A solid waste-based low-carbon gel material and its preparation method

Abstract

This invention discloses a solid waste-based low-carbon gel material and its preparation method. The material comprises, by mass percentage: 40%-60% highly active slag, 20%-35% graded bottom ash from a tower, 3%-8% pH-sensitive composite activator, 0.5%-2% nano-C-S-H seed crystals, 0.1%-1% modified cellulose nanocrystals, and 15%-25% water, with a controlled water-to-solid ratio of 0.15-0.28. The preparation method includes graded pretreatment of bottom ash, preparation and dispersion of nano-C-S-H seed crystals, preparation of the pH-sensitive composite activator, and mixing and slurry preparation. Graded treatment optimizes sulfate release, the pH-sensitive activator dynamically regulates alkalinity, and the nano-C-S-H seed crystals and modified cellulose nanocrystals induce ordered hydration and a multi-level porous structure, significantly improving compressive strength, impermeability, and low expansion rate. This invention effectively utilizes industrial solid waste, reduces energy consumption and carbon emissions, solves problems of uneven hydration and expansion cracking, and is suitable for green building and resource recycling.

Description

Technical Field

[0001] This invention relates to the technical field of gel materials, and in particular to a solid waste-based low-carbon gel material and its preparation method. Background Technology

[0002] Solid waste-based low-carbon gel materials, as a type of green building material, utilize industrial solid waste (such as slag, fly ash, and bottom ash) to prepare cementitious materials through chemical or physical activation. In recent years, they have received widespread attention in the fields of construction, environmental protection, and resource recycling. The preparation of traditional cement-based materials relies on high-temperature calcination of clinker, resulting in high energy consumption and large carbon emissions. In contrast, solid waste-based gel materials, through technologies such as alkali activation, sulfate activation, or combined activation, utilize the potential active components in solid waste (such as SiO2, Al2O3, and CaO) to generate products such as calcium silicate hydrate (CSH), calcium aluminate hydrate (CAH), and ettringite (AFt, 3CaO·Al2O3·3CaSO4·32H2O), significantly reducing energy consumption and carbon footprint. In existing technologies, alkali activation technology (such as using NaOH or Na2SiO3) can effectively activate highly active solid waste such as slag, forming a high-strength three-dimensional network gel structure; while sulfate activation (such as using CaSO4) provides SO4... 2- Ions promote the formation of ettringite, enhancing early strength. In recent years, research has further combined mechanical grinding, fractionation, and chemical pretreatment to optimize the reactivity of solid waste and the microstructure of hydration products, thereby improving the mechanical properties and durability of materials. However, due to the complexity of solid waste sources and the diversity of process conditions, the performance stability and large-scale application of solid waste-based gel materials still face challenges.

[0003] Despite some progress in the field of solid waste-based gel materials, significant shortcomings remain, particularly in the application of sulfate-activated systems. Bottom ash, a common type of solid waste, exhibits fluctuating sulfate (e.g., CaSO4) content (0.5%-10%) and diverse sulfate forms (dihydrate gypsum, hemihydrate gypsum, anhydrous gypsum), leading to SO4 concentration variations. 2- The unstable release rate affects the uniform formation of hydration products (such as AFt and AFm), thereby reducing the early strength and microstructure density of the material. Furthermore, excessive sulfate may induce delayed ettringite formation in the later stages of hydration. Due to its high water content (32H2O), it causes volume expansion, inducing microcracks or macro-cracks, severely impacting durability. The high pH environment in the alkaline activation system further exacerbates the secondary reaction between sulfate and CSH or Ca(OH)2, generating expansive gypsum (CaSO4·2H2O), increasing the risk of cracking. Existing technologies mostly adjust sulfate content through simple pretreatment (such as water washing or heat treatment) or a single activator, but it is difficult to achieve SO42---. 2-The dynamic regulation of release and the insufficient activation efficiency for low-activity solid waste limit the optimization of material performance and economic efficiency. Summary of the Invention

[0004] This application provides a solid waste-based low-carbon gel material, wherein the gel material comprises the following components by mass percentage:

[0005] Highly active slag: 40%-60%;

[0006] Graded bottom ash from the tower: 20%-35%;

[0007] pH-sensitive compound activator: 3%-8%;

[0008] Nano CSH seed crystals: 0.5%-2%;

[0009] Modified cellulose nanocrystals: 0.1%-1%;

[0010] Water: 15%-25%.

[0011] It should be noted that the highly reactive slag is rich in SiO2, Al2O3, and CaO. Through alkali activation, it generates CSH and CAH gels, forming a three-dimensional network structure that contributes significantly to the strength. The graded bottom ash provides SO4. 2- , with Ca 2+ Al 3+ The reaction generates ettringite (AFt), which fills pores and enhances early strength. Staged treatment optimizes the SO42- release rate, reducing hydration unevenness caused by sulfate fluctuations. A pH-sensitive composite activator dynamically regulates alkalinity, initially gently activating low-activity solid waste, and later releasing strong alkali to promote CSH formation. This synergistically activates sulfate, inhibiting secondary gypsum formation at high pH levels and reducing the risk of expansion and cracking. Nano-CSH seed crystals act as nuclei, inducing the orderly growth of hydration products, reducing delayed ettringite formation, and optimizing the microstructure. Modified cellulose nanocrystals induce a multi-level porous structure, buffering sulfate-induced expansion stress and enhancing interfacial bonding and impermeability.

[0012] As a preferred technical solution for a solid waste-based low-carbon gel material, the highly active slag is granulated blast furnace slag with a specific surface area ≥400 m². 2 / kg.

[0013] It should be noted that a specific surface area ≥ 400 m² 2 The / kg setting is achieved through mechanical grinding, which increases the surface reaction area of ​​the particles, accelerates the hydration reaction process, significantly improves early strength and long-term durability, and at the same time reduces dependence on high doses of alkali activators, thereby reducing production costs and environmental impact.

[0014] In addition, this application provides a method for preparing the aforementioned solid waste-based low-carbon gel material, comprising the following steps:

[0015] Step S1. Pre-treatment of bottom ash: The bottom ash is separated into high-activity particles and low-activity particles by air classifier. The high-activity particles are acid washed and the low-activity particles are microwave heat treated to convert them into sulfate form.

[0016] Step S2. Preparation and dispersion of nano CSH seeds: Nano CSH seeds are prepared by chemical precipitation and then uniformly dispersed in water by ultrasonic dispersion to prepare a seed suspension;

[0017] Step S3. Preparation of pH-sensitive composite activator: Sodium carbonate is coated with polylactic acid by spray drying, and then mixed with sodium silicate and triethanolamine in a mass ratio of (5-7):(2-3):(1-2) to prepare a pH-sensitive composite activator;

[0018] Step S4. Mixing and slurry preparation: Add the highly active slag, bottom ash from the classifier tower, nano-CSH seed crystals, modified cellulose nanocrystals, and pH-sensitive composite activator to the mixer according to the mass ratio, dry mix, add water, wet mix, and control the water-to-solid ratio to 0.15-0.28 to form a uniform solid waste-based low-carbon gel material slurry.

[0019] It should be noted that in step S1, the bottom ash of the tower is separated into highly active and low-active particles through airflow classification. The highly active particles are acid-washed to remove chloride salts and heavy metal impurities, reducing the risk of secondary reactions. The low-active particles are microwave-heat-treated to convert low-soluble sulfates (such as anhydrous gypsum) into highly soluble forms (such as dihydrate gypsum), thus optimizing SO4 levels. 2- The release rate promotes the uniform formation of ettringite (AFt) and reduces hydration heterogeneity caused by sulfate fluctuations. Step S2 prepares nano-CSH seed crystals (10-50 nm in size) through chemical precipitation and disperses them ultrasonically to form a uniform suspension. These crystals act as nuclei to induce the orderly growth of CSH and AFt, reducing delayed ettringite formation and optimizing pore structure and early strength. Step S3 prepares a pH-sensitive composite activator, using polylactic acid to coat sodium carbonate to achieve slow alkalinity release. Initially, it provides a moderate pH (10-12) to activate low-activity solid waste. Later, it releases a strong alkali to synergistically promote CSH formation with sodium silicate and triethanolamine, inhibiting the reaction of sulfate with CSH at high pH to form expansive gypsum and reducing the risk of cracking. Step S4 ensures uniform dispersion of highly active slag, bottom ash from the classification tower, nano-CSH seed crystals, modified cellulose nanocrystals (CNC), and the activator through dry mixing. After wet mixing, the water-to-solid ratio is controlled at 0.15-0.28 to balance the slurry fluidity and hydration reaction. CNC induces a multi-level pore structure to buffer expansion stress.

[0020] As a preferred technical solution for a solid waste-based low-carbon gel material, the preparation method of the nano-CSH seed crystals is as follows: 0.1 mol / L calcium nitrate solution and 0.1 mol / L sodium silicate solution are mixed at a molar ratio of 1:1 and stirred at 40 to 50°C for 2 to 3 hours under pH 11 to 12 conditions to allow calcium ions to react with silicate ions to generate CSH nano-seed crystals. After the reaction is completed, the precipitate is separated by centrifugation at 10,000 rpm for 10 minutes, washed 3 to 5 times with deionized water to remove residual salts, and then vacuum dried at 60°C for 8 hours to obtain CSH seed crystal powder with a particle size of 10 to 50 nm.

[0021] It should be noted that the nano-CSH seeds generated by this method can serve as hydration inducers, providing uniform nuclei in solid waste-based materials, accelerating the ordered growth of CSH and ettringite (AFt), reducing disordered stacking and delaying ettringite formation, optimizing the microstructure, and thus improving the early strength and durability of the material.

[0022] As a preferred technical solution for a solid waste-based low-carbon gel material, the preparation method of the modified cellulose nanocrystals is as follows: a CNC suspension with a solid content of 5%-10% is mixed with APTES accounting for 5%-10% of the CNC mass in a water-ethanol mixed solution with a volume ratio of 1:1. The pH is adjusted to 4-5, and the mixture is stirred at 50-60℃ for 2-4 hours to allow the alkoxy groups of silane to chemically bond with the hydroxyl groups on the CNC surface, forming a hydrophobic protective layer. After the reaction is completed, the product is separated by centrifugation at 8000-10000 rpm for 10 minutes, washed alternately with deionized water and ethanol 3-5 times, and then vacuum dried at 60℃ for 12 hours to obtain modified CNC powder.

[0023] It should be noted that a CNC suspension with a solid content of 5%-10% is mixed with APTES (5%-10% by mass of CNC) in a 1:1 water-ethanol mixture. The pH is adjusted to 4-5 to promote the hydrolysis of alkoxy groups of APTES to generate silanol (Si-OH). The mixture is stirred at 50-60℃ for 2-4 hours. The silanol reacts with the abundant hydroxyl groups (-OH) on the CNC surface through dehydration condensation to form Si-OC covalent bonds, generating a hydrophobic protective layer. This reduces the hydrophilicity of CNC and enhances its interfacial compatibility with the gel matrix. After the reaction, the product is separated by centrifugation at 8000-10000 rpm for 10 minutes. The product is then washed 3-5 times alternately with deionized water and ethanol to remove unreacted APTES and byproducts, ensuring the purity of the modified CNC. Subsequently, the product is vacuum dried at 60℃ for 12 hours to avoid damaging the surface modification structure due to high temperature. This method uses chemical bonding and hydrophobic modification to induce a multi-level porous structure in gel materials through CNC, which buffers the expansion stress caused by sulfate and significantly enhances the durability and mechanical properties of the materials.

[0024] A preferred technical solution for preparing a solid waste-based low-carbon gel material is described in the following method for preparing a pH-sensitive composite activator: sodium carbonate is coated with polylactic acid by spray drying, with the shell thickness controlled at 1 to 2 micrometers to obtain coated sodium carbonate. The concentration of the polylactic acid solution is 5% to 10%, the inlet air temperature for spray drying is 120 to 140°C, and the nozzle flow rate is 10 to 15 ml per minute. Subsequently, the coated sodium carbonate, sodium silicate, and triethanolamine are mixed in a high-speed mixer at a mass ratio of 5 to 7: 2 to 3: 1 to 2, with a rotation speed of 500 to 800 rpm and a mixing time of 10 to 15 minutes to obtain the pH-sensitive composite activator.

[0025] It should be noted that coating polylactic acid with sodium carbonate using a spray drying method to form a 1-2 μm thick polylactic acid shell slows down the dissolution rate of sodium carbonate, achieving dynamic release of OH- ions, which then react with SO4 in the bottom ash. 2- This synergistic process activates highly reactive slag, preventing the formation of secondary gypsum caused by high pH and reducing the risk of expansion and cracking. Coated sodium carbonate, sodium silicate, and triethanolamine are mixed uniformly by high-speed stirring at 500-800 rpm for 10-15 minutes. Sodium silicate provides SiO3. 2- With Ca in slag 2+ The reaction produces CSH gel, which enhances the material's strength; triethanolamine acts as a coagulator, accelerating the reaction of Ca... 2+ With SO4 2- The reaction generates ettringite (AFt), which, in synergy with nano-CSH seeds, lowers the nucleation energy barrier of AFt, promotes its uniform distribution in the pores, and optimizes early strength and pore structure.

[0026] As a method for preparing a solid waste-based low-carbon gel material, in step S1, the acid washing process uses a 0.1 mol / L HCl solution, the treatment time is 30 min, and the pH is controlled at 4-5; the microwave heat treatment power is 500-600W, the temperature is 500-600℃, and the treatment time is 10 min.

[0027] It should be noted that the washing process uses a 0.1 mol / L HCl solution, treated for 30 minutes, with the pH controlled at 4-5 to remove chloride salts and heavy metal impurities from the bottom ash of the tower. Microwave heat treatment with a power of 500-600W and a temperature of 500-600℃ for 10 minutes converts the low-soluble sulfates into a highly soluble form, optimizing SO42-. 2- Release rate.

[0028] As a method for preparing a solid waste-based low-carbon gel material, in step S4, the dry mixing process uses a high-speed mixer with a speed of 300-500 rpm and a mixing time of 5 min; the wet mixing process uses a speed of 100-200 rpm and a mixing time of 10 min.

[0029] It should be noted that in step S4, the dry mixing process uses a high-speed mixer with a speed of 300-500 rpm and a mixing time of 5 minutes to ensure that the highly active slag, bottom ash of the classification tower, nano-CSH seed crystals, modified cellulose nanocrystals (CNC), and pH-sensitive composite activator are uniformly dispersed in the solid state, avoiding component agglomeration and promoting the uniformity of subsequent hydration reactions. In the wet mixing process, the speed is reduced to 100-200 rpm and the mixing time is extended to 10 minutes to fully integrate water (15%-25%) with the solid components with moderate shear force, controlling the water-to-solid ratio to 0.15-0.28 to form a slurry with moderate fluidity, while preventing excessive shear from damaging the nano-network structure of CNC or the dispersion state of the seed crystals.

[0030] The solid waste-based low-carbon gel material and its preparation method provided by this invention have significant beneficial effects. Through optimized component ratios (40%-60% highly active slag, 20%-35% graded tower bottom ash, 3%-8% pH-sensitive composite activator, 0.5%-2% nano-CSH seeds, and 0.1%-1% modified cellulose nanocrystals) and innovative processes (graded tower bottom ash pretreatment, pH-sensitive activator slow-release alkalinity, nano-CSH seed-induced hydration, and modified CNC constructing multi-level pores), the material exhibits excellent compressive strength (58.0-62.5 MPa), impermeability (permeability height 9-11 mm), and low expansion rate (0.07%-0.09%). This material effectively utilizes industrial solid waste, reduces carbon emissions and energy consumption, solves the problems of uneven hydration and expansion cracking caused by fluctuations in sulfate content, significantly improves mechanical properties and durability, and is suitable for green building and resource recycling fields, providing reliable technical support for the large-scale industrial application of solid waste-based gel materials. Attached Figure Description

[0031] Figure 1 The particle size curve of the nano-CSH seeds prepared in step S2 of Example 1;

[0032] Figure 2 Pore ​​distribution curves for specimens prepared using the slurry prepared in Example 1;

[0033] Figure 3 Distribution curves of hierarchical pore structure induced by modified cellulose nanocrystals (CNC). Detailed Implementation

[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0035] 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, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0036] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single embodiment or an embodiment selectively excluded from other embodiments.

[0037] Preparation Example

[0038] Preparation Example 1

[0039] The method for preparing the modified cellulose nanocrystals is as follows: A CNC suspension with a solid content of 5%-10% is mixed with APTES accounting for 5%-10% of the CNC mass in a water-ethanol mixture with a volume ratio of 1:1. The pH is adjusted to 4-5, and the mixture is stirred at 50-60°C for 2-4 hours to allow the alkoxy groups of silane to chemically bond with the hydroxyl groups on the CNC surface, forming a hydrophobic protective layer. After the reaction is complete, the product is separated by centrifugation at 8000-10000 rpm for 10 minutes. The product is washed 3-5 times alternately with deionized water and ethanol, and then vacuum dried at 60°C for 12 hours to obtain modified CNC powder.

[0040] Example

[0041] Example 1

[0042] Example 1 provides a solid waste-based low-carbon gel material and its preparation method, wherein the solid waste-based low-carbon gel material comprises the following components by mass percentage:

[0043] Highly active blast furnace slag (highly active blast furnace slag is granulated blast furnace slag with a specific surface area ≥ 400 m²) 2 / kg): 40%, graded bottom ash: 30%, pH-sensitive composite activator: 3%, nano CSH seed crystals: 0.5%, modified cellulose nanocrystals: 0.5%, water: 20%; wherein, the water-to-solid ratio is controlled at 0.27.

[0044] A method for preparing solid waste-based low-carbon gel materials includes the following steps:

[0045] Step S1. Pre-treatment of bottom ash: The bottom ash is separated into high-activity particles and low-activity particles using an air classifier. The high-activity particles have a particle size of less than 0.18 mm, and the low-activity particles have a particle size of more than 0.18 mm. The high-activity particles are acid-washed, and the low-activity particles are microwave-heat-treated to convert them into sulfate form. The acid washing process uses a 0.1 mol / L HCl solution, the treatment time is 30 min, and the pH is controlled at 4. The microwave-heat-treatment power is 600 W, the temperature is 500 °C, and the treatment time is 10 min.

[0046] Step S2. Preparation and dispersion of nano-CSH seeds: 0.1 mol / L calcium nitrate solution and 0.1 mol / L sodium silicate solution were mixed at a molar ratio of 1:1 and stirred at 50°C for 2 to 3 hours under pH 11 conditions to allow calcium ions to react with silicate ions to generate CSH nano-seeds. After the reaction was completed, the precipitate was separated by centrifugation at 10,000 rpm for 10 minutes. The precipitate was washed with deionized water 3 to 5 times to remove residual salts. Then, it was vacuum dried at 60°C for 8 hours to obtain CSH seed powder with a particle size of 10 to 50 nm. The powder was then uniformly dispersed in water by ultrasonic dispersion to prepare a seed suspension.

[0047] Step S3. Preparation of pH-sensitive composite activator: Sodium carbonate is coated with polylactic acid by spray drying, and the shell thickness is controlled to be 1 to 2 micrometers to obtain coated sodium carbonate. The concentration of polylactic acid solution is 5% to 10%, the spray drying inlet air temperature is 120 to 140°C, and the nozzle flow rate is 10 to 15 ml per minute. Subsequently, coated sodium carbonate, sodium silicate and triethanolamine are mixed in a high-speed mixer at a mass ratio of 5:3:1, the speed is 500 to 800 rpm, and the mixing time is 10 to 15 minutes to obtain pH-sensitive composite activator.

[0048] Step S4. Mixing and slurry preparation: Highly active slag, bottom ash from the classifier tower, nano-CSH seed crystals, modified cellulose nanocrystals (Preparation Example 1), and pH-sensitive composite activator are added to a mixer according to the mass ratio. Dry mixing is performed, followed by the addition of water and wet mixing, with the water-to-solid ratio controlled at 0.27 to form a uniform solid waste-based low-carbon gel material slurry. The dry mixing process uses a high-speed mixer at 500 rpm for 5 min, and the wet mixing process uses a mixer at 200 rpm for 10 min.

[0049] Example 2

[0050] Example 2 provides a solid waste-based low-carbon gel material and its preparation method, wherein the solid waste-based low-carbon gel material comprises the following components by mass percentage:

[0051] Highly active blast furnace slag (highly active blast furnace slag is granulated blast furnace slag with a specific surface area ≥ 400 m²) 2 / kg): 60%, graded bottom ash: 20%, pH-sensitive composite activator: 5%, nano CSH seed crystals: 2.0%, modified cellulose nanocrystals: 0.1%, water: 25%; wherein, the water-to-solid ratio is controlled at 0.28.

[0052] A method for preparing solid waste-based low-carbon gel materials includes the following steps:

[0053] Step S1. Pre-treatment of bottom ash: The bottom ash is separated into high-activity particles and low-activity particles using an air classifier. The high-activity particles have a particle size of less than 0.18 mm, and the low-activity particles have a particle size of more than 0.18 mm. The high-activity particles are acid-washed, and the low-activity particles are microwave-heat-treated to convert them into sulfate form. The acid washing process uses a 0.1 mol / L HCl solution, the treatment time is 30 min, and the pH is controlled at 5. The microwave-heat-treatment power is 500 W, the temperature is 600℃, and the treatment time is 10 min.

[0054] Step S2. Preparation and dispersion of nano-CSH seeds: 0.1 mol / L calcium nitrate solution and 0.1 mol / L sodium silicate solution were mixed at a molar ratio of 1:1 and stirred at 40°C for 2 to 3 hours under pH 12 conditions to allow calcium ions to react with silicate ions to generate CSH nano-seeds. After the reaction was completed, the precipitate was separated by centrifugation at 10,000 rpm for 10 minutes. The precipitate was washed with deionized water 3 to 5 times to remove residual salts. Then, it was vacuum dried at 60°C for 8 hours to obtain CSH seed powder with a particle size of 10 to 50 nm. The powder was then uniformly dispersed in water by ultrasonic dispersion to prepare a seed suspension.

[0055] Step S3. Preparation of pH-sensitive composite activator: Sodium carbonate is coated with polylactic acid by spray drying, and the shell thickness is controlled to be 1 to 2 micrometers to obtain coated sodium carbonate. The concentration of polylactic acid solution is 5% to 10%, the spray drying inlet air temperature is 120 to 140°C, and the nozzle flow rate is 10 to 15 ml per minute. Subsequently, coated sodium carbonate, sodium silicate and triethanolamine are mixed in a mass ratio of 7:2:1 in a high-speed mixer at a speed of 500 to 800 rpm for 10 to 15 minutes to obtain pH-sensitive composite activator.

[0056] Step S4. Mixing and slurry preparation: Highly active slag, bottom ash from the classifying tower, nano-CSH seed crystals, modified cellulose nanocrystals (Preparation Example 1), and pH-sensitive composite activator are added to a mixer according to the mass ratio. Dry mixing is performed, followed by the addition of water and wet mixing, controlling the water-to-solid ratio at 0.28 to form a uniform solid waste-based low-carbon gel material slurry. The dry mixing process uses a high-speed mixer at 300 rpm for 5 min, and the wet mixing process uses a mixer at 100 rpm for 10 min.

[0057] Example 3

[0058] Example 3 provides a solid waste-based low-carbon gel material and its preparation method, wherein the solid waste-based low-carbon gel material comprises the following components by mass percentage:

[0059] Highly active blast furnace slag (highly active blast furnace slag is granulated blast furnace slag with a specific surface area ≥ 400 m²) 2 / kg): 50%, graded bottom ash: 35%, pH-sensitive composite activator: 8%, nano CSH seed crystals: 1.0%, modified cellulose nanocrystals: 1.0%, water: 15%; wherein, the water-to-solid ratio is controlled at 0.15.

[0060] A method for preparing solid waste-based low-carbon gel materials includes the following steps:

[0061] Step S1. Pre-treatment of bottom ash: The bottom ash is separated into high-activity particles and low-activity particles using an air classifier. The high-activity particles have a particle size of less than 0.18 mm, and the low-activity particles have a particle size of more than 0.18 mm. The high-activity particles are acid-washed, and the low-activity particles are microwave-heat-treated to convert them into sulfate form. The acid washing process uses a 0.1 mol / L HCl solution, the treatment time is 30 min, and the pH is controlled at 4. The microwave-heat-treatment power is 550 W, the temperature is 600℃, and the treatment time is 10 min.

[0062] Step S2. Preparation and dispersion of nano-CSH seeds: 0.1 mol / L calcium nitrate solution and 0.1 mol / L sodium silicate solution were mixed at a molar ratio of 1:1 and stirred at 50°C for 2 to 3 hours under pH 12 conditions to allow calcium ions to react with silicate ions to generate CSH nano-seeds. After the reaction was completed, the precipitate was separated by centrifugation at 10,000 rpm for 10 minutes. The precipitate was washed with deionized water 3 to 5 times to remove residual salts. Then, it was vacuum dried at 60°C for 8 hours to obtain CSH seed powder with a particle size of 10 to 50 nm. The powder was then uniformly dispersed in water by ultrasonic dispersion to prepare a seed suspension.

[0063] Step S3. Preparation of pH-sensitive composite activator: Sodium carbonate is coated with polylactic acid by spray drying, and the shell thickness is controlled to be 1 to 2 micrometers to obtain coated sodium carbonate. The concentration of polylactic acid solution is 5% to 10%, the inlet air temperature of spray drying is 120 to 140°C, and the nozzle flow rate is 10 to 15 ml per minute. Subsequently, coated sodium carbonate, sodium silicate and triethanolamine are mixed in a high-speed mixer at a mass ratio of 6:2:2, the speed is 500 to 800 rpm, and the mixing time is 10 to 15 minutes to obtain pH-sensitive composite activator.

[0064] Step S4. Mixing and slurry preparation: Add the highly active slag, bottom ash from the classifying tower, nano-CSH seed crystals, modified cellulose nanocrystals (Preparation Example 1), and pH-sensitive composite activator to a mixer according to the mass ratio, dry mix, add water, wet mix, and control the water-to-solid ratio at 0.15 to form a uniform solid waste-based low-carbon gel material slurry; wherein, the dry mixing process uses a high-speed mixer with a speed of 400 rpm and a mixing time of 5 min; the wet mixing process uses a speed of 150 rpm and a mixing time of 10 min.

[0065] Example 4

[0066] Example 4 provides a solid waste-based low-carbon gel material and its preparation method, wherein the solid waste-based low-carbon gel material comprises the following components by mass percentage:

[0067] Highly active blast furnace slag (highly active blast furnace slag is granulated blast furnace slag with a specific surface area ≥ 400 m²) 2 / kg): 55%, graded bottom ash: 30%, pH-sensitive composite activator: 5%, nano CSH seed crystals: 1.0%, modified cellulose nanocrystals: 0.7%, water: 20%; wherein, the water-to-solid ratio is controlled at 0.22.

[0068] A method for preparing solid waste-based low-carbon gel materials includes the following steps:

[0069] Step S1. Pre-treatment of bottom ash: The bottom ash is separated into high-activity particles and low-activity particles using an air classifier. The high-activity particles have a particle size of less than 0.18 mm, and the low-activity particles have a particle size of more than 0.18 mm. The high-activity particles are acid-washed, and the low-activity particles are microwave-heat-treated to convert them into sulfate form. The acid washing process uses a 0.1 mol / L HCl solution, the treatment time is 30 min, and the pH is controlled at 5. The microwave-heat-treatment power is 550 W, the temperature is 600℃, and the treatment time is 10 min.

[0070] Step S2. Preparation and dispersion of nano-CSH seeds: 0.1 mol / L calcium nitrate solution and 0.1 mol / L sodium silicate solution were mixed at a molar ratio of 1:1 and stirred at 50°C for 2 to 3 hours under pH 11 conditions to allow calcium ions to react with silicate ions to generate CSH nano-seeds. After the reaction was completed, the precipitate was separated by centrifugation at 10,000 rpm for 10 minutes. The precipitate was washed with deionized water 3 to 5 times to remove residual salts. Then, it was vacuum dried at 60°C for 8 hours to obtain CSH seed powder with a particle size of 10 to 50 nm. The powder was then uniformly dispersed in water by ultrasonic dispersion to prepare a seed suspension.

[0071] Step S3. Preparation of pH-sensitive composite activator: Sodium carbonate is coated with polylactic acid by spray drying, and the shell thickness is controlled to be 1 to 2 micrometers to obtain coated sodium carbonate. The concentration of polylactic acid solution is 5% to 10%, the spray drying inlet air temperature is 120 to 140°C, and the nozzle flow rate is 10 to 15 ml per minute. Subsequently, coated sodium carbonate, sodium silicate and triethanolamine are mixed in a high-speed mixer at a mass ratio of 6:3:2, the speed is 500 to 800 rpm, and the mixing time is 10 to 15 minutes to obtain pH-sensitive composite activator.

[0072] Step S4. Mixing and slurry preparation: High-activity slag, bottom ash from the classifier tower, nano-CSH seed crystals, modified cellulose nanocrystals (Preparation Example 1), and pH-sensitive composite activator are added to a mixer according to the mass ratio. Dry mixing is performed, followed by the addition of water and wet mixing, with the water-to-solid ratio controlled at 0.22 to form a uniform solid waste-based low-carbon gel material slurry. The dry mixing process uses a high-speed mixer at 400 rpm for 5 min, and the wet mixing process uses a mixer at 200 rpm for 10 min.

[0073] Comparison Example

[0074] Compare with Example 1

[0075] The difference between this comparative example and Example 1 is that the bottom ash of the tower was not graded and was replaced with 30% ungraded bottom ash. The other components and processes are the same as in Example 1.

[0076] Compare with Example 2

[0077] The difference between this comparative example and Example 1 is that the pH-sensitive composite activator is replaced with 3% ordinary Na2CO3, while the other components and processes are the same as in Example 1.

[0078] Compare with Example 3

[0079] The difference between this comparative example and Example 1 is that the modified CNC is replaced with 0.5% unmodified CNC, while the other components and processes are the same as in Example 1.

[0080] Performance Indicators and Testing Methods

[0081] Compressive strength test method: The compressive strength test was conducted according to GB / T 18046-2017 "Granulated Blast Furnace Slag Powder for Cement and Concrete". Solid waste-based low-carbon gel material and standard sand were mixed at a mass ratio of 1:3 to prepare mortar, controlling the water-to-solid ratio at 0.4. After thorough mixing, the mortar was poured into a 40mm×40mm×160mm mold, compacted, and cured for 28 days under standard curing conditions (20±2℃, relative humidity >95%). A universal testing machine (loading rate 0.5MPa / s) was used to test the compressive strength of the specimens. Six specimens were tested in each group, and the average value was recorded (unit: MPa).

[0082] Permeability testing method: The permeability test adopts the water penetration height method in GB / T 50082-2009 "Test Methods for Long-Term Performance and Durability of Ordinary Concrete". The gel material is prepared into cylindrical specimens with a diameter of 100 mm and a height of 50 mm, with a water-to-solid ratio of 0.4, and cured under standard conditions for 28 days (20±2℃, relative humidity >95%). The specimens are placed in a permeability tester, and a constant water pressure (1.2 MPa) is applied for 24 hours. After the test, the specimens are split axially, and the water penetration height (unit: mm) is measured. The average value of 6 specimens in each group is taken.

[0083] Expansion rate test method: The expansion rate test was conducted according to JC / T 313-2009 "Test Method for Performance of Expansion Agent". Prepare mortar (gel material to standard sand 1:3, water-to-solid ratio 0.4), pour it into a 25mm×25mm×280mm mold, embed a length measuring probe, and cure under standard conditions for 28 days (20±2℃, relative humidity >95%). Record the daily changes in specimen length using a high-precision length measuring instrument (accuracy 0.001mm). Calculate the 28-day expansion rate (%) as: (L28-L0) / L0×100%, where L0 is the initial length and L28 is the length after 28 days. Take the average value of 6 specimens in each group.

[0084] Table 1

[0085]

[0086]

[0087] In conjunction with Example 1 and Figure 1 , 2 As can be seen, the particle size distribution curve of the nano-CSH seeds shows the change in volume fraction of CSH seeds (particle size 10-50 nm) prepared by chemical precipitation as a function of particle size, with a peak at approximately 30 nm. The vertical axis represents volume fraction (%), and the horizontal axis represents particle size (nm, 0-100 nm). The curve shows that approximately 80%-90% of the particles are concentrated in the 10-50 nm range. Figure 2 The uniform particles (10-50 nm in diameter) of the nano-CSH seed crystals can be seen, reflecting the uniformity of the preparation process (mixing 0.1 mol / L calcium nitrate and sodium silicate in a 1:1 ratio, pH 11-12, reaction at 40-50℃).

[0088] In conjunction with Example 1 and Figure 3It can be seen that the modified cellulose nanocrystals (CNC) induce a hierarchical porous structure with nanoscale pores accounting for 25%, mesopores accounting for 60%, and microscale pores accounting for <15%. The hydrophobic protective layer formed by APTES chemical bonding enhances the interfacial bonding between CNC and the CSH matrix, optimizes the pore distribution, and significantly reduces the proportion of interconnected pores. This structure effectively buffers the expansion stress induced by sulfate, reduces the formation of microcracks, and promotes the uniform growth of CSH and ettringite (AFt), thereby improving the strength, impermeability, and durability of the material.

[0089] As can be seen from Examples 1 to 4 and Table 1, the performance data of the solid waste-based low-carbon gel material shows that the compressive strength ranges from 58.0 to 62.5 MPa, the impermeability (water penetration height) is 9 to 11 mm, and the expansion rate is 0.07% to 0.09%. This application effectively solves the problems of expansion and cracking caused by fluctuations in sulfate content in the bottom ash of the tower, unstable release rate, and excessive sulfate in the solid waste-based low-carbon gel material through the designed component formulation and innovative preparation process.

[0090] Based on Example 1, Comparative Example 1, and Table 1, it can be seen that Example 1 has a compressive strength of 60.0 MPa, a permeability resistance (water seepage height) of 10 mm, and an expansion rate of 0.08%, which are significantly better than the compressive strength of 52.0 MPa, water seepage height of 14 mm, and expansion rate of 0.18% in Comparative Example 1. Example 1 exhibits 15.4% higher compressive strength, 28.6% lower water seepage height, and 55.6% lower expansion rate. The main difference between Example 1 and Comparative Example 1 lies in whether the bottom ash undergoes graded pretreatment. In Example 1, the bottom ash is separated into high-activity and low-activity particles through airflow classification. Combined with acid washing to remove chloride salts and heavy metal impurities, and microwave heat treatment to convert anhydrous gypsum into highly soluble dihydrate gypsum, optimizing SO4 levels... 2- The release rate, in synergy with the dynamic alkalinity of the pH-sensitive composite activator, matches the hydration process of highly active slag, promoting the uniform formation of CSH and AFt and reducing delayed ettringite formation; in control example 1, ungraded bottom ash caused SO4 2- Uncontrolled release, excessive AFt generation in the early stages consumes Ca. 2+ Later, delayed ettringite induces expansion stress, which damages the CSH network, resulting in high pore connectivity, a decrease in compressive strength to 52.0 MPa, an increase in water penetration height to 14 mm, and an increase in expansion rate to 0.18%, making its performance significantly inferior to that of Example 1.

[0091] Based on Example 1, Comparative Example 2, and Table 1, it can be seen that Example 1 exhibits a compressive strength of 60.0 MPa, impermeability (water seepage height) of 10 mm, and an expansion rate of 0.08%, significantly superior to Comparative Example 2. Example 1 shows a 20.0% higher compressive strength, a 37.5% lower water seepage height, and a 60.0% lower expansion rate. The pH-sensitive composite activator in Example 1 achieves slow-release OH-, initially activating highly active slag and bottom ash of the grading tower with mild alkalinity, and later releasing strong alkali to promote CSH and AFt formation, while sodium silicate replenishes SiO3. 2- Enhanced gel structure. Comparative Example 2 used ordinary Na2CO3, which rapidly released OH-. - This leads to an excessively high initial pH, which accelerates the reaction between sulfate and Ca(OH)2 to form expansive gypsum (CaSO4·2H2O), disrupts the CSH network, increases pore connectivity, reduces strength and impermeability, and increases the expansion rate.

[0092] Combining Example 1, Comparative Example 3, and Table 1, the solid waste-based low-carbon gel material of Example 1 exhibits a compressive strength of 60.0 MPa, a permeability (water penetration height) of 10 mm, and an expansion rate of 0.08%, significantly superior to the compressive strength of 53.0 MPa, water penetration height of 14 mm, and expansion rate of 0.16% of Comparative Example 3. Example 1 shows a 13.2% higher compressive strength, a 28.6% lower water penetration height, and a 50.0% lower expansion rate. Example 1 utilizes modified cellulose nanocrystals (CNC), forming a hydrophobic protective layer through APTES chemical bonding. This enhances the interfacial compatibility between the CNC and the gel matrix, induces a multi-level porous structure, effectively buffers sulfate-induced expansion stress, reduces microcrack formation, and improves permeability and durability. In contrast, Comparative Example 3 uses unmodified CNC, which is highly hydrophilic and has weak interfacial bonding with the matrix, making it difficult to effectively disperse expansion stress. This leads to increased pore connectivity, damage to the CSH network structure, decreased compressive strength and permeability, and a significantly increased expansion rate.

[0093] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a solid waste-based low-carbon gel material, characterized in that, Includes the following steps: Step S1. Pre-treatment of bottom ash: The bottom ash is separated into high-activity particles and low-activity particles by an air classifier. The high-activity particles are acid-washed and the low-activity particles are microwave-heat-treated to convert them into sulfate form. The particle size of the high-activity particles is less than 0.18 mm and the particle size of the low-activity particles is greater than 0.18 mm. Step S2. Preparation and dispersion of nano CSH seeds: Nano CSH seeds are prepared by chemical precipitation and uniformly dispersed in water by ultrasonic dispersion to prepare a seed suspension; Step S3. Preparation of pH-sensitive composite activator: Sodium carbonate is coated with polylactic acid by spray drying to obtain coated sodium carbonate. The coated sodium carbonate is mixed with sodium silicate and triethanolamine in a mass ratio of (5-7):(2-3):(1-2) to prepare pH-sensitive composite activator. Step S4. Mixing and slurry preparation: Add the highly active slag, graded bottom ash, nano-CSH seed suspension, modified cellulose nanocrystals and pH-sensitive composite activator to the mixer according to the mass ratio, dry mix, add water, wet mix, and control the water-to-solid ratio to 0.15-0.28 to form a uniform solid waste-based low-carbon gel material slurry; The gel material prepared by the aforementioned method comprises the following components by mass percentage: Highly active slag: 40%-60%; Graded bottom ash from the tower: 20%-35%; pH-sensitive compound activator: 3%-8%; Nano CSH seed crystals: 0.5%-2%; Modified cellulose nanocrystals: 0.1%-1%; Water: 15%-25%; The highly active slag is granulated blast furnace slag with a specific surface area ≥400 m². 2 / kg; The preparation method of the modified cellulose nanocrystals is as follows: a CNC suspension with a solid content of 5%-10% is mixed with APTES accounting for 5%-10% of the mass of CNC in a water-ethanol mixture with a volume ratio of 1:

1. The pH is adjusted to 4-5, and the mixture is stirred at 50-60℃ for 2-4 hours to allow the alkoxy groups of silane to chemically bond with the hydroxyl groups on the surface of CNC to form a hydrophobic protective layer. After the reaction is completed, the product is separated by centrifugation at 8000-10000 rpm for 10 minutes. The product is washed 3-5 times alternately with deionized water and ethanol, and then vacuum dried at 60℃ for 12 hours to obtain modified cellulose nanocrystal powder.

2. The preparation method according to claim 1, characterized in that, The preparation method of the nano-CSH seed crystals is as follows: 0.1 mol / L calcium nitrate solution and 0.1 mol / L sodium silicate solution are mixed at a molar ratio of 1:1 and stirred at 40 to 50°C for 2 to 3 hours under pH 11 to 12 conditions to allow calcium ions to react with silicate ions to generate CSH nano-seed crystals. After the reaction is completed, the precipitate is separated by centrifugation at 10,000 rpm for 10 minutes, washed 3 to 5 times with deionized water to remove residual salts, and then vacuum dried at 60°C for 8 hours to obtain CSH seed crystal powder with a particle size of 10 to 50 nm.

3. The preparation method according to claim 1, characterized in that, The method for preparing the pH-sensitive composite activator is as follows: Sodium carbonate is coated with polylactic acid by spray drying, and the shell thickness is controlled to be 1 to 2 micrometers to obtain coated sodium carbonate. The concentration of polylactic acid solution is 5% to 10%, the inlet air temperature of spray drying is 120 to 140°C, and the nozzle flow rate is 10 to 15 ml per minute. Subsequently, coated sodium carbonate, sodium silicate, and triethanolamine are mixed in a high-speed mixer at a mass ratio of 5 to 7: 2 to 3: 1 to 2, the speed is 500 to 800 rpm, and the mixing time is 10 to 15 minutes to obtain the pH-sensitive composite activator.

4. The preparation method according to claim 1, characterized in that, In step S1, the pickling process uses a 0.1 mol / L HCl solution, the treatment time is 30 min, and the pH is controlled at 4-5; the microwave heat treatment power is 500-600 W, the temperature is 500-600℃, and the treatment time is 10 min.

5. The preparation method according to claim 1, characterized in that, In step S4, the dry mixing process uses a high-speed mixer with a speed of 300-500 rpm and a mixing time of 5 min; the wet mixing process uses a speed of 100-200 rpm and a mixing time of 10 min.

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