Concrete suitable for high ground temperature tunnel construction and method of making same

Abstract

This invention belongs to the field of concrete technology, specifically relating to a type of concrete suitable for high-temperature tunnel construction and its preparation method. The concrete comprises 65-75 parts of phosphate cement, 8-12 parts of modified silica fume, 3-6 parts of nano-hydrated calcium silicate crystal nuclei, 2-4 parts of zirconium-titanium composite nanoparticles, 35-50 parts of shale ceramsite, 20-30 parts of lightweight aggregate, 70-90 parts of river sand, 0.05-0.1 parts of temperature-sensitive air-entraining agent, 0.8-1.5 parts of biomimetic mineralized hydrophobic sealing agent, 1.2-2 parts of composite fiber, 18-22 parts of mixing water, and 0.3-0.6 parts of water-reducing agent. By adding the temperature-sensitive air-entraining agent, which is part of a ternary composite system of sodium rosinate, polyetheramine, and nano-calcium carbonate, the ternary composite system can prevent air bubble coalescence and release thermal expansion stress by compressing and deforming air bubbles under high temperature conditions, thereby improving the crack resistance of the concrete under high temperature conditions.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, specifically relating to a type of concrete suitable for high-temperature tunnel construction and its preparation method. Background Technology

[0002] High geothermal environments are among the extreme conditions faced in tunnel construction, often occurring in deep-buried tunnels, tunnels in areas with geothermal anomalies, and tunnels traversing special geological structures such as volcanic rocks and igneous rocks. The core characteristic of these environments is that the temperature of the surrounding rock is significantly higher than that of conventional construction environments. Under high geothermal conditions, the high temperature accelerates the cement hydration process, leading to an imbalance in the rate of hydration product formation. The CSH gel structure becomes loose and disordered, and ettringite crystals grow abnormally, generating expansion stress. This, in turn, causes numerous microcracks to appear inside the concrete, reducing the density of the matrix. At the same time, the high temperature intensifies the rapid evaporation and vaporization of water inside the concrete. On the one hand, this results in insufficient hydration reaction, uneven early strength development, and weak or even regressive strength growth in the later stages. On the other hand, the internal expansion pressure generated by water vaporization further expands the scale of cracks, forming interconnected pore channels and significantly increasing the permeability of the concrete. To address this, an improved concrete and its preparation method suitable for high geothermal tunnel construction were designed. Summary of the Invention

[0003] To address the aforementioned shortcomings in the existing technology, this invention provides a type of concrete suitable for high-temperature tunnel construction and its preparation method, thereby solving the problems mentioned in the background technology.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] A method for preparing concrete suitable for high-temperature tunnel construction, comprising the following raw materials in parts by weight:

[0006] Phosphate cement 65-75 parts, modified silica fume 8-12 parts, nano-hydrated calcium silicate crystal nuclei 3-6 parts, zirconium-titanium composite nanoparticles 2-4 parts, shale ceramsite 35-50 parts, lightweight aggregate 20-30 parts, river sand 70-90 parts, temperature-sensitive air-entraining agent 0.05-0.1 parts, biomimetic mineralized hydrophobic sealing agent 0.8-1.5 parts, composite fiber 1.2-2 parts, mixing water 18-22 parts, water-reducing agent 0.3-0.6 parts;

[0007] The method for preparing the concrete includes the following steps:

[0008] S1: Add river sand, shale ceramsite, phosphate cement and modified silica fume in sequence to a forced mixer and mix at a speed of 120r / min-150r / min to form a dry mixture;

[0009] S2: Add the first batch of mixing water to the dry material mixture and stir to form the initial concrete paste;

[0010] S3: Add nano-hydrated calcium silicate solution, zirconium-titanium composite nanoparticle dispersion and water-reducing agent to the initial slurry in sequence, while increasing the rotation speed to 220r / min-250r / min and controlling the slurry temperature to be less than or equal to 35℃, and stir to obtain the intermediate concrete slurry;

[0011] S4: In the intermediate slurry, add biomimetic mineralized hydrophobic sealing agent, temperature-sensitive air-entraining agent, lightweight aggregate, composite fiber and second mixing water in sequence. The temperature-sensitive air-entraining agent is composed of sodium rosinate, polyetheramine and nano calcium carbonate in a mass ratio of 6:2:1. Reduce the speed to 150r / min-180r / min and stir to form the final concrete slurry.

[0012] Preferably, the biomimetic mineralized hydrophobic sealing agent is composed of modified silane hydrophobic agent, nano hydroxyapatite, chitosan, and poly(N-isopropylacrylamide) microspheres in a mass ratio of 1:2:0.2:0.1.

[0013] Preferably, the preparation method of the poly-N-isopropylacrylamide microspheres includes the following steps:

[0014] Step 3-1: Mix deionized water and sodium dodecyl sulfate, and add N-isopropylacrylamide and N,N'-methylenebisacrylamide. Stir at 40°C to obtain an emulsion.

[0015] Step 3-2: Mix deionized water and potassium persulfate, and stir at 70℃-75℃ to prepare an initiator solution;

[0016] Step 3-3: The initiator solution is dropped into the emulsion prepared in step 3-1 to carry out the polymerization reaction, and nitrogen gas is continuously introduced. The reactants after the polymerization reaction are cooled and purified to obtain poly(N-isopropylacrylamide) microspheres.

[0017] Preferably, the preparation method of the modified silane hydrophobic agent includes the following steps:

[0018] Step 4-1: Add anhydrous ethanol, methyltriethoxysilane, hydrochloric acid and deionized water sequentially to the reaction vessel to obtain silane hydrolysate;

[0019] Step 4-2: Heat n-octadecyl alcohol to 65°C to melt it, and pour it into the above silane hydrolysate to allow the hydroxyl groups of n-octadecyl alcohol to undergo a condensation reaction with the silanol groups;

[0020] Step 4-3: After the condensation reaction is completed, the product is cooled, neutralized and purified to obtain the modified silane hydrophobic agent.

[0021] Preferably, the polyetheramine is prepared by: using propylene glycol as an initiator to perform block copolymerization with ethylene oxide and propylene oxide to form a copolymer backbone, and then subjecting the block copolymer backbone to an amination reaction with ethylenediamine to form polyetheramine.

[0022] Preferably, the composite fiber is composed of basalt fiber and silicon nitride whiskers in a mass ratio of 4:1.

[0023] Preferably, the method for preparing the modified silica fume includes the following steps:

[0024] Step 7-1: Add anhydrous ethanol, γ-aminopropyltriethoxysilane and deionized water sequentially to the reaction vessel and stir to obtain silane hydrolysate;

[0025] Step 7-2: Add nano-aluminum nitride to anhydrous ethanol and use ultrasonic dispersion technology to obtain a nano-aluminum nitride suspension;

[0026] Step 7-3: Add silica fume, silane hydrolysate and nano aluminum nitride suspension to a mixer in sequence, and stir to obtain intermediate product;

[0027] Step 7-4: The intermediate product obtained in step 7-3 is dried, cured, cooled, crushed and sieved to obtain modified silica fume.

[0028] Preferably, the zirconium-titanium composite nanoparticles in the zirconium-titanium composite nanoparticle dispersion are composed of zirconium oxide and titanium oxide in a mass ratio of 3:1.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. By adding a temperature-sensitive air-entraining agent, the agent utilizes a ternary composite system of "sodium rosinate-polyetheramine-nano calcium carbonate". When the ambient temperature is below 35℃, the polyetheramine molecular chains expand, and the hydrophilic PEO segments extend outward, without hindering the combination of the hydrophilic groups of sodium rosinate with water molecules. The bubble generation rate remains normal and does not affect the concrete strength. When the temperature is above 40℃, the polyetheramine molecular chains shrink into a spherical shape, and the hydrophobic PPO segments wrap around the outside of the binary composite molecule, partially blocking the hydrophilic groups of sodium rosinate and reducing its gas-liquid interface activity, thereby inhibiting the bubble generation rate. The nano calcium carbonate is anchored in the ternary molecular network, and the three-dimensional spatial barrier structure formed can prevent the aggregation of adjacent composite molecules, avoid bubble merging, and release thermal expansion stress through bubble compression deformation at high temperatures. At the same time, the rigid structure of nano calcium carbonate enhances the mechanical strength of the bubble wall, reduces the probability of bubble rupture at high temperatures, and thus improves the crack resistance of concrete in high-temperature environments.

[0031] 2. By adding a biomimetic mineralizing hydrophobic sealing agent, which is made of modified silane hydrophobic agent, nano-hydroxyapatite, chitosan and poly-N-isopropylacrylamide microspheres, the nano-hydroxyapatite mineralizes and fills the nanopores, the chitosan regulates the directional growth of crystals to form a dense mineralized layer, the modified silane hydrophobic agent is grafted to form a long-lasting hydrophobic film layer, and the poly-N-isopropylacrylamide microspheres achieve elastic sealing and defect repair as the temperature changes. Through the multiple protections constructed together, it can effectively block the intrusion of moisture and harmful substances and avoid internal expansion and cracking caused by moisture vaporization at high temperatures.

[0032] 3. A triple protection system is constructed at the microscopic level: The first layer involves boron doping to modify the lattice stability of nano-hydrated calcium silicate nuclei, which serves as a heterogeneous nucleation site to induce the directional growth of hydration products, avoiding harmful pores caused by the amorphous accumulation of hydration products. At the same time, nano-TiO2 is embedded in the gel gaps to limit crystal slip deformation, and modified silica fume forms a dual structure of amine-grafted and nano-aluminum nitride filling. The second layer involves gradient pore filling to significantly improve the matrix density, and nano-aluminum nitride reacts at high temperatures to generate Al(OH)3 gel, achieving self-repair of microcracks. Zirconium-titanium composite nanoparticles have excellent high-temperature stability, forming a physical barrier to reduce heat conduction. The third layer involves improving the composition of zirconium-titanium composite nanoparticles, nano-hydrated calcium silicate nuclei, and modified silica fume to achieve a high degree of matching of their thermal expansion coefficients, thereby avoiding the generation of internal thermal stress. The three work together to inhibit the dehydration and decomposition of hydration products, ensuring the stability of the concrete microstructure. Attached Figure Description

[0033] Figure 1 This is a flowchart of the concrete preparation method of the present invention. Detailed Implementation

[0034] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0035] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this patent. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0036] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0037] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] like Figure 1 The present invention discloses a method for preparing concrete suitable for high-temperature tunnel construction, comprising the following raw materials in parts by weight:

[0039] Phosphate cement 65-75 parts, modified silica fume 8-12 parts, nano-hydrated calcium silicate crystal nuclei 3-6 parts, zirconium-titanium composite nanoparticles 2-4 parts, shale ceramsite 35-50 parts, lightweight aggregate 20-30 parts, river sand 70-90 parts, temperature-sensitive air-entraining agent 0.05-0.1 parts, biomimetic mineralized hydrophobic sealing agent 0.8-1.5 parts, composite fiber 1.2-2 parts, mixing water 18-22 parts, water-reducing agent 0.3-0.6 parts;

[0040] Further, the modified silica fume is prepared as follows: 6-10 parts of silica fume are placed in a vacuum drying oven and dried at 110℃ for 2 hours, then cooled to room temperature; 8-10 parts of anhydrous ethanol are added to the reaction vessel, and 1.5-2 parts of γ-aminopropyltriethoxysilane are slowly added while stirring, and the mixture is stirred at a constant speed of 300-400 rpm for 10 minutes. Then, 0.05-0.08 parts of acetic acid are added dropwise to adjust the pH of the system to 4.5-5.5. Then add 1-1.5 parts of deionized water and stir to obtain a homogeneous silane hydrolysate; take 0.2-0.3 parts of nano-aluminum nitride, add 2 parts of anhydrous ethanol, and disperse using ultrasonic dispersion technology for 20 minutes to form a nano-aluminum nitride suspension; add the cooled silica fume to a high-speed mixer, spray the silane hydrolysate at a speed of 800 r / min, and continue stirring for 30 minutes to allow the silanol groups in the silane hydrolysate to undergo a condensation reaction with the hydroxyl groups on the silica fume surface to form Si-O- Si chemical bonds were used to achieve amine grafting. After stirring, a nano-aluminum nitride suspension was added, and the stirring speed was increased to 1200 r / min. The mixture was stirred for 40 min to ensure that the nano-aluminum nitride was uniformly loaded on the surface and pores of the amine-grafted silica fume. The mixture was then cooled to room temperature and transferred to a centrifuge tube. The product was centrifuged at 8000 r / min for 15 min to remove the supernatant. The product was washed three times with deionized water until the pH of the washing solution dropped to 7-8. The washed precipitate was placed in a drying oven and dried at 60℃ for 12 h to remove moisture. After drying, the product was pulverized in a high-speed pulverizer and then sieved to obtain modified silica fume. Using silica fume as a matrix, amine functional groups were introduced by grafting γ-aminopropyltriethoxysilane onto the hydroxyl groups on the silica fume surface. Simultaneously, nano-aluminum nitride was loaded to form a dual modified structure of amine grafting and nanofilling, which improved the interfacial adhesion, density, and high-temperature stability of silica fume and phosphate cement hydration products.

[0041] Further, the preparation method of the nano-hydrated calcium silicate crystal nuclei is as follows: Add 1.8-2.5 parts of sodium hydroxide to 20-30 parts of deionized water, and stir at 300 r / min until completely dissolved. The pH of the system is measured to be 12-13, yielding alkaline solution A. Add 3.5-4.5 parts of calcium nitrate to 20-30 parts of deionized water, and stir until completely dissolved. Then add 0.05-0.1 parts of boric acid, and continue stirring for 20 min to fully disperse and partially dissolve the boric acid. Then proceed sequentially... Add 0.04-0.06 parts of carboxylic acid-silane copolymer modifier and 0.04-0.06 parts of nano-TiO2, and disperse using ultrasonic dispersion technology for 25 min to obtain a uniform and stable boron-doped calcium salt solution B. Place solution A in a constant temperature water bath at 25℃, start stirring at 400 r / min, and add solution B dropwise to solution A at a rate of 2 ml / min. When solution B has been added to 50%, simultaneously add tetraethyl orthosilicate at a rate of 2 ml / min, and continue stirring for 10 min. This process allows tetraethyl orthosilicate to fully react with calcium salts to form a hydrated calcium silicate precursor. Simultaneously, boron atoms gradually replace some silicon atoms in the crystal lattice. After the tetraethyl orthosilicate addition is complete, 0.15-0.2 parts of silica sol are added dropwise at a constant rate of 2 ml / min. During the addition, the pH of the system is adjusted to 11-12 with a small amount of acetic acid to ensure the silica sol fully gels and participates in crystal nucleation. After the silica sol addition is complete, the water bath temperature is raised to 60℃, and stirring is continued at 400 r / min for 50 min to promote crystal growth. The complete formation of boron-doped hydrated calcium silicate crystal nuclei is achieved, while a modified layer is formed on the surface of the crystal nuclei by a carboxylic acid and silane copolymer modifier. Nano-TiO2 is embedded in the core-shell structure gap. By introducing boric acid as a boron source, boron atoms replace some silicon atoms in the hydrated calcium silicate lattice, forming a boron-doped modified structure. At the same time, the synergistic effect of carboxylic acid, silane copolymer modifier and nano-TiO2 is retained, ultimately resulting in boron-doped nano-hydrated calcium silicate crystal nuclei with the triple functions of accelerating cement hydration, inhibiting ettringite expansion and improving high-temperature stability.

[0042] Further, the method for preparing zirconium-titanium composite nanoparticles is as follows: Add 4.5-5.5 parts of zirconium oxychloride to 25-30 parts of deionized water, and stir at 300 r / min until completely dissolved to obtain a transparent zirconium salt mother liquor; slowly add 1.2-1.5 parts of titanium tetrachloride dropwise to 5-8 parts of anhydrous ethanol, stirring at 200 r / min while adding, and continue stirring for 15 min after the addition is complete to obtain a titanium salt diluted solution; slowly pour the titanium salt diluted solution into the zirconium salt mother liquor, increasing the stirring speed to... Stir at 400 rpm for 20 minutes to obtain a zirconium-titanium composite salt solution. Add 2.0-2.5 parts sodium hydroxide to 25-30 parts deionized water and stir until completely dissolved to obtain an alkaline precipitant. Place the zirconium-titanium composite salt solution in a 30°C constant temperature water bath and start stirring at 400 rpm. Then, add the alkaline precipitant dropwise to the zirconium-titanium composite salt solution at a rate of 3 ml / min. During the dropwise addition, adjust the pH of the system to 9-10 with hydrochloric acid. Continue stirring for 30 minutes until zirconium is formed. Titanium hydroxide precipitation was performed by adding 0.3-0.5 parts of isopropyl tritiate to the precipitation system. The stirring speed was increased to 500 rpm, the water bath temperature was raised to 50°C, and stirring was continued for 60 minutes. This allowed the titanium oxide groups in the coupling agent molecules to react with the hydroxyl groups on the precipitate surface, forming Zr-O-Ti chemical bonds. Simultaneously, the long-chain groups of the coupling agent covered the surface of the nanoparticles, improving the dispersion stability of the nanoparticles in the cement paste. After the reaction was completed, the precipitate was cooled and then placed in a centrifuge tube and centrifuged at 900 °C. Centrifuge at 0 r / min for 20 min to remove the supernatant; wash repeatedly with deionized water 4 times until the pH of the washing solution drops to 7-8; then place the washed precipitate in a drying oven and dry at 80℃ for 12 h to remove moisture; after drying, transfer to a muffle furnace and heat to 600℃ at a heating rate of 5℃ / min, and calcine at a constant temperature for 2 h. Through the above method and after crushing and sieving, zirconium-titanium composite nanoparticles with high temperature stability and anti-ultraviolet aging function, composed of zirconium oxide and titanium oxide, are finally obtained.

[0043] At the microscopic level, a three-layer protection system is employed: zirconium-titanium composite nanoparticles inhibit the decomposition of hydration products; nano-hydrated calcium silicate crystal nuclei; and amino-modified silica fume fills the nanopores. The first layer utilizes nano-hydrated calcium silicate crystal nuclei as heterogeneous nucleation sites during phosphate cement hydration, adsorbing Ca²⁺ and SiO₃²⁻ ions from the cement paste. This induces the directional growth of hydrated products, such as ettringite or CSH gel, along the crystal nucleus surface, preventing the disordered accumulation of amorphous hydration products. Simultaneously, the carboxylic acid-silane copolymer modification layer on the crystal nucleus surface reduces the surface energy of the hydration products, promoting uniform dispersion of gel particles and reducing harmful pores formed by particle agglomeration. Lattice doping of boron atoms at warm temperatures enhances the thermal stability of hydrated calcium silicate crystals. Simultaneously, the nano-TiO2 within the crystal nuclei embeds into the gaps of the CSH gel, thus limiting crystal slippage and deformation at high temperatures. Secondly, modified silica fume can directly fill the nanopores of the CSH gel network induced by boron-doped nano-hydrated calcium silicate crystal nuclei. Furthermore, the positively charged surface of the modified silica fume due to amine grafting tightly binds to the negatively charged CSH gel through electrostatic adsorption, further reducing porosity. The even smaller nano-aluminum nitride particles loaded on the silica fume surface can penetrate even smaller gel gaps, forming a gradient pore structure where silica fume fills macropores and aluminum nitride fills micropores. The gap-filling structure significantly improves the density of the concrete matrix. Furthermore, the amine groups grafted onto the silica fume surface with γ-aminopropyltriethoxysilane can undergo a condensation reaction with the hydroxyl groups in the hydration products of phosphate cement, forming Si-O-Ca chemical bonds. This firmly connects the modified silica fume to the hydration product skeleton. Nano-aluminum nitride reacts with the moisture in the hydration products at high temperatures, generating Al(OH)3 gel that fills microcracks caused by high temperatures, achieving self-repair of damage. The third layer consists of zirconium-titanium composite nanoparticles, which are ZrO2-TiO2 composite oxide crystals. These particles possess excellent high-temperature stability and are not prone to phase transformation or decomposition at high temperatures. Secondly, when the temperature rises, the CSH gel, a hydration product of phosphate cement, is prone to dehydration and decomposition. However, the zirconium-titanium composite nanoparticles dispersed in the hydration products can reduce the conduction of heat into the hydration products through physical barriers. At the same time, the isopropyl trititanate modified layer on the particle surface can form hydrogen bonds with the amino groups of the amino-modified silica fume, anchoring the nanoparticles at the pore-filling sites and avoiding the protective failure caused by particle migration at high temperatures. In addition, the thermal expansion coefficient of the zirconium-titanium composite nanoparticles is close to that of the amino-modified silica fume and the nano-hydrated calcium silicate crystal nuclei. The volume deformation of the three at high temperatures remains synchronized, avoiding internal thermal stress caused by differences in thermal expansion.

[0044] Furthermore, the shale ceramsite is a multi-level porous shale ceramsite, which is produced by high-temperature foaming and microwave activation. This method is existing technology and will not be described in detail here.

[0045] Furthermore, the lightweight aggregate is a composite aggregate of hollow ceramic microspheres and vitrified microspheres. The specific preparation method is as follows: 15 parts of hollow ceramic microspheres and 25 parts of vitrified microspheres are put into a high-speed mixer and stirred at a speed of 1500 r / min. After the mixer is turned on, a diluted silane coupling agent is slowly sprayed. Through the shear force and thermal effect generated by high-speed stirring, the amino groups in the coupling agent molecules and the hydroxyl groups on the surface of the microspheres undergo a condensation reaction, forming an organic modified layer on the surface of the microspheres, which improves its hydrophobic properties and interfacial compatibility. Then, the modified composite microspheres are placed in a drying oven and dried at 60°C for 12 h to obtain the composite aggregate of hollow ceramic microspheres and vitrified microspheres.

[0046] Further, the preparation method of the temperature-sensitive gas-entraining agent is as follows: 12 parts of a mixed solvent of anhydrous ethanol and 4 parts of deionized water, and 6 parts of sodium rosinate are added sequentially to a reaction vessel. The stirring speed is set to 300 r / min, the temperature is raised to 50℃-55℃, and stirring is continued for 30 min until the solution is completely transparent, obtaining a sodium rosinate composite solution; 1 part of nano-calcium carbonate is added to 4 parts of deionized water, and dispersed using ultrasonic dispersion technology for 20 min, stirring to obtain a nano-calcium carbonate suspension; 2 parts of polyetheramine regulator are added to 4 parts of anhydrous ethanol, and stirred for 15 min at 20℃-25℃ and a stirring speed of 200 r / min to obtain a polyetheramine temperature-sensitive regulator solution; the reaction vessel temperature is maintained at 5℃. At 0℃-55℃ and a rotation speed of 300r / min, the polyetheramine thermosensitive regulator solution was added dropwise to the sodium rosinate composite solution at a rate of 1ml / min. The pH value was adjusted to 5.5-6.5 by adding 1mol / L acetic acid solution. Then, the nano-calcium carbonate suspension was added at a rate of 2ml / min. The temperature was raised to 60℃ and the rotation speed was increased to 400r / min. The mixture was stirred until it became a uniform light yellow emulsion without layering, forming a ternary composite system of sodium rosinate-polyetheramine-nano-calcium carbonate. The ternary composite system was cooled to room temperature and diluted with 10-16 parts of anhydrous ethanol. The diluted composite was then dried at 60℃ for 12h and pulverized to obtain the thermosensitive air-entraining agent.

[0047] Furthermore, the preparation method of the polyetheramine modifier is as follows: propylene glycol is used as an initiator to initiate the block copolymerization of ethylene oxide (EO) and propylene oxide (PO) to form a "polyoxyethylene PEO-polyoxypropylene PPO" block copolymer backbone. The molecular chain contains hydrophilic PEO segments and hydrophobic PPO segments, laying the structural foundation for its temperature-sensitive properties. By adjusting the EO / PO ratio, the molecular weight is controlled at 2000-3000 and the lower critical solution temperature (LCST) is controlled at 35-40℃. The above block copolymer... Amination with ethylenediamine converts the hydroxyl groups (-OH) at both ends of the molecular chain into amino groups (-NH2), ultimately forming a polyetheramine structure of "PEO-PPO block backbone + amino groups at both ends". The amino groups can form hydrogen bonds with the carboxyl groups of sodium arosinate, achieving structural coupling in a ternary composite system. The carboxyl groups of sodium arosinate and the amino groups of polyetheramine are bonded through intermolecular hydrogen bonds, forming a binary composite molecule of "sodium arosinate-polyetheramine". Nano-calcium carbonate, through its surface hydroxyl groups, can then bond with the carboxyl groups of sodium arosinate via hydrogen bonds. The amino groups of polyetheramine undergo physical adsorption, anchoring nano-calcium carbonate onto the surface of the "sodium rosinate-polyetheramine" composite molecule, forming a three-dimensional spatial barrier structure that provides physical support for bubbles. This ultimately constructs a ternary molecular network of "sodium rosinate-polyetheramine-nano-calcium carbonate." When the ambient temperature is below 35℃, the polyetheramine molecular chains expand, and the hydrophilic PEO segments extend outwards, without hindering the binding of the hydrophilic groups of sodium rosinate to water molecules, resulting in a normal bubble generation rate. Above 40℃, the polyetheramine molecular chains contract into a spherical shape, and the hydrophobic PPO segments wrap around the outer side of the binary composite molecule, partially blocking the hydrophilic groups of sodium rosinate and reducing its gas-liquid interface activity, thereby inhibiting the bubble generation rate and achieving temperature-sensitive regulation. The three-dimensional spatial barrier structure formed by the nano-calcium carbonate anchored in the ternary molecular network prevents the aggregation of adjacent composite molecules, avoiding bubble merging. Simultaneously, the rigid structure of the nano-calcium carbonate enhances the mechanical strength of the bubble wall, reducing the probability of bubble rupture at high temperatures, thus preventing cracking on the inner side of the concrete.

[0048] From a macroscopic perspective: the composite aggregate of hollow ceramic microspheres and vitrified microspheres can fill the gaps in shale ceramsite, forming a dense, lightweight packing system with a coarse aggregate skeleton and fine aggregate filling, significantly reducing the apparent density of concrete. Simultaneously, the silane coupling agent modification layer on the surface of the composite microspheres enhances the interfacial adhesion between the aggregate and cement paste, preventing strength loss due to aggregate lightweighting. Furthermore, the hollow cavities of the hollow ceramic microspheres and the closed pores of the vitrified microspheres isolate heat. By introducing a temperature-sensitive air-entraining agent, when the concrete construction temperature is below 35℃, the polyetheramine molecular chains expand, and the hydrophilic PEO segments extend outwards, without hindering the air-entraining activity of sodium rosinate. The air-entraining agent normally generates uniform, fine bubbles, which fill the aggregate and cement paste. The interfacial gaps can buffer the drying shrinkage stress during hydration, improve the toughness of concrete, and prevent early cracking. When the subsequent temperature is greater than 40℃, the polyetheramine molecular chains shrink, and the hydrophobic PPO segments encapsulate the composite molecules, reducing air-entraining activity and inhibiting the formation of new bubbles. At the same time, the ternary molecular network anchored by nano-calcium carbonate enhances the rigidity of the bubble walls, preventing the bubbles from bursting and merging at high temperatures. The stable existence of the bubbles can accommodate the volume expansion of concrete caused by high temperatures, offset thermal stress, and prevent the initiation of internal microcracks. Furthermore, when the temperature continues to rise, the stress generated by the difference in thermal expansion between aggregate and paste can be released through the compression deformation of the bubbles, preventing the interfacial transition zone from becoming a weak point of stress concentration and further improving crack resistance.

[0049] Furthermore, the biomimetic mineralizing hydrophobic sealing agent is composed of modified silane hydrophobic agent, nano-hydroxyapatite, chitosan, and poly(N-isopropylacrylamide) microspheres in a mass ratio of 1:2:0.2:0.1. Nano-hydroxyapatite directly fills the nanoscale pores inside the concrete. Simultaneously, the crystal structure of nano-hydroxyapatite is similar to the calcium salts in concrete hydration products, serving as heterogeneous nucleation sites. This induces the deposition of Ca²⁺ and PO₄³⁻ ions precipitated during cement hydration within the pores, generating hydroxyapatite-like crystals, achieving mineralization filling of the pores, and further improving the density of the concrete matrix. Chitosan... On the one hand, hydrogen bonding adsorption can firmly bind nano-hydroxyapatite particles to the inner wall of pores, preventing the migration and loss of nano-hydroxyapatite particles; on the other hand, -NH3⁺ on the chitosan molecular chain can electrostatically adsorb and bind PO4³⁻ and OH⁻ of hydroxyapatite, while electronegative hydroxyl groups can chelate Ca²⁺ through coordination, thereby anchoring the growth units of hydroxyapatite to the chitosan molecular chain. In this way, chitosan can regulate the growth direction of hydroxyapatite crystals, causing them to grow directionally along the inner wall of pores, forming a dense mineralized layer, thereby repairing microcracks and enhancing the impermeability and mechanical properties of concrete.

[0050] Further, the preparation method of poly(N-isopropylacrylamide) microspheres is as follows: 15-20 parts of deionized water and 0.01-0.02 parts of sodium dodecyl sulfate are mixed and stirred at 40°C and 300 r / min until the sodium dodecyl sulfate is completely dissolved. Then, 2-2.5 parts of N-isopropylacrylamide and 0.02-0.03 parts of N,N'-methylenebisacrylamide are added and stirred continuously to obtain an emulsion; 1 part of deionized water and 0.05-0.08 parts of... Potassium sulfate was used to prepare an initiator solution by stirring at 70℃-75℃. The initiator solution was added dropwise to the emulsion at a rate of 0.5 ml / min, and polymerization was carried out at 70℃-75℃ and 300 r / min with continuous nitrogen purging. This polymerized the monomers into cross-linked microspheres. The reactants were cooled, and the cooled reaction solution was transferred to centrifuge tubes and centrifuged at 10000 r / min for 20 min. The supernatant was removed, and the solution was then processed with deionized water. The mixture was washed three times with water, and the precipitate was then placed in a drying oven and dried at 50°C for 12 hours to obtain white powdered poly(N-isopropylacrylamide) microspheres. At temperatures below 32°C, the hydrophilic poly(N-isopropylacrylamide) chains of the microspheres expanded, causing them to absorb water and swell, increasing in volume to 3-5 times their original size. These microspheres filled the capillary pores and interfacial pores of the concrete, forming an elastic sealant that buffered the drying shrinkage stress of cement hydration while blocking water penetration pathways. When the temperature increased to... At temperatures above 32°C, the hydrophobic segments of N-isopropylacrylamide microspheres shrink, causing the microspheres to shrink in volume and form dense spherical particles. On the one hand, the shrunken microspheres can tightly adhere to the hydrophobic film layer of the modified silane hydrophobic agent, filling local defects in the hydrophobic film layer and enhancing the hydrophobic barrier effect. On the other hand, the shrinkage of the microspheres can form a stress buffer space within the pores, offsetting the volume expansion stress of the concrete matrix at high temperatures, preventing the pores from cracking and expanding due to stress, and further increasing the stability of concrete in high-temperature environments.

[0051] Further, the modified silane hydrophobic agent is prepared as follows: 8-10 parts of anhydrous ethanol and 6-7 parts of methyltriethoxysilane are added sequentially to a reaction vessel and stirred at 300 r / min for 10 min. Then, 0.3-0.5 parts of 1 mol / L hydrochloric acid are added dropwise to adjust the pH to 3.5-4.5. Next, 2-3 parts of deionized water are added, and stirring is continued for 30 min to obtain a silane hydrolysate. 1.5-2 parts of n-octadecyl alcohol are heated to 65℃ to melt and slowly poured into the above silane hydrolysate. The stirring speed is increased to 400 r / min, and the reaction temperature is maintained at 55℃-60℃. Stirring is continued for 2 h to allow the hydroxyl groups of n-octadecyl alcohol to undergo a condensation reaction with the silanol groups, achieving long-chain alkyl grafting. After the condensation reaction is completed, the mixture is cooled to room temperature, and 1 mol / L sodium hydroxide solution is slowly added dropwise to adjust the pH to 6.5-7. 5. Subsequently, the product was transferred to a rotary evaporator and concentrated for 30 minutes at 60°C and a vacuum of 0.08 MPa. Finally, it was purified by vacuum distillation to obtain a modified silane hydrophobic agent. The silanol groups of the modified silane hydrophobic agent can undergo a condensation reaction with the hydroxyl groups on the surface of concrete hydration products to form stable Si-O-Ca chemical bonds. The hydrophobic groups are firmly grafted onto the surface of hydration products and the transition zone between aggregate and paste, and are not easily detached due to high temperature and water flow, thus achieving long-term hydrophobicity. The grafted long-chain alkyl groups are oriented on the surface of the pores inside the concrete to form a continuous hydrophobic film layer, which greatly reduces the surface energy of the pore surface, so that water cannot spread and penetrate in the pores and can only roll off in the form of water droplets. This blocks external water from entering the concrete through capillaries and microcracks, and avoids internal expansion stress and structural cracking caused by water vaporization under high ground temperature conditions.

[0052] Furthermore, the composite fiber is composed of basalt fiber and silicon nitride whiskers in a mass ratio of 4:1.

[0053] A method for preparing concrete suitable for high-temperature tunnel construction includes the following steps:

[0054] Add 70-90 parts of river sand and 35-50 parts of shale ceramsite to a forced mixer in sequence, and mix at 120-150 r / min for 5 min; then add 65-75 parts of phosphate cement and 8-12 parts of modified silica fume, and continue mixing at 120-150 r / min for 8 min to form a dry mixture.

[0055] Add 10.8-13.2 parts of mixing water to the dry mixture, increase the stirring speed of the forced mixer to 180-200 rpm, and stir for 10 minutes to form the initial slurry; prepare a solution of 3-6 parts of nano-hydrated calcium silicate crystal nuclei and a dispersion of 2-4 parts of zirconium-titanium nanoparticles, and pour them into the initial slurry. Increase the stirring speed to 220-250 rpm, and use an ice-water bath to control the slurry temperature ≤35℃. After stirring for 15 minutes, add 0.3-0.6 parts of water-reducing agent, and maintain the stirring speed at 220-250 rpm for 5 minutes to obtain the intermediate slurry;

[0056] Reduce the stirring speed to 150-180 rpm, add 0.8-1.5 parts of biomimetic mineralized hydrophobic sealing agent to the intermediate slurry, and stir for 8 minutes; then add 0.05-0.1 parts of temperature-sensitive air-entraining agent, and continue stirring at 150-180 rpm for 5 minutes until uniform and fine bubbles appear in the slurry; next, add 20-30 parts of lightweight aggregate, reduce the stirring speed to 120-150 rpm, and stir for 6 minutes; then add 1.2-2 parts of composite fiber, and stir at 120-150 rpm for 7 minutes; finally, add 7.2-8.8 parts of mixing water to form the final set concrete slurry.

[0057] Example 1:

[0058] Raw material proportions (parts by weight): 70 parts phosphate cement, 10 parts modified silica fume, 4.5 parts nano-hydrated calcium silicate crystal nuclei, 3 parts zirconium-titanium composite nanoparticles, 42 parts shale ceramsite, 25 parts lightweight aggregate, 80 parts river sand, 0.08 parts temperature-sensitive air-entraining agent, 1.2 parts biomimetic mineralized hydrophobic sealing agent, 1.6 parts composite fiber, 20 parts mixing water (12 parts added for the first time and 8 parts added for the second time in the preparation method), and 0.45 parts water-reducing agent.

[0059] Preparation method: Follow the steps S1-S4 above, strictly control the slurry temperature in stage S3 to ≤35℃, and stir until the slurry contains gas uniformly after adding the temperature-sensitive air-entraining agent in stage S4.

[0060] Performance testing: After the molded standard specimens have been cured to the specified age, they are placed in a high-temperature environment of 80℃ for performance testing.

[0061] Example 2:

[0062] Raw material proportions (parts by weight): 65 parts phosphate cement, 8 parts modified silica fume, 3 parts nano-hydrated calcium silicate crystal nuclei, 2 parts zirconium-titanium composite nanoparticles, 35 parts shale ceramsite, 20 parts lightweight aggregate, 70 parts river sand, 0.05 parts temperature-sensitive air-entraining agent, 0.8 parts biomimetic mineralized hydrophobic sealing agent, 1.2 parts composite fiber, 18 parts mixing water (10.8 parts for the first batch and 7.2 parts for the second batch), and 0.3 parts water-reducing agent.

[0063] Preparation and testing methods: Same as in Example 1.

[0064] Example 3:

[0065] Raw material proportions (parts by weight): 75 parts phosphate cement, 12 parts modified silica fume, 6 parts nano-hydrated calcium silicate crystal nuclei, 4 parts zirconium-titanium composite nanoparticles, 50 parts shale ceramsite, 30 parts lightweight aggregate, 90 parts river sand, 0.1 parts temperature-sensitive air-entraining agent, 1.5 parts biomimetic mineralized hydrophobic sealing agent, 2 parts composite fiber, 22 parts mixing water (13.2 parts for the first batch and 8.8 parts for the second batch), and 0.6 parts water-reducing agent.

[0066] Preparation and testing methods: Same as in Example 1.

[0067] Comparative Example 1:

[0068] Formulation: Based on the formulation of Example 1, the temperature-sensitive air-entraining agent and the biomimetic mineralized hydrophobic blocking agent are removed, while the remaining components and their amounts remain unchanged.

[0069] Objective: To verify the synergistic effect of two core functional additives in resisting high-temperature cracking and preventing water penetration.

[0070] Comparative Example 2:

[0071] Proportioning: Based on the proportioning of Example 1, the modified silica fume is replaced with an equal amount of ordinary silica fume.

[0072] Objective: To verify the effect of modified silica fume on improving interfacial adhesion and high-temperature self-healing ability through amine grafting and nano-aluminum nitride filling.

[0073] Comparative Example 3:

[0074] The proportions are exactly the same as in Example 1.

[0075] Preparation method: Change the order of S3 and S4, and add the nano-hydrated calcium silicate crystal nuclei, zirconium titanium composite nanoparticles, biomimetic mineralized hydrophobic blocking agent and temperature-sensitive air-entraining agent together in the last stage (S4).

[0076] Objective: To verify the criticality of the specific feeding sequence of the present invention for the uniform dispersion of each component and the effective functioning of the components.

[0077] Comparative Example 4:

[0078] Mix proportions: Conventional tunnel concrete prepared using ordinary Portland cement, conventional sand and gravel aggregates, ordinary air-entraining agents and water-reducing agents, without containing any of the special components described in this invention.

[0079] After standard curing, the concrete specimens prepared in the examples and comparative examples were tested under simulated high geothermal environment. The splitting tensile strength test method in GB / T 50081-2019 was used to determine the crack strength, the compressive strength of the concrete was determined using GB / T 50081-2019, the water penetration resistance test method in GB / T 50082-2009 was used to determine the water penetration height, and the coefficient of thermal expansion was determined using the coefficient of thermal expansion test method in GB / T 25995-2010. The test results are summarized in the table below:

[0080]

[0081] Analysis and Explanation:

[0082] Examples 1-3 all exhibited excellent compressive and crack resistance under high geothermal conditions, indicating that the temperature-sensitive air-entraining agent stabilizes the release of stress from air bubbles at high temperatures, and that the composite fibers and dense microstructure work together. In contrast, Comparative Example 1 lacked the key additive, and the strength of the conventional concrete in Comparative Example 4 decreased significantly.

[0083] 2. The water penetration height in the embodiment is much lower than that in the comparative example, proving that the hydrophobic-mineralization-blocking multi-protection system constructed by the biomimetic mineralized hydrophobic sealing agent effectively blocks the water penetration path.

[0084] 3. The embodiment has the lowest coefficient of thermal expansion, indicating that the coefficients of thermal expansion of the zirconium-titanium composite nanoparticles, nano-hydrated calcium silicate crystal nuclei, and modified silica fume are matched, effectively reducing internal thermal stress.

[0085] The above are merely embodiments of the present invention. The circuits, electronic components, and modules involved are all prior art, fully achievable by those skilled in the art, and require no further explanation. The scope of protection in this application does not involve improvements to the software and methods. Commonly known structures and characteristics in the solutions are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all prior art in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for preparing concrete suitable for high ground temperature tunnel construction, characterized by, The raw materials include the following parts by weight: Phosphate cement 65-75 parts, modified silica fume 8-12 parts, nano-hydrated calcium silicate crystal nuclei 3-6 parts, zirconium-titanium composite nanoparticles 2-4 parts, shale ceramsite 35-50 parts, lightweight aggregate 20-30 parts, river sand 70-90 parts, temperature-sensitive air-entraining agent 0.05-0.1 parts, biomimetic mineralized hydrophobic sealing agent 0.8-1.5 parts, composite fiber 1.2-2 parts, mixing water 18-22 parts, water-reducing agent 0.3-0.6 parts; The method for preparing the concrete includes the following steps: S1: Add river sand, shale ceramsite, phosphate cement, and modified silica fume sequentially into a forced mixer and mix at a speed of 120r / min-150r / min to form a dry mixture; S2: Add the first batch of mixing water to the dry material mixture and stir to form the initial concrete paste; S3: Add nano-hydrated calcium silicate crystal nucleus solution, zirconium-titanium composite nanoparticle dispersion and water-reducing agent to the initial slurry in sequence, while increasing the rotation speed to 220r / min-250r / min and controlling the slurry temperature to be less than or equal to 35℃, and stir to obtain the intermediate concrete slurry; S4: In the intermediate slurry, add biomimetic mineralized hydrophobic sealing agent, temperature-sensitive air-entraining agent, lightweight aggregate, composite fiber and second mixing water in sequence. The temperature-sensitive air-entraining agent is composed of sodium rosinate, polyetheramine and nano calcium carbonate in a mass ratio of 6:2:

1. Reduce the speed to 150r / min-180r / min and stir to form the final concrete slurry. The biomimetic mineralized hydrophobic blocking agent is composed of modified silane hydrophobic agent, nano-hydroxyapatite, chitosan, and poly(N-isopropylacrylamide) microspheres in a mass ratio of 1:2:0.2:0.1; the preparation method of the poly(N-isopropylacrylamide) microspheres includes: Deionized water and sodium dodecyl sulfate were mixed, and N-isopropylacrylamide and N,N'-methylenebisacrylamide were added and stirred at 40°C to obtain an emulsion. A solution of initiator is prepared by mixing deionized water and potassium persulfate and stirring at 70℃-75℃. The initiator solution was dropped into the emulsion to carry out the polymerization reaction, and nitrogen gas was continuously introduced. The reactants after the polymerization reaction were cooled and purified to obtain poly(N-isopropylacrylamide) microspheres. The preparation method of the modified silane hydrophobic agent includes: Anhydrous ethanol, methyltriethoxysilane, hydrochloric acid and deionized water were added sequentially to a reaction vessel to obtain a silane hydrolysate. The octadecyl alcohol was heated to 65°C and melted, then poured into the above silane hydrolysate to cause a condensation reaction between the hydroxyl groups of the octadecyl alcohol and the silanol groups. After the condensation reaction is completed, the product is cooled, neutralized and purified to obtain a modified silane hydrophobic agent; The polyetheramine is prepared by: using propylene glycol as an initiator to block copolymerize with ethylene oxide and propylene oxide to form a copolymer backbone, and then subjecting the block copolymer backbone to an amination reaction with ethylenediamine to form polyetheramine.

2. The method for preparing concrete suitable for high-temperature tunnel construction as described in claim 1, characterized in that, The composite fiber is composed of basalt fiber and silicon nitride whiskers in a mass ratio of 4:

1.

3. The method for preparing concrete suitable for high-temperature tunnel construction as described in claim 1, characterized in that, The method for preparing the modified silica fume includes the following steps: Step 31: Add anhydrous ethanol, γ-aminopropyltriethoxysilane and deionized water sequentially to the reaction vessel and stir to obtain silane hydrolysate; Step 32: Add nano-aluminum nitride to anhydrous ethanol and use ultrasonic dispersion technology to obtain a nano-aluminum nitride suspension; Step 33: Add silica fume, silane hydrolysate and nano aluminum nitride suspension to a mixer in sequence, and stir to obtain intermediate product; Step 34: The intermediate product obtained in step 33 is dried, cured, cooled, crushed and sieved to obtain modified silica fume.

4. The method for preparing concrete suitable for high-temperature tunnel construction as described in claim 1, characterized in that, The zirconium-titanium composite nanoparticle dispersion contains zirconium oxide and titanium oxide in a mass ratio of 3:1.

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