A cementitious material based on large amount of shield muck and a preparation method and application thereof

Abstract

The present application relates to the technical field of cementitious materials, in particular to a cementitious material based on large amount of shield muck and a preparation method and application thereof, comprising the following steps: the original shield muck is sequentially subjected to mechanical crushing, forced homogenization, drying to constant weight, gradient temperature calcination, rapid cooling immediately after, two-stage ball milling and sieving to obtain active shield muck powder; preparing solid dry mixture; preparing composite alkali activator solution; mixing the composite alkali activator solution with the solid dry mixture, preliminarily stirring and soaking, adding the remaining mixing water to stir to obtain uniform polymer slurry, then vibrating and forming to obtain the cementitious material. The present application solves the problems of low activity, insufficient strength, small amount of shield muck, single performance and poor volume stability of the high-performance geopolymer cementitious material based on shield muck in the prior art.

Description

Technical Field

[0001] This invention relates to the field of cementitious materials technology, and in particular to a cementitious material based on a large amount of shield tunnel slag, its preparation method, and its application. Background Technology

[0002] Shield tunneling is widely used in infrastructure construction such as urban rail transit and tunnel engineering, but it generates a large amount of tunnel boring machine (TBM) excavated soil during construction. This excavated soil is a construction waste formed by a mixture of soil, mud, etc., characterized by complex composition, loose structure, high initial moisture content (usually ≥25%), and more than 90% of the particles having a diameter between 0.075mm and 1.5mm. Currently, the main methods of disposing of TBM excavated soil are landfilling and stockpiling, which not only occupies a large amount of land resources, but its harmful components may also pollute soil and water resources under the influence of rainfall and severe weather, threatening the ecological environment and human health.

[0003] Existing methods for utilizing tunnel boring machine (TBM) slag are mostly low-value-added, such as brick making, ceramsite production, topsoil improvement, or as inert aggregate for roadbed backfilling and grouting slurry. These methods suffer from limited utilization and difficulty in large-scale disposal, failing to fully realize their potential value. For example, in Chinese patent CN202410990616.1, "A Grouting Slurry Based on TBM Slag and Industrial Solid Waste Cementitious Materials and its Preparation Method," calcium carbide slag and blast furnace slag are used to replace cement as cementitious materials, and TBM slag is used as filler aggregate in the grouting slurry. Although this achieves the reuse of waste materials, the core cementitious components still rely on calcium carbide slag, blast furnace slag, etc. The potential activity of the TBM slag itself is not valued or utilized, and it is only used as inert aggregate, resulting in a low utilization rate. In the study on the mechanism of action and road performance of solid waste-based cementitious materials for solidifying shield tunneling excavation soil, industrial solid wastes such as carbide slag, red mud, mineral powder and desulfurization gypsum were selected as cementitious materials to explore the effect of solidifying shield tunneling excavation soil. The results showed that the solidified shield tunneling excavation soil has the potential to be used as roadbed backfill soil. However, this disposal method is not proportional to the output of shield tunneling excavation soil. At the same time, the transportation, disposal and processing costs of other industrial solid wastes need to be further considered.

[0004] In summary, current research on the disposal of tunnel boring machine (TBM) excavated soil focuses primarily on solidifying it (aggregate) for use as low-carbon engineering materials such as recycled synchronous grouting materials and roadbed backfill materials, failing to fully explore its inherent value. From a compositional perspective, TBM excavated soil mainly contains silica-alumina active components such as SiO2 and Al2O3, possessing the basic conditions to become a raw material for cementitious materials. However, existing technologies have not solved the core problem of transforming it from an inefficient, low-volume, inert filler into a high-efficiency, high-volume, active cementitious component—namely, how to economically and efficiently activate its inherent aluminosilicate activity and construct a material system that allows this activity to be fully realized.

[0005] Specifically, existing technologies suffer from three major technical problems: First, insufficient activation: Most solutions directly use raw or simply dried shield tunneling slag. The silica-alumina minerals (such as quartz and clay minerals) in the slag are mostly in a crystalline state with low chemical activity. Without effective activation treatment, their participation in the alkali activation reaction is extremely low, leading to the final product's strength performance relying on externally added highly active materials. Second, poor synergy of the material system: Existing solutions are mostly simple physical mixtures of various solid wastes, lacking functional design for each component during the alkali activation process; for example, they fail to effectively utilize certain components to provide a sulfate environment to generate reinforcing phases (such as ettringite), or to utilize spherical particles to improve the rheological properties of the slurry. Third, an imbalance between economic efficiency and environmental friendliness: To achieve certain mechanical properties, large amounts of alkali activators (such as sodium hydroxide and water glass) or high-grade solid waste are often required, resulting in high material costs. Furthermore, high alkali consumption itself also brings a certain environmental burden, undermining the environmentally friendly intention of utilizing solid waste. In addition, the content of tunnel boring machine excavation soil in existing technologies is generally less than 30%, which fails to achieve the transformation from inert filler to main cementing component and cannot meet the needs of large-scale disposal. Summary of the Invention

[0006] The purpose of this invention is to provide a cementitious material based on a large amount of shield tunneling slag, its preparation method and application, to solve the problems of low activity, insufficient strength, small amount of shield tunneling slag, single performance and poor volume stability of high-performance geopolymer cementitious materials based on shield tunneling slag in the prior art.

[0007] To achieve the above objectives, the present invention provides a method for preparing a cementitious material based on a large amount of shield tunnel slag, comprising the following steps:

[0008] S1. Preparation of active shield tunneling slag powder: The original shield tunneling slag is mechanically crushed, forced homogenized, and dried to constant weight. Then it is calcined by gradient heating, followed by rapid cooling. After two-stage ball milling, it is passed through a 200-mesh sieve to obtain active shield tunneling slag powder.

[0009] S2. Preparation of solid dry mix: Weigh out 550-650 parts of the active shield tunnel slag powder obtained in S1, 15-25 parts of desulfurized gypsum, 80-120 parts of fly ash, 3-5 parts of diatomaceous earth, 1-2 parts of nano alumina, 4-6 parts of magnesium oxide expanding agent, 0.5-2 parts of polypropylene fiber, and 0.2-0.4 parts of polycarboxylate superplasticizer according to the mass ratio, mix and dry mix evenly to obtain solid dry mix;

[0010] S3. Preparation of composite alkali activator solution: Dissolve sodium hydroxide in part of the mixing water to prepare a concentrated alkali solution of 8-10 mol / L. After cooling to room temperature, add sodium silicate powder and stir until completely dissolved and clear to obtain the composite alkali activator solution.

[0011] S4. Slurry mixing and molding: The composite alkali activator solution of S3 is mixed with the solid dry mixture of S2. The mixture is first initially stirred and soaked, and then the remaining mixing water is added and stirred to obtain a uniform aggregate slurry. Then it is compacted and molded to obtain a cementitious material.

[0012] Preferably, in S1, the initial moisture content of the original shield tunneling excavated soil is ≥25%, and the proportion of particles with a particle size between 0.075mm and 1.5mm is more than 90%.

[0013] Preferably, in S1, the gradient heating calcination involves first heating to 450-500℃ at a rate of 3-5℃ / min and holding the temperature for 30min, then heating to 700-750℃ at a rate of 5-8℃ / min and holding the temperature for calcination for 60-80min.

[0014] Preferably, in S1, the two-stage ball milling is as follows: first, coarse grinding is performed for 10-15 minutes using grinding balls with a diameter of 10-15 mm, and then fine grinding is performed for 15-25 minutes using grinding balls with a diameter of 5-8 mm.

[0015] Preferably, in S1, the specific surface area of ​​the active shield tunneling slag powder is ≥450m². 2 / kg, median particle size D50≤15μm, and amorphous phase content>40%.

[0016] Preferably, in S3, the mass ratio of sodium hydroxide to sodium silicate in the composite alkali activator solution is 1:1 to 1:2.5.

[0017] Preferably, the total amount of mixing water in S3 and S4 is 0.3 to the water-cement ratio of the solid dry mix, and the mixing water in S3 accounts for 30%-50% of the total amount of mixing water.

[0018] Preferably, in S4, the mass fraction of the composite alkali activator solution is 8-12 parts.

[0019] The present invention also provides a cementitious material based on a large amount of shield tunnel slag, which is prepared by the above-mentioned method for preparing a cementitious material based on a large amount of shield tunnel slag.

[0020] The present invention also provides an application of a cementitious material based on a large amount of shield tunnel slag, which is applied to building materials.

[0021] This invention employs the aforementioned cementitious material based on high-volume shield tunneling slag, its preparation method, and its application, which has the following beneficial effects:

[0022] (1) The preparation method of the present invention realizes the transformation of shield tunnel slag from low-value landfill to high-value and the synergistic utilization of multi-source solid waste. Through the optimized targeted multi-stage coupled activation process (gradient heating calcination combined with rapid cooling), the inert shield tunnel slag is transformed into highly active silicon-aluminum raw material, with a dosage far exceeding the level of use as filler in the prior art (dosage <30%). At the same time, it synergistically utilizes desulfurized gypsum, fly ash and other solid wastes to improve the total utilization rate of solid waste and realize the efficient resource utilization of multi-source solid waste.

[0023] (2) The cementitious material prepared by the present invention has excellent comprehensive performance and outstanding mechanical properties. Its compressive strength can reach more than 54 MPa after 28 days and more than 33 MPa after 3 days. It has both early strength and high strength characteristics. Its workability is excellent. Under the condition of water-cement ratio of 0.30, the fluidity of the slurry is still maintained at 180-195 mm, which meets the requirements of various construction.

[0024] (3) The cementitious material based on high-volume shield tunnel slag provided by the present invention has multifunctional components that synergistically enhance each other. Each functional component forms an organic synergistic system. Nano-alumina acts as a nucleating agent to significantly accelerate the formation of geopolymer gel, while precisely controlling the Si / Al ratio of the system. Diatomaceous earth effectively inhibits self-shrinkage and optimizes the pore structure through internal curing effect. The moderate expansion of magnesium oxide expansion agent precisely compensates for the shrinkage of the system. Polypropylene fiber bridges microcracks at multiple scales and improves toughness.

[0025] (4) The preparation method of the present invention has significant environmental and economic benefits, significant carbon emission reduction effect, completely avoids the two grinding and one firing process of traditional cement production, and the carbon footprint of the product is significantly reduced compared with traditional cement; the cost advantage is obvious, by deeply activating the shield tunnel slag, the absolute dependence on expensive composite alkali activator is reduced, and low-cost solid waste is used, and the overall cost is significantly reduced compared with similar geopolymer materials; the process adaptability is good, and the activation temperature (700-750℃) is significantly lower than the traditional sintering temperature of ceramsite (>1000℃), thereby reducing energy consumption.

[0026] (5) The cementitious material based on high-volume shield tunnel slag provided by the present invention can be applied to building materials, realizing the leap from low-performance filler to high-performance building materials. It can directly or partially replace cement and be used to prepare environmentally friendly concrete, highway subgrade materials, mine filling materials, grouting reinforcement materials, etc.

[0027] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0028] Figure 1 This is a SEM image of the high-performance geopolymer cementitious material specimen from Example 1 of the present invention;

[0029] Figure 2This is a schematic diagram of the unconfined compressive strength of Embodiments 1 to 11 and Comparative Examples 1 to 6 of the present invention. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0031] This invention provides a method for preparing a cementitious material based on a large amount of shield tunnel slag, comprising the following steps:

[0032] S1. Preparation of active shield tunneling slag powder (targeted multi-stage coupled activation): The original shield tunneling slag is mechanically crushed, forced homogenized, and dried to constant weight in sequence. Then it is subjected to gradient heating and calcination, followed by rapid cooling. After two-stage ball milling, it is passed through a 200-mesh sieve to obtain active shield tunneling slag powder.

[0033] S2. Preparation of solid dry mix: Weigh out 550-650 parts of the active shield tunnel slag powder obtained in S1, 15-25 parts of desulfurized gypsum, 80-120 parts of fly ash, 3-5 parts of diatomaceous earth, 1-2 parts of nano alumina, 4-6 parts of magnesium oxide expanding agent, 0.5-2 parts of polypropylene fiber, and 0.2-0.4 parts of polycarboxylate superplasticizer according to the mass ratio, mix and dry mix evenly to obtain solid dry mix;

[0034] S3. Preparation of composite alkali activator solution: Dissolve sodium hydroxide in part of the mixing water to prepare a concentrated alkali solution of 8-10 mol / L. After cooling to room temperature, add sodium silicate powder and stir until completely dissolved and clear to obtain the composite alkali activator solution.

[0035] S4. Slurry mixing and molding: The composite alkali activator solution of S3 is mixed with the solid dry mixture of S2. The mixture is first initially stirred and soaked, and then the remaining mixing water is added and stirred to obtain a uniform aggregate slurry. Then it is compacted and molded to obtain a cementitious material.

[0036] This invention uses shield tunneling excavated soil generated during urban tunnel construction as the main silica-alumina raw material. Its amorphous structure rapidly depolymerizes in an alkaline environment to generate silica-aluminate monomers, providing precursors for the polymerization reaction. Through targeted multi-stage coupled activation and multi-source solid waste synergistic stimulation, a geopolymer cementitious material with excellent comprehensive performance is prepared without relying on high alkali dosage, providing a high-value-added and low-environmental-impact resource utilization path for shield tunneling excavated soil.

[0037] In S1 of this invention, the purpose of mechanical crushing and forced homogenization is to eliminate regional differences in the composition and structure of shield tunnel slag and ensure batch stability. Drying is carried out in a forced-air drying oven at 105±5℃ to completely remove free water and avoid particle structure damage caused by rapid evaporation of moisture during subsequent calcination.

[0038] Preferably, in S1, the initial moisture content of the original shield tunneling excavated soil is ≥25%, and the proportion of particles with a particle size between 0.075mm and 1.5mm is more than 90%.

[0039] Preferably, in S1, the gradient heating calcination is a medium-temperature oxygen-controlled activation calcination, which is carried out in a programmed temperature-controlled muffle furnace, including: the first stage (dehydration and organic matter decomposition) first heating to 450-500℃ at a rate of 3-5℃ / min and holding at that temperature for 30min; the second stage (lattice destruction and amorphization) heating to 700-750℃ at a rate of 5-8℃ / min and holding at that temperature for calcination for 60-80min.

[0040] In some embodiments of the present invention, rapid cooling is performed using an air-cooling device. Rapid cooling is part of the activity stabilization stage, where the material is immediately transferred to an air-cooling device for rapid cooling (quenching) after calcination.

[0041] In this invention, the first stage aims to completely remove interlayer bound water and decompose some organic impurities, opening the pore channels of mineral particles. The second stage temperature zone effectively promotes the removal of kaolinite (Al2Si2O3) from the slag soil. 54 Layered silicate minerals undergo dehydroxylation reactions, causing their crystal structures to collapse and transform into highly reactive amorphous metakaolinite (Al₂O₃·2SiO₂) phases. Simultaneously, while stable crystalline phases such as quartz (SiO₂) do not melt at this temperature, their surface lattices loosen and become distorted, significantly increasing their reactivity. The third stage involves rapid cooling (for stable reactivity). The purpose of rapid cooling is to freeze the metastable amorphous structure formed at high temperatures, preventing recrystallization and loss of reactivity during slow cooling.

[0042] Preferably, in S1, the two-stage ball milling is as follows: first, coarse grinding is performed for 10-15 minutes using grinding balls with a diameter of 10-15 mm to break up sintered agglomerates, and then fine grinding is performed for 15-25 minutes using grinding balls with a diameter of 5-8 mm to obtain the required fineness and particle size distribution.

[0043] In some embodiments of the present invention, the two-stage ball milling is performed in a planetary ball mill.

[0044] Preferably, in S1, the specific surface area of ​​the active shield tunneling slag powder is ≥450m². 2 / kg, median particle size D50≤15μm, and amorphous phase content>40%.

[0045] In some embodiments of the present invention, in S2, the dry mixing is performed by dry mixing for 3 minutes in a forced cement mortar mixer.

[0046] In some embodiments of the present invention, in S2, the desulfurizing gypsum serves to provide sulfate activation and dissolve the SO4. 2- With Al in the system 3+ Ca 2+ The reaction produces needle-like ettringite (AFt), which can fill pores and enhance early strength. It can also regulate the reaction process; an appropriate amount of sulfate can adjust the formation rate of the geopolymer gel and intertwine with the silica-alumina gel to form a more stable composite gel system.

[0047] In some embodiments of the present invention, in S2, the role of fly ash is to produce physical water reduction and morphological effects. The spherical glass microspheres rich in fly ash act as "ball bearings," significantly improving the rheological properties of the slurry and increasing its fluidity. In addition, fly ash can also supplement the source of silicon and aluminum. Fly ash itself is also a high-quality silicon and aluminum material. Its glassy body can slowly dissolve under the action of strong alkali and participate in the geopolymer reaction, which helps to increase the strength in the later stage.

[0048] In some embodiments of the present invention, in S2, the porous structure of diatomaceous earth can adsorb and store some of the mixing water. During the later geopolymer reaction, this water is slowly released, producing an internal curing effect. This can effectively reduce the self-drying shrinkage of the material and promote the continued hydration of unreacted particles, optimize the pore structure, and improve impermeability.

[0049] In some embodiments of the present invention, in S2, nano-alumina has an extremely high specific surface area and reactivity. It can act as a crystal nucleus, significantly accelerating the nucleation and growth process of the geopolymer gel phase. At the same time, as an efficient additional aluminum source, it can precisely control the final Si / Al ratio of the system, promoting the formation of a denser and stronger geopolymer network structure.

[0050] In some embodiments of the present invention, in S2, the role of the magnesium oxide expanding agent is that the geopolymer may shrink during the drying process, and the lightly calcined magnesium oxide will generate magnesia (Mg(OH)2) in the later stage of hydration. This process is accompanied by moderate volume expansion, which can effectively compensate for the chemical shrinkage and drying shrinkage of the geopolymer system, thereby greatly improving the crack resistance and volume stability of the product.

[0051] In some embodiments of the present invention, in S2, the role of polypropylene (PP) fibers is to form a three-dimensional network in the matrix by randomly distributed fibers, which effectively bridges and prevents the propagation of cracks, thereby improving the toughness (cracks without breaking) and impact resistance of the material.

[0052] In some embodiments of the present invention, in S2, the role of the polycarboxylate superplasticizer is to further optimize the workability of the slurry while ensuring a low water-binder ratio, thereby ensuring that the material has good workability and ease of application.

[0053] Preferably, in S3, the mass ratio of sodium hydroxide to sodium silicate in the composite alkali activator solution is 1:1 to 1:2.5.

[0054] In some embodiments of the present invention, the mass ratio of sodium hydroxide to sodium silicate is 1:1.8.

[0055] In some embodiments of the present invention, in S3, the role of sodium hydroxide is to provide an initial strongly alkaline environment (high OH-). - (Concentration), rapidly breaking down the Si-O and Al-O bonds on the surface of activated slag particles, promoting their depolymerization. Sodium silicate, besides providing alkalinity, primarily provides soluble silicate ions (SiO3). 2- These silicate groups can act as "templates" or "intermediates," rapidly condensing with dissolved aluminate and silicate groups to form a stable aluminosilicate gel network. The combination of the two plays a synergistic role in "bond breaking" and "network formation."

[0056] Preferably, the total amount of mixing water in S3 and S4 is 0.3 compared to the water-cement ratio of the solid dry mix, with the mixing water in S3 accounting for 30%-50% of the total mixing water. This is to ensure that the sodium hydroxide solid and sodium silicate powder are fully dissolved to form a composite alkali activator solution of suitable concentration, uniformity, and stability. The remaining mixing water is added in the subsequent slurry mixing and molding stage to adjust the rheological properties of the overall slurry.

[0057] In some embodiments of the present invention, in step S3, the composite alkali activator solution is prepared 2-24 hours in advance.

[0058] In some embodiments of the present invention, S3, the composite alkali activator solution is prepared 2-8 hours in advance. This ensures that the solution reaches a better stable state and prevents premature carbonation due to absorption of carbon dioxide from the air, which would affect the activation effect. Instead, it allows the solution to age and become more stable.

[0059] Preferably, in S4, the mass fraction of the composite alkali activator solution is 8-12 parts.

[0060] In some embodiments of the present invention, when the amount of the composite alkali activator solution is high (more than 10 parts by mass), the alkali activator solution can be prepared 6-8 hours in advance. When the amount of the composite alkali activator solution is medium (10 parts by mass), the alkali activator solution can be prepared 4-6 hours in advance. When the amount of the composite alkali activator solution is standard or low (less than 10 parts by mass), the alkali activator solution can be prepared 2-4 hours in advance.

[0061] In some embodiments of the present invention, the initial stirring in S4 is low-speed stirring for 1 minute to allow the solid dry mixture to be initially wetted by the composite alkali activator solution. After adding mixing water, the mixture is stirred at high speed for 2 minutes to form a viscous, uniform, and color-consistent geopolymer slurry. The initial flowability of the geopolymer slurry is then immediately tested. The geopolymer slurry is poured into a 40mm×40mm×40mm triple mold, placed on a vibrating table, and compacted for 30 seconds. The surface is then smoothed to obtain a high-performance geopolymer cementitious material.

[0062] In some embodiments of the present invention, the low-speed stirring rate in S4 is 60-100 rpm, and the high-speed stirring rate is 180-250 rpm.

[0063] In some embodiments of the present invention, the initial fluidity of the geopolymer slurry is tested in accordance with the GB / T 2419-2005 standard.

[0064] The present invention also provides a cementitious material based on a large amount of shield tunnel slag, which is prepared by the above-mentioned method for preparing a cementitious material based on a large amount of shield tunnel slag.

[0065] The present invention also provides an application of a cementitious material based on a large amount of shield tunnel slag, which is applied to building materials.

[0066] In some embodiments of the present invention, the above-mentioned building materials include prefabricated components, 3D printed building materials, rapid road repair materials, mine filling materials, underground engineering grouting materials, or marine engineering concrete.

[0067] All raw materials used in the embodiments of this invention are commercially available, wherein:

[0068] The initial moisture content of the original shield tunneling excavated soil is ≥25%, and the proportion of particles with a particle size between 0.075mm and 1.5mm is more than 90%.

[0069] Desulfurized gypsum can be purchased from Yantai Anda Environmental Protection Technology Co., Ltd. (white powder, main component is CaSO4·2H2O, content ≥93%).

[0070] Fly ash can be purchased from Yantai Anda Environmental Protection Technology Co., Ltd. (Grade I, black powder, apparent density 2.07 g / cm³). 3 Its main chemical components are SiO2 and Al2O3.

[0071] Sodium hydroxide can be purchased from Tianjin Ruijinte Chemical Co., Ltd. (white, uniform granules, purity greater than 99%, analytical grade, NaOH content ≥ 99%).

[0072] The sodium silicate used in the experiment was produced by Sinopharm Chemical Reagent Co., Ltd. (analytical grade, white granular powder, odorless, easily soluble in water and dilute alkaline solution).

[0073] Example 1

[0074] This invention provides a method for preparing a cementitious material based on a large amount of shield tunnel slag, comprising the following steps:

[0075] S1. Preparation of active shield tunnel slag powder:

[0076] S1.1 The original shield tunneling excavation soil is first mechanically crushed and forced to homogenize, and then placed in a forced-air drying oven at 105±5℃ to dry to constant weight.

[0077] S1.2. Perform gradient heating calcination: first, heat to 475℃ at a rate of 4℃ / min and hold at that temperature for 30 min, then heat to 725℃ at a rate of 6℃ / min and hold at that temperature for 70 min. Immediately afterwards, transfer to an air-cooling device for rapid cooling.

[0078] S1.3. The rapidly cooled calcined material is fed into a planetary ball mill and ground using a gradient grinding method. First, Φ12mm grinding balls are used for coarse grinding for 12 minutes; then Φ6mm grinding balls are added for fine grinding for 20 minutes. The ground powder is passed through a 200-mesh (75μm) square hole sieve, and the material that passes through the sieve is the active shield tunnel slag powder.

[0079] S2. Preparation of solid dry mixture:

[0080] Weigh out 600 parts of active shield tunnel slag powder prepared by S1, 20 parts of desulfurized gypsum, 100 parts of fly ash, 4 parts of diatomaceous earth, 1.5 parts of nano alumina, 5 parts of magnesium oxide expanding agent, 1 part of polypropylene fiber, and 0.3 parts of polycarboxylate superplasticizer according to the mass ratio. Place them in a forced cement mortar mixer and dry mix for 3 minutes until the mixture is uniform in color to obtain a solid dry mix.

[0081] S3. Preparation of composite alkaline activator solution:

[0082] The composite alkali activator is composed of sodium hydroxide and sodium silicate in a mass ratio of 1:1.8. Five hours in advance, solid sodium hydroxide is dissolved in a portion of the mixing water (40% of the total mixing water) to prepare a concentrated alkali solution of 9 mol / L. The solution is then allowed to cool to room temperature. Subsequently, a measured amount of sodium silicate powder is added, and the mixture is mechanically stirred until completely dissolved and clear, yielding the composite alkali activator solution.

[0083] S4. Slurry mixing and shaping:

[0084] Ten parts by weight of the S3 composite alkali activator solution and the S2 solid dry mix were poured into a mixing pot and stirred at a low speed of 80 rpm for 1 min. The remaining mixing water was added and stirred at a high speed of 220 rpm for 2 min to form a viscous, uniform, and colorless geopolymer slurry. The initial fluidity of the slurry was immediately tested. The slurry was poured into a 40 mm × 40 mm × 40 mm triple mold, placed on a vibrating table and compacted for 30 s. The surface was then smoothed to obtain a high-performance geopolymer cementitious material.

[0085] Example 2

[0086] This invention provides a method for preparing a cementitious material based on a large amount of shield tunnel slag, comprising the following steps:

[0087] S1. Preparation of active shield tunnel slag powder:

[0088] S1.1 The original shield tunneling excavation soil is first mechanically crushed and forced to homogenize, and then placed in a forced-air drying oven at 105±5℃ to dry to constant weight.

[0089] S1.2. Perform gradient heating calcination: first, heat to 450℃ at a rate of 3℃ / min and hold at that temperature for 30min, then heat to 700℃ at a rate of 5℃ / min and hold at that temperature for 60min. Immediately afterwards, transfer to an air-cooling device for rapid cooling.

[0090] S1.3. The rapidly cooled calcined material is fed into a planetary ball mill and ground using a gradient grinding method. First, Φ10mm grinding balls are used for coarse grinding for 10 minutes; then Φ5mm grinding balls are added for fine grinding for 15 minutes. The ground powder is passed through a 200-mesh (75μm) square hole sieve, and the material that passes through the sieve is the active shield tunnel slag powder.

[0091] S2. Preparation of solid dry mixture:

[0092] Weigh out 580 parts by weight of the active shield tunnel slag powder prepared by S1, 18 parts by weight of desulfurized gypsum, 110 parts by weight of fly ash, 3 parts by weight of diatomaceous earth, 1 part by weight of nano alumina, 4 parts by weight of magnesium oxide expanding agent, 0.8 parts by weight of polypropylene fiber, and 0.35 parts by weight of polycarboxylate superplasticizer. Place them in a forced cement mortar mixer and dry mix for 3 minutes until the mixture is uniform in color to obtain a solid dry mix.

[0093] S3. Preparation of composite alkaline activator solution:

[0094] The composite alkali activator is composed of sodium hydroxide and sodium silicate in a mass ratio of 1:1.8. Two hours in advance, solid sodium hydroxide is dissolved in a portion of the mixing water (30% of the total mixing water) to prepare an 8 mol / L concentrated alkali solution, which is then allowed to cool to room temperature. Subsequently, a measured amount of sodium silicate powder is added, and the solution is mechanically stirred until completely dissolved and clear, yielding the composite alkali activator solution.

[0095] S4. Slurry mixing and shaping:

[0096] Nine parts by weight of the S3 composite alkali activator solution and the S2 solid dry mix were poured into a mixing pot and stirred at a low speed of 60 rpm for 1 min. The remaining mixing water was added and stirred at a high speed of 180 rpm for 2 min to form a viscous, uniform, and colorless geopolymer slurry. The initial fluidity of the slurry was immediately tested. The slurry was poured into a 40 mm × 40 mm × 40 mm triple mold, placed on a vibrating table and compacted for 30 s. The surface was then smoothed to obtain a high-performance geopolymer cementitious material.

[0097] Example 3

[0098] This invention provides a method for preparing a cementitious material based on a large amount of shield tunnel slag, comprising the following steps:

[0099] S1. Preparation of active shield tunnel slag powder:

[0100] S1.1 The original shield tunneling excavation soil is first mechanically crushed and forced to homogenize, and then placed in a forced-air drying oven at 105±5℃ to dry to constant weight.

[0101] S1.2. Perform gradient heating calcination: first, heat to 500℃ at a rate of 5℃ / min and hold at that temperature for 30 min, then heat to 750℃ at a rate of 8℃ / min and hold at that temperature for 80 min. Immediately afterwards, transfer to an air-cooling device for rapid cooling.

[0102] S1.3. The rapidly cooled calcined material is fed into a planetary ball mill and ground using a gradient grinding method. First, Φ15mm grinding balls are used for coarse grinding for 15 minutes; then Φ8mm grinding balls are added for fine grinding for 25 minutes. The ground powder is passed through a 200-mesh (75μm) square hole sieve, and the material that passes through the sieve is the active shield tunnel slag powder.

[0103] S2. Preparation of solid dry mixture:

[0104] Weigh out 620 parts by weight of the active shield tunnel slag powder prepared by S1, 22 parts by weight of desulfurized gypsum, 90 parts by weight of fly ash, 5 parts by weight of diatomaceous earth, 2 parts by weight of nano alumina, 6 parts by weight of magnesium oxide expanding agent, 1.5 parts by weight of polypropylene fiber, and 0.4 parts by weight of polycarboxylate superplasticizer. Place them in a forced cement mortar mixer and dry mix for 3 minutes until the mixture is uniform in color to obtain a solid dry mix.

[0105] S3. Preparation of composite alkaline activator solution:

[0106] The composite alkali activator is composed of sodium hydroxide and sodium silicate in a mass ratio of 1:1.8. Eight hours in advance, solid sodium hydroxide is dissolved in a portion of the mixing water (50% of the total mixing water) to prepare a 10 mol / L concentrated alkali solution, which is then allowed to cool to room temperature. Subsequently, a measured amount of sodium silicate powder is added, and the solution is mechanically stirred until completely dissolved and clear, yielding the composite alkali activator solution.

[0107] S4. Slurry mixing and shaping:

[0108] 11 parts by weight of the S3 composite alkali activator solution and the S2 solid dry mix were poured into a mixing pot and stirred at a low speed of 100 rpm for 1 min. The remaining mixing water was added and stirred at a high speed of 250 rpm for 2 min to form a viscous, uniform, and colorless geopolymer slurry. The initial fluidity of the slurry was immediately tested. The slurry was poured into a 40 mm × 40 mm × 40 mm triple mold, placed on a vibrating table and compacted for 30 s. The surface was then smoothed to obtain a high-performance geopolymer cementitious material.

[0109] Example 4

[0110] The difference from Example 1 is that, in S2, the raw materials, by mass parts, include: 550 parts of the activated shield tunnel slag powder obtained in S1, 20 parts of desulfurized gypsum, 110 parts of fly ash, 4 parts of diatomaceous earth, 1.5 parts of nano-alumina, 5 parts of magnesium oxide expanding agent, 1 part of polypropylene fiber, and 0.28 parts of polycarboxylate superplasticizer. In S3, the composite alkali activator solution is prepared 5 hours in advance. In S4, the amount of composite alkali activator is 10 parts. All other aspects are the same as in Example 1.

[0111] Example 5

[0112] The difference from Example 1 is that, in S2, the raw materials, by mass parts, include: 650 parts of the activated shield tunnel slag powder obtained in S1, 15 parts of desulfurized gypsum, 85 parts of fly ash, 4 parts of diatomaceous earth, 1.5 parts of nano-alumina, 5 parts of magnesium oxide expanding agent, 1 part of polypropylene fiber, and 0.35 parts of polycarboxylate superplasticizer. In S3, the composite alkali activator solution is prepared 5 hours in advance. In S4, the amount of composite alkali activator is 10 parts. All other aspects are the same as in Example 1.

[0113] Example 6

[0114] The difference from Example 1 is that the mass ratio of sodium hydroxide to sodium silicate in S3 is 1:1.5. Everything else is the same as in Example 1.

[0115] Example 7

[0116] The difference from Example 1 is that the mass ratio of sodium hydroxide to sodium silicate in S3 is 1:2. Everything else is the same as in Example 1.

[0117] Example 8

[0118] The difference from Example 1 is that in S2, the amount of nano-alumina is 1 part. Everything else is the same as in Example 1.

[0119] Example 9

[0120] The difference from Example 1 is that in S2, there are 2 parts of nano-alumina. Everything else is the same as in Example 1.

[0121] Example 10

[0122] The difference from Example 1 is that the amount of diatomaceous earth in S2 is 3 parts. Everything else is the same as in Example 1.

[0123] Example 11

[0124] The difference from Example 1 is that diatomaceous earth in S2 is 5 parts. Everything else is the same as in Example 1.

[0125] Comparative Example 1

[0126] The difference from Example 1 is that in S1, the original shield tunneling slag was dried to constant weight and then directly fed into a planetary ball mill for gradient grinding, without gradient heating and calcination or rapid cooling. All other steps are the same as in Example 1.

[0127] Comparative Example 2

[0128] The difference from Example 1 is that, in S2, the raw materials, by mass parts, include 600 parts of the activated shield tunnel slag powder obtained in S1, 20 parts of desulfurized gypsum, 100 parts of fly ash, and 0.3 parts of polycarboxylate superplasticizer, without the addition of diatomaceous earth, nano-alumina, magnesium oxide expanding agent, or polypropylene fiber. In S3, the composite alkali activator solution is prepared 5 hours in advance. In S4, the amount of composite alkali activator is 10 parts. All other aspects are the same as in Example 1.

[0129] Comparative Example 3

[0130] The difference from Example 1 is that in S3, the composite alkali activator solution was not prepared. Instead, 9 parts of solid sodium hydroxide were dissolved in a portion of the mixing water (40% of the total mixing water) 3 hours in advance to prepare a concentrated alkali solution of 9 mol / L. This solution was then allowed to stand and cool to room temperature to obtain the alkali activator solution. In S4, the alkali activator solution was mixed with the solid dry mix from S2. The rest was the same as in Example 1.

[0131] Comparative Example 4

[0132] The difference from Example 1 is that in S3, the composite alkali activator solution was not prepared. Instead, 9 parts of solid sodium silicate powder were dissolved in a portion of the mixing water (accounting for 40% of the total mixing water) 3 hours in advance, and mechanically stirred until completely dissolved and clear to obtain a sodium silicate solution. In S4, the sodium silicate solution was mixed with the solid dry mix from S2. The rest was the same as in Example 1.

[0133] Comparative Example 5

[0134] The difference from Example 1 is that after gradient heating and calcination in S1.2, the furnace was not transferred to an air-cooling device for rapid cooling. Instead, the power to the muffle furnace was turned off, and the furnace was allowed to cool naturally to room temperature. All other aspects are the same as in Example 1.

[0135] Comparative Example 6

[0136] The difference from Example 1 is that in S1.3, a single-size Φ10mm grinding ball is used to grind for a total of 32 minutes, and the ground powder is passed through a 200-mesh sieve. The rest is the same as in Example 1.

[0137] Table 1. Amounts of raw materials used in each embodiment and comparative example.

[0138]

[0139]

[0140] This indicates that targeted multi-stage coupling activation was not performed; This indicates that calcination was performed, but rapid cooling was not. This indicates that calcination and rapid cooling were involved, but gradient grinding was not.

[0141] Performance testing:

[0142] The cementitious material specimens prepared in Examples 1-11 and Comparative Examples 1-6, along with their molds, were placed in a standard curing chamber (temperature 20±2℃, relative humidity ≥95%) and allowed to cure for 24 hours. After demolding, the specimens were placed back in the curing chamber under the same conditions and cured for the specified age (e.g., 3 days, 7 days, 28 days). The specimens cured to the specified age were then characterized by SEM and subjected to a 28-day compressive strength test.

[0143] SEM characterization

[0144] The specimens from Example 1, cured to 28 days old, were used to obtain small pieces (approximately 1 cm) by tapping. 3 The sample should be taken from locations avoiding obvious bubbles and cracks. Immediately immerse the sample in anhydrous ethanol for at least 48 hours to terminate the hydration / polymerization reaction, then dry it in a vacuum oven at 60°C until constant weight. Adhere the dried sample cross-section to conductive adhesive and perform gold sputtering in an ion sputtering apparatus to make the surface conductive. Use a field emission scanning electron microscope for scanning imaging under the following conditions: 1) Accelerating voltage: 5-15kV; 2) Working distance: 8-12mm.

[0145] The results are as follows Figure 1 As shown, the high-performance geopolymer cementitious material specimen prepared in Example 1 exhibits a dense microstructure. The amorphous geopolymer gel, primarily generated from activated shield tunneling slag powder, is interwoven and densely bonded with needle-like ettringite (AFt) crystals excited by desulfurized gypsum. This indicates that the shield tunneling slag powder, after undergoing multi-target stage coupled activation treatment according to the present invention, has fully participated in the reaction, transforming into a continuous geopolymer gel phase, rather than existing in the form of inert particles. This microscopically verifies that it has played a role as the main cementitious material, supporting the feasibility of high-volume utilization.

[0146] 28-day compressive strength and flowability test

[0147] After curing the cementitious material specimens prepared in Examples 1-11 and Comparative Examples 1-6 for 28 days, the unconfined compressive strength of the specimens was tested using a universal compression testing machine according to GB / T 17671-2021 Cement Mortar Strength Test Method (ISO Method): During the test, the loading rate should be controlled at 1.0 mm / min, and the test result is the arithmetic mean of the three specimens measured. If the difference between any measured value and the average value exceeds ±10%, this data should be discarded, and the average value of the remaining specimens should be used as the final result.

[0148] The uncured cementitious materials prepared in Examples 1-11 and Comparative Examples 1-6 were tested for fluidity using a cement mortar fluidity tester (jump table) according to GB / T 2419-2005, "Method for Determination of Flowability of Cement Mortar". During the test, the jump table was activated within 25s ± 1s, allowing the table surface and the mortar on it to complete 25 jumps. The diameter of the expansion in two mutually perpendicular directions at the bottom of the mortar was measured with calipers, and the arithmetic mean of the two diameters (unit: mm) was taken as the fluidity value of the mortar. The results are shown below. Figure 2 And Table 2.

[0149] Table 2. 3-day and 28-day compressive strength and slurry fluidity of different embodiments and comparative examples.

[0150]

[0151] like Figure 2 As shown in Table 2, in Examples 1-3, under the premise of high content (79%~82%) of shield tunneling slag, all exhibited excellent comprehensive performance with high strength (>34MPa in 3 days, >54MPa in 28 days) and good fluidity (>180mm).

[0152] In Example 4, the lower limit of active shield tunneling slag powder (550 parts) was verified: with the reduction of dosage, the total activity of the system may decrease slightly, but it can still maintain high strength (35 MPa at 3 days, 56.1 MPa at 28 days) and excellent fluidity (195 mm). This shows that the shield tunneling slag powder treated by the multi-target stage coupling activation process of the present invention has sufficient activation and strong stability. Even at a low dosage, its high amorphous phase content and optimized particle size distribution can still provide sufficient silicon-aluminum precursors for geopolymer reaction. With the synergistic effect of composite alkali activator and the complementary effect of other functional components, the system can maintain high performance without relying on additional high-activity raw materials. This reflects the deep unlocking and stable empowerment of slag activity by the multi-target stage coupling activation process.

[0153] In Example 5, the upper limit of the active shield tunneling slag powder (650 parts) was verified: at a high dosage, a slight increase in water-reducing agent (0.35 parts) was required to ensure workability. Performance data showed that even with a dosage of 82%, the 3-day and 28-day strengths (33.2 MPa and 54.8 MPa, respectively) and workability (175 mm) remained excellent. This demonstrates that the cementitious material of the high-dosage active shield tunneling slag powder of this invention has good system adaptability and compatibility. Its high specific surface area and active characteristics can form a highly efficient synergy with components such as desulfurized gypsum and fly ash. It will not cause insufficient reaction or slurry agglomeration due to excessive dosage, and the construction fluidity requirements can be met by finely adjusting the amount of water-reducing agent. This breaks through the limitation of small-proportion inert filling of shield tunneling slag in the prior art and achieves the unity of high dosage and high performance.

[0154] In Example 6, the lower limit of the composite alkali activator ratio (NaOH:Na2SiO3=1:1.5) was verified. A relatively smaller amount of sodium silicate resulted in slightly weaker web-forming ability, leading to a slight decrease in strength at 3 days and 28 days (33.9 MPa and 55.0 MPa, respectively). However, due to the relatively higher alkalinity, the fluidity was good (192 mm). In Example 7, the upper limit of the composite alkali activator ratio (NaOH:Na2SiO3=1:2) was verified. A relatively larger amount of sodium silicate increased the slurry viscosity and decreased the fluidity (178 mm), but enhanced web-forming effect. The strength at 3 days and 28 days (35.8 MPa and 56.5 MPa, respectively) remained good, demonstrating the effectiveness of the stated ratio range.

[0155] In Examples 8 and 9, the lower limit (1.0 part) and upper limit (2.0 part) of the amount of nano-alumina were verified, respectively: the data showed that within this range, the material maintained high strength (3 days > 33.0 MPa, 28 days > 54.9 MPa) and good workability. In Examples 10 and 11, the lower limit (3 parts) and upper limit (5 parts) of the amount of diatomaceous earth were verified, respectively: the data showed that within this range, the material performance was stable, with a 3-day strength higher than 34.6 MPa and a 28-day strength higher than 55.5 MPa.

[0156] Compared to Example 1, Comparative Example 1, which simply replaced the activated shield tunneling soil powder with an equal amount of uncalcined raw soil powder, showed a sharp decrease in its 3-day and 28-day compressive strengths of approximately 61% and 65%, respectively. This demonstrates that the multi-stage coupled activation step is an essential key step for unlocking the cementitious activity of shield tunneling soil. Comparative Example 2, based on Example 1, removed all micro-nano-level functional additives (diatomaceous earth, nano-alumina, magnesium oxide expanding agent, and PP fiber). The results showed that although the flowability was still acceptable, the 3-day and 28-day compressive strengths decreased significantly by approximately 22% and 34%, respectively. This comparison fully reveals that the synergistic system composed of these functional components plays a decisive role in achieving high performance, especially in obtaining high volume stability while ensuring high strength.

[0157] Comparative Examples 3 and 4, using NaOH or Na₂SiO₃ alone as activators, showed significantly lower activating strengths than Example 1, which used a composite alkali activator. This demonstrates that the bond-breaking effect of sodium hydroxide and the network-forming effect of sodium silicate have an irreplaceable synergistic effect, and that combining them in a specific ratio is a necessary condition for achieving efficient activation.

[0158] Comparative Example 5, which did not undergo rapid cooling, showed a significant decrease in strength at 3 days and 28 days. This is because the active amorphous structure recrystallized into an inert crystalline phase (such as mullite rudimentary crystals) during slow cooling, resulting in significantly lower activity compared to the rapidly cooled sample. This led to slow early-stage geopolymer reaction kinetics and reduced load-bearing capacity. This indicates that rapid cooling is not simply a temperature reduction step, but rather a synergistic effect with gradient calcination, achieving a complete activation process that combines structural destruction with activity locking.

[0159] Comparative Example 6, which did not undergo gradient grinding, showed a slight decrease in strength at 3 days and 28 days, along with a minor change in fluidity. This is due to poor particle size distribution, reduced reaction efficiency, and consequently, decreased slurry density. The presence of numerous angular particles also increased internal friction, leading to decreased fluidity. This demonstrates that gradient grinding and chemical activation synergistically constitute a physicochemical dual-dimensional activation system, achieving high performance in cementitious materials.

[0160] Therefore, this invention employs the aforementioned cementitious material based on high-volume shield tunneling slag, its preparation method, and its application. Through a targeted multi-stage coupled activation process, the shield tunneling slag is transformed from inert crystals into a highly active amorphous structure, making it a core cementitious component with stable reactivity rather than a simple filler, thus achieving high-volume utilization of the shield tunneling slag. The activated shield tunneling slag is then ground to a specific surface area ≥450 m² through gradient grinding. 2 The specific particle size distribution of / kg and D50≤15μm further unlocks the active sites on the particle surface, providing a sufficient reaction interface for the geopolymer polymerization reaction. By optimizing the particle size distribution, the internal porosity of the system is reduced, achieving a dual improvement in reaction sufficiency and structural compactness. The composite alkali activator uses sodium hydroxide and sodium silicate to form a synergistic activation mechanism of bond breaking and network formation, effectively controlling the amount of alkali while ensuring the activation effect. By introducing the synergistic combination of nano alumina (nucleating agent and aluminum source), diatomaceous earth (internal curing agent), magnesium oxide expansion agent (volume stabilizer) and PP fiber (toughening agent), a multi-level reinforcement structure from the nanoscale to the macroscale is constructed, solving the technical problems of insufficient strength and shrinkage cracking common in high-dosage geopolymer materials.

[0161] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a cementitious material based on a large amount of shield tunnel slag, characterized in that: Includes the following steps: S1. Preparation of active shield tunneling slag powder: The original shield tunneling slag is mechanically crushed, forced homogenized, and dried to constant weight. Then it is calcined by gradient heating, followed by rapid cooling. After two-stage ball milling, it is passed through a 200-mesh sieve to obtain active shield tunneling slag powder. The gradient heating calcination involves first heating to 450-500℃ at a rate of 3-5℃ / min and holding the temperature for 30min, then heating to 700-750℃ at a rate of 5-8℃ / min and holding the temperature for calcination for 60-80min. The two-stage ball milling process is as follows: first, use Φ10-15mm grinding balls for coarse grinding for 10-15 minutes, and then use Φ5-8mm grinding balls for fine grinding for 15-25 minutes. The initial moisture content of the original shield tunnel excavation soil is ≥25%, and the proportion of particles with a particle size between 0.075mm and 1.5mm is more than 90%. S2. Preparation of solid dry mix: Weigh out 550-650 parts of the active shield tunnel slag powder obtained in S1, 15-25 parts of desulfurized gypsum, 80-120 parts of fly ash, 3-5 parts of diatomaceous earth, 1-2 parts of nano alumina, 4-6 parts of magnesium oxide expanding agent, 0.5-2 parts of polypropylene fiber, and 0.2-0.4 parts of polycarboxylate superplasticizer according to the mass ratio, mix and dry mix evenly to obtain solid dry mix; S3. Preparation of composite alkali activator solution: Dissolve sodium hydroxide in part of the mixing water to prepare a concentrated alkali solution of 8-10 mol / L. After cooling to room temperature, add sodium silicate powder and stir until completely dissolved and clear to obtain the composite alkali activator solution; the mass ratio of sodium hydroxide to sodium silicate in the composite alkali activator solution is 1:1-1:2.

5. S4. Slurry mixing and molding: The composite alkali activator solution of S3 is mixed with the solid dry mixture of S2. The mixture is first initially stirred and soaked, and then the remaining mixing water is added and stirred to obtain a uniform aggregate slurry. Then it is compacted and molded to obtain a cementitious material.

2. The method for preparing a cementitious material based on a large amount of shield tunnel slag as described in claim 1, characterized in that: In S1, the specific surface area of ​​the active shield tunneling slag powder is ≥450m². 2 / kg, median particle size D50≤15μm, and amorphous phase content>40%.

3. The method for preparing a cementitious material based on a large amount of shield tunnel slag as described in claim 1, characterized in that: The total amount of mixing water in S3 and S4 is 0.3 compared to the water-cement ratio of the solid dry mix. In S3, the mixing water accounts for 30%-50% of the total amount of mixing water.

4. The method for preparing a cementitious material based on a large amount of shield tunnel slag as described in claim 1, characterized in that: In S4, the mass fraction of the composite alkali activator solution is 8-12 parts.

5. A cementitious material based on a large amount of shield tunneling slag, characterized in that: It is prepared by the method for preparing a cementitious material based on a large amount of shield tunnel slag as described in any one of claims 1-4.

6. An application of a cementitious material based on high-volume shield tunneling slag, characterized in that: The cementitious material based on a large amount of shield tunnel slag, as described in claim 5, is applied to building materials.

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