High-performance concrete for filling tunnel inverted arch and preparation method thereof

Abstract

The invention relates to the technical field of concrete, in particular to high-performance concrete for filling a tunnel inverted arch and a preparation method of the high-performance concrete. The high-performance concrete for filling the tunnel inverted arch is prepared from the following preparation raw materials in parts by mass: 430 to 470 parts of cement, 660 to 700 parts of fine aggregate, 1000 to 1050 parts of coarse aggregate, 58 to 62 parts of fly ash, 15 to 20 parts of modified bentonite, 12 to 15 parts of modified mullite fiber, 0.6 to 1 part of nano calcium sulfate, 5.5 to 6.5 parts of a high-efficiency water reducing agent and 140 to 170 parts of water. The high-performance concrete for filling the tunnel inverted arch has excellent early compressive strength, slump, setting time, crack resistance, durability and the like, in addition, the compressive strength reaches 95% or above of design strength 7 days after pouring, and the high-performance concrete is suitable for large-scale application and popularization.

Description

Technical Field

[0001] The present application relates to the field of concrete technology, and in particular to a high-performance concrete for tunnel invert filling and a preparation method thereof. Background Art

[0002] Tunnel inverts are load-bearing structures, and the performance of their filling materials directly impacts the tunnel's safety and durability. Conventional concrete requires a curing period of 1-2 months to reach its designed strength, resulting in low construction efficiency and high costs. While existing technologies have attempted to shorten curing times by adding admixtures, these technologies generally suffer from insufficient early strength, poor fluidity, and high costs. Therefore, there is an urgent need for a concrete material that combines rapid hardening, high fluidity, and high strength to meet the engineering requirements of tunnel invert filling. Summary of the Invention

[0003] The purpose of this application is to address the shortcomings of current technology and provide a high-performance concrete for tunnel invert filling and a preparation method thereof. The high-performance concrete for tunnel invert filling prepared in this application has the advantages of simple preparation, low cost, and green environmental protection. It also has excellent early compressive strength, slump, setting time, crack resistance and durability. In addition, the compressive strength reaches more than 95% of the design strength 7 days after pouring, which is suitable for large-scale promotion and application.

[0004] In a first aspect, the present application provides a high-performance concrete for tunnel invert filling, which adopts the following technical solution: A high-performance concrete for tunnel invert filling comprises the following raw materials, calculated by weight: 430-470 parts of cement, 660-700 parts of fine aggregate, 1000-1050 parts of coarse aggregate, 58-62 parts of fly ash, 15-20 parts of modified bentonite, 12-15 parts of modified mullite fiber, 0.6-1 part of nano-calcium sulfate, 5.5-6.5 parts of high-efficiency water reducer, and 140-170 parts of water.

[0005] By adopting the above technical solution, cement (such as Tongling Conch P.II52.5 cement) serves as the core of the cementitious material, providing the initial strength and stability of the concrete. Together with fly ash and nano-calcium sulfate, it promotes hydration reactions and accelerates early strength development. Fine aggregate (such as 0.5-0.9mm quartz sand, SiO2>95%) fills the gaps between coarse aggregates, optimizes particle grading, and enhances density and compressive strength. Together with coarse aggregate, it forms a dense skeleton, reduces porosity, and improves impermeability. Coarse aggregate (such as 5-20mm continuously graded gravel) provides the main skeleton of the concrete and bears the main mechanical load. Combined with fine aggregate and modified bentonite, it reduces shrinkage stress and reduces the risk of cracking. Fly ash (such as Class F Grade I) mineral admixture improves workability, reduces hydration heat, and enhances later durability. Together with cement and nano-calcium sulfate, it promotes secondary hydration reactions and optimizes the interface transition zone. Modified bentonite enhances stability through interlayer modification (dodecyl bis(hydroxyethyl)methylammonium chloride, magnesium manganese oxide), inhibits shrinkage, and improves early strength. Together with nano-calcium sulfate, it fills micropores, reduces chemical shrinkage, and prevents cracking. Modified mullite fiber optimizes its temperature resistance and mechanical properties through heat treatment and melt blending, resisting thermal stress and enhancing crack resistance. Combined with a high-efficiency water reducer, it improves fiber dispersion and enhances concrete toughness. The filling effect of nano-calcium sulfate (e.g., 80-100nm) reduces porosity, while its nucleation effect accelerates the nucleation of hydration products, improving density and ultra-early strength. It synergizes with fly ash and cement to promote early hydration and shorten setting time. The high-efficiency water reducer reduces water consumption and improves fluidity without sacrificing strength. It synergizes with modified bentonite and mullite fiber to optimize slump and ensure workability. Synergistic Effects: 1) Early Strength Enhancement: Nano-calcium sulfate (nucleation effect) + modified bentonite (fast reaction) → 7-day compressive strength reaches 95% of design strength. 2) Crack resistance and durability: Modified mullite fiber (resistance to thermal stress) + modified bentonite (shrinkage suppression) → High volume stability, preventing cracking. 3) Optimized compactness: Quartz sand + coarse aggregate (skeletal density) + nano-calcium sulfate (filling effect) → Enhanced impermeability and freeze-thaw resistance. 4) Balanced construction performance: High-efficiency water reducer (fluidity) + fly ash (retarded setting) → Controllable slump and setting time, suitable for tunnel pouring. Through these synergistic effects, this concrete's comprehensive performance meets the requirements for high strength, crack resistance, durability, and construction efficiency for tunnel invert filling.

[0006] Preferably, the preparation method of the modified bentonite comprises the following steps: S21, adding 100 parts by mass of bentonite to 150 parts by mass of an aqueous solution of dodecyl bis(hydroxyethyl)methylammonium chloride having a concentration of 4-5%, heating to 60-65° C. and stirring for 5-6 hours to obtain pretreated bentonite; S22. Add 100 parts of pretreated bentonite, 50-60 parts of magnesium nitrate, and 120-150 parts of manganese nitrate to 1500 parts of water, in parts by mass, to obtain a mixed solution A; add 50 parts of magnesium chloride and 10-12 parts of sodium dihydrogen phosphate to 300 parts of water to obtain a mixed solution B; S23, heating the mixed solution A to 91-95° C., then adding the mixed solution B under stirring, heating to 91-95° C., stirring and reacting for 8-10 hours, then naturally cooling, filtering, washing, and drying to obtain a mixture C; S24. Place the mixture C in a muffle furnace for sintering, then cool naturally and grind into powder to obtain modified bentonite.

[0007] By adopting the above technical solution, step S21: pre-treating bentonite, dodecyl bis (hydroxyethyl) methyl ammonium chloride enters the bentonite interlayer through intercalation, weakening the interlayer bonding force, expanding the interlayer spacing, and providing a channel for subsequent ion exchange and chemical modification. Step S22: preparing a mixed solution, magnesium nitrate and manganese nitrate provide Mg 2+ 、Mn 2+ ions; magnesium chloride and sodium dihydrogen phosphate introduce Mg 2+ and PO4 3- , providing raw materials for the subsequent generation of magnesium phosphate compounds and magnesium manganese oxides. Step S23: Coprecipitation reaction, at high temperature, Mg 2+ 、Mn 2+It enters the interlayer of bentonite through ion exchange and reacts with sodium dihydrogen phosphate to form a magnesium phosphate precursor, which preliminarily stabilizes the interlayer structure. Step S24: Sintering treatment, calcination decomposes the interlayer nitrate to generate magnesium manganese oxide (such as MgO-MnO2 complex), magnesium phosphate (such as Mg3(PO4)2) crystallization, forming a stable interlayer support structure, and enhancing the thermal stability and bonding properties of bentonite. The role and synergistic effect of modified bentonite in this application, early strength improvement: magnesium manganese oxide and magnesium phosphate serve as active components to accelerate cement hydration reaction and provide early strength support. The stable interlayer structure reduces shrinkage caused by water evaporation, ensures no volume shrinkage, and the 7-day compressive strength reaches more than 95% of the design strength. Enhanced crack resistance and durability: magnesium phosphate and oxides between bentonite layers form a rigid skeleton to resist chemical shrinkage and drying shrinkage stress, and prevent cracking and degassing. High bonding force optimizes the interface transition zone and reduces the propagation of microcracks. Synergy with nano-calcium sulfate: The filling effect of nano-calcium sulfate fills the micropores uncovered by bentonite, and the two together improve compactness. The nucleation effect of nano-calcium sulfate accelerates hydration, and synergistically with the early active reaction of bentonite shortens setting time. Synergy with high-efficiency water reducers: The water reducer improves the dispersion of bentonite, prevents interlaminar particle agglomeration, and ensures uniform distribution of the modified bentonite in the concrete. This synergy reduces water consumption and porosity while maintaining high fluidity. Synergy with modified mullite fiber: Bentonite suppresses shrinkage stress, while mullite fiber resists thermal expansion tensile stress, jointly maintaining concrete volume stability. The high bonding strength of magnesium phosphate strengthens the interfacial bond between the fiber and the matrix, improving crack resistance. In summary, through interlaminar chemical modification and high-temperature stabilization, modified bentonite becomes a key functional component in concrete that combines early strength stimulation, volume stability regulation, and durability enhancement. Its synergistic effect with nano-calcium sulfate, high-efficiency water reducers, and other components achieves the comprehensive performance requirements of high strength, crack resistance, and shrinkage-free tunnel invert concrete, while also meeting environmental protection requirements.

[0008] Preferably, the sintering process conditions are: sintering at 320-350° C. for 6-7 hours.

[0009] Preferably, the preparation method of the modified mullite fiber comprises the following steps: S31. According to the mass ratio, 20 parts of mullite fiber and 6-8 parts of spodumene were placed in a ball mill and ground for 5-6 hours. The mixture was then heated to 260-280°C at a rate of 2°C / min and kept warm for 10-12 hours. The mixture was then heated to 460-500°C at a rate of 6°C / min and kept warm for 10-12 hours. Finally, the mixture was heated to 680-700°C at a rate of 8°C / min and kept warm for 2-3 hours. The mixture was then cooled in the furnace to obtain a mixed powder. S32. According to the mass parts, 20 parts of mixed powder are mixed evenly with 15 parts of nylon powder, 18-20 parts of calcium carbonate powder, 10 parts of compatibilizer and 7 parts of silicon dioxide, and the mixture is heated to 270-280°C for melt blending for 1.2-1.4 hours. Then, a twin-screw extruder is used to extrude the roving at a speed of 200 rpm / min, and the roving is connected to a wire drawing machine. The temperature in the wire drawing machine is controlled at 280°C and the speed of the wire drawing machine is controlled at 320-350 m / min to obtain filaments with a diameter of 10-15 μm. Finally, the filaments are cut into a length of 10-12 mm by a cutting machine to obtain modified mullite fibers.

[0010] By adopting the above technical solution, step S31: ball milling and segmented high-temperature treatment, ball milling: mullite fiber (20 parts) and spodumene (6-8 parts) are ball milled for 5-6 hours to refine the particles and achieve uniform mixing. Segmented heating: 260-280℃ insulation for 10-12 hours: remove organic matter and adsorbed water, and preliminarily activate the mineral surface. 460-500℃ insulation for 10-12 hours: promote the solid-phase reaction of mullite and spodumene to generate a highly heat-resistant aluminosilicate composite phase (such as lithium aluminum silicate). 680-700℃ insulation for 2-3 hours: high-temperature sintering to form a stable crystalline structure (such as mullite-spodumene eutectic phase), enhancing chemical inertness and mechanical strength. High-temperature treatment eliminates structural defects, forms a high-temperature resistant mineral phase, and reduces the performance degradation of concrete under high-temperature environment. The eutectic phase enhances the rigidity and compressive strength of the fiber, providing a basis for subsequent wire drawing. Step S32: melt blending and wire drawing, nylon powder melts to form a bonding phase, wrapping the inorganic particles; the compatibilizer improves the inorganic-organic interface bonding and prevents phase separation; silicon dioxide (SiO2) improves the melt viscosity and high-temperature stability. Silicon dioxide and calcium carbonate synergistically improve the high-temperature stability of the fiber; nylon and the compatibilizer enhance the fiber toughness, and the wire drawing process makes the fiber diameter (10-15μm) and length (10-12mm) adapt to the concrete matrix to form a three-dimensional reinforced network. The role and synergistic effect of modified mullite fiber in this application, crack resistance: the fiber generates tensile stress at high temperature (difference in thermal expansion coefficient), which offsets the thermal expansion stress of the concrete and prevents crack expansion. The three-dimensional network structure prevents crack penetration and improves the crack resistance level. The bridging effect of short fibers delays the propagation of microcracks and improves toughness. Synergistic with modified bentonite: Bentonite inhibits shrinkage stress, while fibers resist tensile stress, a dual mechanism ensuring volume stability (no shrinkage, no cracking); magnesium phosphate between bentonite layers strengthens fiber-matrix interfacial bonding and reduces fiber slippage. Synergistic with nano-calcium sulfate: Nano-calcium sulfate fills the matrix micropores, while fibers bridge macro-cracks, forming a "micro-macro" dual anti-cracking system; nano-calcium sulfate accelerates hydration, and the fiber network locks in hydration products, jointly improving early strength (reaching 95% of design strength in 7 days). Synergistic with high-efficiency water reducers: The water reducer improves fiber dispersion (preventing agglomeration) and ensures uniform fiber distribution; the long side chains of the polycarboxylate water reducer wrap around the fiber surface, reducing negative effects on fluidity and maintaining a slump greater than 600mm. Durability is enhanced, and the spodumene-mullite eutectic phase resists acid and alkali corrosion, extending the life of concrete in the humid environment of tunnels; the fiber network dissipates dynamic load energy, reducing fatigue damage accumulation. In summary, modified mullite fiber, through segmented high-temperature crystallization and melt-composite modification, becomes a core component that combines high heat resistance, mechanical reinforcement, and crack resistance. Its multi-layered synergy with modified bentonite, nano-calcium sulfate, and other components achieves the combined properties of ultra-early strength, high crack resistance, and long-term durability of tunnel invert concrete. Furthermore, it is compatible with the construction requirements of high-efficiency water-reducing agents, meeting the demands for rapid construction and long-term service under the demanding working conditions of tunnel engineering.

[0011] Preferably, the compatibilizer is maleic anhydride grafted polyethylene with a grafting rate of 2%.

[0012] Preferably, the high-efficiency water reducer is composed of a polycarboxylic acid high-efficiency water reducer and an amino high-efficiency water reducer in a mass ratio of 4:3. The polycarboxylic acid high-efficiency water reducer is a ZWL-A-IX high-efficiency water reducer produced by Zhejiang Wulong Chemical Co., Ltd.; the amino high-efficiency water reducer is a ZWL-A-IX high-efficiency water reducer produced by Jiangsu Subote New Materials Co., Ltd. -MAS amino high-efficiency water reducer.

[0013] By adopting the above technical solutions, the polycarboxylic acid high-efficiency water-reducing agent (dominant dispersant) with its comb-like molecular structure effectively disperses cement particles through electrostatic repulsion and steric hindrance, reducing the water-cement ratio and significantly increasing the slump to over 600mm, meeting the requirements of pumping construction. The dispersing groups are continuously released through the slow hydrolysis of the ester group, ensuring that the 2-hour slump loss rate of the concrete is less than 10%, adapting to long-distance tunnel transportation conditions. The amino high-efficiency water-reducing agent (functional enhancement) with its amino group accelerates the early hydration of C3A and synergizes with nano-calcium sulfate (nucleation effect) to achieve a 1-day compressive strength of over 25MPa and a 3-day strength exceeding the design value by 70%. The slurry viscosity is reduced through adsorption-lubrication, forming a dynamic equilibrium with the thixotropy of modified bentonite, inhibiting segregation and bleeding, and improving the filling density of the invert. Synergistic enhancement mechanism: Time gradient effect: The polycarboxylic acid water-reducing agent delays the initial hydration of C3S, while the amino water-reducing agent selectively promotes the C3A reaction. The two regulate the exothermic peak in stages to avoid temperature stress cracks. Composite nucleation effect: Amino molecules adsorb on Ca 2+ The enriched areas, along with nano-calcium sulfate, provide heterogeneous nucleation sites, resulting in a dense nanosheet structure for the CSH gel. The ether bonds of the polycarboxylic acid side chains form hydrogen bonds with the silanol groups on the surface of the modified mullite fibers, enhancing the fiber-matrix interfacial bond strength. The cationic properties of the amino-based water-reducing agent neutralize the negative charge of the modified bentonite (including quaternary ammonium salt modification), forming a "house of cards" structure that achieves both self-leveling and anti-segregation properties. The combined water-reducing agent achieves a dynamic equilibrium of "dispersion-reflocculation" of cement particles. Combined with the nucleation effect of nano-calcium sulfate, it achieves a 5-7 day compressive strength exceeding 95% of the design strength, shortening the curing cycle by over 50% compared to traditional naphthalene-based water-reducing agent systems. By reducing the water-cement ratio and compensating for the micro-expansion of the modified bentonite, the system meets the P12 anti-permeability grade for tunnel inverts. Overall, this combined system transcends the single-function limitations of traditional water-reducing agents. Through molecular design, it achieves synergistic improvements in workability, mechanical properties, and durability, providing an innovative solution for tunnel invert projects under complex geological conditions.

[0014] Preferably, the cement is Tongling Conch P.II52.5 cement; and the fly ash is Class F Grade I fly ash.

[0015] Preferably, the fine aggregate is quartz sand with a particle size of 0.5-0.9 mm and a SiO2 content greater than 95%; the coarse aggregate is gravel with a continuous grading of 5-20 mm.

[0016] Preferably, the average particle size of the nano-calcium sulfate is 80-100 nanometers.

[0017] In a second aspect, the present application provides a method for preparing high-performance concrete for tunnel invert filling, which adopts the following technical solution: As a general technical concept, the present application also provides a method for preparing the high-performance concrete for tunnel invert filling, comprising the following steps: S101. Mix cement, fine aggregate, coarse aggregate, fly ash, modified bentonite, modified mullite fiber, nano-calcium sulfate, high-efficiency water reducer, and water in parts by mass to obtain a high-performance concrete slurry for tunnel invert filling. S102, mold the high-performance concrete slurry for tunnel invert filling, shape it, demould it, and continue to maintain it to obtain the high-performance concrete for tunnel invert filling.

[0018] In summary, the beneficial technical effects of this application are: 1. Super early strength performance The compressive strength reaches more than 95% of the design strength 7 days after pouring, which significantly shortens the construction period and is especially suitable for the rapid construction needs of tunnel projects.

[0019] 2.Excellent crack resistance Modified mullite fiber works synergistically with bentonite to effectively prevent defects such as cracking and voiding, thereby improving structural integrity through thermal stress compensation and shrinkage inhibition.

[0020] 3. High volume stability Modified bentonite achieves "zero shrinkage" characteristics, simultaneously eliminating chemical shrinkage and drying shrinkage, and ensuring concrete density and interface bonding strength.

[0021] 4. Enhanced durability The filling effect and nucleation effect of nano-calcium sulfate optimize the interface transition zone, improve impermeability, and extend the service life of the structure.

[0022] 5.Excellent workability The compound water-reducing agent system (polycarboxylic acid + amino) achieves high slump and meets the needs of pumping and long-distance pouring. DETAILED DESCRIPTION

[0023] The following embodiments of the present application will be described in detail with reference to the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be considered to limit the scope of the present application. If the specific conditions are not specified in the examples, the process shall be carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, the polycarboxylic acid high-efficiency water reducer is purchased from the ZWL-A-IX high-efficiency water reducer produced by Zhejiang Wulong Chemical Co., Ltd.; the amino high-efficiency water reducer is purchased from the ZWL-A-IX high-efficiency water reducer produced by Jiangsu Subote New Materials Co., Ltd. -MAS amino high-efficiency water reducer.

[0024] In the following examples and preparation examples, 1 part means 1 kg.

[0025] Preparation Example 1 Preparation of modified bentonite The preparation method of modified bentonite comprises the following steps: S21, adding 100 parts by mass of bentonite to 150 parts by mass of an aqueous solution of dodecyl bis(hydroxyethyl)methylammonium chloride having a concentration of 4.5%, heating to 63° C. and stirring for 5.6 hours to obtain pretreated bentonite; S22. Add 100 parts of pretreated bentonite, 55 parts of magnesium nitrate, and 130 parts of manganese nitrate to 1500 parts of water, in parts by mass, to obtain a mixed solution A; add 50 parts of magnesium chloride and 11 parts of sodium dihydrogen phosphate to 300 parts of water to obtain a mixed solution B; S23. Heat the mixed solution A to 94° C., then add the mixed solution B under stirring, heat to 94° C., stir and react for 9 hours, then naturally cool, filter, wash, and dry to obtain a mixture C; S24, placing the mixture C in a muffle furnace for sintering treatment, wherein the process conditions of the sintering treatment are: sintering at 330° C. for 6.7 hours, then naturally cooling, and grinding into powder to obtain modified bentonite.

[0026] Preparation Example 2 Preparation of modified mullite fiber The preparation method of modified mullite fiber comprises the following steps: S31. According to the mass ratio, 20 parts of mullite fiber and 7 parts of spodumene were placed in a ball mill and ground for 5.6 hours. The mixture was then heated to 270°C at a rate of 2°C / min and kept warm for 11 hours. The mixture was then heated to 480°C at a rate of 6°C / min and kept warm for 11 hours. Finally, the mixture was heated to 690°C at a rate of 8°C / min and kept warm for 2.5 hours. The mixture was cooled in the furnace to obtain a mixed powder. S32. According to the mass ratio, 20 parts of mixed powder were mixed evenly with 15 parts of nylon powder, 19 parts of calcium carbonate powder, 10 parts of compatibilizer (maleic anhydride grafted polyethylene, grafting rate of 2%) and 7 parts of silicon dioxide, and the mixture was heated to 275°C for melt blending for 1.3 hours. Then, a twin-screw extruder was used to extrude the roving at a speed of 200 rpm / min, and the roving was connected to a wire drawing machine. The temperature in the wire drawing machine was controlled at 280°C and the speed of the wire drawing machine was controlled at 330 m / min to obtain filaments with a diameter of 12 μm. Finally, the filaments were cut into a length of 11 mm by a cutting machine to obtain modified mullite fibers.

[0027] Example 1 A high-performance concrete for tunnel invert filling comprises the following raw materials, measured by mass: 430 parts of cement, 660 parts of fine aggregate, 1000 parts of coarse aggregate, 58 parts of fly ash, 15 parts of modified bentonite, 12 parts of modified mullite fiber, 0.6 parts of nano-calcium sulfate (particle size of 90 nanometers), 5.5 parts of a high-efficiency water reducer, and 140 parts of water, wherein the high-efficiency water reducer comprises a polycarboxylate high-efficiency water reducer and an amino high-efficiency water reducer in a mass ratio of 4:3; the cement is Tongling Conch P.II52.5 cement; the fly ash is Class F, Grade I fly ash; the fine aggregate is quartz sand with a particle size of 0.5-0.9 mm and an SiO2 content of greater than 95%; and the coarse aggregate is continuously graded gravel with a particle size of 5-20 mm. The method for preparing the high-performance concrete for tunnel invert filling comprises the following steps: S101. Mix cement, fine aggregate, coarse aggregate, fly ash, modified bentonite, modified mullite fiber, nano-calcium sulfate, high-efficiency water reducer, and water in parts by mass to obtain a high-performance concrete slurry for tunnel invert filling. S102, mold the high-performance concrete slurry for tunnel invert filling, shape it, demould it, and continue to maintain it to obtain the high-performance concrete for tunnel invert filling.

[0028] Example 2 A high-performance concrete for tunnel invert filling comprises the following raw materials, measured by mass: 470 parts of cement, 700 parts of fine aggregate, 1050 parts of coarse aggregate, 62 parts of fly ash, 20 parts of modified bentonite, 15 parts of modified mullite fiber, 1 part of nano-calcium sulfate (particle size of 90 nanometers), 6.5 parts of high-efficiency water reducer, and 170 parts of water, wherein the high-efficiency water reducer comprises a polycarboxylate high-efficiency water reducer and an amino high-efficiency water reducer in a mass ratio of 4:3; the cement is Tongling Conch P.II52.5 cement; the fly ash is Class F, Grade I fly ash; the fine aggregate is quartz sand with a particle size of 0.5-0.9 mm and an SiO2 content of greater than 95%; and the coarse aggregate is continuously graded gravel with a particle size of 5-20 mm. The method for preparing the high-performance concrete for tunnel invert filling comprises the following steps: S101. Mix cement, fine aggregate, coarse aggregate, fly ash, modified bentonite, modified mullite fiber, nano-calcium sulfate, high-efficiency water reducer, and water in parts by mass to obtain a high-performance concrete slurry for tunnel invert filling. S102, mold the high-performance concrete slurry for tunnel invert filling, shape it, demould it, and continue to maintain it to obtain the high-performance concrete for tunnel invert filling.

[0029] Example 3 A high-performance concrete for tunnel invert filling comprises the following raw materials, measured by mass: 450 parts of cement, 690 parts of fine aggregate, 1030 parts of coarse aggregate, 60 parts of fly ash, 18 parts of modified bentonite, 13 parts of modified mullite fiber, 0.8 parts of nano-calcium sulfate (particle size of 90 nanometers), 6 parts of a high-efficiency water reducer, and 150 parts of water, wherein the high-efficiency water reducer comprises a polycarboxylate high-efficiency water reducer and an amino high-efficiency water reducer in a mass ratio of 4:3; the cement is Tongling Conch P.II52.5 cement; the fly ash is Class F, Grade I fly ash; the fine aggregate is quartz sand with a particle size of 0.5-0.9 mm and an SiO2 content of greater than 95%; and the coarse aggregate is continuously graded gravel with a particle size of 5-20 mm. The method for preparing the high-performance concrete for tunnel invert filling comprises the following steps: S101. Mix cement, fine aggregate, coarse aggregate, fly ash, modified bentonite, modified mullite fiber, nano-calcium sulfate, high-efficiency water reducer, and water in parts by mass to obtain a high-performance concrete slurry for tunnel invert filling. S102, mold the high-performance concrete slurry for tunnel invert filling, shape it, demould it, and continue to maintain it to obtain the high-performance concrete for tunnel invert filling.

[0030] Comparative Example 1 The same as Example 3, except that unmodified mullite fibers in equal parts by mass are used instead of modified mullite fibers.

[0031] Comparative Example 2 The same as Example 3, except that unmodified bentonite is used in equal parts by mass instead of modified bentonite.

[0032] Comparative Example 3 The same as Example 3, except that the high-efficiency water reducer is a polycarboxylic acid high-efficiency water reducer.

[0033] Comparative Example 4 The same as Example 3, except that the high-efficiency water reducer is an amino-based high-efficiency water reducer.

[0034] Comparative Example 5 The same as Example 3, except that the amount of nano calcium sulfate (particle size of 90 nanometers) is 0 parts.

[0035] Performance Testing The high-performance concrete for tunnel invert filling prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was used to make test specimens. The test specimens were cubes with a side length of 150 mm. The surfaces were sealed with polyethylene film and cured at room temperature for 24 hours before demolding. The specimens were moved to a standard curing box and cured to the corresponding age. The following tests were performed. The test results are shown in Table 1.

[0036] Compressive strength: After curing for 7 days and 28 days, test according to the relevant provisions of GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Ordinary Concrete"; The crack resistance of concrete shall be tested after 28 days of curing in accordance with the relevant provisions of GB / T 50082-2009 "Standard for Test Methods of Long-term Properties and Durability of Ordinary Concrete"; The setting time is tested in accordance with the relevant provisions of GB / T1346-2011 "Test methods for water consumption, setting time and soundness of cement of standard consistency"; The slump is tested in accordance with GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures"; The impermeability grade is determined according to GB / T50082-2009 "Standard for Test Methods of Long-term Properties and Durability of Ordinary Concrete" after the specimens have been cured for 28 days.

[0037] Table 1 Performance test Analyzing the data in Table 1, we can see that: 1) The high-performance concrete for tunnel invert filling prepared in Examples 1 to 3 has excellent early compressive strength, slump, setting time, crack resistance and durability. In addition, the compressive strength reaches more than 95% of the design strength 7 days after pouring, making it suitable for large-scale promotion and application.

[0038] 2) A comparative analysis of the performance of high-performance concrete for tunnel invert filling, prepared in Example 3 and Comparative Example 1, demonstrates that the modified mullite fiber prepared in this application, through staged high-temperature crystallization and melt-composite modification, becomes a core component with high heat resistance, mechanical reinforcement, and crack resistance. Its multi-layered synergy with modified bentonite, nano-calcium sulfate, and other components achieves the combined properties of ultra-early strength, high crack resistance, and long durability of the tunnel invert concrete. Furthermore, it meets the construction requirements of high-efficiency water-reducing agents, meeting the demands for rapid construction and long-term service under the demanding working conditions of tunnel engineering.

[0039] 3) A comparative analysis of the performance of high-performance concrete for tunnel invert filling prepared in conjunction with Example 3 and Comparative Example 2 shows that the modified bentonite prepared in this application, through interlayer chemical modification and high-temperature stabilization, becomes a key functional component in concrete that combines early strength stimulation, volume stability regulation, and durability enhancement. Its synergistic effect with components such as nano-calcium sulfate and a high-efficiency water reducer achieves the comprehensive performance requirements of high-strength, crack-resistant, and shrinkage-free tunnel invert concrete, while also meeting environmental protection requirements.

[0040] 4) A comparative analysis of the performance of the high-performance concrete for tunnel invert filling prepared in combination with Example 3 and Comparative Examples 3-4 shows that the high-efficiency water reducer is composed of a polycarboxylic acid high-efficiency water reducer and an amino high-efficiency water reducer in a mass ratio of 4:3. By utilizing the synergistic effect between them, the fluidity of the concrete can be significantly improved, while also improving the overall performance of the concrete.

[0041] 5) A comparative analysis of the performance of the high-performance concrete for tunnel invert filling prepared in combination with Example 3 and Comparative Example 5 shows that the addition of nano-calcium sulfate can effectively improve the compactness and ultra-early strength of concrete. It has a filling effect and a nucleation effect, improves the compactness of concrete, accelerates the nucleation and staggered growth of hydration products, improves the interface transition zone, promotes the early strength development of concrete, and further improves the comprehensive performance of concrete.

[0042] The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the above embodiments provide a detailed description of the present application, relevant technical personnel should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the scope of protection of the present application.

Claims

1. A high performance concrete for tunnel invert filling, characterized in that: The preparation comprises the following raw materials in parts by mass: 430-470 parts of cement, 660-700 parts of fine aggregate, 1000-1050 parts of coarse aggregate, 58-62 parts of fly ash, 15-20 parts of modified bentonite, 12-15 parts of modified mullite fiber, 0.6-1 part of nano calcium sulfate, 5.5-6.5 parts of high-efficiency water reducing agent and 140-170 parts of water.

2. The high performance concrete for tunnel invert filling according to claim 1, characterized in that: The preparation method of the modified bentonite comprises the following steps: S21, adding 100 parts by mass of bentonite to 150 parts by mass of an aqueous solution of dodecyl bis(hydroxyethyl)methylammonium chloride having a concentration of 4-5%, heating to 60-65° C. and stirring for 5-6 hours to obtain pretreated bentonite; S22. Add 100 parts of pretreated bentonite, 50-60 parts of magnesium nitrate, and 120-150 parts of manganese nitrate to 1500 parts of water, in parts by mass, to obtain a mixed solution A; add 50 parts of magnesium chloride and 10-12 parts of sodium dihydrogen phosphate to 300 parts of water to obtain a mixed solution B; S23, the mixed solution A was heated to 91-95 ℃, and then the mixed solution B was added under stirring, the temperature was raised to 91-95 ℃ and the reaction was stirred for 8-10h, after which it was naturally cooled, filtered, washed, and dried to obtain a mixture C; S24. Place the mixture C in a muffle furnace for sintering, then cool naturally and grind into powder to obtain modified bentonite.

3. The high performance concrete for tunnel invert filling according to claim 2, characterized in that: The process conditions of the sintering treatment are: sintering at 320-350° C. for 6-7 hours.

4. The high performance concrete for tunnel invert filling according to claim 1, characterized in that: The preparation method of the modified mullite fiber comprises the following steps: S31. According to the mass ratio, 20 parts of mullite fiber and 6-8 parts of spodumene were placed in a ball mill and ground for 5-6 hours. The mixture was then heated to 260-280°C at a rate of 2°C / min and kept warm for 10-12 hours. The mixture was then heated to 460-500°C at a rate of 6°C / min and kept warm for 10-12 hours. Finally, the mixture was heated to 680-700°C at a rate of 8°C / min and kept warm for 2-3 hours. The mixture was then cooled in the furnace to obtain a mixed powder. S32. According to the mass parts, 20 parts of mixed powder are mixed evenly with 15 parts of nylon powder, 18-20 parts of calcium carbonate powder, 10 parts of compatibilizer and 7 parts of silicon dioxide, and the mixture is heated to 270-280°C for melt blending for 1.2-1.4 hours. Then, a twin-screw extruder is used to extrude the roving at a speed of 200 rpm / min, and the roving is connected to a wire drawing machine. The temperature in the wire drawing machine is controlled at 280°C and the speed of the wire drawing machine is controlled at 320-350 m / min to obtain filaments with a diameter of 10-15 μm. Finally, the filaments are cut into a length of 10-12 mm by a cutting machine to obtain modified mullite fibers.

5. The high performance concrete for tunnel invert filling according to claim 4, characterized in that: The compatibilizer is maleic anhydride grafted polyethylene, and the grafting rate is 2%.

6. The high performance concrete for tunnel invert filling according to claim 1, characterized in that: The high-efficiency water reducer is composed of a polycarboxylic acid high-efficiency water reducer and an amino high-efficiency water reducer in a mass ratio of 4:

3.

7. The high performance concrete for tunnel invert filling according to claim 1, characterized in that: The cement is Tongling Conch P.II52.5 cement; the fly ash is Class F Grade I fly ash.

8. The high performance concrete for tunnel invert filling according to claim 1, characterized in that: The fine aggregate is quartz sand with a particle size of 0.5-0.9 mm and a SiO2 content of more than 95%; the coarse aggregate is gravel with a continuous grading of 5-20 mm.

9. The high performance concrete for tunnel invert filling according to claim 1, characterized in that: The average particle size of the nano calcium sulfate is 80-100 nanometers.

10. A method for preparing a high performance concrete for tunnel invert filling according to any one of claims 1 to 9, characterized in that: The following steps are involved: S101. Mix cement, fine aggregate, coarse aggregate, fly ash, modified bentonite, modified mullite fiber, nano-calcium sulfate, high-efficiency water reducer, and water in parts by mass to obtain a high-performance concrete slurry for tunnel invert filling. S102, mold the high-performance concrete slurry for tunnel invert filling, shape it, demould it, and continue to maintain it to obtain the high-performance concrete for tunnel invert filling.

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