Superfine ultrasulfate cementing material and preparation method thereof

Abstract

The invention discloses a superfine super-sulfate cementing material and a preparation method thereof, and belongs to the technical field of building materials, and the preparation method comprises the following steps: carrying out superfine grinding on granulated blast-furnace slag, steel slag and desulfurized gypsum, and carrying out surface modification with a composite modification liquid to obtain a superfine solid waste-based cementing main material; the preparation method comprises the following steps: activating nano silicon dioxide by a silane coupling agent, and then carrying out graft copolymerization on the nano silicon dioxide and a polycarboxylic acid water reducing agent monomer to prepare a reactive PCE-nano SiO2 composite dispersion; carrying out carbonization and alkaline pretreatment on a biomass raw material to prepare modified charcoal; uniformly mixing the superfine solid waste-based cementing main material, Portland cement and modified charcoal, stirring the compounded composite dispersion and mixing water to prepare slurry, and forming and curing to obtain the superfine super-sulfate cementing material. According to the method, the hydration activity of industrial solid waste is effectively stimulated, the dispersity and the hydration process of a cementing system are optimized, the obtained cementing material is high in strength, good in volume stability and excellent in durability, the preparation process is reasonable, and remarkable technical advantages and application value are achieved.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to an ultrafine ultrasulfate cementitious material and its preparation method. Background Technology

[0002] Driven by the "dual carbon" goals, the building materials industry urgently needs to develop green cementitious materials with low energy consumption and high solid waste utilization. Supersulfate cement (SSC), due to its low clinker content, low heat of hydration, and excellent resistance to sulfate attack, is considered a key pathway to replace traditional silicate cement. However, its engineering applications have long been limited by problems such as slow early strength development, poor fluidity of freshly mixed cement paste with rapid loss over time, and significant shrinkage of the hardened body under drying conditions, which easily leads to cracking. These issues severely restrict its promotion in the field of high-performance concrete.

[0003] In existing technologies, on the one hand, nanofillers, such as nano-SiO2 and kaolin, are incorporated to optimize the microstructure; on the other hand, ultrafine grinding and surface modification processes are used to enhance the reactivity of solid waste-based admixtures. However, these technologies each have inherent drawbacks: in the highly alkaline environment required for SSC activation, the high surface energy of the nanofillers strongly adsorbs Na. + K + The presence of alkali metal ions causes a sharp drop in the concentration of effective activators in the liquid phase, severely inhibiting the deagglomeration and hydration reaction of slag and steel slag. At the same time, nanofillers significantly increase the water demand of the system and deteriorate workability. Although simple ultrafine grinding can improve the reaction rate, the high specific surface area of ​​ultrafine powders easily aggravates particle agglomeration. Furthermore, when combined with nanofillers, it accelerates the development of capillary negative pressure, exacerbates self-drying shrinkage, and destroys volume stability.

[0004] Therefore, there is an urgent need to develop an ultrafine supersulfate cementitious material and its preparation method, which can systematically solve the core technical problems of supersulfate cement, such as low early strength, poor workability retention and insufficient volume stability, while maintaining high solid waste content and low carbon properties. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides an ultrafine supersulfate cementitious material and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: an ultrafine supersulfate cementitious material and its preparation method, comprising:

[0007] S1. Granulated blast furnace slag, steel slag, and desulfurized gypsum are crushed and mixed, and a grinding aid is added for ultrafine grinding to obtain ultrafine powder. The ultrafine powder is then surface-modified using a composite modification liquid of water glass and γ-aminopropyltriethoxysilane to obtain ultrafine solid waste-based cementitious main material.

[0008] S2. After pretreatment and activation with a silane coupling agent, nano-SiO2 is copolymerized with polycarboxylate superplasticizer monomer via free radical grafting reaction. After neutralization, a reactive PCE-nano-SiO2 composite dispersion is obtained.

[0009] S3. After carbonizing and pulverizing the biomass raw material, it is soaked in alkaline solution, washed and dried to obtain alkaline pretreated biochar.

[0010] S4. Mix the ultrafine solid waste-based cementitious main material, silicate cement, and alkaline pretreated biochar in a certain proportion to obtain a premixed dry material;

[0011] S5. The reactive PCE-nano SiO2 composite dispersion and mixing water are added to the premixed dry material, and a uniform fresh slurry is formed by stirring. After curing, the ultrafine supersulfate cementitious material is obtained.

[0012] In a preferred embodiment of the present invention, in step S1, the mass ratio of the granulated blast furnace slag, steel slag and desulfurized gypsum is 40-50:15-25:10-15;

[0013] The grinding time is 40-50 minutes; the grinding aid is triethanolamine; the specific surface area of ​​the ultrafine powder is 730-770 m². 2 / kg.

[0014] In a preferred embodiment of the present invention, in step S1, the composite modified liquid is prepared by diluting water glass with a modulus of 1.5-2.0 to a mass concentration of 15-25% and then mixing it with γ-aminopropyltriethoxysilane at a mass ratio of 8-12:1.

[0015] The amount of the composite modified liquid sprayed is 1.5-2.5% of the total mass of the powder;

[0016] The modification treatment temperature is 75-85℃, and the reaction time is 25-35 min.

[0017] In a preferred embodiment of the present invention, in step S2, the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane, and the amount added is 4-6% of the mass of nano-SiO2;

[0018] The pretreatment activation process includes:

[0019] Nano-SiO2 was dispersed in water to form a suspension with a concentration of 180-220 g / L. The suspension was sonicated for 20-40 min, the pH was adjusted to 4-5, and the suspension was reacted in a water bath at 65-75℃ for 3-5 h. After centrifugation and washing, the suspension was vacuum dried at 100-120℃ for 10-14 h.

[0020] In a preferred embodiment of the present invention, in step S2, the polycarboxylate superplasticizer monomer includes methyl allyl polyoxyethylene ether, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid;

[0021] The molar ratio of methyl allyl polyoxyethylene ether, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid is 1:3-5:0.3-0.7;

[0022] The free radical graft copolymerization reaction was carried out by simultaneously adding polycarboxylate superplasticizer monomer and initiator solution at 60-70℃ under nitrogen protection; after the addition was completed, the reaction was continued at 60-70℃ for 1-3 hours.

[0023] The initiator is a redox system composed of ammonium persulfate and vitamin C, and its total amount is 0.6-1.0% of the total mass of polycarboxylate superplasticizer monomers.

[0024] In a preferred embodiment of the present invention, in step S3, the biomass raw material includes one or more of bamboo shavings, rice husks, wood chips, or straw;

[0025] The carbonization heating rate of the biomass raw material is 8-12℃ / min, the carbonization temperature is 550-650℃, and the carbonization time is 1-3h;

[0026] The alkaline solution is a 0.3-1.0 mol / L potassium hydroxide solution, the solid-liquid mass ratio for soaking is 1:8-12, the soaking temperature is 55-65℃, and the soaking time is 4-8 hours.

[0027] In a preferred embodiment of the present invention, in step S4, the clinker mineral composition of the silicate cement contains 50-58% C3S, 18-22% C2S, 6-8% C3A, 8-10% C4AF, and has a specific surface area of ​​350-380 m². 2 / kg;

[0028] The mass ratio of the surface-modified ultrafine solid waste-based cementitious material, silicate cement, and alkaline pretreated biochar is 75-85:3-8:3-5.

[0029] In a preferred embodiment of the present invention, in step S5, 100 parts by weight of the premixed dry material includes 0.3-1.0 parts by weight of the reactive PCE-nano SiO2 composite dispersion and 30-38 parts by weight of mixing water.

[0030] In a preferred embodiment of the present invention, in step S5, the stirring includes low-speed stirring and high-speed stirring. The reactive PCE-nano SiO2 composite dispersion and mixing water are added by low-speed stirring at 130-150 r / min, and then stirred at high speed at 270-300 r / min for 100-140 s.

[0031] In a preferred embodiment of the present invention, the dry base components, by weight, include: 75-85 parts of ultrafine solid waste-based cementitious main material, 3-8 parts of silicate cement, and 3-5 parts of alkaline pretreated biochar.

[0032] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0033] (1) This invention utilizes a synergistic technical solution of surface modification of ultrafine solid waste-based cementitious material, reactive PCE-nano SiO2 composite dispersion, and alkaline pretreated biochar to effectively stimulate the water treatment activity of industrial solid waste. Simultaneously, it optimizes the microstructure of the cementitious system by leveraging the long-term dispersion effect of covalent grafting and the internal maintenance and regulation mechanism. Compared to the common problems of low early strength and large drying shrinkage in existing persulfate cementitious materials, the material obtained by this invention exhibits rapid strength development and stable improvement in the later stages, excellent volume stability, and can effectively inhibit cracking in engineering structures. It is suitable for complex working conditions with stringent requirements for the mechanical properties and durability of the material.

[0034] (2) The reactive PCE-nano SiO2 composite dispersion used in this invention overcomes the defect of traditional physical mixing dispersants being prone to failure in high-alkali environments. Combined with the anti-agglomeration effect brought about by ultrafine solid waste surface modification, the freshly mixed slurry has excellent fluidity and strong slump retention, greatly reducing the difficulty of construction such as mixing and casting. Compared with the current situation in the prior art where it is difficult to balance the workability and durability of cementitious materials, this invention significantly improves the durability of materials through microstructure densification and hydration process control. It can be stably applied to harsh service environments such as marine engineering and underground pipe corridors, thus broadening the application scenarios of persulfate cementitious materials.

[0035] (3) This invention uses granulated blast furnace slag, steel slag and other industrial solid wastes as core raw materials. Through ultrafine grinding and surface modification, it achieves high-volume resource utilization of solid wastes, significantly reducing the amount of silicate cement used. Compared with the problems of low solid waste content and insufficient resource utilization efficiency in the prior art, this invention not only reduces pollution from industrial solid waste stockpiling, but also significantly reduces the carbon footprint of cementitious materials throughout their entire life cycle, meeting the development needs of green buildings under the "dual carbon" goal. At the same time, the resource utilization of biomass raw materials further expands the recycling path of agricultural and forestry wastes, achieving a dual improvement in environmental benefits and resource recycling.

[0036] (4) The present invention adopts a process route of premixed dry material preparation and gradient stirring molding. The parameters of each link are clear and the operation is simple. No complicated special equipment is required. Compared with the shortcomings of existing modified cementitious materials, such as complicated process, high cost and difficulty in large-scale production, the production process of the present invention is easy to standardize and control, the raw material supply is stable and the cost is controllable. It can be directly adapted to existing building material production lines for upgrading and transformation. While ensuring the high performance of materials, it also takes into account production efficiency and economy, and has broad engineering application prospects and industrialization value. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a flowchart of the preparation method of the present invention. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some 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.

[0040] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0041] Unless otherwise specified in the following examples, all raw materials were commercially available or prepared using conventional methods in the art. These included water (conductivity ≤10 μS / cm), triethanolamine (Sinopharm Chemical Reagent Co., Ltd., purity ≥99%), γ-aminopropyltriethoxysilane (KH-550, Sinopharm Chemical Reagent Co., Ltd., purity ≥98%), nano-SiO2 (Sinopharm Chemical Reagent Co., Ltd.), γ-methacryloyloxypropyltrimethoxysilane (KH-570, Sinopharm Chemical Reagent Co., Ltd., purity ≥98%), and dilute hydrochloric acid (Sinopharm Chemical Reagent Co., Ltd., purity ≥36.0-38.0%). ), methyl allyl polyoxyethylene ether (HPEG, Guangdong Wengjiang Chemical Reagent Co., Ltd., purity ≥98%), acrylic acid (AA, Sinopharm Chemical Reagent Co., Ltd., purity ≥99.0%), 2-acrylamide-2-methylpropanesulfonic acid (AMPS, Sinopharm Chemical Reagent Co., Ltd., purity ≥98%), ammonium persulfate (Sinopharm Chemical Reagent Co., Ltd., purity ≥98.0%), vitamin C (Luwei Pharmaceutical Group), potassium hydroxide (Sinopharm Chemical Reagent Co., Ltd., purity ≥85.0%).

[0042] like Figure 1 As shown, a method for preparing an ultrafine supersulfate cementitious material includes:

[0043] S1. Granulated blast furnace slag, steel slag, and desulfurized gypsum are crushed and mixed, and a grinding aid is added for ultrafine grinding to obtain ultrafine powder. The ultrafine powder is then surface-modified using a composite modification liquid of water glass and γ-aminopropyltriethoxysilane to obtain ultrafine solid waste-based cementitious main material.

[0044] S2. After pretreatment and activation with a silane coupling agent, nano-SiO2 is copolymerized with polycarboxylate superplasticizer monomer via free radical grafting reaction. After neutralization, a reactive PCE-nano-SiO2 composite dispersion is obtained.

[0045] S3. After carbonizing and pulverizing the biomass raw material, it is soaked in alkaline solution, washed and dried to obtain alkaline pretreated biochar.

[0046] S4. Mix the ultrafine solid waste-based cementitious main material, silicate cement, and alkaline pretreated biochar in a certain proportion to obtain a premixed dry material;

[0047] S5. The reactive PCE-nano SiO2 composite dispersion and mixing water are added to the premixed dry material, and a uniform fresh slurry is formed by stirring. After curing, the ultrafine supersulfate cementitious material is obtained.

[0048] The steps described above will be described in detail below.

[0049] Specifically, step S1 is used to prepare surface-modified ultrafine solid waste-based cementitious main material.

[0050] Granulated blast furnace slag, steel slag, and desulfurized gypsum were selected as the core solid waste raw materials, all sourced from industrial solid waste recycling and treatment enterprises. The moisture content of the granulated blast furnace slag was controlled below 1%, the Fe2O3 content of the steel slag after magnetic separation and iron removal was no more than 25%, and the dihydrate gypsum content of the desulfurized gypsum was no less than 90%. Before mixing, the three materials were crushed to ensure that the maximum particle size was less than 5 mm. Triethanolamine (0.8-1.2% by mass) was added to the mixed raw materials as a grinding aid, and the mixture was fed into a high-efficiency ball mill for co-ultrafine grinding for 40-50 minutes, ultimately yielding a specific surface area of ​​730-770 m². 2 / kg of ultrafine powder.

[0051] Specifically, the above steps enhance the reactivity of solid waste raw materials through physical activation, achieve uniform mixing of each component at the molecular level through co-grinding, shorten the ion diffusion path during subsequent hydration, and effectively reduce grinding energy consumption and prevent particle agglomeration by adding grinding aids.

[0052] Furthermore, the ultrafine powder is subjected to surface modification treatment. The composite modification liquid is diluted with water glass of modulus 1.5-2.0 to a mass concentration of 15-25%, and then mixed with γ-aminopropyltriethoxysilane (KH-550) at a mass ratio of 8-12:1. The mixture is then sprayed evenly onto the powder surface by atomization at a dosage of 1.5-2.5% of the total mass of the ultrafine powder, and reacted at high speed with stirring at 75-85℃ for 25-35 minutes.

[0053] Specifically, the core principle of surface modification is to form an organic-inorganic composite coating layer on the powder surface. This composite layer can slowly hydrolyze and release active siloxane groups in the subsequent high-alkali hydration environment, promoting the nucleation and growth of CASH gel, while inhibiting secondary agglomeration between particles, ensuring the long-term dispersion stability of the slurry, and finally obtaining a stable ultrafine solid waste-based gelling agent.

[0054] Furthermore, step S2 is to prepare a reactive PCE-nano SiO2 composite dispersion.

[0055] Specifically, hydrophilic nano-SiO2 with a primary particle size of 15-45 nm was selected, and γ-methacryloxypropyltrimethoxysilane (KH-570) was added at a mass ratio of 4-6% as a silane coupling agent for pretreatment and activation. During the pretreatment process, the nano-SiO2 was first dispersed in water to form a suspension of 180-220 g / L. After initial dispersion by ultrasonic treatment for 20-40 min, the pH of the system was adjusted to 4-5 with dilute hydrochloric acid, and the reaction was carried out at a constant temperature of 65-75℃ for 3-5 h. After the reaction, the nano-SiO2 was separated by centrifugation, washed, and vacuum dried at 100-120℃ for 10-14 h to obtain activated nano-SiO2.

[0056] Specifically, during the pretreatment activation process, carbon-carbon double bonds are introduced on the surface of nano-SiO2 using a silane coupling agent, providing active sites for the subsequent grafting reaction.

[0057] Further, a free radical graft copolymerization reaction was carried out. Activated nano-SiO2 was dispersed in water, and nitrogen gas was introduced for protection for 30 minutes to remove oxygen from the system. After heating to 60-70℃, a mixture of polycarboxylate superplasticizer monomers and an initiator solution were added dropwise simultaneously. After the addition was completed, the reaction was continued at 60-70℃ for 1-3 hours.

[0058] Specifically, the polycarboxylate superplasticizer monomer mixture is prepared by mixing methyl allyl polyoxyethylene ether, acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid in a molar ratio of 1:3-5:0.3-0.7. The initiator is a redox system composed of ammonium persulfate and vitamin C, and its total amount is 0.6-1.0% of the total mass of the polycarboxylate superplasticizer monomer.

[0059] Specifically, the purpose of this free radical graft copolymerization reaction is to anchor the polycarboxylate superplasticizer molecular chains to the surface of nano-SiO2 via covalent bonds. This avoids the polycarboxylate superplasticizer from being competitively adsorbed by alkali metal ions and becoming ineffective in a highly alkaline environment during traditional physical mixing. Simultaneously, the pozzolanic activity inherent in nano-SiO2 can react with Ca during hydration. 2+ The reaction generates a dense gel that fills capillary pores and refines the microstructure.

[0060] Further, after the free radical graft copolymerization reaction is completed and cooled to room temperature, the system is neutralized with sodium hydroxide solution to a neutral pH value, resulting in a reactive PCE-nano SiO2 composite dispersion with a solid content of 35-45%.

[0061] Furthermore, step S3 is the preparation of alkaline pretreated biochar.

[0062] Specifically, the biomass raw material is cleaned to remove impurities and dried to constant weight. It is then placed in a tube furnace for carbonization under a nitrogen atmosphere. The heating rate is controlled at 8-12℃ / min. After heating to 550-650℃, the material is held at that temperature for 1-3 hours. After carbonization, the material is naturally cooled, pulverized, and then passed through an 80-mesh standard sieve.

[0063] Specifically, biomass raw materials include one or more of bamboo shavings, rice husks, wood chips, or straw.

[0064] Further, the pulverized biochar powder was added to a 0.3-1.0 mol / L potassium hydroxide solution at a solid-liquid mass ratio of 1:8-12, and soaked at a constant temperature of 55-65℃ for 4-8 hours, with continuous shaking to ensure a complete reaction. After soaking, the solution was repeatedly washed with water until the pH of the filtrate was neutral, and then dried in an oven at 105℃ to constant weight to obtain alkaline pretreated biochar.

[0065] Specifically, carbonization forms a bimodal pore structure with both micron and nanoscale dimensions, and alkaline pretreatment further enhances the hydroxyl density and hydrophilicity of the biochar surface. Simultaneously, ion exchange introduces K+ onto the surface. + This endows biochar with three functions: adsorbing free water during the mixing stage, releasing water in the middle and late stages of hydration to achieve internal curing, and buffering shrinkage stress through its low elastic modulus after hardening.

[0066] Furthermore, step S4 is the preparation of the premixed dry material.

[0067] Specifically, according to the mass ratio of 75-85:3-8:3-5, the ultrafine solid waste-based cementitious main material, silicate cement and alkaline pretreated biochar prepared above are weighed and put into a double cone mixer and mixed at a speed of 30 rpm for 30 minutes to ensure that each component is evenly dispersed.

[0068] The silicate cement is grade 42.5 ordinary silicate cement conforming to GB175-2023 standard, with clinker mineral composition meeting the requirements of C3S content 50-58%, C2S content 18-22%, C3A content 6-8%, C4AF content 8-10%, and specific surface area 350-380 m². 2 / kg.

[0069] Specifically, the purpose of step S4 is to achieve homogenization of the dry components, providing a stable material basis for subsequent slurry mixing. The silicate cement can provide initial alkalinity to initiate the hydration reaction, while the uniform distribution of alkaline pretreated biochar creates conditions for the subsequent internal curing function and avoids performance defects caused by uneven local moisture distribution.

[0070] Furthermore, step S5 involves the mixing and preparation of the fresh slurry and its molding process.

[0071] Specifically, in step S5, 100 parts by weight of the premixed dry material includes 0.3-1.0 parts by weight of reactive PCE-nano SiO2 composite dispersion and 30-38 parts by weight of mixing water; the premixed dry material is placed in a slurry mixing pot, the mixing equipment is started and adjusted to low-speed mixing mode, with the speed controlled at 130-150 r / min, and the reactive PCE-nano SiO2 composite dispersion and mixing water are added to the pot in one go within 10 seconds to ensure that the premixed dry material and liquid components are initially in uniform contact and wetted, avoiding material agglomeration caused by insufficient local moisture; switch to high-speed mixing mode, adjust the speed to 270-300 r / min, and continue mixing for 100-140 seconds to form a uniform fresh slurry with no bleeding, no segregation, and excellent flowability.

[0072] Specifically, the core principle of this mixing process is to match the material wetting and dispersion requirements through a two-stage mixing mode. Low-speed mixing ensures that the material is fully wetted without splashing, while high-speed mixing ensures that the material is fully dispersed without agglomeration, providing a good foundation for the uniform progress of the subsequent hydration reaction and the densification of the structure.

[0073] Further, after mixing, the molding process is carried out. A standard mold meeting the testing or engineering requirements is selected. The inner wall of the mold must be pre-coated with a release agent or lined with a release film to prevent the freshly mixed slurry from sticking to the mold surface. The uniformly mixed slurry is slowly poured into the mold, maintaining a slight tilt during the pouring process and continuously shaking it gently to reduce air bubbles trapped within the slurry. After pouring, the mold is placed on a vibrating table and vibrated at a frequency of 50-60Hz for 1-2 minutes to remove any remaining tiny air bubbles, ensuring the slurry fills every corner of the mold and achieves a dense filling. After vibration, the slurry surface is smoothed along the mold edge with a scraper to remove excess material. Then, the mold surface is covered with plastic wrap or a moisturizing film to prevent surface cracking or structural loosening caused by rapid evaporation of moisture.

[0074] Specifically, the purpose of the molding operation is to transform the freshly mixed slurry into a green body of a specific shape. Through vibration degassing and surface moisturizing treatment, a regular and dense structural foundation is provided for subsequent hydration reactions and strength development, so as to avoid molding defects from affecting the final material properties.

[0075] Further, standard curing conditions are applied to obtain ultrafine supersulfate cementitious material. The mold, covered with a moisturizing film, is placed in a standard curing environment with a curing temperature controlled at 20±1℃ and a relative humidity not lower than 95%. Under these conditions, it is left to cure for 24 hours to ensure the slurry undergoes initial hydration and hardening and acquires sufficient strength, preventing premature demolding and structural damage. After reaching the required demolding strength, the mold is carefully removed, and the green body is placed in the same standard curing environment for continued curing until the specified age. During the curing process, the ambient temperature and humidity must be checked regularly to ensure stable curing conditions.

[0076] Specifically, during the curing stage, a stable temperature and humidity environment allows the slag and steel slag in the ultrafine solid waste-based cementitious material to continuously depolymerize under the action of an alkaline activator, reacting with Ca... 2+ SO4 2- Plasma reaction generates an ettringite interwoven network and CASH gel; the nano-SiO2 in the reactive PCE-nano-SiO2 composite dispersion exerts volcanic ash activity, further filling capillary pores and refining the microstructure; the alkaline pretreated biochar continuously releases stored moisture through an internal curing effect, alleviating self-drying shrinkage and buffering shrinkage stress. Through this curing process, the mechanical properties, volume stability, and durability of the cementitious material gradually mature, yielding an ultrafine ultrasulfate cementitious material. By weight, its dry basis components include: 75-85 parts ultrafine solid waste-based cementitious main material, 3-8 parts silicate cement, and 3-5 parts alkaline pretreated biochar.

[0077] Example 1:

[0078] Step S1: Select granulated blast furnace slag with a moisture content of 0.8%, converter steel slag with a Fe2O3 content of 23% after magnetic separation to remove iron, and desulfurized gypsum with a dihydrate gypsum content of 92%. Weigh the raw materials according to a mass ratio of 45:20:12. Crush the three materials separately until the maximum particle size is less than 5 mm, and then mix them evenly. Add 1% of triethanolamine grinding aid to the mixed raw materials and put them into a high-efficiency ball mill for joint ultrafine grinding. Continue grinding for 45 minutes to finally obtain a specific surface area of ​​750 m². 2 / kg, ultrafine powder with D50 particle size of 4.2μm; dilute water glass with modulus of 1.8 to a mass concentration of 20% and mix it with γ-aminopropyltriethoxysilane at a mass ratio of 10:1 to obtain a composite modified liquid. The liquid is sprayed evenly onto the powder surface through an atomizing spray gun at a dosage of 1.5% of the total mass of the ultrafine powder under low-speed stirring. The sprayed powder is placed in a high-speed mixer, heated to 80℃ and stirred at high speed for 30 minutes. After the reaction is completed, it is immediately sealed and stored in a moisture-proof environment to obtain ultrafine solid waste-based cementitious main material.

[0079] Step S2: Select hydrophilic nano-SiO2 with a primary particle size of 20-40 nm, disperse it in water to form a suspension with a concentration of 200 g / L, sonicate for 30 min, and adjust the pH to 4-5 with dilute hydrochloric acid; add γ-methacryloyloxypropyltrimethoxysilane at 5% of the mass of nano-SiO2, and react at a constant temperature of 70℃ for 4 h; after the reaction, centrifuge the product, wash it three times with anhydrous ethanol, and vacuum dry it at 110℃ for 12 h to obtain activated nano-SiO2; weigh 20 g of activated nano-SiO2 and disperse it in 200 g of water, sonicate for 15 min, and then purge with nitrogen gas for 30 min to remove oxygen. The temperature was raised to 65°C and maintained under a nitrogen protective atmosphere. A mixture of polycarboxylate superplasticizer monomers and an initiator solution were added dropwise simultaneously over 3 hours. The monomer mixture was prepared from methyl allyl polyoxyethylene ether (number average molecular weight 2400), acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid in a molar ratio of 1:4:0.5. The initiator was a redox system composed of ammonium persulfate and vitamin C, with a total amount of 0.8% of the total monomer mass. After the addition was complete, the reaction was continued at 65°C for 2 hours. After cooling to room temperature, the system was neutralized with sodium hydroxide solution to a neutral pH, yielding a reactive PCE-nano SiO2 composite dispersion with a solid content of 40%.

[0080] Step S3: Select dry, impurity-free bamboo shavings, wash them, and dry them in an oven at 105℃ to constant weight. Place them in a tube furnace under nitrogen atmosphere protection and heat them to 600℃ at a rate of 10℃ / min, then carbonize them for 2 hours. After carbonization, allow them to cool naturally to room temperature, pulverize them with a high-speed pulverizer, and pass them through an 80-mesh standard sieve to obtain biochar powder. Prepare a 0.5 mol / L potassium hydroxide solution, add the biochar powder to the solution at a solid-liquid mass ratio of 1:10, and soak them at a constant temperature of 60℃ with shaking for 6 hours, stirring once every 1 hour during the soaking process. After soaking, filter to separate the biochar, wash repeatedly until the pH of the filtrate is 7, and then dry it in an oven at 105℃ to constant weight to obtain alkaline pretreated biochar.

[0081] Step S4: Select ordinary Portland cement of grade 42.5 conforming to GB175-2023 standard, with a clinker mineral composition of C3S content of 50-58%, C2S content of 18-22%, C3A content of 6-8%, C4AF content of 8-10%, and a specific surface area of ​​350-380 m². 2 / kg; Weigh the ultrafine solid waste-based cementitious main material, silicate cement and alkaline pretreated biochar prepared in step S1 according to the mass ratio of 80:5:4, put the three together into a double cone mixer, mix at 30 rpm for 30 min to obtain homogeneous premixed dry material.

[0082] Step S5: 100 parts by weight of premixed dry material includes 0.6 parts by weight of reactive PCE-nano SiO2 composite dispersion and 34 parts by weight of mixing water; place the premixed dry material in a paste mixing pot, turn on the mixing equipment and adjust to a low-speed mixing mode of 140 r / min, add the reactive PCE-nano SiO2 composite dispersion and mixing water at once within 10 seconds, then switch to a high-speed mixing mode of 285 r / min and continue mixing for 120 seconds to form a uniform fresh slurry; select a standard cubic mold, apply a release agent to the inner wall, and slowly pour the fresh slurry into the mold. The mold was gently shaken, then placed on a vibrating table and vibrated at 55Hz for 2 minutes to remove residual air bubbles in the slurry. Excess slurry on the surface of the mold was smoothed with a scraper, and covered with plastic wrap to prevent moisture evaporation. The mold was then placed in a standard curing environment with a temperature of 20±1℃ and a relative humidity of over 95% for 24 hours of static curing. After reaching the demolding strength, the mold was removed, and the green body was placed in the same standard curing environment for another 28 days to obtain an ultrafine ultrasulfate cementitious material. By weight, it includes 80 parts of surface-modified ultrafine solid waste-based cementitious main material, 5 parts of silicate cement, and 4 parts of alkaline pretreated biochar.

[0083] Example 2:

[0084] Compared with Example 1, in this embodiment, the composite modified liquid in step S1 is sprayed at a dosage of 2.0% of the total mass of the ultrafine powder. The remaining steps are exactly the same as in Example 1.

[0085] Example 3:

[0086] Compared with Example 1, in this embodiment, the composite modified liquid in step S1 is sprayed at a dosage of 2.5% of the total mass of the ultrafine powder. The remaining steps are exactly the same as in Example 1.

[0087] Example 4:

[0088] Compared with Example 2, in this embodiment, step S5 includes 0.3 parts by weight of reactive PCE-nano SiO2 composite dispersion and 34 parts by weight of mixing water in 100 parts by weight of premixed dry material. The remaining steps are exactly the same as in Example 2.

[0089] Example 5:

[0090] Compared with Example 2, in this embodiment, step S5 includes 0.5 parts by weight of reactive PCE-nano SiO2 composite dispersion and 34 parts by weight of mixing water in 100 parts by weight of premixed dry material. The remaining steps are exactly the same as in Example 2.

[0091] Example 6:

[0092] Compared with Example 2, in this embodiment, step S5 includes 0.8 parts by weight of reactive PCE-nano SiO2 composite dispersion and 34 parts by weight of mixing water in 100 parts by weight of premixed dry material. The remaining steps are exactly the same as in Example 2.

[0093] Example 7:

[0094] Compared with Example 2, in this embodiment, step S5 includes 1.0 part by weight of reactive PCE-nano SiO2 composite dispersion and 34 parts by weight of mixing water in 100 parts by weight of premixed dry material. The remaining steps are exactly the same as in Example 2.

[0095] Comparative Example 1:

[0096] This comparative example uses an ultrafine solid waste-based gelling agent that has not undergone surface modification. That is, the step of surface modification of the fine powder by the composite modification liquid of water glass and γ-aminopropyltriethoxysilane is omitted. The remaining components, proportions, and preparation process parameters are consistent with those in Example 2.

[0097] Step S1: Select granulated blast furnace slag with a moisture content of 0.8%, converter steel slag with a Fe2O3 content of 23% after magnetic separation to remove iron, and desulfurized gypsum with a dihydrate gypsum content of 92%. Weigh the raw materials according to a mass ratio of 45:20:12. Crush the three materials separately until the maximum particle size is less than 5 mm, and then mix them evenly. Add 1% of triethanolamine grinding aid to the mixed raw materials and put them into a high-efficiency ball mill for joint ultrafine grinding. Continue grinding for 45 minutes to finally obtain a specific surface area of ​​750 m². 2 Ultrafine powder with a density of 4.2 μm and a D50 particle size of 4.2 μm per kg.

[0098] Step S2: Completely consistent with step S2 of Example 2, to obtain a reactive PCE-nano SiO2 composite dispersion with a solid content of 40%.

[0099] Step S3: Completely consistent with step S3 of Example 2, obtaining alkaline pretreated biochar.

[0100] Step S4: Select ordinary Portland cement of grade 42.5 conforming to GB175-2023 standard. Its clinker mineral composition should contain 50-58% C3S, 18-22% C2S, 6-8% C3A, and 8-10% C4AF, with a specific surface area of ​​350-380 m². 2 / kg; Weigh the ultrafine powder prepared in step S1, silicate cement and alkaline pretreated biochar prepared in step S3 according to the mass ratio of 80:5:4, put the three into a double cone mixer and mix at 30 rpm for 30 min to obtain homogeneous premixed dry material.

[0101] Step S5: Completely consistent with step S5 of implementation 2, to obtain the cementitious material.

[0102] Comparative Example 2:

[0103] In this comparative example, a physical mixture of ordinary polycarboxylate superplasticizer and nano-SiO2 was used to replace the reactive PCE-nano-SiO2 composite dispersion.

[0104] Step S1: Completely consistent with Step S1 of Example 2, to obtain ultrafine solid waste-based cementitious main material.

[0105] Step S2: Select hydrophilic nano-SiO2 with a primary particle size of 20-40 nm, disperse it in water to form a suspension with a concentration of 200 g / L, and after ultrasonic treatment for 30 min, adjust the pH to 4-5 with dilute hydrochloric acid; select a commercially available methyl allyl polyoxyethylene ether type polycarboxylate superplasticizer as the ordinary polycarboxylate superplasticizer. This ordinary polycarboxylate superplasticizer is copolymerized from methyl allyl polyoxyethylene ether (number average molecular weight 2400), acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid in a molar ratio of 1:4:0.5. Weigh the ordinary polycarboxylate superplasticizer in a proportion equivalent to the effective content of the polycarboxylate superplasticizer in the reactive PCE-nano-SiO2 composite dispersion in Example 1, add it to the nano-SiO2 suspension, and stir continuously for 15 min to achieve physical uniform mixing, thereby obtaining an ordinary PCE-nano-SiO2 physical mixture with a solid content of 40%.

[0106] Step S3: Completely consistent with step S3 of Example 2, obtaining alkaline pretreated biochar.

[0107] Step S4: Completely consistent with step S4 of Example 2, to obtain homogeneous premixed dry material.

[0108] Step S5: In step S5, 100 parts by weight of the premixed dry material includes 0.6 parts by weight of ordinary PCE-nano SiO2 physical mixture and 34 parts by weight of mixing water; place the premixed dry material in a slurry mixing pot, turn on the mixing equipment and adjust it to a low-speed mixing mode of 140 r / min, add the ordinary PCE-nano SiO2 physical mixture and mixing water at once within 10 seconds, then switch to a high-speed mixing mode of 285 r / min and continue mixing for 120 seconds to form a uniform fresh slurry; select standard cubic meters After applying a release agent to the inner wall of the mold, the freshly mixed slurry is slowly poured into the mold, with slight shaking during the pouring process. The mold is then placed on a vibrating table and vibrated at 55 Hz for 2 minutes to remove any residual air bubbles. Excess slurry is scraped smooth from the mold surface with a scraper, and plastic wrap is used to prevent moisture evaporation. The mold is then placed in a standard curing environment with a temperature of 20 ± 1 ℃ and a relative humidity of 95% or higher for 24 hours of static curing. Once the demolding strength is reached, the mold is removed, and the green body is further cured in the same standard curing environment for 28 days to obtain the cementitious material.

[0109] Comparative Example 3:

[0110] In this comparative example, untreated biochar was used instead of alkaline pretreated biochar.

[0111] Step S1: Completely consistent with Step S1 of Example 2, to obtain ultrafine solid waste-based cementitious main material.

[0112] Step S2: Completely consistent with step S2 of Example 2, to obtain a reactive PCE-nano SiO2 composite dispersion with a solid content of 40%.

[0113] Step S3: Select dry bamboo shavings free of impurities, wash them, and dry them in an oven at 105℃ to constant weight. Place them in a tube furnace and heat them to 600℃ at a rate of 10℃ / min under nitrogen atmosphere protection. Keep them at this temperature for 2 hours for carbonization. After carbonization, allow them to cool naturally to room temperature, pulverize them with a high-speed pulverizer, and pass them through an 80-mesh standard sieve to obtain untreated biochar.

[0114] Step S4: Select ordinary Portland cement of grade 42.5 conforming to GB175-2023 standard. Its clinker mineral composition should contain 50-58% C3S, 18-22% C2S, 6-8% C3A, and 8-10% C4AF, with a specific surface area of ​​350-380 m². 2 / kg; Weigh the ultrafine solid waste-based cementitious main material, silicate cement and untreated biochar prepared in step S1 according to the mass ratio of 80:5:4, put the three together into a double cone mixer, mix at 30 rpm for 30 min to obtain homogeneous premixed dry material.

[0115] Step S5: Completely consistent with step S5 of Example 2, to obtain a cementitious material.

[0116] Comparative Example 4:

[0117] Compared with Example 2, in step S1 of this comparative example, co-ultrafine grinding was performed for 25 minutes, resulting in a final specific surface area of ​​650 m². 2 The powder is an ultrafine powder with a density of 8.4 μm and a D50 particle size of 8.4 μm. All other components, proportions, and preparation process parameters remain the same as in Example 2.

[0118] Comparative Example 5:

[0119] Compared with Example 2, in step S1 of this comparative example, co-ultrafine grinding was performed for 60 minutes, ultimately obtaining a specific surface area of ​​800 m². 2 The powder is an ultrafine powder with a density of 2.2 μm and a D50 particle size of 2.2 μm. All other components, proportions, and preparation process parameters remain the same as in Example 2.

[0120] Experimental Example 1:

[0121] For initial fluidity and 2-hour fluidity loss, the spread of freshly mixed mortar was tested according to GB / T 8077-2023 "Test Method for Homogeneity of Concrete Admixtures". The 2-hour fluidity loss was the difference between the initial fluidity and the fluidity after standing for 2 hours. 40mm×40mm×160mm specimens were prepared according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)". Compressive strength was tested after curing under standard conditions (20±1℃, relative humidity ≥95%) for 3 days, 7 days, and 28 days. The results are shown in Table 1.

[0122] The cumulative heat release during 72 hours of hydration of the cement paste was tested according to GB / T 12959-2024 "Determination of Heat of Hydration of Cement", i.e., the 72-hour heat of hydration. The shrinkage deformation of the specimen after 28 days of standard curing in a dry environment was tested according to GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete", obtaining the 56-day drying shrinkage. For the 28-day electrical flux, the rapid chloride ion migration coefficient method in GB / T 50082-2024 was used to characterize the material's resistance to chloride ion penetration. The sulfate attack resistance coefficient K was tested according to GB / T 749-2008 "Test Method for Sulfate Attack Resistance of Cement". The results are shown in Table 2.

[0123]

[0124]

[0125] Examples 1-3 used the same 0.6 parts reactive PCE-nano SiO2 composite dispersion, 750m 2With a specific surface area of ​​ / kg and a D50 particle size of 4.2μm, the dosage of the modified liquid was adjusted to 1.5%, 2.0%, and 2.5%, respectively. Example 2 exhibited the most outstanding overall performance, with an initial flowability of 265mm, a flowability loss of only 15mm after 2 hours, compressive strengths of 27.5MPa, 42.3MPa, and 61.8MPa at 3d, 7d, and 28d, respectively, and a drying shrinkage as low as 285×10⁻⁶ at 56d. -6 The 28-day electrical flux is 860C, and the sulfate resistance coefficient reaches 1.12.

[0126] In Example 1, the modified liquid dosage was 1.5%, and all properties showed a significant decline. The initial flowability decreased to 252 mm, the flowability loss increased to 23 mm after 2 hours, the compressive strength decreased to 59.5 MPa after 28 days, and the drying shrinkage increased to 305 × 10⁻⁶ after 56 days. -6 This is because when the amount of modified liquid is insufficient, a complete organic-inorganic composite coating layer cannot be formed on the surface of the ultrafine solid waste particles, the tendency for particle aggregation is enhanced, the dispersion stability decreases, and consequently, the hydration reaction is incomplete, resulting in insufficient microstructural density. In Example 3, the amount of modified liquid was increased to 2.5%, and the performance showed a slight deterioration: the initial flowability decreased to 262 mm, the 2-hour flowability loss increased to 18 mm, the 28-day compressive strength decreased to 60.7 MPa, and the 56-day drying shrinkage increased to 298 × 10⁻⁶. -6 Excessive moisture introduced by the modified liquid will form additional pores during hydration, weakening the compactness of the microstructure. It may also lead to an excessively thick modified layer, affecting the interfacial bonding between solid waste particles and other components.

[0127] Examples 4-7 maintain a modified solution dosage of 2.0% and a concentration of 750m. 2 With the specific surface area per kg and D50 particle size remaining constant, the dosage of the reactive PCE-nano SiO2 composite dispersion was adjusted to 0.3, 0.5, 0.8, and 1.0 parts, respectively, forming a clear contrast with Example 2 with 0.6 parts. Example 4, with a dispersion dosage of 0.3 parts, exhibited an initial flowability of only 230 mm, a flowability loss of up to 48 mm after 2 hours, compressive strengths of 21.2 MPa, 35.8 MPa, and 53.6 MPa at 3, 7, and 28 days, respectively, and a drying shrinkage of 380 × 10⁻⁶ at 56 days. -6 The performance of Example 5 was significantly inferior to that of Example 2. This is because when the amount of dispersion is insufficient, it is impossible to effectively overcome the attraction between ultrafine particles, resulting in severe particle agglomeration, poor slurry flowability, and insufficient stability over time, thus inhibiting the hydration reaction. With the dosage increased to 0.5 parts, the performance of Example 5 improved significantly, with the initial flowability increasing to 252 mm, the 2-hour flowability loss decreasing to 22 mm, the 28-day compressive strength reaching 59.3 MPa, and the 56-day drying shrinkage decreasing to 310 × 10⁻⁶. -6The dispersing effect of the dispersion gradually becomes apparent. In Example 2, with a dosage of 0.6 parts, the performance reached its peak, demonstrating optimal synergy between the dispersion effect and the pozzolanic activity of nano-SiO2. When the dosage exceeded 0.6 parts, the performance of Examples 6-7 showed a slight decline. In Example 7, with a dosage of 1.0 part, the initial flowability decreased to 264 mm, the 2-hour flowability loss increased to 22 mm, the 28-day compressive strength decreased to 60.5 MPa, and the drying shrinkage increased to 310 × 10⁻⁶. -6 This is because excessive dispersion can easily lead to weak agglomeration between nanoparticles, and may also introduce a small amount of redundant air, which can damage the compactness of the microstructure and prevent the performance from being continuously improved.

[0128] The performance differences between Example 2 and the comparative examples visually demonstrate the key roles and synergistic effects of each functional component in the system.

[0129] Comparative Example 1, which omitted surface modification treatment, had an initial flowability of only 220 mm, a flowability loss of 45 mm after 2 hours, a compressive strength of only 42.3 MPa after 28 days, and a drying shrinkage of up to 510 × 10⁻⁶ after 56 days. -6 The 28-day electrical flux was 1580C, which was significantly worse than that of Example 2, indicating that the organic-inorganic composite layer formed by surface modification can effectively inhibit particle agglomeration, promote the full hydration reaction, and improve the compactness of the microstructure.

[0130] Comparative Example 2 uses a physical mixture of ordinary polycarboxylate superplasticizer and nano-SiO2 to replace the reactive composite dispersion. Its 2-hour flow loss is 52 mm, its 28-day compressive strength is 48.5 MPa, and its sulfate erosion resistance coefficient is 0.92, which is far inferior to Example 2. This demonstrates the stable dispersion effect brought about by the covalent graft structure, avoiding the problems of dispersant failure or nanoparticle agglomeration in the physical mixing system.

[0131] Comparative Example 3, where untreated biochar replaced alkaline pretreated biochar, showed a 56-day drying shrinkage of 410 × 10⁻⁶. -6 The 28-day electrical flux was 1150C and the 28-day compressive strength was 52.1MPa, indicating that the alkali-treated biochar can alleviate self-drying shrinkage through internal curing effect, and at the same time inhibit the propagation of microcracks through stress relaxation, thereby improving structural stability and durability.

[0132] Comparative Example 4 uses a specific surface area of ​​650 m² 2 The powder, with a particle size of 8.4 μm and a density of 8 kg / kg, has a 3-day compressive strength of only 16.5 MPa and a 28-day electric flux of 1490 C. Due to insufficient particle fineness and a long ion diffusion path, the hydration activity is difficult to be fully activated.

[0133] Comparative Example 5 extended the grinding time to 60 minutes, resulting in a specific surface area of ​​800 m². 2The powder has a density of 2.2 μm and a D50 particle size, but its 28-day compressive strength is 55.4 MPa and its drying shrinkage is 330 × 10⁻⁶. -6 The results were still inferior to those of Example 2, indicating that excessive grinding exacerbated the tendency of particle agglomeration, which in turn affected the performance. This confirms that only moderate ultrafine grinding can balance activity activation and dispersion stability.

[0134] The superior performance of Example 2 is essentially the result of the synergistic effect of the three components: the surface-modified ultrafine solid waste-based cementitious material, the reactive PCE-nano SiO2 composite dispersion, and the alkaline pretreated biochar. The composite layer formed by the modified liquid ensures the stability of particle dispersion, the reactive composite dispersion achieves efficient dispersion and nano-reinforcement, and the alkaline pretreated biochar provides internal curing and stress relaxation. The organic integration of these three components, rather than a simple superposition, ultimately optimizes the material's workability, strength, volumetric stability, and durability simultaneously. The comparative examples, due to the absence or performance defects of individual functional components, experienced a comprehensive decline in overall performance, further highlighting the innovation and superiority of this synergistic system and confirming the rationality of the process parameters and component design.

[0135] Therefore, in the application of this invention, granulated blast furnace slag, steel slag, and desulfurized gypsum are used as core solid waste raw materials. These materials are then subjected to ultrafine grinding and surface modification to obtain an ultrafine solid waste-based cementitious material. Simultaneously, a covalently grafted reactive PCE-nano SiO2 composite dispersion and alkaline pretreated biochar are prepared. The ultrafine solid waste-based cementitious material, specific silicate cement, and alkaline pretreated biochar are then mixed in a specific ratio to form a premixed dry material. The reactive PCE-nano SiO2 composite dispersion and mixing water are then mixed using a gradient stirring process to form a uniform fresh slurry. After molding and standard curing, the finished ultrafine supersulfate cementitious material is obtained. The core principle of this invention is to effectively stimulate the hydration of ultrafine solid waste powder through surface modification. The active material relies on reactive PCE-nano SiO2 composite dispersion to achieve long-term dispersion and synergistic effect of pozzolanic activity. Combined with the internal curing effect of alkaline pretreated biochar to regulate the hydration process and alleviate self-drying shrinkage, a synergistic and complementary system is formed among the core processes and components. Ultimately, the resulting supersulfate cementitious material has excellent workability, high mechanical properties, good volume stability and excellent durability. At the same time, by making extensive use of industrial solid waste and biochar-based materials, this invention effectively reduces the amount of silicate cement used. While improving the comprehensive performance of cementitious materials, it also realizes the high-value resource utilization of industrial solid waste, which has significant technical advantages and environmental benefits.

[0136] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing an ultrafine supersulfate cementitious material, characterized in that, include: S1. Granulated blast furnace slag, steel slag, and desulfurized gypsum are crushed and mixed, and a grinding aid is added for ultrafine grinding to obtain ultrafine powder. The ultrafine powder is then surface-modified using a composite modification liquid of water glass and γ-aminopropyltriethoxysilane to obtain ultrafine solid waste-based cementitious main material. S2. After pretreatment and activation with a silane coupling agent, nano-SiO2 is copolymerized with polycarboxylate superplasticizer monomer via free radical grafting reaction. After neutralization, a reactive PCE-nano-SiO2 composite dispersion is obtained. S3. After carbonizing and pulverizing the biomass raw material, it is soaked in alkaline solution, washed and dried to obtain alkaline pretreated biochar. S4. Mix the ultrafine solid waste-based cementitious main material, silicate cement, and alkaline pretreated biochar in a certain proportion to obtain a premixed dry material; S5. The reactive PCE-nano SiO2 composite dispersion and mixing water are added to the premixed dry material, and a uniform fresh slurry is formed by stirring. After curing, the ultrafine supersulfate cementitious material is obtained.

2. The method for preparing an ultrafine ultrasulfate cementitious material according to claim 1, characterized in that: In step S1, the mass ratio of the granulated blast furnace slag, steel slag and desulfurized gypsum is 40-50:15-25:10-15; The grinding time is 40-50 minutes; the grinding aid is triethanolamine; the specific surface area of ​​the ultrafine powder is 730-770 m². 2 / kg.

3. The method for preparing an ultrafine ultrasulfate cementitious material according to claim 1, characterized in that: In step S1, the composite modified liquid is prepared by diluting water glass with a modulus of 1.5-2.0 to a mass concentration of 15-25% and then mixing it with γ-aminopropyltriethoxysilane at a mass ratio of 8-12:

1. The amount of the composite modified liquid sprayed is 1.5-2.5% of the total mass of the powder; The modification treatment temperature is 75-85℃, and the reaction time is 25-35 min.

4. The method for preparing an ultrafine ultrasulfate cementitious material according to claim 1, characterized in that: In step S2, the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane, and the amount added is 4-6% of the mass of nano-SiO2; The pretreatment activation process includes: Nano-SiO2 was dispersed in water to form a suspension with a concentration of 180-220 g / L. The suspension was sonicated for 20-40 min, the pH was adjusted to 4-5, and the suspension was reacted in a water bath at 65-75℃ for 3-5 h. After centrifugation and washing, the suspension was vacuum dried at 100-120℃ for 10-14 h.

5. The method for preparing an ultrafine ultrasulfate cementitious material according to claim 1, characterized in that: In step S2, the polycarboxylate superplasticizer monomer includes methyl allyl polyoxyethylene ether, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid; The molar ratio of methyl allyl polyoxyethylene ether, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid is 1:3-5:0.3-0.7; The free radical graft copolymerization reaction was carried out by simultaneously adding polycarboxylate superplasticizer monomer and initiator solution at 60-70℃ under nitrogen protection; after the addition was completed, the reaction was continued at 60-70℃ for 1-3 hours. The initiator is a redox system composed of ammonium persulfate and vitamin C, and its total amount is 0.6-1.0% of the total mass of polycarboxylate superplasticizer monomers.

6. The method for preparing an ultrafine ultrasulfate cementitious material according to claim 1, characterized in that: In step S3, the biomass raw material includes one or more of bamboo shavings, rice husks, wood chips, or straw; The carbonization heating rate of the biomass raw material is 8-12℃ / min, the carbonization temperature is 550-650℃, and the carbonization time is 1-3h; The alkaline solution is a 0.3-1.0 mol / L potassium hydroxide solution, the solid-liquid mass ratio for soaking is 1:8-12, the soaking temperature is 55-65℃, and the soaking time is 4-8 hours.

7. The method for preparing an ultrafine supersulfate cementitious material according to claim 1, characterized in that: In step S4, the clinker mineral composition of the silicate cement contains 50-58% C3S, 18-22% C2S, 6-8% C3A, 8-10% C4AF, and has a specific surface area of ​​350-380 m². 2 / kg; The mass ratio of the surface-modified ultrafine solid waste-based cementitious material, silicate cement, and alkaline pretreated biochar is 75-85:3-8:3-5.

8. The method for preparing an ultrafine ultrasulfate cementitious material according to claim 1, characterized in that: In step S5, 100 parts by weight of the premixed dry material includes 0.3-1.0 parts by weight of the reactive PCE-nano SiO2 composite dispersion and 30-38 parts by weight of mixing water.

9. The method for preparing an ultrafine ultrasulfate cementitious material according to claim 1, characterized in that: In step S5, the stirring includes low-speed stirring and high-speed stirring. The reactive PCE-nano SiO2 composite dispersion and mixing water are added at a low speed of 130-150 r / min, and then stirred at a high speed of 270-300 r / min for 100-140 s.

10. An ultrafine supersulfate cementitious material prepared by the preparation method according to any one of claims 1-9, characterized in that: By weight, its dry basis components include: 75-85 parts of ultrafine solid waste-based cementitious main material, 3-8 parts of silicate cement, and 3-5 parts of alkaline pretreated biochar.

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