Composite activator for cement mixing pile, preparation method thereof, low-carbon cementitious material and application thereof

Abstract

The present application relates to the field of cementitious materials, and particularly relates to a composite activator for cement mixing pile, a preparation method thereof, low-carbon cementitious material and application thereof; the composite activator comprises 60%-75% of inorganic activation main body and 25%-40% of organic activation synergist; the inorganic activation main body comprises sodium hydroxide, sodium sulfate, metakaolin and nano silicon dioxide; the organic activation synergist comprises modified lignin sulfonate, modified potassium humate and modified corn straw biochar; a core-shell structure is formed with the inorganic activation main body component as the core and the organic synergist component as the shell; the inorganic core provides continuous activation power and ensures the activation efficiency of solid waste; the organic component and the inorganic component are directionally chemically bonded, which prevents inorganic particle agglomeration, realizes uniform dispersion of the activation component, solves the agglomeration and uncontrolled activation of the traditional activator; the organic shell slowly releases the inorganic activation component, controls the hydration rate, adapts to construction, improves the interface affinity with soft soil and solid waste, and reduces interface defects and shrinkage cracks.

Description

Technical Field

[0001] This invention relates to the field of cementitious materials, and more particularly to a composite activator for cement mixing piles and its preparation method, low-carbon cementitious materials and their applications. Background Technology

[0002] Soft soil foundations along coastlines, rivers, and lakes typically have high water content, large porosity, and low bearing capacity, requiring reinforcement to meet engineering requirements. Cement mixing piles utilize cementitious materials mixed with soft soil, forming strong piles through a hydration reaction to reinforce the soft soil. Their convenient construction and significant reinforcement effects have made them the mainstream technology for soft soil foundation treatment.

[0003] Currently, ordinary Portland cement is commonly used as the cementitious material for cement mixing piles, but its production process is energy-intensive and emits a lot of pollutants. To reduce carbon emissions, industrial solid wastes such as slag, fly ash, and steel slag are commonly used to replace part of the cement, which can both realize the resource utilization of solid waste and reduce carbon emissions. However, there is a core problem: industrial solid waste has low activity, and the internal active SiO2 and Al2O3 are difficult to be fully activated, resulting in insufficient hydration of the cementitious material, substandard strength of the cement mixing pile, and easy formation of shrinkage cracks.

[0004] Existing technologies mostly use single inorganic activators or simple inorganic composite activators (such as sodium hydroxide and sodium sulfate) to activate the activity of solid waste, but they have obvious drawbacks: First, the activation efficiency is low, only activating a small amount of active components on the surface of solid waste, with a solid waste utilization rate of less than 40%, and the 28-day compressive strength of the pile body is difficult to reach 1.8 MPa; Second, the compatibility is poor, and the hydration reaction rate cannot be controlled, easily resulting in excessively fast or slow coagulation, affecting the construction quality; Third, the carbon sequestration effect is limited, only able to reduce carbon by replacing cement, with a reduction of only 20%-30%, failing to tap the carbon sequestration potential of solid waste; Fourth, the preparation process is simple, involving only physical mixing, resulting in uneven dispersion of components and poor synergistic effect; Fifth, it is difficult to balance mechanical properties and durability, with insufficient impermeability, frost resistance, and erosion resistance of the pile body, making it unable to adapt to complex engineering environments.

[0005] Therefore, there is an urgent need to develop a composite activator for cement mixing piles with high activation efficiency and high revitalization efficiency of industrial solid waste, as well as its preparation method and application. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, this invention provides a composite activator for cement mixing piles with high activation efficiency and high reactivity of industrial solid waste, as well as its preparation method and application.

[0007] On the one hand, the present invention provides a composite activator for cement mixing piles, comprising the following raw material components by mass percentage: 60%-75% inorganic activator and 25%-40% organic activator synergist; The inorganic excitation substrate comprises the following raw materials by mass percentage: sodium hydroxide 18%-20%, sodium sulfate 14%-20%, metakaolin 25%-30%, and nano-silica 3%-5%; The organic activator comprises the following raw materials in the following mass percentages: 10%-15% modified lignin sulfonate, 8%-12% modified potassium humate, and 7%-13% modified corn straw biochar.

[0008] In some embodiments of this application, the modified lignin sulfonate is an alkali-modified lignin sulfonate with a molecular weight of 5000-10000.

[0009] In some embodiments of this application, the modified potassium humate is an oxidized-potassium-modified composite potassium humate, wherein the humic acid content is ≥70%.

[0010] In some embodiments of this application, the modified corn stalk biochar is amino-modified corn stalk biochar with a specific surface area ≥300m² / g.

[0011] On the other hand, this application also provides a method for preparing the above-mentioned composite activator, specifically including the following steps: Preparation of organic activator masterbatch: Modified lignin sulfonate, modified potassium humate, and modified corn straw biochar were activated at 50-60℃ for 30 min, vacuum dried to a moisture content of ≤3%, and pulverized to a particle size of ≤30μm to obtain organic activator masterbatch; Preparation of inorganic excitation masterbatch: Sodium hydroxide, sodium sulfate and metakaolin are ball-milled at 30-38℃ for 60-90 min to obtain an inorganic mixture. The inorganic mixture and nano-silica are ultrasonically dispersed for 15-20 min and dried to obtain the inorganic excitation masterbatch. In-situ coating: Under stirring conditions of 40-50℃ and 100-150r / min, the organic activator masterbatch is added to the inorganic activator masterbatch at a rate of 5-10g / min and coated for 20-25min to form a composite activator semi-finished product with an inorganic core-organic shell structure. Drying and shaping: The composite activator semi-finished product obtained in the in-situ coating step is vacuum dried at 60-70℃ until the moisture content is ≤2%, pulverized to a particle size of ≤20μm, and then sieved to obtain the composite activator.

[0012] In another aspect, this application provides a low-carbon cementitious material, which comprises the following raw materials in the indicated mass fractions: The cementitious material comprises 14%-16% silicate cement, 59%-68% industrial solid waste, and 18%-22% carbonized modified steel slag powder, with the sum of the mass fractions of each component being 100%. It also includes the aforementioned composite activator, which accounts for 7%-10% of the total mass of the cementitious material.

[0013] In some embodiments of this application, the industrial solid waste includes raw materials with the following mass fractions: 44%-46% slag powder and 15%-22% fly ash.

[0014] In some embodiments of this application, the method for preparing the carbonized modified steel slag powder is as follows: The steel slag is crushed and then ball-milled. Under the conditions of 30-40℃ and 0.4-0.7MPa, CO2 with a concentration of 12%-18% is introduced for carbonization for 2.5-3.5h. After cooling to room temperature, the carbonized modified steel slag powder is obtained by sieving.

[0015] Furthermore, this application also provides a method for preparing the aforementioned low-carbon cementitious material, comprising the following steps: Raw material pretreatment: The industrial solid waste is dried until its moisture content is ≤2%; Raw material mixing: The silicate cement, the industrial solid waste, and the carbonized modified steel slag powder are mixed in proportion and stirred to obtain a low-carbon cementitious material semi-finished product; Activation process: Add the composite activator to the low-carbon cementitious material semi-finished product, stir, and the low-carbon cementitious material is obtained.

[0016] On the other hand, the above-mentioned low-carbon cementitious material is applied to the reinforcement of soft soil foundation. The soft soil, water and the low-carbon cementitious material are mixed and stirred in a mass ratio of (720-820):(130-170):(90-110) and molded. After curing, cement mixing piles are formed, and the cement mixing piles are used for the reinforcement of soft soil foundation.

[0017] Based on the above technical solution, the composite activator of this invention, sodium hydroxide, provides a strongly alkaline environment that breaks the inert Si-O-Si and Al-O-Al bonds inside slag, fly ash, and carbide steel slag powder, releasing active SiO3². - AlO2 - Sodium sulfate reacts with the hydration product Ca(OH)2 to form ettringite, which rapidly improves early strength; metakaolin participates in the formation of CASH gel, filling micropores; nano-silica exerts a nucleation effect, accelerating the formation of hydration gel and improving the density of the system; Modified lignin sulfonate is modified by alkalization, which forms hydrogen bonds with inorganic particles through sulfonic acid groups and hydroxyl groups, thereby achieving efficient dispersion, preventing activator agglomeration, regulating hydration rate, improving the interfacial adhesion between cementitious materials and soft soil, and reducing shrinkage cracks. Potassium humate is modified by potassiumization to chelate Ca²⁺ with carboxyl and phenolic hydroxyl groups. + Mg² + Plasma disrupts the inert structure of solid waste, activates carbon fixation sites, stabilizes the alkalinity of the system, and prevents cracking by strong alkali. In existing technologies, potassium humate is only used as a pH adjuster. Amino-modified corn straw biochar undergoes a condensation reaction between amino groups and hydroxyl groups of inorganic excitation substrates to form a porous and toughened structure, which synergistically performs carbon fixation and improves the stability of the system. The composite activator has an inorganic activating main component as the core and an organic synergist component as the shell, forming a core-shell structure: the inorganic core provides continuous activating power to ensure the activation efficiency of solid waste; the organic component and the inorganic component undergo directional chemical bonding to prevent the inorganic particles from agglomerating and achieve uniform dispersion of the activating component, solving the problems of agglomeration and uncontrolled activation of traditional activators, and increasing the activation rate of industrial solid waste to 82%-90%; the organic shell slowly releases inorganic activating components, controls the hydration rate, adapts to construction, improves the interface affinity with soft soil and solid waste, reduces interface defects and shrinkage cracks, and significantly improves impermeability, frost resistance and erosion resistance. The cementitious material of this invention is low-carbon and environmentally friendly, reducing the amount of silicate cement to 10%-18%, and the amount of composite activator is greater than that of conventional alkaline activator, which enhances the deep activation effect of industrial solid waste, makes up for the strength gap caused by insufficient cement, and synergistically achieves deep activation and performance improvement of solid waste. Compared to the traditional 100% cement mix ratio, the carbon emissions per unit volume of the mixing pile are reduced to 240-275 kg / m³, a carbon reduction of 65%-75%, which is far higher than the carbon reduction level of 20%-30% of the existing technology. At the same time, it achieves an industrial solid waste utilization rate of 82%-90%, promoting the resource utilization of industrial solid waste. Cementitious materials can be used to make concrete mixing piles to reinforce soft soil foundations. Carbonized modified steel slag powder utilizes its carbon-fixing components such as CaO and MgO to tap the carbon-fixing potential of steel slag powder and improve its volume stability. With the synergistic effect of composite activators, the mixing piles are crack-free, and their impermeability and frost resistance are improved by more than 30% compared with traditional cement. They can be adapted to complex engineering scenarios such as high-grade highways and port terminals, and solve the problem of easy cracking of existing piles. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a SEM image of the composite activator of Embodiment 1 of the present invention; Figure 2 This is a surface morphology image of a cement mixing pile after 28 days of standard curing according to Embodiment 1 of the present invention; Figure 3 This is a surface morphology diagram of the cement mixing pile of Comparative Example 1 of the present invention after 28 days of standard curing. Figure 4 This is a surface morphology diagram of the cement mixing pile of Comparative Example 2 of the present invention after 28 days of standard curing; Figure 5 This is a surface morphology diagram of the cement mixing pile of Comparative Example 3 of the present invention after 28 days of standard curing; Figure 6 This is a surface morphology diagram of the cement mixing pile of Comparative Example 4 of the present invention after 28 days of standard curing. Figure 7 This is a surface morphology diagram of the cement mixing pile of Comparative Example 5 of the present invention after 28 days of standard curing. Figure 8 This is a surface morphology diagram of the cement mixing pile of Comparative Example Six of the present invention after 28 days of standard curing; Figure 9 This is a surface morphology diagram of the cement mixing pile of Comparative Example 7 of the present invention after 28 days of standard curing. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides a composite activator comprising the following raw material components by mass percentage: 60%-75% inorganic activating body and 25%-40% organic activating synergist; The inorganic excitation substrate comprises the following raw materials by mass percentage: sodium hydroxide 18%-20%, sodium sulfate 14%-20%, metakaolin 25%-30%, and nano-silica 3%-5%; The organic activator and synergist comprises the following raw materials in the following weight percentages: 10%-15% modified lignin sulfonate, 8%-12% modified potassium humate, and 7%-13% modified corn straw biochar.

[0021] Sodium hydroxide is a strong alkaline activator that breaks the inert Si-O-Si and Al-O-Al bonds inside industrial solid waste, releasing active ingredients. Excessive dosage can easily cause cracks, while insufficient dosage leads to inadequate activation. Sodium sulfate is a sulfate activator that reacts with Ca(OH)2, a cement hydration product, to form ettringite, which can rapidly improve early strength. It works synergistically with sodium hydroxide to improve activation efficiency, but excessive dosage can easily cause expansion and cracking. Active Al2O3 in metakaolin assists in activation, participates in the formation of CASH gel, fills micropores, and improves the structure. Excessive dosage increases water demand and cost. In some embodiments, nano-silica has a specific surface area ≥500m² / g and a particle size of 20-50nm. It exerts a nucleation effect, accelerates the formation of hydrated gel, fills pores, promotes hydration, improves compatibility, and increases the density of the system. However, excessive use of nano-silica can easily lead to agglomeration.

[0022] In some embodiments, the modified lignin sulfonate is an alkali-modified lignin sulfonate with a molecular weight of 5000-10000. Through alkali modification, lignin sulfonate forms hydrogen bonds with inorganic particles via sulfonic acid groups and hydroxyl groups, achieving efficient dispersion, preventing activator agglomeration, regulating hydration rate, improving the interfacial adhesion between cementitious materials and soft soil, and reducing shrinkage cracks. However, excessive dosage can delay strength development. In the prior art, lignin sulfonate is used as a water-reducing agent and a retarder.

[0023] When preparing alkali-modified lignin sulfonate, industrial-grade calcium lignin sulfonate or sodium lignin sulfonate are selected as raw materials. The lignin content must be no less than 55%, the moisture content no more than 5%, and the fineness must meet the requirement of 80 mesh for complete passage. Analytical grade sodium hydroxide, 1 mol / L dilute hydrochloric acid, anhydrous ethanol, and a resistivity of no less than 18.2 MΩ are used. . cm of deionized water was modified in a constant temperature stirred reactor, vacuum filter, vacuum drying oven and ultrafine pulverization equipment.

[0024] Specifically, the raw materials are first pretreated by drying the lignin sulfonate raw materials in a 105℃ forced-air drying oven for 2 hours until the moisture content is ≤3%; the raw materials are then pulverized at high speed and passed through an 80-mesh standard sieve to remove mechanical impurities and large particles, thus obtaining the pretreated lignin sulfonate. Subsequently, deionized water was added to the constant temperature reactor at a liquid-to-solid mass ratio of 5:1, and stirring was started at 300 r / min. The pretreated lignin sulfonate was added until completely dissolved, and sodium hydroxide solid was slowly added to adjust the pH of the system to 10.5±0.2. The constant temperature reactor was heated to 55±2℃ and stirred for 30 minutes to activate the lignin molecular chain segments and expose the active sites. Maintain a stirring speed of 250 r / min, raise the temperature of the constant temperature reactor to 62±3℃, and carry out an alkaline depolymerization modification reaction for 2 hours to directionally enhance the dissociation and activation of sulfonic acid groups and hydroxyl groups, thereby improving the coordination and binding, dispersion and retardation, and interface modification capabilities of the components with the inorganic excited phase. After the reaction is complete, slowly add 1 mol / L dilute hydrochloric acid to adjust the pH of the system to 7.5±0.2 to neutral. Add anhydrous ethanol at a volume ratio of 1:1 between the liquid and anhydrous ethanol. Stir for 15 minutes to allow the modified product to precipitate fully. Remove the filtrate and soluble impurities by vacuum filtration, and retain the filter cake. Finally, the filter cake was placed in a vacuum drying oven at 65±5℃ and dried for 4 hours until the moisture content was ≤2%. After being ultra-finely pulverized and passed through a 100-mesh standard sieve, alkalized modified lignin sulfonate was obtained. The molecular weight of the product was controlled at 5000-10000, the particle size was ≤30μm, the sulfonic acid group content was ≥1.2mmol / g, and the hydroxyl content was ≥0.8mmol / g.

[0025] In some embodiments, the modified potassium humate is an oxidized-potassium-modified potassium humate, wherein the humic acid content is ≥70%. Currently, potassium humate is generally used as a pH adjuster. The potassium-modified potassium humate chelates Ca²⁺ with carboxyl and phenolic hydroxyl groups. + Mg² + Metal ions can disrupt the inert structure of industrial solid waste, activate carbon fixation sites, stabilize the alkalinity of the system, and improve the binding force with soft soil. However, excessive dosage can affect the pH value.

[0026] When preparing oxidized-potassium-modified potassium humate, humic acid extracted from lignite or weathered coal is used as raw material. The humic acid content is required to be ≥50%, ash content ≤15%, moisture content ≤5%, and fineness 100 mesh. It is then combined with analytical grade potassium hydroxide, potassium carbonate, and deionized water, and the modification is completed in a constant temperature stirred reactor, vacuum filter, and spray dryer.

[0027] Specifically, the raw materials are first dried in a 105℃ forced-air drying oven for 2 hours, then pulverized and passed through a 100-mesh standard sieve to remove ash, sand and other impurities. Add deionized water to the reactor at a liquid-to-solid mass ratio of 4:1, heat the reactor to 42±3℃, start stirring at 300r / min and add humic acid powder for pre-hydration oxidation activation for 30 minutes to increase the exposure of reactive sites of humic acid molecules. Add a composite potassium oxidizing agent of potassium hydroxide and potassium carbonate in a mass ratio of 1:1 to (13±2)% of humic acid. Raise the temperature of the reactor to (72±3)℃, maintain a stirring speed of 200 r / min, and carry out the oxidation-potassium oxidizing composite modification reaction for 3 hours to complete the potassium ion replacement, carboxyl and phenolic hydroxyl activation of humic acid, and enhance the component's effect on Ca²⁺. + Mg² + The chelating ability and alkalinity stability of the system; After the reaction is complete, keep the temperature of the reactor at no less than 60°C, and immediately remove the insoluble residue by vacuum filtration, retaining the filtrate containing modified potassium humate. The filtrate was spray-dried or vacuum-dried at (70±5)℃ for 6 hours until the product moisture content was ≤2%. It was then pulverized through an 80-mesh standard sieve to obtain an oxidized-potassium modified potassium humate product that can be used for industrial solid waste activation and carbon fixation. The product has a humic acid content ≥70%, a particle size ≤30μm, a potassium oxide content ≥8%, a pH value of 9.0-10.0, and a chelation capacity ≥2.8mmol / g.

[0028] In some embodiments, the modified corn stalk biochar is an amino-modified corn stalk biochar with a specific surface area ≥300m² / g; the amino group undergoes a condensation reaction with the inorganic phase hydroxyl group to form a porous and toughened structure, which synergistically fixes carbon and improves the stability of the system, thereby realizing the resource utilization of agricultural waste.

[0029] The preparation of amino-modified corn stalk biochar involves using naturally air-dried corn stalks free from mold and impurities as raw materials, combined with industrial-grade 3-aminopropyltriethoxysilane (KH550, silane coupling agent), anhydrous ethanol, 25%-28% concentrated ammonia, and deionized water, and completing the preparation in a tubular carbonization furnace, ultrasonic disperser, constant temperature reflux reactor, and vacuum drying oven.

[0030] Specifically, the corn stalks are first washed to remove mud and sand, dried at 105℃ to constant weight, and then cut into 2-5mm small pieces. They are then placed in a tube furnace and high-purity nitrogen gas with a flow rate of 50mL / min is introduced to remove oxygen for 30 minutes. The temperature is then raised to 500±50℃ at a rate of 5℃ / min and carbonized under limited oxygen for 2 hours. After naturally cooling to room temperature, the stalks are pulverized at high speed and passed through a 100-mesh standard sieve to obtain basic corn stalk biochar. Subsequently, the basic corn straw biochar was added to a mixed solvent of anhydrous ethanol and deionized water in a volume ratio of 7:3 at a liquid-to-solid mass ratio of 10:1, and treated with a 420W ultrasonic disperser for 20 minutes to form a uniform and stable suspension. Add 3-aminopropyltriethoxysilane at (6±1)% of the mass of basic corn straw biochar to the suspension, add concentrated ammonia to adjust the pH of the system to 9.5±0.3, heat to (62±3)℃ and turn on reflux condenser, maintain stirring speed of 200r / min, and carry out amino grafting modification reaction at constant temperature for 3 hours to achieve directional condensation bonding between amino functional groups and hydroxyl groups on the surface of corn straw biochar. After the reaction was completed, the solid product was separated by vacuum filtration, washed three times with anhydrous ethanol and twice with deionized water until the pH of the washing solution reached 7.0±0.2, so as to completely remove unreacted 3-aminopropyltriethoxysilane and soluble impurities. Finally, the washed product was placed in a vacuum drying oven at (80±5)℃ and dried for 5 hours until the moisture content was ≤2%. It was then ultra-finely pulverized and passed through a 120-mesh standard sieve to obtain amino-modified corn straw biochar. The product had a specific surface area ≥300m² / g, amino grafting rate ≥1.2%, particle size ≤30μm, and pore volume ≥0.25cm³ / g.

[0031] The preparation method of the above-mentioned composite activator specifically includes the following steps: S1. Preparation of organic activator masterbatch: Alkali-modified lignin sulfonate, potassium-modified potassium humate, and amino-modified corn straw biochar are mixed and activated at 50-60℃ for 30 min, vacuum dried to a moisture content of ≤3%, and pulverized to a particle size of ≤30μm to obtain organic activator masterbatch. It should be noted that after modification, alkalization-modified lignin sulfonate, oxidation-potassium compound modified potassium humate, and modified corn straw biochar may absorb water during the preparation process. After activation, they need to be dried again. The vacuum drying temperature is 50-70℃, which is higher than the activation temperature. After drying, they are put into a planetary ball mill for pulverization.

[0032] S2. Preparation of inorganic excitation masterbatch: Sodium hydroxide, sodium sulfate and metakaolin are ball-milled in a ball mill at 30-38℃ for 60-90 min to obtain an inorganic mixture. The inorganic mixture and nano-silica are placed in a 400-450W probe ultrasonic crusher and dispersed for 15-20 min. After drying, the inorganic excitation masterbatch is obtained. S3. In-situ coating: Using a constant temperature magnetic stirrer, at 40-50℃ and 100-150r / min stirring conditions, add the organic activator masterbatch from step S1 to the inorganic activator masterbatch at a rate of 5-10g / min, and coat for 20-25min to form a composite activator semi-finished product with an inorganic core-organic shell structure. S4 Drying and Shaping: The composite activator semi-finished product obtained in step S3 is vacuum dried at 60-70℃ until the moisture content is ≤2%, pulverized to a particle size ≤20μm, and then sieved to obtain the composite activator.

[0033] The resulting composite activator is a grayish-white to grayish-brown uniform powder with a moisture content of ≤2.0%, a D90 particle size of ≤20 μm, an 80 μm sieve residue of ≤1.0%, and a pH value of 11.5–13.5 for a 10% aqueous solution. It also exhibits no obvious agglomeration or clumping and good dispersion stability.

[0034] By forming a core-shell structure with an inorganic activating component as the core and an organic synergistic component as the outer shell through in-situ coating, the inorganic core provides continuous activation power to ensure the activation efficiency of industrial solid waste; the organic shell prevents the agglomeration of inorganic activating component particles and achieves uniform dispersion of the activating component; the organic shell slowly releases inorganic activating components, which can control the hydration rate and adapt to construction; the organic shell improves the interface affinity with soft soil and industrial solid waste, and reduces interface defects and shrinkage cracks; the core-shell structure synergistically optimizes micro-density, which greatly improves impermeability, frost resistance and erosion resistance.

[0035] Organic and inorganic components undergo directional chemical bonding, solving the problems of aggregation and uncontrolled activation of traditional inorganic activators, and increasing the activation rate of industrial solid waste to 82%-90%.

[0036] In another aspect, in some embodiments, this application also provides a low-carbon cementitious material, including the above-mentioned composite activator, wherein the composite activator accounts for 7%-10% of the total mass of the cementitious material, and the low-carbon cementitious material further includes the following raw materials by mass fraction: The composition consists of 14%-16% silicate cement, 59%-68% industrial solid waste, and 18%-22% carbonized modified steel slag powder, with the sum of the mass fractions of each component being 100%.

[0037] Adding 7%–10% of the composite activator by mass to low-carbon cementitious materials can increase the activity index of low-carbon cementitious materials to about 80% at 7 days and about 90% at 28 days.

[0038] Silicate cement provides basic hydration activity. Compared with the proportion of traditional cementitious materials, this invention significantly reduces the amount of cement used, to below 20%, and significantly reduces carbon emissions. Through the synergistic effect of composite activators and industrial solid waste, it compensates for the strength loss caused by the significant reduction in cement usage, and achieves a balance between low carbon and strength.

[0039] Compared to the traditional 100% cement mix ratio, the carbon emissions per unit volume of the mixing pile are reduced to 240-275 kg / m³, a carbon reduction of 65%-75%, which is far higher than the 20%-30% carbon reduction level of existing technologies. At the same time, it achieves an industrial solid waste utilization rate of 82%-90%, promoting the resource utilization of industrial solid waste.

[0040] In some embodiments, industrial solid waste includes raw materials in the following mass fractions: 44%-46% slag powder and 15%-22% fly ash.

[0041] The slag powder is granulated blast furnace slag powder with a specific surface area of ​​400-450 m² / kg and a fineness (80 μm sieve residue) of ≤8%. It contains a large amount of active SiO2 and Al2O3, which generate cementing products under the action of composite activators. These products serve as the core strength source, compensating for the strength loss caused by the significant reduction in cement dosage and significantly improving the strength of cement mixing piles. The substantial increase in the amount of slag powder can fully leverage its active advantages.

[0042] The fly ash selected is Grade II or above, with a fineness of ≤12% and a loss on ignition of ≤5%. It has pozzolanic activity, can fill micropores, improve density and impermeability. The synergistic effect of fly ash and slag powder further improves the utilization rate of industrial solid waste, reduces dependence on silicate cement, and supports the integrity of the microstructure of cement mixing piles.

[0043] In some embodiments, the preparation method of carbonized modified steel slag powder is as follows: After crushing the steel slag, it is ball-milled and carbonized with CO2 at a concentration of 12%-18% for 2.5-3.5 hours at 30-40℃ and 0.4-0.7MPa. After cooling to room temperature, it is sieved to obtain carbonized modified steel slag powder.

[0044] Specifically, the steel slag is crushed to ≤10mm, ball-milled to ≤60μm, and then sieved for later use; the carbonization rate of the carbonized modified steel slag powder is ≥35%, and the particle size is ≤60μm.

[0045] The application of carbonized modified steel slag powder not only taps the carbon fixation potential of steel slag, but also improves the volume stability of steel slag. With the synergistic effect of composite activators, cement mixing piles are crack-free, and their impermeability and frost resistance are improved by more than 30% compared with traditional cement. They can be adapted to complex engineering scenarios such as high-grade highways and port terminals, and solve the problem of easy cracking of existing pile bodies.

[0046] In some embodiments, the preparation method of the above-mentioned low-carbon cementitious material includes the following steps: Raw material pretreatment: The slag powder and fly ash are dried until their moisture content is ≤2%; Raw material mixing: Silicate cement, slag powder, fly ash, and carbonized modified steel slag powder are mixed in proportion and stirred at 350-450 r / min for about 20 minutes to obtain a low-carbon cementitious material semi-finished product; Activation process: Add composite activator to the low-carbon cementitious material semi-finished product, stir at 200-250 r / min for 15-18 min to obtain the low-carbon cementitious material.

[0047] The preparation process of cementitious materials is simple, requiring no additional special equipment. It can be adapted to existing cement mixing pile construction equipment, and the preparation cost is 8%-12% lower than that of traditional cementitious materials. It balances economy and practicality, and is easy to industrialize and apply in engineering.

[0048] On the other hand, the aforementioned low-carbon cementitious material is applied to the reinforcement of soft soil foundations. Soft soil, water, and the aforementioned low-carbon cementitious material are mixed and stirred at a mass ratio of (720-820):(130-170):(90-110) to form cement-mixed piles after standard curing. These cement-mixed piles are used for soft soil foundation reinforcement. The 28-day compressive strength of the cement-mixed piles reaches approximately 1.9–2.0 MPa, and the pile body shows no obvious cracks.

[0049] To provide a clearer and more detailed description of the composite activator for cement mixing piles and its preparation method, as well as the low-carbon cementitious material and its application provided in the embodiments of the present invention, the following description will be based on specific embodiments.

[0050] Example 1 The composite activator for cement mixing piles in this embodiment comprises the following raw material components by mass percentage: The inorganic excitation component comprises 70%, including 20% ​​sodium hydroxide, 15% sodium sulfate, 30% metakaolin, and 5% nano-silica. The organic activator and synergist comprises 30%, including 13% alkalized modified lignin sulfonate, 10% oxidized potassium humate, and 7% amino-modified corn straw biochar. Preparation of composite activators: S1. Preparation of organic activator masterbatch: Alkali-modified lignin sulfonate, potassium-modified humate and amino-modified corn straw biochar of the above mass fractions are mixed and activated at 55℃ for 30 min, vacuum dried to moisture content ≤3%, and stirred and pulverized at 100 r / min to particle size ≤30 μm to obtain organic activator masterbatch. S2. Preparation of inorganic excitation masterbatch: Sodium hydroxide, sodium sulfate and metakaolin of the above mass fractions are spherically milled in a ball mill at 35°C and 250 r / min for 80 min to obtain an inorganic mixture. The inorganic mixture and nano silica are placed in a 400W probe ultrasonic breaker and dispersed for 18 min. After drying, the inorganic excitation masterbatch is obtained. S3. In-situ coating: Using a constant temperature magnetic stirrer, under stirring conditions of 45℃ and 130r / min, the organic activator masterbatch from step S1 is added to the inorganic activator masterbatch at a rate of 8g / min, and the coating is carried out for 22min to form a composite activator semi-finished product with an inorganic core-organic shell structure. S4 Drying and Shaping: The composite activator semi-finished product obtained in step S3 is vacuum dried at 65℃ until the moisture content is ≤2%, pulverized to a particle size of 18μm, and sieved to obtain the composite activator. For example... Figure 1 As shown, the composite activator exhibits no obvious agglomeration or clustering and demonstrates good dispersion stability.

[0051] Preparation of carbonized modified steel slag powder: The steel slag was crushed and ball-milled at 180 r / min. It was carbonized for 3 h with 15% CO2 at 35℃ and 0.5 MPa. After cooling to room temperature, the carbonized modified steel slag powder with a carbonization rate of 38% and a particle size of 50 μm was obtained by sieving.

[0052] The low-carbon cementitious material comprises the following raw material components by mass percentage: 15% commercially available PO42.5 grade silicate cement, 45% slag powder with a specific surface area of ​​430 m² / kg, 18% Grade I fly ash, and 22% of the aforementioned carbonized modified steel slag powder; the aforementioned composite activator accounts for 8% of the mass percentage of the low-carbon cementitious material. Dry the slag powder and fly ash until their moisture content is ≤2%; mix silicate cement, slag powder, fly ash and carbonized modified steel slag powder in proportion, stir at 400 r / min for 20 min, then add the composite activator and stir at 230 r / min for 16 min to obtain the low-carbon cementitious material.

[0053] The composite activator cementitious material prepared in Example 1, soft soil, and water were mixed in a mass ratio of 100:770:150 to obtain cement mixing piles, which were then subjected to standard curing. The soft soil used was silty soil with a moisture content of 35%-40% and a liquid limit index of 1.1-1.3. The 7-day activity index of the aforementioned cementitious material is 79%, and the 28-day activity index is 89%; the 7-day compressive strength of the cement mixing pile body is 1.2 MPa, and the 28-day compressive strength is 1.9 MPa; the carbon emission per unit volume of the cement mixing pile is 260 kg / m³, achieving a carbon reduction of 68%; Figure 2 As shown, after 28 days of standard curing, the surface of the cement mixing pile is intact and without cracks.

[0054] Example 2 The composite activator for cement mixing piles in this embodiment comprises the following raw material components by mass percentage: The inorganic excitation component comprises 75%, including 20% ​​sodium hydroxide, 18% sodium sulfate, 30% metakaolin, and 5% nano-silica. The organic activator and synergist comprises 25%, including 10% alkalized modified lignin sulfonate, 8% oxidized potassium humate, and 7% amino-modified corn straw biochar. Preparation of composite activators: S1. Preparation of organic activator masterbatch: Alkali-modified lignin sulfonate, potassium-modified humate and amino-modified corn straw biochar of the above mass fractions are mixed and activated at 52℃ for 30 min, vacuum dried to moisture content ≤3%, and stirred and pulverized at 90 r / min to particle size ≤30 μm to obtain organic activator masterbatch. S2. Preparation of inorganic excitation masterbatch: Sodium hydroxide, sodium sulfate and metakaolin of the above mass fractions are spherically milled in a ball mill at 240 r / min for 75 min at 38℃ to obtain an inorganic mixture. The inorganic mixture and nano silica are placed in a 420W probe ultrasonic breaker and dispersed for 17 min. After drying, the inorganic excitation masterbatch is obtained. S3. In-situ coating: Using a constant temperature magnetic stirrer, under stirring conditions of 48℃ and 120r / min, the organic activator masterbatch from step S1 is added to the inorganic activator masterbatch at a rate of 6g / min, and the coating is carried out for 23min to form a composite activator semi-finished product with an inorganic core-organic shell structure. S4 Drying and Shaping: The composite activator semi-finished product obtained in step S3 is vacuum dried at 65°C until the moisture content is ≤1.8%, pulverized to a particle size of 16μm, and then sieved to obtain the composite activator.

[0055] Preparation of carbonized modified steel slag powder: The steel slag was crushed and ball-milled at 190 r / min. It was carbonized for 3 h with 16% CO2 at 38℃ and 0.6 MPa. After cooling to room temperature, the carbonized modified steel slag powder with a carbonization rate of 40% and a particle size of 45 μm was obtained by sieving.

[0056] The low-carbon cementitious material comprises the following raw material components by mass percentage: 15% commercially available PO42.5 grade silicate cement, 45% slag powder with a specific surface area of ​​440 m² / kg, 20% grade I fly ash, and 19% carbonized modified steel slag powder; the aforementioned composite activator accounts for 7% of the mass percentage of the low-carbon cementitious material. Dry the slag powder and fly ash until their moisture content is ≤2%; mix silicate cement, slag powder, fly ash and carbonized modified steel slag powder in proportion, stir at 420 r / min for 19 min, then add the composite activator and stir at 220 r / min for 17 min to obtain the low-carbon cementitious material.

[0057] The composite activator cementitious material prepared in Example 2, soft soil, and water were mixed in a mass ratio of 95:750:140 to obtain cement mixing piles, which were then subjected to standard curing. The soft soil used was silty soil with a moisture content of 35%-40% and a liquid limit index of 1.1-1.3. The 7-day activity index of the above-mentioned cementitious material is 82%, and the 28-day activity index is 91%; the 7-day compressive strength of the cement mixing pile body is 1.25 MPa, and the 28-day compressive strength is 1.95 MPa; the carbon emission per unit volume of the cement mixing pile is 275 kg / m³, achieving a carbon reduction of 66%; and the pile body has no cracks.

[0058] Example 3 The composite activator for cement mixing piles in this embodiment comprises the following raw material components by mass percentage: The inorganic excitation component comprises 65%, including 20% ​​sodium hydroxide, 14% sodium sulfate, 28% metakaolin, and 3% nano-silica. The organic activator / synergist comprises 35%, including 14% alkalized modified lignin sulfonate, 11% oxidized potassium humate, and 10% amino-modified corn straw biochar. Preparation of composite activators: S1. Preparation of organic activator masterbatch: Alkali-modified lignin sulfonate, potassium-modified humate and amino-modified corn straw biochar of the above mass fractions are mixed and activated at 58℃ for 30 min, vacuum dried to moisture content ≤3%, and stirred and pulverized at 110 r / min to particle size ≤30 μm to obtain organic activator masterbatch. S2. Preparation of inorganic excitation masterbatch: Sodium hydroxide, sodium sulfate and metakaolin of the above mass fractions are spherically milled in a ball mill at 260 r / min for 85 min at 30℃ to obtain an inorganic mixture. The inorganic mixture and nano silica are placed in a 450W probe ultrasonic crusher and dispersed for 19 min. After drying, the inorganic excitation masterbatch is obtained. S3. In-situ coating: Using a constant temperature magnetic stirrer, at 42℃ and 140r / min stirring conditions, the organic activator masterbatch from step S1 is added to the inorganic activator masterbatch at a rate of 10g / min and coated for 24min to form a composite activator semi-finished product with an inorganic core-organic shell structure. S4 Drying and Shaping: The composite activator semi-finished product obtained in step S3 is vacuum dried at 65°C to a moisture content of 2%, pulverized to a particle size of 19μm, and then sieved to obtain the composite activator.

[0059] Preparation of carbonized modified steel slag powder: The steel slag was crushed and ball-milled at 170 r / min. It was carbonized for 2.8 h by passing CO2 with a concentration of 14% under the conditions of 32℃ and 0.5 MPa. After cooling to room temperature, the carbonized modified steel slag powder with a carbonization rate of 36% and a particle size of 55 μm was obtained by sieving.

[0060] The low-carbon cementitious material comprises the following raw material components by mass percentage: 16% commercially available PO42.5 grade silicate cement, 45% slag powder with a specific surface area of ​​420 m² / kg, 19% grade II fly ash, and 20% carbonized modified steel slag powder; the aforementioned composite activator accounts for 9% of the mass percentage of the low-carbon cementitious material. Dry the slag powder and fly ash until their moisture content is ≤2%; mix silicate cement, slag powder, fly ash and carbonized modified steel slag powder in proportion, stir at 380 r / min for 21 min, then add the composite activator and stir at 240 r / min for 16 min to obtain the low-carbon cementitious material.

[0061] The composite activator cementitious material prepared in Example 3, soft soil, and water were mixed in a mass ratio of 105:790:160 to obtain cement mixing piles, which were then subjected to standard curing. The soft soil used was silty soil with a moisture content of 35%-40% and a liquid limit index of 1.1-1.3. The 7-day activity index of the above-mentioned cementitious materials is 78%, and the 28-day activity index is 88%; the 7-day compressive strength of the cement mixing pile body is 1.18 MPa, and the 28-day compressive strength is 1.88 MPa; the carbon emission per unit volume of the cement mixing pile is 255 kg / m³, achieving a carbon reduction of 70%; and the pile body has no cracks.

[0062] Example 4 The composite activator for cement mixing piles in this embodiment comprises the following raw material components by mass percentage: The inorganic excitation component comprises 60%, including 20% ​​sodium hydroxide, 14% sodium sulfate, 25% metakaolin, and 5% nano-silica. The organic activator and synergist comprises 40%, including 15% alkalized modified lignin sulfonate, 12% oxidized potassium humate, and 13% amino-modified corn straw biochar. Preparation of composite activators: S1. Preparation of organic activator masterbatch: Alkali-modified lignin sulfonate, potassium-modified humate and amino-modified corn straw biochar of the above mass fractions are mixed and activated at 50℃ for 30 min, vacuum dried to moisture content ≤3%, and stirred and pulverized at 80 r / min to particle size ≤30 μm to obtain organic activator masterbatch. S2. Preparation of inorganic excitation masterbatch: Sodium hydroxide, sodium sulfate and metakaolin of the above mass fractions are spherically milled in a ball mill at 230 r / min for 90 min at 32℃ to obtain an inorganic mixture. The inorganic mixture and nano silica are placed in a 450W probe ultrasonic breaker and dispersed for 16 min. After drying, the inorganic excitation masterbatch is obtained. S3. In-situ coating: Using a constant temperature magnetic stirrer, under stirring conditions of 40℃ and 110r / min, the organic activator masterbatch from step S1 is added to the inorganic activator masterbatch at a rate of 5g / min, and the coating is carried out for 25min to form a composite activator semi-finished product with an inorganic core-organic shell structure. S4 Drying and Shaping: The composite activator semi-finished product obtained in step S3 is vacuum dried at 65°C to a moisture content of 1.9%, pulverized to a particle size of 20μm, and then sieved to obtain the composite activator.

[0063] Preparation of carbonized modified steel slag powder: The steel slag was crushed and ball-milled at 160 r / min. It was carbonized for 2.5 h by passing CO2 with a concentration of 12% under the conditions of 30℃ and 0.4 MPa. After cooling to room temperature, the carbonized modified steel slag powder with a carbonization rate of 35% and a particle size of 60 μm was obtained by sieving.

[0064] The low-carbon cementitious material comprises the following raw material components by mass percentage: 14% commercially available PO42.5 grade silicate cement, 46% slag powder with a specific surface area of ​​400 m² / kg, 18% grade II fly ash, and 22% of the aforementioned carbonized modified steel slag powder; the aforementioned composite activator accounts for 10% of the mass percentage of the low-carbon cementitious material. Dry the slag powder and fly ash until their moisture content is ≤2%; mix silicate cement, slag powder, fly ash and carbonized modified steel slag powder in proportion, stir at 350 r / min for 22 min, then add the composite activator and stir at 200 r / min for 18 min to obtain the low-carbon cementitious material.

[0065] The composite activator cementitious material prepared in Example 4, soft soil, and water were mixed in a mass ratio of 110:820:170 to obtain cement mixing piles, which were then subjected to standard curing. The soft soil used was silty soil with a moisture content of 35%-40% and a liquid limit index of 1.1-1.3. The 7-day activity index of the above-mentioned cementitious material is 77%, and the 28-day activity index is 87%; the 7-day compressive strength of the cement mixing pile body is 1.15 MPa, and the 28-day compressive strength is 1.85 MPa; the carbon emission per unit volume of the cement mixing pile is 240 kg / m³, achieving a carbon reduction of 75%; and the pile body has no cracks.

[0066] Example 5 The composite activator for cement mixing piles in this embodiment comprises the following raw material components by mass percentage: The inorganic excitation component comprises 72%, including 20% ​​sodium hydroxide, 20% sodium sulfate, 27% metakaolin, and 5% nano-silica. The organic activator and synergist comprises 28%, including 10% alkalized modified lignin sulfonate, 8% oxidized potassium humate, and 10% amino-modified corn straw biochar. Preparation of composite activators: S1. Preparation of organic activator masterbatch: Alkali-modified lignin sulfonate, potassium-modified humate and amino-modified corn straw biochar of the above mass fractions are mixed and activated at 56℃ for 30 min, vacuum dried to moisture content ≤3%, and stirred and pulverized at 120 r / min to particle size ≤30 μm to obtain organic activator masterbatch. S2. Preparation of inorganic excitation masterbatch: Sodium hydroxide, sodium sulfate and metakaolin of the above mass fractions are spherically milled in a ball mill at 280 r / min for 60 min at 36℃ to obtain an inorganic mixture. The inorganic mixture and nano silica are placed in a 430W probe ultrasonic breaker and dispersed for 15 min. After drying, the inorganic excitation masterbatch is obtained. S3. In-situ coating: Using a constant temperature magnetic stirrer, at 46℃ and 150r / min stirring conditions, the organic activator masterbatch from step S1 is added to the inorganic activator masterbatch at a rate of 7g / min, and the coating is carried out for 22min to form a composite activator semi-finished product with an inorganic core-organic shell structure. S4 Drying and Shaping: The composite activator semi-finished product obtained in step S3 is vacuum dried at 65°C to a moisture content of 1.7%, pulverized to a particle size of 15μm, and then sieved to obtain the composite activator.

[0067] Preparation of carbonized modified steel slag powder: The steel slag was crushed and ball-milled at 200 r / min. It was carbonized for 3.5 h by passing CO2 with a concentration of 18% under the conditions of 36℃ and 0.7 MPa. After cooling to room temperature, the carbonized modified steel slag powder with a carbonization rate of 37% and a particle size of 40 μm was obtained by sieving.

[0068] The low-carbon cementitious material comprises the following raw material components by mass percentage: 16% commercially available PO42.5 grade silicate cement, 44% slag powder with a specific surface area of ​​450 m² / kg, 22% grade I fly ash, and 18% of the aforementioned carbonized modified steel slag powder; the aforementioned composite activator accounts for 8.5% of the mass percentage of the low-carbon cementitious material. Dry the slag powder and fly ash until their moisture content is ≤2%; mix silicate cement, slag powder, fly ash and carbonized modified steel slag powder in proportion, stir at 450 r / min for 18 min, then add the composite activator and stir at 250 r / min for 15 min to obtain the low-carbon cementitious material.

[0069] The composite activator cementitious material prepared in Example 5, soft soil, and water were mixed in a mass ratio of 90:720:130 to obtain cement mixing piles, which were then subjected to standard curing. The soft soil used was silty soil with a moisture content of 35%-40% and a liquid limit index of 1.1-1.3. The 7-day activity index of the above-mentioned cementitious materials is 80%, and the 28-day activity index is 90%; the 7-day compressive strength of the cement mixing pile body is 1.22 MPa, and the 28-day compressive strength is 1.92 MPa; the carbon emission per unit volume of the cement mixing pile is 265 kg / m³, achieving a carbon reduction of 67%; and the pile body has no cracks.

[0070] Example 6 The composite activator for cement mixing piles in this embodiment comprises the following raw material components by mass percentage: The inorganic excitation component comprises 64%, including 19% sodium hydroxide, 16% sodium sulfate, 26% metakaolin, and 3% nano-silica. The organic activator and synergist comprises 36%, including 15% alkalized modified lignin sulfonate, 12% oxidized potassium humate, and 9% amino-modified corn straw biochar. Preparation of composite activators: S1. Preparation of organic activator masterbatch: Alkali-modified lignin sulfonate, potassium-modified humate and amino-modified corn straw biochar of the above mass fractions are mixed and activated at 60℃ for 30 min, vacuum dried to moisture content ≤3%, and stirred and pulverized at 100 r / min to particle size ≤30 μm to obtain organic activator masterbatch. S2. Preparation of inorganic excitation masterbatch: Sodium hydroxide, sodium sulfate and metakaolin of the above mass fractions are spherically milled in a ball mill at 260 r / min for 90 min at 30℃ to obtain an inorganic mixture. The inorganic mixture and nano silica are placed in a 450W probe ultrasonic crusher and dispersed for 15 min. After drying, the inorganic excitation masterbatch is obtained. S3. In-situ coating: Using a constant temperature magnetic stirrer, under stirring conditions of 40℃ and 150r / min, the organic activator masterbatch from step S1 is added to the inorganic activator masterbatch at a rate of 5g / min, and the coating is carried out for 25min to form a composite activator semi-finished product with an inorganic core-organic shell structure. S4 Drying and Shaping: The composite activator semi-finished product obtained in step S3 is vacuum dried at 70°C until the moisture content is ≤2%, pulverized to a particle size of 16μm, and then sieved to obtain the composite activator.

[0071] Preparation of carbonized modified steel slag powder: After crushing the steel slag, it was ball-milled at 180 r / min. Under the conditions of 40℃ and 0.4 MPa, CO2 with a concentration of 12% was introduced for carbonization for 3.5 h. After cooling to room temperature, the carbonization rate of the carbonized modified steel slag powder with a particle size of 50 μm was obtained by sieving.

[0072] The low-carbon cementitious material comprises the following raw material components by mass percentage: 16% commercially available PO42.5 grade silicate cement, 46% slag powder with a specific surface area of ​​400 m² / kg, 16% Grade I fly ash, and 22% of the aforementioned carbonized modified steel slag powder; the aforementioned composite activator accounts for 10% of the mass percentage of the low-carbon cementitious material. Dry the slag powder and fly ash until their moisture content is ≤2%; mix silicate cement, slag powder, fly ash and carbonized modified steel slag powder in proportion, stir at 350 r / min for 20 min, then add the composite activator and stir at 250 r / min for 15 min to obtain the low-carbon cementitious material.

[0073] The composite activator cementitious material prepared in Example 6, soft soil, and water were mixed in a mass ratio of 96:740:135 to obtain cement mixing piles, which were then subjected to standard curing. The soft soil used was silty soil with a moisture content of 35%-40% and a liquid limit index of 1.1-1.3. The 7-day activity index of the above-mentioned cementitious materials is 82%, and the 28-day activity index is 91%; the 7-day compressive strength of the cement mixing pile body is 1.28 MPa, and the 28-day compressive strength is 1.94 MPa; the carbon emission per unit volume of the cement mixing pile is 275 kg / m³, achieving a carbon reduction of 66%; and the pile body has no cracks.

[0074] Example 7 The composite activator for cement mixing piles in this embodiment comprises the following raw material components by mass percentage: The inorganic excitation component comprises 69%, including 20% ​​sodium hydroxide, 17% sodium sulfate, 28% metakaolin, and 4% nano-silica. The organic activator and synergist comprises 31%, including 14% alkalized modified lignin sulfonate, 9% oxidized potassium humate, and 8% amino-modified corn straw biochar. Preparation of composite activators: S1. Preparation of organic activator masterbatch: Alkali-modified lignin sulfonate, potassium-modified humate and amino-modified corn straw biochar of the above mass fractions are mixed and activated at 58℃ for 30 min, vacuum dried to moisture content ≤3%, and stirred and pulverized at 120 r / min to particle size ≤30 μm to obtain organic activator masterbatch. S2. Preparation of inorganic excitation masterbatch: Sodium hydroxide, sodium sulfate and metakaolin of the above mass fractions are spherically milled in a ball mill at 240 r / min for 90 min at 33℃ to obtain an inorganic mixture. The inorganic mixture and nano silica are placed in a 450W probe ultrasonic crusher and dispersed for 16 min. After drying, the inorganic excitation masterbatch is obtained. S3. In-situ coating: Using a constant temperature magnetic stirrer, under stirring conditions of 50℃ and 100r / min, the organic activator masterbatch from step S1 is added to the inorganic activator masterbatch at a rate of 6g / min, and the coating is carried out for 23min to form a composite activator semi-finished product with an inorganic core-organic shell structure. S4 Drying and Shaping: The composite activator semi-finished product obtained in step S3 is vacuum dried at 60°C until the moisture content is ≤2%, pulverized to a particle size of 16μm, and then sieved to obtain the composite activator.

[0075] Preparation of carbonized modified steel slag powder: After crushing the steel slag, it was ball-milled at 180 r / min. Under the conditions of 30℃ and 0.7 MPa, CO2 with a concentration of 18% was introduced for carbonization for 2.5 h. After cooling to room temperature, the carbonized modified steel slag powder with a carbonization rate of 37% and a particle size of 55 μm was obtained by sieving.

[0076] The low-carbon cementitious material comprises the following raw material components by mass percentage: 14% commercially available PO42.5 grade silicate cement, 44% slag powder with a specific surface area of ​​430 m² / kg, 21% Grade I fly ash, and 21% of the aforementioned carbonized modified steel slag powder; the aforementioned composite activator accounts for 7% of the mass percentage of the low-carbon cementitious material. Dry the slag powder and fly ash until their moisture content is ≤2%; mix silicate cement, slag powder, fly ash and carbonized modified steel slag powder in proportion, stir at 350 r / min for 20 min, then add the composite activator and stir at 200 r / min for 18 min to obtain the low-carbon cementitious material.

[0077] The composite activator cementitious material prepared in Example 7, soft soil, and water were mixed in a mass ratio of 106:760:155 to obtain cement mixing piles, which were then subjected to standard curing. The soft soil used was silty soil with a moisture content of 35%-40% and a liquid limit index of 1.1-1.3. The 7-day activity index of the above-mentioned cementitious material is 82%, and the 28-day activity index is 91%; the 7-day compressive strength of the cement mixing pile body is 1.16 MPa, and the 28-day compressive strength is 1.93 MPa; the carbon emission per unit volume of the cement mixing pile is 240 kg / m³, achieving a carbon reduction of 75%; and the pile body has no cracks.

[0078] Example 8 The composite activator for cement mixing piles in this embodiment comprises the following raw material components by mass percentage: The inorganic excitation component comprises 70%, including 18% sodium hydroxide, 19% sodium sulfate, 29% metakaolin, and 4% nano-silica. The organic activator and synergist comprises 30%, including 11% alkalized modified lignin sulfonate, 8% oxidized potassium humate, and 11% amino-modified corn straw biochar. Preparation of composite activators: S1. Preparation of organic activator masterbatch: Alkali-modified lignin sulfonate, potassium-modified humate and amino-modified corn straw biochar of the above mass fractions are mixed and activated at 53℃ for 30 min, vacuum dried to moisture content ≤3%, and stirred and pulverized at 100 r / min to particle size ≤30 μm to obtain organic activator masterbatch. S2. Preparation of inorganic excitation masterbatch: Sodium hydroxide, sodium sulfate and metakaolin of the above mass fractions are spherically milled in a ball mill at 35°C and 250 r / min for 65 min to obtain an inorganic mixture. The inorganic mixture and nano silica are placed in a 400W probe ultrasonic breaker and dispersed for 17 min. After drying, the inorganic excitation masterbatch is obtained. S3. In-situ coating: Using a constant temperature magnetic stirrer, under stirring conditions of 48℃ and 140r / min, the organic activator masterbatch from step S1 is added to the inorganic activator masterbatch at a rate of 7g / min, and the coating is carried out for 24min to form a composite activator semi-finished product with an inorganic core-organic shell structure. S4 Drying and Shaping: The composite activator semi-finished product obtained in step S3 is vacuum dried at 68°C until the moisture content is ≤2%, pulverized to a particle size of 19μm, and then sieved to obtain the composite activator.

[0079] Preparation of carbonized modified steel slag powder: The steel slag was crushed and ball-milled at 180 r / min. It was carbonized for 3 h with 13% CO2 at 35℃ and 0.6 MPa. After cooling to room temperature, the carbonized modified steel slag powder with a carbonization rate of 36% and a particle size of 60 μm was obtained by sieving.

[0080] The low-carbon cementitious material comprises the following raw material components by mass percentage: 15% commercially available PO42.5 grade silicate cement, 46% slag powder with a specific surface area of ​​430 m² / kg, 15% grade I fly ash, and 22% of the aforementioned carbonized modified steel slag powder; the aforementioned composite activator accounts for 9% of the mass percentage of the low-carbon cementitious material. Dry the slag powder and fly ash until their moisture content is ≤2%; mix silicate cement, slag powder, fly ash and carbonized modified steel slag powder in proportion, stir at 430 r / min for 20 min, then add the composite activator and stir at 240 r / min for 17 min to obtain the low-carbon cementitious material.

[0081] The composite activator cementitious material prepared in Example 8, soft soil, and water were mixed in a mass ratio of 106:780:165 to obtain cement mixing piles, which were then subjected to standard curing. The soft soil used was silty soil with a moisture content of 35%-40% and a liquid limit index of 1.1-1.3. The 7-day activity index of the above-mentioned cementitious material is 80%, and the 28-day activity index is 92%; the 7-day compressive strength of the cement mixing pile body is 1.23 MPa, and the 28-day compressive strength is 1.94 MPa; the carbon emission per unit volume of the cement mixing pile is 260 kg / m³, achieving a carbon reduction of 68%; and the pile body has no cracks.

[0082] Example 9 The composite activator for cement mixing piles in this embodiment comprises the following raw material components by mass percentage: The inorganic excitation component comprises 66%, including 19% sodium hydroxide, 18% sodium sulfate, 26% metakaolin, and 3% nano-silica. The organic activator and synergist comprised 34%, including 12% alkalized modified lignin sulfonate, 9% oxidized potassium humate, and 13% amino-modified corn straw biochar. Preparation of composite activators: S1. Preparation of organic activator masterbatch: Alkali-modified lignin sulfonate, potassium-modified humate and amino-modified corn straw biochar of the above mass fractions are mixed and activated at 55℃ for 30 min, vacuum dried to moisture content ≤3%, and stirred and pulverized at 100 r / min to particle size ≤30 μm to obtain organic activator masterbatch. S2. Preparation of inorganic excitation masterbatch: Sodium hydroxide, sodium sulfate and metakaolin of the above mass fractions are spherically milled in a ball mill at 260 r / min for 70 min at 33℃ to obtain an inorganic mixture. The inorganic mixture and nano silica are placed in a 450W probe ultrasonic breaker and dispersed for 16 min. After drying, the inorganic excitation masterbatch is obtained. S3. In-situ coating: Using a constant temperature magnetic stirrer, at 44℃ and 110r / min stirring conditions, the organic activator masterbatch from step S1 is added to the inorganic activator masterbatch at a rate of 9g / min, and the coating is carried out for 24min to form a composite activator semi-finished product with an inorganic core-organic shell structure. S4 Drying and Shaping: The composite activator semi-finished product obtained in step S3 is vacuum dried at 68°C until the moisture content is ≤2%, pulverized to a particle size of 18μm, and then sieved to obtain the composite activator.

[0083] Preparation of carbonized modified steel slag powder: The steel slag was crushed and ball-milled at 180 r / min. It was carbonized for 2.8 h by passing CO2 with a concentration of 14% under the conditions of 36℃ and 0.6 MPa. After cooling to room temperature, the carbonized modified steel slag powder with a carbonization rate of 35% and a particle size of 50 μm was obtained by sieving.

[0084] The low-carbon cementitious material comprises the following raw material components by mass percentage: 15% commercially available PO42.5 grade silicate cement, 46% slag powder with a specific surface area of ​​430 m² / kg, 17% grade I fly ash, and 20% of the aforementioned carbonized modified steel slag powder; the aforementioned composite activator accounts for 8% of the mass percentage of the low-carbon cementitious material. Dry the slag powder and fly ash until their moisture content is ≤2%; mix silicate cement, slag powder, fly ash and carbonized modified steel slag powder in proportion, stir at 400 r / min for 20 min, then add the composite activator and stir at 230 r / min for 16 min to obtain the low-carbon cementitious material.

[0085] The composite activator cementitious material prepared in Example 9, soft soil, and water were mixed in a mass ratio of 108:800:145 to obtain cement mixing piles, which were then subjected to standard curing. The soft soil used was silty soil with a moisture content of 35%-40% and a liquid limit index of 1.1-1.3. The 7-day activity index of the above-mentioned cementitious material is 82%, and the 28-day activity index is 91%; the 7-day compressive strength of the cement mixing pile body is 1.18 MPa, and the 28-day compressive strength is 1.92 MPa; the carbon emission per unit volume of the cement mixing pile is 255 kg / m³, achieving a carbon reduction of 70%; and the pile body has no cracks.

[0086] Comparative Example 1 According to Example 1, the cement mixing pile is prepared by mixing cementitious material, soft soil and water in a mass ratio of 100:770:150. The cement mixing pile is then cured according to standard conditions. The cementitious material is 100% commercially available PO42.5 grade silicate cement. The difference from Example 1 is that the cementitious material does not use an activator and does not contain industrial solid waste or carbonized modified steel slag powder. Testing revealed that the 7-day compressive strength of the cement-mixed pile was 1.10 MPa, and the 28-day compressive strength was 1.78 MPa. Using the same reinforcement strength and treated soil volume as a functional unit, the carbon emissions of the traditional cement-based system were calculated to be 812.5 kg / m³, showing no carbon reduction effect. Figure 3 As shown, after 28 days of standard curing, the cement-mixed cement piles exhibited slight shrinkage cracks. These cracks were mainly distributed locally along the surface of the specimens. The reason for this phenomenon is that the system relies entirely on the hydration of ordinary Portland cement to provide strength, without introducing potentially active low-carbon components such as slag, fly ash, and carbonized modified steel slag powder. Furthermore, no composite activator was added to disperse, regulate, and strengthen the soft soil-cement interface. In high-moisture-content silty soil environments, localized weak interfaces easily form between cement hydration products and soil particles. During the slurry hardening process, water migration and drying shrinkage deformation are concentrated, leading to slight shrinkage cracks on the pile surface. Simultaneously, this system has a high cement content, which, while providing some early strength, significantly increases carbon emissions, failing to achieve the technical goal of replacing cement with low-carbon cementitious materials.

[0087] Comparative Example 2 According to the composition of the cementitious material in Example 1, commercially available PO42.5 grade silicate cement is 15%. The difference from Example 1 is that it does not include carbonized modified steel slag powder, and industrial solid waste is 85%, and the industrial solid waste is only slag powder, and no activator is used. According to Example 1, the cement mixing pile is prepared by mixing cementitious material, soft soil and water in a mass ratio of 100:770:150. The cement mixing pile is then subjected to standard curing. The cementitious material used is the cementitious material prepared in Comparative Example 2. Testing revealed that the activity index of the cementitious material was 51% after 7 days and 64% after 28 days; the compressive strength of the cement mixing pile was 0.8 MPa after 7 days and 1.4 MPa after 28 days; the carbon emission per unit volume was 320 kg / m³, representing a carbon reduction of 56%. Figure 4As shown, after 28 days of standard curing, the cement-mixed piles exhibited obvious cracks on their surface, forming an irregular network. Some cracks were wide and interconnected. This phenomenon is attributed to the fact that while the comparative example reduced cement content and increased slag content, no composite activator was added. The active SiO2 and Al2O3 in the slag were not fully activated, and the hydration reaction mainly remained at the cement's own hydration stage and the slow reaction stage on the slag surface. This resulted in insufficient formation of cementing products such as C-(A)-SH gel and ettringite, leading to inadequate internal filling and high pore connectivity within the pile. Consequently, the activity index and compressive strength at 7 days and 28 days were significantly reduced. Furthermore, this system lacked carbonized modified steel slag powder, resulting in a lack of stable micro-aggregate filling and carbon fixation stabilization. The cementitious skeleton lacked continuity, making it prone to network cracks and even locally interconnected cracks under the combined effects of high water content in soft soil and curing shrinkage. This comparative example demonstrates that simply increasing the industrial solid waste substitution rate without effective activation makes it difficult to simultaneously achieve low carbon content, strength, and crack resistance.

[0088] Comparative Example 3 The composition of the cementitious material is the same as in Example 1, including 15% commercially available PO42.5 grade silicate cement, 45% slag powder with a specific surface area of ​​430 m² / kg, 18% grade I fly ash, and 22% carbonized modified steel slag powder. The difference is that an inorganic activator is used, which includes 20% sodium hydroxide, 15% sodium sulfate, 30% metakaolin, and 5% nano silica. It does not contain any organic components, and the amount of inorganic activator accounts for 8% of the mass of the low-carbon cementitious material. According to Example 1, the cement mixing pile is prepared by mixing cementitious material, soft soil and water in a mass ratio of 100:770:150. The cement mixing pile is then subjected to standard curing. The cementitious material used is the cementitious material prepared in Comparative Example 3. Testing revealed that the cementitious material had a 7-day activity index of 64% and a 28-day activity index of 74%; the pile's 7-day compressive strength was 1.0 MPa and its 28-day compressive strength was 1.6 MPa; and the carbon emission per unit volume was 270 kg / m³, representing a 67% reduction in carbon emissions. Figure 5As shown, after 28 days of standard curing, slight cracks appeared on the surface of the cement mixing pile, and fine shrinkage cracks could be observed in some areas. The reason for this phenomenon is that this comparative example only used an inorganic activation system composed of sodium hydroxide, sodium sulfate, metakaolin, and nano-silica. Although this system can activate the potential activity of slag, fly ash, and carbonized modified steel slag powder to a certain extent, it lacks the dispersion, slow-release, and interface regulation effects of organic synergistic components on the inorganic activator. The rapid release of the inorganic activating components easily leads to excessively high local alkalinity and concentrated hydration reactions, causing some areas to generate hydration products quickly while some solid waste particles remain unreacted, resulting in uneven distribution of hydration products within the pile and a weak interface transition zone. Due to the lack of the dispersion and retarding effect of modified lignin sulfonate, the alkalinity stabilization and ion chelation effect of modified potassium humate, and the porous toughening effect of amino-modified biochar, the system's shrinkage resistance is insufficient, thus resulting in fine shrinkage cracks. This comparative example illustrates that a single inorganic activation cannot replace the organic-inorganic synergistic activation structure of this invention.

[0089] Comparative Example 4 The difference from Example 1 is that the preparation of the composite activator uses physical stirring and mixing, in which the components of the inorganic activator and the organic activator are stirred and mixed. The organic activator is not activated, and the inorganic activator is not spheroidized or ultrasonically dispersed, nor is it coated or dried in situ.

[0090] According to the cement mixing pile of Example 1, the mass ratio of cementitious material, soft soil and water is 100:770:150. The cement mixing pile is mixed and molded to obtain a cement mixing pile. The cement mixing pile is then subjected to standard curing. The cementitious material used is the cementitious material prepared in Comparative Example 4 above. Testing revealed that the activity index of the cementitious material was 68% at 7 days and 79% at 28 days; the compressive strength of the cement mixing pile was 1.1 MPa at 7 days and 1.8 MPa at 28 days; the carbon emission per unit volume was 265 kg / m³, representing a carbon reduction of 68%. Figure 6As shown, after 28 days of standard curing, slight cracks appeared on the surface of the cement-mixed pile, mainly distributed at the pile edges and in localized surface areas. The reason for this phenomenon is that although this comparative example used the same inorganic activating agent and organic activating enhancer as Example 1, it was prepared solely through ordinary physical mixing. The organic enhancer was not activated, the inorganic activating agent was not ball-milled or ultrasonically dispersed, and an in-situ coating structure of inorganic core-organic shell was not formed. Due to the lack of stable directional bonding and coating interfaces between the components, the inorganic activating components easily aggregated and locally accumulated, resulting in uneven distribution of the activator in the cementitious system. Some areas reacted too quickly, while others were under-activated, leading to a decrease in the continuity and uniformity of hydration products. Simultaneously, the organic components could not effectively exert their function of slowly releasing inorganic activating components, improving soft soil interface affinity, and reducing shrinkage stress concentration. Therefore, the pile strength was lower than in Example 1, and slight cracks appeared at the edges and in localized surface areas. This comparative example illustrates that the in-situ coating process is not a simple mixing step, but a key technical feature for achieving uniform activation, slow-release regulation, and crack resistance and toughening.

[0091] Comparative Example 5 The difference from Example 1 is that the steel slag powder was not carbonized, but only crushed and ball-milled to 50μm; According to Example 1, the cement mixing pile is prepared by mixing cementitious material, soft soil and water in a mass ratio of 100:770:150. The cement mixing pile is then subjected to standard curing. The cementitious material used is the cementitious material prepared in Comparative Example 5 above. Testing revealed that the cementitious material had an activity index of 71% at 7 days and 84% at 28 days; the cement mixing pile body had a 7-day compressive strength of 1.15 MPa and a 28-day compressive strength of 1.85 MPa; and carbon emissions per unit volume were 275 kg / m³, representing a 66% reduction in carbon emissions. Figure 7 As shown, after 28 days of standard curing, slight cracks appeared on the surface of the cement mixing pile. Due to the insufficient volume stability of the uncarbonized steel slag, fine cracks caused by the insufficient volume stability of the steel slag were visible on the local surface of the pile. The reason for this phenomenon is that the uncarbonized steel slag powder may contain a large amount of potentially expansive components such as free CaO and free MgO. During the curing process, these components continue to hydrate and generate Ca(OH)2 or Mg(OH)2, resulting in delayed volume expansion and the formation of local expansion stress and microcrack sources around the steel slag particles. At the same time, the surface of the uncarbonized steel slag powder lacks a stable carbonated layer. Its particle surface activity, volume stability, and interfacial interlocking ability with C-(A)-SH gel are all weaker than those of carbonized modified steel slag powder, making it difficult to form a stable and dense cementitious skeleton. Therefore, although this comparative example still has a certain strength, the appearance of fine cracks on the pile surface indicates that carbonization modification of steel slag powder is necessary to improve volume stability, reduce the risk of later cracking, and exert a carbon fixation effect.

[0092] Comparative Example 6 The difference from Example 1 is that the composite activator comprises the following raw material components in the following mass percentages: The inorganic excitation component comprises 50%, including 16% sodium hydroxide, 12% sodium sulfate, 20% metakaolin, and 2% nano-silica. The organic activator / synergist comprises 50%, including 20% ​​alkalized modified lignin sulfonate, 15% oxidized potassium humate, and 15% amino-modified corn straw biochar. According to Example 1, the cement mixing pile is prepared by mixing cementitious material, soft soil and water in a mass ratio of 100:770:150. The cement mixing pile is then subjected to standard curing. The cementitious material used is the cementitious material prepared in Comparative Example 6 above. Testing revealed that the activity index of the cementitious material was 66% at 7 days and 78% at 28 days; the compressive strength of the cement mixing pile was 1.05 MPa at 7 days and 1.76 MPa at 28 days; the carbon emission per unit volume was 260 kg / m³, representing a carbon reduction of 68%. Figure 8 As shown, after 28 days of standard curing, fine shrinkage cracks appeared on the surface of the cement mixing pile. The reason for this phenomenon is that the inorganic activating component in this comparative example is only 50%, which is lower than the 60%–75% range specified in this invention, while the organic activating synergist is increased to 50%. Due to the insufficient total amount of sodium hydroxide, sodium sulfate, metakaolin, and nano-silica, the system's alkali activation and sulfate activation capabilities decrease, the release of active Si, Al, and Ca components in slag, fly ash, and carbonized modified steel slag powder is insufficient, and the formation of C-(A)-SH gel and ettringite is insufficient, resulting in insufficient development of the cementitious skeleton and a decrease in pore filling effect, ultimately manifested as a decrease in activity index and compressive strength. At the same time, excessive organic components enhance the retarding and coating effects, delaying the early hydration reaction and resulting in insufficient early structure establishment; during the subsequent drying shrinkage process, a sufficiently continuous and dense cementitious network has not yet formed inside the pile, thus causing fine shrinkage cracks. This comparative example illustrates that when the inorganic activating agent is too low, even with a large amount of organic synergists, it is difficult to ensure that industrial solid waste is fully activated and its intensity remains stable.

[0093] Comparative Example 7 The difference from Example 1 is that the composite activator comprises the following raw material components in the following mass percentages: The inorganic excitation component comprises 80%, including 21% sodium hydroxide, 21% sodium sulfate, 31% metakaolin, and 7% nano-silica. The organic activator / synergist comprises 20%, including 8% alkalized modified lignin sulfonate, 7% oxidized potassium humate, and 5% amino-modified corn straw biochar. According to Example 1, the cement mixing pile is prepared by mixing cementitious material, soft soil and water in a mass ratio of 100:770:150. The cement mixing pile is then subjected to standard curing. The cementitious material used is the cementitious material prepared in Comparative Example 7. Testing revealed that the cementitious material had an activity index of 76% at 7 days and 82% at 28 days; the cement mixing pile body had a 7-day compressive strength of 1.21 MPa and a 28-day compressive strength of 1.80 MPa; and carbon emissions per unit volume were 260 kg / m³, representing a 68% reduction in carbon emissions. Figure 9 As shown, after 28 days of standard curing, the cement mixing pile exhibited shrinkage cracks, which were more pronounced than those in Comparative Example 6 and were locally distributed continuously. The reason for this phenomenon is that the inorganic activating component in this comparative example increased to 80%, exceeding the 60%–75% range specified in this invention, while the organic activating synergist was only 20%, lower than the 25%–40% range specified in this invention. Excessive sodium hydroxide and sodium sulfate can cause excessively high early alkalinity and ion concentration in the system, resulting in excessively rapid hydration reactions, concentrated formation of local hydration products, and potentially inducing rapid accumulation of crystalline products such as ettringite, leading to significant early shrinkage stress and local expansion stress within the slurry. Due to insufficient organic synergist, the system lacks sufficient dispersion, slow release, alkalinity stabilization, and interfacial toughening effects, making it difficult for the inorganic activating components to be uniformly coated and stably released, and the soft soil-cement material interface to be effectively improved. Therefore, although this comparative example has higher early strength, its later structural uniformity and volume stability are insufficient, and the cracks are more pronounced and locally distributed continuously than those in Comparative Example 6. The results indicate that higher levels of inorganic activating components are not necessarily better. Only by controlling the ratio of inorganic activating components to organic synergists within a reasonable range can strength development, reaction regulation, and crack resistance be achieved simultaneously.

[0094] As can be seen from the above comparative examples, the performance degradation and crack formation of cement mixing piles correspond to different failure mechanisms: Comparative example 1 shows that although the traditional cement system has a certain strength, it lacks low carbon content and has limited interfacial crack resistance; Comparative example 2 shows that simply increasing the industrial solid waste replacement rate without effective activation will lead to insufficient solid waste activation, significant strength reduction, and through cracks; Comparative example 3 shows that using only inorganic activators will make it difficult to control the reaction rate and spatial distribution, making it difficult to avoid shrinkage cracks; Comparative example 4 shows that ordinary physical mixing cannot replace the in-situ coating structure, making it difficult to achieve uniform dispersion and slow-release control of the activating components; Comparative example 5 shows that steel slag powder without carbonization modification has insufficient volume stability and is prone to inducing surface microcracks; Comparative examples 6 and 7 show that there is a reasonable ratio range between the inorganic activating body and the organic activating synergist, and deviation in any direction will lead to an imbalance in activation efficiency, slow-release control, and crack resistance. Therefore, this invention achieves deep activation of industrial solid waste, controllable reaction rate, enhanced soft soil interface and improved volume stability through the synergistic design of "in-situ coating structure formed by 60%–75% inorganic activating body and 25%–40% organic activating synergist and carbonized modified steel slag powder". This enables cement mixing piles to still have high compressive strength and avoid obvious cracks under low carbon conditions.

[0095] The composite activator of this invention, sodium hydroxide, provides a strongly alkaline environment that breaks the inert Si-O-Si and Al-O-Al bonds inside slag, fly ash, and carbide steel slag powder, releasing active SiO3². - AlO2 - Sodium sulfate reacts with the hydration product Ca(OH)2 to form ettringite, which rapidly improves early strength; metakaolin participates in the formation of CASH gel, filling micropores; nano-silica exerts a nucleation effect, accelerating the formation of hydration gel and improving the density of the system; Modified lignin sulfonate is modified by alkalization, which forms hydrogen bonds with inorganic particles through sulfonic acid groups and hydroxyl groups, thereby achieving efficient dispersion, preventing activator agglomeration, regulating hydration rate, improving the interfacial adhesion between cementitious materials and soft soil, and reducing shrinkage cracks. Potassium humate is modified by potassiumization to chelate Ca²⁺ with carboxyl and phenolic hydroxyl groups. + Mg² + Plasma disrupts the inert structure of solid waste, activates carbon fixation sites, stabilizes the alkalinity of the system, and prevents cracking by strong alkali. In existing technologies, potassium humate is only used as a pH adjuster. Amino-modified corn straw biochar undergoes a condensation reaction between amino groups and hydroxyl groups of inorganic excitation substrates to form a porous and toughened structure, which synergistically performs carbon fixation and improves the stability of the system. The composite activator has an inorganic activating main component as the core and an organic synergist component as the shell, forming a core-shell structure: the inorganic core provides continuous activating power to ensure the activation efficiency of solid waste; the organic component and the inorganic component undergo directional chemical bonding to prevent the inorganic particles from agglomerating and achieve uniform dispersion of the activating component, solving the problems of agglomeration and uncontrolled activation of traditional activators, and increasing the activation rate of industrial solid waste to 82%-90%; the organic shell slowly releases inorganic activating components, controls the hydration rate, adapts to construction, improves the interface affinity with soft soil and solid waste, reduces interface defects and shrinkage cracks, and significantly improves impermeability, frost resistance and erosion resistance. The cementitious material of this invention is low-carbon and environmentally friendly, reducing the amount of silicate cement to 10%-18%, and the amount of composite activator is greater than that of conventional alkaline activator, which enhances the deep activation effect of industrial solid waste, makes up for the strength gap caused by insufficient cement, and synergistically achieves deep activation and performance improvement of solid waste. Compared to the traditional 100% cement mix ratio, the carbon emissions per unit volume of the mixing pile are reduced to 240-275 kg / m³, a carbon reduction of 65%-75%, which is far higher than the carbon reduction level of 20%-30% of the existing technology. At the same time, it achieves an industrial solid waste utilization rate of 82%-90%, promoting the resource utilization of industrial solid waste. Cementitious materials can be used to make concrete mixing piles to reinforce soft soil foundations. Carbonized modified steel slag powder utilizes its carbon-fixing components such as CaO and MgO to tap the carbon-fixing potential of steel slag powder and improve its volume stability. With the synergistic effect of composite activators, the mixing piles are crack-free, and their impermeability and frost resistance are improved by more than 30% compared with traditional cement. They can be adapted to complex engineering scenarios such as high-grade highways and port terminals, and solve the problem of easy cracking of existing piles.

[0096] 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 preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A composite activator for cement mixing piles, characterized in that, The raw material components include the following percentages by weight: 60%-75% inorganic activator and 25%-40% organic activator synergist; The inorganic excitation substrate comprises the following raw materials by mass percentage: sodium hydroxide 18%-20%, sodium sulfate 14%-20%, metakaolin 25%-30%, and nano-silica 3%-5%; The organic activator comprises the following raw materials in the following mass percentages: 10%-15% modified lignin sulfonate, 8%-12% modified potassium humate, and 7%-13% modified corn straw biochar.

2. The composite activator for cement mixing piles according to claim 1, characterized in that, The modified lignin sulfonate is an alkali-modified lignin sulfonate with a molecular weight of 5000-10000.

3. The composite activator for cement mixing piles according to claim 1, characterized in that, The modified potassium humate is an oxidized-potassium-modified composite potassium humate, wherein the humic acid content is ≥70%.

4. The composite activator for cement mixing piles according to claim 1, characterized in that, The modified corn stalk biochar is an amino-modified corn stalk biochar with a specific surface area ≥300m² / g.

5. The method for preparing the composite activator for cement mixing piles according to any one of claims 1-4, characterized in that, Specifically, the steps include the following: Preparation of organic activator masterbatch: Modified lignin sulfonate, modified potassium humate, and modified corn straw biochar were activated at 50-60℃ for 30 min, vacuum dried to a moisture content of ≤3%, and pulverized to a particle size of ≤30μm to obtain organic activator masterbatch; Preparation of inorganic excitation masterbatch: Sodium hydroxide, sodium sulfate and metakaolin are ball-milled at 30-38℃ for 60-90 min to obtain an inorganic mixture. The inorganic mixture and nano-silica are ultrasonically dispersed for 15-20 min and dried to obtain the inorganic excitation masterbatch. In-situ coating: Under stirring conditions of 40-50℃ and 100-150r / min, the organic activator masterbatch is added to the inorganic activator masterbatch at a rate of 5-10g / min and coated for 20-25min to form a composite activator semi-finished product with an inorganic core-organic shell structure. Drying and shaping: The composite activator semi-finished product obtained in the in-situ coating step is vacuum dried at 60-70℃ until the moisture content is ≤2%, pulverized to a particle size ≤20μm, and then sieved to obtain the composite activator.

6. A low-carbon cementitious material, characterized in that, Includes the composite activator for cement mixing piles as described in any one of claims 1-4; The low-carbon cementitious material also includes the following raw materials by mass fraction: The composition consists of 14%-16% silicate cement, 59%-68% industrial solid waste, and 18%-22% carbonized modified steel slag powder, with the sum of the mass fractions of all components being 100%. The composite activator accounts for 7%-10% of the total mass of the cementitious material.

7. The low-carbon cementitious material according to claim 6, characterized in that, The industrial solid waste includes the following raw materials by mass fraction: 44%-46% slag powder and 15%-22% fly ash.

8. The low-carbon cementitious material according to claim 6, characterized in that, The carbide-modified steel slag powder is prepared by the following method: The steel slag is crushed and then ball-milled. Under the conditions of 30-40℃ and 0.4-0.7MPa, CO2 with a concentration of 12%-18% is introduced for carbonization for 2.5-3.5h. After cooling to room temperature, the carbonized modified steel slag powder is obtained by sieving.

9. The method for preparing the low-carbon cementitious material according to any one of claims 6-8, characterized in that, Includes the following steps: Raw material pretreatment: The industrial solid waste is dried until its moisture content is ≤2%; Raw material mixing: The silicate cement, the industrial solid waste, and the carbonized modified steel slag powder are mixed in proportion and stirred to obtain a low-carbon cementitious material semi-finished product; Activation process: Add the composite activator for cement mixing piles to the semi-finished low-carbon cementitious material and stir to obtain the low-carbon cementitious material.

10. The application of a low-carbon cementitious material in the reinforcement of soft soil foundations, characterized in that, Soft soil, water, and the low-carbon cementitious material described in any one of claims 6-9 are mixed and stirred in a mass ratio of (720-820):(130-170):(90-110) to form cement mixing piles after curing. The cement mixing piles are used for soft soil foundation reinforcement.

Images