A kind of roadbed filler based on curing agent treatment tunnel excavation abandoned salinization loess and its preparation method

Abstract

The application discloses a kind of based on solidified agent processing tunnel excavation waste salinization loess roadbed filler and preparation method thereof, belong to tunnel abandoned soil comprehensive utilization technical field, wherein the roadbed filler includes tunnel waste slag, solidified agent and water, the solidified agent includes magnesium slag 23~27 parts, fly ash 3~5 parts, activator 1~3 parts, reinforcing agent 6~8 parts, adsorbent 3~5 parts, and the adsorbent is magnesium aluminum carbonate hydrotalcite.The application makes full use of high content of sulfate in tunnel waste slag, and in the curing process, solidified agent generates hydrated magnesium silicate aluminate and hydrated calcium silicate aluminate gel, and the cation in hydrated magnesium silicate aluminate and hydrated calcium silicate aluminate and magnesium aluminum carbonate hydrotalcite occurs ion exchange and synergistic reaction, forms stable phase, effectively improves the mechanical properties and environmental stability of solidified soil.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization technology of tunnel excavation waste soil, and more specifically, it relates to a roadbed filler based on solidifying agent treatment of saline loess waste soil from tunnel excavation and its preparation method. Background Technology

[0002] With the economic development of western China, the construction of highways in mountainous areas is increasing. A key characteristic of these mountain highways is their high bridge-to-tunnel ratio, generally exceeding 50%, with some exceptions like the Sichuan-Guang'an-Gansu Expressway where the ratio reaches as high as 80%. The number of long tunnels, extra-long tunnels, and tunnel clusters is also rising, leading to a significant increase in tunnel excavation and waste soil. Due to limitations in construction technology and management, the utilization of tunnel excavation soil is inadequate and limited, failing to be comprehensively utilized as high-quality road construction material. The utilization rate is generally low, around 20%. Tunnel excavation soil requires substantial land use, causing resource waste and environmental pollution, and potentially leading to soil erosion. Therefore, the comprehensive utilization and optimized resource allocation of tunnel excavation soil in mountainous areas is a pressing issue that needs to be addressed in highway construction, especially in mountainous regions.

[0003] The Fenghuangshan Tunnel is a key project on the G30 Lianyungang-Horgos Expressway, specifically the section from Qingshuiyi to Zhonghe. Located in Jinya Town, Yuzhong County, Lanzhou City, it is designed as a long, twin-bore tunnel with separate left and right tunnels, measuring 3,945 meters in length, making it an exceptionally long tunnel with a maximum burial depth of 180 meters. During the excavation and construction process, a large amount of abandoned tunnel excavation soil was generated.

[0004] Patent CN116143468A discloses a premixed fluidized solidified saline soil and its preparation method. The premixed fluidized solidified saline soil uses chloride-containing cohesive soil from coastal areas as the main material, and comprises the following raw materials by weight: 80-100 parts saline soil, 25-30 parts iron tailings sand, 6-8 parts cement, 8-10 parts slag, 5-7 parts steel slag, 3-4 parts fly ash, 1.2-1.4 parts magnesium salt, 0.7-0.9 parts activator, 0.4-0.6 parts water-reducing agent, and 65-70 parts water. However, the saline soil in this patent is specifically designed for chloride-containing cohesive soil. Its solidifying agent formulation contains a high proportion of iron tailings sand, slag, and steel slag, which exhibit good resistance to salt erosion in high-chloride environments, and the synergistic effect of cement and activator improves the initial strength of the soil. However, this formulation is primarily designed for clayey soils and chloride-rich environments, and may not be suitable for sulfate-rich environments found in tunnel waste. The presence of sulfates can cause calcium ions in cement and slag to react with sulfate ions, generating expansive products (such as gypsum), thus affecting the curing effect. Therefore, the curing agent in this patent may face the problem of generating expansive salts when treating tunnel waste and cannot be applied directly.

[0005] Patent CN117088626A discloses a solid waste soil stabilizer for stabilizing saline soil and its preparation method. The solid waste soil stabilizer for stabilizing saline soil provided by this invention comprises 20-50 parts of carbide slag, 10-40 parts of blast furnace slag, 10-30 parts of recycled micro-powder from brick-concrete construction waste, and 5-15 parts of modified desulfurized gypsum; wherein CaO accounts for 35%-50%, Al2O3 and SiO2 account for 30%-45% of the total, Fe2O3, MgO and SO3 account for 5%-20% of the total, and other chemical components account for 2%-10%. This solidifier is designed for stabilizing saline soil and uses solid waste materials such as carbide slag, blast furnace slag, and modified desulfurized gypsum, making it suitable for high-salt soils. Its high CaO content effectively increases the alkalinity of the soil, which helps in the formation of ettringite and other stable phases. However, this curing agent is primarily designed for high-salinity environments, especially those containing sulfates and chlorides. Although its composition includes carbide slag and mineral slag, exhibiting strong activity and reactivity, its effectiveness may be limited in tunnel waste due to the complex composition containing impurities such as rock fragments and high salt concentrations. This may result in the formation of expansion products or insufficient curing without adjusting the formulation. Summary of the Invention

[0006] 1. The problem to be solved

[0007] To address the problem of unstable strength when exposed to water due to excessive sulfate ions in existing saline soils, this invention provides a roadbed filler based on the treatment of saline loess waste from tunnel excavation with a curing agent and its preparation method. The resulting roadbed filler has certain strength and water stability, meeting the technical requirements for filling highway roadbeds.

[0008] 2. Technical Solution

[0009] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0010] A roadbed filler based on a curing agent for treating saline loess waste from tunnel excavation, the roadbed filler comprising tunnel waste, curing agent and water, wherein the dry mass ratio of tunnel waste to curing agent is 1:0.08-0.12, and the moisture content of tunnel waste is controlled at 15%-16%.

[0011] The amount of curing agent added and the water content affect the formation of hydration products.

[0012] The curing agent includes magnesium slag, fly ash, activator, reinforcing agent, and adsorbent:

[0013] The weight percentages of each component are as follows: 23-29 parts magnesium slag, 3-9 parts fly ash, 1-3 parts activator, 6-8 parts reinforcing agent, and 3-5 parts adsorbent.

[0014] Preferably, the apparent density of the magnesium slag is 3000–3250 kg / m³. 3 The particle size is 2-4 mm. If the content is too high, it may increase the alkalinity, causing problems such as cracking or expansion during the later curing process, affecting the overall stability. If the content is too low, the amount of cementitious products such as hydrated magnesium aluminosilicate will decrease, resulting in a decrease in the strength and compressive strength of the material.

[0015] Preferably, the activator is a mixture of carbide slag and desulfurized gypsum in a mass ratio of 9-10:1. Excessive activator content may intensify the alkali-silica reaction in the material, leading to microcracks and reducing its durability and crack resistance. Furthermore, excessive activator may cause poor volume stability and expansion; insufficient content results in a reduced amount of cementitious products such as hydrated calcium silicate and hydrated calcium aluminosilicate. This directly affects the material's strength, density, and durability, failing to meet the mechanical and durability requirements in engineering applications.

[0016] Preferably, the reinforcing agent is steel slag powder with a particle size ≤200μm. Excessive content may increase the rigidity of the material, making it more brittle under external force and reducing its impact resistance. Simultaneously, excessive steel slag powder may increase the material's density, making it less workable and potentially increasing costs; insufficient content may result in a less dense microstructure, affecting the overall stability of the material.

[0017] Preferably, the adsorbent is magnesium aluminum carbonate hydrotalcite, which needs to be baked in a muffle furnace at a high temperature of 490-510℃ for 3 hours in advance. If the content is too high, it may affect the curing speed of the material, resulting in a longer curing time during construction; if the content is too low, the excess harmful ions (such as sulfates) in the material may not be effectively adsorbed and fixed, which may lead to problems such as expansion or decrease in strength during long-term use, affecting its durability and stability.

[0018] The carbonate ions inside magnesium aluminum carbonate hydrotalcite affect its adsorption effect. To enhance the adsorption effect of magnesium aluminum carbonate hydrotalcite, it is necessary to replace the carbonate ions inside the magnesium aluminum carbonate hydrotalcite in advance so that they can more effectively exchange with target ions or molecules in the subsequent adsorption process.

[0019] Adding too much hardener results in an excess of reactants in the material, potentially leading to unreacted hardener residue. This not only increases material costs but can also cause localized excessive alkalinity within the material, increasing the risk of cracking or expansion. Conversely, adding too little hardener results in incomplete hydration, reducing the amount of gelling products and causing insufficient strength and durability. Furthermore, insufficient hardener may fail to adequately neutralize harmful ions or particles in the material, significantly reducing its durability and stability and making it unsuitable for engineering requirements.

[0020] Excessive moisture content may accelerate the hydration reaction in the material, but it can also lead to excessive porosity, reducing its density and compressive strength. Furthermore, excessive moisture content can cause uneven curing, resulting in unstable material properties. Conversely, insufficient moisture content will limit the hydration reaction, reducing the formation of gelling products and significantly decreasing the material's strength and durability. It may also make it difficult to fully compact the material during molding, resulting in an uneven microstructure and affecting the overall stability of the material. In addition, insufficient moisture may prevent the active components in the curing agent from fully dissolving and diffusing, affecting the reaction and the formation of hydration products.

[0021] Preferably, 95-98% of the tunnel waste is loess and 2-5% is rock debris. According to the combined liquid and plastic limit test, the liquid limit is 29.2% and the plastic limit index is 10.9, which belongs to low plastic clay.

[0022] Preferably, in the tunnel waste, 19% to 20% is tunnel waste with a particle size of less than 0.005 mm, 77% to 78% is tunnel waste with a particle size of 0.005 mm to 0.075 mm, and 2% to 3% is tunnel waste with a particle size of 0.075 mm to 2 mm.

[0023] Preferably, the total soluble salt content of the tunnel waste is 3.0%–3.1%, the total chloride ion content is 0.20%–0.30%, and the sulfate ion concentration is 1.10%–1.30%, classifying it as a strong sulfate soil, and SO42-... 2- / Cl - >2.

[0024] This invention also provides a method for preparing the above-mentioned roadbed filler based on the treatment of saline loess waste from tunnel excavation with a curing agent, comprising the following steps:

[0025] The tunnel excavated soil, solidifying agent, and water are mixed and then sequentially molded and cured to obtain the roadbed filler.

[0026] Preferably, the curing is constant temperature and humidity curing; the curing temperature is 23±1℃, the relative humidity is 98%, and the curing period is set to 7 days, 14 days, and 28 days.

[0027] Preferably, the specimens with a curing period of 28 days are immersed in distilled pure water on the 27th day and cured for another 24 hours; the vertical distance between the water surface and the top of the specimen is 2.5 cm.

[0028] Preferably, the molding method is static compaction.

[0029] The obtained roadbed filler has an unconfined compressive strength of >1.70 MPa at 7 days and >7.84 MPa at 28 days; the water stability coefficient is 70-80%. This invention overcomes the problem of instability when exposed to water in the original scheme; at the same time, the sulfate ion concentration is also significantly reduced, and the leaching concentration meets the national groundwater quality Class IV standard.

[0030] This application addresses the comprehensive utilization of waste saline-alkali loess. This type of waste loess not only exhibits unstable strength when exposed to water but also contains a large amount of sulfate, possessing some engineering properties of saline soil, such as high salt content, poor soil structure, low soil fertility, and soil moisture conditions affected by salt concentration. Therefore, during on-site construction, construction teams typically incorporate 5% quicklime as a solidifying agent into the waste saline-alkali loess, combined with physical reinforcement methods such as geomembranes and geotextiles, to mitigate the adverse effects of the waste saline-alkali loess. However, this treatment method still has many shortcomings that need improvement, such as poor water stability, high cost, environmental pollution, low strength, and excessive sulfate ion levels.

[0031] It is important to note that this invention primarily targets engineering waste with excessive sulfate content, not engineering waste with excessive chloride content. When chloride reacts with materials such as cement and lime, the products are relatively simple, mainly compounds like calcium chloride. Therefore, the solidification of chloride-containing engineering waste relies mainly on physical processes rather than complex chemical reactions, as illustrated in patent CN117088626A. However, this invention takes the opposite approach for engineering waste with excessive sulfate (such as calcium sulfate and sodium sulfate), utilizing the "harmful" component Cl... - and SO4 2- Through chemical reactions, hydration products beneficial to the mechanical properties of solidified soil are generated, such as AFt (ettringite), Friedel salt, and Kuzel salt, forming a dense solidified body, thereby significantly improving the strength and stability of the soil.

[0032] 3. Beneficial effects

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) The roadbed filler of the present invention makes full use of the high sulfate content in the tunnel waste. During the solidification process of the tunnel waste soil, the calcium carbide slag in the solidifying agent and the tunnel waste soil are solidified to generate hydrated magnesium aluminosilicate and hydrated calcium aluminosilicate gel. The hydrated magnesium aluminosilicate and hydrated calcium aluminosilicate undergo ion exchange and synergistic reaction with the cations in magnesium aluminum hydrotalcite to form a stable phase, which effectively improves the mechanical properties and environmental stability of the solidified soil.

[0035] (2) The tunnel waste of the roadbed filler of the present invention contains rock fragments. After the pyrite rock fragments are mixed with carbide slag, the hydrolysis of FeS2 is promoted, more sulfate ions are generated, and more ettringite and Friedel salt are generated. At the same time, the SiO2 glass structure in the rock fragments is deconstructed, generating more CAH and CASH structures. These hydration products are cemented together, which significantly improves the strength of the solidified soil, reduces the porosity, and improves the strength of the roadbed filler.

[0036] (3) The roadbed filler of the present invention improves the strong alkalinity of tunnel waste by adding carbide slag, increases the pH value of soil solution, breaks the binding of soil particles on sulfate ions, thereby enhancing the accessibility of sulfate ions and improving the adsorption capacity of magnesium aluminum carbonate hydrotalcite on sulfate ions in soil.

[0037] (4) The present invention uses tunnel waste with a small particle size distribution as the matrix material. The material with a smaller particle size has a larger specific surface area, which helps to accelerate the hydration reaction and generate hydration products uniformly, reduce porosity, enhance the overall strength and stability of the material, and in a high alkaline environment, it is easier to form uniform CASH and MASH gels, which further promotes the generation of stable phases such as ettringite and layered double hydroxides. Attached Figure Description

[0038] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that these drawings are designed for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless specifically indicated, these drawings are intended only to conceptually illustrate the structural construction described herein and are not necessarily drawn to scale.

[0039] Figure 1 This is the particle size distribution curve of the tunnel waste soil of the present invention;

[0040] Figure 2 This is a photograph of the microstructure of the hydration products of this invention. Detailed Implementation

[0041] The following detailed description of exemplary embodiments of the invention is taken with reference to the accompanying drawings, which form part of the description and illustrate exemplary embodiments in which the invention may be practiced. While these exemplary embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be implemented and various changes may be made to the invention without departing from the spirit and scope thereof. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and not restrictive of the description of the features and characteristics of the invention, to suggest the best mode for carrying out the invention, and is sufficient to enable those skilled in the art to practice the invention. Therefore, the scope of the invention is defined only by the appended claims.

[0042] It should be understood that the following text is merely used to describe one or more specific embodiments of the present invention and does not strictly limit the scope of protection specifically claimed by the present invention. As used herein, the terms "parallel" and "perpendicular" are not limited to their strict geometric definitions, but include tolerance for reasonable and inconsistent machining or human errors.

[0043] By using local industrial solid waste unique to Gansu Province as a blending material, the comprehensive utilization rate of tunnel spoil has been improved. This not only enables large-scale, low-cost, and high-value-added utilization of solid waste resources, but also avoids long-distance transportation of spoil, turning tunnel spoil into a valuable resource. This significantly reduces construction costs and overall carbon emissions in roadbed engineering in Gansu Province, resulting in high economic and environmental benefits.

[0044] The tunnel spoil used in this invention was extracted from the excavated waste soil of the Fenghuangshan Tunnel on the Lanzhou section of the G30 Lianyungang-Horgos Expressway in Lanzhou, Gansu Province. The soil was yellowish-brown, lumpy, and cracked. After drying and crushing, its particle size and gradation were as follows: 20.96% tunnel waste with a particle size of less than 0.005 mm, 77.48% tunnel waste with a particle size of 0.005 mm to 0.075 mm, and 1.56% tunnel waste with a particle size of 0.075 mm to 2 mm. The selected solidifying agents included fly ash and magnesium slag, both purchased from Nanjing, Jiangsu Province. The particle size distribution is as follows. Figure 1 As shown in Table 1, the main chemical components and their contents are listed below.

[0045] Table 1 Chemical composition and content of various solid wastes

[0046] Material <![CDATA[Al2O3]]> <![CDATA[SiO2]]> CaO <![CDATA[Fe2O3]]> MgO <![CDATA[SO3]]> Tunnel spoil 16.27 58.49 9.36 5.10 3.89 0.75 fly ash 37.25 44.65 6.91 4.59 1.68 1.28 magnesium slag 1.31 30.73 45.09 10.08 11.26 0.12

[0047] The preparation process of the roadbed filler in the examples and comparative examples includes the following steps:

[0048] A. Moistening of waste soil:

[0049] First, dry the soil in an oven at 105℃. Then, crush it with a wooden mallet and roller, and pass it through a 5mm sieve. Spread the sieved material in a square pan, and spray it evenly with the required amount of water until the target moisture content is reached. Mix it thoroughly again. Then, pack the moistened waste soil into woven bags with a PVC liner and seal them for at least 24 hours to ensure even distribution of pore water. Take soil samples at a rate of one sample per kilogram to test the moisture content, ensuring that the maximum difference in moisture content is within 1%.

[0050] B. Mixing of curing agent and waste soil:

[0051] Add the weighed curing agent to the moistened waste soil prepared in step A and mix until the mixture shows no obvious color difference. Then, use an NJ-160 benchtop cement paste electric mixer to intensify the mixing for 5 minutes to further increase its homogeneity. After mixing, transfer the uniformly mixed cured soil sample to a polyethylene plastic basin and cover it with plastic wrap to prevent moisture evaporation. To avoid cross-contamination between cured soil samples, thoroughly clean the mixing bowl and mixing blades after preparing different cured soil samples.

[0052] C. Static compression sample:

[0053] Currently, there is no unified sampling method or specimen size in the industry for evaluating the remediation effect of solidified soil. Since the evaluation of the solidification effect in this invention mainly focuses on the strength and water stability of the solidified soil, this invention refers to the provisions of GB / T50123—2019 "Standard for Geotechnical Testing Methods," using a static compression method to prepare solidified soil strength specimens with a diameter of 5 cm and a height of 10 cm.

[0054] D. Demolding and curing:

[0055] After demolding, the soil samples are quickly tested for size and mass using vernier calipers and an electronic platform scale. If the deviation of the soil sample diameter or height from the design value exceeds 1%, or if the deviation of the soil sample mass from the design value exceeds 1%, the soil sample is discarded and a new sample is prepared. Then, the soil samples that meet the requirements are placed in polyethylene sealed bags (to prevent moisture loss) and transferred to a standard curing room (relative humidity 98%, temperature 23±1℃) for curing until the design age.

[0056] E. Test Measurement:

[0057] Examples 1-4 and Comparative Examples 1-4 were subjected to unconfined compressive strength tests at curing ages of 7d, 14d, and 28d according to GB / T 50123-2019 "Standard for Geotechnical Testing Methods". At 27 days, they were immersed in distilled pure water and cured for another 24 hours for water stability tests.

[0058] Example 1

[0059] A roadbed filler based on the treatment of tunnel excavation waste soil with a curing agent comprises the following components: 420 parts of tunnel waste soil, 23 parts of magnesium slag, 3 parts of fly ash, 2.7 parts of carbide slag, 0.3 parts of desulfurized gypsum, 8 parts of steel slag powder, and 5 parts of magnesium aluminum carbonate hydrotalcite.

[0060] Example 2

[0061] A roadbed filler based on the treatment of tunnel excavation waste soil with a curing agent comprises the following components: 420 parts of tunnel waste soil, 27 parts of magnesium slag, 3 parts of fly ash, 0.9 parts of carbide slag, 0.1 parts of desulfurized gypsum, 6 parts of steel slag powder, and 5 parts of magnesium aluminum carbonate hydrotalcite.

[0062] Example 3

[0063] A roadbed filler based on the treatment of tunnel excavation waste soil with a curing agent comprises the following components: 420 parts of tunnel waste soil, 25 parts of magnesium slag, 4 parts of fly ash, 1.8 parts of carbide slag, 0.2 parts of desulfurized gypsum, 7 parts of steel slag powder, and 4 parts of magnesium aluminum carbonate hydrotalcite.

[0064] Example 4

[0065] A roadbed filler based on the treatment of tunnel excavation waste soil with a curing agent comprises the following components: 420 parts of tunnel waste soil, 27 parts of magnesium slag, 5 parts of fly ash, 0.9 parts of carbide slag, 0.1 parts of desulfurized gypsum, 6 parts of steel slag powder, and 3 parts of magnesium aluminum carbonate hydrotalcite.

[0066] Example 5

[0067] A roadbed filler based on the treatment of tunnel excavation waste soil with a curing agent comprises the following components: 525 parts of tunnel waste soil, 25 parts of magnesium slag, 4 parts of fly ash, 1.8 parts of carbide slag, 0.2 parts of desulfurized gypsum, 7 parts of steel slag powder, and 4 parts of magnesium aluminum carbonate hydrotalcite.

[0068] Example 6

[0069] A roadbed filler based on the treatment of tunnel excavation waste soil with a curing agent comprises the following components: 350 parts of tunnel waste soil, 25 parts of magnesium slag, 7 parts of fly ash, 1.8 parts of carbide slag, 0.2 parts of desulfurized gypsum, 7 parts of steel slag powder, and 4 parts of magnesium aluminum carbonate hydrotalcite.

[0070] Comparative Example 1

[0071] A roadbed filler based on the treatment of tunnel excavation waste soil with a curing agent comprises the following components: 420 parts of tunnel waste soil and 25 parts of magnesium slag.

[0072] Comparative Example 2

[0073] A roadbed filler based on a curing agent for treating tunnel excavation waste soil comprises the following components: 420 parts of tunnel waste soil and 21 parts of quicklime.

[0074] Comparative Example 3

[0075] A roadbed filler based on the treatment of tunnel excavation waste soil with a curing agent comprises the following components: 450 parts of tunnel waste soil, 25 parts of magnesium slag, 4 parts of fly ash, 1.8 parts of carbide slag, 0.2 parts of desulfurized gypsum, and 7 parts of steel slag powder.

[0076] Comparative Example 4

[0077] A roadbed filler based on the treatment of tunnel excavation waste soil with a curing agent and its preparation process, comprising the following components: 450 parts of tunnel waste soil, 25 parts of magnesium slag, 4 parts of fly ash, 1.8 parts of carbide slag, 0.2 parts of desulfurized gypsum, 7 parts of steel slag powder, and 30 parts of magnesium aluminum carbonate hydrotalcite.

[0078] Table 2. Experimental Results

[0079]

[0080] The experimental results are shown in Table 2. Curing time has a significant effect on strength improvement. With the amount of calcium carbide slag remaining constant, the addition of fly ash significantly improves early strength. The unconfined compressive strength increases rapidly from 0d to 14d, while the increase is relatively slow from 14d to 28d. Furthermore, the overall strength of the solidified soil is improved with the addition of fly ash compared to calcium carbide slag alone. However, more fly ash is not necessarily better. Numerous studies have shown that the amount of magnesium slag is still a decisive factor, and the experimental results corroborate this.

[0081] In summary, this application fully utilizes the high sulfate content in tunnel waste. During the solidification process of tunnel waste soil, due to the dual activation effect of sulfate and carbide slag, magnesium slag undergoes a complex reaction with steel slag and fly ash to generate key hydrated magnesium aluminosilicate (MASH) and calcium aluminosilicate (CASH) gels. The network structure formed by these gels significantly enhances the mechanical properties of the soil. Further stability arises from the reaction between these hydration products and the adsorbent magnesium aluminum hydrotalcite (MAH). In the reaction with MAH, hydrated magnesium aluminosilicate and calcium aluminosilicate undergo ion exchange and synergistic reactions with the cations in MAH to form stable phases, including but not limited to ettringite (AFt), hydrated magnesium sulfate, and layered double hydroxides (LDHs). The amount of these stable phases generated is related to factors such as reaction conditions and material ratios. Typically, under optimized reaction conditions, ettringite accounts for 15%–25% of the formation, magnesium sulfate hydrate accounts for 5%–10%, magnesium aluminum sulfate hydrotalcite accounts for 1%–3%, and the remainder consists of common hydration cementitious products such as calcium silicate hydrate and calcium aluminosilicate hydrate. The formation of these stable phases further strengthens the structure of the solidified soil, improving its compressive strength, crack resistance, and long-term durability. However, excessive ettringite formation can lead to internal volume expansion, increasing the risk of cracking or deformation. This is because ettringite absorbs water and expands during hydration; excessive formation can increase internal stress, reducing overall stability and durability. Furthermore, excessive ettringite occupies a large amount of pore space, reducing the formation of other beneficial hydration products and affecting the material's overall performance. Conversely, insufficient ettringite formation can result in inadequate sulfate stability, making the material susceptible to structural degradation in sulfur-containing environments, leading to decreased resistance to sulfate attack and shortening its service life. Excessive formation of magnesium sulfate hydrate can negatively impact the chemical stability of materials, particularly in high-humidity environments, potentially leading to dissolution or migration and resulting in instability within the material's internal structure. Conversely, insufficient formation of magnesium sulfate hydrate may compromise the material's durability, accelerating damage, especially under sulfate attack conditions. Excessive formation of magnesium aluminum sulfate hydrotalcite can make the material's structure overly dense, reducing its permeability and gas diffusion, thus affecting its workability. Insufficient formation of magnesium aluminum sulfate hydrotalcite may fail to adequately stabilize sulfate ions within the material, leading to decreased durability under sulfate attack conditions.

[0082] like Figure 2As shown, the hydration products contain 1%–3% magnesium aluminum hydrotalcite, 10%–15% ettringite, 5%–10% hydrated magnesium sulfate, and the remainder being cementing substances such as CASH and MASH. Furthermore, the hydration products contain relatively few large pores, with pore diameters all less than 0.1 μm, ensuring the material's density and impermeability, thereby improving its long-term performance.

[0083] Furthermore, the incorporation of carbide slag into pyrite rock fragments promotes the hydrolysis of FeS2, generating more sulfate ions, which in turn produce more ettringite and Friedel salts. Simultaneously, the glassy structure of SiO2 in the rock fragments decomposes, generating more CAH and CASH structures. These hydration products bind together, significantly improving the strength of the solidified soil and reducing its porosity. The strength at 28 days reaches approximately 13 MPa, far exceeding the strength of traditional lime-based solidifying agents, reaching more than 10 times its strength.

[0084] Regarding environmental safety, the adsorption capacity of magnesium aluminum carbonate (MgA) layered double hydroxides (LDHs) for sulfate ions is limited by the medium. In aqueous solutions, MgA effectively adsorbs sulfate ions through ion exchange, but in soil, the adsorption process is more difficult because sulfate ions are physically or chemically bound by soil particles. Adding carbide slag can increase the pH of the soil solution through its strong alkalinity, breaking down the binding of sulfate ions by soil particles, thereby enhancing the accessibility of sulfate ions and improving the adsorption effect.

[0085] The influence of particle size on hydration products is also significant. Smaller particle sizes result in a larger specific surface area, which facilitates faster hydration reactions and more uniform formation of hydration products, reduces porosity, and enhances the overall strength and stability of the material. Furthermore, the larger specific surface area of ​​small-particle-size materials makes it easier to form uniform CASH and MASH gels in highly alkaline environments, further promoting the formation of other stable phases, such as ettringite and layered double hydroxides, thus enhancing the material's durability and corrosion resistance.

[0086] In summary, the sulfate-activating effect of calcium carbide slag and tunnel waste soil, combined with the complex reaction of magnesium slag, steel slag, and fly ash, as well as the stability contribution of magnesium aluminum carbonate hydrotalcite, collectively enhance the mechanical properties and environmental stability of the solidified soil. The synergistic effect of these factors ensures a comprehensive improvement in both the strength and environmental safety of the solidified soil.

[0087] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0088] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A roadbed filler based on a curing agent for treating saline loess waste from tunnel excavation, comprising tunnel waste, a curing agent, and water, characterized in that, The curing agent comprises 23-27 parts magnesium slag, 3-5 parts fly ash, 1-3 parts activator, 6-8 parts reinforcing agent, and 3-5 parts adsorbent; The tunnel waste contains chloride ions and sulfate ions. c (SO4) 2- ) / c (Cl) - >2; The total soluble salt content of the tunnel waste is 3.0% to 3.1%, the total chloride ion content is 0.20% to 0.30%, and the sulfate ion concentration is 1.10% to 1.30%. The adsorbent is magnesium aluminum carbonate hydrotalcite; The activator is a mixture of carbide slag and desulfurized gypsum in a mass ratio of (9-10):1; the reinforcing agent is steel slag powder. The roadbed filler is cured by a curing agent. In the cured product, the amount of ettringite generated accounts for 15% to 25%, the amount of hydrated magnesium sulfate generated accounts for 5% to 10%, the amount of magnesium aluminum sulfate hydrotalcite generated accounts for 1% to 3%, and the remainder is hydrated cementitious products other than ettringite.

2. The roadbed filler according to claim 1, characterized in that, The dry mass ratio of the tunnel waste to the solidifying agent is 1:0.08 to 0.12, and the moisture content of the tunnel waste is controlled at 15% to 16%.

3. The roadbed filler according to claim 2, characterized in that, The particle size distribution of the tunnel waste is as follows: 19% to 20% of the tunnel waste with a particle size of less than 0.005 mm, 77% to 78% of the tunnel waste with a particle size of 0.005 mm to 0.075 mm, and 2% to 3% of the tunnel waste with a particle size of 0.075 mm to 2 mm.

4. The subgrade filler according to claim 3, characterized in that, The 7-day unconfined compressive strength of the subgrade fill material is >1.70 MPa; the 28-day unconfined compressive strength is >7.84 MPa; and the water stability coefficient is 70%–80%.

5. The subgrade filler according to claim 4, characterized in that, The sulfate ion leaching concentration of the roadbed filler is 1701 mg / L ~ 1758 mg / L.

6. A method for preparing the roadbed filler according to any one of claims 1-5, characterized in that, Includes the following steps: The tunnel waste soil, solidifying agent, and water are mixed and then sequentially molded and cured. The dry mass ratio of the tunnel waste to the solidifying agent is 1:0.08 to 0.12, and the moisture content of the tunnel waste is controlled at 15% to 16%. The curing method is constant temperature and humidity curing, resulting in roadbed filler.

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