Preparation method of micro-nano solid waste-based soil stabilizer

Abstract

This invention relates to the fields of inorganic cementitious materials, solid waste resource utilization, and soil solidification materials, specifically to a method for preparing micro-nano-scale solid waste-based soil solidification agents. It aims to solve the technical problems of limited functionality and insufficient durability in existing technologies. This invention involves co-grinding granulated blast furnace slag with hydrated calcium silicate seeds to obtain modified slag micropowder; co-grinding steel slag and fly ash into ultrafine powder to obtain steel slag-fly ash composite micropowder; preparing a mesoporous nano-slag-biochar composite core, which, after impregnation with sodium metasilicate and nano-zero-valent iron, sequentially deposits a calcium alginate-chitosan intermediate shell layer and a silane coupling agent-modified nano-silica and nano-waste concrete recycled micropowder composite outer shell layer to obtain multi-layered coated active particles; ball milling sodium silicate, sodium sulfate, and nano-calcium hydroxide into a composite activator; and compounding the above components with a dispersant and stabilizer under inert gas protection.

Description

Technical Field

[0001] This invention relates to the fields of inorganic cementitious materials, solid waste resource utilization and soil solidification materials, specifically to a method for preparing micro-nano-scale solid waste-based soil solidification agents. Background Technology

[0002] Soil stabilizers are widely used in roadbeds, site slabs, soft soil foundations, silty soil treatment, trench backfilling, and low-strength fluidized soil stabilization. Traditional stabilization materials mainly consist of cement, lime, gypsum, and common mineral admixtures, which can improve soil strength through hydration products, ion exchange, flocculation and agglomeration, and pore filling. However, in environments with high water content, fine particles, high salinity, or repeated wet-drying, ordinary stabilized soils often exhibit problems such as loose interfacial transition zones, weak bonding between soil particles and cementitious products, uneven early reactions, development of drying shrinkage microcracks, and insufficient durability.

[0003] Existing patent CN101100854A discloses an environmentally friendly soil stabilizer, which is a compound of fly ash, granulated blast furnace slag, sodium silicate, sulfate, lime or gypsum, surfactant, etc., for use in roadbed reinforcement, pavement hardening, and soft soil foundation treatment. This scheme is a multi-component powder compound, and does not include structural design for solid waste powder interface activation, micro-nano-level nucleation sites, and slow-release interface layer. Existing patent CN112142406B discloses a soil stabilizer for high-fluidity solidified soil, whose components include cement, mineral powder, fly ash, steel slag, hydrophobic nano-silica, inorganic polyphosphate, polyquaternary ammonium salt, etc. The preparation method is mainly a proportional mixing, and the technical focus is on improving the fluidity and construction performance of the fluidized solidified soil. This scheme still has the problems of direct release of active components, easy agglomeration of nano-components, and insufficient gradient at the soil-cementation product interface.

[0004] To address the above problems, this invention provides a method for preparing micro-nano-scale solid waste-based soil stabilizers. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing micro-nano-scale solid waste-based soil stabilizers, thereby solving the technical problems of weak interfacial bonding and insufficient durability in the prior art.

[0006] A method for preparing a micro / nano-scale solid waste-based soil stabilizer, the technical solution of which is as follows: S1: The granulated blast furnace slag is dried at 105℃ for 2 hours, cooled and then mixed with hydrated calcium silicate seed crystals at a mass ratio of 100:2 to 100:6 and ground together to obtain modified slag powder. S2: After removing iron by magnetic separation, the converter steel slag is crushed to a particle size ≤5mm, dried, and then mixed with fly ash at a mass ratio of 1:1.5. The mixture is then ground at a speed of 550r / min for 90min to obtain composite micro powder. S3: Nano-slag and mesoporous biochar were added to deionized water, bubbled with nitrogen for 10 min, ultrasonically dispersed for 20 min, and spray-dried to obtain a mesoporous nano-slag-biochar composite core; sodium metasilicate was dissolved in deoxygenated water, mixed with the composite core, and added to a vacuum impregnation tank, and impregnated at -0.06 to -0.095 MPa for 60 to 90 min; then, under nitrogen protection, a molten dispersion containing 10% by mass of nano-zero ferric iron was added, and stirring was continued for 30 min, followed by vacuum drying to obtain a loaded core; an intermediate shell was deposited on the loaded core to obtain particles with an intermediate shell; then an outer shell was deposited to obtain multi-layered coated active particles; S4: Sodium silicate, sodium sulfate and nano calcium hydroxide are mixed in a mass ratio of 2:1:1 and added to a ball mill for grinding to obtain a composite activator; S5: In a mixing chamber under nitrogen protection and with an oxygen volume fraction of less than 0.5%, add modified slag micro powder, steel slag-fly ash composite micro powder, multi-layer coated active particles, composite activator, and dispersant stabilizer, and stir for 15 minutes to obtain a curing agent.

[0007] Further, the curing agent comprises, by weight: 35-45 parts modified slag micro powder, 30-40 parts steel slag-fly ash composite micro powder, 5-15 parts multi-layer coated active particles, 10-18 parts composite activator, and 1-3 parts dispersant stabilizer.

[0008] Further, the co-grinding described in step S1 specifically involves adding the material to a ball mill at a ball-to-material ratio of 8:1 to 12:1, a rotation speed of 450 to 500 r / min, and grinding for 60 to 90 minutes. The specific surface area is measured to be 700 m² using the Blaine method. 2 / kg.

[0009] Furthermore, the drying described in step S2 specifically involves drying to constant weight in an oven at 105°C.

[0010] Furthermore, the composite micro powder described in step S2 has a D50 ≤ 5 μm and a D90 ≤ 10 μm.

[0011] Furthermore, the vacuum drying described in step S3 specifically involves vacuum drying at 50℃~60℃ for 5~6 hours.

[0012] Further, the deposition of the intermediate shell in step S3 specifically involves adding the loaded core to a 0.5–1.5 wt% sodium alginate solution and stirring, with a solid-liquid ratio of 1 g: 15 mL; then adding a 0.05–0.25 mol / L calcium chloride solution until the solid is submerged, and crosslinking for 20–30 min; then adding an equal volume of 1 wt% chitosan-acetic acid solution to the sodium alginate solution, adjusting the pH to 5.5, stirring for 30 min, filtering, washing, and freeze-drying.

[0013] Further, the deposition of the outer shell layer in step S3 specifically involves adding KH-560 to an ethanol / water mixture with a volume ratio of ethanol to water of 4:1, adjusting the pH to 5.0 with dilute acetic acid, and hydrolyzing for 40 minutes; then adding nano-silica and nano-recycled waste concrete powder, stirring and dispersing; then adding particles with an intermediate shell layer, adjusting the pH to 5.0, stirring at 400 rpm for 60 minutes, filtering, pre-freezing at -45°C, and then freeze-drying under vacuum for 36 hours.

[0014] Further, the grinding described in step S4 specifically involves a ball-to-material ratio of 15:1, a rotation speed of 350–450 r / min, and grinding for 3–4 hours.

[0015] Further, the dispersion stabilizer described in step S5 is obtained by mixing polycarboxylate copolymer, sodium hexametaphosphate and hydroxypropyl methylcellulose in a ratio of 4:2:1.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, calcium silicate seed crystals are ground together with slag, so that the seed crystals are directly fixed on the newly formed surface of the slag, thereby improving the uniformity of the early reaction. Through ultrafine co-grinding of steel slag and fly ash, the calcium source and aluminum-silicon source react synergistically in the micro-region, reducing the risk of expansion of single steel slag.

[0017] (2) This invention achieves the graded release of alkali source, silicon source, iron source and interfacial active components through multi-layer coating of active particles, avoiding the local strong alkali and microcracks caused by direct addition of activators. The calcium alginate-chitosan intermediate shell improves the interfacial adhesion of soil particles and the ability to resist water erosion.

[0018] (3) The present invention improves the microfilling, nucleation and outer layer roughness by modifying the outer shell layer of nano-silica / nano-regenerated micro powder with silane, thereby improving the strength retention rate of solidified soil after wet-dry cycle, freeze-thaw cycle and water softening. Attached Figure Description

[0019] Figure 1 This is the modulus mapping heatmap for Experiment Example 1.

[0020] Figure 2 The results of the interface modulus and low modulus region width test in Experiment Example 1 are shown in the figure.

[0021] Figure 3 The image shows the freeze-thaw micro-CT results of Experiment Example 2. in Figure 3 In the figure, 'a' represents the CT result image of sample H1 from Example 1. Figure 3 In the image, b represents the CT result of the test on Comparative Example 2, i.e., sample C2. Figure 3In the figure, 'c' represents the test results of the volume fraction of connected cracks in each sample. Figure 3 In the figure, d represents the test results of the maximum crack width for each sample. Detailed Implementation

[0022] The following embodiments further explain and illustrate the technical solutions of the present invention. It is particularly noted that each specific embodiment is a specific interpretation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention. A method for preparing a micro-nano-scale solid waste-based soil stabilizer, the detailed preparation steps of which are as follows: 1. Preparation of modified slag powder Granulated blast furnace slag and hydrated calcium silicate seed crystals are ground together to obtain modified slag powder. During the grinding process, the hydrated calcium silicate seed crystals are dispersed and embedded on the newly formed surface of the slag, forming nucleation sites. The hydrated calcium silicate seed crystals can provide nucleation sites for hydration products, reduce the nucleation barrier, and promote early hydration of cement or alkali-activated slag systems.

[0023] 2. Preparation of steel slag-fly ash composite micro powder Steel slag and fly ash are ultra-finely ground to obtain steel slag-fly ash composite micro powder. Steel slag provides calcium, iron and alkaline mineral phases, while fly ash provides glassy aluminum and silicon components. After ultra-fine co-grinding, the two form micro-region contact, which can improve the subsequent pozzolanic reaction and CASH (hydrated calcium aluminosilicate) gel formation.

[0024] 3. Preparation of multilayer coated active particles Mesoporous nano-slag-biochar composite cores were prepared using nano-slag and mesoporous biochar. The composite cores were then vacuum impregnated with sodium metasilicate and nano-zero-valent iron. Then, a calcium alginate-chitosan intermediate shell layer and a silane coupling agent modified nano-silica and nano-waste concrete recycled micro powder composite outer shell layer were sequentially deposited to obtain multi-layered coated active particles. Mesoporous biochar provides channels, adsorption sites, and moisture regulation space, while nano-slag provides potential hydraulic activity. After vacuum impregnation and loading of sodium metasilicate and nano-zero-valent iron, the sodium metasilicate acts as a slow-release silicate and alkali source, while the nano-zero-valent iron, after controlled oxidation, generates iron oxide / ferric hydroxide microbridges, which is beneficial for improving interfacial bonding and reducing oxygen diffusion. The calcium alginate-chitosan intermediate shell utilizes calcium cross-linking and electrostatic composite effects to control the release of excitation components in the core and increase polar bonding with the surface of clay minerals. The outer shell is composed of silane coupling agent-modified nano-silica and nano-recycled waste concrete powder.

[0025] 4. Preparation of composite activators Sodium silicate, sodium sulfate, and nano-calcium hydroxide were mixed and ball-milled to obtain a composite activator. Sodium silicate provides alkaline silicates, sodium sulfate promotes the aluminum phase reaction and forms ettringite, and nano-calcium hydroxide provides a calcium source that can be rapidly dissolved. The three together promote the synergistic reaction of slag, fly ash, and steel slag.

[0026] 5. Preparation of curing agent Under nitrogen protection, the modified slag micro powder, steel slag-fly ash composite micro powder, multi-layer coated active particles, composite activator and dispersant stabilizer are mixed and compounded to obtain a micro-nano-scale solid waste-based soil stabilizer; inert gas is used to reduce the oxidation of nano-zero valent iron and prevent the premature failure of the active components loaded in the core-shell particles.

[0027] Example 1: Table 1 Raw Material Information Table , S1: Granulated blast furnace slag was dried at 105℃ for 2 hours, cooled, and then mixed with hydrated calcium silicate seed crystals at a mass ratio of 100:4. The mixture was then added to a planetary ball mill with a ball-to-material ratio of 10:1, a rotation speed of 475 r / min, and milled for 75 minutes. The specific surface area was measured to be 700 m² using the Blaine method. 2 / kg, to obtain modified slag powder; S2: After removing iron by magnetic separation, the converter steel slag is crushed to a particle size ≤5mm, dried to constant weight in an oven at 105℃, and then mixed with fly ash at a mass ratio of 1:1.5 and ground at 550r / min for 90min to obtain composite micro powder with D50≤5μm and D90≤10μm. S31: 30 parts by weight of nano-slag and 13 parts by weight of mesoporous biochar were added to 150 parts by weight of deionized water, bubbled with nitrogen for 10 min, ultrasonically dispersed for 20 min, and spray-dried to obtain a mesoporous nano-slag-biochar composite core; 12 parts by weight of sodium metasilicate were dissolved in 60 parts by weight of deoxygenated water, mixed with the composite core, and added to a vacuum impregnation tank, impregnated at -0.078 MPa for 75 min; then, under nitrogen protection, 1.5 parts by weight of nano-zero valent iron aqueous dispersion was added, wherein the mass fraction of nano-zero valent iron in the aqueous dispersion was 10%, stirring was continued for 30 min, and vacuum dried at 55℃ for 5.5 h to obtain a loaded core, wherein the loading rate of sodium metasilicate was 18.2% and the loading rate of nano-zero valent iron was 0.23%; S32: The loaded core was deposited with an intermediate shell. The loaded core was added to a 1 wt% sodium alginate solution and stirred, with a solid-liquid ratio of 1 g:15 mL. Then, 0.15 mol / L calcium chloride solution was added until the solid was submerged, and crosslinking was carried out for 25 min. Then, an equal volume of 1 wt% chitosan-acetic acid solution was added to the sodium alginate solution, the pH was adjusted to 5.5, and the mixture was stirred for 30 min. The mixture was then filtered, washed, and freeze-dried to obtain particles with an intermediate shell, in which the retention rate of sodium metasilicate was 88% and the retention rate of nano-zero valent iron was 90%. S33: The particles with the intermediate shell layer are deposited to form an outer shell layer. 1.5 parts of KH-560 are added to 100 parts of ethanol / water mixture (ethanol to water volume ratio 4:1). The pH is adjusted to 5.0 with dilute acetic acid and hydrolyzed for 40 min. Then, 8 parts of nano-silica and 16 parts of nano-waste concrete recycled powder are added and stirred to disperse. Then, the particles with the intermediate shell layer are added, the pH is adjusted to 5.0, and the mixture is stirred at 400 r / min for 60 min. After filtration, the mixture is pre-frozen at -45℃ and then freeze-dried under vacuum for 36 h to obtain multi-layer coated active particles. S4: Sodium silicate, sodium sulfate and nano calcium hydroxide are mixed in a mass ratio of 2:1:1 and added to a ball mill. The ball-to-material ratio is 15:1, the speed is 400 r / min, and the mixture is ground for 3.5 h to obtain a composite activator. S5: In a mixing chamber under nitrogen protection and with an oxygen volume fraction of less than 0.5%, add 40 parts of modified slag micro powder, 35 parts of steel slag-fly ash composite micro powder, 10 parts of multi-layer coated active particles, 14 parts of composite activator, and 2 parts of dispersant stabilizer. The dispersant stabilizer is obtained by mixing polycarboxylate copolymer, sodium hexametaphosphate, and hydroxypropyl methylcellulose in a ratio of 4:2:1. Stir for 15 minutes to obtain the curing agent.

[0028] Example 2: The preparation method is the same as in Example 1, but with the following differences: In step S5: add 35 parts modified slag micro powder, 30 parts steel slag-fly ash composite micro powder, 5 parts multi-layer coated active particles, 10 parts composite activator, and 1 part dispersant stabilizer.

[0029] Example 3: The preparation method is the same as in Example 1, but with the following differences: In step S5: 45 parts of modified slag micro powder, 40 parts of steel slag-fly ash composite micro powder, 15 parts of multi-layer coated active particles, 18 parts of composite activator, and 3 parts of dispersant stabilizer are added.

[0030] Example 4: The preparation method is the same as in Example 1, but with the following differences: In step S1: blast furnace slag and hydrated calcium silicate seed crystals are mixed at a mass ratio of 100:2, with a ball-to-material ratio of 8:1, and ground at a speed of 450 r / min for 90 min until the specific surface area reaches 700 m². 2 / kg.

[0031] In step S4: grind at 350 r / min for 4 hours.

[0032] Example 5: The preparation method is the same as in Example 1, but with the following differences: In step S1: blast furnace slag and hydrated calcium silicate seed crystals are mixed at a mass ratio of 100:6, with a ball-to-material ratio of 12:1, and ground at a speed of 500 r / min for 60 min until the specific surface area reaches 700 m². 2 / kg.

[0033] In step S4: grind at 450 r / min for 3 hours.

[0034] Example 6: The preparation method is the same as in Example 1, but with the following differences: In step S31: 35 parts by weight of nano-slag and 15 parts by weight of mesoporous biochar are added to 160 parts by weight of deionized water; 15 parts by weight of sodium metasilicate are dissolved in 65 parts by weight of deoxygenated water and impregnated at -0.095 MPa for 60 min; 1 part by weight of nano-zero ferrous molten dispersion is added and vacuum dried at 50 °C for 6 h.

[0035] In step S32: the loaded core is added to a 0.5wt% sodium alginate solution and stirred, with a solid-liquid ratio of 1g:15mL; then a 0.05mol / L calcium chloride solution is added until the solid is submerged, and crosslinking is performed for 30min.

[0036] In step S33: 1 part of KH-560 is added to 100 parts of ethanol / water mixture; then 6 parts of nano silica and 14 parts of nano waste concrete recycled powder are added.

[0037] Example 7: The preparation method is the same as in Example 1, but with the following differences: In step S31: 25 parts by weight of nano-slag and 10 parts by weight of mesoporous biochar are added to 140 parts by weight of deionized water; 10 parts by weight of sodium metasilicate are dissolved in 55 parts by weight of deoxygenated water and impregnated at -0.06 MPa for 90 min; 2 parts by weight of nano-zero ferric iron molten dispersion are added and vacuum dried at 60℃ for 5 h.

[0038] In step S32: the loaded core is added to a 1.5wt% sodium alginate solution and stirred, with a solid-liquid ratio of 1g:15mL; then 0.25mol / L calcium chloride solution is added until the solid is submerged, and crosslinking is performed for 20min.

[0039] In step S33: 2 parts of KH-560 are added to 100 parts of ethanol / water mixture; then 10 parts of nano silica and 18 parts of nano waste concrete recycled powder are added.

[0040] Comparative Example 1: The preparation method of Example 1 was followed, but calcium silicate hydrate seed crystals were not added in step S1. Instead, granulated blast furnace slag was ground separately to the same specific surface area. All other steps were the same.

[0041] Comparative Example 2: Following the preparation method of Example 1, but without preparing multilayer coated active particles, the mesoporous nano-slag-biochar composite core from step S31 was directly used as a filler to replace the multilayer coated active particles in the compound system, with the amount remaining unchanged. All other steps were the same.

[0042] Comparative Example 3: The preparation method of Example 1 was followed, but the core-shell particles did not have a calcium alginate-chitosan intermediate shell. All other steps were the same.

[0043] Comparative Example 4: The preparation method of Example 1 was followed, but the core-shell particles were not provided with a silane-modified nano-silica regenerated micropowder outer shell layer. All other steps were the same.

[0044] Experimental Example 1: The curing agents prepared in Example 1 and Comparative Examples 1-4 were designated as samples H1 and C1-C4, respectively. They were mixed into the same batch of silty clay at 12% of the dry soil mass. Φ50mm×50mm specimens were formed using the static pressing method and cured for 28 days at 20±2℃ and relative humidity ≥95%. For each specimen, a block of approximately 10mm×10mm×5mm was cut from the central region, avoiding areas within 5mm of the outer surface. The block was cut using a low-speed precision diamond cutter. The block was then placed in anhydrous isopropanol for solvent exchange, with the solvent changed every 24 hours for a total of 48 hours. Subsequently, it was vacuum dried at below 40℃ for 24 hours, then vacuum impregnated with low-viscosity cold-mounted epoxy resin, ground, and the surface roughness was measured using a white light interferometer. Under an optical microscope, areas with clear boundaries between soil particles and the cementitious matrix were selected, and two tiny positioning scratches were made as coordinate markers. After indentation, a low-voltage BSE / EDS verification was performed. The test results are as follows: Figure 1 , Figure 2 As shown; from Figure 1 As can be seen from the H1 heatmap, it shows a continuous gradient from the low modulus region of soil particles to the high modulus region of the cementitious matrix. The interface is narrow and there are basically no continuous low-value patches. A continuous transition layer with high bearing capacity is formed between the edge of the soil particles and the cementitious matrix. Figure 2 Among them, C2 has the lowest median interface modulus. Figure 2 In b, C2 has the widest low-modulus region, and Figure 1 The heatmap shows interconnected blue-green weak zones, reflecting insufficient sequential release, continuous hydration filling, and interfacial activity due to the lack of multilayer particles. C3 is the second weakest, indicating that the absence of the intermediate shell layer causes an initial burst release of active components and insufficient supply in the later stages, while also losing the polar binding between calcium alginate-chitosan and clay minerals. Figure 2In the a-type, the interfacial modulus of C4 is higher than that of C1 and C3. C4 still retains the seed crystal and intermediate shell, and has a higher static interfacial modulus.

[0045] Experimental Example 2: The curing agents prepared in Example 1 and Comparative Examples 1-4 were designated as samples H1 and C1-C4, respectively. Φ8mm×16mm cylindrical specimens were directly molded using a dedicated small-size mold. The same specimen was subjected to repeated scans after 0, 5, and 10 freeze-thaw cycles. The specimen curing conditions were 20±2℃ and relative humidity ≥95%, for 28 days. After the 0th scan, a freeze-thaw cycle was performed: freezing at -20±2℃ for 12 hours, followed by thawing in water at 20±2℃ for 12 hours, constituting one cycle. CT scans were performed immediately after the 5th and 10th thawing cycles; the test results are as follows: Figure 3 As shown; Figure 3 In the case of a, H1, there were only a few isolated microcracks at the 0th freeze-thaw cycle; after 5 cycles, the number and length of cracks increased slowly; after 10 cycles, short, non-penetrating cracks still dominated. Figure 3 In the case of b, C2 has more structural defects at 0 times, the cracks merge and branch after 5 times, and a highly connected network is formed after 10 times. Figure 3 In the d-cell model, C1 exhibits fewer freeze-thaw cracks than C4 because C1 retains a complete intermediate layer and inorganic outer shell, resulting in a more intact water-resistant interface between the core and shell particles. C4, on the other hand, loses its outer shell micro-filling, rough interlocking, and silane bonding. Figure 3 C3 is more prone to cracking at the particle-matrix interface under cyclic volume changes. C3 crack damage is greater than C4: the absence of the calcium alginate-chitosan intermediate layer leads to early burst release and later depletion of active components. The lack of flexible buffer and polar adhesion at the interface makes pore water migration and crack propagation more pronounced during freeze-thaw cycles.

[0046] Experimental Example 3: The comprehensive performance of the curing agents prepared by combining Examples 1-7 and Comparative Examples 1-4 was determined; (1) Mechanical, durability and water stability coefficient tests: Unconfined compressive strength: The curing agents prepared in each example and comparative example were added to typical silty clay at a dosage of 12% of the dry soil mass and mixed evenly. Cylindrical specimens with a diameter of 50 mm × 50 mm were prepared by static pressing. After the specimens were formed, they were cured at a temperature of 20 ± 2℃ and a relative humidity of ≥ 95% for 7 days, 28 days and 90 days respectively. One day before the specified curing age, the specimens were immersed in water for 24 hours, with the water level 2.5 cm above the top surface of the specimens. After being removed, the surface free water was wiped off with a damp cloth, and the unconfined compressive strength test was immediately carried out. The loading rate of the press was controlled at 1 mm / min.

[0047] Water stability coefficient: The ratio of the unconfined compressive strength of the specimens prepared in each embodiment and comparative example after curing at 20±2℃ and relative humidity ≥95% for 6 days and then immersing in water for 1 day to the unconfined compressive strength measured after standard curing for 7 days.

[0048] Freeze-thaw cycle strength retention rate: 28-day-old specimens were subjected to a freeze-thaw cycle test: frozen at -20±2℃ for 12 hours, then thawed in water at 20±2℃ for 12 hours, constituting one cycle. After 10 freeze-thaw cycles, the unconfined compressive strength of the specimens was tested. The ratio of this unconfined compressive strength to that of standard-cured 28-day-old specimens from the same batch is the freeze-thaw strength retention rate.

[0049] The specific test comparison results are shown in Table 2: Table 2 Comparison of mechanical properties, durability, and water stability coefficient between Examples 1-7 and Comparative Examples 1-4 , (2) Heavy metal leaching concentration and microscopic testing: Heavy metal leaching concentration: 28-day-old solidified soil specimens were crushed to a particle size ≤9.5 mm. A mixture of concentrated sulfuric acid and concentrated nitric acid (mass ratio 2:1), adjusted to pH 3.20 ± 0.05, was used as the leaching agent and mixed with the specimen at a liquid-to-solid ratio of 10:1 (L / kg). The mixture was shaken for 18 hours at 20 r / min on a rotary shaker. After shaking, the mixture was allowed to stand and filtered through a 0.45 μm filter membrane. The concentrations of Cr, Pb, Cu, and Zn in the filtrate were determined using inductively coupled plasma mass spectrometry (ICP-MS).

[0050] Microstructure analysis: The fresh fracture morphology of 28-day-old solidified soil specimens was observed using a scanning electron microscope with an accelerating voltage of 15-20 kV, a working distance of 10-15 mm, and a magnification of 1000-10000 times. The pore structure parameters of the 28-day-old solidified soil specimens, including total porosity and most probable pore size, were tested using a fully automatic mercury porosimeter.

[0051] The specific test comparison results are shown in Table 3: Table 3. Comparison of heavy metal leaching concentrations and microstructures in Examples 1-7 and Comparative Examples 1-4 , The comparison results above show that, in Comparative Example 1, without the addition of hydrated calcium silicate seeds, only granulated blast furnace slag was ground to the same specific surface area, resulting in lower mechanical properties compared to the Example 1. This indicates that the introduction of hydrated calcium silicate seeds improves strength throughout all ages. During the grinding process, the seeds disperse and embed on the newly formed slag surface, forming nucleation sites, lowering the nucleation barrier of hydration products, and promoting the uniformity and rate of early hydration reactions in the slag. Simultaneously, the seed-induced effect generates more active sites on the slag particle surface, enhancing its reactivity with the activator and contributing to later strength growth. In terms of durability, it is lower than the Example 1. The absence of seeds leads to a reduction in the amount and uneven distribution of hydration products, increased porosity of the solidified body, and a larger most probable pore size, making it easier for moisture to penetrate the pores, thus reducing water stability and freeze-thaw resistance. Regarding heavy metal fixation, the leaching concentration is high, and the absence of seeds leads to a reduction in hydration products, resulting in decreased physical coating and chemical bonding ability for heavy metals. Comparative Example 2 did not include multilayer coated active particles; instead, a mesoporous nano-slag-biochar composite core was directly added to the compound system as a filler. Compared to the previous example, the mechanical properties were lower, durability was poorer, total porosity was high, and the most probable pore size was large. The absence of multilayer coated active particles prevented the solidified body from continuously generating hydration products to fill the pores through the time-sequential release of the core-shell structure. The solidified body structure was loose and porous, making it highly susceptible to moisture and freeze-thaw damage; heavy metal leaching concentration was also high. Comparative Example 3 did not include a calcium alginate-chitosan intermediate shell layer in the core-shell particles, resulting in reduced mechanical properties. The sodium metasilicate and nano-zero-valent iron in the core lacked a slow-release barrier, leading to a large release of active components in the initial mixing stage, creating a locally strong alkaline environment that inhibited uniform hydration of the slag. Furthermore, the active components were depleted later, resulting in weak strength growth. The calcium alginate-chitosan coating layer has semi-permeable membrane properties; without this layer, there was no buffer transition between the core and shell layers, reducing the overall stability of the core-shell structure. Poor durability; the absence of the intermediate shell prevents the core-shell particles from continuously providing active components through the swelling-slow release mechanism, resulting in insufficient formation of hydration products and inadequate pore filling. High heavy metal leaching concentration; the absence of the intermediate shell causes the release of nano-zero-valent iron to lose temporal control. A large amount of nano-zero-valent iron released in the early stages is oxidized and deactivated before sufficient contact with heavy metals, and there is insufficient nano-zero-valent iron to continuously exert a reducing effect in the later stages. Comparative Example 4's core-shell particles did not have a silane-modified nano-silica / nano-waste concrete recycled powder outer shell layer.The mechanical properties are reduced due to the loss of the crystal nucleation effect of nano-silica and the reduction in the amount of early CASH (hydrated calcium aluminosilicate) gel formation; the pozzolanic reaction and micro-filling effect of nano-waste concrete recycled powder are lost; the interfacial chemical bonding caused by silane coupling agent modification is lost, and the interfacial bonding between core-shell particles and soil particles and slag matrix is ​​reduced from chemical bonding to physical contact. The lack of the outer shell layer not only affects the early strength but also weakens the potential for sustained growth in later strength, resulting in poor durability; the high concentration of heavy metal leaching and the lack of the outer shell layer reduce the overall structural stability of the core-shell particles. During mixing and curing, some core-shell structures may break, causing premature leakage of the active components loaded in the core, which reduces the long-term stabilization effect.

Claims

1. A method for preparing a micro / nano-scale solid waste-based soil stabilizer, characterized in that, Includes the following steps: S1: The granulated blast furnace slag was dried at 105℃ for 2 hours, cooled, and then mixed with hydrated calcium silicate seed crystals in a mass ratio and ground together to obtain modified slag powder. S2: After removing iron by magnetic separation, the converter steel slag is crushed to a particle size ≤5mm, dried, and then mixed with fly ash at a mass ratio of 1:1.

5. The mixture is then ground at a speed of 550r / min for 90min to obtain composite micro powder. S3: Nano-slag and mesoporous biochar were added to deionized water, bubbled with nitrogen for 10 min, ultrasonically dispersed for 20 min, and spray-dried to obtain a mesoporous nano-slag-biochar composite core; sodium metasilicate was dissolved in deoxygenated water, mixed with the composite core, and added to a vacuum impregnation tank, and impregnated at -0.06 to -0.095 MPa for 60 to 90 min; then, under nitrogen protection, a molten dispersion containing 10% by mass of nano-zero ferric iron was added, and stirring was continued for 30 min, followed by vacuum drying to obtain a loaded core; the loaded core was then deposited with an intermediate shell to obtain particles with an intermediate shell; Then, a shell layer is deposited to obtain multi-layered coated active particles; S4: Sodium silicate, sodium sulfate and nano calcium hydroxide are mixed in a mass ratio of 2:1:1 and added to a ball mill for grinding to obtain a composite activator; S5: In a mixing chamber under nitrogen protection and with an oxygen volume fraction of less than 0.5%, add modified slag micro powder, steel slag-fly ash composite micro powder, multi-layer coated active particles, composite activator, and dispersant stabilizer, and stir for 15 minutes to obtain a curing agent; The curing agent, by weight, comprises 35-45 parts modified slag micro powder, 30-40 parts steel slag-fly ash composite micro powder, 5-15 parts multi-layer coated active particles, 10-18 parts composite activator and 1-3 parts dispersant stabilizer. The modified slag powder is obtained by grinding granulated blast furnace slag and hydrated calcium silicate seed crystals together. The steel slag-fly ash composite micro powder is obtained by grinding converter steel slag and fly ash together. The multilayer coated active particles, from the inside out, include a composite core, a calcium cross-linked alginate / chitosan composite coating layer, and a KH-560-mediated nano silica / nano waste concrete recycled micro powder composite outer layer. The composite core includes nano slag, mesoporous biochar, and sodium metasilicate and nano zero-valent iron loaded in the composite core. The composite activator includes sodium silicate, sodium sulfate, and nano-calcium hydroxide; The dispersion stabilizer includes polycarboxylate copolymer, sodium hexametaphosphate, and hydroxypropyl methylcellulose.

2. The method for preparing a micro / nano-scale solid waste-based soil stabilizer according to claim 1, characterized in that, The mass ratio mentioned in step S1 is specifically a mixture of granulated blast furnace slag and hydrated calcium silicate seed crystals at a mass ratio of 100:2 to 100:

6.

3. The method for preparing a micro-nano-scale solid waste-based soil stabilizer according to claim 1, characterized in that, The co-grinding mentioned in step S1 specifically involves adding the material to a ball mill at a ball-to-material ratio of 8:1 to 12:1, a rotation speed of 450 to 500 r / min, and grinding for 60 to 90 minutes until a specific surface area of ​​700 m² is achieved. 2 / kg.

4. The method for preparing a micro-nano-scale solid waste-based soil stabilizer according to claim 1, characterized in that, The drying described in step S2 specifically involves drying in an oven at 105°C until constant weight.

5. The method for preparing a micro / nano-scale solid waste-based soil stabilizer according to claim 1, characterized in that, The composite micro powder described in step S2 has a D50≤5μm and a D90≤10μm.

6. The method for preparing a micro / nano-scale solid waste-based soil stabilizer according to claim 1, characterized in that, The vacuum drying described in step S3 specifically involves vacuum drying at 50℃~60℃ for 5~6 hours.

7. The method for preparing a micro / nano-scale solid waste-based soil stabilizer according to claim 1, characterized in that, The deposition of the intermediate shell in step S3 specifically involves adding the loaded core to a 0.5–1.5 wt% sodium alginate solution and stirring, with a solid-liquid ratio of 1 g: 15 mL; then adding a 0.05–0.25 mol / L calcium chloride solution until the solid is submerged, and crosslinking for 20–30 min; then adding an equal volume of 1 wt% chitosan-acetic acid solution to the sodium alginate solution, adjusting the pH to 5.5, stirring for 30 min, filtering, washing, and freeze-drying.

8. The method for preparing a micro-nano-scale solid waste-based soil stabilizer according to claim 1, characterized in that, The deposition of the outer shell layer in step S3 is specifically achieved by adding KH-560 to an ethanol / water mixture with a volume ratio of 4:1, adjusting the pH to 5.0 with dilute acetic acid, and hydrolyzing for 40 min; then adding nano-silica and nano-recycled waste concrete powder, and stirring to disperse; then adding particles with an intermediate shell layer, adjusting the pH to 5.0, stirring at 400 r / min for 60 min, filtering, pre-freezing at -45℃, and then freeze-drying under vacuum for 36 h.

9. The method for preparing a micro-nano-scale solid waste-based soil stabilizer according to claim 1, characterized in that, The grinding described in step S4 specifically involves a ball-to-material ratio of 15:1, a rotation speed of 350–450 r / min, and grinding for 3–4 hours.

10. The method for preparing a micro / nano-scale solid waste-based soil stabilizer according to claim 1, characterized in that, The dispersion stabilizer described in step S5 is obtained by mixing polycarboxylate copolymer, sodium hexametaphosphate and hydroxypropyl methylcellulose in a ratio of 4:2:1.

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