A solidifying agent, a tunnel waste regeneration low-permeability material based on solid waste solidification and a preparation method thereof

Abstract

The application discloses a solidifying agent, a tunnel waste slag regenerated low-permeability material based on solidifying of multiple solid wastes and a preparation method thereof, and belongs to the technical field of comprehensive utilization of tunnel waste slag. The solidifying agent comprises a cementing component, an alkali excitation component, a binding component and a reinforcing component, and the proportion of the cementing component, the alkali excitation component, the binding component and the reinforcing component is (6-7): 1:(0.45-0.7):(1.6-1.7). The material prepared by using the solidifying agent comprises tunnel waste slag, the solidifying agent and water. The binding component and the multiple solid wastes are used to improve the impermeability of the material, the three-dimensional network formed by the binding component and the hydration products of the blast furnace slag and the nickel-iron slag jointly act on the material, the three-dimensional network fills the small pores in the material, and the porosity is reduced; the material has higher thermal stability and gel capacity, is more resistant to acid and alkali environments, and can provide better support and stability when the mixed solid wastes are used.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization technology of tunnel waste, and more specifically, it relates to a curing agent, a low-permeability material for the recycling of tunnel waste based on the curing of various solid wastes, and a method for preparing the same. Background Technology

[0002] Roads serve as vital links connecting people and facilitating communication, while tunnels are crucial channels traversing mountains and promoting the exchange of spiritual and material cultures between different regions. With the gradual economic development of western China, transportation construction has become increasingly important, leading to the rapid advancement of tunnel projects and the generation of substantial amounts of tunnel spoil. Due to outdated management models and the inherent limitations of tunnel spoil itself, the utilization rate of this spoil is only about 20%, with the majority failing to be effectively utilized and requiring centralized dumping. This not only occupies a large amount of land, resulting in a significant waste of resources and space, but also, due to its loose structure and difficulty in soil formation, may trigger soil erosion, mudslides, and other disasters. Furthermore, due to the varying mineral resources in the tunnel areas, the spoil may contain harmful ions, and long-term storage could lead to excessive levels of elements such as iron, manganese, nickel, and beryllium in groundwater or soil, causing environmental pollution. Therefore, how to effectively and comprehensively utilize tunnel spoil in western China and optimize resource allocation has become a critical issue that urgently needs to be addressed.

[0003] Taking the Fenghuangshan Tunnel on the Qingshuiyi-Zhonghe section of the G30 Lianyungang-Horgos Expressway as an example, this project is located in Jinya Town, Yuzhong County, Lanzhou City. Designed as a long, twin-bore tunnel with separate left and right sides, it is 3945 meters long, classifying it as an extra-long highway tunnel with a maximum burial depth of 180 meters. During construction, a large amount of tunnel waste soil was generated. This waste soil exhibits unstable strength when exposed to water and is rich in sulfates, possessing the engineering characteristics of saline soil. Due to the concentrated and prolonged rainfall in Lanzhou, Gansu Province during July and August, prolonged water accumulation is prone to occur at the construction site. Under such conditions, traditional lime-based soil stabilization methods are highly susceptible to instability, severely threatening the safety and stability of the roadbed. To address this issue, the construction site typically employs a "two-layer geotextile and one-layer geomembrane" seepage prevention measure, which involves laying two layers of geotextile and one layer of geomembrane in the roadbed. However, while this traditional method achieves some seepage prevention, it significantly increases construction costs and extends the construction period. In addition, geomembranes, geotextiles and other geosynthetic materials are plastic products that are difficult to degrade naturally, causing long-term damage to the ecological environment, and urgently require technological innovation and improvement.

[0004] A search revealed that patent CN101182139A discloses a masonry cement with high strength and water retention. This cement incorporates an organic thickener, which may be starch or modified starch, starch ether, agar, gum arabic, soybean gum, guar gum and its derivatives, xylan, xanthan gum, or other polysaccharides. However, biological gums such as xanthan gum and guar gum are prone to degradation or loss of viscosity at high temperatures, affecting structural strength.

[0005] Patent CN104478361A discloses a pretreatment method for industrial solid waste. This method uses industrial exhaust gas to treat solid waste, and the resulting red mud-based polymer-like cementitious material uses one or more of the following as solidifying agents: bio-polysaccharides, phosphates, porous materials, silicates, organic polymers, heavy metals, and alkaline solidification / stabilizing components. However, this patent does not address the treatment of soils with high sulfate and strong sulfate content. The disclosed technology is mainly used for the stabilization of heavy metal-contaminated solid waste and does not involve mechanisms for inhibiting or solidifying high-concentration sulfate ions. The high sulfate leaching problem in tunnel waste may lead to material expansion and damage, affecting the solidification effect. Summary of the Invention

[0006] 1. The problem to be solved

[0007] To address the problem that existing curing agents are not suitable for tunnel spoil disposal, the primary objective of this invention is to provide a curing agent that can significantly reduce the porosity of soil and decrease the permeability coefficient, making it suitable for environments with high impermeability and high durability.

[0008] The second objective of this invention is to provide a low-permeability material for the recycling of tunnel waste based on the solidification of various solid wastes and its preparation method. The material obtained can significantly reduce the porosity of the soil and reduce the permeability coefficient. The material also has sufficient strength and excellent water stability.

[0009] 2. Technical Solution

[0010] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0011] The first objective of this invention is to provide a curing agent for curing low-permeability materials used in the recycling of tunnel waste. The agent comprises a cementing component, an alkali-activated component, a binder component, and a reinforcing component, wherein the mass ratio of the cementing component, alkali-activated component, binder component, and reinforcing component is (6-7):1:(0.45-0.7):(1.6-1.7). The binder component is composed of repeating tetrasaccharide units forming a stable double helix structure through hydrogen and ionic bonds. Each tetrasaccharide unit comprises D-glucose, D-glucuronic acid, D-glucose, and L-rhamnose linked sequentially. The four sugars are connected by oxygen bridges, forming a long-chain structure, and their stability is enhanced by the interaction of hydrogen and ionic bonds. Specifically, D-glucose and D-glucuronic acid are linked by β-1,4 glycosidic bonds, and L-rhamnose and D-glucose are linked by α-1,3 glycosidic bonds, constituting a cyclic tetrasaccharide unit. Based on the above linkage, the molecular formula of the binder component is (C6H2O). 10 O5) n (C6H 10 O5) m (C5H 10 O4) k In this molecular formula, n, m, and k represent the degree of polymerization of the molecular chain (C6H 10 O5) n This represents the glucose (Glc) unit, (C6H) 10 O5) m It represents the glucuronic acid (GlcA) unit, (C5H 10 O4) k This represents the rhamnose (Rha) unit, where the values ​​of n, m, and k are 20-25, and n, m, and k satisfy a ratio of 2:1:1. The specific degree of polymerization can be designed according to actual needs.

[0012] Furthermore, a common method for preparing the binder component is to synthesize polysaccharides via an enzyme-catalyzed reaction, with the specific steps as follows:

[0013] S1. Prepare raw materials: Ensure that the ratio of glucose (Glc), rhamnose (Rha), and glucuronic acid (GlcA) is 2:1:1;

[0014] S2. Catalytic reaction: Select transglycosidase and mix glucose, rhamnose and glucuronic acid in a certain proportion to promote the formation of glycosidic bonds between them.

[0015] The enzyme-catalyzed reaction involves the following key steps: dissolving glucose, rhamnose, and glucuronic acid in water; adding transglycosidase at 0.1wt%-0.8wt% of the total dry weight of the polysaccharide; adjusting the pH to a suitable range for enzyme catalysis, typically pH 5.5-7.0; adding transglycosidase at a temperature of 30℃-50℃ to catalyze the reaction, which catalyzes the formation of glycosidic bonds between glucose, rhamnose, and glucuronic acid; and monitoring the formation of glycosidic bonds and the growth of polysaccharide chains during the reaction using high-performance liquid chromatography (HPLC).

[0016] S3. Purification and molecular weight control: Set the reaction time to 48h-72h. After the reaction is complete, use dialysis, gel permeation chromatography (GPC) or ultrafiltration to remove unreacted monosaccharides, enzymes and byproducts to obtain pure binder components.

[0017] S4. Purification and Molecular Weight Control: Drying and Storage: The purified polysaccharide solution is freeze-dried to obtain a powdered binder component. This powder can be stored for a long time and used in the subsequent preparation of curing agents.

[0018] Furthermore, the amount of the binder added is 0.6%-0.8% of the dry mass of the tunnel spoil.

[0019] Preferably, the average molar mass of the binder component is not less than 500,000 g / mol, and the particle size is not greater than 0.15 mm.

[0020] Furthermore, the mass ratio of the cementing component to the alkali-activated component is (6-7):1, and the cementing material is composed of nickel-iron slag and blast furnace slag, with a mass ratio of nickel-iron slag to blast furnace slag of (2-3):1.

[0021] Preferably, the specific surface area of ​​the nickel-iron slag is not less than 400 m². 2 / kg, moisture content less than 1%; the density of the blast furnace slag is not less than 2.8g / cm³. 3 Specific surface area not less than 400m² 2 / kg, moisture content less than 1%.

[0022] Furthermore, the alkali-activated material is composed of carbide slag and phosphogypsum, with a mass ratio of carbide slag to phosphogypsum of 10 / 1 to 11 / 1.

[0023] Preferably, the carbide slag has a specific surface area of ​​not less than 200 mesh, a calcium hydroxide content of not less than 60%, and a water content of less than 1%; the phosphogypsum has a specific surface area of ​​400 m². 2 / kg-500m 2 / kg, soluble phosphate content 1%-2%, moisture content less than 1%.

[0024] The binder component used in this patent has a unique molecular structure. Its molecules consist of repeating tetrasaccharide units (glucose, rhamnose, and glucuronic acid), forming a stable double helix structure through hydrogen and ionic bonds. The formation of the double helix structure lowers the free energy of the molecular system, making the binder component less prone to decomposition at high temperatures and unaffected by strength at low temperatures, exhibiting excellent thermal stability. Its structure remains stable over a wide temperature range (from freezing conditions to above 100°C), maintaining high strength and performance stability not only under high-temperature conditions but also at low temperatures. Compared to agar, although agar has better heat resistance, its strength at low temperatures is lower, and its ability to adapt to extreme temperature differences is not as good as the binder component of this invention. Therefore, the binder component of this invention can maintain its strength and stability under more demanding conditions in engineering applications. Furthermore, the binder component can rapidly form a gel at low concentrations, and the resulting gel structure is robust, exhibiting excellent mechanical strength and long-term stability. Compared to other bio-adhesives (such as guar gum), the binder component has stronger gelling ability and exhibits higher stability in both acidic and alkaline environments. This property enables the binder component to provide better support and stability when mixed with solid waste materials, thus offering significant advantages in complex engineering environments.

[0025] Furthermore, the amount of the reinforcing component added is 13%-25% of the dry mass of the tunnel spoil, and the reinforcing component is peanut shells and steel slag, wherein the mass ratio of peanut shells to steel slag is (3-2):(7-3).

[0026] Preferably, the peanut shell ash has a fineness of no more than 30%, a silica content of more than 90%, and a moisture content of less than 1%; the steel slag has a specific surface area of ​​400 m². 2 / kg-500m 2 / kg, moisture content less than 1%.

[0027] The second objective of this invention is to provide a low-permeability material for the recycling of tunnel slag based on the solidification of various solid wastes. The material comprises tunnel slag, a solidifying agent, and water. The solidifying agent includes a gelling component, an alkali-activated component, a binder component, and a reinforcing component. The binder component is composed of repeating tetrasaccharide units forming a stable double helix structure through hydrogen and ionic bonds. Each tetrasaccharide unit comprises D-glucose, D-glucuronic acid, D-glucose, and L-rhamnose linked sequentially. The four sugars are connected by oxygen bridges, forming a long-chain structure, and their stability is enhanced by the interaction of hydrogen and ionic bonds. Specifically, D-glucose and D-glucuronic acid are linked by β-1,4 glycosidic bonds, and L-rhamnose and D-glucose are linked by α-1,3 glycosidic bonds, constituting a cyclic tetrasaccharide unit. Based on the above linkage, the molecular formula of the binder component is (C6H2O). 10 O5) n (C6H10 O5) m (C5H 10 O4) k In this molecular formula, n, m, and k represent the degree of polymerization of the molecular chain (C6H 10 O5) n This represents the glucose (Glc) unit. (C6H) 10 O5) m This represents the glucuronic acid (GlcA) unit. (C5H) 10 O4) k This represents the rhamnose (Rha) unit, where the values ​​of n, m, and k are 20-25, and n, m, and k satisfy a ratio of 2:1:1. The specific degree of polymerization can be designed according to actual needs.

[0028] The dry mass ratio of the tunnel waste to the curing agent is 1:(0.08-0.1), and the moisture content of the tunnel waste is controlled at 15%-16%.

[0029] Furthermore, 80%-85% of the tunnel spoil is loess, and 15%-20% is basalt 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.

[0030] Furthermore, the total soluble salt content of the tunnel spoil 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. 2- ) / c(Cl - >2.

[0031] Furthermore, the sulfate ion leaching concentration of the tunnel waste is 1701 mg / L-1758 mg / L.

[0032] This invention also provides a method for preparing the above-mentioned low-permeability material for tunnel spoil recycling based on solidification of various solid wastes, comprising the following steps:

[0033] The tunnel waste, curing agent, and water are mixed and then sequentially molded and cured to obtain the roadbed filler.

[0034] Furthermore, due to insufficient water temperature, the binder components are difficult to dissolve fully, easily forming particle agglomerates in the liquid, resulting in uneven dissolution. Therefore, the bio-adhesive material is added in advance when the water is boiled to 100°C, and stirred until completely dissolved using a liquid mixer. Simultaneously, the water temperature is maintained at approximately 90°C before adding water.

[0035] Furthermore, in the molding step, the molding method is static compaction.

[0036] Furthermore, in the maintenance steps: constant temperature and humidity maintenance is adopted, with a maintenance temperature of 23±1℃, a relative humidity of 98%, and a maintenance period of 7 days and 28 days.

[0037] This patented solidification system, formed through chemical reactions and physical interactions among its components, creates a multi-layered, multi-dimensional curing system. The cementing effect of nickel-iron slag and blast furnace slag is enhanced by the alkali-activated reaction of carbide slag and phosphogypsum. The three-dimensional network structure provided by the binder further enhances the packing's adhesion and moisture retention, while the reinforcing effect of peanut shell ash and steel slag provides better structural stability and strength. When this curing agent is used in the solidification of tunnel spoil, the activation of rock fragments in the spoil relies on a highly efficient alkali-activated reaction. This patent provides a curing technology more suited to the characteristics of tunnel spoil by activating rock fragment components through alkali activation, inhibiting sulfate ion expansion and leaching, and enhancing the performance of the composite cementitious product. This technology offers significant technical advantages and applicability.

[0038] The material prepared by the above method exhibits significantly improved impermeability and mechanical properties. Its performance parameters include a permeability coefficient of 3.19 × 10⁻⁶ after 28 days. -8 -7.15×10 -9 m / s, with an unconfined compressive strength of 13.05 MPa.

[0039] 3. Beneficial effects

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] (1) The curing agent of the present invention is composed of repeating tetrasaccharide units, forming a stable double helix structure through hydrogen bonds and ionic bonds. The binder component works synergistically with the multi-component solid waste to improve the impermeability of the material. The three-dimensional network formed by the binder component works together with the hydration products of blast furnace slag and nickel-iron slag to fill the micropores in the material and reduce the porosity. It also has higher thermal stability and gelation ability, and is more resistant to acid and alkali environments, which enables it to provide better support and stability when mixing tunnel waste.

[0042] (2) The material of the present invention significantly improves the unconfined compressive strength of the recycled material of tunnel waste by optimizing the curing agent formula. Nickel-iron slag and blast furnace slag generate cementitious products through volcanic ash reaction under the action of alkali-activated components. The active calcium, aluminum and silicon elements released by the enhancing components further promote the hydration reaction. The binding components effectively improve the density and mechanical properties of the material by forming a network structure with the hydration products.

[0043] (3) The present invention uses a double helix structured binder as a curing agent. The binder can effectively resist the problem of sulfate ions changing the pH value of the aqueous solution during the curing process of tunnel waste through its network structure of hydrogen bonds and ionic bonds, thereby affecting the cementing reaction and the curing process, and maintaining the strength and stability of the material.

[0044] (4) The present invention uses tunnel spoil as the main material, and utilizes the rock fragments in the tunnel spoil to participate in chemical reactions in an alkaline environment to generate additional cementitious products, which are used as aggregates to improve the density and compressive strength of the material, thereby further enhancing the performance of the material.

[0045] (5) This invention achieves resource recycling by utilizing industrial by-products such as nickel-iron slag, blast furnace slag, carbide slag, phosphogypsum, steel slag and peanut shell ash, which has good environmental friendliness and reduces raw material costs.

[0046] (6) The curing agent of the present invention has a variety of components that work synergistically with each other, and can adapt to different construction environments and material requirements, especially in projects that require high impermeability and high durability;

[0047] (7) The present invention uses environmentally friendly materials such as peanut shell ash and industrial waste, which reduces the use of traditional materials such as cement and meets the requirements of sustainable development. Attached Figure Description

[0048] 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.

[0049] Figure 1 This is an electron microscope image of the hydration products of the present invention. Detailed Implementation

[0050] 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.

[0051] 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.

[0052] The chemical composition of each component used in this application is shown in Table 1.

[0053] Table 1. Chemical composition and content (wt%) of each component in this application.

[0054] <![CDATA[Al2O3]]> <![CDATA[SiO2]]> MgO CaO <![CDATA[Cr2O3]]> <![CDATA[Fe2O3]]> C <![CDATA[SO3]]> <![CDATA[P2O5]]> Nickel-iron slag 27.63 28.83 23.43 4.45 8.88 4.20 - - - Blast furnace slag 15.8 27.56 7.51 42.19 - - - 2.88 - calcium carbide slag 1.33 1.41 - 95.2 - 0.12 - 0.34 - phosphogypsum 0.75 7.88 - 38.53 - 0.85 - 49.2 1.39 steel slag 2.20 12.83 10.04 41.25 - 27.48 - 13.83 1.91 Peanut shell ash 0.73 70.90 2.07 - - 0.62 22.29 - - loess 16.58 56.71 4.24 10.46 - 5.09 - 0.54 0.22 Rock cuttings 16.91 56.29 4.74 8.57 - 4.91 - 2.84 0.18

[0055] The chemical formula of the binder component is (C6H). 10 O5) 44 (C6H 10 O5) 22 (C5H 10 O4) 22 (C6H) 10 O5) 44 This represents the glucose (Glc) unit, (C6H) 10 O5) 22 It represents the glucuronic acid (GlcA) unit, (C5H 10 O4) 22 It represents the rhamnose (Rha) unit.

[0056] The common preparation method for the binder component is to synthesize polysaccharides through an enzyme-catalyzed reaction. The specific steps are as follows:

[0057] S1. Prepare raw materials: Ensure that the ratio of D-glucose (Glc), L-rhamnose (Rha) and D-glucuronic acid (GlcA) is 2:1:1;

[0058] S2. Catalytic reaction: Select a transglycosidase and mix D-glucose, L-rhamnose and D-glucuronic acid in a certain proportion to promote the formation of glycosidic bonds between them.

[0059] The enzyme-catalyzed reaction has the following key steps: D-glucose, L-rhamnose, and D-glucuronic acid are dissolved in water, the amount of transglycosidase added is 0.5 wt% of the total dry weight of the polysaccharide, and the pH value is adjusted to 6.0; under the temperature condition of 40°C, the transglycosidase is added to catalyze the reaction, and this enzyme catalyzes the formation of glycosidic bonds between glucose, rhamnose, and glucuronic acid;

[0060] S3. Purification and molecular weight control: Set the reaction time to 60h. After the reaction is complete, use dialysis, gel permeation chromatography (GPC) or ultrafiltration to remove unreacted monosaccharides, enzymes and byproducts to obtain pure binder components.

[0061] S4. Purification and molecular weight control: Drying and storage: The purified polysaccharide solution is freeze-dried to obtain a powdered binder component.

[0062] The preparation process of the roadbed filler in the examples and comparative examples includes the following steps:

[0063] The tunnel waste, curing agent, and water are mixed and then sequentially molded and cured to obtain the roadbed filler.

[0064] In this process, the binder is added in advance when the water is boiled to 100°C and stirred until completely dissolved using a liquid mixer. Meanwhile, the water temperature is kept at 90°C before adding water.

[0065] This invention refers to the provisions of GB / T 50123—2019 "Standard for Geotechnical Testing Methods", and the diameter and height of the solidified soil strength specimen are 5cm and 10cm, respectively, and it is prepared by static compression sampling method.

[0066] Then, demolding and curing: After demolding, the soil sample is 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 sample that meets the requirements is placed in a polyethylene sealed bag (to prevent moisture loss) and transferred to a standard curing room (relative humidity 98%, temperature 23±1℃) for curing until the design age.

[0067] Test measurements:

[0068] Examples 1-6 and Comparative Examples 1-3 were subjected to unconfined compressive strength tests at curing ages of 7 days and 28 days, respectively, in accordance with 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.

[0069] Examples 1-6

[0070] Examples 1-6 are examples of preparation methods for low-permeability recycled tunnel waste materials based on the solidification of various solid wastes, as detailed in Table 2.

[0071] Table 2 Specific Material Dosage Design Scheme (Dry Mass Ratio, Dimensionless)

[0072]

[0073] Comparative Example 1

[0074] The curing agent in Comparative Example 1 was quicklime used in on-site construction. The composition of this material is as follows: 1200 parts of tunnel waste, of which 960 parts were loess, 240 parts were rock debris, and 100 parts were quicklime.

[0075] Comparative Example 2

[0076] The tunnel spoil in Comparative Example 2 does not contain rock cuttings. The composition of the material is as follows: 1200 parts of tunnel spoil, of which loess accounts for 1200 parts, rock cuttings account for 0 parts, nickel-iron slag accounts for 58.3 parts, blast furnace slag accounts for 29.2 parts, calcium carbide slag accounts for 11.4 parts, phosphogypsum accounts for 1.1 parts, steel slag accounts for 6 parts, peanut shell ash accounts for 14 parts, and binder components account for 6 parts.

[0077] Comparative Example 3

[0078] The curing agent in Comparative Example 3 does not contain any binder components. The composition of the material is as follows: 1200 parts of tunnel waste, of which loess accounts for 960 parts, rock chips account for 240 parts, nickel-iron slag accounts for 58.3 parts, blast furnace slag accounts for 29.2 parts, calcium carbide slag accounts for 11.4 parts, phosphogypsum accounts for 1.1 parts, steel slag accounts for 6 parts, and peanut shell ash accounts for 14 parts.

[0079] In practical engineering, unconfined compressive strength is one of the most important mechanical indicators for evaluation, and it is a key indicator for determining whether a material meets the requirements for effective service as a subgrade material. Subgrade base, surface cover, and bottom lining all require compaction during construction; therefore, the compaction degree of the samples needs to be controlled indoors. In this implementation case, the compaction degree was controlled at 96%. Table 3 shows the comparison results of the unconfined compressive strength of the cured and compacted samples from Examples 1-6 and Comparative Examples 1-3.

[0080] Table 3. Test results of unconfined compressive strength of cured and compacted specimens.

[0081] Sample Name 7-day unconfined compressive strength (MPa) 28-day unconfined compressive strength (MPa) Example 1 1.54 7.26 Example 2 1.67 7.83 Example 3 1.85 8.72 Example 4 2.12 10.75 Example 5 2.27 11.02 Example 6 2.38 13.05 Compare with Example 1 0.62 1.48 Compare with Example 2 1.05 5.35 Compare with Example 3 1.39 6.54

[0082] Table 2 shows the unconfined compressive strength test results for different curing formulations at 7 days and 28 days. The results indicate that the unconfined compressive strength of all samples significantly increases with increasing curing time. Specifically, the 28-day unconfined compressive strengths of Examples 1-6 are 7.26 MPa, 7.83 MPa, 8.72 MPa, 10.75 MPa, 11.02 MPa, and 13.05 MPa, respectively, which are significantly higher than the 28-day unconfined compressive strengths of Comparative Examples 1-3, which are 1.48 MPa, 5.35 MPa, and 6.54 MPa, respectively. These data demonstrate that the material prepared by this invention has significant advantages in mechanical properties, especially exhibiting higher unconfined compressive strength under longer curing times.

[0083] Comparative analysis of Examples 1-6 shows that the unconfined compressive strength of the samples gradually increased with the optimization of the curing agent formulation. This indicates that the combination of the cementitious components, alkali-activated components, binder components, and reinforcing components has a significant synergistic effect. Specifically, nickel-iron slag and blast furnace slag, as cementitious components, significantly improved the material's strength through the cementitious products generated by the pozzolanic reaction under the action of the alkali-activated components, carbide slag and phosphogypsum. Simultaneously, the active calcium, aluminum, and silicon elements released by the reinforcing components, peanut shell ash and steel slag, further promoted the hydration reaction, increasing the material's density and strength. In particular, Example 6 achieved an unconfined compressive strength of 13.05 MPa after 28 days, demonstrating that under the optimal formulation, this material possesses excellent mechanical properties, fully meeting or even exceeding the engineering requirements of roadbed materials.

[0084] This paper uses tunnel spoil as the main material and fully utilizes its role as rock fragments. First, rock fragments, as coarse aggregate, together with other fine aggregates and solidification products, form the material's skeletal structure. This structure effectively improves the material's density and overall mechanical properties, enhancing its compressive strength and stability. The presence of aggregates reduces shrinkage during the hardening process, lowering the risk of cracking and ensuring long-term durability. Second, rock fragments do not merely exist as inert fillers; in the alkaline environment provided by alkali-activated components such as carbide slag and phosphogypsum, certain chemical reactions may occur. Especially when the rock fragments contain active silica and alumina, they can react with calcium hydroxide and other components in the alkali-activated components to generate additional cementitious products such as hydrated calcium silicate (CSH) and hydrated calcium aluminate (CAH). These reacted cementitious substances fill the pores inside the material, further enhancing its density and compressive strength.

[0085] The binder component plays a crucial role in this invention. Its molecular chain contains numerous hydroxyl and carboxyl groups. These functional groups can undergo physical or chemical adsorption with other components in the material (such as the gelling component and the alkali-activated component), thereby enhancing the internal adhesion of the material. The hydroxyl groups (-OH) have strong hydrophilicity and can interact with hydrogen bonds in water molecules and other hydrates, promoting the hydration of the binder component. This not only helps extend the molecular chain of the binder component but also enhances the stability of hydration products during curing, thus helping to form a more robust network structure and improving the overall strength of the material. The carboxyl groups (-COOH) undergo ion exchange reactions with cations (such as calcium ions, magnesium ions, aluminum ions, etc.) through their negative charge, forming an ion cross-linked structure and enhancing the strength of the material. During curing, the carboxyl groups of the binder component can react with calcium ions (Ca... 2Magnesium ions (Mg2+) and other elements form gel products such as hydrated calcium silicate (CSH), which then cross-link with the material, further enhancing its compressive strength. Furthermore, the double-helix structure of the binder component imparts stability under high-temperature and high-intensity environments. Due to its unique molecular structure, the binder component can undergo stronger physical adsorption and chemical reactions with various components in the mixed waste (such as minerals in the waste residue), thereby enhancing the stability and strength of the cured material.

[0086] During the solidification process of tunnel spoil, sulfate ions in the waste can alter the pH of the aqueous solution, potentially affecting the cementation reaction and thus the solidification process. However, the binder component, through its network structure of hydrogen and ionic bonds, effectively resists this effect, maintaining the material's strength and stability. In particular, the double-helix structure of the binder component can mitigate the adverse effects of acidic environments on its cementation process to some extent, allowing it to maintain good stability even in strongly acidic environments. Overall, the structural characteristics of the binder component enable it to exhibit excellent stability and strength in high-temperature, strongly acidic environments and strongly sulfate-rich soils, ensuring superior performance of the material under extreme conditions.

[0087] As a novel low-permeability material, to improve its wide applicability in roadbed layers and landfill subgrades, the permeability coefficient of the novel low-permeability material should be regarded as a key indicator. This invention mainly verifies its permeability performance through flexible wall permeability experiments, and the test results are shown in Table 4.

[0088] Flexible wall permeability testing was conducted according to ASTM D5084-10 and USEPA 1314, using a Geotest TK2000 testing apparatus with two parallel samples. The permeability test was set with an osmotic pressure of 50 kPa, a confining pressure of 55 kPa, and a hydraulic gradient of 100.

[0089] The steps of the flexible wall permeability test are as follows: ① Specimen saturation. Take out the specimen cured to the designed age (28 days) from the curing room. Then place the specimen in a saturator and put it in a vacuum saturation cylinder to complete saturation. In this test, the soil sample is under a vacuum of -100 kPa for 8 hours, and deionized water is injected and left standing for 4 hours. ② Specimen installation. Take out the saturated soil, measure its mass and calculate the degree of saturation. Then place the specimen in a latex film matching the permeability tester and put it on the base of the chamber of the permeability tester. Permeable stones and glass fiber filter papers are placed successively between the specimen and the base and the top cover from bottom to top. Then use a water-stop rubber ring to seal the connection surfaces of the latex film and the base and the top cover respectively. Finally, after installing the top cover of the chamber, connect it to the permeation test control panel and connect the osmotic pressure and the confining pressure to the water guide pipe. ③ Test start. After the specimen installation is completed, inject deionized water into the chamber of the permeability tester and apply a small confining pressure (3 kPa) to check the airtightness of the chamber. Then increase the confining pressure and the osmotic pressure to 55 kPa and 50 kPa respectively. The increase of the confining pressure and the osmotic pressure adopts a simultaneous step-by-step method and is completed within 2 minutes. In the permeability test, the effluent is introduced into a conical flask with a rubber stopper for collection. ④ Calculation of permeability coefficient. After the test, calculate the permeability coefficient of the specimen according to the volume of the permeation liquid collected.

[0090] Table 4 Flexible wall permeability test results of the solidified and compacted specimens

[0091] Sample Name 28-day flexible wall permeability test (m / s) Example 1 <![CDATA[3.19×10 -8 ]]> Example 2 <![CDATA[5.46×10 -8 <!-- 8 -->]]> Example 3 <![CDATA[6.53×10 -8 ]]> Example 4 <![CDATA[5.32×10 -9 ]]> Example 5 <![CDATA[6.24×10 -9 ]]> Example 6 <![CDATA[7.15×10 -9 ]]> Compare with Example 1 <![CDATA[3.24×10 -6 ]]> Compare with Example 2 <![CDATA[1.28×10 -7 ]]> Compare with Example 3 <![CDATA[9.35×10 -7 ]]>

[0092] According to the analysis of the results of the 28-day flexible wall permeability test in Table 3, the low-permeability materials show significant advantages in terms of permeability. The following is the reason analysis:

[0093] The gelling components nickel ferrite slag and blast furnace slag used in the present invention generate a large amount of gelling products through pozzolanic reaction under alkaline conditions, such as calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). These gelling products have high density and adhesiveness, effectively filling the pores inside the material and significantly reducing the permeability. The test results show that the permeability coefficients of the examples are all in the order of 10 -8 -10 -9 m / s, which benefits from the optimization of the material ratio, making the density and pore filling effect of these specimens reach the best.

[0094] Furthermore, the rock fragments in the tunnel spoil, through synergistic effects with the cementing and alkali-activating components in the curing agent, effectively improved the material's permeability coefficient. The excellent bonding between the rock fragments and the cured products formed a superior gradation, reducing the internal porosity and increasing its density, resulting in lower permeability. Moreover, the rock fragments exhibited minimal volume change, providing a stable framework structure during material curing and hydration. This stable framework structure prevents increased porosity due to internal structural loosening or expansion, ensuring the material maintains low permeability during long-term use. The addition of rock fragments also effectively filled the internal pore structure of the material. Because rock fragments typically have irregular shapes and large particle sizes, they can fill the larger pores between cementing products, reducing the number and size of interconnected channels. This filling effect significantly reduces the flow path of moisture within the material, thereby lowering permeability.

[0095] Furthermore, the binder component is highly hydrophilic, capable of absorbing water and swelling to form a highly viscous gel-like substance. This gel-like substance can fill the tiny pores within the material, significantly reducing its permeability. By reducing the flow path of water and other fluids within the material, the binder component enhances its impermeability, making it more suitable for engineering applications requiring high durability and impermeability.

[0096] This invention significantly improves the impermeability of materials. By employing a binder component and a combination of solid waste materials to synergistically enhance the material's impermeability, the three-dimensional network formed by the binder component, together with the hydration products of blast furnace slag and nickel-iron slag, fills the micropores in the material, reducing porosity. Small particles of filler, such as blast furnace slag and phosphogypsum, together with tunnel waste, form an excellent gradation. The permeability coefficient after 28 days is 3.19 × 10⁻⁶. -8 -7.15×10 -9 m / s, far exceeding the original lime-based solidified cementitious materials.

[0097] Furthermore, the mechanical properties of the material are significantly improved. By optimizing the curing agent formulation, the unconfined compressive strength of the recycled tunnel spoil material is significantly enhanced. Nickel-iron slag and blast furnace slag, under the action of alkali-activated components (carbide slag and phosphogypsum), generate cementitious products through pozzolanic reaction, which greatly improves the strength of the material. The active calcium, aluminum, and silicon elements released by the reinforcing components (peanut shell ash and steel slag) further promote the hydration reaction, improving the density and mechanical properties of the material. In particular, in Example 6, the unconfined compressive strength reached 13.05 MPa after 28 days, indicating that the material can meet the engineering requirements of roadbed materials. In addition, rock fragments not only act as aggregates to improve the density and compressive strength of the material, but also participate in chemical reactions in an alkaline environment to generate additional cementitious products, further enhancing the material's performance. The binding component improves the overall adhesion and strength of the material by forming a network structure with the hydration products.

[0098] This curing agent achieves resource recycling by utilizing industrial by-products such as nickel-iron slag, blast furnace slag, carbide slag, phosphogypsum, steel slag, and peanut shell ash, exhibiting good environmental friendliness and reducing raw material costs. The curing agent has diverse components that work synergistically to adapt to different construction environments and material requirements, and it performs particularly well in projects requiring high impermeability and high durability.

[0099] During the hydration reaction, the reinforcing components (peanut shell ash and steel slag) continuously release active calcium, aluminum and silicon elements, maintaining and promoting the continuous progress of the hydration reaction, thereby improving the strength and durability of the cured material.

[0100] 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.

[0101] 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 low-permeability material for the recycling of tunnel spoil based on the solidification of various solid wastes, characterized in that, The mixture comprises a curing agent, tunnel waste, and water. The dry mass ratio of the tunnel waste to the curing agent is 1:(0.08 - 0.1). The moisture content of the tunnel waste is controlled at 15%-16%. The curing agent includes a cementing component, an alkali-activated component, a binder component, and a reinforcing component. The mass ratio of the cementing component, alkali-activated component, binder component, and reinforcing component is (6-7):1:(0.45-0.7):(1.6-1.7). The binding component is composed of repeating tetrasaccharide units, which include D-glucose, D-glucuronic acid, D-glucose and L-rhamnose connected in sequence. The D-glucose and D-glucuronic acid are connected by β-1,4 glycosidic bonds, and the L-rhamnose and D-glucose are connected by α-1,3 glycosidic bonds, forming a double helix structure. The low-permeability material meets the following requirement: a permeability coefficient of 3.19 × 10⁻⁶ after 28 days. -8 - 7.15 × 10 -9 m / s; The cementing component is composed of nickel-iron slag and blast furnace slag, and the mass ratio of nickel-iron slag to blast furnace slag is (2-3):1; The alkaline activation component is composed of carbide slag and phosphogypsum, with a mass ratio of carbide slag to phosphogypsum of (10-11):

1. The reinforcing components are peanut shell ash and steel slag, with a mass ratio of (3-2):(7-3).

2. The low-permeability material according to claim 1, characterized in that, The molecular formula of the adhesive component is (C6H) 10 O5) n (C6H 10 O5) m (C5H 10 O4) k , among which, (C6H 10 O5) n For glucose units, (C6H 10 O5) m It is a glucuronic acid unit, (C5H 10 O4) k The unit is rhamnose (Rha), where the values ​​of n, m, and k are 20-25, and n, m, and k satisfy 2:1:

1. The average molar mass of the binder component is not less than 500,000 g / mol, and the particle size is not greater than 0.15 mm.

3. The low-permeability material according to claim 2, characterized in that, The binding component is prepared from D-glucose, L-rhamnose and D-glucuronic acid under the catalysis of transglycosidase. The amount of transglycosidase added is 0.1wt%-0.8wt% of the total dry weight of D-glucose, L-rhamnose and D-glucuronic acid. The reaction pH is 5.5-7.0, the reaction temperature is 30℃-50℃ and the reaction time is 48h-72h.

4. The low-permeability material according to claim 3, characterized in that, The tunnel spoil consists of 80%-85% loess and 15%-20% basalt rock fragments. According to the combined liquid and plastic limit test, the liquid limit is 29.2% and the plastic limit index is 10.9, which indicates that it is a low-plasticity clay.

5. The low-permeability material according to claim 4, characterized in that, The total soluble salt content of the tunnel spoil 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. c (SO4) 2- ) / c (Cl) - >2.

6. The low-permeability material according to claim 5, characterized in that, The sulfate ion leaching concentration of the tunnel waste was 1701 mg / L - 1758 mg / L.

7. A method for preparing the low-permeability material according to any one of claims 1-6, characterized in that, Including the following steps: The tunnel waste, curing agent, and water are mixed and then sequentially molded and cured to obtain a material for roadbed filling.

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