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

Abstract

This invention relates to the field of solid waste management technology, specifically to a red mud-graphite tailings road base material, its preparation method, and its application. The base material comprises the following components by weight: 0.05-0.07 parts of ionomer solidifier (ISS), 0.0012-0.0015 parts of early-strength agent, 0.25-0.35 parts of anti-hard water agent, 4-5 parts of cement, 60 parts of gravel, 5-20 parts of red mud, 5-20 parts of graphite tailings, 0-30 parts of stone chips, and 5-7 parts of water; the particle size range of the gravel is 5-20 mm; the particle size of the red mud and graphite tailings is ≤5 mm; the particle size of the stone chips is ≤5 mm; the ISS is sodium ricinoleate sulfate, the early-strength agent is triethanolamine, and the anti-hard water agent is sodium dodecyl diphenyl ether disulfonate; the 7-day unconfined compressive strength range of the red mud-graphite tailings road base material is 5.3-6.8 MPa.

Description

Technical Field

[0001] This invention relates to the field of solid waste management technology, specifically to a red mud-graphite tailings road base material, its preparation method, and its application. Background Technology

[0002] Red mud is an industrial solid waste discharged during the extraction of alumina in the aluminum industry, containing a certain amount of useful metals and minerals. Due to its strong alkalinity, fine particle size, and complex mineral composition, red mud is difficult to utilize on a large scale. As a major alumina producer, China discharges up to 100 million tons of red mud annually. Currently, most of my country's red mud is stored in stockpiles, which not only occupies valuable land resources but also pollutes surrounding soil and groundwater. Furthermore, maintaining red mud dams requires substantial investment and poses significant safety risks, including the possibility of dam failure and landslides, which greatly threaten the safety of surrounding factories and nearby residents. In addition, red mud itself contains a large amount of highly alkaline chemicals, as well as fluorine, aluminum, and other harmful ions; preventing the diffusion of these harmful ions during stockpiling also increases storage costs.

[0003] Graphite tailings are emissions generated during graphite mining. With the continuous exploitation and utilization of graphite resources, my country's annual output of crystalline graphite is around 500,000 tons, and the annual discharge of graphite tailings after beneficiation exceeds 6 million tons. The most common method for disposing of graphite tailings in my country is stockpiling. However, stockpiling not only occupies a large amount of land resources, but also easily generates dust and leaks during severe weather, causing serious environmental pollution.

[0004] On the other hand, with the implementation of the national strategy of building a strong transportation network, the number of newly built and expanded highways in my country is increasing daily, leading to a growing demand for sand and gravel resources. However, my country's sand and gravel resources are facing increasing shortages and even depletion. The large-scale mining of mineral resources also contradicts the national green development strategy. Therefore, red mud and graphite tailings, as substitutes for sand and gravel resources, have attracted considerable attention from scholars. According to incomplete statistics, the cumulative stockpiled amount of red mud in my country has exceeded 1 billion tons, and the cumulative stockpiled amount of graphite tailings has reached over 60 million tons, both showing a year-on-year increasing trend. However, the utilization rate of solid waste is extremely low, making the comprehensive utilization of red mud and graphite tailings imperative.

[0005] Existing patented technologies for preparing road base or subbase layers using red mud or graphite tailings generally focus on the following aspects:

[0006] 1. Red mud is cured using a curing agent to prepare hydraulic road base materials. For example, Chinese patent document CN104926230A provides a method for curing red mud using elastic styrene-acrylic emulsion and nano aluminum sol and applying it to the road base. However, the amount of cement used in the preparation process is too large (up to 20%), which increases the production cost. This is inconsistent with the characteristic of traditional roadbed materials that require a small amount of cement. In addition, the price of the curing agents used, such as elastic styrene-acrylic emulsion and nano aluminum sol, is expensive, which further increases the production cost.

[0007] 2. Using a variety of materials mixed with graphite tailings to prepare graphite tailings road water-stabilized layer materials, such as Chinese patent document CN 115947583A, which provides a method for preparing road base material by mixing phosphogypsum powder, silicate cement, sea pebbles, quartz sandstone, modified fly ash, calcium lignosulfonate and sodium dodecyl sulfonate with graphite tailings. The preparation process of this method is cumbersome, requires too many types of raw materials, and the amount of aggregate is too small, the gradation is unreasonable, and it cannot form a dense structure. The base material obtained has low 7d unconfined strength, which makes it difficult to widely promote and apply in engineering.

[0008] 3. The direct application of various environmentally harmful and health-damaging solid waste materials to road base layers is problematic. For example, Chinese patent document CN 114656234A provides a road base formulation and preparation process using red mud, slag, desulfurized gypsum, and coal gangue as main raw materials. However, this process uses thermal activation of the red mud, which inevitably generates significant carbon emissions, contradicting the theme of low-carbon and green development. Furthermore, heating the red mud to 850℃-900℃ during thermal activation will inevitably cause the leaching of harmful ions, but this paper does not address this leaching issue further.

[0009] In summary, none of the existing technologies combine red mud with graphite tailings, and none have proposed a red mud-graphite tailings road base material that is easy to construct, low in cost, high in strength, and reduces the leaching of harmful ions. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of the prior art and provide a red mud-graphite tailings road base material, its preparation method, and its application. The base material provided by this invention can replace inorganic binder-type stabilized materials as road (sub) base materials. Its technical indicators meet the requirements of JTG D50-2017 "Specifications for Design of Highway Asphalt Pavement" and its strength indicators meet the design specifications of JTGT F20-2015 "Technical Details for Construction of Highway Pavement Base". It alleviates the environmental problems caused by the shortage of sand and gravel resources during road construction and has significant social and economic benefits.

[0011] To achieve the above-mentioned technical effects, the present invention adopts the following technical solution:

[0012] A red mud-graphite tailings road base material comprises the following components in parts by weight: 0.05-0.07 parts of ion hardening agent (ISS), 0.0012-0.0015 parts of early strength agent, 0.25-0.35 parts of anti-hardening water agent, 4-5 parts of cement, 60 parts of gravel, 5-20 parts of red mud, 5-20 parts of graphite tailings, 0-30 parts of stone chips, and 5-7 parts of water;

[0013] The total mass fraction of red mud, graphite tailings and stone chips is 40 parts.

[0014] The particle size range of the pebbles is 5-20mm; the particle size of the red mud and graphite tailings is ≤5mm; the particle size of the stone chips is ≤5mm.

[0015] The ISS is sodium ricinoleate sulfate, the early strength agent is triethanolamine, and the hard water resistant agent is sodium dodecyl diphenyl ether disulfonate.

[0016] The 7-day unconfined compressive strength range of the red mud-graphite tailings road base material is 5.3-6.8 MPa.

[0017] The red mud-graphite tailings road base material provided by this invention requires only 4-5 parts of cement, and the proportion of cement in the base material is much smaller than that in existing technologies. Graphite tailings contain a certain amount of calcium oxide and a large amount of silicon oxide, while red mud contains a certain amount of iron oxide and aluminum oxide. There is no need to activate the red mud at high temperature. After they are mixed together, they react with water to generate hydration products such as calcium silicate and calcium aluminate, which can improve the 7d unconfined strength of the red mud-graphite tailings material to a certain extent. In addition, the red mud provides a strongly alkaline environment, which promotes the hydration of cement and can also effectively avoid the problem of leaching of harmful ions generated during the high-temperature activation of red mud.

[0018] In the base material, gravel acts as coarse aggregate, forming a skeleton. Gravel of different sizes interlocks to form the material's skeleton. Stone chips, red mud, graphite tailings, and cement hydration products constitute fine aggregate, filling the gaps in the skeleton. The coarse and fine aggregates are mixed in a 6:4 ratio to form a dense skeleton structure, which supports the overall integrity of the material and improves its strength. Since red mud and graphite tailings contain a large number of particles smaller than 0.075mm, they can fill the micro-voids in the material to a certain extent, which is beneficial to improving the overall water stability of the material.

[0019] Stone chips fill the gaps in the formed skeleton, acting as a filler and making the overall skeleton structure more compact. Furthermore, the mixing of stone chips with red mud and graphite tailings can reduce the liquid and plastic limits of the red mud-graphite tailings, reduce water consumption, and also reduce viscosity, preventing wheel sticking during road roller compaction, thus significantly reducing construction difficulty and improving construction efficiency.

[0020] ISS, early-strength agent, and anti-hardness agent are three admixtures that together constitute the admixtures in the base material. All three materials are inexpensive and have a synergistic effect, jointly improving the strength of the base material. Specifically, the individual functions of the three admixtures are as follows:

[0021] The ISS is selected from sodium ricinoleate sulfate, which has a unique structure: a hydrophilic head composed of the organic compound sulfonic acid (RSO3H) and a hydrophobic tail composed of carbon and hydrogen atoms. Its main functions are as follows:

[0022] 1. Ion exchange occurs with the surface of tailings particles, reducing the thickness of the double electric layer, making the bound water film thinner, causing changes in the forces between tailings particles, which in turn leads to a denser soil structure and improves the overall strength of road base materials.

[0023] 2. By wetting the surface of tailings particles, they spread on the surface of tailings soil particles. Under the action of hydrogen bonds and ionic bonds, they adsorb onto the surface of soil particles. Then, through a special "dual" structure, the polar groups face the soil particles, while the hydrophobic groups of the main chain face outwards. The bound water adsorbed on the surface of the soil particles is squeezed out by the "hydrophobic tails" and forms a coating film on the surface of the soil particles. The strong electrostatic effect of the ISS solution weakens the negative electrostatic repulsion between the layers of tailings soil minerals, promotes the aggregation and coagulation between soil particles, and significantly improves the overall strength of the material.

[0024] 3. It works synergistically with alcohol amine admixtures to reduce the water-binding capacity of tailings particles, thus limiting the aggregation behavior of tailings particles when exposed to water, thereby allowing more water to participate in the hydration reaction of cement.

[0025] 4. By utilizing the positive charge or -OH on adjacent bonds, adjacent soil particles are linked together through molecular chains, ultimately forming a strong, integrated spatial network structure in the entire soil. This improves the adsorption capacity of heavy metal ions, reduces the leaching of heavy metal ions, and is beneficial to protecting the ecological environment.

[0026] The early strength agent selected is triethanolamine, which mainly has the following functions:

[0027] 1. The N and O atoms with lone pairs of electrons in triethanolamine can more easily enter the crystal lattice of cement mineral C3A and react with Al. 3+ Formation of complexes, weakening Al 3+The chemical bonds between the complex and cement minerals accelerate the hydration of C3A; the complex forms a soluble zone on the surface of cement particles, accelerating the diffusion rate of hydration products; at the same time, the formation of the complex disrupts the hydration products formed on the surface of cement particles (such as ettringite, a hydration product of C3A), thereby accelerating the dissolution rate of C3A and C4AF, promoting the faster formation rate of calcium sulfoaluminate, completing volume expansion before the cement paste hardens, and improving the early strength and density of cement;

[0028] 2. The negative potential generated by adsorption on cement particles causes the dipoles of water to align in a specific direction, hindering the approach of cement particles to each other, increasing the effective hydration area of ​​cement particles, and improving the hydration rate of cement. At the same time, it works synergistically with ISS. The negative potential generated on the surface of cement particles makes ISS more likely not to combine with cement particles, but to adhere entirely to the surface of soil minerals, each exerting its maximum effect.

[0029] The anti-hard water agent is selected from sodium dodecyl diphenyl ether disulfonate, and mainly performs the following functions:

[0030] Because the water used at construction sites contains a large amount of silt, when admixtures such as ionic soil stabilizers and early-strength agents are added, the admixtures first undergo a complexation reaction with the cations on the surface of the silt particles in the water. This prevents the admixtures from fully exerting their intended effect. However, after adding an appropriate amount of sodium dodecyl diphenyl ether disulfonate, it complexes with the cations on the surface of the silt particles before the other two admixtures. This allows the remaining admixtures to fully complex with the cations on the surface of red mud and graphite tailings particles, improving the overall strength of the material.

[0031] Preferably, the red mud has a plasticity index of 12-14, and the optimal moisture content determined by compaction test is 7%-10%; the graphite tailings have a plasticity index of 11-13, and the optimal moisture content determined by compaction test is 5%-8%. The particle size of both red mud and graphite tailings is less than 5 mm.

[0032] Preferably, the cement is ordinary Portland cement, whose main components are calcium oxide and silicon dioxide, and its strength grade is 42.5. In ordinary Portland cement, calcium oxide and silicon dioxide react with water in the early stage to form hydrated calcium silicate gel, which plays a bonding role and can improve early strength. At the same time, due to the addition of the early strength agent triethanolamine, it is difficult for it to get close to the surrounding cement particles, thereby increasing the effective hydration area and improving its own hydration rate.

[0033] Preferably, in the aggregate, 32% of the aggregate has a particle size of 15-20mm, 25% has a particle size of 10-15mm, and 43% has a particle size of 5-10mm. The aggregates of different sizes interlock to form the skeleton of the road base material. Stone chips, red mud, graphite tailings, and cement hydration products fill the gaps in the skeleton, forming a dense structure that supports the overall integrity of the material and improves its strength.

[0034] This invention also provides a method for preparing the above-mentioned red mud-graphite tailings road base material, comprising the following steps:

[0035] 1) Determine the optimum moisture content and maximum dry density based on the compaction test, and calculate the required mass of gravel, graphite tailings, red mud, stone chips and cement, as well as the total water consumption;

[0036] 2) Add the anti-hardening agent to the water and stir until there are no obvious particles at the bottom of the solution to obtain a mixed solution;

[0037] 3) Dry the gravel, graphite tailings, red mud and stone chips, and crush the red mud and graphite tailings so that the particle size after crushing is less than or equal to 5mm.

[0038] 4) Mix the gravel, graphite tailings, red mud and stone chips together, add the mixed solution prepared in step 2), and stir evenly;

[0039] 5) Add cement and mix. After mixing evenly, add ISS, early strength agent and remaining water, and mix thoroughly again to obtain red mud-graphite tailings road base material.

[0040] Preferably, in step 1), the materials for the compaction test include red mud, graphite tailings, cement, gravel, stone chips, ISS, and an early-strength agent. The specific method for the compaction test refers to Method B of JTG E51-2009 "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering": the test cylinder dimensions are an inner diameter of 15.2 cm, a height of 12 cm, and a volume of 2177 cm³. 3 The material was added to the test tube in five batches, with each batch weighing 1100g ± 100g. The number of hammering layers was five, and the number of hammerings per batch was set to 59.

[0041] Preferably, in step 2), the mass of the added water accounts for 70%-80% of the mass of water calculated according to the optimum moisture content.

[0042] Preferably, in step 3), the drying temperature is 110℃±5℃, and the drying time is 12h. Drying at the above temperature can remove free water from the stones, red mud, graphite tailings, and stone chips.

[0043] Preferably, in step 4), the input mass of graphite tailings and red mud is the same, and the total mass of gravel, red mud, graphite tailings and stone chips is 100 parts.

[0044] Preferably, in step 5), the amount of cement used accounts for 4.5% of the total mass of gravel, red mud, graphite tailings, and stone chips. At this cement content, the 7-day unconfined compressive strength of the resulting red mud-graphite tailings roadbed material meets the strength requirements of expressways and first-class highways, and it can save costs, resulting in significant economic benefits.

[0045] Preferably, in steps 4) and 5), the stirring temperature is room temperature, the stirring time is 6 to 10 minutes, and the stirring speed is controlled at 60 r / min.

[0046] The method for compounding the ISS, early strength agent, and water includes the following steps:

[0047] 1. Add 1% of the mass of water calculated according to the optimum moisture content to the water and stir. The stirring temperature is room temperature, the stirring speed is 100 r / min, and the stirring time is controlled at 2 to 3 min.

[0048] 2. When the solution gradually changes from colorless and transparent to milky white turbid liquid and there is no sediment at the bottom, add 0.03% of the cement mass as an early strength agent, and continue stirring under the same stirring conditions as in step 1. When there are no obvious particles at the bottom of the solution, the compound solution is obtained.

[0049] Finally, this invention provides the application of the red mud-graphite tailings road base material or the red mud-graphite tailings road base material prepared by the above-mentioned red mud-graphite tailings road base material or preparation method in road engineering.

[0050] Preferably, the application specifically involves using red mud-graphite tailings road base material for roadbed construction.

[0051] The working mechanism of the red mud-graphite tailings roadbed material of this invention is mainly manifested in:

[0052] 1. The use of ISS, after being incorporated, causes a series of complex physicochemical reactions with red mud and graphite particles, reducing porosity and increasing strength; ISS can connect adjacent soil particles through molecular chains, ultimately forming a strong and integral spatial network structure in the entire soil, which improves the adsorption capacity of heavy metal ions, reduces the leaching of heavy metal ions, and is beneficial to protecting the ecological environment.

[0053] 2. Triethanolamine can accelerate the dissolution rate of C3A and C4AF, promote the formation rate of calcium sulfoaluminate, complete the volume expansion before the cement paste hardens, and improve the early strength and density of cement.

[0054] 3. Ammonium dodecyl sulfate can inhibit the complexation reaction between other admixtures and cations on the surface of sediment particles in engineering construction water, thereby improving the efficiency of other admixtures.

[0055] 4. Red mud provides an alkaline environment for cement hydration, which is beneficial to the cement hydration reaction;

[0056] 5. A reasonable order of addition used in the preparation method can ensure uniform mixing of the components and improve the overall strength of the material.

[0057] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0058] 1. The red mud-graphite tailings road base material provided by this invention uses inexpensive ISS, anti-hardening water agent and early strength agent, and the cement demand is much less than that of the prior art. Through reasonable gradation, it achieves a 7-day unconfined compressive strength of 5.3-6.8MPa, which meets the strength requirements of expressways and first-class highways in JTG / T F50-2015 "Technical Specifications for Construction of Highway Pavement Base".

[0059] 2. The red mud-graphite tailings composite fine aggregate in the red mud-graphite tailings road base material provided by this invention can significantly reduce the viscosity of the red mud-graphite tailings road base material, thereby reducing the difficulty of construction.

[0060] 3. The red mud-graphite tailings road base material provided by this invention utilizes ISS, an early-strength agent, and an anti-hardening water agent to facilitate ion exchange between positively charged groups and the positive charges on the surface of soil particles, thereby thinning the double electric layer and improving water stability. Its highly alkaline environment promotes the formation of hydroxides from heavy metal ions or the formation of complex hydroxides in conjunction with calcium, which precipitate on the surface of solid particles, reducing the leaching of heavy metal ions.

[0061] 4. In the preparation method of red mud-graphite tailings road base material provided by the present invention, there is no need to activate the red mud at high temperature, which effectively avoids the leaching of harmful ions. At the same time, by controlling the order of addition of ISS, early strength agent and anti-hard water agent, the leaching of harmful ions in red mud is further inhibited, ensuring that the preparation process and the use process are green and environmentally friendly. Detailed Implementation

[0062] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0063] Both the examples and comparative examples used red mud from Weiqiao Village in Zouping City and graphite tailings from Pingdu City, which were collected on-site and then sealed. The red mud had a plasticity index of 12-14 and an optimum moisture content of 7%-10%, while the graphite tailings had a plasticity index of 11-13 and an optimum moisture content of 5%-8%. Ordinary Portland cement with a strength grade of 42.5, produced by Shandong Cement Plant, was used. The aggregate and stone chips were obtained from Jinan Luguan Mixing Plant. Other experimental reagents were all commercially available and will not be described further.

[0064] The experimental procedure was conducted in accordance with the "Test Regulations for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG E51-2009). All strengths described below are 7-day unconfined compressive strengths, and water stability indicators are expressed as immersion strength. Immersion strength was determined by placing the specimens in a standard curing chamber for 6 days, with the last day being immersion curing.

[0065] The leaching 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 to be determined were hexavalent chromium ions and copper ions.

[0066] Example 1

[0067] A red mud-graphite tailings road base material is composed of the following components in parts by weight: 0.07 parts ISS, 0.00135 parts early strength agent, 0.35 parts anti-hard water agent, 4.5 parts ordinary Portland cement, 60 parts gravel, 7 parts water, 20 parts red mud, and 20 parts graphite tailings.

[0068] ISS uses sodium ricinoleate sulfate, the early strength agent uses triethanolamine, and the hard water resistance agent uses sodium dodecyl diphenyl ether disulfonate.

[0069] Of the pebbles, those with a diameter of 5–10 mm account for 32% of the total mass, those with a diameter of 10–15 mm account for 25% of the total mass, and those with a diameter of 15–20 mm account for 43% of the total mass.

[0070] The plasticity index of red mud is 13, and the optimum moisture content determined by compaction test is 7.5%; the plasticity index of graphite tailings is 11, and the optimum moisture content determined by compaction test is 6.5%.

[0071] The specific steps of the preparation method of the above-mentioned red mud-graphite tailings road base material are as follows:

[0072] 1) Determine the maximum dry density and optimum moisture content through compaction tests, referring to Method B of JTG E51-2009 "Test Procedures for Inorganic Binder Stabilized Materials in Highway Engineering". Calculate the required total mass of dry materials based on the determined maximum dry density. The dry materials specifically include gravel, red mud, graphite tailings, and cement, with cement accounting for 4.5% of the total mass of gravel, red mud, and graphite tailings. The quantities of gravel, red mud, graphite tailings, and cement can then be calculated.

[0073] 2) Dry the weighed stones, red mud, and graphite tailings at 110℃ for 12 hours. The red mud and graphite tailings also need to be pre-crushed to make their particle size between 0-5mm.

[0074] 3) Add the anti-hardness agent to 70% of the water mass calculated according to the optimum moisture content and stir until there are no obvious particles at the bottom to obtain a mixed solution;

[0075] 4) Transfer the gravel, red mud, and graphite tailings into the mixing equipment for mixing, add the mixed solution obtained in step 2), and stir at 60 r / min for 6 min at room temperature.

[0076] 5) After adding cement, mix again; after mixing evenly, add ISS, early strength agent and remaining water, and stir at 60r / min for 10 minutes at room temperature to obtain red mud-graphite tailings road base material.

[0077] The preparation method of ISS, early strength agent and water includes the following steps:

[0078] 1. Add 1% of the mass of water calculated according to the optimum moisture content to the water and stir. The stirring temperature is room temperature, the stirring speed is 100 r / min, and the stirring time is controlled at 3 min.

[0079] 2. When the solution gradually changes from colorless and transparent to milky white turbid liquid and there is no sediment at the bottom, add 0.03% of the cement mass as an early strength agent, and continue stirring under the same stirring conditions as in step 1. When there are no obvious particles at the bottom of the solution, the compound solution is obtained.

[0080] Example 2

[0081] A red mud-graphite tailings road base material is composed of the following components in parts by weight: 0.063 parts ISS, 0.00135 parts early strength agent, 0.315 parts anti-hardening water agent, 4.5 parts ordinary silicate cement, 60 parts gravel, 10 parts stone chips, 6.3 parts water, 15 parts red mud, and 15 parts graphite tailings.

[0082] The specific preparation method is the same as in Example 1.

[0083] Example 3

[0084] A red mud-graphite tailings road base material is composed of the following components in parts by weight: 0.057 parts ISS, 0.00135 parts early strength agent, 0.285 parts anti-hardening water agent, 4.5 parts ordinary silicate cement, 60 parts gravel, 20 parts stone chips, 5.7 parts water, 10 parts red mud, and 10 parts graphite tailings.

[0085] The specific preparation method is the same as in Example 1.

[0086] Example 4

[0087] A red mud-graphite tailings road base material is composed of the following components in parts by weight: 0.053 parts ISS, 0.00135 parts early strength agent, 0.265 parts anti-hardening water agent, 4.5 parts ordinary silicate cement, 60 parts gravel, 30 parts stone chips, 5.3 parts water, 5 parts red mud, and 5 parts graphite tailings.

[0088] The specific preparation method is the same as in Example 1.

[0089] Example 5

[0090] The application of a red mud-graphite tailings road base material in road engineering, specifically the use of red mud-graphite tailings road base material in roadbed construction.

[0091] Comparative Example 1

[0092] In this comparative example, to clarify the feasibility of using red mud and graphite tailings in road base materials, a cement-stabilized crushed stone road base material is provided, which is composed of the following components in the indicated weight proportions: 4.5 parts ordinary Portland cement, 60 parts gravel, 40 parts stone chips, and 5.1 parts water.

[0093] The specific preparation method is as follows:

[0094] 1) Determine the maximum dry density and optimum moisture content through compaction tests, referring to Method B of JTG E51-2009 "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering". Calculate the required total mass of dry material based on the determined maximum dry density. The dry material specifically includes gravel, stone chips, and cement, with cement accounting for 4.5% of the total mass of gravel and stone chips. The required amounts of gravel, stone chips, and cement can then be calculated.

[0095] 2) Dry the weighed stones and stone chips at 110℃ for 12 hours.

[0096] 3) Transfer the stones and stone chips into the mixing equipment for dry mixing.

[0097] 4) After dry mixing, add 70% to 80% of the mass of water calculated according to the optimum moisture content and mix. After mixing evenly, add the cement, then add the remaining water and mix again.

[0098] Comparative Example 2

[0099] In this comparative example, to clarify the synergistic effect of the three admixtures, a red mud-graphite tailings road base material is composed of the following components in the indicated weight proportions: 4.5 parts ordinary silicate cement, 60 parts gravel, 20 parts red mud, 20 parts graphite tailings, and 7 parts water.

[0100] Specifically, the preparation method of this comparative example does not include the step of preparing additives; the remaining steps are the same as in Example 1.

[0101] Comparative Example 3

[0102] In this comparative example, to compare with cement-stabilized materials that use red mud to replace fine aggregate, ordinary silicate cement was used as an inorganic curing agent and added to the red mud in a certain proportion. Specimens were prepared and their 7-day unconfined compressive strength was determined in accordance with the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG E51-2009).

[0103] A red mud road base material is composed of the following components in parts by weight: 4.5 parts ordinary silicate cement (the specific water requirement is determined by compaction test), 60 parts gravel, and 40 parts red mud.

[0104] The specific preparation method is the same as that of Comparative Example 1.

[0105] Comparative Example 4

[0106] In this comparative example, in order to compare with cement-stabilized materials that use graphite tailings to replace fine aggregate, ordinary silicate cement was used as an inorganic curing agent and added to red mud in a certain proportion. Specimens were prepared in accordance with the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTG E51-2009), and the seven-day unconfined compressive strength and water stability index of the solidified soil were measured respectively.

[0107] A red mud road base material is composed of the following components in parts by weight: 4.5 parts of ordinary silicate cement (the specific water requirement is determined by compaction test), 60 parts of gravel, and 40 parts of graphite tailings.

[0108] The specific preparation method is the same as that of Comparative Example 1.

[0109] Comparative Example 5

[0110] This comparative example includes four parallel samples. To ensure the red mud-graphite tailings blending ratio is 1:1, a red mud-graphite tailings mixed soil is composed of the following components in the indicated weight ratios: 1. 60 parts red mud, 40 parts graphite tailings; 2. 40 parts red mud, 60 parts graphite tailings; 3. 70 parts red mud, 30 parts graphite tailings; 4. 30 parts red mud, 70 parts graphite tailings.

[0111] The specific preparation steps are as follows:

[0112] 1) The dried red mud and graphite tailings were divided into the above 4 groups according to the mass ratio. Each group was further divided into 5 subgroups according to the determined proportion, in order to prepare red mud-graphite tailings mixed soil with different water content. The total mass of red mud and graphite tailings in each subgroup was 200g.

[0113] 2) Thoroughly mix the grouped red mud-graphite tailings dry materials. Based on engineering experience, add different masses of water to the five groups of red mud-graphite tailings mixed soil in the same proportion to adjust the moisture content of the mixed soil.

[0114] 3) The liquid and plastic limits of different red mud-graphite tailings blending ratios were determined using a combined liquid and plastic limit tester.

[0115] In step 2), the five different moisture contents are: 1. Soil moisture content below the plastic limit; 2. Soil moisture content near the plastic limit; 3. Soil moisture content between the plastic limit and the liquid limit; 4. Soil moisture content near the liquid limit; 5. Soil moisture content above the liquid limit.

[0116] In step 3), the plasticity index of the red mud-graphite tailings mixed soil can be determined by referring to the relevant provisions in JTG 3430—2020 "Specifications for Geotechnical Testing of Highways".

[0117] Comparative Example 6

[0118] In this comparative example, to clarify the mass ratio of gravel, red mud, graphite tailings and stone chips in the red mud-graphite tailings road base material, a red mud-graphite tailings road base material is composed of the following components in the following weight proportions: 4.5 parts ordinary silicate cement, 30 parts gravel, 35 parts red mud, 35 parts graphite tailings, and 8 parts water.

[0119] The specific preparation method is the same as in Example 1. In particular, there is no step of preparing additives in this comparative example.

[0120] Comparative Example 7

[0121] In this comparative example, to clarify the influence of the order of cement and admixture addition on the strength of red mud-graphite tailings road base material, a red mud-graphite tailings road base material is provided, which is composed of the following components in the following weight proportions: 0.07 parts ISS, 0.00135 parts early strength agent, 0.35 parts anti-hardening water agent, 4.5 parts ordinary Portland cement, 60 parts gravel, 20 parts red mud, 20 parts graphite tailings, and 7 parts water.

[0122] The specific preparation method is as follows:

[0123] 1) Dry the gravel, red mud, graphite tailings and cement, and crush the red mud and graphite tailings to make their particle size between 0-5mm.

[0124] 2) Transfer all dry materials, including cement, into the mixing equipment for mixing. Add ISS, early strength agent and anti-hard water agent to water calculated according to the optimum moisture content in advance, stir evenly, and add them together to the dry materials for mixing.

[0125] Comparative Example 8

[0126] In this comparative example, to clarify the role of the dosage of early strength agent, a red mud-graphite tailings road base material is composed of the following components in the indicated weight proportions: ISS 0.07 parts, early strength agent 0.045 parts, anti-hardening water agent 0.35 parts, ordinary Portland cement 4.5 parts, gravel 60 parts, water 7 parts, red mud 20 parts, and graphite tailings 20 parts.

[0127] The specific preparation method is the same as in Example 1.

[0128] Comparative Example 9

[0129] In this comparative example, to clarify the role of ISS, a red mud-graphite tailings road base material is composed of the following components in parts by weight: 0.00135 parts early strength agent, 0.35 parts anti-hardening water agent, 4.5 parts cement, 60 parts gravel, 7 parts water, 20 parts red mud, and 20 parts graphite tailings.

[0130] The specific preparation method is the same as in Example 1.

[0131] Comparative Example 10

[0132] In this comparative example, to clarify the role of the early strength agent, a red mud-graphite tailings road base material is composed of the following components in the indicated weight ratios: ISS 0.07 parts, anti-hardening water agent 0.35 parts, cement 4.5 parts, gravel 60 parts, water 7 parts, red mud 20 parts, and graphite tailings 20 parts.

[0133] The specific preparation method is the same as in Example 1.

[0134] Comparative Example 11

[0135] In this comparative example, to clarify the role of the anti-hardening agent, a red mud-graphite tailings road base material is composed of the following components in the indicated weight ratios: 0.07 parts ISS, 0.00135 parts early strength agent, 4.5 parts cement, 60 parts gravel, 7 parts water, 20 parts red mud, and 20 parts graphite tailings.

[0136] The specific preparation method is the same as in Example 1.

[0137] The weight percentages of the above embodiments and comparative examples are shown in Table 1.

[0138] Table 1. Weight ratios of the embodiments and comparative examples

[0139]

[0140]

[0141] Table 2 Experimental Results

[0142]

[0143]

[0144] The 7-day unconfined compressive strength of Examples 1-4 is greater than 5.0 MPa, meeting the strength requirements for road base (subbase) materials under extremely heavy and extra-heavy traffic conditions on expressways and Class I highways as specified in JTGT F20—2015 "Technical Specifications for Construction of Highway Pavement Base". The 7-day unconfined compressive strength of Comparative Example 1 meets the requirements for extremely heavy and extra-heavy traffic conditions on expressways and Class I highways, and its hexavalent chromium leaching meets the prescribed requirements. Compared with Comparative Example 1, Examples 1-4 all meet the corresponding strength requirements, proving the feasibility of using red mud and graphite tailings as road base materials. Compared with Comparative Example 2, the 7-day unconfined compressive strength values ​​of Examples 1-4 are all improved. In particular, the 7-day unconfined compressive strength of Example 1 is 71.0% higher than that of Comparative Example 2, showing a very significant strength improvement, and the leaching of heavy metal ions is less than that of Comparative Example 2. This indicates that the incorporation of admixtures can not only improve the strength of red mud-graphite tailings road base materials but also bind heavy metal ions.

[0145] Compared with Comparative Example 1, Comparative Examples 3 and 4 showed a significant decrease in their 7d-unconfined compressive strength values, decreasing by 62.3% and 85.2% respectively. This indicates that red mud and graphite tailings cannot be used alone as road base materials, and the hexavalent chromium ion leaching in Comparative Example 3 exceeded the specified requirements.

[0146] In Comparative Example 5, when the proportion of red mud is high, the viscosity of the red mud-graphite tailings soil is too high, which can lead to wheel sticking during construction, hindering the process. When the proportion of graphite tailings is high, the plasticity of the red mud-graphite tailings soil decreases, making it difficult to shape. For red mud-graphite tailings road base materials, when the proportion of graphite tailings is high, the overall strength of the material is low, the bonding force is weak, and it is impossible to effectively bond coarse aggregates and other fine aggregates together.

[0147] Compared to Comparative Examples 1-4, Comparative Example 6 showed a significant decrease in its 7d unconfined compressive strength. This is because the proportion of coarse aggregate in Comparative Example 6 was less than that of fine aggregate, thus failing to form a "dense skeleton" structure and instead creating a "suspended dense" structure. For cement-stabilized crushed stone base materials, their strength primarily depends on the "interlocking force" between coarse aggregates and the partial "cohesion" between fine aggregates. In a "dense skeleton" structure, the proportion of coarse aggregate is large, and they rub and compress against each other, forming a "net" structure. Fine aggregate fills the gaps in this "net" structure, making the overall structure dense. However, in a "suspended dense" structure, the proportion of coarse aggregate is small, making it difficult for friction to occur between them, thus preventing the formation of "interlocking force." The coarse aggregate is "suspended" within the fine aggregate, and its strength mainly comes from the "cohesion" between the fine aggregates, resulting in a strength far lower than that of a "dense skeleton" structure.

[0148] Compared with Example 1, Comparative Example 7 had a different order of adding cement and admixtures, and its 7d-unconfined compressive strength decreased by 20.1%, indicating that the order of adding admixtures and cement has a significant impact on strength.

[0149] Compared with Example 1, Comparative Example 8 had a higher dosage of early strength agent than 1%, and its 7-day unconfined compressive strength increased slightly. This indicates that the dosage of early strength agent affects its early strength. However, when the dosage of early strength agent is greater than 1%, it strongly promotes the setting of cement, which not only makes on-site construction impossible, but also leads to slow growth of the later strength of cement-based materials.

[0150] Compared with Example 1, Comparative Example 9 showed a 2.1 MPa decrease in 7d-unconfined compressive strength and a 223 MPa increase in drying shrinkage strain. Its ability to solidify hexavalent chromium was also significantly reduced. This indicates that the unique "dual" structure of ISS and the ion exchange reaction can form a coating film on the surface of soil particles and weaken the negative electrostatic repulsion between tailings soil mineral layers, promoting the aggregation and coagulation of soil particles, significantly improving the overall strength of the material and its solidification effect on heavy metal ions.

[0151] Compared with Example 1, Comparative Example 10 showed a decrease of 1 MPa in 7-day unconfined compressive strength and an increase of 106 in drying shrinkage strain. This indicates that the effect of the accelerator is far less than that of the ISS. The main effect of the accelerator is reflected in its dosage. When its dosage is less than 0.05%, it will play a role in increasing early strength. When its dosage is greater than 1%, it will play a role in rapid setting, resulting in a significant decrease in the strength of the cement paste.

[0152] Compared with Example 1, Comparative Example 11 showed a decrease of 0.3 MPa in 7d-unconfined compressive strength and an increase of 18 in drying shrinkage strain. It can be seen that the addition of a water hardener does not have a significant impact on the overall material. This is mainly reflected in the mechanism of action of the water hardener, which mainly forms a complex with the cations on the surface of mud and sand particles in the water, providing a working environment closer to the laboratory for ISS and early strength agents.

Claims

1. A red mud-graphite tailings road base material, characterized in that, The following components are included in parts by weight: ISS 0.05~0.07 parts, early strength agent 0.0012~0.0015 parts, anti-hardening water agent 0.25~0.35 parts, cement 4~5 parts, gravel 60 parts, red mud 5~20 parts, graphite tailings 5~20 parts, stone chips 10~30 parts, and water 5~7 parts. The total mass fraction of red mud, graphite tailings and stone chips is 40 parts. The particle size range of the pebbles is 5-20mm; the particle size of the red mud and graphite tailings is ≤5mm; the particle size of the stone chips is ≤5mm. The ISS is sodium ricinoleate sulfate, the early strength agent is triethanolamine, and the hard water resistant agent is sodium dodecyl diphenyl ether disulfonate. The 7-day unconfined compressive strength range of the red mud-graphite tailings road base material is 5.3-6.8 MPa; The ratio of red mud to graphite tailings is 1:

1.

2. The red mud-graphite tailings road base material as described in claim 1, characterized in that: The plasticity index of the red mud is 12-14, and the optimal moisture content determined by the compaction test is 7%-10%; the plasticity index of the graphite tailings is 11-13, and the optimal moisture content determined by the compaction test is 5%-8%; the particle size of both the red mud and the graphite tailings is less than 5 mm.

3. The red mud-graphite tailings road base material as described in claim 1, characterized in that: The cement is silicate cement with a strength grade of 42.5; the stone chips are limestone.

4. The red mud-graphite tailings road base material as described in claim 1, characterized in that: Of the stones, stones with a diameter of 15-20mm account for 32% of the total stone mass, stones with a diameter of 10-15mm account for 25% of the total stone mass, and stones with a diameter of 5-10mm account for 43% of the total stone mass.

5. A method for preparing red mud-graphite tailings road base material as described in any one of claims 1-4, characterized in that, Includes the following steps: 1) Determine the optimum moisture content and maximum dry density based on the compaction test, and calculate the required mass of gravel, graphite tailings, red mud, stone chips and cement, as well as the total water consumption; 2) Add the anti-hardening agent to the water and stir until there are no obvious particles at the bottom of the solution to obtain a mixed solution; 3) Dry the stones, graphite tailings, red mud and stone chips, and crush the red mud and graphite tailings; 4) Dry mix the gravel, graphite tailings, red mud and stone chips, add the mixed solution obtained in step 2), and stir evenly; 5) Add cement and mix. After mixing evenly, add ISS, early strength agent and remaining water, and mix thoroughly again to obtain red mud-graphite tailings road base material.

6. The preparation method according to claim 5, characterized in that, In step 2), the water required for mixing the anti-hardness agent accounts for 70%-80% of the mass of water calculated according to the optimum moisture content; In step 3), the drying temperature is 110℃±5℃ and the drying time is 12h.

7. The preparation method according to claim 5, characterized in that, In step 4), the input mass of graphite tailings and red mud is the same, and the total mass of stones, red mud, graphite tailings and stone chips is 100 parts. In step 5), the amount of cement used accounts for 4.5% of the total mass of gravel, red mud, graphite tailings, and stone chips; In steps 4) and 5), the stirring temperature is room temperature, the stirring time is 6-10 minutes, and the stirring speed is controlled at 60 r / min.

8. The preparation method according to claim 5, characterized in that, In step 5), the compounding method of ISS, early strength agent and water includes the following steps:

1. Add 1% of ISS by mass of water calculated according to the optimum moisture content to the water and stir. The stirring temperature is room temperature, the stirring speed is 100 r / min, and the stirring time is controlled at 2~3 min; 2. When the solution gradually changes from colorless and transparent to milky white turbid liquid and there is no sediment at the bottom, add 0.03% of the cement mass of early strength agent and continue stirring. The stirring conditions are the same as in step 1. When there are no obvious particles at the bottom of the solution, the compounded solution is obtained.

9. The application of a red mud-graphite tailings road base material as described in any one of claims 1-4 or a red mud-graphite tailings road base material prepared by the preparation method described in any one of claims 5-8 in road engineering.

10. The application as described in claim 9, characterized in that, The specific application involves using red mud-graphite tailings road base materials for roadbed construction.

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