcoholization condensation reaction with the hydroxyl groups on the surface of Mg(OH)2. Finally, the mixture was cooled to room temperature and discharged to obtain the final component, self-made functionalized fly ash.

[0017] Furthermore, the calcination temperature of the muffle furnace is 700 degrees Celsius.

[0018] Furthermore, in the preparation process of the self-made functionalized fly ash, the MgCl2 solution and NaOH solution need to be added slowly and synchronously to the suspension, and the pH value of the reaction system is constantly fine-tuned with dilute hydrochloric acid or dilute NaOH during the addition to keep it at 10.

[0019] A green and low-carbon cementitious material for roadbeds and its preparation method: self-made functionalized fly ash, slag powder, steel slag powder and desulfurized gypsum are added to a dry powder mixer according to the specified ratio and stirred at low speed for 3-5 minutes to ensure that they are fully mixed and uniform; finally, modified basalt fiber is added to the mixer and stirred at low speed for another 2-3 minutes to ensure that the fiber is evenly dispersed in the powder and to avoid clumping, thus obtaining a green and low-carbon cementitious material for roadbeds.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. The modified basalt fiber in the cementitious material of this application, through sodium alginate and calcium chloride, forms a strong calcium alginate cementitious layer on the basalt fiber, which transforms the originally hydrophobic and inert fiber surface into a fiber surface rich in carboxyl and hydroxyl groups, greatly improving the dispersibility of basalt fiber in cementitious material, preventing fiber agglomeration, and enhancing the microstructural strength of the prepared roadbed material.

[0022] 2. The self-made functionalized fly ash in the cementitious material of this application breaks the surface inertness of fly ash through alkali activation, and coats its surface with a layer of Mg(OH)2. It is also grafted with N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, which has a propyl group and a double amino group at its end. The two amino groups are connected by a relatively flexible ethylene, which allows the two amino groups to rotate and stretch to a certain extent. When the interface is subjected to shear stress, it can dissipate some energy through the torsion and deformation of its own molecular chains, thereby making the cementitious material have better toughness.

[0023] 3. The modified basalt fiber in the cementitious material of this application has carboxyl and hydroxyl groups on its surface, and the self-made functionalized fly ash has hydroxyl and amino groups on its surface. Under the action of water molecules, a multi-dimensional hydrogen bond network with various strong and weak hydrogen bonds is formed at the interface between the micro-fiber and fly ash. When the material is subjected to stress and micro-cracks are generated, a large number of hydrogen bonds can efficiently dissipate the crack propagation energy. This makes the fracture toughness, impact resistance and fatigue life of the material more excellent, and it is more suitable for application in roadbed materials.

[0024] 4. The cementitious material of this application, as a roadbed material, contains a large number of hydroxyl and carboxyl groups in its components. During application, it will strongly combine with pore water molecules through hydrogen bonding, converting most of the free water into bound water. This greatly reduces the freezing point of pore water and inhibits the formation of destructive ice crystals. This allows the roadbed material with the cementitious material of this application to maintain structural integrity and stable performance even under repeated freeze-thaw cycles, exhibiting excellent freeze-thaw resistance and thus excellent durability.

[0025] 5. The cementitious material of this application utilizes a large amount of solid waste. Applying it to roadbed materials, which are also widely used, can not only solve the environmental problems caused by the accumulation of these solid wastes, but also make good use of them. This is in line with the strategic development direction of green, circular and sustainable development and has huge market potential. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The illustrative embodiments and descriptions of this invention are for explanation only and are not intended to limit the invention. Furthermore, regarding numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0028] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0029] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0030] In the following examples, "parts" refers to parts by weight.

[0031] Example 1

[0032] A green and low-carbon cementitious material for roadbeds, by weight, comprises the following: 40 parts slag powder, 25 parts self-made functionalized fly ash, 15 parts steel slag powder, 8 parts desulfurized gypsum, and 2 parts modified basalt fiber.

[0033] The slag powder is S95 grade granulated blast furnace slag powder;

[0034] The steel slag powder is a powder obtained by grinding steel slag using a ball mill, and the specific surface area of ​​the steel slag powder is 450-650 m². 2 / kg, alkalinity greater than 1.8;

[0035] The specific surface area of ​​the desulfurized gypsum is ≥450m². 2 / kg; the P2O5 content of the desulfurized gypsum is 0.6-0.8 wt%;

[0036] In specific applications, the desulfurized gypsum meets the requirements of GB / T23456-2018 standard.

[0037] The modified basalt fiber is prepared as follows: 50g of basalt fiber is weighed and placed in a reaction vessel; 400mL of 1.0mol / L sodium hydroxide aqueous solution is added to ensure complete immersion of the fiber; the mixture is stirred at a low speed of 60rpm and heated to 80℃, and reacted at a constant temperature for 2 hours; after the reaction is completed, heating is stopped, the alkaline solution is discharged, and the fiber is repeatedly rinsed with deionized water until the pH of the washing water is 7.0±0.2; the washed fiber is transferred to an oven and dried at 80℃ for 12 hours to obtain the surface-activated dried basalt fiber.

[0038] 50g of dried activated basalt fiber was immersed in 1L of a 2.0% (w / v) sodium alginate aqueous solution. The solution was stirred at a low speed of 30 rpm for 1 hour at room temperature to ensure all fibers were fully and evenly wetted. The fibers were then removed and centrifuged to remove excess sodium alginate solution, allowing each 50g of basalt fiber to absorb 50g of sodium alginate solution, bringing the total fiber weight to 100g. This 100g wet fiber solution containing sodium alginate was immediately immersed in 2L of a 2.0% (w / v) calcium chloride aqueous solution. The solution was stirred continuously at 60 rpm for 4 hours at a constant temperature of 25°C. During this process, the sodium alginate on the fiber surface reacted with Ca²⁺ to form a water-insoluble calcium alginate gel layer.

[0039] After the reaction is complete, the fibers are taken out and preliminarily drained. Then, the cross-linked fibers are thoroughly rinsed 3-5 times with a large amount of deionized water until no chloride ion precipitate is detected in the washing water using silver nitrate solution. Finally, the washed fibers are centrifuged to remove water and placed in a vacuum oven at 60°C for 24 hours to dry, thus obtaining modified basalt fibers.

[0040] In specific implementation, the basalt fiber has a single filament diameter of 9μm to 15μm and a length of 2cm to 4cm.

[0041] The method for preparing the self-made functionalized fly ash is as follows: Weigh 100g of fly ash and 80g of sodium hydroxide granules, place them in a mortar, grind and mix them thoroughly, transfer the uniformly mixed powder to a high-temperature resistant ceramic crucible, place it in a muffle furnace, and calcine it at 700℃ for 1 hour; after the mixture cools, take it out, grind it finely with a grinder and pass it through a 200-mesh sieve; then wash it repeatedly with a large amount of deionized water until the pH of the filtrate is neutral, and then place the final product in a 105℃ oven to dry for 12 hours, thus obtaining alkali-activated fly ash;

[0042] Take 50g of the prepared alkali-activated fly ash; place it in a reaction vessel equipped with a stirrer and a constant temperature jacket, add 2000ml of deionized water, and form a uniform suspension under stirring at 300rpm; heat the fly ash suspension in the reaction vessel and keep it at 90℃; add a total of 508ml of 0.4mol / L MgCl2 solution and 400ml of 0.6mol / L NaOH solution dropwise over 30min; during the preparation process, the MgCl2 solution and NaOH solution need to be added slowly and synchronously to the suspension, and the pH value of the reaction system should be continuously finely adjusted with dilute hydrochloric acid or dilute NaOH to keep it at 10; after the addition is completed, maintain the constant temperature of 90℃ for another 90min; then filter the product after the reaction and wash it with a large amount of deionized water until neutral, and then dry it at 105℃ for 12 hours to obtain Mg(OH)2-coated modified fly ash;

[0043] The prepared Mg(OH)2-coated fly ash was placed in a high-speed heating mixer and preheated to 110°C at 1000 rpm. N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane was uniformly sprayed into the high-speed rotating powder through an atomizing nozzle. The mixture was continued to be mixed at high speed at 110°C for 20 minutes to allow the methoxy end of N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane to undergo a complete de-alcoholization condensation reaction with the hydroxyl groups on the surface of Mg(OH)2. Finally, the mixture was cooled to room temperature and discharged to obtain the final component, the self-made functionalized fly ash.

[0044] In practice, the N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane was purchased from Hubei Xinlantian New Materials Co., Ltd.

[0045] A method for preparing a green and low-carbon cementitious material for roadbeds: self-made functionalized fly ash, slag powder, steel slag powder, and desulfurized gypsum are added to a dry powder mixer according to the specified ratio and stirred at low speed for 3-5 minutes to ensure thorough and uniform mixing; finally, modified basalt fibers are added to the mixer and stirred at low speed for another 2-3 minutes to ensure that the fibers are evenly dispersed in the powder and to avoid clumping, thus obtaining a green and low-carbon cementitious material for roadbeds.

[0046] Example 2

[0047] A green and low-carbon cementitious material for roadbeds, by weight, comprises the following: 42 parts slag powder, 27 parts self-made functionalized fly ash, 17 parts steel slag powder, 9 parts desulfurized gypsum, and 3 parts modified basalt fiber.

[0048] In Example 2, the preparation methods for self-made functionalized fly ash, modified basalt fiber, and green low-carbon cementitious materials for roadbed are all the same as those in Example 1.

[0049] Example 3

[0050] A green and low-carbon cementitious material for roadbeds, by weight, comprises the following: 45 parts slag powder, 29 parts self-made functionalized fly ash, 19 parts steel slag powder, 10 parts desulfurized gypsum, and 3 parts modified basalt fiber.

[0051] In Example 3, the preparation methods for self-made functionalized fly ash, modified basalt fiber, and green low-carbon cementitious materials for roadbed are all the same as those in Example 1.

[0052] Example 4

[0053] A green and low-carbon cementitious material for roadbeds, by weight, comprises the following: 48 parts slag powder, 32 parts self-made functionalized fly ash, 22 parts steel slag powder, 12 parts desulfurized gypsum, and 4 parts modified basalt fiber.

[0054] In Example 4, the preparation methods for self-made functionalized fly ash, modified basalt fiber, and green low-carbon cementitious materials for roadbed are all the same as those in Example 1.

[0055] Example 5

[0056] A green and low-carbon cementitious material for roadbeds, by weight, comprises the following: 50 parts slag powder, 35 parts self-made functionalized fly ash, 25 parts steel slag powder, 15 parts desulfurized gypsum, and 4 parts modified basalt fiber.

[0057] In Example 5, the preparation methods for self-made functionalized fly ash, modified basalt fiber, and green low-carbon cementitious materials for roadbed are all the same as those in Example 1.

[0058] Comparative Example 1

[0059] A green and low-carbon cementitious material for roadbeds, by weight, comprises the following: 48 parts slag powder, 32 parts self-made functionalized fly ash, 22 parts steel slag powder, 12 parts desulfurized gypsum, and 4 parts basalt fiber.

[0060] The difference between Comparative Example 1 and Example 4 is that the modification operation on basalt fiber was omitted, and the commercially available product was directly applied to the green low-carbon cementitious material for roadbed.

[0061] Comparative Example 2

[0062] A green and low-carbon cementitious material for roadbeds, by weight, comprises the following: 48 parts slag powder, 32 parts fly ash, 22 parts steel slag powder, 12 parts desulfurized gypsum, and 4 parts modified basalt fiber.

[0063] The difference between Comparative Example 2 and Example 4 is that the functional modification of fly ash was omitted, and commercially available fly ash products were directly applied to green and low-carbon cementitious materials for roadbeds.

[0064] Comparative Example 3

[0065] A green and low-carbon cementitious material for roadbeds, by weight, comprises the following: 48 parts slag powder, 32 parts fly ash, 22 parts steel slag powder, 12 parts desulfurized gypsum, and 4 parts basalt fiber.

[0066] The difference between Comparative Example 2 and Example 4 is that the functional modification of fly ash and the modification of basalt fiber were omitted. Instead, the corresponding commercially available products were directly applied to green and low-carbon cementitious materials for roadbeds.

[0067] Comparative Example 4

[0068] A green and low-carbon cementitious material for roadbeds, by weight, comprises the following: 48 parts slag powder, self-made functionalized fly ash, 22 parts steel slag powder, 12 parts desulfurized gypsum, and 4 parts modified basalt fiber.

[0069] The difference between Comparative Example 4 and Example 4 is that, in the functional modification of fly ash, the silane coupling agent sprayed from the atomizing nozzle is an equal amount of γ-aminopropyltriethoxysilane.

[0070] Comparative Example 5

[0071] A green and low-carbon cementitious material for roadbeds, by weight, comprises the following: 48 parts slag powder, self-made functionalized fly ash, 22 parts steel slag powder, 12 parts desulfurized gypsum, and 4 parts modified basalt fiber.

[0072] The difference between Comparative Example 4 and Example 4 is that, in the functional modification of fly ash, the operation of spraying silane coupling agent from the atomizing nozzle was not performed. Instead, the modified fly ash coated with Mg(OH)2 was directly used in the green low-carbon cementitious material for roadbed.

[0073] The concrete formula used in the experiment, by weight, includes: 100 parts cementitious material, 135 parts fine aggregate, 195 parts coarse aggregate, 1.5 parts polycarboxylate superplasticizer, and 32 parts water; wherein the coarse aggregate is 5-15mm continuously graded crushed stone; and the fine aggregate is manufactured sand.

[0074] The concrete preparation method for the experiment involved placing the cementitious materials prepared in Examples 1-5 and Comparative Examples 1-5 into a mixer, adding fine and coarse aggregates together, and mixing slowly for 3-5 minutes to ensure that the surfaces of the coarse and fine aggregates were uniformly coated with the cementitious material. Subsequently, polycarboxylate superplasticizer was dissolved in water, and the mixer was turned on. The polycarboxylate superplasticizer aqueous solution was slowly and evenly added to the mixture. After all the mixture was added, it was quickly mixed for 3-5 minutes until a uniform, non-segregated, and well-flowing concrete mixture was formed. The mixture was then poured into a test mold, vibrated to compact it, and then cured according to standard. After curing, the following performance tests were performed.

[0075] Test case

[0076] Compressive strength test: The compressive strength of the prepared test concrete was tested in accordance with the "Standard for Test Method of Performance of Ordinary Concrete Mixtures", and the 7-day and 28-day compressive strengths were calculated.

[0077] Freeze-thaw resistance test: Refer to the slow freezing test conditions in standard GB / T 50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete". After 75 cycles of freeze-thaw, retest the compressive strength and record the compressive strength retention rate.

[0078] Impact resistance test: Following ACI 544.2R-89, the impact compression test method for concrete was used, employing a drop hammer impact test apparatus. The test specimen was a standard specimen (Φ150×64mm) cured for 28 days. The impact hammer weighed 4.5kg, the drop height was 457mm, the diameter of the force transmission ball was 64mm, and the distance between the four baffles and the specimen was 5mm. During the test, the impact hammer fell freely, and the number of initial impacts (n1) at which the first crack appeared was recorded. The test continued; after the initial crack, the specimen expanded in volume. When the specimen came into contact with any three of the four baffles, it was considered to have failed, and the number of failure impacts (n2) was recorded.

[0079] The results of various performance tests are shown in Table 1:

[0080] Table 1:

[0081]

[0082] Comprehensive performance analysis: Comparative Example 3, using unmodified basalt fiber and fly ash, exhibited the worst performance in all aspects, including compressive strength, freeze-thaw resistance, and impact resistance. Comparative Examples 1 and 2 showed certain performance advantages over Comparative Examples 3 and 4 in terms of impact resistance and freeze-thaw resistance. This may be because the modified basalt fiber in the cementitious material of this application, through the use of sodium alginate and calcium chloride, forms a strong calcium alginate cementitious layer on the basalt fiber, transforming the originally hydrophobic and inert fiber surface into a fiber surface rich in carboxyl and hydroxyl groups. This significantly improves the dispersibility of the basalt fiber in the cementitious material. This process prevents fiber agglomeration and enhances the microstructural strength of the prepared roadbed material. The self-made functionalized fly ash, through alkali activation, breaks down the surface inertia of the fly ash and coats its surface with a layer of Mg(OH)2. It also grafts N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, which has a propyl group and a dual-amino group at its end. The two amino groups are connected by a relatively flexible ethylene, allowing for a certain degree of rotation and stretching between them. When the interface is subjected to shear stress, it can dissipate some energy through the twisting and deformation of its own molecular chains, thus giving the cementitious material better toughness.

[0083] The only difference between Comparative Example 4 and Example 4 is that, in the functional modification of fly ash, the silane coupling agent sprayed from the atomizing nozzle is an equal amount of γ-aminopropyltriethoxysilane. While γ-aminopropyltriethoxysilane can function as a grafting agent when grafted onto the fly ash surface and connected to the matrix or fibers, its shorter molecular structure and rigidity prevent it from effectively dissipating energy when the material is impacted or develops microcracks. Instead, its rigidity causes stress concentration at the interface, creating new microcrack initiations. This direct stress transfer accelerates the damage. Comparative Example 5, without any silane coupling agent grafting, exhibits slightly better freeze-thaw resistance and impact resistance than Comparative Example 4, possibly due to the performance degradation resulting from the grafting of γ-aminopropyltriethoxysilane in Comparative Example 4.

[0084] Furthermore, through Examples 1-5, it can be confirmed that as long as the surface of the specific modified basalt fiber in the cementitious material of this application has carboxyl and hydroxyl groups, and the surface of the specific self-made functionalized fly ash has hydroxyl and amino groups, under the action of water molecules, a multi-dimensional hydrogen bond network interwoven with various strong and weak hydrogen bonds is formed at the interface between the micro-fiber and fly ash. When the material is subjected to stress and microcracks are generated, a large number of hydrogen bonds can efficiently dissipate the crack propagation energy. This makes the fracture toughness, impact resistance and fatigue life of the material more excellent, and it is more suitable for application in roadbed materials.

[0085] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A green low-carbon cementitious material for subgrade, characterized in that, The composition comprises, in parts by weight, 40-50 parts of slag powder, 25-35 parts of self-made functionalized fly ash, 15-25 parts of steel slag powder, 8-15 parts of desulfurization gypsum, and 2-4 parts of modified basalt fiber. The modified basalt fiber is prepared by the following method: taking basalt fiber and placing it in a reaction container; adding sodium hydroxide solution to completely immerse the fiber; stirring at low speed and heating to 80 DEG C, constant temperature reaction for 2 hours; stop heating after the reaction is completed, discharge the lye, and repeatedly rinse the fiber with deionized water until the pH value of the washing water is 7.0+ / -0.2; after the washed fiber is air dried, the dried basalt fiber after surface activation is prepared; taking the dried activated basalt fiber, immerse it in a sodium alginate aqueous solution; stirring at low speed for 1 hour at room temperature; the fiber is fished out, and the centrifuge is used to spin off the excess sodium alginate aqueous solution to obtain wet fiber with sodium alginate aqueous solution; then immerse it in a calcium chloride aqueous solution; continue stirring for 4 hours under the condition of constant temperature at 25 DEG C; after the reaction is completed, the fiber is fished out, and after preliminary draining, the crosslinked fiber is rinsed with a large amount of deionized water for 3-5 times until there is no chlorine ion precipitation in the washing water detected by silver nitrate solution; finally, the washed fiber is centrifuged and dried to obtain the modified basalt fiber; The self-made functionalized fly ash is prepared by the following method: taking fly ash and NaOH particles, placing them in a mortar, grinding and mixing them thoroughly, then transferring them to a crucible and placing them in a muffle furnace for calcination for 1 hour; after the mixture is cooled, it is taken out, ground finely with a grinder, and passed through a 200-mesh sieve; then it is repeatedly washed with a large amount of deionized water until the pH value of the filtrate is neutral, and then the final product is placed in a 105 DEG C oven for drying for 12 hours to obtain alkali-activated fly ash; taking the prepared alkali-activated fly ash, placing it in a reaction kettle, adding deionized water, and stirring to form a uniform suspension; and constant temperature at 90 DEG C; dropwise adding MgCl2 solution and NaOH solution; after the dropwise addition is completed, maintain 90 DEG C and continue constant temperature reaction for 90 minutes; then filter the reaction product and wash it with a large amount of deionized water until it is neutral, and then dry it at 105 DEG C for 12 hours to obtain modified fly ash coated with Mg(OH)2; taking the prepared Mg(OH)2-coated fly ash, placing it in a high-speed heating mixer, preheating to 110 DEG C at 1000 rpm; N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane is uniformly sprayed into the high-speed rotating powder through an atomizing nozzle; continue high-speed mixing at 110 DEG C for 20 minutes, and finally cool to room temperature to discharge, to obtain self-made functionalized fly ash.

2. The green low-carbon cementitious material for subgrade according to claim 1, characterized in that, The composition comprises, in parts by weight, 48 parts of slag powder, 32 parts of self-made functionalized fly ash, 22 parts of steel slag powder, 12 parts of desulfurization gypsum, and 4 parts of modified basalt fiber.

3. The green low-carbon cementitious material for subgrade according to claim 1, characterized in that, The slag powder is S95 grade granulated blast furnace slag powder.

4. The green low-carbon cementitious material for subgrade according to claim 1, characterized in that, The steel slag powder is a powder formed by ball milling of steel slag, and the specific surface area of the steel slag powder is 450-650 m 2 / kg, and the basicity is greater than 1.

8.

5. The green low-carbon cementitious material for subgrade according to claim 1, characterized in that, The specific surface area of the desulfurization gypsum is ≥450 m 2 / kg; the P2O5 content of the desulfurization gypsum is 0.6-0.8 wt%.

6. The green low-carbon cementitious material for subgrade according to claim 1, characterized in that, The calcination temperature of the muffle furnace is 700 DEG C.

7. The green low-carbon cementitious material for subgrade according to claim 1, characterized in that, In the preparation process of the self-made functionalized fly ash, the MgCl2 solution and the NaOH solution need to be slowly and synchronously added dropwise into the suspension; and at the same time of the dropwise adding, the pH value of the reaction system is constantly adjusted by using dilute hydrochloric acid or dilute NaOH, so that the pH value is always maintained at 10.

8. A method for preparing a green low-carbon cementitious material for roadbeds according to any one of claims 1-5, characterized in that, The preparation method is as follows: the self-made functionalized fly ash, the slag powder, the steel slag powder and the desulfurization gypsum are added into a dry powder mixer according to a proportion, are low-speed stirred for 3-5 minutes, so that they are fully mixed and uniform; finally, the modified basalt fiber is put into the mixer, and low-speed stirring is continued for 2-3 minutes, so that the fiber is uniformly dispersed in the powder and agglomeration is avoided, and a green low-carbon cementing material for roadbed is prepared.

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