A full solid waste-based composite backfill material and a preparation method thereof

Abstract

This invention provides a composite backfill material based on solid waste and its preparation method. The backfill material comprises the following raw materials in parts by weight: 30-50 parts Bayer red mud, 20-40 parts fly ash, 5-10 parts desulfurization ash, 5-10 parts blast furnace slag powder, 10-30 parts steel slag, 1-3 parts water-reducing agent, 5-8 parts organic aerogel-modified layered bimetallic hydroxide, 0.1-0.3 parts polyethylene glycol, and 10-30 parts water. The organic aerogel-modified layered bimetallic hydroxide is synthesized by co-precipitation. The layered bimetallic hydroxide is dispersed in a sol formed by the reaction of diphenol and formaldehyde, and the composite material with organic aerogel modification on the surface is obtained by gelation, aging, and supercritical drying. This not only improves the tolerance of the layered bimetallic hydroxide to the high-alkali environment containing red mud, but also synergistically improves the chloride ion penetration resistance of the backfill material.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to an all-solid waste-based composite backfill material and its preparation method. Background Technology

[0002] Most infrastructure projects involve excavation and backfilling of the original ground. During this process, the backfilling stage faces a pressing problem: the excessive consumption of natural resources. Researchers have attempted to incorporate solid waste such as construction debris, silt, industrial sludge, slag, ash, coal gangue, and construction waste into the preparation of backfill materials, and have achieved some success.

[0003] For example, patent CN114940600B discloses a solid waste backfill material and its preparation method, wherein the mass mixing ratio of the gel material and aggregate is 1:3-7; the gel material comprises the following components in parts by weight: 6-12 parts desulfurized gypsum, 5-17 parts fly ash, 40-60 parts slag, 10-20 parts steel slag, 10-30 parts magnesium slag, 15-25 parts calcium carbide slag, 0.5-1.5 parts water-reducing agent, 0.5-1.5 parts water-retaining dispersant, and 2-12 parts alkaline activator; the aggregate is tailings. Patent CN111995275B discloses a solid waste underground backfill cementitious material and its preparation method, comprising the following components in parts by weight: 44-48 parts steel slag, 16-17 parts slag, 18-22 parts phosphogypsum, 15.5-17 parts water, and 0.7-2.9 parts surface modifier.

[0004] The above are common technologies that use solid waste as the main raw material for backfill materials, which not only meet the needs of engineering construction but also alleviate the pressure of natural resource shortages. However, with the shift in national development strategy towards the development and utilization of marine resources, marine engineering and coastal engineering are booming. Because these projects are in direct contact with seawater or face the risk of seawater intrusion, higher requirements are placed on the chloride ion penetration resistance of backfill materials to resist seawater erosion and salinization. Traditional solid waste-based backfill materials are mainly suitable for land-based engineering and cannot meet the special needs of marine and coastal engineering.

[0005] In recent years, layered bimetallic hydroxides (LDHs) have attracted widespread attention and application from materials researchers due to their unique layered structure and ion adsorption capabilities. These materials can effectively adsorb harmful anions (such as Cl-) in concrete. - SO4 2-Layered bimetallic hydroxides (LDHs) are considered one of the most effective materials for improving concrete durability. Although LDHs possess some acid and alkali resistance, their long-term stability in highly alkaline environments remains insufficient. Therefore, LDHs cannot be directly used in conjunction with strongly alkaline solid wastes (such as red mud and steel slag). Substances that can reduce alkalinity need to be added, such as the ion-curing agent and red mud-fly ash cementitious material mentioned in patent CN108516707B, and the cement-based curing material and curing method for curing nuclear waste containing high concentrations of boric acid described in patent CN108585722B. This requirement significantly limits the selection and source of solid waste raw materials in backfill materials.

[0006] Therefore, it is necessary to further improve the layered bimetallic hydroxide without affecting its adsorption performance for harmful anions, so as to improve its applicability in general alkaline and strongly alkaline environments and broaden the selection and sources of solid waste raw materials in backfill materials. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a solid waste-based composite backfill material and its preparation method. The backfill material contains an organic aerogel-modified layered bimetallic hydroxide. This material is prepared by first using solid waste carbide slag and high-alumina fly ash as raw materials to prepare calcium and aluminum sources, respectively, and then synthesizing the layered bimetallic hydroxide using a co-precipitation method. The layered bimetallic hydroxide is dispersed in a sol formed by the reaction of diphenol and formaldehyde, and then processed through gelation, aging, and supercritical drying to obtain a composite material with an organic aerogel-modified surface. The organic aerogel layer not only improves the tolerance of the layered bimetallic hydroxide to the high-alkaline environment containing red mud, but also synergistically enhances the chloride ion permeability resistance of the backfill material.

[0008] To achieve the above objectives, the following technical solution is adopted:

[0009] A composite backfill material based entirely on solid waste comprises the following raw materials in parts by weight: 30-50 parts Bayer red mud, 20-40 parts fly ash, 5-10 parts desulfurization ash, 5-10 parts blast furnace slag powder, 10-30 parts steel slag, 1-3 parts water-reducing agent, 5-8 parts organic aerogel-modified layered bimetallic hydroxide, 0.1-0.3 parts polyethylene glycol, and 10-30 parts water. The organic aerogel-modified layered bimetallic hydroxide is prepared by a method comprising the following steps:

[0010] 1) Dry, crush, calcine, and grind the carbide slag to obtain carbide slag powder. Mix the carbide slag powder with water evenly, centrifuge, retain the supernatant, adjust the calcium ion concentration to 0.3-1.6 mol / L, and obtain a calcium source solution for later use.

[0011] 2) Dry, calcine, and grind high-alumina fly ash to obtain high-alumina fly ash powder. Mix the high-alumina fly ash powder with sodium hydroxide solution evenly, heat to react, cool to room temperature after the reaction is complete, adjust the pH, wait until no precipitate is produced, filter, wash, dissolve the precipitate again, adjust the aluminum ion concentration to 0.1-0.8 mol / L to obtain aluminum source solution for later use.

[0012] 3) Mix the calcium source solution and aluminum source solution evenly to obtain a mixed solution. Under stirring conditions, add an equal volume of the mixed solution and the mixed alkaline solution dropwise into the reactor to carry out a co-precipitation reaction. At the same time, add sodium hydroxide solution to adjust the pH of the mixed system in the reactor. After the addition is complete, control the temperature to carry out the reaction. After the reaction is completed, centrifuge, wash, dry, heat treat, and grind to obtain a layered bimetallic hydroxide for later use. The amount of calcium source solution and aluminum source solution used should meet the requirement that the molar ratio of calcium ions to aluminum ions is 2-3:1.

[0013] 4) Add bisphenol and formaldehyde to water and mix evenly. Adjust the pH to form a sol. Add layered bimetallic hydroxide and dispersant and disperse evenly by ultrasonication. Place in a sealed container to carry out gelation and aging reactions to obtain organic wet gel.

[0014] 5) The wet gel was placed in an organic solvent for organic solvent replacement, and then dried under supercritical conditions using carbon dioxide as the drying medium. Finally, it was ground to obtain an organic aerogel-modified layered bimetallic hydroxide.

[0015] In step 1), the CaO content of the calcium carbide slag is ≥85%. Drying is performed at 80-110℃ for 12-24 hours. Crushing is done using a jaw crusher to achieve an average particle size of 1-5 mm. Calcination is performed at 300-600℃ for 2-4 hours. Grinding is performed using a planetary ball mill to achieve a D50 of 10-20 μm and a specific surface area of ​​400-500 m². 2 / kg. The mass ratio of the calcium carbide slag powder to water is 1:10-15. The mixing temperature of the calcium carbide slag powder and water is 60-80℃. The concentration is adjusted by evaporation or by adding water.

[0016] In step 2), the high-alumina fly ash has an Al2O3 content ≥ 50%. Drying is performed at 80-110℃ for 12-24 hours. Calcination is performed at 300-600℃ for 2-4 hours. Grinding is performed using a planetary ball mill to a D50 of 10-20 μm and a specific surface area of ​​400-500 m². 2 / kg. The solid-liquid mass ratio of the high-alumina fly ash powder to the sodium hydroxide solution is 1:5-10, and the concentration of the sodium hydroxide solution is 10-15wt%. The heating is raised to 90-100℃, the reaction time is 2-4 hours, and the pH is adjusted to 7-8. The washing is performed 1-3 times with water. The precipitate is redissolved by dissolving the precipitate in a 20-30wt% hydrochloric acid solution at a solid-liquid mass ratio of 1:3-5. The concentration is adjusted by evaporation or by adding water.

[0017] In step 3), the mixed alkaline solution is a mixed alkaline aqueous solution prepared from NaOH and Na₂CO₃, wherein the concentration of NaOH is 0.30-2.40 mol / L and the concentration of Na₂CO₃ is 0.10-0.80 mol / L. The concentration of the sodium hydroxide solution is 0.30-2.40 mol / L. The pH is adjusted to 9-11. The stirring speed is 90-120 r / min. The temperature is controlled at 40-60℃. The reaction time is 6-24 h. The washing is performed until the pH of the washing solution reaches 7. The drying is performed at 60℃ for 12-24 h. The heat treatment is performed at 150-200℃ for 6-12 h. The grinding is performed until the average particle size is 1-5 μm.

[0018] In step 4), the diphenol is selected from one or a combination of two or more of resorcinol, hydroquinone, and catechol. The pH is adjusted to 8-11 using an alkali. The alkali is selected from one or a combination of two or more of sodium hydroxide, potassium hydroxide, and sodium carbonate. The dispersant is a nonionic fluorocarbon surfactant selected from DuPont. One of FSO, FSO-100, FSN-100, and FS-300. The gelation reaction conditions are 70-100℃ for 6-24 hours. The aging reaction conditions are 40-60℃ for 2-4 days. The molar ratio of the bisphenol, formaldehyde, and dispersant is 1:2-4:0.001-0.002, and the layered bimetallic hydroxide is 20-25 wt% of the bisphenol. The ultrasonic dispersion frequency is 20-25 kHz for 5-15 minutes.

[0019] In step 5), the organic solvent is selected from one or a combination of two or more of methanol, ethanol, propanol, isopropanol, and acetone. The displacement time is 2-5 days. The supercritical drying time is 1-10 hours. The grinding is performed until the average particle size is 1.5-2.5 times the average particle size of the layered bimetallic hydroxide.

[0020] In organic aerogel-modified layered bimetallic hydroxides, optimizing the amount of layered bimetallic hydroxide relative to bisphenol and the average particle size before and after modification are crucial for improving material performance. If the amount of layered bimetallic hydroxide is too small relative to bisphenol or the average particle size after modification is too large, a relatively dense or excessively thick "shell" will form on the aerogel surface, severely hindering the adsorption of chloride ions by the layered bimetallic hydroxide. Conversely, if the amount of layered bimetallic hydroxide is relatively excessive or the average particle size after modification is too small, it will affect its tolerance in highly alkaline environments, leading to decomposition and still resulting in unsatisfactory chloride ion permeation resistance of the backfill material.

[0021] The Bayer red mud contains 2-12% Na2O, has a leachate pH of 10-12, and an average particle size of ≤3mm.

[0022] The fly ash contains ≥80% CaO+Al2O3+SiO2, ≤8% SO3, and has a specific surface area of ​​400-500 m². 2 / kg, selected from one or a combination of two of circulating fluidized bed fly ash and ordinary pulverized coal boiler fly ash.

[0023] The desulfurization ash contains ≥30% CaO, ≥10% SO3, and has a specific surface area of ​​400-500 m². 2 / kg.

[0024] The blast furnace slag powder is S95 grade ore powder, with an activity index ≥75% after 7 days, an activity index ≥96% after 28 days, and a specific surface area of ​​400-500 m². 2 / kg, with CaO+Al2O3+SiO2 content ≥90% in the composition.

[0025] The steel slag gradation is as follows: steel slag with a particle size <2.36mm accounts for 25-42%, steel slag with a particle size of 2.36mm-4.75mm accounts for 30-40%, and steel slag with a particle size of 4.75mm-9.5mm accounts for 33-45%.

[0026] The water-reducing agent has a water reduction rate of 15-25 wt% and is selected from one or a combination of two of polycarboxylate water-reducing agents and naphthalene-based water-reducing agents.

[0027] The number average molecular weight of the polyethylene glycol is 4000-6000.

[0028] This invention also provides a method for preparing the above-mentioned all-solid waste-based composite backfill material, comprising the following steps:

[0029] Organic aerogel-modified layered bimetallic hydroxide and polyethylene glycol were added to water and ultrasonically dispersed to form a suspension. Bayer red mud, fly ash, desulfurization ash, blast furnace slag powder, water-reducing agent and the prepared suspension were added to a mixer and stirred evenly. Then the mixture was sealed and allowed to stand for curing. After curing, steel slag was added and mixed evenly to obtain a solid waste-based composite backfill material.

[0030] The ultrasonic power is 200-400W, and the ultrasonic time is 10-30min. The mass ratio of the organic aerogel-modified layered bimetallic hydroxide to water is 1:3-10.

[0031] The stirring speed is 120-150 r / min, and the stirring time is 60-90 s. The curing time is 12-24 h.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] (1) The organic aerogel-modified layered bimetallic hydroxide in the solid waste-based composite backfill material of the present invention is prepared by first preparing calcium source and aluminum source using solid waste carbide slag and high-alumina fly ash as raw materials, and then synthesizing layered bimetallic hydroxide by co-precipitation method. The layered bimetallic hydroxide is dispersed in a sol formed by the reaction of diphenol and formaldehyde, and the composite material with organic aerogel modification on the surface is obtained by gelation, aging and supercritical drying. The organic aerogel layer can not only improve the tolerance of layered bimetallic hydroxide to high-alkali environment containing red mud, but also synergistically improve the chloride ion penetration resistance of backfill material.

[0034] (2) This invention uses solid wastes such as red mud, steel slag, fly ash, and desulfurization ash as main raw materials to prepare a composite backfill material based on all solid wastes, realizing cross-industry collaborative large-scale value-added utilization of various industrial solid wastes. By utilizing the complementary physical and chemical properties of different solid wastes and leveraging the composite synergistic effect between multiple solid wastes, the prepared composite backfill material based on all solid wastes has the characteristics of high compressive strength, environmental friendliness, and strong waste utilization capacity. Attached Figure Description

[0035] Figure 1 The image shows the SEM image of the layered bimetallic hydroxide obtained in step 3) of Example 1. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments, but is not limited to the contents of the specification. Unless otherwise specified, all "parts" mentioned in the embodiments of the present invention are parts by weight. All reagents used are commercially available in the art.

[0037] The calcium carbide slag has a CaO content of ≥85% and comes from Hebei Shougang Jingtang Company.

[0038] The high-alumina fly ash has an Al2O3 content of ≥50% and comes from Shougang Jingtang Company in Tangshan, Hebei Province.

[0039] Bayer red mud comes from Hebei Tangshan Wenfeng Industrial Group Co., Ltd., with a Na2O content of 10%, a leachate pH of 12, and an average particle size of 1.3 mm.

[0040] The circulating fluidized bed fly ash comes from Hebei Tangshan Wenfeng Industrial Group Co., Ltd., with CaO+Al2O3+SiO2 content ≥80%, SO3 content ≤8%, and specific surface area of ​​4820 m². 2 / kg.

[0041] The desulfurization ash comes from Hebei Tangshan Wenfeng Industrial Group Co., Ltd., with CaO content ≥30%, SO3 content ≥10%, and specific surface area of ​​4440 m². 2 / kg.

[0042] The blast furnace slag powder is sourced from Hebei Tangshan Wenfeng Industrial Group Co., Ltd. It is S95 grade ore powder with an activity index ≥75% after 7 days, an activity index ≥96% after 28 days, and a specific surface area of ​​4790 m². 2 / kg, with CaO+Al2O3+SiO2 content ≥90% in the composition.

[0043] The steel slag comes from Hebei Tangshan Wenfeng Industrial Group Co., Ltd. The proportion of steel slag with a particle size of <2.36mm is 25%, the proportion of steel slag with a particle size of 2.36mm-4.75mm is 40%, and the proportion of steel slag with a particle size of 4.75mm-9.5mm is 35%.

[0044] SSF-1000 series naphthalene-based high-efficiency water-reducing agent with a water reduction rate of 21.8%, purchased from Hubei Shanshufeng Building Materials Technology Co., Ltd.

[0045] The polyethylene glycol has an average molecular weight of 4000 and was purchased from Haian Petrochemical Plant in Jiangsu Province.

[0046] Example 1

[0047] 1) The calcium carbide slag was dried at 100℃ for 24 hours, crushed in a jaw crusher to an average particle size of 3.5 mm, calcined at 600℃ for 2 hours, and then ground in a planetary ball mill to a D50 of 11.3 μm and a specific surface area of ​​423 m². 2 / kg, obtain calcium carbide slag powder, mix the calcium carbide slag powder with water evenly, centrifuge, retain the supernatant, adjust the concentration, and obtain a calcium source solution with a calcium ion molar concentration of 0.3mol / L for later use;

[0048] 2) High-alumina fly ash was dried at 100℃ for 24 hours, calcined at 600℃ for 2 hours, and then ground in a planetary ball mill to a D50 of 14.5μm and a specific surface area of ​​451m². 2 / kg, high-alumina fly ash powder was obtained. The high-alumina fly ash powder was mixed with a 15wt% sodium hydroxide solution at a mass ratio of 1:5. The mixture was heated to 100℃ and reacted for 2 hours. After the reaction was completed, the mixture was cooled to room temperature and the pH was adjusted to 7. When no precipitate was formed, the mixture was filtered and washed with water 3 times. The precipitate was dissolved in a 20wt% hydrochloric acid solution and the concentration was adjusted to obtain an aluminum source solution with an aluminum ion concentration of 0.1mol / L for later use.

[0049] 3) Take calcium source solution and aluminum source solution, mix them evenly to obtain a mixed solution, and under stirring at 100 r / min, add an equal volume of the mixed solution and a mixed alkaline solution prepared by NaOH and Na2CO3 (where the concentration of NaOH is 0.32 mol / L and the concentration of Na2CO3 is 0.1 mol / L) dropwise into the reactor to carry out a co-precipitation reaction. At the same time, add 0.32 mol / L sodium hydroxide solution to adjust the pH of the mixed system in the reactor to 10.5. After the dropwise addition is completed, control the temperature at 60℃ and react for 6 h. After the reaction is completed, centrifuge, wash the precipitate with water until the pH of the washing solution is 7, dry at 60℃ for 24 h, heat treat at 200℃ for 12 h, grind to an average particle size of 1.8 μm to obtain layered bimetallic hydroxide for later use.

[0050] 4) Add 1 mol resorcinol and 4 mol formaldehyde to 300 mL of water and mix well. Adjust the pH to 8 with sodium hydroxide to form a sol. Add 27.5 g of the layered bimetallic hydroxide obtained in step 3) and 0.002 mol DuPont FSO-100. Disperse the mixture by ultrasonication at 20 Hz for 15 min and place it in a sealed container. Gel at 70 ℃ for 12 h and age at 40 ℃ for 2 days to obtain an organic wet gel.

[0051] 5) The wet gel was placed in propanol for organic solvent replacement for 4 days, and then dried under supercritical conditions for 10 hours with carbon dioxide as the drying medium. Finally, it was ground until the average particle size was 2.5 times that of the layered bimetallic hydroxide to obtain organic aerogel modified layered bimetallic hydroxide.

[0052] 6) Add 8g of organic aerogel-modified layered bimetallic hydroxide and 0.3g of polyethylene glycol to 30g of water and ultrasonically disperse for 10min at 400W to form a suspension. Take 30g of Bayer red mud, 40g of fly ash, 5g of desulfurization ash, 10g of blast furnace slag powder, 3g of SSF-1000 series naphthalene-based high-efficiency water-reducing agent and the prepared suspension and add them to a mixer and stir at 150r / min for 60s until uniform. Then seal and let stand for 24h for curing. After curing, add 30g of steel slag and mix evenly to obtain the all-solid waste-based composite backfill material.

[0053] Example 2

[0054] The rest is the same as in Example 1, except that the amount of layered bimetallic hydroxide used in step 4) is 22g.

[0055] Example 3

[0056] The rest is the same as in Example 1, except that the amount of layered bimetallic hydroxide used in step 4) is 20g.

[0057] Example 4

[0058] The rest is the same as in Example 1, except that the amount of layered bimetallic hydroxide used in step 4) is 30g.

[0059] Example 5

[0060] The rest is the same as in Example 1, except that in step 4), DuPont FSO-100 is replaced with an equimolar amount of FS-300.

[0061] Example 6

[0062] The rest is the same as in Example 1, except that in step 4), an equimolar amount of sodium dodecylbenzenesulfonate is used instead of DuPont FSO-100.

[0063] Example 7

[0064] The rest is the same as in Example 1, except that the average particle size of the organic aerogel-modified layered bimetallic hydroxide in step 5) is 1.5 times the average particle size of the layered bimetallic hydroxide.

[0065] Example 8

[0066] The rest is the same as in Example 1, except that in step 5), the amount of organic aerogel-modified layered bimetallic hydroxide is 5g.

[0067] Example 9

[0068] 1) The calcium carbide slag was dried at 100℃ for 24 hours, crushed in a jaw crusher to an average particle size of 3.5 mm, calcined at 600℃ for 2 hours, and then ground in a planetary ball mill to a D50 of 11.3 μm and a specific surface area of ​​423 m². 2 / kg, obtain calcium carbide slag powder, mix the calcium carbide slag powder with water evenly, centrifuge, retain the supernatant, adjust the concentration, and obtain a calcium source solution with a calcium ion molar concentration of 0.2mol / L for later use;

[0069] 2) High-alumina fly ash was dried at 100℃ for 24 hours and then ground in a planetary ball mill until the D50 was 14.5μm and the specific surface area was 451m². 2 / kg, high-alumina fly ash powder was obtained. The high-alumina fly ash powder was mixed with a 15wt% sodium hydroxide solution at a mass ratio of 1:5. The mixture was heated to 100℃ and reacted for 2 hours. After the reaction was completed, the mixture was cooled to room temperature and the pH was adjusted to 7. When no precipitate was formed, the mixture was filtered and washed with water 3 times. The precipitate was dissolved in a 20wt% hydrochloric acid solution and the concentration was adjusted to obtain an aluminum source solution with an aluminum ion concentration of 0.1mol / L for later use.

[0070] 3) Mix equal volumes of calcium source solution and aluminum source solution to obtain a mixed solution. Under stirring at 100 r / min, add an equal volume of the mixed solution and a mixed alkaline solution prepared from NaOH and Na2CO3 (where the concentration of NaOH is 0.32 mol / L and the concentration of Na2CO3 is 0.1 mol / L) dropwise into the reactor to carry out a co-precipitation reaction. At the same time, add 0.32 mol / L sodium hydroxide solution to adjust the pH of the mixed system in the reactor to 10.5. After the addition is complete, control the temperature at 60℃ and react for 6 h. After the reaction is completed, centrifuge, wash the precipitate with water until the pH of the washing solution is 7, dry at 60℃ for 24 h, heat treat at 200℃ for 12 h, and grind to an average particle size of 2.0 μm to obtain a layered bimetallic hydroxide for later use.

[0071] 4) Add 1 mol resorcinol and 2 mol formaldehyde to 300 mL of water and mix well. Adjust the pH to 8 with sodium hydroxide to form a sol. Add 27.5 g of the layered bimetallic hydroxide obtained in step 3) and 0.002 mol DuPont FSO-100. Disperse the mixture by ultrasonication at 20 Hz for 15 min and place it in a sealed container. Gel at 70 ℃ for 12 h and age at 40 ℃ for 2 days to obtain an organic wet gel.

[0072] 5) The wet gel was placed in propanol for organic solvent replacement for 4 days, and then dried under supercritical conditions for 10 hours with carbon dioxide as the drying medium. Finally, it was ground until the average particle size was 1.5 times that of the layered bimetallic hydroxide to obtain organic aerogel modified layered bimetallic hydroxide.

[0073] 6) Add 5g of organic aerogel-modified layered bimetallic hydroxide and 0.3g of polyethylene glycol to 30g of water and ultrasonically disperse for 10min at 400W to form a suspension. Take 50g of Bayer red mud, 20g of fly ash, 10g of desulfurization ash, 10g of blast furnace slag powder, 3g of SSF-1000 series naphthalene-based high-efficiency water-reducing agent and the prepared suspension and add them to a mixer and stir at 150r / min for 60s until uniform. Then seal and let stand for 24h for curing. After curing, add 30g of steel slag and mix evenly to obtain the all-solid waste-based composite backfill material.

[0074] Comparative Example 1

[0075] The rest is the same as in Example 1, except that polyethylene glycol is not added in step 5).

[0076] Comparative Example 2

[0077] The rest is the same as in Example 1, except that the layered bimetallic hydroxide is not modified with an organic aerogel, i.e., steps 4) and 5) are omitted. Specifically:

[0078] 1) The calcium carbide slag was dried at 100℃ for 24 hours, crushed in a jaw crusher to an average particle size of 3.5 mm, calcined at 600℃ for 2 hours, and then ground in a planetary ball mill to a D50 of 11.3 μm and a specific surface area of ​​423 m². 2 / kg, obtain calcium carbide slag powder, mix the calcium carbide slag powder with water evenly, centrifuge, retain the supernatant, adjust the concentration, and obtain a calcium source solution with a calcium ion molar concentration of 0.3mol / L for later use;

[0079] 2) High-alumina fly ash was dried at 100℃ for 24 hours, calcined at 600℃ for 2 hours, and then ground in a planetary ball mill to a D50 of 14.5μm and a specific surface area of ​​451m². 2 / kg, high-alumina fly ash powder was obtained. The high-alumina fly ash powder was mixed with a 15wt% sodium hydroxide solution at a mass ratio of 1:5. The mixture was heated to 100℃ and reacted for 2 hours. After the reaction was completed, the mixture was cooled to room temperature and the pH was adjusted to 7. When no precipitate was formed, the mixture was filtered and washed with water 3 times. The precipitate was dissolved in a 20wt% hydrochloric acid solution and the concentration was adjusted to obtain an aluminum source solution with an aluminum ion concentration of 0.1mol / L for later use.

[0080] 3) Take calcium source solution and aluminum source solution, mix them evenly to obtain a mixed solution, and under stirring at 100 r / min, add an equal volume of the mixed solution and a mixed alkaline solution prepared by NaOH and Na2CO3 (where the concentration of NaOH is 0.32 mol / L and the concentration of Na2CO3 is 0.1 mol / L) dropwise into the reactor to carry out a co-precipitation reaction. At the same time, add 0.32 mol / L sodium hydroxide solution to adjust the pH of the mixed system in the reactor to 10.5. After the dropwise addition is completed, control the temperature at 60℃ and react for 6 h. After the reaction is completed, centrifuge, wash the precipitate with water until the pH of the washing solution is 7, dry at 60℃ for 24 h, heat treat at 200℃ for 12 h, grind to an average particle size of 1.8 μm to obtain layered bimetallic hydroxide for later use.

[0081] 4) Add 8g of layered bimetallic hydroxide and 0.3g of polyethylene glycol to 30g of water and ultrasonically disperse for 10min at 400W to form a suspension. Take 30g of Bayer red mud, 40g of fly ash, 5g of desulfurization ash, 10g of blast furnace slag powder, 3g of SSF-1000 series naphthalene-based high-efficiency water-reducing agent and the prepared suspension and add them to a mixer and stir at 150r / min for 60s until uniform. Then seal and let stand for 24h for curing. After curing, add 30g of steel slag and mix evenly to obtain the all-solid waste-based composite backfill material.

[0082] The all-solid waste-based composite backfill materials prepared in the above embodiments and comparative examples were subjected to the following performance tests:

[0083] Chloride ion penetration resistance test: The test was conducted according to the Rapid Chloride Ion Migration Coefficient Method (RCM Method) in GB / T 50082-2009 "Standard for Test Methods of Long-Term and Durability Performance of Ordinary Concrete", using the chloride ion migration coefficient D... RCM Size matters.

[0084] Unconfined compressive strength performance test: The test was conducted in accordance with JTG / TF 20-2015 "Technical Specifications for Construction of Highway Pavement Base Course", with the 7-day unconfined saturated compressive strength of the backfill material as the standard.

[0085] Freeze-thaw resistance test: The test was conducted in accordance with the standard JTG 3441-2024 "Test Procedure for Inorganic Binder Stabilized Materials for Highway Engineering", and the compressive strength retention rate of the backfill material test block after 5 freeze-thaw cycles after 28 days of curing was used as the standard.

[0086] Table 1 Performance Tests of All-Solid Waste-Based Composite Backfill Materials

[0087]

[0088]

[0089] As shown in Table 1, the chloride ion penetration resistance test results of Example 1 and Comparative Example 2 indicate that the organic aerogel-modified layered bimetallic hydroxide prepared in this invention exhibits good tolerance to highly alkaline environments containing red mud, and its chloride ion penetration resistance can be improved without the need for additional aids such as substances that reduce alkalinity. Furthermore, the freeze-thaw resistance test results of Examples 1 and 6 show that when sodium dodecylbenzenesulfonate is used as the dispersant, the chloride ion penetration resistance, strength, and freeze-thaw resistance of the backfill material significantly decrease. This is presumably because, under the action of sodium dodecylbenzenesulfonate, the layered bimetallic hydroxide easily agglomerates, ultimately resulting in a mixture of organic aerogel particles and organic aerogel-modified layered bimetallic hydroxide particles, leading to a weakening of the chloride ion penetration resistance, strength, and freeze-thaw resistance of the backfill material. As can be seen from Example 1 and Comparative Example 1, the layered bimetallic hydroxide prepared in this invention has poor dispersibility in the backfill material system, severely affecting the chloride ion penetration resistance, compressive strength, and freeze-thaw resistance of the backfill material. The advantages of polyethylene glycol-dispersed layered bimetallic hydroxide can only be realized in the backfill material.

[0090] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A composite backfill material based entirely on solid waste, characterized in that, The raw materials comprise the following parts by weight: 30-50 parts Bayer red mud, 20-40 parts fly ash, 5-10 parts desulfurization ash, 5-10 parts blast furnace slag powder, 10-30 parts steel slag, 1-3 parts water-reducing agent, 5-8 parts organic aerogel-modified layered bimetallic hydroxide, 0.1-0.3 parts polyethylene glycol, and 10-30 parts water. The organic aerogel-modified layered bimetallic hydroxide is prepared by a method comprising the following steps: The calcium carbide slag is dried, crushed, calcined, and ground to obtain calcium carbide slag powder. The calcium carbide slag powder is mixed evenly with water, centrifuged, and the supernatant is retained. The calcium ion concentration is adjusted to 0.3-1.6 mol / L to obtain a calcium source solution for later use. High-alumina fly ash is dried, calcined, and ground to obtain high-alumina fly ash powder. The high-alumina fly ash powder is mixed evenly with sodium hydroxide solution, heated to carry out the reaction, cooled to room temperature after the reaction is completed, pH is adjusted, and when no precipitate is formed, it is filtered, washed, and the precipitate is dissolved again. The aluminum ion concentration is adjusted to 0.1-0.8 mol / L to obtain an aluminum source solution for later use. Take calcium source solution and aluminum source solution and mix them evenly to obtain a mixed solution. Under stirring conditions, add an equal volume of the mixed solution and mixed alkaline solution dropwise into the reactor to carry out a co-precipitation reaction. At the same time, add sodium hydroxide solution to adjust the pH of the mixed system in the reactor. After the dropwise addition is completed, control the temperature to carry out the reaction. After the reaction is completed, centrifuge, wash, dry, heat treat, and grind the precipitate to obtain a layered bimetallic hydroxide for later use. The amounts of calcium source solution and aluminum source solution should meet the requirement that the molar ratio of calcium ions to aluminum ions is 2-3:1; Diphenol and formaldehyde were added to water and mixed evenly. The pH was adjusted to form a sol. Layered bimetallic hydroxide and dispersant were added and ultrasonically dispersed evenly. The mixture was then placed in a sealed container to carry out gelation and aging reactions to obtain an organic wet gel. 5) The wet gel was placed in an organic solvent for organic solvent replacement, then dried under supercritical conditions using carbon dioxide as the drying medium, and finally ground to obtain an organic aerogel-modified layered bimetallic hydroxide.

2. The all-solid-waste-based composite backfill material according to claim 1, characterized in that, In step 1), the CaO content of the carbide slag is ≥85%; in step 2), the Al2O3 content of the high-alumina fly ash is ≥50%.

3. The all-solid-waste-based composite backfill material according to claim 1, characterized in that, In step 3), the mixed alkaline solution is a mixed alkaline aqueous solution prepared from NaOH and Na2CO3, wherein the concentration of NaOH is 0.30-2.40 mol / L and the concentration of Na2CO3 is 0.10-0.80 mol / L; the pH is adjusted to 9-11; the stirring speed is 90-120 r / min; the temperature is controlled at 40-60℃; the reaction time is 6-24 h; the heat treatment is heat treatment at 150-200℃ for 6-12 h; and the grinding is grinding to an average particle size of 3-5 μm.

4. The all-solid-waste-based composite backfill material according to claim 1, characterized in that, In step 4), the diphenol is selected from one or a combination of two or more of resorcinol, hydroquinone, and catechol; the dispersant is a nonionic fluorocarbon surfactant selected from DuPont Zonyl. ® One of FSO, FSO-100, FSN-100, and FS-300; the molar ratio of the bisphenol, formaldehyde, and dispersant is 1:2-4:0.001-0.002, and the layered bimetallic hydroxide is 20-25 wt% of the bisphenol.

5. The all-solid-waste-based composite backfill material according to claim 1, characterized in that, In step 4), the pH is adjusted to 8-11 using alkali; the gelation reaction conditions are 70-100℃ for 6-24h; the aging reaction conditions are 40-60℃ for 2-4d; and the ultrasonic dispersion frequency is 20-25kHz for 5-15min.

6. The all-solid-waste-based composite backfill material according to claim 1, characterized in that, In step 5), the organic solvent is selected from one or a combination of two or more of methanol, ethanol, propanol, isopropanol, and acetone; the grinding is grinding until the average particle size is 1.5-2.5 times the average particle size of the layered bimetallic hydroxide.

7. The all-solid-waste-based composite backfill material according to claim 1, characterized in that, The Bayer red mud contains 2-12% Na2O, has a leachate pH of 10-12, and an average particle size ≤3mm; the fly ash contains ≥80% CaO+Al2O3+SiO2, ≤8% SO3, and has a specific surface area of ​​400-500m². 2 / kg, selected from one or a combination of two of circulating fluidized bed fly ash and ordinary pulverized coal boiler fly ash; the desulfurization ash has a CaO content ≥30%, an SO3 content ≥10%, and a specific surface area of ​​400-500m². 2 / kg; the blast furnace slag powder is S95 grade ore powder, with an activity index ≥75% after 7 days, an activity index ≥96% after 28 days, and a specific surface area of ​​400-500 m². 2 / kg, the composition contains ≥90% CaO+Al2O3+SiO2; the steel slag gradation is as follows: steel slag with a particle size <2.36mm accounts for 25-42%, steel slag with a particle size of 2.36mm-4.75mm accounts for 30-40%, and steel slag with a particle size of 4.75mm-9.5mm accounts for 33-45%.

8. The all-solid-waste-based composite backfill material according to claim 1, characterized in that, The water-reducing agent has a water reduction rate of 15-25 wt% and is selected from one or a combination of two of polycarboxylate water-reducing agents and naphthalene-based water-reducing agents; the number average molecular weight of the polyethylene glycol is 4000-6000.

9. A method for preparing the all-solid waste-based composite backfill material according to any one of claims 1-8, characterized in that, Includes the following steps: Organic aerogel-modified layered bimetallic hydroxide and polyethylene glycol were added to water and ultrasonically dispersed to form a suspension. Bayer red mud, fly ash, desulfurization ash, blast furnace slag powder, water-reducing agent and the prepared suspension were added to a mixer and stirred evenly. Then the mixture was sealed and allowed to stand for curing. After curing, steel slag was added and mixed evenly to obtain a solid waste-based composite backfill material.

10. The method for preparing the all-solid waste-based composite backfill material according to claim 9, characterized in that, The ultrasonic power is 200-400W, the ultrasonic time is 10-30 min, and the mass ratio of the organic aerogel-modified layered bimetallic hydroxide to water is 1:3-10.

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