Sprayed concrete suitable for high geothermal tunnel environment and preparation method thereof

Abstract

The invention discloses sprayed concrete suitable for a high geothermal tunnel environment and a preparation method of the sprayed concrete. The sprayed concrete is prepared from cement, hollow glass beads, modified hydrophobic aerogel, coarse aggregate, fine aggregate, water, an additive, silica mortar, a high-temperature applicable accelerator and the like. The high-strength hollow glass beads and the aerogel are introduced as thermal insulation aggregates, the hollow glass beads are graded and optimized by adopting three particle sizes, and the aerogel is hydrophobically modified by adopting a co-precursor method, so that the heat conductivity coefficient of the sprayed concrete can be greatly reduced and the thermal insulation performance of the sprayed concrete can be improved by introducing the high-strength hollow glass beads and the aerogel; the silicon mortar and the high-temperature applicable accelerator are introduced, so that the working performance of the sprayed concrete can be improved, and the high-temperature stability of a hydration product is guaranteed. The application of the sprayed concrete can effectively reduce the cavern temperature in a high-ground-temperature tunnel and weaken the influence of a high-temperature environment on the long-term performance of the sprayed concrete, so that the service life of the sprayed concrete in the high-temperature environment is effectively prolonged.

Description

Technical Field

[0002] The invention belongs to building materials and relates to shotcrete suitable for high geothermal tunnel environment and a preparation method thereof. Background Art

[0004] High geothermal heat raises the temperature of the cavern and rock wall, resulting in an increase in the porosity and pore size of the concrete, which significantly reduces the internal density of the concrete and seriously affects its later strength and durability. In addition, the temperature stress generated by the temperature field gradient distribution can easily cause concrete cracking, threatening the overall stability of the tunnel support structure.

[0005] In order to meet these challenges, improving the thermal insulation performance of concrete has become a key research direction. The improvement of thermal insulation performance mainly depends on the introduction of low thermal conductivity aggregates or the formation of effective thermal insulation holes to effectively prevent air convection, thereby reducing thermal radiation and heat conduction. Hollow glass microspheres, as a hollow tiny spherical powder, have attracted much attention due to their good dispersibility and good thermal insulation. However, to achieve the ideal thermal insulation effect, a higher dosage is required, which will have an adverse effect on the working state and strength of concrete. Aerogel, as an ultra-light material with dense nanopores and multi-level fractal pore microstructure, has an extremely low thermal conductivity of about 0.01W / (m·K)~0.02W / (m·K), showing excellent thermal insulation performance. However, aerogel itself has the disadvantages of strong hydrophilicity and high brittleness. It is easy to absorb moisture in the air, resulting in the destruction of the fine nano-skeleton inside, making it difficult to store and apply for a long time.

[0006] Patent CN 117719065 A discloses a shotcrete with low thermal conductivity and high heat resistance and its preparation method, which improves the thermal insulation performance of concrete by adding saturated ceramsite, but does not consider the impact of the low density and uneven distribution of ceramsite itself on working performance. Patent CN110510954B discloses a high-strength shotcrete for high-temperature tunnels and its preparation method, which reduces the thermal conductivity by introducing modified rubber powder and vitrified microspheres to achieve thermal insulation effect, but does not consider the impact of excessively high amounts of lightweight aggregate on concrete strength. Summary of the invention

[0008] The object of the present invention is to solve the above problems, provide a shotcrete suitable for high geothermal tunnel environment, and provide a preparation method thereof.

[0009] The shotcrete suitable for high geothermal tunnel environment described in the present invention comprises the following raw materials in parts by weight: 400-500 parts of cement, 750-880 parts of coarse aggregate, 300-650 parts of fine aggregate, 110-180 parts of water, 3.5-6.0 parts of admixture, 14-40 parts of hollow glass microspheres, 0.2-0.8 parts of modified hydrophobic aerogel, 20-40 parts of silica mortar, and 30-40 parts of high temperature adaptable alkali-free accelerator; wherein the hollow glass microspheres are obtained by mixing three hollow glass microspheres with different particle sizes through grading optimization; wherein the modified hydrophobic aerogel is obtained by silicon source A and silicon source B through a co-precursor method.

[0010] The hollow glass microspheres are obtained through grading optimization and are divided into three particle sizes: coarse, medium and fine. Among them, the coarse particle size ranges from 0.6mm to 0.8mm, the medium particle size ranges from 0.3mm to 0.6mm, and the fine particle size ranges from 0.02mm to 0.3mm. The proportion of each grade is coarse: medium: fine = 5-7: 1-3: 1-3.

[0011] The aerogel has a thermal conductivity of less than 0.05 W / m·K and a hydrophobic angle of more than 140°. The silicon source A is at least one of water glass, methyl orthosilicate, and ethyl orthosilicate. The silicon source B is at least one of methyltrimethoxysilane, methyltriethoxysilane, ethoxytrimethylsilane, dimethyldimethoxysilane, trimethyltriethylsilane, and phenyltriethoxysilane.

[0012] The silica ash slurry is a stable suspension slurry obtained by multi-stage dispersion of silica ash, water and a dispersant, and has a solid content greater than 50%.

[0013] The cement used in the shotcrete is P·O42.5 ordinary Portland cement; the fine aggregate is river sand or machine-made sand with a fineness modulus of 2.5-3.0; and the coarse aggregate is natural crushed stone with a particle size of 5mm-10mm.

[0014] The quick-setting agent used in the shotcrete is a high temperature adaptable alkali-free quick-setting agent, which is compounded with aluminum sulfate, alcohol amine, and reinforcing phase. The alcohol amine includes at least one of ethanolamine, diethanolamine, and triethanolamine, and the reinforcing phase includes at least one of sodium carbonate, magnesium sulfate, sodium sulfate, magnesium fluorosilicate, and sodium fluorosilicate. The initial setting time of the pure slurry (5°C) is ≤5min, the final setting time of the pure slurry (5°C) is ≤10min, and the 28d compressive strength ratio of the mortar (80°C) is ≥90%; the admixture is a polycarboxylic acid high-performance water-reducing agent, and the water reduction rate is ≥25%.

[0015] The preparation method of the shotcrete comprises the following steps:

[0016] (1) Add cement, fine aggregate, coarse aggregate, hollow glass microspheres and aerogel into a mixer and stir for 30 seconds to obtain a dry mix;

[0017] (2) Add water and admixtures to the dry mix and stir for 3 minutes to obtain a concrete mixture;

[0018] (3) The mixture is added to the wet spraying equipment, mixed with the accelerating agent, and then sprayed onto the sprayed surface to obtain a sprayed concrete suitable for high geothermal tunnel environment.

[0019] The sprayed concrete is used in high geothermal tunnels, high-temperature water-gushing tunnels and underground projects with high geothermal conditions.

[0020] The positive effects of the shotcrete of the present invention suitable for high geothermal tunnel environment are:

[0021] The present invention proposes a shotcrete suitable for high geothermal tunnel environment and a preparation method thereof. Hollow glass microspheres and aerogels are used together to reduce the thermal conductivity of concrete and improve the thermal insulation performance of concrete. The grading of glass microspheres is optimized to make them more evenly distributed inside the concrete, forming a more compact and stable structure, thereby effectively improving the compressive strength of concrete. The hydrophobic aerogel is prepared by the co-precursor method, which improves its own shortcomings such as easy water absorption and easy agglomeration, improves its stability and durability in concrete, and at the same time, the hydrophobic aerogel can also form a protective layer inside the concrete to reduce the deterioration effect of moisture and high temperature in the environment on the concrete.

[0022] In addition, a shotcrete suitable for high geothermal tunnel environment uses a high temperature adaptable alkali-free quick-setting agent composed of aluminum sulfate, alcohol amine, and reinforcing phase, which can effectively improve the early strength function and stability of the quick-setting agent under high temperature environment. The addition of silica fume suspension can improve the high temperature stability of hydration products such as hydrated calcium silicate and calcium aluminate, and prevent the hydration products from affecting the performance of concrete due to high temperature degradation. The 56d thermal conductivity of the shotcrete prepared by this method is not more than 2.0W / (m·K), and the 56d heat resistance index (80℃) is not less than 90%. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below with reference to specific embodiments.

[0025] Example 1: A shotcrete suitable for high geothermal tunnel environment, the preparation process of which is as follows:

[0026] (1) Dilute methyl orthosilicate to an 8% solution, add hydrochloric acid to adjust the pH value to 2-3, and generate a silica sol. Mix methyl triethoxysilane and anhydrous ethanol according to a ratio, then add it dropwise to the silica sol and stir for 1 hour to mix it evenly. During the process, add hydrochloric acid to adjust the pH value to 2-3. After stirring, add ammonia water to adjust the pH value to 6-7, and let it stand to obtain wet gel a1; soak the wet gel in anhydrous ethanol under normal pressure and age it for 24 hours, then wash it with n-hexane solution; place the wet gel a1 in an 80°C drying oven, dry it for 3-4 hours, and cool it to obtain hydrophobically modified aerogel A1.

[0027] (2) Hollow glass microspheres of three sizes were selected: coarse particles with a size range of 0.6 mm to 0.8 mm, medium particles with a size range of 0.3 mm to 0.6 mm, and fine particles with a size range of 0.02 mm to 0.3 mm. The coarse particles were mixed at a ratio of 5:2:3 to obtain hollow glass microspheres B1.

[0028] (3) Add 460 parts of cement, 500 parts of sand, 885 parts of gravel, 0.3 parts of modified hydrophobic aerogel A1, and 14 parts of hollow glass microspheres B1 into a mixer, stir for 30 seconds, then add 165 parts of water, 5 parts of water reducer, and 28 parts of silica mortar, and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment and mix it with 36 parts of a high-concentration fluorine-free and alkali-free quick-setting agent, then spray it onto the sprayed surface to obtain a sprayed concrete suitable for a high geothermal tunnel environment.

[0029] Example 2: A shotcrete suitable for high geothermal tunnel environment, the preparation process of which is as follows:

[0030] (1) Dilute water glass to an 8% solution, add hydrochloric acid to adjust the pH value to 2-3, and generate silica sol. Mix ethoxytrimethylsilane and anhydrous ethanol according to a ratio, then add it dropwise to the silica sol and stir for 1 hour to mix it evenly. During the process, add hydrochloric acid to adjust the pH value to 2-3. After stirring, add ammonia water to adjust the pH value to 6-7, and let it stand to obtain wet gel a2; soak the wet gel in anhydrous ethanol under normal pressure and age it for 24 hours, then wash it with n-hexane solution; place the wet gel a2 in an 80°C drying oven, dry it for 3-4 hours, and cool it to obtain hydrophobically modified aerogel A2.

[0031] (2) Hollow glass microspheres of three particle sizes were selected: coarse particles with a particle size range of 0.6 mm to 0.8 mm, medium particles with a particle size range of 0.3 mm to 0.6 mm, and fine particles with a particle size range of 0.02 mm to 0.3 mm. The coarse: medium: fine particles were mixed in a ratio of 6:2:2 to obtain hollow glass microspheres B2.

[0032] (3) Add 456 parts of cement, 480 parts of sand, 880 parts of gravel, 0.4 parts of modified hydrophobic aerogel A2, and 30 parts of hollow glass microspheres B2 into a mixer, stir for 30 seconds, then add 167 parts of water, 4.5 parts of water reducer, and 25 parts of silica mortar, and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment and mix it with 35 parts of high temperature adaptable alkali-free quick-setting agent, then spray it onto the sprayed surface to obtain a shotcrete suitable for high geothermal tunnel environments.

[0033] Example 3: A shotcrete suitable for high geothermal tunnel environment, the preparation process of which is as follows:

[0034] (1) Dilute water glass to an 8% solution, add hydrochloric acid to adjust the pH value to 2-3, and generate a silica sol. Phenyltriethoxysilane and anhydrous ethanol are mixed according to a ratio, and then added dropwise to the silica sol, and stirred for 1 hour to make it evenly mixed. During the process, hydrochloric acid is added dropwise to adjust the pH value to 2-3. After stirring, ammonia water is added to adjust the pH value to 6-7, and the wet gel a3 is obtained by standing. Under normal pressure drying conditions, the wet gel is immersed in anhydrous ethanol for aging for 24 hours, and then washed with a n-hexane solution. The wet gel a3 is placed in an 80°C drying oven, dried for 3-4 hours, and cooled to obtain a hydrophobically modified aerogel A3.

[0035] (2) Hollow glass microspheres of three sizes were selected: coarse particles with a size range of 0.6 mm to 0.8 mm, medium particles with a size range of 0.3 mm to 0.6 mm, and fine particles with a size range of 0.02 mm to 0.3 mm. The coarse particles were mixed at a ratio of 7:1:2 to obtain hollow glass microspheres B3.

[0036] (3) Add 466 parts of cement, 483 parts of sand, 882 parts of gravel, 0.5 parts of modified hydrophobic aerogel A3, and 35 parts of hollow glass microspheres B3 into a mixer, stir for 30 seconds, then add 167 parts of water, 4.5 parts of water reducer, and 25 parts of silica mortar, and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment and mix it with 35 parts of high temperature adaptable alkali-free quick-setting agent, then spray it onto the sprayed surface to obtain a shotcrete suitable for high geothermal tunnel environment.

[0037] Example 4: A shotcrete suitable for high geothermal tunnel environment, the preparation process of which is as follows:

[0038] (1) Dilute ethyl orthosilicate to a 7% solution, add hydrochloric acid to adjust the pH value to 2-3, and generate a silica sol. Mix phenyltriethoxysilane and anhydrous ethanol according to a ratio, then add it dropwise to the silica sol and stir for 1 hour to mix it evenly. During the process, add hydrochloric acid to adjust the pH value to 2-3. After stirring, add ammonia water to adjust the pH value to 6-7, and let it stand to obtain wet gel a4; soak the wet gel in anhydrous ethanol under normal pressure and age it for 24 hours, then wash it with n-hexane solution; place the wet gel a4 in an 80°C drying oven, dry it for 3-4 hours, and cool it to obtain a hydrophobically modified aerogel A4.

[0039] (2) Hollow glass microspheres of three particle sizes were selected: coarse particles with a particle size range of 0.6 mm to 0.8 mm, medium particles with a particle size range of 0.3 mm to 0.6 mm, and fine particles with a particle size range of 0.02 mm to 0.3 mm. The coarse: medium: fine particles were mixed in a ratio of 5:3:2 to obtain hollow glass microspheres B4.

[0040] (3) Add 468 parts of cement, 488 parts of sand, 885 parts of gravel, 0.6 parts of modified hydrophobic aerogel A4, and 35 parts of hollow glass microspheres B4 into a mixer, stir for 30 seconds, then add 167 parts of water, 4.5 parts of water reducer, and 25 parts of silica mortar, and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment and mix it with 33 parts of a high temperature adaptable alkali-free quick-setting agent, then spray it onto the sprayed surface to obtain a sprayed concrete suitable for a high geothermal tunnel environment.

[0041] Example 5: A shotcrete suitable for high geothermal tunnel environment, the preparation process of which is as follows:

[0042] (1) Dilute water glass to a 6% solution, add hydrochloric acid to adjust the pH value to 2-3, and generate silica sol. Mix dimethyldimethoxysilane and anhydrous ethanol according to a ratio, then add it dropwise to the silica sol and stir for 1 hour to mix it evenly. During the process, add hydrochloric acid to adjust the pH value to 2-3. After stirring, add ammonia water to adjust the pH value to 6-7, and let it stand to obtain wet gel a5; soak the wet gel in anhydrous ethanol under normal pressure and age it for 24 hours, then wash it with n-hexane solution; place the wet gel a5 in an 80°C drying oven, dry it for 3-4 hours, and cool it to obtain hydrophobic modified aerogel A5.

[0043] (2) Hollow glass microspheres of three particle sizes were selected: coarse particles with a particle size range of 0.6 mm to 0.8 mm, medium particles with a particle size range of 0.3 mm to 0.6 mm, and fine particles with a particle size range of 0.02 mm to 0.3 mm. The coarse: medium: fine particles were mixed in a ratio of 6:1:3 to obtain hollow glass microspheres B5.

[0044] (3) Add 476 parts of cement, 485 parts of sand, 887 parts of gravel, 0.7 parts of modified hydrophobic aerogel A5, and 35 parts of hollow glass microspheres B5 into a mixer, stir for 30 seconds, then add 167 parts of water, 4.5 parts of water reducer, and 35 parts of silica mortar, and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment and mix it with 32 parts of a high temperature adaptable alkali-free quick-setting agent, then spray it onto the sprayed surface to obtain a shotcrete suitable for a high geothermal tunnel environment.

[0045] Example 6: A shotcrete suitable for high geothermal tunnel environment, the preparation process of which is as follows:

[0046] (1) Dilute water glass to a 7% solution, add hydrochloric acid to adjust the pH value to 2-3, and generate silica sol. Mix methyltriethoxysilane and anhydrous ethanol according to a ratio, then add it dropwise to the silica sol and stir for 1 hour to mix it evenly. During the process, add hydrochloric acid to adjust the pH value to 2-3. After stirring, add ammonia water to adjust the pH value to 6-7, and let it stand to obtain wet gel a6; soak the wet gel in anhydrous ethanol under normal pressure and age it for 24 hours, then wash it with n-hexane solution; place the wet gel a6 in an 80°C drying oven, dry it for 3-4 hours, and cool it to obtain hydrophobic modified aerogel A6.

[0047] (2) Hollow glass microspheres of three sizes were selected: coarse particles with a size range of 0.6 mm to 0.8 mm, medium particles with a size range of 0.3 mm to 0.6 mm, and fine particles with a size range of 0.02 mm to 0.3 mm. The coarse particles: medium particles: fine particles were mixed in a ratio of 6:3:1 to obtain hollow glass microspheres B6.

[0048] (3) Add 498 parts of cement, 440 parts of sand, 886 parts of gravel, 0.7 parts of modified hydrophobic aerogel A6, and 37 parts of hollow glass microspheres B6 into a mixer, stir for 30 seconds, then add 160 parts of water, 5.0 parts of water reducer, and 38 parts of silica mortar, and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment and mix it with 39 parts of high temperature adaptable alkali-free quick-setting agent, then spray it onto the sprayed surface to obtain a shotcrete suitable for high geothermal tunnel environment.

[0049] Example 7: A shotcrete suitable for high geothermal tunnel environment, the preparation process of which is as follows:

[0050] (1) Methyl orthosilicate was diluted to a 6% solution, and hydrochloric acid was added to adjust the pH value to 2-3 to generate a silica sol. Phenyltriethoxysilane and anhydrous ethanol were mixed according to a ratio, and then added dropwise to the silica sol, and stirred for 1 hour to make it evenly mixed. During the process, hydrochloric acid was added dropwise to adjust the pH value to 2-3. After stirring, ammonia water was added to adjust the pH value to 6-7, and the wet gel a7 was obtained by standing. Under normal pressure drying conditions, the wet gel was immersed in anhydrous ethanol for aging for 24 hours, and then washed with a n-hexane solution. The wet gel a7 was placed in an 80°C drying oven, dried for 3-4 hours, and cooled to obtain a hydrophobically modified aerogel A7.

[0051] (2) Hollow glass microspheres of three sizes were selected: coarse particles with a size range of 0.6 mm to 0.8 mm, medium particles with a size range of 0.3 mm to 0.6 mm, and fine particles with a size range of 0.02 mm to 0.3 mm. The coarse particles: medium particles: fine particles were mixed in a ratio of 6:3:1 to obtain hollow glass microspheres B6.

[0052] (3) Add 466 parts of cement, 460 parts of sand, 886 parts of gravel, 0.7 parts of modified hydrophobic aerogel A7, and 37 parts of hollow glass microspheres B6 into a mixer, stir for 30 seconds, then add 160 parts of water, 5.0 parts of water reducer, and 38 parts of silica mortar, and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment and mix it with 39 parts of high temperature adaptable alkali-free quick-setting agent, then spray it onto the sprayed surface to obtain a shotcrete suitable for high geothermal tunnel environment.

[0053] Comparative Example 1: Ordinary shotcrete

[0054] Put 498 parts of cement, 810 parts of sand and 880 parts of gravel into a mixer, stir for 30 seconds, then add 165 parts of water and 5.0 parts of water reducing agent, and stir for 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying device, mix it with 38 parts of accelerator, and then spray it onto the sprayed surface to obtain a shotcrete.

[0055] Comparative Example 2: Shotcrete with hollow glass microspheres

[0056] (1) Hollow glass microspheres of three sizes were selected: coarse particles with a particle size range of 0.6 mm to 0.8 mm, medium particles with a particle size range of 0.3 mm to 0.6 mm, and fine particles with a particle size range of 0.02 mm to 0.3 mm. The coarse particles were mixed at a ratio of 6:3:1 to obtain hollow glass microspheres B6.

[0057] (2) Add 498 parts of cement, 615 parts of sand, 886 parts of gravel, and 37 parts of hollow glass microspheres B6 into a mixer, stir for 30 seconds, then add 160 parts of water, 5.0 parts of water reducer, and 38 parts of silica mortar, and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment and mix it with 39 parts of a high temperature adaptable alkali-free quick-setting agent, then spray it onto the sprayed surface to obtain a shotcrete.

[0058] Comparative Example 3: Shotcrete with Aerogel

[0059] (1) Dilute water glass to an 8% solution, add hydrochloric acid to adjust the pH value to 2-3, and generate silica sol. Mix methyltriethoxysilane and anhydrous ethanol according to a ratio, then add it dropwise to the silica sol and stir for 1 hour to mix it evenly. During the process, add hydrochloric acid to adjust the pH value to 2-3. After stirring, add ammonia water to adjust the pH value to 6-7, and let it stand to obtain wet gel a8; soak the wet gel in anhydrous ethanol under normal pressure and age it for 24 hours, then wash it with n-hexane solution; place the wet gel a8 in an 80℃ drying oven, dry it for 3-4 hours, and cool it to obtain hydrophobic modified aerogel A8.

[0060] (2) Add 498 parts of cement, 590 parts of sand, 886 parts of gravel, and 0.7 parts of modified hydrophobic aerogel A8 into a mixer, stir for 30 seconds, then add 165 parts of water, 5.0 parts of water reducer, and 38 parts of silica mortar, and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment and mix it with 38 parts of high temperature adaptable alkali-free quick-setting agent, then spray it onto the sprayed surface to obtain sprayed concrete.

[0061] Comparative Example 4: Shotcrete without gradation optimization of hollow glass microspheres

[0062] (1) Dilute ethyl orthosilicate to a 7% solution, add hydrochloric acid to adjust the pH value to 2-3, and generate a silica sol. Mix ethoxytrimethylsilane and anhydrous ethanol according to a ratio, then add it dropwise to the silica sol and stir for 1 hour to mix it evenly. During the process, add hydrochloric acid to adjust the pH value to 2-3. After stirring, add ammonia water to adjust the pH value to 6-7, and let it stand to obtain wet gel a9; soak the wet gel in anhydrous ethanol under normal pressure and age it for 24 hours, then wash it with n-hexane solution; place the wet gel a9 in an 80°C drying oven, dry it for 3-4 hours, and cool it to obtain hydrophobically modified aerogel A9.

[0063] (2) Hollow glass microspheres of three sizes were selected: coarse particles with a particle size range of 0.6 mm to 0.8 mm, medium particles with a particle size range of 0.3 mm to 0.6 mm, and fine particles with a particle size range of 0.02 mm to 0.3 mm. The coarse particles: medium particles: fine particles were mixed in a ratio of 1:1:1 to obtain hollow glass microspheres B7.

[0064] (3) Add 490 parts of cement, 430 parts of sand, 886 parts of gravel, 0.7 parts of modified hydrophobic aerogel A9, and 35 parts of hollow glass microspheres B7 into a mixer, stir for 30 seconds, then add 162 parts of water, 5.0 parts of water reducer, and 38 parts of silica mortar, and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment and mix it with 40 parts of high temperature adaptable alkali-free quick-setting agent, then spray it onto the sprayed surface to obtain sprayed concrete.

[0065] Comparative Example 5: Shotcrete without aerogel modification

[0066] (1) Hollow glass microspheres of three sizes were selected: coarse particles with a particle size range of 0.6 mm to 0.8 mm, medium particles with a particle size range of 0.3 mm to 0.6 mm, and fine particles with a particle size range of 0.02 mm to 0.3 mm. The coarse particles were mixed at a ratio of 6:3:1 to obtain hollow glass microspheres B6.

[0067] (2) Add 490 parts of cement, 430 parts of sand, 886 parts of gravel, 0.7 parts of aerogel, and 35 parts of hollow glass microspheres B6 into a mixer and stir for 30 seconds. Then add 162 parts of water, 5.0 parts of water reducer, and 38 parts of silica mortar and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment and mix it with 40 parts of high temperature adaptable alkali-free quick-setting agent and spray it onto the sprayed surface to obtain sprayed concrete.

[0068] Comparative Example 6: Shotcrete without using high temperature applicable alkali-free accelerating agent and silica mortar

[0069] (1) Dilute ethyl orthosilicate to a 6% solution, add hydrochloric acid to adjust the pH value to 2-3, and generate a silica sol. Mix methyltrimethoxysilane and anhydrous ethanol in a certain ratio, then add them dropwise to the silica sol and stir for 1 hour to mix them evenly. During the process, add hydrochloric acid to adjust the pH value to 2-3. After stirring, add ammonia water to adjust the pH value to 6-7, and let it stand to obtain wet gel a10; soak the wet gel in anhydrous ethanol under normal pressure and age it for 24 hours, then wash it with n-hexane solution; place the wet gel a9 in an 80°C drying oven, dry it for 3-4 hours, and cool it to obtain hydrophobically modified aerogel A10.

[0070] (2) Hollow glass microspheres of three particle sizes were selected: coarse particles with a particle size range of 0.6 mm to 0.8 mm, medium particles with a particle size range of 0.3 mm to 0.6 mm, and fine particles with a particle size range of 0.02 mm to 0.3 mm. The coarse: medium: fine particles were mixed in a ratio of 6:1:3 to obtain hollow glass microspheres B7.

[0071] (3) Add 480 parts of cement, 290 parts of sand, 886 parts of gravel, 0.6 parts of modified hydrophobic aerogel A10, and 70 parts of hollow glass microspheres B7 into a mixer, stir for 30 seconds, then add 168 parts of water and 5.0 parts of water reducer, and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment, mix it with 36 parts of alkali-free accelerator, and then spray it onto the sprayed surface to obtain sprayed concrete.

[0072] Comparative Example 7: Shotcrete with high content of hollow glass microspheres

[0073] (1) Dilute ethyl orthosilicate to a 6% solution, add hydrochloric acid to adjust the pH value to 2-3, and generate a silica sol. Mix dimethyldimethoxysilane and anhydrous ethanol in a certain ratio, then add them dropwise to the silica sol and stir for 1 hour to mix them evenly. During the process, add hydrochloric acid to adjust the pH value to 2-3. After stirring, add ammonia water to adjust the pH value to 6-7, and let it stand to obtain a wet gel a11; soak the wet gel in anhydrous ethanol under normal pressure and age it for 24 hours, then wash it with a n-hexane solution; place the wet gel a11 in an 80°C drying oven, dry it for 3-4 hours, and cool it to obtain a hydrophobically modified aerogel A11.

[0074] (2) Hollow glass microspheres of three particle sizes were selected: coarse particles with a particle size range of 0.6 mm to 0.8 mm, medium particles with a particle size range of 0.3 mm to 0.6 mm, and fine particles with a particle size range of 0.02 mm to 0.3 mm. The coarse: medium: fine particles were mixed in a ratio of 6:1:3 to obtain hollow glass microspheres B7.

[0075] (3) Add 480 parts of cement, 290 parts of sand, 886 parts of gravel, 0.6 parts of modified hydrophobic aerogel A11, and 70 parts of hollow glass microspheres B7 into a mixer, stir for 30 seconds, then add 168 parts of water, 5.0 parts of water reducer, and 38 parts of silica mortar, and stir for another 3 minutes to obtain a concrete mixture. Add the mixture into a wet spraying equipment and mix it with 36 parts of high temperature adaptable alkali-free quick-setting agent, then spray it onto the sprayed surface to obtain sprayed concrete.

[0076] Effect description:

[0077] After the shotcrete suitable for high geothermal tunnels prepared in Examples 1-7 of the present invention and the shotcrete of Comparative Examples 1-7 were sprayed on site, the remaining indicators were cut to the required size for testing and placed in a standard curing room and a 80°C high-temperature steam curing box, and the corresponding tests were carried out after curing to a fixed age.

[0078] Table 1 Shotcrete Example and Comparative Example Test Results

[0079]

[0080] From the data in Table 1, it can be seen that the thermal insulation performance of the shotcrete in the embodiment and the strength development and retention ability at a rock temperature of 80°C are very excellent, which ensures the stability of the primary support concrete in long-term service in a high temperature environment.

[0081] Comparing the comparative example with the embodiment, it can be seen that the thermal insulation performance of the comparative example is poor, the strength growth is slow in the later stage under high temperature autoclaving, and there is even a phenomenon of strength shrinkage.

[0082] Comparative Example 1 is conventional shotcrete. Since no heat-insulating and heat-resistant materials are added, the thermal conductivity is high and the heat resistance index is low, so it cannot be well applied to high geothermal tunnels.

[0083] Comparative Examples 2 and 3 are shotcrete to which hollow glass microspheres and modified aerogels after gradation optimization are added separately. After being added separately, the thermal insulation performance can be improved to a certain extent, but the thermal conductivity cannot meet the requirement of less than 2.0 W / (m·K).

[0084] Comparative Example 4 is a shotcrete to which hollow glass microspheres are added but without gradation optimization. The microspheres are not densely packed inside the concrete, so the strength and thermal insulation performance are inferior to those of the embodiment.

[0085] Comparative Example 5 is a shotcrete using aerogel that has not been hydrophobically modified. The aerogel has not been hydrophobically modified and is easy to absorb water and agglomerate. After absorbing water, it is easy to cause damage to the internal skeleton. After agglomeration, it is easy to disperse unevenly. Therefore, the thermal conductivity of the prepared shotcrete is relatively high, and the thermal insulation performance is reduced compared with the example.

[0086] Comparative Example 6 is a shotcrete that does not use high-temperature applicable alkali-free accelerators and silica mortar. Although aerogel and hollow glass microspheres improve the thermal insulation performance of concrete, the hydration products generated by ordinary accelerators and cement have poor heat resistance. Therefore, the age strength increases slowly at high temperatures and the overall heat resistance is insufficient.

[0087] Comparative Example 7 is a shotcrete with a high amount of glass beads added. Although the increase in the amount of glass beads can improve the thermal insulation to a certain extent, the rolling effect of the glass beads themselves can easily cause concrete segregation, resulting in a decrease in the strength of the shotcrete.

[0088] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A shotcrete suitable for high geothermal tunnel environment, characterized by: The invention comprises the following raw materials in parts by weight: 400-500 parts of cement, 750-880 parts of coarse aggregate, 300-650 parts of fine aggregate, 110-180 parts of water, 3.5-6.0 parts of admixture, 14-40 parts of hollow glass microspheres, 0.2-0.8 parts of modified hydrophobic aerogel, 20-40 parts of silica mortar, and 30-40 parts of high-temperature adaptable alkali-free quick-setting agent; wherein the hollow glass microspheres are obtained by mixing three hollow glass microspheres with different particle sizes through grading optimization; and wherein the modified hydrophobic aerogel is obtained by a co-precursor method of silicon source A and silicon source B.

2. The shotcrete suitable for high geothermal tunnel environment according to claim 1, characterized in that The hollow glass microspheres are obtained through grading optimization and are divided into three particle sizes: coarse, medium and fine. Among them, the coarse particle size ranges from 0.6mm to 0.8mm, the medium particle size ranges from 0.3mm to 0.6mm, and the fine particle size ranges from 0.02mm to 0.3mm. The proportion of each grade is coarse: medium: fine = 5-7: 1-3: 1-3.

3. The shotcrete suitable for high geothermal tunnel environment according to claim 1, characterized in that The aerogel has a thermal conductivity of less than 0.05 W / m·K and a hydrophobic angle of more than 140°. The silicon source A is at least one of water glass, methyl orthosilicate, and ethyl orthosilicate. The silicon source B is at least one of methyltrimethoxysilane, methyltriethoxysilane, ethoxytrimethylsilane, dimethyldimethoxysilane, trimethyltriethylsilane, and phenyltriethoxysilane.

4. The shotcrete suitable for high geothermal tunnel environment according to claim 1, characterized in that The silica ash slurry is a stable suspension slurry obtained by multi-stage dispersion of silica ash, water and a dispersant, and has a solid content greater than 50%.

5. The shotcrete suitable for high geothermal tunnel environment according to claim 1, characterized in that The cement is P·O42.5 ordinary Portland cement; the fine aggregate is river sand or machine-made sand with a fineness modulus of 2.5 to 3.0; and the coarse aggregate is natural crushed stone with a particle size of 5 mm to 10 mm.

6. The shotcrete suitable for high geothermal tunnel environment according to claim 1, characterized in that The high temperature adaptable alkali-free quick setting agent is compounded by aluminum sulfate, alcohol amine, and reinforcing phase, wherein the alcohol amine includes at least one of ethanolamine, diethanolamine, and triethanolamine, and the reinforcing phase includes at least one of sodium carbonate, magnesium sulfate, sodium sulfate, magnesium fluorosilicate, and sodium fluorosilicate. The initial setting time of the pure slurry (5°C) is ≤5min, the final setting time of the pure slurry (5°C) is ≤10min, and the 28d compressive strength ratio of the mortar (80°C) is ≥90%.

7. The shotcrete suitable for high geothermal tunnel environment according to claim 1, characterized in that The admixture is a polycarboxylic acid high-performance water-reducing agent with a water-reducing rate of ≥25%.

8. A method for preparing shotcrete suitable for a high geothermal tunnel environment according to any one of claims 1 to 7, characterized in that The following steps are involved: (1) Add cement, fine aggregate, coarse aggregate, hollow glass microspheres and aerogel into a mixer and stir for 30 seconds to obtain a dry mix; (2) Add water and admixtures to the dry mix and stir for 3 minutes to obtain a concrete mixture; (3) The mixture is added into the wet spraying equipment, mixed with the accelerating agent and then sprayed onto the sprayed surface to obtain a shotcrete suitable for high geothermal tunnel environment.

9. Application of the shotcrete suitable for high geothermal tunnel environment according to any one of claims 1 to 7 in high geothermal tunnels, high-temperature water-gushing tunnels and underground projects with high geothermal conditions.

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