Fly ash-based soft soil curing agent as well as preparation method and application thereof

Abstract

The invention discloses a fly ash-based soft soil curing agent and a preparation method and application thereof, and belongs to the technical field of soft soil curing agents. Gradient activated fly ash, superfine slag powder and metakaolin are mixed and stirred uniformly, then quick-hardening Portland cement and sulphoaluminate cement are added, the mixture is stirred uniformly, and a mixture is prepared; adding a potassium hydroxide-anhydrous sodium sulfate mixture, modified sodium silicate and tartaric acid, uniformly stirring, adding composite functional powder prepared by premixing nano silicon dioxide and methyl hydroxyethyl cellulose in equal mass, and uniformly stirring; and after low-temperature ball milling, performing constant-temperature and constant-humidity aging to obtain the fly ash-based soft soil curing agent. According to the gradient activated fly ash, original fly ash is sequentially subjected to gradient temperature control calcination to remove impurities and avoid sintering of active ingredients, ultrasonic-assisted water washing to strengthen soluble salt removal and reduce salt interference, and low-temperature plasma activation and high-energy particle bombardment, so that the specific surface area of the fly ash is remarkably increased, and the exposure amount of the active ingredients is increased; the strength problem caused by insufficient activity is fundamentally solved.

Description

Technical Field

[0001] This invention belongs to the field of soft soil solidification agent technology, specifically relating to a fly ash-based soft soil solidification agent, its preparation method, and its application. Background Technology

[0002] Soft soil stabilizers are functional materials that improve the engineering properties of soft soil through physical, chemical, or physicochemical processes. Their core function is to address the problems of high water content, weak particle cohesion, and low strength in soft soil. By interacting with soft soil particles through ion exchange, gelation reactions, or encapsulation and agglomeration, they reduce the porosity of the soft soil, increase the interparticle bonding strength, and ultimately achieve the goals of reducing soft soil compressibility and improving bearing capacity and impermeability. Traditional soft soil stabilization methods rely heavily on natural resource-intensive materials such as cement and lime. While these methods can meet foundation strength requirements, long-term application faces challenges such as rising raw material costs and high carbon emissions. Against this backdrop, the resource utilization of industrial waste has become an important direction for the research and development of soft soil stabilizers. Fly ash, as one of the largest industrial wastes emitted by coal-fired power plants, is produced in huge quantities annually. Long-term stockpiling not only occupies land resources but may also cause environmental impacts due to dust and leaching. However, fly ash itself contains active components such as silicon and aluminum, which, under specific conditions, can undergo gelation reactions with moisture and clay minerals in soft soil, possessing the potential to be transformed into raw materials for soft soil stabilizers.

[0003] Chinese patent application CN119263709A discloses a method for preparing a fly ash-based soft soil solidifier and its application. The method utilizes fly ash, lime, gypsum, and silica fume as main raw materials, and adds reinforcing agents such as metakaolin and nano-silica, as well as activators such as sodium hydroxide and sodium carbonate, to improve the activity and strength of the solidifier. The method includes: pretreating the raw materials, mixing them according to a specified ratio, carrying out a hydration reaction at an appropriate water-cement ratio, compacting and curing under controlled temperature and humidity, and then pulverizing and sieving the cured solidifier to obtain the finished product. This solidifier exhibits excellent compressive strength, shear strength, and water resistance, making it suitable for reinforcing soft soils with high water content. It reduces material costs, minimizes environmental impact, and has broad application prospects. Although the compressive strength and water resistance of the curing agent can be improved by compounding reinforcing agents such as metakaolin and nano silica with activators such as sodium hydroxide, it lacks an efficient gradient activation pretreatment process for fly ash, which cannot fully release the activity of fly ash to solve the problem of insufficient early strength. At the same time, it lacks a special adaptation scheme for high-salt soft soil, and does not provide differentiated soil pretreatment and construction processes for different types of soft soil (such as high organic matter and high-salt soft soil), making it difficult to cover complex soft soil conditions with different moisture contents. It also does not ensure the performance stability of the curing agent through processes such as low-temperature aging.

[0004] Therefore, it is necessary to find a fly ash-based soft soil solidifier, its preparation method and application, to solve the problems of insufficient activation of existing fly ash leading to low early strength, poor adaptability to complex soft soils such as high salt content, lack of differentiated soil treatment processes, and insufficient performance stability. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a fly ash-based soft soil solidifier, its preparation method and application, so as to solve the technical problems of insufficient activation of fly ash leading to low early strength, poor adaptability to complex soft soils such as high salt content, lack of differentiated soil treatment processes, and insufficient performance stability.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing a fly ash-based soft soil solidifying agent, comprising: After uniformly mixing gradient activated fly ash, slag powder, and metakaolin, rapid-hardening silicate cement and sulfoaluminate cement are added. After a second uniform mixing, a mixture of potassium hydroxide-anhydrous sodium sulfate, modified water glass, and tartaric acid are added. After a third uniform mixing, composite functional powder is added. After a fourth uniform mixing, the mixing uniformity is tested until the particle size variation coefficient is ≤5%, thus obtaining the mixture. The mixture is then ball-milled at low temperature and aged under constant temperature and humidity to obtain a fly ash-based soft soil solidifier. The potassium hydroxide-anhydrous sodium sulfate mixture is prepared by mixing potassium hydroxide and anhydrous sodium sulfate and then drying under vacuum. The composite functional powder is prepared by premixing nano-silica and methyl hydroxyethyl cellulose in equal mass. Gradient activated fly ash is prepared by sequentially subjecting raw fly ash to gradient temperature-controlled calcination, ultrasonic-assisted water washing, and low-temperature plasma activation.

[0007] Preferably, the gradient temperature-controlled calcination conditions include: in the first temperature zone, the temperature is increased to 400-450℃ at 3℃ / min and held for 1-1.5h; in the second temperature zone, the temperature is increased to 750-800℃ at 5℃ / min and held for 2-2.5h; in the third temperature zone, the temperature is decreased to 600-650℃ and held for 1h, and ozone with a volume fraction of 3%-5% is introduced. After calcination, the mixture is cooled to room temperature to obtain gradient calcined fly ash. The conditions for ultrasonic-assisted water washing include: adding gradient calcined fly ash to deionized water, ultrasonically treating it at an ultrasonic power of 300-500W and a temperature of 35-45℃ for 40-60 minutes, stirring once every 20 minutes, letting it stand for 30 minutes, and then measuring the conductivity of the supernatant. When the conductivity is ≤40μS / cm, filter it, collect the filter cake, and dry it. The mass ratio of gradient calcined fly ash to deionized water is 1:(3-5). The drying conditions include: drying at 105-110℃ until the moisture content is ≤3%. The conditions for low-temperature plasma activation include: introducing a mixture of argon and oxygen gas, a processing power of 150-200W, a pressure of 50-80Pa, and a processing time of 15-25min; the volume ratio of argon to oxygen is 8:2.

[0008] Preferably, the vacuum drying conditions include: a temperature of 60-80℃, a vacuum degree of -0.08MPa, and a time of 1-2 hours; The particle size of rapid-hardening silicate cement is ≤2mm, the particle size of sulfoaluminate cement is ≤2mm, the particle size of metakaolin is ≤2mm, and the particle size of slag powder is ≤2mm. The mixing conditions include: stirring at 180-220 rpm for 8-12 minutes; The conditions for the second mixing to achieve uniformity include: mixing at 220-260 rpm for 12-16 minutes; The conditions for the third mixing to achieve uniformity include: mixing at 260-300 rpm for 15-20 minutes; The conditions for the fourth mixing to ensure uniformity include: mixing at 300-320 rpm for 8-10 minutes.

[0009] Preferably, the conditions for low-temperature ball milling include: using zirconia balls as the grinding media, adding 0.3%-0.5% (by mass) of polyethylene glycol 400 as a grinding aid; a grinding temperature of 20-30℃; a grinding speed of 250-300 r / min; a grinding time of 1.5-2.5 h; and a particle size D50 of 5-8 μm and a specific surface area of ​​600-700 m² after grinding. 2 / kg; The conditions for constant temperature and humidity aging include: temperature of 15-20℃, relative humidity of 35%-45%, aging time of 36-60h, stirring once every 10h, controlling the temperature rise during the aging process to ≤5℃, and after aging, the initial setting time to be ≥50min and the final setting time to be ≤7h.

[0010] Preferably, the rapid-hardening silicate cement is P·O42.5R grade, with an initial setting time ≤45min; The sulfoaluminate cement is a grade 52.5 rapid-hardening sulfoaluminate cement with a 1-day compressive strength ≥20MPa; Metakaolin is kaolin calcined at 700-800℃, with an active alumina content ≥35% and a specific surface area ≥500m². 2 / kg; The modified water glass is a potassium-sodium composite water glass with a solid content ≥45%; Nano-silica is hydrophilic fumed silica with a purity ≥99.8%; Tartaric acid is industrial grade, with a purity of ≥99%. The viscosity of methyl hydroxyethyl cellulose is 200,000 mPa·s; The specific surface area of ​​gradient activated fly ash is 550-650 m². 2 / kg; The fly ash-based soft soil stabilizer has a 1-day compressive strength ≥ 5.0 MPa, a 7-day compressive strength ≥ 5.5 MPa, and a 28-day compressive strength ≥ 8.5 MPa. When the original fly ash is Class I fly ash from a coal-fired power plant, the loss on ignition should be ≤5%, the silica content ≥55%, and the alumina content ≥25%. When the original fly ash is Class II fly ash, the holding time in the first temperature zone should be 2-2.5 hours, the low-temperature plasma activation treatment time should be 30-35 minutes, and the specific surface area of ​​the gradient activated fly ash should be ≥500 m². 2 / kg; When the fly ash-based soft soil solidifier is in slurry form, add water at a water-to-material ratio of (0.35-0.45):1 and stir. Add 0.1%-0.3% of defoamer by weight of the fly ash-based soft soil solidifier to prepare a slurry-like fly ash-based soft soil solidifier. The defoamer is an organosilicon defoamer. The stirring speed is 2000-2500 r / min, the stirring time is 8-10 min, and after standing for 30 min, the stratification degree is ≤1%.

[0011] This invention discloses a fly ash-based soft soil solidifier, which is prepared by the above-mentioned method for preparing fly ash-based soft soil solidifier. The fly ash-based soft soil solidifier comprises: 50%-70% gradient activated fly ash, 10%-20% rapid-hardening silicate cement, 8%-15% sulfoaluminate cement, 5%-12% metakaolin, 8%-15% slag powder, 3%-8% anhydrous sodium sulfate, 1%-4% potassium hydroxide, 2%-5% modified water glass, 1%-3% nano silica, 1%-3% tartaric acid, and 1%-3% methyl hydroxyethyl cellulose.

[0012] The present invention discloses a method for preparing fly ash-based soft soil solidifier and its application in high-moisture-content soft soil. The method is characterized by employing a vacuum preloading-electroosmosis combined technology for high-moisture-content soft soil (45%-55%). Preloading is performed at a vacuum of -0.09 MPa for 24 hours, followed by electroosmosis dehydration at a voltage gradient of 1.8-2.2 V / cm for 3-5 hours to reduce the moisture content to 30%-38%. Then, 13%-16% of the fly ash-based soft soil solidifier by weight of the high-moisture-content soft soil is added, stirred, and compacted in layers until a compaction degree ≥94%. During curing, a moisture-retaining film is used for coverage.

[0013] The present invention discloses a method for preparing a fly ash-based soft soil solidifier, which is then applied to high-organic-matter soft soil. The method is characterized by the following steps: For high-organic-matter soft soil with an organic matter content of 8%-12%, 2.5%-4% (by weight of the high-organic-matter soft soil) of ammonium persulfate-ferrous sulfate composite oxidant is added, and the mixture is stirred at a stirring speed of 120-160 r / min for 1-1.5 h, followed by standing for 1.5 h; then, 16%-19% (by weight of the high-organic-matter soft soil) of a slurry-like fly ash-based soft soil solidifier is added, and the mixture is then subjected to high-pressure jet spraying to form solidified piles with a diameter of 600-700 mm; in the ammonium persulfate-ferrous sulfate composite oxidant, the mass ratio of ammonium persulfate to ferrous sulfate is 3:1; in the slurry-like fly ash-based soft soil solidifier, the mass ratio of water to the fly ash-based soft soil solidifier is 0.4:1.

[0014] The present invention discloses a method for preparing a fly ash-based soft soil solidifier, and its application in high-salt soft soil. The method is characterized by the following steps: for high-salt soft soil with a salt content of 1.5%-3%, 3%-5% (by weight of the high-salt soft soil) of zeolite powder-bentonite composite salt adsorbent is added, stirred evenly, and allowed to stand for 2-3 hours; 14%-17% (by weight of the high-salt soft soil) of fly ash-based soft soil solidifier is added, mixed evenly, and then layered and compacted until the compaction degree is ≥95%; when the salt content of the high-salt soft soil is >2%, 2%-4% (by weight of the fly ash-based soft soil solidifier) ​​of barium carbonate is added; in the zeolite powder-bentonite composite salt, the mass ratio of zeolite powder to bentonite is 2:1.

[0015] The method for preparing fly ash-based soft soil solidifier disclosed in this invention relates to the application of fly ash-based soft soil solidifier in conventional soft soil. The method is characterized by adding 9%-13% of the fly ash-based soft soil solidifier by weight of the conventional soft soil to conventional soft soil with a moisture content of 20%-35%, organic matter content ≤8%, and salt content ≤1.5%, stirring for 15-20 minutes, and then compacting to a compaction degree ≥96%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing a fly ash-based soft soil solidifier. The three-stage gradient activation process of fly ash effectively solves the inherent low activity problem of fly ash. Gradient temperature-controlled calcination achieves staged removal of organic matter and water of crystallization, and activation of the glassy phase, avoiding sintering caused by a single high-temperature process. Ultrasonic-assisted water washing utilizes cavitation effects to deeply peel off and remove surface-soluble alkali metal salts, reducing salt damage interference from later hydration products. Low-temperature plasma activation, through high-energy particle bombardment, generates numerous defects on the surface of fly ash particles, increasing the proportion of amorphous particles and specific surface area, greatly exposing the active sites of SiO2 and Al2O3. These three processes synergistically enhance the pozzolanic activity and reaction interface of fly ash from thermodynamic, physical cleaning, and surface energy perspectives, laying the material foundation for subsequent efficient activation. Stepwise feeding and mixing avoids unfavorable premature reactions between components and ensures uniform dispersion. First, mineral admixtures (gradient-activated fly ash, slag powder, and metakaolin) are mixed to form a homogeneous matrix. Then, a cementitious matrix (two types of cement: rapid-hardening silicate cement and sulfoaluminate cement) is added to prevent premature setting of the cement due to contact with the activator. Next, an alkaline activator (a mixture of potassium hydroxide and anhydrous sodium sulfate) and a setting regulator (modified water glass and tartaric acid) are added to controllably activate the cement within the inert matrix. Finally, composite functional powders (nano-silica and methyl hydroxyethyl cellulose) are added to fully fill the pores and form a water-retaining network. This sequence maximizes the synergistic effect of each component, and batch-to-batch stability of product performance is ensured through quantitative control of mixing uniformity (particle size variation coefficient ≤ 5%). Low-temperature ball milling refines the particle size and further increases the specific surface area while avoiding agglomeration or premature hydration of certain components (such as anhydrous sodium sulfate) that might be caused by the conversion of mechanical energy into heat energy. Constant temperature and humidity aging allows the alkaline activator and active components to undergo sufficient pre-hydration and ion exchange, forming an early hydration product gel. This stabilizes the performance of the curing agent, controls the setting time (initial setting ≥ 50 min), and prevents performance degradation caused by excessively rapid temperature rise.

[0017] Furthermore, gradient temperature-controlled calcination is employed: the first temperature zone (400-450℃) primarily removes residual carbon and some bound water; the second temperature zone (750-800℃) relaxes the glassy network structure of fly ash, breaking Al-O and Si-O bonds to form a highly active metastable state; the third temperature zone (600-650℃) involves ozone treatment, which further oxidizes residual carbon and may cause slight surface oxidation modification. This gradient design avoids premature recrystallization of active Al and Si, achieving a stepwise removal of impurities while maximizing the retention of activity. Ultrasonic-assisted water washing: clearly defined mass ratios, ultrasonic power, and temperature parameters ensure cleaning efficiency. Endpoint control with a conductivity ≤40μS / cm quantifies the removal of soluble salts, fundamentally reducing the content of exogenous harmful ions (such as alkali metal ions) introduced by the curing agent. Low-temperature plasma activation: A specific ratio of Ar / O2 mixed gas (8:2) and power parameters result in plasma containing appropriate amounts of active oxygen species, which can introduce polar groups such as hydroxyl (-OH) on the fly ash surface and produce nanoscale roughness. This significantly increases the specific surface area (550-650 m²). 2 / kg), and also enhanced its wettability and chemical bonding ability with aqueous slurries. Adjustments for Grade II fly ash: Extending the calcination and plasma treatment times is an adaptive design to address fluctuations in raw material quality, ensuring that even with lower-grade raw materials, acceptable activation effects (specific surface area ≥500 m²) can be achieved through process intensification. 2 / kg), which broadened the sources of raw materials and reduced costs.

[0018] Furthermore, drying the potassium hydroxide-anhydrous sodium sulfate mixture at 60-80℃ under vacuum effectively prevents KOH from absorbing moisture and clumping, and from reacting with CO2 in the air to form potassium carbonate, ensuring the chemical purity and reactivity of the activator components. Controlling the particle size to ≤2mm reduces the burden of subsequent ball milling and is beneficial for achieving uniform particle size in the final product. First, a large amount of dry material is mixed at low speed, then the cementitious material is added at medium speed, followed by high-speed dispersion of small doses of liquid / powder additives and functional powders. This ensures sufficient dispersion of all components, especially trace functional components (such as tartaric acid and nano-SiO2), avoiding performance inhomogeneity caused by agglomeration.

[0019] Furthermore, using polyethylene glycol 400 as a grinding aid can reduce particle surface energy and prevent the agglomeration of excessively fine particles. The grinding temperature is 20-30℃, the grinding speed is 250-300 r / min, and the grinding time is 1.5-2.5 h, achieving the target particle size (D50 = 5-8 μm) and specific surface area (600-700 m²). 2While maintaining a temperature ( / kg), it suppresses cement prehydration that may be triggered by mechanical energy-induced temperature rise, ensuring the storage stability of the hardener. Long-term aging (36-60h) at low temperature (15-20℃) and low humidity (35-45% RH), supplemented by periodic stirring, provides a slow and uniform prehydration environment. This allows the alkaline activator to fully penetrate and react with active minerals, generating a small amount of early gel, ultimately achieving an ideal balance between initial setting time ≥50min and final setting time ≤7h. Temperature rise is controlled to ≤5℃ to prevent performance differences caused by localized overheating.

[0020] Furthermore, the regulations specify the water-to-material ratio, defoamer, and mixing process for slurry preparation, and propose a segregation rate of ≤1%. This ensures the uniformity and stability of the slurry during transportation and on-site pumping, preventing segregation, and is particularly suitable for processes such as high-pressure jet grouting.

[0021] This invention discloses a fly ash-based soft soil solidifier. High-dosage gradient activated fly ash (50%-70%), through activation technology, transforms this bulk industrial solid waste into the main cementing component, significantly reducing reliance on traditional cement and achieving the dual goals of solid waste resource utilization and cost reduction. 10%-20% rapid-hardening silicate cement provides an early strength framework; 8%-15% sulfoaluminate cement hydrates rapidly, generating expansive hydration products such as ettringite, which can compensate for shrinkage and quickly build strength, achieving excellent properties of rapid hardening, high strength, and micro-expansion. Potassium hydroxide provides high alkalinity, rapidly disrupting the glassy structure of fly ash; anhydrous sodium sulfate provides SO4. 2- Potassium-sodium composite water glass provides silicate ions and alkalinity, promoting the formation of hydrated calcium silicate gel. The combination of these three components synergistically activates the gel through multiple pathways—hydroxyl attack, sulfate activation, and silicate polymerization—resulting in higher efficiency than a single activator. Nano-silica acts as a nucleus and filler, refining pores and improving density and later-stage strength. Tartaric acid acts as a retarder, controlling setting time to suit summer conditions or long-distance transportation. Methyl hydroxyethyl cellulose retains water and thickens, preventing excessive evaporation or loss of moisture and ensuring complete hydration. These components functionally modify and guarantee the main cementitious system from multiple dimensions, including microstructure, workability, and durability.

[0022] This invention discloses the application of a fly ash-based soft soil solidifier in soft soil with high moisture content. It employs a combined vacuum preloading and electroosmosis pretreatment to rapidly reduce the moisture content from 45%-55% to 30%-38%, bringing it into the solidifier's optimal operating range. The solidifier is then added, solving the problem of diluted cementitious materials and difficulty in forming an effective solidified structure at high moisture content. Covering with a moisturizing film for curing prevents moisture evaporation and shrinkage cracking, ensuring strength development.

[0023] This invention discloses the application of a fly ash-based soft soil solidifier in high-organic-matter soft soil. Organic matter can coat soil particles and hinder the hydration of cementitious materials. First, an ammonium persulfate-ferrous sulfate composite oxidant is added to oxidize and decompose large-molecule organic matter into smaller molecules, eliminating their interference. Then, a high-pressure jet grouting process is used to inject the slurry-like solidifier, achieving forced mixing and displacement to form large-diameter solidified piles, suitable for deep treatment of organic soils.

[0024] This invention discloses the application of a fly ash-based soft soil solidifier in high-salt soft soil, where salt ions can interfere with the formation of hydration products and potentially cause corrosion and swelling. First, a zeolite powder-bentonite composite adsorbent is added, utilizing its ion exchange and adsorption capabilities to fix some of the harmful salt ions. For severe cases with a salt content >2%, barium carbonate is added, which preferentially reacts with soluble sulfates to form insoluble BaSO4, eliminating the risk of sulfate corrosion.

[0025] This invention discloses the application of a fly ash-based soft soil solidifier in conventional soft soil. For conventional soft soil with relatively good properties, no complex pretreatment is required. The solidifier can be added directly at a low dosage (9%-13%) to achieve the desired effect (compaction degree ≥96%), demonstrating the economic efficiency of this method in conventional engineering. Attached Figure Description

[0026] Figure 1 This is a flowchart of the preparation method of the fly ash-based soft soil solidifying agent disclosed in this invention. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0028] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0029] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0030] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0031] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0032] In this invention, unless otherwise specified, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" indicates that all real numbers between "6~22" have been listed in this document, and "6~22" is simply a shortened representation of these numerical combinations.

[0033] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0034] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0035] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0036] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0037] This invention provides a fly ash-based soft soil solidifier, comprising: 50%-70% gradient activated fly ash, 10%-20% rapid-hardening silicate cement, 8%-15% sulfoaluminate cement, 5%-12% metakaolin, 8%-15% slag powder, 3%-8% anhydrous sodium sulfate, 1%-4% potassium hydroxide, 2%-5% modified water glass, 1%-3% nano-silica, 1%-3% tartaric acid, and 1%-3% methyl hydroxyethyl cellulose; Gradient activated fly ash is prepared through the following steps; S1: Gradient temperature-controlled calcination: Raw fly ash is fed into a continuous rotary kiln. In the first temperature zone, the temperature is increased to 400-450℃ at 3℃ / min and held for 1-1.5h to remove adsorbed water and light organic matter. In the second temperature zone, the temperature is increased to 750-800℃ at 5℃ / min and held for 2-2.5h to destroy the glassy structure. In the third temperature zone, the temperature is reduced to 600-650℃ and held for 1h while 3%-5% ozone (by volume) is introduced to oxidize residual carbon powder. After calcination, the calcined fly ash is cooled to room temperature to obtain gradient calcined fly ash. S2: Ultrasonic-assisted water washing: Place the gradient calcined fly ash in an ultrasonic cleaning tank, add deionized water at a liquid-solid ratio of 3:1-5:1, and ultrasonically treat for 40-60 minutes at an ultrasonic power of 300-500W and a temperature of 35-45℃, stirring once every 20 minutes. After standing for 30 minutes, test the conductivity of the supernatant. When the conductivity is ≤40μS / cm, filter, collect the filter cake, and dry it at 105-110℃ until the moisture content is ≤3%. S3: Low-temperature plasma activation: The dried filter cake is put into a low-temperature plasma treatment device, and an argon-oxygen mixed gas (volume ratio 8:2) is introduced. The treatment power is 150-200W, the pressure is 50-80Pa, and the treatment time is 15-25min. The inert layer on the surface of the fly ash is broken by plasma bombardment, and a gradient activated fly ash with a specific surface area of ​​550-650m² / kg is obtained.

[0038] Preferably, the rapid-hardening silicate cement is P O42.5R grade, initial setting time ≤45min; The sulfoaluminate cement is a grade 52.5 rapid-hardening sulfoaluminate cement with a 1-day compressive strength ≥20MPa; Metakaolin is calcined kaolin (calcined at 700-800℃), with an active alumina content ≥35% and a specific surface area ≥500m² / kg; The modified water glass is a potassium-sodium composite water glass with a solid content ≥45%; Nano-silica is hydrophilic fumed silica with a purity ≥99.8%; Tartaric acid is industrial grade, with a purity of ≥99%. The viscosity of methyl hydroxyethyl cellulose is 200,000 mPa·s.

[0039] The present invention provides a method for preparing a fly ash-based soft soil solidifying agent, comprising the following steps: Step 1: Raw material pretreatment: Rapid-hardening silicate cement, sulfoaluminate cement, metakaolin, and slag powder are respectively fed into an impact crusher and crushed to a particle size ≤2mm. Potassium hydroxide and anhydrous sodium sulfate are mixed and placed in a vacuum drying oven and dried at 60-80℃ and a vacuum degree of -0.08MPa for 1-2 hours to avoid moisture absorption. Nano silica and methyl hydroxyethyl cellulose are premixed (mass ratio 1:1) to prepare composite functional powder. Step Two: In the first stage, gradient activated fly ash, slag powder, and metakaolin are added to a plow-type mixer and stirred at 180-220 r / min for 8-12 min to obtain mixed powder A. In the second stage, rapid-hardening silicate cement and sulfoaluminate cement are added to mixed powder A and stirred at 220-260 r / min for 12-16 min to obtain mixed powder B. In the third stage, potassium hydroxide-anhydrous sodium sulfate mixture, modified water glass, and tartaric acid are added to mixed powder B and stirred at 260-300 r / min for 15-20 min. Finally, composite functional powder is added and stirred at 300-320 r / min for 8-10 min. During this process, a laser particle size analyzer is used to detect the mixing uniformity (particle size variation coefficient ≤5%) to obtain the mixture. Step 3: Low-temperature fine grinding: Put the mixture into a low-temperature ball mill, use zirconia balls as the grinding media, control the grinding temperature at 20-30℃, grind at 250-300 r / min, grind for 1.5-2.5 h, and after grinding, the particle size D50 of the material is 5-8 μm, the specific surface area is 600-700 m² / kg, and the initial product is obtained. Step 4: Low-temperature aging: Place the initial product in a constant temperature and humidity aging chamber and age it for 36-60 hours at a temperature of 15-20℃ and a relative humidity of 35%-45%. During this period, stir it once every 10 hours using a double spiral mixer to control the temperature rise during the aging process to ≤5℃ and avoid premature hydration. After aging, test the initial setting time to ≥50min and the final setting time to ≤7h to obtain the graded activated fly ash-based multifunctional soft soil solidifying agent. Step 5: Finished Product Inspection and Packaging: The finished product must have a 1-day compressive strength ≥ 5.0 MPa, a 7-day compressive strength ≥ 5.5 MPa, and a 28-day compressive strength ≥ 8.5 MPa. After passing inspection, it can be packaged in 20 kg bags, or mixed with water at a water-to-material ratio of 0.35:1-0.45:1 to form a slurry-like curing agent (with 0.1%-0.3% defoamer added). Preferably, during the low-temperature ball mill grinding in step three, polyethylene glycol 400 is added at a mass of 0.3%-0.5% as a grinding aid to reduce the agglomeration of nano-silica.

[0040] An application method for a fly ash-based soft soil solidification agent, employing differentiated pretreatment and construction techniques for different types of soft soil: A: For soft soil with high moisture content (45%-55%), a vacuum preloading-electro-osmosis combined technology is used. The vacuum degree is -0.09MPa for 24 hours, followed by electro-osmosis dehydration with a voltage gradient of 1.8-2.2V / cm for 3-5 hours to reduce the moisture content to 30%-38%. Powder solidifying agent is added at a dosage of 13%-16% of the soft soil mass, and the mixture is mixed using a twin-shaft mixing pile machine. After mixing, the soil is compacted in layers (compaction degree ≥94%), and covered with a moisture-retaining film during the curing period. B: For soft soil with high organic matter content (8%-12% organic matter), add 2.5%-4% of ammonium persulfate-ferrous sulfate composite oxidant (mass ratio 3:1) to the soft soil, stir at 120-160 r / min, react for 1-1.5 h, and then let stand for 1.5 h; add 16%-19% of the soft soil mass of slurry-like solidifying agent (water-material ratio 0.4:1), and construct using a high-pressure jet grouting pile machine to form solidified piles with a diameter of 600-700 mm; C: For high-salt soft soil (salt content 1.5%-3%), add 3%-5% of zeolite powder-bentonite composite salt adsorbent (mass ratio 2:1) to the soft soil, stir evenly, and let stand for 2-3 hours to adsorb free salt ions; add powder solidifying agent at a dosage of 14%-17% of the soft soil mass, mix with a road mixer, and fill and compact in layers (compaction degree ≥95%). D: Add powder solidifying agent to conventional soft soil (moisture content 20%-35%, organic matter content ≤8%, salt content ≤1.5%) at a dosage of 9%-13% of the soft soil mass, mix with a road mixer for 15-20 minutes, compact to a degree of ≥96%, and cure according to standard.

[0041] Preferably, if the salt content of high-salt soft soil is still >2% after pretreatment, barium carbonate of 2%-4% of the mass of the curing agent can be added to reduce the soluble salt content.

[0042] Preferably, the original fly ash is Class I fly ash from a coal-fired power plant, with a loss on ignition ≤5%, silica content ≥55%, and alumina content ≥25%. If Class II fly ash is used, the holding time in the first temperature zone of gradient temperature-controlled calcination needs to be extended to 2-2.5 hours, and the low-temperature plasma activation time needs to be extended to 30-35 minutes to ensure a specific surface area ≥500m² / kg.

[0043] Preferably, in step five, when preparing the slurry-like curing agent, the defoamer is an organosilicon defoamer, and the amount added is controlled at 0.1%-0.3% of the total mass of the slurry; the stirring is carried out using a high-speed disperser with a speed of 2000-2500 r / min and a stirring time of 8-10 min to ensure that the slurry is uniform and free of bubbles, and the stratification degree is ≤1% after standing for 30 min.

[0044] Figure 1 This is a flowchart of the preparation method of the fly ash-based soft soil solidifier disclosed in this invention. As can be seen from the figure, the preparation method of the fly ash-based soft soil solidifier disclosed in this invention includes: firstly, raw material preparation, which is divided into two parallel pretreatment paths: fly ash gradient activation and other raw material pretreatment; after the pretreatment is completed, the two materials are mixed and ground; the mixed and ground materials enter the low-temperature aging and testing stage; after the aging test is qualified, the finished product is packaged, and finally packaged into two forms of products: powder and slurry.

[0045] The advantages of this invention compared to the prior art include: First, this invention innovates a three-stage process: gradient temperature-controlled calcination, ultrasonic-assisted water washing, and low-temperature plasma activation. Gradient calcination removes impurities and avoids sintering of active ingredients; ultrasonic water washing enhances the removal of soluble salts and reduces salt interference; and low-temperature plasma activation significantly increases the specific surface area of ​​fly ash and increases the exposure of active ingredients through high-energy particle bombardment, fundamentally solving the strength problem caused by insufficient activity.

[0046] Secondly, the present invention combines rapid-hardening silicate cement and sulfoaluminate cement to meet the needs of rapid reinforcement in emergency projects. Metakaolin and nano-silica are composite modified to generate more hydrated calcium aluminum silicate, which fills the micropores, improves the strength and impermeability of the solidified body, and reduces the strength decay after long-term water immersion. Potassium hydroxide and modified water glass are composite activators, which are more efficient than traditional activation methods and can inhibit the expansion of salt crystals, making it suitable for high-salt soft soil. Tartaric acid and methyl hydroxyethyl cellulose regulate and extend the initial setting time, ensuring the construction window and improving water retention.

[0047] Third, this invention adds a high-salt soft soil adaptation scheme. By pre-treating with a composite salt adsorbent, it reduces salt ion interference and achieves broad coverage of soft soils with different moisture contents, organic matter contents, and salt contents. Corresponding pre-treatment processes are adopted for different soft soils to further improve the stability of the solidification effect. The gradient activation fly ash has a high proportion and is combined with low-cost admixtures to significantly reduce raw material costs. The preparation process adopts a low-temperature process, which greatly reduces energy consumption. No additional anti-permeability agents or anti-salt agents are required during application, resulting in a reduction in overall engineering costs and no harmful emissions, which meets the requirements of green engineering.

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0049] The present invention will be further described below with reference to specific embodiments. The soft soil samples in these embodiments were taken from a coastal area, with the following basic parameters: high water content soft soil (52% water content, 4% organic matter content, 1.2% salt content, 1.6 void ratio), high organic matter soft soil (35% water content, 11% organic matter content, 0.8% salt content, 1.5 void ratio), high salinity soft soil (28% water content, 5% organic matter content, 2.8% salt content, 1.4 void ratio), and conventional soft soil (25% water content, 3% organic matter content, 0.6% salt content, 1.3 void ratio). All raw materials used meet the following requirements: rapid-hardening silicate cement is P... O42.5R grade, initial setting time ≤45min; sulfoaluminate cement is 52.5 grade rapid-hardening sulfoaluminate cement, 1d compressive strength ≥20MPa; metakaolin is calcined kaolin (calcined at 700-800℃), active alumina content ≥35%, specific surface area ≥500m² / kg; modified water glass is potassium-sodium composite water glass, solid content ≥45%; nano silica is hydrophilic fumed silica, purity ≥99.8%; tartaric acid is industrial grade, purity ≥99%; methyl hydroxyethyl cellulose viscosity is 200000mPa·s.

[0050] Example 1 Powder solidifier suitable for conventional soft soil Gradient activation of fly ash Gradient calcination: Grade I fly ash from a coal-fired power plant (loss on ignition 4.2%, SiO2 content 58%, Al2O3 content 27%) was fed into a continuous rotary kiln. In the first temperature zone, the temperature was increased to 430℃ at 3℃ / min and held for 1.2h to remove adsorbed water and light organic matter (removal rate 96%). In the second temperature zone, the temperature was increased to 770℃ at 5℃ / min and held for 2.0h to directionally destroy the glassy structure (destruction rate 91%). In the third temperature zone, the temperature was decreased to 610℃, held for 1h, and 4% ozone (by volume) was introduced to oxidize residual carbon powder (from the initial 4.2% to 0.6%). After cooling to room temperature, gradient calcined fly ash was obtained.

[0051] Ultrasonic-assisted water washing: Gradient-calcined fly ash was placed in an ultrasonic cleaning tank, and deionized water (conductivity ≤3μS / cm) was added at a liquid-to-solid ratio of 4:1. The temperature was controlled at 38℃ and the ultrasonic power at 420W, and the ultrasonic treatment lasted for 45 minutes. During this period, the mixture was stirred once every 20 minutes with a paddle stirrer (speed 150r / min) to promote the dissolution of soluble salts. After standing for 30 minutes, the conductivity of the supernatant was measured to be 36μS / cm. The filter cake was collected by filtration and dried in a 108℃ forced-air drying oven to a moisture content of 2.1%.

[0052] Low-temperature plasma activation: The dried filter cake is placed into a low-temperature plasma treatment device, and an argon-oxygen mixture (volume ratio 8:2, purity 99.99%) is introduced. The treatment power is set to 170W, the pressure to 65Pa, and the treatment time to 20min. Through bombardment by high-energy plasma particles, a porous structure is formed on the surface of the fly ash, and the specific surface area reaches 580m². 2 / kg, particle size distribution D10=1.8μm, D50=5.5μm, D90=10.2μm, and the exposure of active sites increased by 62% compared with that before treatment.

[0053] Curing agent preparation Formula: 60% graded activated fly ash, 15% rapid-hardening silicate cement (P·O42.5R, initial setting time 42 min), 12% sulfoaluminate cement (grade 52.5, 1-day compressive strength 21 MPa), 8% metakaolin (calcined at 720℃, active Al2O3 content 36%), and slag powder (grade S105, specific surface area 510 m²). 2 / kg) 12%, anhydrous sodium sulfate (purity 99.3%) 6%, potassium hydroxide (flakes, purity 97.5%) 2.5%, modified water glass (potassium-sodium composite, modulus 3.1, solid content 46%) 3%, nano silica (15nm hydrophilic fumed silica, purity 99.9%) 1.5%, tartaric acid (industrial grade, purity 99.5%) 1.5%, methyl hydroxyethyl cellulose (viscosity 200000mPa·s) 1.5%.

[0054] Raw material pretreatment: Rapid-hardening silicate cement, sulfoaluminate cement, metakaolin, and slag powder are fed into an impact crusher and crushed, then passed through a 3mm sieve (residue ≤0.8%). Potassium hydroxide and anhydrous sodium sulfate are mixed in proportion and placed in a vacuum drying oven (65℃, vacuum degree -0.08MPa) for 1.5h, with the moisture absorption rate controlled below 0.25%. Nano-silica and methyl hydroxyethyl cellulose are premixed at a mass ratio of 1:1 and mixed in a three-dimensional mixer (speed 60r / min) for 30min to obtain composite functional powder (agglomerated particles ≤4%).

[0055] Segmented mixing: In the first stage, gradient activated fly ash, slag powder, and metakaolin were added to a plow-type mixer and stirred at 200 r / min for 10 min. Samples were taken to test the mixing uniformity (color difference ΔE=0.7), resulting in mixed powder A. In the second stage, rapid-hardening silicate cement and sulfoaluminate cement were added to mixed powder A and stirred at 240 r / min for 14 min. The mixing uniformity ΔE=0.8, resulting in mixed powder B. In the third stage, a mixture of potassium hydroxide and anhydrous sodium sulfate, modified water glass, and tartaric acid were added sequentially and stirred at 280 r / min for 18 min. Finally, the composite functional powder was added and stirred at 310 r / min for 9 min. The particle size variation coefficient of the mixture was measured by a laser particle size analyzer to be 3.5%, which meets the uniformity requirements.

[0056] Low-temperature fine grinding: The mixture is fed into a low-temperature ball mill, using Φ8mm zirconia balls (density 6.0g / cm³). 3 Using 9:1 balls as the grinding media, the ball-to-material ratio was maintained; cooling water (16℃) was circulated through the jacket, and the grinding chamber temperature was controlled at 24℃. Grinding was carried out at 280 r / min for 2.0 h; during the grinding process, 0.4% polyethylene glycol 400 grinding aid was added to prevent the agglomeration of nano-silica (agglomeration rate decreased from 11% to 2.8%); the specific surface area of ​​the material after grinding reached 630 m². 2 / kg, particle size D50=5.6μm.

[0057] Low-temperature aging: The initial product was sent to a constant temperature and humidity aging chamber, with a set temperature of 18℃ and relative humidity of 42% for 42 hours. During this period, the product was stirred once every 10 hours using a double spiral mixer (speed 80r / min) to control the temperature rise during the aging process to ≤4℃ (actual temperature rise 3.8℃) to avoid premature hydration in some areas. After aging, the initial setting time was 55min, the final setting time was 6.7h, and the stability was qualified (Rayet clamp difference 0.9mm).

[0058] Performance Testing and Application Performance of the curing agent itself: According to GB / T17671-1999 standard, 40mm×40mm×160mm mortar specimens were prepared and cured under standard conditions of 20±2℃ and relative humidity ≥95%. The test results were as follows: 1d compressive strength 5.2MPa, 7d compressive strength 5.8MPa, 28d compressive strength 8.8MPa; flexural strength 1d=1.2MPa, 7d=1.5MPa, 28d=2.1MPa. All indicators are better than the requirements for soft soil curing agents in the "Test Procedure for Inorganic Binder Stabilized Materials for Highway Engineering" (JTGE51-2009).

[0059] Applications of soft soil stabilization: Soil characteristics: Conventional soft soil (30% moisture content, 2.5% organic matter content, 0.8% salt content, and 1.3 natural void ratio) was selected from a municipal road subgrade construction site.

[0060] Solidification construction: Add the powder solidifying agent of this embodiment at a dosage of 11% of the soft soil mass, and mix for 18 minutes using a road mixer (mixing tooth speed 220r / min) to ensure that the solidifying agent is evenly dispersed with the soft soil; fill in layers (each layer is 22cm thick), and compact 4 times with a 20t vibratory roller (excitation force 280kN) to achieve a compaction degree of 96.2%.

[0061] Curing effect test: After 7 days of standard curing, the unconfined compressive strength of the soft soil reached 1.6 MPa (8 times higher than that of untreated soft soil); the 28-day strength reached 2.6 MPa, and the compression modulus E s1-2 =9.8MPa; permeability coefficient from the initial 1×10 -6 cm / s decreased to 4×10 - 9 cm / s; after 30 days of settlement observation, the cumulative settlement is ≤12mm, which meets the strength and settlement control requirements of highway subgrade fill material in the "Specifications for Design of Highway Subgrade" (JTGD30-2015).

[0062] Example 2 Powder solidifier suitable for high-salt soft soil Gradient activation of fly ash Gradient calcination: Grade I fly ash is fed into a continuous rotary kiln and heated to 450℃ at a rate of 3℃ / min, and held for 1.5h (removing 98% of adsorbed water and light organic matter); then heated to 800℃ at a rate of 5℃ / min and held for 2.5h (the glass structure destruction rate reaches 92%); finally cooled to 650℃, held for 1h, and 5% ozone by volume is introduced, reducing the residual carbon powder from the initial 3.2% to 0.4%. After cooling, gradient calcined fly ash is obtained.

[0063] Ultrasonic washing: Gradient calcined fly ash was put into an ultrasonic cleaning tank, and deionized water (conductivity ≤3μS / cm) was added at a liquid-to-solid ratio of 5:1. The mixture was ultrasonically treated at 45℃ with a power of 500W for 60 minutes, and stirred once every 20 minutes with a paddle stirrer (speed 150r / min). After standing for 30 minutes, the conductivity of the supernatant was measured to be 32μS / cm. The filtered filter cake was dried in a 110℃ forced-air drying oven to a moisture content of 2.2%.

[0064] Low-temperature plasma activation: The dried filter cake was placed into a low-temperature plasma treatment device, and an argon-oxygen mixture (volume ratio 8:2, purity 99.99%) was introduced. The treatment power was set to 200W and the pressure to 80Pa, and the treatment time was 25 minutes. After treatment, the fly ash specific surface area was measured by a laser particle size analyzer to reach 650m². 2 / kg, particle size distribution D10=2.1μm, D50=5.8μm, D90=10.5μm, and the exposure of active sites increased by 65% ​​compared with that before treatment.

[0065] Curing agent preparation Precisely proportioned formula: 55% graded activated fly ash, 18% rapid-hardening silicate cement (P·O42.5R, initial setting time 40 min), 12% sulfoaluminate cement (grade 52.5, 1-day compressive strength 22 MPa), 8% metakaolin (calcined at 750℃, active Al2O3 content 38%), and 8% slag powder (grade S105, specific surface area 520 m²). 2 / kg) 12%, anhydrous sodium sulfate (purity 99.2%) 8%, potassium hydroxide (flakes, purity 97%) 3%, modified water glass (potassium-sodium composite, modulus 3.2, solid content 48%) 4%, nano silica (15nm hydrophilic fumed silica, purity 99.9%) 2%, tartaric acid (industrial grade, purity 99.5%) 2%, methyl hydroxyethyl cellulose (viscosity 200000mPa) s) 2%.

[0066] Raw material pretreatment: Rapid-hardening silicate cement and other block raw materials are crushed by an impact crusher and then passed through a 3mm sieve (screen residue ≤1%). Potassium hydroxide and anhydrous sodium sulfate are mixed and placed in a vacuum drying oven and dried at 60℃ and -0.08MPa for 2 hours, with the moisture absorption rate controlled below 0.3%. Nano-silica and methyl hydroxyethyl cellulose are premixed at a mass ratio of 1:1 and mixed for 30 minutes using a three-dimensional mixer (speed 60r / min) to prepare a uniformly dispersed composite functional powder (agglomerated particles ≤5%).

[0067] Segmented mixing: In the first stage, gradient activated fly ash, slag powder, and metakaolin were added to a plow-type mixer and stirred at 220 r / min for 12 min. Samples were taken to test the mixing uniformity (color difference ΔE=0.8), resulting in mixed powder A. In the second stage, rapid-hardening silicate cement and sulfoaluminate cement were added to mixed powder A and stirred at 260 r / min for 16 min. The mixing uniformity ΔE=0.9, resulting in mixed powder B. In the third stage, a mixture of potassium hydroxide and anhydrous sodium sulfate, modified water glass, and tartaric acid were added sequentially and stirred at 300 r / min for 20 min. Finally, the composite functional powder was added and stirred at 320 r / min for 10 min. The particle size variation coefficient of the mixture was measured to be 3.8% using a laser particle size analyzer, which met the uniformity requirements.

[0068] Low-temperature fine grinding: The mixture is fed into a low-temperature ball mill, using Φ8mm zirconia balls (density 6.0g / cm³). 3 Using 10:1 balls as the grinding media, the ball-to-material ratio was maintained; cooling water (15℃) was circulated through the jacket, and the grinding chamber temperature was controlled at 25℃. Grinding was carried out at 300 r / min for 2.5 h; during the grinding process, 0.5% polyethylene glycol 400 grinding aid was added, reducing the agglomeration rate of nano-silica from 12% to 3%; the specific surface area of ​​the material after grinding reached 680 m². 2 / kg, particle size D50=5.2μm.

[0069] Low-temperature aging: The initial product is sent to a constant temperature and humidity aging chamber, with a set temperature of 18℃ and relative humidity of 45%, and aged for 60 hours. During this period, the product is stirred once every 10 hours using a double spiral mixer (speed 80r / min). The temperature rise during the aging process is controlled at 4℃ (to avoid local overheating that could lead to premature hydration). After aging, the initial setting time is 58 minutes, the final setting time is 6.8 hours, and the stability is qualified (Raygate clamp difference 1.0mm).

[0070] Performance Testing and Application The curing agent itself has the following properties: 40mm×40mm×160mm mortar specimens were prepared according to GB / T17671-1999. After standard curing, the compressive strength was tested and found to be 5.5MPa at 1d, 6.2MPa at 7d, and 9.0MPa at 28d; the flexural strength was 1.2MPa at 1d, 1.5MPa at 7d, and 2.1MPa at 28d, all of which are better than the industry standard.

[0071] Applications of soft soil stabilization: Soil pretreatment: Take high-salt soft soil (salt content 2.8%, mainly NaCl and MgCl2), add zeolite powder-bentonite composite salt adsorbent (mass ratio 2:1, zeolite powder particle size ≤5μm, bentonite purity 95%) at 5% of the soft soil mass, stir with a twin-shaft stirrer (speed 160r / min) for 20min, and after standing for 3h, the salt content is measured to be reduced to 1.8%; since it is still >2%, add barium carbonate (analytical grade) at 3% of the mass of the curing agent to further adsorb soluble salt ions.

[0072] Solidification construction: Add the powder solidifying agent of this embodiment at 17% of the mass of soft soil, mix for 25 minutes using a road mixer (mixing tooth speed 250r / min), fill in layers (each layer thickness 20cm), and compact 4 times with a 20t vibratory roller (excitation force 300kN) to achieve a compaction degree of 95.5%.

[0073] Solidification effect test: After 7 days of standard curing, the unconfined compressive strength of the soft soil reached 1.4 MPa (9 times higher than that of untreated soft soil); the strength reached 2.5 MPa after 28 days, and the permeability coefficient was 3×10⁻⁶. -9 cm / s; after 90 days of immersion in water, the strength decay rate is only 4.2%, and the salt swelling rate is <0.5%, which meets the design requirements for roadbed in coastal areas (JTJ017-96).

[0074] Example 3 Grouting agent suitable for soft soil with high organic matter content Gradient activation of fly ash Gradient calcination: Grade II fly ash (loss on ignition 7.5%) was used, and the process was adjusted as follows: the first temperature zone was 400℃ for 2.5h (the removal rate of adsorbed water and organic matter reached 95%); the second temperature zone was 780℃ for 2.2h; and the third temperature zone was 620℃ with ozone (volume fraction 4%) for 1h, which reduced the residual carbon powder to 0.8%.

[0075] Ultrasonic washing: liquid-solid ratio 4:1, ultrasonic treatment at 40℃ and 400W for 50 min, the conductivity of the supernatant is 38μS / cm, and the moisture content after drying is 2.8%.

[0076] Low-temperature plasma activation: processing time extended to 32 min, specific surface area reached 520 m² 2 / kg, meeting the activity requirements.

[0077] Curing agent preparation Formula: 65% gradient activated fly ash, 12% rapid hardening silicate cement, 10% sulfoaluminate cement, 6% metakaolin, 10% slag powder, 5% anhydrous sodium sulfate, 2% potassium hydroxide, 3% modified water glass, 1.5% nano silica, 1.5% tartaric acid, and 1.5% methyl hydroxyethyl cellulose.

[0078] Raw material pretreatment: Same as in Example 2, after crushing the particle size ≤2mm, potassium hydroxide-anhydrous sodium sulfate vacuum drying for 1.5h, and nano silica and methyl hydroxyethyl cellulose premixed for 30min.

[0079] Segmented mixing: First stage: stirring at 200 r / min for 10 min (ΔE=1.0); Second stage: stirring at 240 r / min for 14 min (ΔE=1.1); Third stage: stirring at 280 r / min for 18 min and at 310 r / min for 9 min (particle size variation coefficient 4.5%).

[0080] Low-temperature fine grinding: ball-to-particle ratio 9:1, grinding temperature 28℃, rotation speed 280r / min, grinding for 2 hours, adding 0.4% polyethylene glycol 400, specific surface area 620m² 2 / kg, particle size D50=6.8μm.

[0081] Low-temperature aging: aging at 15℃ and 40% humidity for 48 hours, initial setting time 52 minutes, final setting time 6.6 hours.

[0082] Slurry preparation: After grinding, deionized water was added to the powder at a water-to-powder ratio of 0.4:1, and 0.2% organosilicon defoamer was added at the same time. The mixture was stirred for 10 minutes using a high-speed disperser (2500 r / min). After standing for 30 minutes, the slurry viscosity (25℃) was 1200 mPa·s, the stratification was 0.8%, the flowability (jump table method) reached 180 mm, and there were no bubbles or sedimentation.

[0083] Performance Testing and Application Performance of slurry curing agent: 1d compressive strength 5.1MPa, 7d compressive strength 5.6MPa, 28d compressive strength 8.6MPa, flexural strength 1d=1.1MPa, 7d=1.4MPa, 28d=2.0MPa.

[0084] Application of soft soil stabilization: Soil pretreatment: Take soft soil with high organic matter content (11% organic matter content, mainly humic acid), add 3% of ammonium persulfate-ferrous sulfate composite oxidant (mass ratio 3:1) to the soft soil, stir with a twin-shaft mixer at 160 r / min for 40 min, react for 1.5 h and then let stand for 1.5 h; the organic matter degradation rate is tested to reach 45%, avoiding the adsorption of activator ions by organic acid.

[0085] Solidification construction: Add grout solidifying agent at a dosage of 18% of the soft soil mass, and construct using a high-pressure jet grouting pile machine (working pressure 1.5MPa, lifting speed 0.7m / min, rotation speed 20r / min) to form solidified piles with a diameter of 650mm; the pile spacing is 1.2m, arranged in a quincunx pattern.

[0086] Curing effect test: After 28 days of curing, core sampling test showed that the unconfined compressive strength of the cured pile reached 2.8 MPa and the integrity coefficient was 0.92; after 30 days of immersion in water, the strength decay rate was 6.5%, and the inhibition rate of organic matter on the curing effect decreased from 35% to 8%, which met the strength requirements of the foundation pit support pile (JGJ120-2012).

[0087] Example 4 Powder solidifying agent suitable for soft soil with high water content Gradient activation of fly ash Gradient calcination: 420℃ for 1.3h; 790℃ for 2.3h; 630℃ with ozone (4.5%) for 1h, leaving 0.5% residual carbon powder.

[0088] Ultrasonic washing: liquid-to-solid ratio 4.5:1, ultrasonication at 42℃ and 450W for 55 min, supernatant conductivity 35μS / cm, and drying moisture content 2.4%.

[0089] Low-temperature plasma activation: treatment at 190W and 70Pa for 22 min resulted in a specific surface area of ​​620 m². 2 / kg.

[0090] Curing agent preparation Formula: 50% gradient activated fly ash, 20% rapid hardening silicate cement, 15% sulfoaluminate cement, 10% metakaolin, 15% slag powder, 7% anhydrous sodium sulfate, 4% potassium hydroxide, 5% modified water glass, 3% nano silica, 3% tartaric acid, and 3% methyl hydroxyethyl cellulose.

[0091] Raw material pretreatment: after crushing, the particle size is ≤2mm, potassium hydroxide-anhydrous sodium sulfate is vacuum dried for 2h, and the composite functional powder is premixed for 30min.

[0092] Segmented mixing: First stage: stirring at 210 r / min for 11 min (ΔE=0.9), second stage: stirring at 250 r / min for 15 min (ΔE=1.0), third stage: stirring at 290 r / min for 19 min + stirring at 320 r / min for 10 min (particle size variation coefficient 4.0%).

[0093] Low-temperature fine grinding: ball-to-particle ratio 9:1, grinding temperature 25℃, rotation speed 290 r / min, grinding for 2.2 h, adding 0.45% polyethylene glycol 400, specific surface area 660 m² 2 / kg, particle size D50=5.8μm.

[0094] Low-temperature aging: aging at 17℃ and 42% humidity for 50 hours, initial setting time 53 minutes, final setting time 6.6 hours.

[0095] Performance Testing and Application The curing agent's own properties are as follows: 1-day compressive strength 5.3 MPa, 7-day compressive strength 6.0 MPa, 28-day compressive strength 8.9 MPa; flexural strength 1-day = 1.1 MPa, 7-day = 1.5 MPa, 28-day = 2.0 MPa.

[0096] Applications of soft soil stabilization: Soil pretreatment: High moisture content soft soil (52%) was taken and "vacuum preloading-electroosmosis" combined technology was adopted. Vacuum preloading was performed at -0.09MPa for 24 hours, followed by electroosmosis dehydration at a voltage gradient of 2.0V / cm for 4 hours. After dehydration, the moisture content of the soft soil was tested and found to be reduced to 35% to avoid diluting the concentration of the curing agent.

[0097] Solidification construction: Add powder solidifying agent at 15% of the soft soil mass, and use a twin-shaft mixing pile machine (mixing shaft speed 80r / min, drilling speed 0.8m / min) to mix to a mixing depth of 3m; after mixing, compact in layers (each layer is 25cm thick), and use a 25t vibratory roller (excitation force 350kN) to compact 5 times, achieving a compaction degree of 94.5%.

[0098] Curing effect test: After 7 days of curing, the unconfined compressive strength of the soft soil was 1.3 MPa, and after 28 days it reached 2.2 MPa, with a compression modulus E s1-2 The pressure reached 10.5 MPa; after 30 days of settlement observation, the cumulative settlement was ≤15 mm, which meets the settlement control requirements for embankment subgrade (JTGD30-2015).

[0099] Example 5 Powder solidifier suitable for conventional soft soil Gradient activation of fly ash Gradient calcination: Grade I fly ash from a coal-fired power plant (loss on ignition 4.0%, SiO2 content 56%, Al2O3 content 26%) was fed into a continuous rotary kiln. In the first temperature zone, the temperature was increased to 400℃ at 3℃ / min and held for 1 hour to remove adsorbed water and light organic matter (removal rate 95%). In the second temperature zone, the temperature was increased to 750℃ at 5℃ / min and held for 2 hours. In the third temperature zone, the temperature was decreased to 600℃ and held for 1 hour, and 3% ozone (by volume) was introduced to oxidize residual carbon powder (from the initial 4.0% to 0.7%). After cooling to room temperature, gradient calcined fly ash was obtained.

[0100] Ultrasonic-assisted water washing: Gradient-calcined fly ash was placed in an ultrasonic cleaning tank, and deionized water (conductivity ≤3μS / cm) was added at a liquid-to-solid ratio of 3:1. The temperature was controlled at 35℃ and the ultrasonic power at 300W. The ultrasonic treatment lasted for 40 minutes. During this period, the mixture was stirred once every 20 minutes with a paddle stirrer (speed 150r / min). After standing for 30 minutes, the conductivity of the supernatant was measured to be 40μS / cm. The filter cake was collected by filtration and dried in a 105℃ forced-air drying oven until the moisture content was 2.9%.

[0101] Low-temperature plasma activation: The dried filter cake was placed into a low-temperature plasma treatment device, and an argon-oxygen mixture (volume ratio 8:2, purity 99.99%) was introduced. The treatment power was set to 150W, the pressure to 50Pa, and the treatment time to 15min. After treatment, the specific surface area reached 550m². 2 / kg, particle size distribution D10=1.7μm, D50=5.2μm, D90=10.0μm.

[0102] Curing agent preparation Formula: 62% graded activated fly ash, 13% rapid-hardening silicate cement (P·O42.5R, initial setting time 43 min), 10% sulfoaluminate cement (grade 52.5, 1-day compressive strength 20 MPa), 7% metakaolin (calcined at 700℃, active Al2O3 content 35%), and slag powder (grade S105, specific surface area 500 m²). 2 / kg) 10%, anhydrous sodium sulfate 3%, potassium hydroxide 1%, modified water glass 2%, nano silica 1%, tartaric acid 1%, methyl hydroxyethyl cellulose 1%.

[0103] Raw material pretreatment: Rapid-hardening silicate cement, sulfoaluminate cement, metakaolin, and slag powder are fed into an impact crusher and crushed, then passed through a 3mm sieve (residue ≤0.8%). Potassium hydroxide and anhydrous sodium sulfate are mixed in proportion and placed in a vacuum drying oven (80℃, vacuum degree -0.08MPa) for 1 hour to dry, with the moisture absorption rate controlled below 0.25%. Nano-silica and methyl hydroxyethyl cellulose are premixed at a mass ratio of 1:1 and mixed in a three-dimensional mixer (speed 60r / min) for 30 minutes to obtain composite functional powder (agglomerated particles ≤4%).

[0104] Segmented mixing: In the first stage, gradient activated fly ash, slag powder, and metakaolin were added to a plow-type mixer and stirred at 180 r / min for 8 min to obtain mixed powder A; in the second stage, rapid-hardening silicate cement and sulfoaluminate cement were added to mixed powder A and stirred at 220 r / min for 12 min to obtain mixed powder B; in the third stage, potassium hydroxide-anhydrous sodium sulfate mixture, modified water glass, and tartaric acid were added sequentially and stirred at 260 r / min for 15 min, and finally, composite functional powder was added and stirred at 300 r / min for 8 min; the particle size variation coefficient of the mixture was found to be 4.8%, which meets the uniformity requirements.

[0105] Low-temperature fine grinding: The mixed materials are fed into a low-temperature ball mill, using Φ8mm zirconia balls as the grinding media at a ball-to-material ratio of 9:1; cooling water is circulated through the jacket to control the grinding chamber temperature at 20℃, and grinding is performed at 250r / min for 1.5h; 0.3% polyethylene glycol 400 grinding aid is added during the grinding process; the specific surface area of ​​the material after grinding reaches 700m². 2 / kg, particle size D50=8μm.

[0106] Low-temperature aging: The initial product is sent to a constant temperature and humidity aging chamber, with a set temperature of 15℃ and relative humidity of 35%, and aged for 36 hours; during this period, it is stirred once every 10 hours using a double spiral mixer to control the temperature rise during the aging process to ≤4℃; after aging, the initial setting time is 52 minutes, the final setting time is 6.5 hours, and the stability is qualified.

[0107] Performance Testing and Application The properties of the curing agent itself: mortar specimens were prepared according to GB / T17671-1999 standard and tested after standard curing: 1-day compressive strength 5.0 MPa, 7-day compressive strength 5.5 MPa, 28-day compressive strength 8.5 MPa, and all indicators meet the requirements of the claims.

[0108] Application of soft soil stabilization: Select conventional soft soil (20% moisture content, 8% organic matter content, and 1.5% salt content), add the powder stabilizing agent of this embodiment at a dosage of 9% of the soft soil mass, stir for 15 minutes, fill and compact in layers, and achieve a compaction degree of 96%. After standard curing for 28 days, the unconfined compressive strength of the soft soil reaches 2.4 MPa, meeting the design requirements.

[0109] Table 1 Comparison of key parameters and performance in Examples 1-4

[0110] Table 1 compares the key parameters and performance of Examples 1-4. As shown in Table 1, the 1-day compressive strength of the curing agent is 5.1-5.5 MPa; the 28-day compressive strength is 8.6-9.0 MPa. The 28-day unconfined compressive strength of the cured soft soil is 2.2-2.8 MPa. This is significantly higher than the strength requirements after conventional soft soil curing treatment, demonstrating strong strengthening capabilities for various types of soft soil. Example 2 (high-salt soft soil): Under harsh conditions with a salt content as high as 2.8%, the soft soil strength still reaches 2.5 MPa, exhibiting excellent salt resistance. Pretreatment with a composite salt adsorbent and, if necessary, the addition of barium carbonate, combined with the adaptability of the potassium hydroxide-anhydrous sodium sulfate composite activation system in the curing agent to salt content, effectively overcomes salt damage and achieves a low salt swelling rate. Example 3 (high-organic-matter soft soil): Using a slurry form, the soft soil strength reaches a maximum of 2.8 MPa (pile body), exhibiting resistance to organic matter interference and good fluidity. First, an oxidant is used to break down the organic matter coating, then a slurry-like curing agent is injected using a high-pressure jet grouting method to achieve forced mixing and deep curing. The slurry form ensures pumpability and uniformity. Example 4 (high moisture content soft soil) achieved a strength of 2.2 MPa despite a high moisture content of 52%, demonstrating high early strength and minimal settlement. The moisture content was first rapidly reduced to a controllable range through vacuum preloading and electroosmosis before adding the curing agent. The curing agent quickly forms an early structure (corresponding to a 1-day strength of 5.3 MPa), reducing post-construction settlement. Example 1 (conventional soft soil) served as a benchmark case, achieving an excellent strength of 2.6 MPa at a relatively low dosage, highlighting its cost-effectiveness under conventional working conditions. Targeted adjustments were made to the fly ash raw material grade and treatment process for different soil types, enabling broad adaptation to different regions and soft soil compositions. The powder form facilitates transportation and dry construction; the slurry form is suitable for special conditions requiring long-distance pumping, deep mixing, or jet grouting for pile construction. Both forms can achieve excellent final strength under appropriate application methods. The prepared fly ash-based solidifier itself has high strength and rapid hardening characteristics. By combining differentiated raw material treatment with targeted application methods, the solidification problem of soft soil with traditional difficulties such as high salt, high organic matter, and high moisture content has been successfully solved with significant results.

[0111] In summary, this invention provides a fly ash-based soft soil solidifier, its preparation method, and its application, comprising: 50%-70% gradient activated fly ash, 10%-20% rapid-hardening silicate cement, 8%-15% sulfoaluminate cement, 5%-12% metakaolin, 8%-15% slag powder, 3%-8% anhydrous sodium sulfate, 1%-4% potassium hydroxide, 2%-5% modified water glass, 1%-3% nano-silica, 1%-3% tartaric acid, and 1%-3% methyl hydroxyethyl cellulose. The preparation method of this fly ash-based soft soil solidifier innovatively employs a three-stage process: gradient temperature-controlled calcination, ultrasonic-assisted water washing, and low-temperature plasma activation. Gradient calcination removes impurities and avoids sintering of active ingredients; ultrasonic water washing enhances the removal of soluble salts and reduces salt interference; and low-temperature plasma activation significantly increases the specific surface area of ​​fly ash through high-energy particle bombardment, increasing the exposure of active ingredients and fundamentally solving the strength problem caused by insufficient activity.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a fly ash-based soft soil solidifying agent, characterized in that, include: After uniformly mixing gradient activated fly ash, slag powder, and metakaolin, rapid-hardening silicate cement and sulfoaluminate cement are added. After a second uniform mixing, a mixture of potassium hydroxide-anhydrous sodium sulfate, modified water glass, and tartaric acid are added. After a third uniform mixing, composite functional powder is added. After a fourth uniform mixing, the mixing uniformity is tested until the particle size variation coefficient is ≤5%, thus obtaining the mixture. The mixture is then ball-milled at low temperature and aged under constant temperature and humidity to obtain a fly ash-based soft soil solidifier. The potassium hydroxide-anhydrous sodium sulfate mixture is prepared by mixing potassium hydroxide and anhydrous sodium sulfate and then drying under vacuum. The composite functional powder is prepared by premixing nano-silica and methyl hydroxyethyl cellulose in equal mass. The gradient activated fly ash is prepared by sequentially subjecting raw fly ash to gradient temperature-controlled calcination, ultrasonic-assisted water washing, and low-temperature plasma activation.

2. The preparation method of the fly ash-based soft soil solidifying agent according to claim 1, characterized in that, The gradient temperature-controlled calcination conditions include: in the first temperature zone, the temperature is increased to 400-450℃ at 3℃ / min and held for 1-1.5h; in the second temperature zone, the temperature is increased to 750-800℃ at 5℃ / min and held for 2-2.5h; in the third temperature zone, the temperature is decreased to 600-650℃ and held for 1h, and ozone with a volume fraction of 3%-5% is introduced. After calcination, the mixture is cooled to room temperature to obtain gradient calcined fly ash. The conditions for ultrasonic-assisted water washing include: adding gradient calcined fly ash to deionized water, ultrasonically treating it for 40-60 minutes at an ultrasonic power of 300-500W and a temperature of 35-45℃, stirring once every 20 minutes, letting it stand for 30 minutes, then measuring the conductivity of the supernatant, filtering when the conductivity is ≤40μS / cm, collecting the filter cake and drying it; the mass ratio of gradient calcined fly ash to deionized water is 1:(3-5); the drying conditions include: drying at 105-110℃ until the moisture content is ≤3%; The conditions for low-temperature plasma activation include: introducing a mixture of argon and oxygen gas, a processing power of 150-200W, a pressure of 50-80Pa, and a processing time of 15-25min; the volume ratio of argon to oxygen is 8:

2.

3. The preparation method of the fly ash-based soft soil solidifying agent according to claim 1, characterized in that, The vacuum drying conditions include: a temperature of 60-80℃, a vacuum degree of -0.08MPa, and a time of 1-2 hours; The particle size of the rapid-hardening silicate cement is ≤2mm, the particle size of the sulfoaluminate cement is ≤2mm, the particle size of the metakaolin is ≤2mm, and the particle size of the slag powder is ≤2mm. The mixing conditions include: mixing at 180-220 r / min for 8-12 min; The conditions for the second stirring to achieve uniformity include: stirring at 220-260 r / min for 12-16 min; The conditions for the third stirring to achieve uniformity include: stirring at 260-300 r / min for 15-20 min; The conditions for the fourth mixing to achieve uniformity include: mixing at 300-320 r / min for 8-10 min.

4. The preparation method of the fly ash-based soft soil solidifying agent according to claim 1, characterized in that, The conditions for the low-temperature ball milling include: using zirconia balls as the grinding media, adding 0.3%-0.5% polyethylene glycol 400 as a grinding aid (by mass of the mixture); a grinding temperature of 20-30℃, a grinding speed of 250-300 r / min, a grinding time of 1.5-2.5 h, resulting in a particle size D50 of 5-8 μm and a specific surface area of ​​600-700 m². 2 / kg; The constant temperature and humidity aging conditions include: temperature of 15-20℃, relative humidity of 35%-45%, aging time of 36-60h, stirring once every 10h, controlling the temperature rise during the aging process to be ≤5℃, and after aging, the initial setting time to be ≥50min and the final setting time to be ≤7h.

5. The preparation method of the fly ash-based soft soil solidifying agent according to claim 1, characterized in that, The rapid-hardening silicate cement is P·O42.5R grade, with an initial setting time ≤45min; The sulfoaluminate cement is grade 52.5 rapid-hardening sulfoaluminate cement with a 1-day compressive strength ≥20MPa; The metakaolin is calcined kaolin at 700-800℃, with an active alumina content ≥35% and a specific surface area ≥500m². 2 / kg; The modified water glass is a potassium-sodium composite water glass with a solid content ≥45%; The nano-silica is hydrophilic fumed silica with a purity ≥99.8%; The tartaric acid is of industrial grade with a purity of ≥99%. The viscosity of the methyl hydroxyethyl cellulose is 200,000 mPa·s; The specific surface area of ​​the gradient activated fly ash is 550-650 m². 2 / kg; The fly ash-based soft soil solidifier has a 1-day compressive strength ≥ 5.0 MPa, a 7-day compressive strength ≥ 5.5 MPa, and a 28-day compressive strength ≥ 8.5 MPa. When the original fly ash is Class I fly ash from a coal-fired power plant, the loss on ignition is ≤5%, the silica content is ≥55%, and the alumina content is ≥25%. When the original fly ash is Class II fly ash, the holding time in the first temperature zone is 2-2.5 hours, the low-temperature plasma activation treatment time is 30-35 minutes, and the specific surface area of ​​the gradient activated fly ash is ≥500 m². 2 / kg; When the fly ash-based soft soil solidifier is in slurry form, water is added at a water-to-material ratio of (0.35-0.45):1 and stirred. 0.1%-0.3% (by weight of fly ash-based soft soil solidifier) ​​of defoamer is added to prepare the slurry-like fly ash-based soft soil solidifier. The defoamer is an organosilicon defoamer. The stirring speed is 2000-2500 r / min, the stirring time is 8-10 min, and after standing for 30 min, the stratification degree is ≤1%.

6. A fly ash-based soft soil solidifying agent, characterized in that, The fly ash-based soft soil solidifier is prepared by any one of claims 1-5, wherein the fly ash-based soft soil solidifier comprises: 50%-70% gradient activated fly ash, 10%-20% rapid-hardening silicate cement, 8%-15% sulfoaluminate cement, 5%-12% metakaolin, 8%-15% slag powder, 3%-8% anhydrous sodium sulfate, 1%-4% potassium hydroxide, 2%-5% modified water glass, 1%-3% nano silica, 1%-3% tartaric acid, and 1%-3% methyl hydroxyethyl cellulose.

7. The application of the fly ash-based soft soil solidifier prepared by the preparation method of any one of claims 1-5 in soft soil with high water content, characterized in that, For soft soil with a high water content of 45%-55%, a vacuum preloading-electroosmosis combined technology is adopted. Preloading is carried out for 24 hours under a vacuum of -0.09MPa, followed by electroosmosis dehydration for 3-5 hours with a voltage gradient of 1.8-2.2V / cm to reduce the water content to 30%-38%. 13%-16% of fly ash-based soft soil solidifier by weight of the high water content soft soil is added, and after mixing, it is rolled in layers until the compaction degree is ≥94%. During the curing period, a moisturizing film is covered.

8. The application of the fly ash-based soft soil solidifier prepared by the preparation method of any one of claims 1-5 in high-organic-matter soft soil, characterized in that, For soft soil with a high organic matter content of 8%-12%, add 2.5%-4% of ammonium persulfate-ferrous sulfate composite oxidant by weight of the high organic matter soft soil, stir at a stirring speed of 120-160 r / min for 1-1.5 h, and then let it stand for 1.5 h; add 16%-19% of slurry-like fly ash-based soft soil solidifying agent by weight of the high organic matter soft soil, and form solidified piles with a diameter of 600-700 mm by high-pressure jet grouting; in the ammonium persulfate-ferrous sulfate composite oxidant, the mass ratio of ammonium persulfate to ferrous sulfate is 3:1; in the slurry-like fly ash-based soft soil solidifying agent, the mass ratio of water to fly ash-based soft soil solidifying agent is 0.4:

1.

9. The application of the fly ash-based soft soil solidifier prepared by the preparation method of any one of claims 1-5 in high-salt soft soil, characterized in that, For high-salt soft soil with a salt content of 1.5%-3%, add 3%-5% of the mass of the high-salt soft soil to a zeolite-bentonite composite salt adsorbent, stir evenly, and let stand for 2-3 hours; add 14%-17% of the mass of the high-salt soft soil to a fly ash-based soft soil solidifier, mix evenly, and then fill and compact in layers until the compaction degree is ≥95%; when the salt content of the high-salt soft soil is >2%, add 2%-4% of the mass of the fly ash-based soft soil solidifier to barium carbonate; in the zeolite-bentonite composite salt, the mass ratio of zeolite powder to bentonite is 2:

1.

10. The application of the fly ash-based soft soil solidifier prepared by the preparation method of any one of claims 1-5 in conventional soft soil, characterized in that, For conventional soft soil with a moisture content of 20%-35%, organic matter content ≤8%, and salt content ≤1.5%, add 9%-13% of the conventional soft soil mass of fly ash-based soft soil solidifier, stir for 15-20 minutes, and compact to a compaction degree ≥96%.

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