A sawdust-graphite tailings road base material, its preparation method and application

Abstract

This invention belongs to the technical field of comprehensive utilization of industrial solid waste, specifically relating to a sawdust-graphite tailings road base material, its preparation method, and its application. This road base material is composed of sawdust, graphite tailings, red mud-based cementitious materials, reinforcing agents, and water. The sawdust-graphite tailings road base material is used in heavy traffic load road bases requiring a strength of 4.0-6.0 MPa. This sawdust-graphite tailings road base material replaces all aggregates in traditional road base materials with a combination of sawdust and graphite tailings, and is solidified using the aforementioned red mud-based cementitious materials. This significantly improves the efficiency of solid waste resource utilization and alleviates the problems of sand and gravel resource shortages and high material costs in road construction.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of comprehensive utilization of industrial solid waste, and particularly relates to a saw mud-graphite tailing road base material and a preparation method and application thereof. BACKGROUND

[0002] Saw mud is a waste generated in the process of cutting stone, and its annual emission exceeds one million tons. Graphite tailings are by-products of graphite production, and about 10-15 tons of graphite tailings are generated per ton of graphite produced. Long-term storage of saw mud and graphite tailings not only occupies a large amount of land, but also brings significant environmental risks to soil, water and atmospheric environment. At present, the resource utilization of saw mud and graphite tailings mainly focuses on valuable metal recovery and production of building materials, but these routes still have deficiencies in solid waste disposal capacity and construction cost.

[0003] With the continuous expansion of road construction scale in China, the consumption of cement and natural sand and gravel aggregates continues to grow, leading to resource depletion and intensified ecological pressure. Under this background, using saw mud and graphite tailings for road base construction becomes a feasible choice that takes into account scale disposal and resource substitution.

[0004] However, saw mud particles are fine, with high water content and large liquid-plastic limit, and have high viscosity after adding water. It is difficult to solidify using traditional cementitious materials. The properties of graphite tailings are similar to those of sand, with low plasticity index, poor plasticity, and little adhesion between particles. After solidification using traditional cementitious materials, it is relatively loose.

[0005] Saw mud and graphite tailings have great differences in physical and chemical properties. When used as a substitute for fine aggregate in road base, the following defects exist: high porosity, low strength, dry shrinkage, insufficient frost resistance and erosion resistance, and easy to cause reflective cracks, which can damage asphalt pavement and cause serious impact.

[0006] Patent CN115724638A discloses a method for preparing cementitious material using granite saw mud. The invention uses cement, granite saw mud, organic silicon bentonite, zeolite powder, and water reducing agent to prepare a new organic activated cementitious material. Although the cementitious material has excellent mechanical properties, the cementitious material composition contains a large amount of P·O42.5 cement, and a large amount of organic silicon bentonite and water reducing agent, which are high-priced materials. This will result in high cost of the cementitious material, thereby limiting its large-scale application. In addition, the solid waste disposal method of using saw mud to prepare cementitious material has relatively small effect on the large amount of saw mud.

[0007] Patent CN115304316A discloses a shrinkage-compensating concrete and its preparation method. This invention utilizes graphite tailings, cement, siderite, water-reducing agent, coarse aggregate, and other materials to prepare shrinkage-compensating concrete, overcoming the problem of large concrete shrinkage. It also confirms that graphite tailings, as aggregate, can play a role in compensating for shrinkage. However, the aggregate in the concrete provided by this invention is still mainly natural sand and gravel aggregate, with a relatively small proportion of graphite tailings, resulting in a relatively low solid waste resource utilization rate.

[0008] Patent CN116924740A discloses a red mud-graphite tailings road base material, its preparation method, and its application. The raw material components include ISS (sodium ricinoleate sulfate), an early-strength agent (triethanolamine), an anti-hardening agent (sodium dodecyl diphenyl ether disulfonate), cement, gravel, red mud, graphite tailings, stone chips, and water; wherein the total mass fraction of red mud, graphite tailings, and stone chips is 40 parts. This road base material is made by mixing and compacting raw materials such as cement, gravel, red mud, graphite tailings, and stone chips. This invention utilizes red mud and graphite tailings solid waste to replace the fine aggregate in cement-stabilized crushed stone, with a maximum replacement rate of 40%. However, more than 60% of the aggregate is still natural aggregate (gravel and stone chips), which is not only expensive but also scarce; excessive mining will only cause damage to the natural environment.

[0009] Furthermore, when the content of red mud and graphite tailings is high (40%), their combination with gravel forms a "suspended-dense" structure. This structure results in low material compaction, making it difficult to compact in practical applications, increasing construction difficulty and costs. The triethanolamine used as the early-strength agent is highly sensitive to the cement dosage and requires different modifications depending on the mix proportion. It is evident that the red mud-graphite tailings road base material in this patent has poor economic benefits, high construction difficulty, and low solid waste resource utilization rate.

[0010] In summary, there is an urgent need to provide a sawdust-graphite tailings road base material that is easy to implement, low in cost, high in strength, and durable. Summary of the Invention

[0011] The purpose of this invention is to address the aforementioned deficiencies by providing a sawdust-graphite tailings road base material, its preparation method, and its application. This sawdust-graphite tailings road base material replaces all aggregates in traditional road base materials with sawdust-graphite tailings and is solidified using the aforementioned red mud-based cementitious material. This significantly improves the utilization efficiency of solid waste resources and alleviates the problems of sand and gravel resource shortages and high material costs in road construction.

[0012] During the research process, it was found that if sawdust and graphite tailings were used together to replace all aggregates, the following problems would occur: (1) Insufficient strength. Without coarse aggregates (such as gravel) in the system, it is impossible to form a stone-stone skeleton interlocking structure. The internal friction angle is low, which leads to a decrease in the overall strength of the material; (2) Large drying shrinkage and easy drying shrinkage cracking. The sawdust fine material has a large specific surface area and a high water absorption rate, which leads to large drying shrinkage caused by water evaporation, which in turn causes the material to crack; (3) Poor scouring performance. The sawdust fine material is easily carried away by the water flow of the wheel, and the scouring quality loss rate is relatively large; (4) The sawdust fine material is sensitive to frost heave. It is easy to swell and bulge under saturated water and low temperature conditions. After melting, the strength drops sharply; (5) Poor construction adaptability. It is easy to generate dust and is difficult to compact.

[0013] To address the aforementioned problems, extensive research and design have resulted in the sawdust-graphite tailings combined material system described in this invention. This sawdust-graphite tailings road base material not only solves the inherent problem of low strength caused by the poor engineering properties of fine-grained sawdust and graphite tailings when used together, but also simultaneously solves the durability problems of traditional cementitious materials, such as large drying shrinkage, poor freeze-thaw resistance, and poor erosion resistance when solidifying fine-grained materials. In other words, the sawdust-graphite tailings road base material described in this invention improves both strength and durability.

[0014] The specific technical solution is as follows:

[0015] A sawdust-graphite tailings road base material is composed of the following components in parts by weight: 30-70 parts sawdust, 30-70 parts graphite tailings, 12-16 parts red mud-based cementitious material, 0.1-0.3 parts reinforcing agent, and 12-18 parts water; wherein the total weight of sawdust and graphite tailings is 100 parts.

[0016] As mentioned earlier, sawdust and graphite tailings, as industrial solid wastes, suffer from poor engineering properties, small particle size, high mud content, high porosity, and incompatibility with cementitious materials. When used as road base materials, they often result in poor mechanical properties, insufficient resistance to shrinkage cracking, frost resistance, and erosion resistance, thus limiting their large-scale application. However, this invention discovered that when the material components are proportioned according to the aforementioned ratio, the plasticity index of the mixture can be controlled within the range of 14 < PI < 17. This effectively avoids the mixture being too dry, making it difficult to spread and compact; or too brittle, easily disintegrating, and generating dust after compaction. Simultaneously, it further improves the mechanical properties of the mixture. Under the same compaction work, the optimum moisture content of the mixture decreases, the maximum dry density increases, and the porosity decreases accordingly.

[0017] The sawdust can be made from granite sawdust.

[0018] The red mud-based cementitious material is composed of the following components in parts by weight: 50 parts red mud, 7.5-22.5 parts slag powder, 3-9 parts fly ash, 13.5-34.5 parts hydrated lime, and 2.5-7.5 parts desulfurized gypsum.

[0019] The pH value of the red mud is 11-13; the red mud can be Bayer process red mud.

[0020] S95 granulated blast furnace slag powder can be selected as the slag powder.

[0021] The calcination coefficient of fly ash should be ≤8.0%, the free calcium oxide content should be ≤1.0%, and the content of SiO2+Fe2O3+Al2O3 in fly ash should be ≥70%. Class F fly ash can be selected.

[0022] The effective calcium and magnesium content of slaked lime should be ≥65%, and it should be dry.

[0023] The desulfurized gypsum should have a pH ≥ 5 and a chloride ion content ≤ 0.5%; dihydrate gypsum can be used as the desulfurized gypsum.

[0024] This red mud-based cementitious material uses a physical filling-hydration refilling process. First, it physically fills the large pores formed between sawdust and graphite tailings. Then, the hydration products generated subsequently fill the mesopores and interconnecting pores that have the greatest impact on the material's drying shrinkage and durability, thereby reducing water penetration into the material and improving its durability.

[0025] The reinforcing agent is composed of the following components in the indicated mass percentages: 58%-62% sodium hexametaphosphate, 16%-20% sodium tetrapolyphosphate, 18%-22% calcium chloride, and 2%-4% alkyl polysaccharide; wherein the degree of polymerization n of the alkyl polysaccharide is 1.4-1.8, and the number of carbon atoms in the alkyl group is 10-14.

[0026] The reinforcing agent components work synergistically: sodium hexametaphosphate disperses sawdust and graphite tailings particles, sodium tetrapolyphosphate maintains the dispersion between particles, calcium chloride gathers them together, and alkyl polysaccharides wet them. During the mixing process, the system first transitions from a state where particles can rearrange to a state where particles can be compacted, and then to a state of densification and volume stabilization. This optimizes the pore structure of the material, reduces the optimum moisture content, and increases the maximum dry density, thereby improving the strength and durability of the material.

[0027] Sodium hexametaphosphate makes the originally easily flocculated sawdust and graphite tailings particles easier to disperse and release the trapped water; under the same water content conditions, it promotes the secondary arrangement and slippage of fine particles, forming an initial skeleton that is easy to rearrange. During mixing, it helps the slurry of red mud-based cementitious materials to enter more easily and be evenly coated, resulting in more complete subsequent hydration products and a denser structure.

[0028] Sodium tetrapolyphosphate, in synergy with sodium hexametaphosphate, provides sustained charge shielding and pH buffering, resulting in a more durable particle dispersion and inhibiting particle re-agglomeration and re-adhesion. Sodium tetrapolyphosphate provides a wider compaction range for the system, allowing sawdust-graphite tailings base material to maintain a high dry density during compaction without being confined to a very narrow moisture content range. Furthermore, it lowers the optimum moisture content and results in more uniform cementitious slurry coverage and more stable later-stage strength development.

[0029] Calcium chloride helps to suppress excessive particle dispersion and slippage, making compaction difficult and allowing particles to achieve a dense packing state under the action of compaction work. It reduces the interconnected pore ratio of sawdust-graphite tailings road base materials, lowers the total porosity, and increases the maximum dry density macroscopically. At the same time, calcium chloride helps to promote the early nucleation of red mud-based cementitious materials in the system, improving the early strength of the material.

[0030] The alkyl polysaccharides used enhance the wetting and spreading of sawdust and graphite tailings particles by the mixing water, homogenizing the water film thickness; reducing mixing energy consumption and friction, improving particle-cement interface lubrication, assisting in the formation of a dense structure, and simultaneously inhibiting foam generation, ensuring compaction stability and molding quality, resulting in a finer and denser road surface after molding. The selected alkyl polysaccharides not only facilitate system mixing and construction but also contribute to the long-term stability of the system.

[0031] In this invention, the graphite tailings have a particle size range of 0.6-2.36 mm, wherein particles with a diameter less than 1.18 mm account for ≤20%, and the plasticity index of the graphite tailings ranges from 6 to 10; the sawdust has a particle size range of 0.3-1.18 mm, wherein particles with a diameter less than 0.6 mm account for ≤60%; the slag powder has a particle size range of 0.15-0.6 mm, wherein particles with a diameter less than 0.3 mm account for ≤10%; the red mud has a particle size range of 0.075-0.15 mm; and the fly ash has a particle size range of ≤0.075 mm.

[0032] The preparation method of the above-mentioned sawdust-graphite tailings road base material includes the following steps:

[0033] (1) First, sawdust and graphite tailings are mixed according to the weight ratio described above, and stirred thoroughly. The total weight of sawdust and graphite tailings is 100 parts. Then, red mud-based cementitious material is added and dry-mixed to obtain the mixture. The red mud-based cementitious material is added externally. This prevents the red mud-based cementitious material from prematurely hydrating, thus ensuring the strength of the mixture.

[0034] (2) Add the reinforcing agent to the water and stir for 3-5 minutes until it is completely dissolved, i.e. there are no obvious particles at the bottom of the solution, to obtain the reinforcing agent mother liquor.

[0035] (3) Add the reinforcing agent mother liquor obtained in step (2) to the mixing material obtained in step (1) and mix evenly to obtain the mixture.

[0036] (4) Vacuum seal the well-mixed material and place it in a cool place to ferment for 2-3 hours.

[0037] (5) Finally, the material is shaped, demolded, and cured to obtain the sawdust-graphite tailings road base material.

[0038] In this invention, the molding method of step (5) of the preparation method of the sawdust-graphite tailings road base material is static pressure molding, wherein the molding pressure is 35~45kN and the holding time is 2-3min; after the holding time is completed, the mold (together with the specimen) is left to stand for 10-15min, and then demolded. After demolding, the specimen should be immediately placed in a sealed bag and sealed, and then transferred to a standard curing environment for curing, wherein the curing temperature is 20℃±2℃ and the relative humidity is ≥95%.

[0039] The maximum dry density of the sawdust-graphite tailings road base material prepared by this method can be increased by up to 15.2%. After 7 days of standard curing, the unconfined compressive strength can be increased by up to 327%, the 180-day drying shrinkage strain can be reduced by up to 64.7%, the frost resistance is greatly improved, and the scouring mass loss rate of the material can be reduced by up to 93.5%.

[0040] This invention also provides the application of the above-mentioned sawdust-graphite tailings road base material in heavy traffic load road bases with strength requirements of 4.0-6.0 MPa. It can be applied to heavy traffic load road bases for expressways and Class I highways.

[0041] The beneficial effects of this invention are as follows: The sawdust-graphite tailings road base material of this invention has a solid waste utilization rate of up to 100%. Compared with traditional cementitious materials that have problems such as insufficient strength and poor durability, the red mud-based cementitious material used in this invention fills the pores formed by sawdust and graphite tailings through multiple physical / chemical pathways in a continuous distribution, improving the internal pore structure of the material, reducing porosity and the proportion of interconnected pores, weakening water penetration, and further improving the density of the material. At the same time, the reinforcing agent further improves the particle interface state, keeping the material particles in a relatively stable state, avoiding flocculation between particles, reducing resistance during mixing, compressing the double electric layer structure, making the particle arrangement more compact, the spatial structure more stable, and improving the density, strength, and durability of the material. The reinforcing agent also promotes the hydration of the cementitious material, improving the strength and durability of the material.

[0042] The sawdust-graphite tailings road base material proposed in this invention can be used to replace conventional cement-stabilized crushed stone, which greatly alleviates the problems of high consumption of natural sand and gravel and resource shortage in road construction. At the same time, it can also dispose of industrial solid waste such as sawdust and graphite tailings on a large scale, which can reduce production costs and bring significant environmental benefits.

[0043] The road base material provided by this invention can replace inorganic binder-based stabilized materials for use as road bases. Its technical indicators meet the requirements of JTG D50-2017 "Specifications for Design of Highway Asphalt Pavement," and its strength indicators meet the requirements for "heavy traffic" loads of highway or Class I highway bases in JTG / T F20-2015 "Technical Details for Construction of Highway Pavement Bases." The 7-day unconfined compressive strength range of the sawdust-graphite tailings road base material is 4.1-4.7 MPa, and the 180-day cumulative drying shrinkage strain range is 317 × 10⁻⁶ MPa. ﹣6 -439×10 ﹣6 After 5 freeze-thaw cycles, the strength retention rate ranged from 88.3% to 93.3%, after 10 freeze-thaw cycles, the strength retention rate ranged from 81.1% to 89.4%, and the mass loss rate after 30 minutes of scouring ranged from 1.9% to 3.5%. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the road base material prepared in Example 1 undergoing 10 freeze-thaw cycles.

[0045] Figure 2 This is a schematic diagram of the road base material prepared in Comparative Example 6 after 10 freeze-thaw cycles. Detailed Implementation

[0046] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0047] 1. Method for determining the 7-day unconfined compressive strength: Refer to T0805-2024 "Test Method for Unconfined Compressive Strength of Inorganic Binder Stabilized Materials" in the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG 3441—2024).

[0048] 2. Method for determining 180-day drying shrinkage strain: Refer to T0854-2009 "Test Method for Drying Shrinkage of Inorganic Binder Stabilized Materials" in the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG 3441—2009).

[0049] Test methods for strength retention rate after 3, 5, and 10 freeze-thaw cycles: Refer to T0858-2009 "Freeze-thaw test method for inorganic binder stabilized materials" in the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG 3441—2024).

[0050] 4. Method for determining the erosion mass loss rate: Refer to T0860-2009 "Test method for erosion resistance of inorganic binder stabilized materials" in the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG 3441—2024).

[0051] 5. The fly ash used in Examples 1-5 below shall be Class F fly ash, with a calcination vector ≤ 8.0%, free calcium oxide content ≤ 1.0%, and the content of SiO2+Fe2O3+Al2O3 in the fly ash ≥ 70%, and the particle size range ≤ 0.075 mm; the effective calcium and magnesium content of the hydrated lime shall be ≥ 65%, and it shall be dry; the desulfurization gypsum shall be dihydrate gypsum with a pH ≥ 5 and a chloride ion content ≤ 0.5%.

[0052] 6. The graphite tailings in Examples 1-5 below have a particle size range of 0.6-2.36 mm, of which particles with a particle size less than 1.18 mm account for ≤20%, and the plasticity index of the graphite tailings ranges from 6 to 10; the sawdust has a particle size range of 0.3-1.18 mm, of which particles with a particle size less than 0.6 mm account for ≤60%; the slag powder has a particle size range of 0.15-0.6 mm, of which particles with a particle size less than 0.3 mm account for ≤10%; the red mud has a particle size range of 0.075-0.15 mm; and the fly ash has a particle size range of ≤0.075 mm.

[0053] Example 1

[0054] The aforementioned sawdust-graphite tailings road base material comprises the following components in parts by weight: 50 parts sawdust, 50 parts graphite tailings, 12 parts red mud-based cementitious material, 14 parts water, and 0.2 parts reinforcing agent. The sawdust is granite sawdust.

[0055] The red mud-based cementitious material is composed of the following components in parts by weight: 50 parts red mud, 12.5 parts slag powder, 5.0 parts fly ash, 25.0 parts hydrated lime, and 5.0 parts desulfurized gypsum.

[0056] The red mud used is Bayer process red mud with a pH of 13.

[0057] The slag powder used is S95 granulated blast furnace slag powder.

[0058] The reinforcing agent is composed of the following components in the indicated mass percentages: 60% sodium hexametaphosphate, 18% sodium tetrapolyphosphate, 20% calcium chloride, and 2.0% alkyl polysaccharide; wherein the degree of polymerization of the alkyl polysaccharide is 1.6, and the alkyl group has 12 carbon atoms.

[0059] The preparation method of the sawdust-graphite tailings road base material includes the following specific steps:

[0060] (1) First, the sawdust and graphite tailings are thoroughly mixed according to the weight ratio; then, red mud-based cementitious materials are added and dry-mixed to obtain the mixture.

[0061] (2) Add the reinforcing agent to the water and stir for 3 minutes until it is completely dissolved, i.e. there are no obvious particles at the bottom of the solution, to obtain the reinforcing agent mother liquor.

[0062] (3) Add the reinforcing agent mother liquor obtained in step (2) to the mixing material obtained in step (1) and mix evenly to obtain the mixture.

[0063] (4) Vacuum seal the well-mixed material and place it in a cool place to ferment for 3 hours.

[0064] (5) Finally, the material is shaped, demolded, and cured to obtain the sawdust-graphite tailings road base material.

[0065] The molding method is static pressure molding, the molding pressure is 35kN, and the holding time is 3min. After the holding time is completed, the mold (together with the specimen) is left to stand for 15min, and then demolded. After demolding, the specimen should be immediately placed in a sealed bag and sealed, and then transferred to a standard curing environment for curing, where the curing temperature is 22℃ and the relative humidity is ≥95%.

[0066] pass Figure 1 and Figure 2 The comparison shows that Figure 1 The material in Example 1, after 10 freeze-thaw cycles, showed a more intact appearance, lower freeze-thaw mass loss rate, and better freeze resistance; while Figure 2 The material in Comparative Example 6 underwent 10 freeze-thaw cycles, resulting in severe flaking of the specimen surface, high freeze-thaw mass loss rate, and poor freeze resistance.

[0067] Example 2

[0068] The sawdust-graphite tailings road base material is composed of the following components in the indicated mass ratios: 30 parts sawdust, 70 parts graphite tailings, 13 parts red mud-based cementitious material, 12 parts water, and 0.15 parts reinforcing agent.

[0069] The red mud-based cementitious material is composed of the following components in parts by weight: 50 parts red mud, 22.5 parts slag powder, 8.0 parts fly ash, 27.5 parts hydrated lime, and 3.0 parts desulfurized gypsum.

[0070] The red mud used is Bayer process red mud with a pH of 13.

[0071] The slag powder used is S95 granulated blast furnace slag powder.

[0072] The reinforcing agent is composed of the following components in the indicated mass percentages: 58% sodium hexametaphosphate, 20% sodium tetrapolyphosphate, 20% calcium chloride, and 2.0% alkyl polysaccharide; wherein the degree of polymerization of the alkyl polysaccharide is 1.4, and the alkyl group has 11 carbon atoms.

[0073] The specific preparation method is the same as in Example 1.

[0074] Example 3

[0075] The sawdust-graphite tailings road base material is composed of the following components in the indicated mass ratios: 40 parts sawdust, 60 parts graphite tailings, 14 parts red mud-based cementitious material, 13 parts water, and 0.17 parts reinforcing agent.

[0076] The red mud-based cementitious material is composed of the following components in parts by weight: 50 parts red mud, 17.5 parts slag powder, 7.0 parts fly ash, 20.5 parts hydrated lime, and 4.0 parts desulfurized gypsum.

[0077] The red mud used was Bayer process red mud with a pH of 12.

[0078] The slag powder used is S95 granulated blast furnace slag powder.

[0079] The reinforcing agent is composed of the following components in the indicated mass percentages: 59% sodium hexametaphosphate, 16% sodium tetrapolyphosphate, 22% calcium chloride, and 3.0% alkyl polysaccharide; wherein the degree of polymerization of the alkyl polysaccharide is 1.5, and the alkyl group has 10 carbon atoms.

[0080] The specific preparation method is the same as in Example 1.

[0081] Example 4

[0082] The sawdust-graphite tailings road base material is composed of the following components in the indicated mass ratios: 60 parts sawdust, 40 parts graphite tailings, 15 parts red mud-based cementitious material, 16 parts water, and 0.25 parts reinforcing agent.

[0083] The red mud-based cementitious material is composed of the following components in parts by weight: 50 parts red mud, 22.5 parts slag powder, 8.0 parts fly ash, 27.5 parts hydrated lime, and 6.0 parts desulfurized gypsum.

[0084] The red mud used is Bayer process red mud with a pH of 13.

[0085] The slag powder used is S95 granulated blast furnace slag powder.

[0086] The reinforcing agent is composed of the following components in the indicated mass percentages: 62% sodium hexametaphosphate, 17% sodium tetrapolyphosphate, 18% calcium chloride, and 3.0% alkyl polysaccharide; wherein the degree of polymerization of the alkyl polysaccharide is 1.4, and the alkyl group has 11 carbon atoms.

[0087] The specific preparation method is the same as in Example 1.

[0088] Example 5

[0089] The sawdust-graphite tailings road base material is composed of the following components in the indicated mass ratios: 70 parts sawdust, 30 parts graphite tailings, 16 parts red mud-based cementitious material, 18 parts water, and 0.3 parts reinforcing agent.

[0090] The red mud-based cementitious material is composed of the following components in parts by weight: 50 parts red mud, 7.5 parts slag powder, 4.0 parts fly ash, 13.5 parts hydrated lime, and 6.5 parts desulfurized gypsum.

[0091] The red mud used is Bayer process red mud with a pH of 13.

[0092] The slag powder used is S95 granulated blast furnace slag powder.

[0093] The reinforcing agent is composed of the following components in the indicated mass percentages: 62% sodium hexametaphosphate, 17% sodium tetrapolyphosphate, 18% calcium chloride, and 3% alkyl polysaccharide; wherein the degree of polymerization of the alkyl polysaccharide is 1.8, and the alkyl group has 14 carbon atoms.

[0094] The specific preparation method is the same as in Example 1.

[0095] Comparative Example 1

[0096] The sawdust-graphite tailings road base material described in this comparative example is composed of the following parts by weight: 80 parts sawdust, 20 parts graphite tailings, 12 parts red mud-based cementitious material, 20 parts water, and 0.3 parts reinforcing agent.

[0097] The others are the same as in Example 1.

[0098] Comparative Example 2

[0099] The sawdust-graphite tailings road base material described in this comparative example is composed of the following parts by weight: 20 parts sawdust, 80 parts graphite tailings, 12 parts red mud-based cementitious material, 9.0 parts water, and 0.15 parts reinforcing agent.

[0100] The others are the same as in Example 1.

[0101] Comparative Example 3

[0102] The sawdust-graphite tailings road base material described in this comparative example is composed of the following parts by weight: 50 parts sawdust, 50 parts graphite tailings, 12 parts red mud-based cementitious material, 14 parts water, and 0.2 parts reinforcing agent. In the reinforcing agent, sodium hexametaphosphate is replaced with sodium pyrophosphate, and sodium tetrapolyphosphate is replaced with sodium tripolyphosphate.

[0103] The others are the same as in Example 1.

[0104] Comparative Example 4

[0105] The sawdust-graphite tailings road base material described in this comparative example is composed of the following parts by weight: 50 parts sawdust, 50 parts graphite tailings, 12 parts red mud-based cementitious material, 14 parts water, and 0.2 parts reinforcing agent. The slag powder in the red mud-based cementitious material is replaced with steel slag powder, and the desulfurized gypsum is replaced with titanium gypsum.

[0106] The others are the same as in Example 1.

[0107] Comparative Example 5

[0108] The sawdust-graphite tailings road base material described in this comparative example is composed of the following parts by weight: 50 parts sawdust, 50 parts graphite tailings, 12 parts P·O 42.5 cement, 14 parts water, and 0.2 parts reinforcing agent.

[0109] The others are the same as in Example 1.

[0110] Comparative Example 6

[0111] The sawdust-graphite tailings road base material described in this comparative example is composed of the following parts by weight: 50 parts sawdust, 50 parts graphite tailings, 12 parts red mud-based cementitious material, 14 parts water, and 0.2 parts reinforcing agent. The red mud-based cementitious material is composed of the following components by weight: 50 parts red mud, 25 parts slag powder, 10 parts fly ash, 7 parts hydrated lime, and 8 parts desulfurized gypsum.

[0112] The others are the same as in Example 1.

[0113] Comparative Example 7

[0114] The sawdust-graphite tailings road base material described in this comparative example is composed of the following parts by weight: 50 parts sawdust, 50 parts graphite tailings, 12 parts red mud-based cementitious material, 14 parts water, and 0.2 parts reinforcing agent. The degree of polymerization of the alkyl polysaccharide in the reinforcing agent is n=2.2, and the alkyl group has 16 carbon atoms.

[0115] The others are the same as in Example 1.

[0116] Comparative Example 8

[0117] The sawdust-graphite tailings road base material described in Comparative Example 7 is composed of the following parts by weight: 50 parts sawdust, 50 parts graphite tailings, 12 parts red mud-based cementitious material, 14 parts water, and 0.2 parts reinforcing agent. The reinforcing agent is composed of the following components by weight percentage: 20% sodium hexametaphosphate, 62% sodium tetrapolyphosphate, 10% calcium chloride, and 8% alkyl polysaccharide glycoside.

[0118] The others are the same as in Example 1.

[0119] Comparative Example 9

[0120] The sawdust-graphite tailings road base material described in this comparative example differs from that in Example 1 in that the particle size range of the graphite tailings is 0.6-2.36 mm, with particles smaller than 1.18 mm accounting for more than 20% and less than or equal to 40%, and the plasticity index of the graphite tailings is 8-12; the particle size range of the sawdust is 0.3-1.18 mm, with particles smaller than 0.6 mm accounting for ≤40%; the particle size range of the slag powder is 0.15-0.6 mm, with particles smaller than 0.3 mm accounting for more than 10% and less than or equal to 20%; the particle size range of the red mud is 0.075-0.15 mm; and the particle size range of the fly ash is ≤0.075 mm.

[0121] The others are the same as in Example 1.

[0122] The performance of the mixtures obtained from each embodiment and comparative example was tested, and the test results are shown in Table 1.

[0123] Table 1 Experimental Results

[0124]

[0125] Note: The “strength retention rate” in Table 1 reflects the material’s freeze-thaw resistance, and the standard term is BDR value (strength retention rate); BDR = (unconfined compressive strength of the material after n freeze-thaw cycles / unconfined compressive strength of the material that has not undergone freeze-thaw cycles) × 100%, and the corresponding strength loss rate = 1 - BDR.

[0126] As shown in Table 1, the maximum dry density range of the sawdust-graphite tailings road base material described in Examples 1-5 is 1.938 g / cm³. 3 ~1.973g / cm 3 The 7-day unconfined compressive strength is greater than 4.0 MPa, meeting the requirements for "heavy traffic" loads on the base course of expressways and first-class highways in the "Technical Specifications for Construction of Highway Pavement Base Course" JTG F20-2015; the 180-day drying shrinkage strain range is 317 × 10⁻⁶ MPa. ﹣6 -439×10 ﹣6 Its drying shrinkage index is comparable to that of water-stabilized crushed stone (300×10). ﹣6 -700×10 ﹣6 ).

[0127] After 5 freeze-thaw cycles, the unconfined compressive strength retention rate of the material ranges from 88.3% to 93.3%, and after 10 freeze-thaw cycles, the unconfined compressive strength retention rate ranges from 81.1% to 89.4%, which can meet the strength retention rate requirements of "heavy freezing areas". The 30-minute scouring mass loss rate of the materials described in Examples 1-5 ranges from 1.9% to 3.5%, indicating that the materials have excellent scouring resistance.

[0128] In summary, the sawdust-graphite tailings road base material described in Examples 1-5 of this invention possesses excellent compaction characteristics, mechanical properties, and durability.

[0129] Compared with Examples 1-5, Comparative Examples 1 and 2 showed that the mass ratio of graphite tailings to sawdust exceeded the specified range, resulting in varying degrees of decrease in maximum dry density. Furthermore, the 7-day unconfined compressive strengths of the materials were 2.3 and 1.6 MPa, respectively, failing to meet the strength requirements for heavy traffic loads. The materials also exhibited large shrinkage strain and poor resistance to shrinkage cracking. In addition, the materials' freeze-thaw resistance and erosion resistance were significantly deteriorated.

[0130] In Comparative Example 3, sodium hexametaphosphate was replaced with sodium pyrophosphate and sodium tetrapolyphosphate was replaced with sodium tripolyphosphate in the reinforcing agent. As a result, many properties of the material deteriorated, indicating that the composition of the reinforcing agent in this invention is correct and the other components cannot be substituted.

[0131] In Comparative Example 4, when the slag powder in the red mud-based cementitious material was replaced with steel slag powder and the desulfurized gypsum was replaced with titanium gypsum, the 7-day unconfined compressive strength of the material decreased significantly, reaching only 1.1 MPa, which failed to meet the strength standard for the base layer. This is because steel slag powder has strong expansibility, causing internal expansion of the material and generating numerous cracks, making it highly susceptible to cracking under stress. Furthermore, after five freeze-thaw cycles, the specimens exhibited freeze-thaw failure, demonstrating extremely poor freeze-thaw resistance and significant deterioration in erosion resistance. This indicates that the selection of slag powder and desulfurized gypsum in this invention is highly reasonable.

[0132] Comparative Example 5 replaced the red mud-based cementitious material with P·O 42.5 cement. The 7-day unconfined compressive strength of the material was 5.2 MPa, and the strength retention rates after 5 and 10 freeze-thaw cycles were 96.7% and 91.2%, respectively. The 30-minute scouring mass loss rate was 1.8%. These properties were all superior to those of Examples 1-5, but its 180-day drying shrinkage strain was 671 × 10⁻⁶. ﹣6 The strength is much higher than that in Examples 1-5. This is because cement has high hydration activity, which can provide sufficient strength to the system, but at the same time it will also bring about large drying shrinkage strain.

[0133] The proportions of the red mud-based cementitious materials, the degree of polymerization of alkyl polysaccharides and the number of alkyl carbons, the range of reinforcing agents, and the particle size range of graphite tailings, sawdust, and slag powder in Comparative Examples 6-9 are all outside the ranges defined in this invention. The strength and durability of the materials are significantly reduced, indicating that the range of components defined in this invention is irreplaceable.

Claims

1. A sawed argillaceous-graphitic tailings road base material, characterized in that, Is made by mixing the following components by weight: saw mud 30-70 parts, graphite tailings 30-70 parts, red mud-based cementitious material 12-16 parts, reinforcing agent 0.1-0.3 parts, water 12-18 parts; wherein the total weight of saw mud and graphite tailings is 100 parts; The red mud-based cementitious material is composed of the following components by weight: red mud 50 parts, slag powder 7.5-22.5 parts, fly ash 3-9 parts, slaked lime 13.5-34.5 parts, desulfurization gypsum 2.5-7.5 parts; The reinforcing agent is composed of the following components by mass percentage: sodium hexametaphosphate 58%-62%, sodium tetraphosphate 16%-20%, calcium chloride 18%-22%, alkyl polyglycoside 2%-4%; wherein the polymerization degree n of the alkyl polyglycoside is 1.4-1.8, and the number of carbon atoms of the alkyl group is 10-14.

2. The sawed argillic-graphite tailings road base material according to claim 1, characterized in that, The particle size range of the graphite tailings is 0.6-2.36 mm, wherein the proportion of particles with a particle size less than 1.18 mm is ≤20%, and the plasticity index of the graphite tailings is in the range of 6-10; The particle size range of the saw mud is 0.3-1.18 mm, wherein the proportion of particles with a particle size less than 0.6 mm is ≤60%; The particle size range of the slag powder is 0.15-0.6 mm, wherein the proportion of particles with a particle size less than 0.3 mm is ≤10%; The particle size range of the red mud is 0.075-0.15 mm; the particle size range of the fly ash is ≤0.075 mm.

3. The sawed argillic-graphite tailings road base material according to claim 1, characterized in that, The saw mud is selected from granite saw mud.

4. The sawed argillic-graphite tailings road base material according to claim 1, characterized in that, The pH value of the red mud is 11-13.

5. The sawed argillic-graphite tailings road base material according to claim 1, characterized in that, The slag powder is selected from S95 granulated blast furnace slag powder.

6. The sawed argillic-graphite tailings road base material according to claim 1, characterized in that, The burning vector of the fly ash is ≤8.0%, the free calcium oxide content is ≤1.0%, and the content of SiO2+Fe2O3+Al2O3 in the fly ash is ≥70%.

7. The sawed argillic-graphitic tailings road base material according to claim 1, characterized in that, The effective calcium and magnesium content of the slaked lime is ≥65%; The pH of the desulfurization gypsum is ≥5, and the chloride ion content is ≤0.5%.

8. A method of preparing a sawed argillaceous-graphitic tailings road base material according to any one of claims 1 to 7, characterized in that, Comprising the following steps: (1) First, mix the saw mud and graphite tailings according to the weight ratio, and stir well; Then, add the red mud-based cementitious material for dry mixing to obtain the mixed material; (2) Add the reinforcing agent to the water, stir for 3-5 min until completely dissolved to obtain the reinforcing agent mother liquor; (3) Add the reinforcing agent mother liquor obtained in step (2) to the mixed material obtained in step (1) and mix evenly to obtain the mixed material; (4) Vacuum seal the mixed material and steam for 2-3 h; (5) Finally, shape, demold, and cure to obtain the saw mud-graphite tailings road base material.

9. The method of claim 8, wherein the sawed mud-graphite tailings road base material is prepared by the steps of: The shaping method in step (5) is static pressure shaping, wherein the shaping pressure is 35~45kN, and the pressure holding time is 2-3 min; The curing temperature is 18-22℃, and the relative humidity is ≥95%.

10. The application of the saw mud-graphite tailings road base material in heavy traffic load road base with a strength requirement of 4.0-6.0 MPa according to any one of claims 1-7.

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