Graphite tailings-saw mud road subbase material and its preparation method and application

Abstract

The present invention relates to the technical field of comprehensive utilization of industrial solid waste, specifically a graphite tailings-saw mud road subbase material and its preparation method and application, including the following components in parts by weight: 40-55 parts of graphite tailings, 45-60 parts of saw mud, 0.5-2 parts of phase change microcapsules, 5-10 parts of slaked lime, 10-20 parts of fly ash, 0.5-1.5 parts of titanium gypsum, 0.5-2 parts of steel slag powder, 5-15 parts of water and 0.05-0.2 parts of dispersant; the 7d unconfined compressive strength range of the graphite tailings-saw mud road subbase material is 2.64-3.87MPa, and the compressive strength loss rate (BDR) range is 82.1%-86.2%. By using titanium gypsum and steel slag powder, a gelling material with micro-expansion properties, to solidify the graphite tailings-saw mud, the shrinkage and temperature shrinkage properties of the subbase material are optimized, and the antifreeze ability of the subbase material is improved by adding phase change microcapsules.

Description

Technical Field

[0001] The invention relates to the technical field of comprehensive utilization of industrial solid waste, in particular to a graphite tailings-sawdust road subbase material and a preparation method and application thereof. Background Art

[0002] Graphite tailings are industrial slag discharged during the graphite production process. To date, the cumulative amount of graphite tailings accumulated in my country has exceeded 100 million tons. The storage of graphite tailings occupies a large amount of land. Furthermore, due to its fine particle size, graphite tailings weather severely during long-term storage, easily generating secondary dust and polluting the atmosphere. Furthermore, the pH value of graphite tailings is only 3-4, and the dissolution of acidic substances can easily contaminate groundwater and cause soil acidification.

[0003] Sawdust is the waste product of granite cutting, including stone dust. Its primary minerals are feldspar and quartz, along with high levels of oxides such as SiO2, Al2O3, Na2O, and K2O. During the stone processing process, a water solution containing lubricants and other additives is used to cool the stone. Coagulants and flocculants are added to the stone dust in a sedimentation tank to allow it to settle. The resulting precipitate is known as sawdust.

[0004] Industrial solid wastes like graphite tailings and sawdust are technically challenging to reuse due to additives added during production and their inherent low reactivity. While some research is exploring the use of these wastes to replace a small amount of fine aggregate in concrete production, these wastes often have drawbacks, such as limited replacement of fine aggregate.

[0005] Some researchers have conducted relevant research on the use of graphite tailings to prepare highway subbase. For example, the paper “Graphite tailings used as highway subbase” (Fang Jianguo, Yao Zhanyong, Su Gongcan, et al. Journal of Shandong University, 2003, (5): 562-567) disclosed the feasibility of using cement-stabilized graphite tailings as highway pavement subbase. The experiment verified that when cement and graphite tailings were used to prepare the subbase material, the maximum shrinkage strain reached 1657-2127×10 -6 Even with watering, the seven-day maximum shrinkage strain is high, posing risks for its use as a subgrade material. During the flotation process, flotation agents are added to graphite ore, resulting in a low pH value in the graphite tailings after plate and frame filter pressing. Furthermore, the graphite tailings have poor plasticity and can be classified as "tailings sand." Therefore, the large amount of traditional cement binder required for curing results in poor crack resistance and frost resistance.

[0006] Currently, there is little research on the application of graphite tailings-sawdust combination as roadbed materials. However, when it is used as a pavement base material, based on existing research, it has the following inherent defects of stabilized fine-grained materials: the drying shrinkage and temperature shrinkage are larger than those of commonly used base materials (cement-stabilized crushed stone), resulting in the inability to guarantee the strength of the pavement base; the water absorption rate is large, and the frost resistance and erosion resistance are insufficient, which can easily cause asphalt pavement cracking, slurry pumping and other diseases.

[0007] Therefore, ensuring the strength of graphite tailings-saw mud road base materials, reducing water absorption and improving their frost resistance and erosion resistance are the prerequisites for the widespread application of graphite tailings-saw mud roadbed materials. Summary of the Invention

[0008] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and provide a road subbase material based on graphite tailings-saw mud, a preparation method and application thereof. By using a gelling material with micro-expansion properties to solidify the graphite tailings-saw mud, the drying shrinkage and temperature shrinkage properties of the subbase material are optimized, and at the same time, the anti-freezing ability of the subbase material is improved by adding phase change microcapsules.

[0009] In order to achieve the above technical effects, the present invention adopts the following technical solutions:

[0010] A graphite tailings-sawdust road subbase material, comprising the following components in parts by weight: 40-55 parts of graphite tailings, 45-60 parts of sawdust, 0.5-2 parts of phase change microcapsules, 5-10 parts of slaked lime, 10-20 parts of fly ash, 0.5-1.5 parts of titanium gypsum, 0.5-2 parts of steel slag powder, 5-15 parts of water, and 0.05-0.2 parts of a dispersant;

[0011] The 7d unconfined compressive strength of the graphite tailings-saw mud road subbase material ranges from 2.64 to 3.87 MPa, and the compressive strength loss rate (BDR) ranges from 82.1% to 86.2%.

[0012] The graphite tailings-saw mud road subbase material provided by the present invention has the following action mechanisms:

[0013] (1) The weight ratio of graphite tailings and saw mud to the base material, i.e., the replacement amount of fine aggregate, is much greater than that of the existing technology. At the same time, taking advantage of the large difference in particle size between graphite tailings and saw mud, a method of close packing of multi-scale solid particles is proposed to reasonably determine the optimal blending ratio of graphite tailings and saw mud, which effectively ensures the strength of the obtained base material, i.e., significantly improves the BDR range;

[0014] (2) In order to address the shortcomings of large shrinkage and temperature shrinkage when cement-based inorganic gelling materials stabilize fine-grained materials, industrial solid waste titanium gypsum and steel slag are used. The AFt produced by the volcanic ash reaction product of CaSO4·2H2O in titanium gypsum and lime fly ash is used to inhibit the shrinkage of the base material; the shrinkage of the subbase material is compensated by the slow hydration reaction rate and volume expansion of f-CaO and MgO in steel slag;

[0015] (3) The Fe(OH)3 and Al(OH)3 colloids contained in titanium gypsum are used to adsorb heavy metal ions in graphite tailings.

[0016] Preferably, the phase-change microcapsules include a shell and a core material, the shell is made of silica aerogel, the core material is made of polyethylene glycol, and the particle size of the phase-change microcapsules is in the range of 15-25 μm.

[0017] The main functions of phase change microcapsules are: (1) Phase change materials undergo phase change and release a certain amount of heat during the temperature drop in winter, which improves the freeze-thaw resistance of graphite tailings-saw mud roadbed materials; and phase change microcapsules have a low thermal conductivity, which delays the overall temperature drop of roadbed materials; (2) When the temperature is high in summer, phase change materials can absorb part of the heat, avoiding temperature shrinkage caused by excessively fast temperature rise rate, thereby reducing thermal shrinkage cracks in the road base; (3) SiO2 aerogel shell material is conducive to the volcanic ash reaction and hydration reaction process in the entire reaction system; (4) Even if a small amount of phase change microcapsules are damaged, the core material polyethylene glycol has little effect on the volcanic ash reaction; (5) Phase change microcapsules also provide nucleation sites for the hydration of C2S and C3S in steel slag powder to a certain extent, which is conducive to the hydration reaction process.

[0018] Phase change microcapsules with SiO2 aerogel as shell material and polyethylene glycol as core material greatly improve the freeze-thaw resistance of roadbed materials. The microcapsules supplement the solid accumulation of nanoscale particles, and SiO2 aerogel is conducive to the volcanic ash reaction and hydration reaction processes in the entire reaction system.

[0019] Preferably, the preparation method of the phase change microcapsules comprises the following steps:

[0020] 0.5-0.8 parts of polysorbate 80 and 0.6-0.8 parts of Span-80 surfactant were uniformly mixed to form solution A. 10-15 parts of polyethylene glycol were dissolved in 100 parts of toluene to form solution B. Solution A was then added to solution B and stirred in a 50°C water bath at 400-700 rpm for 30 minutes to form a stable emulsion. 0.1-0.3 parts of acetic acid and 10-13 parts of ethyl orthosilicate were then added to the stable emulsion. The temperature was raised to 55°C and the polymerization reaction was continued for 3 hours to obtain the product. Finally, the product was washed with anhydrous ethanol 2-3 times, then rinsed with deionized water, and filtered to obtain the phase change microcapsules.

[0021] Preferably, the particle size of the graphite tailings ranges from 0 to 9.5 mm, wherein particles smaller than 0.3 mm account for less than 30%; and the particle size of the saw mud material is ≤0.3 mm.

[0022] The main functions of using graphite tailings and sawdust of different particle sizes are: (1) to use the different particle sizes of the two industrial solid wastes to determine their reasonable dosage to achieve close stacking of multi-scale solid particles and ensure their strength; (2) to regulate the plasticity index of the two industrial solid wastes to make them easier to construct.

[0023] Preferably, the grade of slaked lime is national standard Grade II or above. The main functions of lime are: (1) reacting with fly ash to form hydration products such as AFt and CASH gel, which provide strength; (2) using slaked lime to increase the alkalinity of the reaction system, stimulate the potential activity of steel slag, and improve strength; (3) some Ca(OH)2 refines the pore structure of the compacted base material through carbonization reaction, thereby improving the durability of graphite-saw mud.

[0024] Preferably, the fly ash is Grade II ash or above. The main functions of fly ash are: (1) providing the silicon and aluminum minerals required for the pozzolanic reaction, thereby improving strength; (2) the fine particle size of fly ash can adjust the liquid and plastic limits of the graphite-sawdust mixture, facilitating rolling and compaction during construction.

[0025] Preferably, the content of CaSO4·2H2O in the titanium gypsum is ≥70wt%. The main functions of titanium gypsum are as follows: (1) CaSO4·2H2O in titanium gypsum can react with the hydration products of lime and fly ash to produce ettringite (AFt), and at the same time react with C2S and C3S in steel slag powder to generate AFt, which promotes the volume expansion of AFt and prevents the shrinkage caused by cement hydration to a certain extent; (2) Titanium gypsum contains a certain amount of Fe(OH)3 and Al(OH)3 colloids, which can adsorb heavy metal ions contained in graphite tailings and sawdust to a certain extent; (3) Titanium gypsum can slow down the hydration reaction process of cementitious materials, prolong the initial and final setting time of cementitious materials, and help slow down the hydration and hardening of base materials during construction, thereby affecting the compaction degree.

[0026] Preferably, the steel slag powder has a fineness of ≥300 mesh. Steel slag powder contains a certain amount of CaO, MgO, C3S, C2S, and active silica-alumina minerals, with the CaO content being 30-40%, the MgO content being 3-5%, the C3S content being 20-25%, the C2S content being 35-45%, and the balance being active silica-alumina minerals. When steel slag powder is used in cement concrete, the delayed hydration of CaO can cause cracking in the concrete. However, when it is used to solidify graphite tailings-sawdust materials as a base layer, it can play the following roles: (1) Since CaO hydrates slowly after adding water, its volume will expand after hydration to generate Ca(OH)2. A small amount of CaO will have a certain compensatory effect on the shrinkage and temperature shrinkage of the fine-grained materials stabilized by inorganic cementitious materials; but excessive CaO will cause expansion and cracking of the base layer. Therefore, the optimal addition range of steel slag powder should be controlled within 0.5-2 parts; (2) The Si-O and Al-O dense glass bodies on the surface of the steel slag powder after grinding are destroyed, forming C3S and C2S with gelling activity. After contacting with water during the preparation process, a hydration reaction occurs, which fully activates its reaction activity and provides strength for the base layer material.

[0027] Preferably, the dispersant is composed of sulfonated oil, sodium tripolyphosphate, and sodium pyrophosphate, and the mass ratio of the components is 75-85%: 5-10%: 10-15%.

[0028] The main functions of the dispersant are: (1) the dispersant can reduce the ζ potential of the surface of the phase change microcapsules, reduce the surface energy of the particles, avoid the agglomeration of the phase change microcapsules in the solution, and make them evenly distributed in the solution; (2) the sulfonated oil has a "hydrophilic head" and a "hydrophobic tail". The "hydrophilic head" can be adsorbed on the surface of the graphite tailings-saw mud, and the "hydrophobic tail" blocks the intrusion of water outward, thereby improving the water erosion resistance of the base material; the sulfonated oil has the characteristics of one end being hydrophilic and the other end being hydrophobic. After being added to the base material, the hydrophilic head is adsorbed on the surface of the graphite-saw mud particles. The outward-facing hydrophobic tail reduces the water absorption rate of the base material, thereby improving the base material's resistance to water erosion; (3) Sodium tripolyphosphate has the function of chelating metal ions, and sodium pyrophosphate has the function of complexing heavy metal ions, which has a solidifying effect on the metal ions in the tailings; (4) Since the dispersant also complexes the calcium ions and aluminum ions dissolved in the pore solution of the cementitious material, the ion concentration in the pore solution is reduced, which further promotes the dissolution and hydration of the cementitious material (C2S, C3S, etc.), which is beneficial to improving the early strength of the solid waste pavement base.

[0029] The present invention also provides a method for preparing the graphite tailings-saw mud road subbase material, comprising the following steps:

[0030] S1. Add a dispersant to the mixing water and stir for 2-5 minutes to prepare dispersion A. Adding a dispersant can prevent the agglomeration of the phase change microcapsules and facilitate their dispersion in the aqueous solution.

[0031] S2. Add phase change microcapsules to dispersion A and disperse using an ultrasonic disperser for 5-10 minutes, followed by stirring for 2-5 minutes to obtain solution B. Ultrasonic dispersion can better distribute the microcapsule material in water and avoid flocculation and sedimentation of the microcapsule material.

[0032] S3. Sawdust, graphite tailings, slaked lime, fly ash, titanium gypsum, and steel slag powder are mixed evenly, and then solution B is added and stirring is continued for 1.5-3 minutes to obtain a solidified graphite tailings-sawdust roadbed material.

[0033] In the preparation method provided by the present invention, dispersants, ultrasonic dispersion and other means are used to make the microcapsule material more uniformly dispersed, thereby avoiding the occurrence of microcapsule material agglomeration and further ensuring the microcapsule material's promoting effect on the volcanic ash reaction and hydration reaction in the reaction system.

[0034] The present invention also provides an application of the graphite tailings-saw mud road subbase material, which is specifically applied to the subbase of secondary and lower-level highways.

[0035] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0036] 1. The present invention provides an antifreeze graphite tailings-sawdust road subbase material suitable for cold regions. The material has a large fine aggregate replacement capacity, maintains strength while exhibiting micro-expansion characteristics, and compensates for shrinkage caused by drying and temperature changes. To address the shortcomings of inorganic gelling materials in stabilizing fine-grained materials, which suffer from large shrinkage due to drying and temperature changes, the material utilizes industrial solid wastes such as titanium gypsum and steel slag. The material generates AFt from the pozzolanic reaction product of CaSO4·2H2O in the titanium gypsum and lime fly ash, thereby inhibiting its shrinkage. The material also utilizes the slow hydration reaction rate and volume expansion of f-CaO and MgO in the steel slag to compensate for the shrinkage of the subbase material. Furthermore, the incorporation of phase change microcapsules significantly improves the antifreeze ability of the roadbed, making the material particularly suitable for the construction of road subbases in cold regions of northern my country.

[0037] 2. The antifreeze graphite tailings-saw mud road subbase material proposed in the present invention can be used to replace the commonly used road base material cement-stabilized gravel, greatly alleviating the problem of sand and gravel shortage in the engineering construction process. At the same time, the Fe(OH)3 and Al(OH)3 colloids contained in the titanium gypsum are used to adsorb heavy metal ions in the graphite tailings, which is beneficial to protecting the ecological environment.

[0038] 3. In the preparation method provided by the present invention, dispersants, ultrasonic dispersion and other means are used to make the microcapsule material more uniformly dispersed, thereby avoiding the occurrence of microcapsule material agglomeration and further ensuring the microcapsule material's promoting effect on the volcanic ash reaction and hydration reaction in the reaction system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the base material after freeze-thaw obtained in Example 3;

[0040] Figure 2 This is a schematic diagram of the base material prepared in Comparative Example 6 after freeze-thaw. DETAILED DESCRIPTION

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0042] In the following examples and comparative examples, the graphite tailings were sourced from a graphite tailings mountain accumulated in Pingdu City, Qingdao City, Shandong Province, and the saw mud was sourced from waste saw mud accumulated in Pingdu City; the fly ash was Class II ash produced by the Jinan North Suburb Thermal Power Plant; the slaked lime was Class III ash produced by Jinan Baode Metallurgical Limestone Co., Ltd.; the aluminum salt, magnesium salt, and calcium salt were all purchased from Sinopharm Chemical Reagent Co., Ltd. and were analytically pure; the sulfonated oil was sodium castor oil sulfonate purchased from Lusen Chemical in Linyi, Shandong Province; and sodium tripolyphosphate and sodium pyrophosphate were both purchased from Chenyang Chemical in Weifang, Shandong Province.

[0043] The experiments were conducted in accordance with the "Test Procedure for Stabilized Materials with Inorganic Binders for Highway Engineering" (JTG E51-2009). The strengths listed below are all seven-day unconfined compressive strengths. The freeze-thaw test protocol was based on the aforementioned standard. The compressive strength loss rate (BDR) is the ratio of the compressive strengths of the specimens before and after freeze-thaw cycles. The 7-day unconfined compressive strength is calculated by curing the specimens in a standard curing chamber for six days, with the final day being immersed in water. Drying shrinkage is based on the shrinkage strain measured over 30 days of continuous monitoring.

[0044] The dissolution of heavy metal ions was carried out in accordance with the “Determination of Leachable Heavy Metals in Cement Mortar” (GB / T 30810-2014), and the heavy metal ions measured were hexavalent cadmium ions and copper ions.

[0045] Example 1

[0046] A graphite tailings-sawdust road subbase material is composed of the following components in the following proportions by mass: 45 parts of sawdust, 55 parts of graphite tailings, 5 parts of slaked lime, 10 parts of fly ash, 0.5 parts of titanium gypsum, 0.5 parts of steel slag powder, 0.5 parts of phase change microcapsules, 0.05 parts of dispersant, and 7 parts of water.

[0047] In this embodiment, the particle size range of the graphite tailings is 0-9.5 mm, of which particles less than 0.3 mm account for 15 wt%; the particle size range of the saw mud material is <3 mm, the CaSO4·2H2O content in the titanium gypsum is 75 wt%, the fineness of the steel slag powder is 350 mesh, the CaO content in the steel slag powder is 40 wt%, the MgO content is 3 wt%, the C3S content is 25 wt%, the C2S content is 35 wt%, and the balance is active silica-alumina minerals; the shell of the phase change microcapsule is SiO2 aerogel, the core material is polyethylene glycol, and the particle size range of the phase change microcapsule is 15 μm; the sulfonated oil in the dispersant: sodium tripolyphosphate: sodium pyrophosphate = 75%: 10%: 15% (mass ratio).

[0048] In this embodiment, the preparation method of phase change microcapsules is as follows:

[0049] Solution A was formed by uniformly mixing 0.5 parts of polysorbate 80 and 0.8 parts of Span-80 surfactant. Solution B was formed by dissolving 10 parts of polyethylene glycol in 100 parts of toluene. Solution A was then added to Solution B and stirred at 700 rpm in a 50°C water bath for 30 minutes to form a stable emulsion. To this emulsion, 0.1 parts of acetic acid and 13 parts of ethyl orthosilicate were added, and the mixture was heated to 55°C for polymerization for 3 hours to obtain the product. Finally, the product was washed twice with anhydrous ethanol and then rinsed with deionized water, and filtered to obtain the phase change microcapsules.

[0050] The specific steps of the preparation method of the above-mentioned graphite tailings-saw mud road subbase material are as follows:

[0051] S1. Add 0.5 g of dispersant to 70 mL of mixing water and stir for 2 min to prepare dispersion A;

[0052] S2. 5 g of phase change microcapsules were added to dispersion A and dispersed using an ultrasonic disperser for 5 min, followed by stirring for 2 min to obtain solution B;

[0053] S3. After 450 g of sawdust, 550 g of graphite tailings, 50 g of slaked lime, 100 g of fly ash, 5 g of titanium gypsum and 5 g of steel slag powder were mixed evenly, solution B was added and stirring was continued for 1.5 min to obtain a solidified graphite tailings-sawdust roadbed material.

[0054] Example 2

[0055] A graphite tailings-sawdust road subbase material is composed of the following components in the following proportions by mass: 60 parts of sawdust, 40 parts of graphite tailings, 10 parts of slaked lime, 20 parts of fly ash, 1.5 parts of titanium gypsum, 2 parts of steel slag powder, 2 parts of phase change microcapsules, 0.2 parts of a dispersant, and 15 parts of water.

[0056] In this embodiment, the particle size range of the graphite tailings is 0-9.5 mm, of which particles less than 0.15 mm account for 15 wt%; the particle size range of the saw mud material is <3 mm, the CaSO4·2H2O content in the titanium gypsum is 80 wt%, the fineness of the steel slag powder is 400 mesh, the CaO content in the steel slag powder is 30 wt%, the MgO content is 5 wt%, the C3S content is 20 wt%, the C2S content is 40 wt%, and the balance is active silica-alumina minerals; the shell of the phase change microcapsule is SiO2 aerogel, the core material is polyethylene glycol, and the particle size range of the phase change microcapsule is 25 μm; the sulfonated oil in the dispersant: sodium tripolyphosphate: sodium pyrophosphate = 85%:5%:10% (mass ratio).

[0057] In this embodiment, the preparation method of phase change microcapsules is as follows:

[0058] Solution A was formed by uniformly mixing 0.8 parts of polysorbate 80 and 0.6 parts of Span-80 surfactant. Solution B was formed by dissolving 15 parts of polyethylene glycol in 100 parts of toluene. Solution A was then added to Solution B and stirred at 400 rpm in a 50°C water bath for 30 minutes to form a stable emulsion. To this emulsion, 0.3 parts of acetic acid and 10 parts of ethyl orthosilicate were added, and the temperature was raised to 55°C for polymerization for 3 hours to obtain the product. Finally, the product was washed three times with anhydrous ethanol and then rinsed with deionized water. Phase change microcapsules were then filtered to obtain the product.

[0059] The specific steps of the preparation method of the above-mentioned graphite tailings-saw mud road subbase material are as follows:

[0060] S1. Add 2 g of dispersant to 150 mL of mixing water and stir for 5 min to prepare dispersion A;

[0061] S2. 20 g of phase change microcapsules were added to dispersion A and dispersed using an ultrasonic disperser for 10 min, followed by stirring for 5 min to obtain solution B;

[0062] S3. 600 g of sawdust, 400 g of graphite tailings, 100 g of slaked lime, 200 g of fly ash, 15 g of titanium gypsum and 20 g of steel slag powder were mixed evenly, and then solution B was added and stirred for 3 min to obtain a solidified graphite tailings-sawdust roadbed material.

[0063] Example 3

[0064] A graphite tailings-sawdust road subbase material is composed of the following components in the following proportions by mass: 50 parts of sawdust, 50 parts of graphite tailings, 7 parts of slaked lime, 15 parts of fly ash, 1 part of titanium gypsum, 1 part of steel slag powder, 1 part of phase change microcapsules, 0.1 part of dispersant, and 10 parts of water.

[0065] In this embodiment, the particle size range of the graphite tailings is 0-9.5 mm, of which particles less than 0.15 mm account for 28 wt%; the particle size range of the saw mud material is <3 mm, the CaSO4·2H2O content in the titanium gypsum is 70 wt%, the fineness of the steel slag powder is 300 mesh, the CaO content in the steel slag powder is 32 wt%, the MgO content is 4 wt%, the C3S content is 21 wt%, the C2S content is 40 wt%, and the remainder is active silica-alumina minerals; the shell of the phase change microcapsule is SiO2 aerogel, the core material is polyethylene glycol, the particle size range of the phase change microcapsule is 20 μm, and the sulfonated oil: sodium tripolyphosphate: sodium pyrophosphate in the dispersant is 80%:8%:12% (mass ratio).

[0066] In this embodiment, the preparation method of phase change microcapsules is as follows:

[0067] Solution A was formed by uniformly mixing 0.7 parts of polysorbate 80 and 0.7 parts of Span-80 surfactant. Solution B was formed by dissolving 13 parts of polyethylene glycol in 100 parts of toluene. Solution A was then added to Solution B and stirred at 580 rpm in a 50°C water bath for 30 minutes to form a stable emulsion. To this emulsion, 0.2 parts of acetic acid and 11.5 parts of tetraethyl orthosilicate were added, and the mixture was heated to 55°C for polymerization for 3 hours to obtain the product. Finally, the product was washed three times with anhydrous ethanol and then rinsed with deionized water. Phase change microcapsules were then filtered to obtain the product.

[0068] The specific steps of the preparation method of the above-mentioned graphite tailings-saw mud road subbase material are as follows:

[0069] S1. Add 1 g of dispersant to 100 mL of mixing water and stir for 7.5 min to prepare dispersion A;

[0070] S2. 10 g of phase change microcapsules were added to dispersion A and dispersed using an ultrasonic disperser for 8 min, followed by stirring for 3.5 min to obtain solution B;

[0071] S3. 500 g of saw mud, 500 g of graphite tailings, 70 g of slaked lime, 150 g of fly ash, 10 g of titanium gypsum and 10 g of steel slag powder were mixed evenly, and then solution B was added and stirred for 2.5 min to obtain a solidified graphite tailings-saw mud roadbed material.

[0072] Comparative Example 1

[0073] A graphite tailings-sawdust road subbase material. In this comparative example, for comparison with traditional "fly ash-lime stabilized fine-grained material", lime fly ash was used to prepare test specimens in accordance with the "Test Procedure for Inorganic Binder Stabilized Materials for Highway Engineering" (JTG E51-2009). The seven-day unconfined compressive strength and freeze-thaw index of the stabilized soil were measured.

[0074] 50 parts of sawdust, 50 parts of graphite tailings, 10 parts of slaked lime, and 20 parts of fly ash.

[0075] The preparation method of the graphite tailings-saw mud road subbase material is the same as that in Example 3.

[0076] Comparative Example 2

[0077] A graphite tailings-saw mud road subbase material. In this comparative example, in order to clarify the effect of the dosage of saw mud and graphite tailings on the close packing of multi-scale solid particles, the material is composed of the following components in the following mass proportions: 20 parts of saw mud, 80 parts of graphite tailings, 7 parts of slaked lime, 15 parts of fly ash, 1 part of steel slag powder, 1 part of phase change microcapsules, 0.1 part of dispersant, and 10 parts of water.

[0078] The preparation method of the graphite tailings-saw mud road subbase material and the preparation method of the phase change microcapsules are the same as those in Example 3.

[0079] Comparative Example 3

[0080] A graphite tailings-saw mud road subbase material. In this comparative example, in order to clarify the role of titanium gypsum, the material is composed of the following components in the following mass proportions: 50 parts of saw mud, 50 parts of graphite tailings, 7 parts of slaked lime, 15 parts of fly ash, 1 part of steel slag powder, 1 part of phase change microcapsules, 0.1 part of dispersant, and 10 parts of water.

[0081] The preparation method of the graphite tailings-saw mud road subbase material and the preparation method of the phase change microcapsules are the same as those in Example 3.

[0082] Comparative Example 4

[0083] A graphite tailings-saw mud road subbase material. In this comparative example, in order to clarify the role of steel slag powder, the material is composed of the following components in the following mass proportions: 50 parts of saw mud, 50 parts of graphite tailings, 7 parts of slaked lime, 15 parts of fly ash, 1 part of titanium gypsum, 1 part of phase change microcapsules, 0.1 part of dispersant, and 10 parts of water.

[0084] The preparation method of the graphite tailings-saw mud road subbase material and the preparation method of the phase change microcapsules are the same as those in Example 3.

[0085] Comparative Example 5

[0086] A graphite tailings-sawdust road subbase material. In this comparative example, in order to clarify the effect of phase change microcapsules, the material is composed of the following components in the following mass proportions: 50 parts of sawdust, 50 parts of graphite tailings, 7 parts of slaked lime, 15 parts of fly ash, 1 part of titanium gypsum, 1 part of steel slag powder, and 10 parts of water.

[0087] The preparation method of the graphite tailings-saw mud road subbase material is the same as that in Example 3.

[0088] Comparative Example 6

[0089] A graphite tailings-saw mud road subbase material. In this comparative example, in order to clarify the role of the dispersant, the material is composed of the following components in the following mass proportions: 50 parts of saw mud, 50 parts of graphite tailings, 7 parts of slaked lime, 15 parts of fly ash, 1 part of titanium gypsum, 1 part of steel slag powder, 1 part of phase change microcapsules, and 10 parts of water.

[0090] The preparation method of the graphite tailings-saw mud road subbase material and the preparation method of the phase change microcapsules are the same as those in Example 3.

[0091] Comparative Example 7

[0092] A graphite tailings-saw mud road subbase material. In this comparative example, in order to clarify the effect of the preparation method of the graphite tailings-saw mud road subbase material, the material ratios are the same as those in Example 3. Unlike Example 3, the preparation method is to directly mix the various raw materials and then prepare test pieces for experimentation.

[0093] Comparative Examples 8-10

[0094] A graphite tailings-sawdust road subbase material is composed of the following components in the following proportions by mass to clarify the role of a dispersant composition ratio: 50 parts of sawdust, 50 parts of graphite tailings, 7 parts of slaked lime, 15 parts of fly ash, 1 part of titanium gypsum, 1 part of steel slag powder, 1 part of phase change microcapsules, 0.1 part of a dispersant, and 10 parts of water.

[0095] The difference from Example 3 is that the dispersant composition is sulfonated oil: sodium tripolyphosphate = 80%: 20% (mass ratio), Comparative Example 8; sulfonated oil: sodium pyrophosphate = 80%: 20% (mass ratio), Comparative Example 9; sodium tripolyphosphate: sodium pyrophosphate = 40%: 60% (mass ratio), Comparative Example 10.

[0096] The preparation method of the graphite tailings-saw mud road subbase material and the preparation method of the phase change microcapsules are the same as those in Example 3.

[0097] Table 1 Weight ratio of examples and comparative examples

[0098] Serial number Sawdust graphite tailings Stone-dissolving fly ash Titanium plaster Steel slag powder Phase change microgel dispersants water Example 1 45 55 5 10 0.5 0.5 0.5 0.05 7 Example 2 60 40 10 20 1.5 2 2 0.2 15 Example 3 50 50 7 15 1 1 1 0.1 10 Comparative Example 1 50 50 10 20 — — — — 10 Comparative Example 2 20 80 7 15 1 1 1 0.1 10 Comparative Example 3 50 50 7 15 — 1 1 0.1 10 Comparative Example 4 50 50 7 15 1 — 1 0.1 10 Comparative Example 5 50 50 7 15 1 1 — 0.1 10 Comparative Example 6 50 50 7 15 1 1 1 — 10 Comparative Example 7 50 50 7 15 1 1 1 0.1 10 Comparative Example 8 50 50 7 15 1 1 1 0.1 10 Comparative Example 9 50 50 7 15 1 1 1 0.1 10 Comparative Example 10 50 50 7 15 1 1 1 0.1 10

[0099] Table 2 Experimental results

[0100]

[0101]

[0102] From the data in Table 2, we can see that

[0103] The 7d unconfined compressive strength of Examples 1-3 is all greater than 1.1 MPa, which meets the strength requirement of "Highway Asphalt Pavement Design Code" JTGD50-2017 that the strength of fly ash stabilized fine-grained material is not less than 1.1 MPa when used as the base layer. When only fly ash solidified iron tailings (Comparative Example 1) is used, the strength index requirement cannot be met.

[0104] Compared with Example 3, the strength of Comparative Example 2 cannot meet the strength standard, and its BDR value is significantly smaller, indicating poor antifreeze performance. Comparative Example 2 illustrates the effect of reasonable and tight stacking of solid waste particles on the performance of the sample. At the same time, the copper content in Comparative Example 2 is measured to be higher. This is because (1) heavy metal ions are mainly present in graphite tailings, and an increase in the proportion of graphite tailings will increase the content of heavy metal ions; (2) due to the increase in the proportion of graphite tailings, the pores of the specimen increase during the molding process, and the most compact stacking state cannot be achieved, which also affects the contact area of ​​lime and fly ash, resulting in a decrease in the production of CSH gel and a decrease in the adsorption capacity of heavy metal ions.

[0105] Comparative Examples 3 and 4 showed significantly greater 30-day drying shrinkage strain values ​​compared to the Example, demonstrating that titanium gypsum and steel slag powder exhibit certain micro-expansion properties, compensating for the drying shrinkage of the roadbed material. Furthermore, the amount of heavy metal ion dissolution in Comparative Example 3 was significantly greater than that in the other samples, indicating that the Fe(OH)3 and Al(OH)3 colloids in the titanium gypsum adsorb heavy metal ions in the tailings particles. Titanium gypsum and steel slag powder can also participate in the hydration reaction, increasing the number of hydration products and improving the strength of the roadbed material.

[0106] The frost resistance of Comparative Example 5 significantly decreased compared to the Example, demonstrating the significant positive effect of phase-change microcapsules on the frost resistance of roadbed materials. Phase-change microcapsules undergo a phase change during temperature fluctuations, reducing the roadbed material's temperature sensitivity and thus improving its frost resistance. Furthermore, the nano-SiO2 shells can, to a certain extent, promote the volcanic ash reaction of the cementitious material, thereby increasing the strength of the sample.

[0107] Combined with the data in Table 2 and Figure 1 and Figure 2 It can be seen that the base material prepared in Comparative Example 6 showed obvious cracking after the freeze-thaw experiment, and the antifreeze performance decreased, indicating that the dispersant can make the phase change microcapsules better dispersed evenly in the roadbed material, thereby improving the antifreeze ability of the roadbed material.

[0108] Comparative Example 7 shows that the preparation method has a positive effect on the dispersion of phase change microcapsule materials. The ultrasonic dispersion has a synergistic effect with the dispersant, and the phase change microcapsules can be evenly dispersed.

[0109] Compared with Example 3, Comparative Examples 8-10 showed decreased heavy metal ion leaching and freeze-thaw resistance due to different dispersant compositions. Because sodium pyrophosphate and sodium tripolyphosphate chelate and complex heavy metal ions, the heavy metal ion content increased. Sodium pyrophosphate and sodium tripolyphosphate also have the function of dispersing heavy metal ions, so the phase change microcapsules were not dispersed promptly and effectively, resulting in decreased freeze-thaw resistance. The absence of sulfonated oil can lead to increased water absorption, thus affecting the freeze-thaw resistance.

Claims

1. A graphite tailings-saw mud road subbase material, characterized in that: The invention comprises the following components in parts by weight: 40-55 parts of graphite tailings, 45-60 parts of saw mud, 0.5-2 parts of phase change microcapsules, 5-10 parts of slaked lime, 10-20 parts of fly ash, 0.5-1.5 parts of titanium gypsum, 0.5-2 parts of steel slag powder, 5-15 parts of water and 0.05-0.2 parts of dispersant; The 7d unconfined compressive strength of the graphite tailings-sawdust road subbase material ranges from 2.64 to 3.87 MPa, and the compressive strength loss rate ranges from 82.1% to 86.2%; The dispersant consists of sulfonated oil, sodium tripolyphosphate and sodium pyrophosphate, and the mass ratio of the components is 75-85%: 5-10%: 10-15%.

2. The graphite tailings-saw mud road subbase material according to claim 1, characterized in that: The phase-change microcapsule comprises a shell and a core material, wherein the shell is made of silicon dioxide aerogel, and the core material is made of polyethylene glycol. The particle size of the phase-change microcapsule ranges from 15 to 25 μm.

3. The graphite tailings-saw mud road subbase material according to claim 1, characterized in that: The particle size of the graphite tailings ranges from 0 to 9.5 mm, of which particles smaller than 0.3 mm account for less than 30%; the particle size of the saw mud material is ≤0.3 mm.

4. The graphite tailings-saw mud road subbase material according to claim 1, characterized in that: The grade of the slaked lime is national standard grade II ash or above; the grade of the fly ash is national standard grade II ash or above.

5. The graphite tailings-saw mud road subbase material according to claim 1, characterized in that: The content of CaSO4·2H2O in the titanium gypsum is ≥70wt%.

6. The graphite tailings-saw mud road subbase material according to claim 1, characterized in that: The steel slag powder has a fineness of ≥300 mesh; the steel slag powder contains CaO, MgO, C3S, C2S and active silica-alumina minerals, with the CaO content being 30-40%, the MgO content being 3-5%, the C3S content being 20-25%, the C2S content being 35-45%, and the balance being active silica-alumina minerals.

7. A method for preparing the graphite tailings-saw mud road subbase material according to any one of claims 1 to 6, comprising the following steps: S1. Add dispersant to the mixing water and stir for 2-5 minutes to prepare dispersion A; S2. Phase change microcapsules were added to dispersion A and dispersed using an ultrasonic disperser for 5-10 min, followed by stirring for 2-5 min to obtain solution B; S3. Sawdust, graphite tailings, slaked lime, fly ash, titanium gypsum, and steel slag powder are mixed evenly, and then solution B is added and stirring is continued for 1.5-3 minutes to obtain a solidified graphite tailings-sawdust roadbed material.

8. The preparation method according to claim 7, wherein In step S2, the preparation method of phase change microcapsules is as follows: 0.5-0.8 parts of polysorbate 80 and 0.6-0.8 parts of Span-80 surfactant are uniformly mixed to form solution A, and 10-15 parts of polyethylene glycol are dissolved in 100 parts of toluene solution to form solution B; solution A is then added to solution B and stirred at a speed of 400-700 r / min for 30 minutes in a 50°C water bath to form a stable emulsion; 0.1-0.3 parts of acetic acid and 10-13 parts of ethyl orthosilicate are then added to the stable emulsion, the temperature is raised to 55°C, and the polymerization reaction is carried out for 3 hours to obtain the product; finally, the product is washed with anhydrous ethanol 2-3 times, then rinsed with deionized water, and filtered to obtain phase change microcapsules.

9. An application of the graphite tailings-saw mud road subbase material according to any one of claims 1 to 6 or the graphite tailings-saw mud road subbase material prepared by the preparation method according to any one of claims 7 to 8, specifically in the subbase of secondary and lower-level highways.

Images