A thermal insulation material for hard rock tunnels in cold regions, its preparation method and application

Abstract

The present invention relates to the technical field of concrete for hard rock tunnels in cold regions, and specifically discloses a thermal insulation material for hard rock tunnels in cold regions, a preparation method thereof, and an application thereof. The raw materials of the thermal insulation material for hard rock tunnels in cold regions include, by mass, 70-100 parts of cement, 10-14 parts of pretreated silica, 10-16 parts of fly ash, 10-20 parts of thermal insulation aggregate, 100-120 parts of machine-made sand, 0.5-1.2 parts of potassium silicate, 2-2.6 parts of water reducer, 0.1-0.5 parts of defoamer, 1-2 parts of accelerator, and 17-22 parts of water; the pretreated silica is prepared by the following specific operation: adding nylon 66 to a formic acid solution, stirring at 60-80°C for 1-2 hours, adding ethyl orthosilicate and continuing to stir for 10-20 minutes, adding nano-graphene oxide and stirring for 1-2 hours, cooling to 100-80°C, keeping warm for 1-2 hours, and freeze-drying.

Description

Technical Field

[0001] The present invention relates to the technical field of cold region hard rock tunnel concrete, and in particular to a thermal insulation material for cold region hard rock tunnels, a preparation method thereof, and an application thereof. Background Art

[0002] Tunnels offer advantages in overcoming terrain obstacles, shortening distances, and improving the operational quality of land transportation projects. In recent years, tunnels have gradually evolved towards deeper and longer tunnels, and the associated problems have become increasingly prominent.

[0003] my country is increasingly constructing tunnels in cold regions. Due to the large temperature fluctuations in these regions, tunnel lining structures are subject to temperature stresses caused by these large temperature swings. Currently, the main approaches to reducing the thermal conductivity of shotcrete are to extend the heat transfer pathways within the concrete and introduce air pores with low thermal conductivity. For example, fiber-insulated concrete, produced by incorporating low-thermal-conductivity fibers, reduces thermal conductivity by increasing the heat transfer pathways through fiber orientation, but its insulation performance is relatively weak. Lightweight aggregate concrete, produced by incorporating porous lightweight aggregate, can significantly reduce thermal conductivity, but its abundant pores result in poor strength.

[0004] At present, the early hydration rate of shotcrete insulation materials is too fast, which affects the later strength development. In addition, the frost heave force in cold environments can easily cause freeze-thaw damage to the concrete, forming shrinkage cracks, which will not only result in poor insulation effect, but also cause a significant loss of strength and affect durability. Summary of the Invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a thermal insulation material for hard rock tunnels in cold regions, a preparation method thereof and an application thereof.

[0006] A thermal insulation material for hard rock tunnels in cold regions, the raw materials of which include, by mass, 70-100 parts of cement, 10-14 parts of pretreated silica, 10-16 parts of fly ash, 10-20 parts of thermal insulation aggregate, 100-120 parts of machine-made sand, 0.5-1.2 parts of potassium silicate, 2-2.6 parts of water reducer, 0.1-0.5 parts of defoamer, 1-2 parts of accelerating setting agent, and 17-22 parts of water; the pretreated silica adopts The specific preparation operation is as follows: add nylon 66 to formic acid solution, stir at 60-80°C for 1-2 hours, add ethyl orthosilicate and continue stirring for 10-20 minutes, add nano-graphene oxide and stir for 1-2 hours, cool to -100--80°C, keep warm for 1-2 hours, and freeze-dry; the thermal insulation aggregate includes: hydrophobic vitrified microspheres and expanded perlite, and the mass ratio of hydrophobic vitrified microspheres to expanded perlite is 10:1-3.

[0007] Preferably, the mass ratio of nylon 66, tetraethyl orthosilicate, and nano-graphene oxide is 1-5:5-10:1-2.

[0008] Preferably, the mass fraction of the formic acid solution is 70-80%.

[0009] Preferably, the hydrophobic glass microspheres are prepared by the following specific operation: adding the hollow glass microspheres to a sulfuric acid solution, stirring at 40-50°C for 10-20 minutes, filtering, washing, drying, adding to an ammonia solution, stirring at 40-50°C for 10-30 minutes, filtering, washing, drying, adding to an ethanol aqueous solution, adding a fluorinated silane coupling agent thereto, adjusting the pH value of the system to 3-4, stirring at 70-80°C for 1-2 hours, filtering, and drying.

[0010] Preferably, the mass ratio of the hollow glass microspheres to the fluorine-containing silane coupling agent is 10-30:1-2.

[0011] Preferably, the fluorine-containing silane coupling agent is tridecafluorooctyltriethoxysilane or perfluorooctanesulfonylaminopropyltriethoxysilane.

[0012] Preferably, the accelerator is prepared by the following specific operation: aluminum sulfate, citric acid, aluminum hydroxide, early strength agent, dispersant and water are mixed, stirred at 70-90° C. for 1-2 hours, organic alcohol amine is added, stirred for 1-2 hours, and cooled to room temperature.

[0013] Preferably, the mass ratio of aluminum sulfate, citric acid, aluminum hydroxide, early strength agent, dispersant, water and organic alcohol amine is 1-3:0.1-0.5:1-2:1-2:1-2:10-20:1-2.

[0014] Preferably, the organic alcoholamine is at least one of ethanolamine, diethanolamine, and triisopropanolamine.

[0015] Preferably, the early strength agent is calcium formate and / or sodium nitrate.

[0016] Preferably, the dispersant is sodium methylene bisnaphthalene sulfonate.

[0017] The above-mentioned method for preparing the thermal insulation material for hard rock tunnels in cold regions comprises the following steps:

[0018] S1. Stir cement, pretreated silica, fly ash, and thermal insulation aggregate for 50-100 seconds to obtain a premix;

[0019] S2. Add machine-made sand, potassium silicate and water to the premix and mix evenly. Then add water reducer, defoamer and accelerator and stir for 5-15 seconds.

[0020] The above-mentioned method for applying the thermal insulation material for hard rock tunnels in cold regions comprises the following steps: pre-wetting the surface to be sprayed, and then spraying the above-mentioned thermal insulation material for hard rock tunnels in cold regions onto the surface, with a spraying thickness of 30-50 mm.

[0021] Beneficial effects:

[0022] The present invention dissolves nylon 66 in a formic acid solution, deposits and combines nano-silica particles on the PA66 skeleton, and then combines it with the layered structure of nano-graphene oxide. After freeze-drying, an aerogel structure is formed. The aerogel structure not only has a large number of pore structures inside, but also can effectively extend the heat transfer path and greatly reduce the thermal conductivity coefficient. At the same time, it is compounded with cement and has good dispersibility in the slurry, effectively increasing the viscous resistance to floating in the slurry and significantly improving the homogeneity of the mixture.

[0023] The present invention combines the hollow vitrified microspheres with a fluorine-containing silane coupling agent after acid and alkali treatment, which not only has an excellent hydrophobic effect, but also is compounded with pretreated silica and cement to effectively reduce the density and thermal conductivity, improve thermal insulation performance, and make the mortar light and high-strength, thereby improving the workability of the concrete mixture, reducing rebound, and increasing the thickness of a single spraying.

[0024] The pretreated silica obtained by the present invention has a strong water retention and slow-release ability, and plays a role of water slow-release internal curing inside the concrete in the cold eastern region. It not only significantly reduces freeze-thaw damage, reduces the risk of cracking, ensures the later strength development, and improves durability, but also can compensate for shrinkage, reduce cracking, and extend the service life of the tunnel.

[0025] The invention has good construction performance, can be well adapted to hard rock tunnels in cold regions, effectively improves durability and crack resistance, and has a simple preparation method, making it suitable for large-scale promotion and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a comparison chart of the initial setting time and final setting time of the thermal insulation material for hard rock tunnels in cold regions obtained in Example 5 and Comparative Examples 1-2.

[0027] Figure 2 This is a comparison chart of the 1d compressive strength and 28d compressive strength of the insulation materials for hard rock tunnels in cold regions obtained in Example 5 and Comparative Examples 1-2 after standard curing for 28d.

[0028] Figure 3 This is a comparison chart of the thermal conductivity and early-stage autogenous shrinkage of the insulation materials for hard rock tunnels in cold regions obtained in Example 5 and Comparative Examples 1-2 after standard curing.

[0029] Figure 4This is a comparison chart of the strength loss rates of the insulation materials for cold-region hard rock tunnels obtained in Example 5 and Comparative Examples 1-2 after standard curing for 28 days and then freezing and thawing 100 times. DETAILED DESCRIPTION

[0030] The present invention will be further explained below with reference to specific embodiments.

[0031] The parameters of the machine-made sand used are as follows: apparent density 2640 kg / m 3 , bulk density (compact) 1710kg / m 3 , bulk density (loose) 1640kg / m 3 , mud content is 1.60%, water content is 0.36%, grading zone is super 1 zone, fineness modulus is 3.37.

[0032] The polycarboxylate water reducer used below was purchased from Jiangsu Moulait New Materials Co., Ltd., model number M171. The polyether modified silicone defoamer used below was purchased from Qingdao Meiside Silicone Co., Ltd., model number MSD-916.

[0033] The bulk density of the glass beads used below is 125 kg / m 3 The particle size of the expanded perlite used below is 2-3 mm.

[0034] Example 1

[0035] A thermal insulation material for hard rock tunnels in cold regions, comprising raw materials including: 70 kg of PO 42.5 grade ordinary Portland cement, 10 kg of pretreated silica, 10 kg of Class II fly ash, 10 kg of thermal insulation aggregate, 100 kg of machine-made sand, 0.5 kg of potassium silicate, 2 kg of polycarboxylate water reducer, 0.1 kg of polyether-modified organic silicon defoamer, 1 kg of accelerator, and 17 kg of water.

[0036] The pretreated silica was prepared by the following specific operation: 1 kg of nylon 66 was added to 30 kg of 70% formic acid solution, stirred at 60°C for 1 hour, 5 kg of ethyl orthosilicate was added and stirring was continued for 10 minutes, 1 kg of nano-graphene oxide was added and stirred for 1 hour, the temperature was lowered to -100°C, kept warm for 1 hour, and freeze-dried.

[0037] The thermal insulation aggregate is composed of hydrophobic vitrified microspheres and expanded perlite in a mass ratio of 10:1. The hydrophobic vitrified microspheres are prepared using the following specific steps: 10 kg of hollow vitrified microspheres are added to 50 kg of a 70% sulfuric acid solution, stirred at 40°C for 10 minutes, filtered, washed, and dried. The solution is then added to 50 kg of a 10% ammonia solution, stirred at 40°C for 10 minutes, filtered, washed, and dried. The solution is then added to 50 kg of a 30% ethanol solution, to which 1 kg of perfluorooctanesulfonylaminopropyltriethoxysilane is added. The pH of the solution is adjusted to 3-4 with hydrochloric acid, stirred at 70°C for 1 hour at a stirring speed of 1000 rpm, filtered, and dried.

[0038] The accelerator is prepared by the following specific operation: 1 kg of aluminum sulfate, 0.1 kg of citric acid, 1 kg of aluminum hydroxide, 1 kg of calcium formate, 1 kg of sodium methylene bisnaphthalene sulfonate, and 10 kg of water are mixed, stirred at a temperature of 70° C. for 1 hour, 1 kg of ethanolamine is added and stirred for 1 hour, and then cooled to room temperature.

[0039] The above method for preparing thermal insulation materials suitable for hard rock tunnels in cold regions comprises the following steps:

[0040] S1. Add PO 42.5 grade ordinary Portland cement, pretreated silica, grade II fly ash, and thermal insulation aggregate into a mixer and stir at 100 r / min for 50 s to obtain a premix;

[0041] S2. Add machine-made sand, potassium silicate and water to the premix and mix evenly. Then add polycarboxylate water reducer, polyether modified silicone defoamer and accelerator and stir for 5 seconds.

[0042] Example 2

[0043] A thermal insulation material for hard rock tunnels in cold regions, comprising raw materials including: 100 kg of PO 42.5 grade ordinary Portland cement, 14 kg of pretreated silica, 16 kg of Class II fly ash, 20 kg of thermal insulation aggregate, 120 kg of machine-made sand, 1.2 kg of potassium silicate, 2.6 kg of polycarboxylate water reducer, 0.5 kg of polyether-modified organic silicon defoamer, 2 kg of accelerator, and 22 kg of water.

[0044] The pretreated silica was prepared by the following specific operation: 5 kg of nylon 66 was added to 50 kg of 80% formic acid solution, stirred at 80°C for 2 h, 10 kg of ethyl orthosilicate was added and stirring was continued for 20 min, 2 kg of nano-graphene oxide was added and stirred for 2 h, the temperature was lowered to -80°C, kept warm for 2 h, and freeze-dried.

[0045] The thermal insulation aggregate is composed of hydrophobic vitrified microspheres and expanded perlite in a mass ratio of 10:3. The hydrophobic vitrified microspheres are prepared using the following specific steps: 30 kg of hollow vitrified microspheres are added to 100 kg of 80% sulfuric acid solution, stirred at 50°C for 20 minutes, filtered, washed, and dried. The solution is then added to 100 kg of 20% ammonia solution, stirred at 50°C for 30 minutes, filtered, washed, and dried. The solution is then added to 100 kg of 50% ethanol solution, to which 2 kg of tridecafluorooctyltriethoxysilane is added. The pH of the solution is adjusted to 3-4 with hydrochloric acid, stirred at 80°C for 2 hours at a stirring speed of 4000 rpm, filtered, and dried.

[0046] The accelerator is prepared by the following specific operation: 3 kg of aluminum sulfate, 0.5 kg of citric acid, 2 kg of aluminum hydroxide, 2 kg of sodium nitrate, 2 kg of sodium methylene bisnaphthalene sulfonate, and 20 kg of water are mixed, stirred at a temperature of 90° C. for 1-2 hours, 2 kg of diethanolamine is added, stirred for 2 hours, and cooled to room temperature.

[0047] The above method for preparing thermal insulation materials suitable for hard rock tunnels in cold regions comprises the following steps:

[0048] S1. Add PO 42.5 grade ordinary Portland cement, pretreated silica, grade II fly ash, and thermal insulation aggregate into a mixer and stir at 200 r / min for 100 s to obtain a premix;

[0049] S2. Add machine-made sand, potassium silicate and water to the premix and mix evenly. Then add polycarboxylate water reducer, polyether modified silicone defoamer and accelerator and stir for 15 seconds.

[0050] Example 3

[0051] A thermal insulation material for hard rock tunnels in cold regions, comprising raw materials including: 80 kg of PO 42.5 grade ordinary Portland cement, 13 kg of pretreated silica, 12 kg of Class II fly ash, 18 kg of thermal insulation aggregate, 105 kg of machine-made sand, 1 kg of potassium silicate, 2.2 kg of polycarboxylate water reducer, 0.4 kg of polyether-modified organosilicon defoamer, 1.3 kg of accelerator, and 21 kg of water.

[0052] The pretreated silica was prepared by the following specific operation: 2 kg of nylon 66 was added to 45 kg of 73% formic acid solution, stirred at 75°C for 80 min, 9 kg of ethyl orthosilicate was added and stirring was continued for 12 min, 1.7 kg of nano-graphene oxide was added and stirred for 80 min, the temperature was lowered to -85°C, kept warm for 80 min, and freeze-dried.

[0053] The thermal insulation aggregate is composed of hydrophobic vitrified microspheres and expanded perlite in a mass ratio of 10:2.5. The hydrophobic vitrified microspheres are prepared using the following specific steps: 15 kg of hollow vitrified microspheres are added to 90 kg of a 73% sulfuric acid solution, stirred at 48°C for 12 minutes, filtered, washed, and dried. The solution is then added to 90 kg of a 12% ammonia solution, stirred at 48°C for 15 minutes, filtered, washed, and dried. The solution is then added to 90 kg of a 35% ethanol solution, to which 1.7 kg of perfluorooctanesulfonylaminopropyltriethoxysilane is added. The pH of the solution is adjusted to 3-4 with hydrochloric acid, stirred at 73°C for 100 minutes at a stirring speed of 2000 rpm, filtered, and dried.

[0054] The accelerator is prepared by the following specific operation: 2.5 kg of aluminum sulfate, 0.2 kg of citric acid, 1.7 kg of aluminum hydroxide, 1.2 kg of sodium nitrate, 1.7 kg of sodium methylene bisnaphthalene sulfonate, and 12 kg of water are mixed, stirred at a temperature of 85° C. for 80 minutes, 1.7 kg of triisopropanolamine is added, stirred for 80 minutes, and cooled to room temperature.

[0055] The above method for preparing thermal insulation materials suitable for hard rock tunnels in cold regions comprises the following steps:

[0056] S1. Add PO 42.5 grade ordinary Portland cement, pretreated silica, grade II fly ash, and thermal insulation aggregate into a mixer and stir at 180 r / min for 90 s to obtain a premix;

[0057] S2. Add machine-made sand, potassium silicate and water to the premix and mix evenly. Then add polycarboxylate water reducer, polyether modified silicone defoamer and accelerator and stir for 10 seconds.

[0058] Example 4

[0059] A thermal insulation material for hard rock tunnels in cold regions, comprising raw materials including: 90 kg of PO 42.5 grade ordinary Portland cement, 12 kg of pretreated silica, 15 kg of Class II fly ash, 12 kg of thermal insulation aggregate, 115 kg of machine-made sand, 0.6 kg of potassium silicate, 2.4 kg of polycarboxylate water reducer, 0.2 kg of polyether-modified organosilicon defoamer, 1.7 kg of accelerator, and 19 kg of water.

[0060] The pretreated silica was prepared by the following specific operation: 4 kg of nylon 66 was added to 35 kg of 77% formic acid solution, stirred at 65°C for 100 min, 7 kg of ethyl orthosilicate was added and stirring was continued for 18 min, 1.3 kg of nano-graphene oxide was added and stirred for 100 min, the temperature was lowered to -95°C, kept warm for 100 min, and freeze-dried.

[0061] The thermal insulation aggregate is composed of hydrophobic vitrified microspheres and expanded perlite in a mass ratio of 10:1.5. The hydrophobic vitrified microspheres are prepared using the following specific steps: 25 kg of hollow vitrified microspheres are added to 70 kg of a 77% sulfuric acid solution, stirred at 42°C for 18 minutes, filtered, washed, and dried. The solution is then added to 70 kg of an 18% ammonia solution, stirred at 42°C for 25 minutes, filtered, washed, and dried. The solution is then added to 70 kg of a 45% ethanol solution, to which 1.3 kg of tridecafluorooctyltriethoxysilane is added. The pH of the solution is adjusted to 3-4 with hydrochloric acid, stirred at 77°C for 80 minutes at a stirring speed of 3000 rpm, filtered, and dried.

[0062] The accelerator is prepared by the following specific operation: 1.5 kg of aluminum sulfate, 0.4 kg of citric acid, 1.3 kg of aluminum hydroxide, 1.8 kg of calcium formate, 1.3 kg of sodium methylene bisnaphthalene sulfonate, and 18 kg of water are mixed, stirred at a temperature of 75° C. for 100 minutes, 1.3 kg of diethanolamine is added, stirred for 100 minutes, and cooled to room temperature.

[0063] The above method for preparing thermal insulation materials suitable for hard rock tunnels in cold regions comprises the following steps:

[0064] S1. Add PO 42.5 grade ordinary Portland cement, pretreated silica, grade II fly ash, and thermal insulation aggregate into a mixer and stir at 120 r / min for 90 s to obtain a premix;

[0065] S2. Add machine-made sand, potassium silicate and water to the premix and mix evenly. Then add polycarboxylate water reducer, polyether modified silicone defoamer and accelerator and stir for 10 seconds.

[0066] Example 5

[0067] A thermal insulation material for hard rock tunnels in cold regions, comprising raw materials including: 85 kg of PO 42.5 grade ordinary Portland cement, 12.5 kg of pretreated silica, 14.5 kg of Class II fly ash, 15 kg of thermal insulation aggregate, 110 kg of machine-made sand, 0.8 kg of potassium silicate, 2.3 kg of polycarboxylate water reducer, 0.3 kg of polyether-modified organic silicon defoamer, 1.5 kg of accelerator, and 20 kg of water.

[0068] The pretreated silica was prepared by the following specific operation: 3 kg of nylon 66 was added to 40 kg of 75% formic acid solution, stirred at 70°C for 90 min, 8 kg of ethyl orthosilicate was added and stirred for 15 min, 1.5 kg of nano-graphene oxide was added and stirred for 90 min, the temperature was lowered to -90°C, kept warm for 90 min, and freeze-dried.

[0069] The thermal insulation aggregate is composed of hydrophobic vitrified microspheres and expanded perlite in a mass ratio of 10:2. The hydrophobic vitrified microspheres are prepared using the following specific steps: 20 kg of hollow vitrified microspheres are added to 80 kg of a 75% sulfuric acid solution, stirred at 45°C for 15 minutes, filtered, washed, and dried. The solution is then added to 80 kg of a 15% ammonia solution, stirred at 45°C for 20 minutes, filtered, washed, and dried. The solution is then added to 80 kg of a 40% ethanol solution, to which 1.5 kg of perfluorooctanesulfonylaminopropyltriethoxysilane is added. The pH of the solution is adjusted to 3-4 with hydrochloric acid, stirred at 75°C for 90 minutes at a stirring speed of 2500 rpm, filtered, and dried.

[0070] The accelerator is prepared by the following specific operation: 2 kg of aluminum sulfate, 0.3 kg of citric acid, 1.5 kg of aluminum hydroxide, 1.5 kg of calcium formate, 1.5 kg of sodium methylene bisnaphthalene sulfonate, and 15 kg of water are mixed, stirred at a temperature of 80° C. for 90 minutes, 1.5 kg of triisopropanolamine is added, stirred for 90 minutes, and then cooled to room temperature.

[0071] The above method for preparing thermal insulation materials suitable for hard rock tunnels in cold regions comprises the following steps:

[0072] S1. Add PO 42.5 grade ordinary Portland cement, pretreated silica, grade II fly ash, and thermal insulation aggregate into a mixer and stir at 150 r / min for 90 s to obtain a premix;

[0073] S2. Add machine-made sand, potassium silicate and water to the premix and mix evenly. Then add polycarboxylate water reducer, polyether modified silicone defoamer and accelerator and stir for 10 seconds.

[0074] Comparative Example 1

[0075] Ordinary shotcrete insulation material

[0076] A thermal insulation material for hard rock tunnels in cold regions, the raw materials of which include: 85 kg of PO 42.5 grade ordinary Portland cement, 12.5 kg of silicon dioxide (i.e., silica fume, purchased from Shijiazhuang Baijiang Mineral Products Co., Ltd., 1250 mesh), 14.5 kg of Class II fly ash, 15 kg of thermal insulation aggregate, 110 kg of machine-made sand, 0.8 kg of potassium silicate, 2.3 kg of polycarboxylic acid water reducer, 0.3 kg of polyether modified silicone defoamer, 1.5 kg of alkali-free liquid accelerator (purchased from Jiangsu Moulait New Materials Co., Ltd., model SL15), and 20 kg of water.

[0077] The thermal insulation aggregate is composed of vitrified microspheres and expanded perlite in a mass ratio of 10:2.

[0078] The above method for preparing thermal insulation materials suitable for hard rock tunnels in cold regions comprises the following steps:

[0079] S1. Add PO 42.5 grade ordinary Portland cement, silicon dioxide, grade II fly ash, and thermal insulation aggregate into a mixer and stir at 150 r / min for 90 s to obtain a premix;

[0080] S2. Add machine-made sand, potassium silicate and water to the premix and mix evenly. Then add polycarboxylate water reducer, polyether modified silicone defoamer and accelerator and stir for 10 seconds.

[0081] Comparative Example 2

[0082] A thermal insulation material for hard rock tunnels in cold regions, comprising raw materials including: 85 kg of PO 42.5 grade ordinary Portland cement, 6.99 kg of pretreated silica, 14.5 kg of Class II fly ash, 5.51 kg of nylon 66, 15 kg of thermal insulation aggregate, 110 kg of machine-made sand, 0.8 kg of potassium silicate, 2.3 kg of polycarboxylate water reducer, 0.3 kg of polyether-modified organic silicon defoamer, 1.5 kg of accelerator, and 20 kg of water.

[0083] The pretreated silica was prepared by the following specific operation: 8 kg of ethyl orthosilicate was added to 40 kg of 75% formic acid solution and stirred for 15 min, 1.5 kg of nano-graphene oxide was added and stirred for 90 min, the mixture was cooled to -90°C, kept warm for 90 min, and freeze-dried.

[0084] The thermal insulation aggregate is composed of hydrophobic vitrified microspheres and expanded perlite in a mass ratio of 10:2. The hydrophobic vitrified microspheres are prepared using the following specific steps: 20 kg of hollow vitrified microspheres are added to 80 kg of a 75% sulfuric acid solution, stirred at 45°C for 15 minutes, filtered, washed, and dried. The solution is then added to 80 kg of a 15% ammonia solution, stirred at 45°C for 20 minutes, filtered, washed, and dried. The solution is then added to 80 kg of a 40% ethanol solution, to which 1.5 kg of perfluorooctanesulfonylaminopropyltriethoxysilane is added. The pH of the solution is adjusted to 3-4 with hydrochloric acid, stirred at 75°C for 90 minutes at a stirring speed of 2500 rpm, filtered, and dried.

[0085] The accelerator is prepared by the following specific operation: 2 kg of aluminum sulfate, 0.3 kg of citric acid, 1.5 kg of aluminum hydroxide, 1.5 kg of calcium formate, 1.5 kg of sodium methylene bisnaphthalene sulfonate, and 15 kg of water are mixed, stirred at a temperature of 80° C. for 90 minutes, 1.5 kg of triisopropanolamine is added, stirred for 90 minutes, and then cooled to room temperature.

[0086] The above method for preparing thermal insulation materials suitable for hard rock tunnels in cold regions comprises the following steps:

[0087] S1. Add PO 42.5 grade ordinary Portland cement, pretreated silica, grade II fly ash, thermal insulation aggregate and nylon 66 into a mixer and stir at 150 r / min for 90 seconds to obtain a premix;

[0088] S2. Add machine-made sand, potassium silicate and water to the premix and mix evenly. Then add polycarboxylate water reducer, polyether modified silicone defoamer and accelerator and stir for 10 seconds.

[0089] The fluidity of the thermal insulation materials for cold-region hard rock tunnels obtained in Example 5 and Comparative Examples 1-2 was measured using a cement mortar fluidity tester with reference to GB / T 2419-2005, "Determination of Fluidity of Cement Mortar." The fluidity of the thermal insulation materials for cold-region hard rock tunnels obtained in Example 5 and Comparative Examples 1-2 was 230 mm, the fluidity of the thermal insulation materials for cold-region hard rock tunnels obtained in Comparative Example 1 was 205 mm, and the fluidity of the thermal insulation materials for cold-region hard rock tunnels obtained in Comparative Example 2 was 220 mm. All three materials were greater than 200 mm, making them suitable for use as shotcrete.

[0090] The initial setting time and final setting time of the thermal insulation materials for hard rock tunnels in cold regions obtained in Example 5 and Comparative Examples 1-2 were tested with reference to the corresponding testing methods in JC477-2005 "Accelerators for Shotcrete".

[0091] like Figure 1 As shown, the initial setting time and final setting time of the thermal insulation material for hard rock tunnels in cold regions obtained in Example 5 are both the shortest, which are better than those of Comparative Examples 1-2 (P < 0.05).

[0092] Referring to GB / T 17671-2021, "Test Method for Cement Mortar Strength (ISO Method)," the insulation materials for cold-region hard rock tunnels obtained in Example 5 and Comparative Examples 1-2 were cast into 40 mm × 40 mm × 160 mm specimens. These specimens were then cured for 28 days. Compressive strength tests were performed on the specimens after curing for 1 and 28 days.

[0093] like Figure 2 As shown, the 1d compressive strength and 28d compressive strength of the thermal insulation material for hard rock tunnels in cold regions obtained in Example 5 are both the highest, which are better than those of Comparative Examples 1-2 (P < 0.05), and the 1d compressive strength of the thermal insulation material for hard rock tunnels in cold regions obtained in Example 5 can reach more than 80% of the 28d compressive strength, which proves that the early strength of the thermal insulation material for hard rock tunnels in cold regions obtained in Example 5 is high.

[0094] With reference to ISO 22007-2:2015, the transient flat plate heat source method was used to measure the thermal conductivity of the concrete specimens in the above groups after 28 days of standard curing.

[0095] According to T / CECS 864-2021 "Standard for Test Methods of Ultra-High Performance Concrete", the early-age autogenous shrinkage of the above-mentioned groups of standard cured concrete specimens was measured.

[0096] like Figure 3 As shown, the thermal conductivity of the thermal insulation material for hard rock tunnels in cold regions obtained in Example 5 is the lowest, and its thermal insulation effect is the best, which is better than that of comparative examples 1-2 (P < 0.05); the early-age autogenous shrinkage of the thermal insulation material for hard rock tunnels in cold regions obtained in Example 5 is the smallest, which proves that it can reduce the risk of cracking.

[0097] The concrete samples from each group were tested for impermeability after 28 days of standard curing in accordance with GB 50164-2011, "Concrete Quality Control Standard." The concrete obtained in Example 5 had an impermeability grade exceeding P20, while the concrete obtained in Comparative Example 1 had an impermeability grade of P15 and the concrete obtained in Comparative Example 2 had an impermeability grade of P17.

[0098] After 28 days of standard curing, the concrete specimens of each group were immersed in 20±2℃ water for 4 days, with the water surface 25.0±5.0mm higher than the top surface of the specimen. After the immersion, the specimens were taken out and the moisture on the surface of the specimens was wiped off. The external dimensions were measured and weighed. Each specimen was placed in a specimen box and then placed in a freeze-thaw chamber, with a 20mm gap between the specimen and the wall of the specimen box. In the quick freezing test, clean water should be injected into the specimen box, with the water surface 50mm higher than the specimen. When the temperature in the freeze-thaw chamber dropped to -18℃, the timing began. The freezing time in each freeze-thaw cycle was 4h. After the freezing was completed, water at a temperature of 19.0±1.0℃ was immediately added within 10min. The water surface was at least 20mm higher than the specimen, and the thawing time was 4h. After thawing, the freeze-thaw cycle was considered to be over and the next freeze-thaw cycle could be carried out.

[0099] The freeze-thaw test was stopped after 100 freeze-thaw cycles, the compressive strength of the specimens was tested, and the strength loss rate was calculated.

[0100] Strength loss rate = 1-compressive strength of sample after 100 freeze-thaw cycles ÷ original compressive strength of sample × 100%

[0101] like Figure 3 As shown, the thermal insulation material for cold region hard rock tunnels obtained in Example 5 has the lowest strength loss rate and the best freeze-thaw resistance effect, which is better than that of Comparative Examples 1-2 (P < 0.05).

[0102] The applicant believes that this is due to the fact that the present invention dissolves nylon 66 (PA66) in a formic acid solution, deposits and binds nano-silica particles on the PA66 skeleton, and then combines them with the lamellar structure of nano-graphene oxide. This aerogel structure is freeze-dried to form an aerogel structure, which not only has a large number of pores within it but also effectively extends the heat transfer path, significantly reducing the thermal conductivity. Furthermore, when compounded with cement, it has good dispersibility in the slurry, effectively increasing the viscous resistance to floating in the slurry and significantly improving the homogeneity of the mixture. The present invention further combines hollow vitrified microspheres after acid and alkali treatment with a fluorinated silane coupling agent, resulting in not only excellent hydrophobicity but also, when compounded with pretreated silica and cement, effectively reducing density and thermal conductivity, improving thermal insulation properties, and making the mortar lightweight and high-strength. This improves the workability of the concrete mix, reduces rebound, and increases the thickness of a single shot. Since the pretreated silica obtained by the present invention has a strong water retention and slow-release ability, it plays a role of water slow-release internal curing inside the concrete in the cold eastern zone, which not only significantly reduces freeze-thaw damage, reduces the risk of cracking, ensures the later strength development, and improves durability, but also can compensate for shrinkage, reduce cracking, and extend the service life of the tunnel.

[0103] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A thermal insulation material for hard rock tunnels in cold regions, characterized in that: The raw materials include, by mass: 70-100 parts of cement, 10-14 parts of pretreated silica, 10-16 parts of fly ash, 10-20 parts of thermal insulation aggregate, 100-120 parts of machine-made sand, 0.5-1.2 parts of potassium silicate, 2-2.6 parts of water reducer, 0.1-0.5 parts of defoamer, 1-2 parts of accelerating setting agent, and 17-22 parts of water; The pretreated silica was prepared by the following specific operation: adding nylon 66 to a formic acid solution, stirring at 60-80°C for 1-2 hours, adding ethyl orthosilicate and continuing to stir for 10-20 minutes, adding nano-graphene oxide and stirring for 1-2 hours, cooling to -100 to -80°C, keeping warm for 1-2 hours, and freeze-drying; The thermal insulation aggregate comprises: hydrophobic vitrified microspheres and expanded perlite, and the mass ratio of the hydrophobic vitrified microspheres to the expanded perlite is 10:1-3.

2. The thermal insulation material for hard rock tunnels in cold regions according to claim 1, characterized in that: The mass ratio of nylon 66, ethyl orthosilicate and nano-graphene oxide is 1-5:5-10:1-2.

3. The thermal insulation material for hard rock tunnels in cold regions according to claim 1, characterized in that: The mass fraction of the formic acid solution is 70-80%.

4. The thermal insulation material for hard rock tunnels in cold regions according to claim 1, characterized in that: The hydrophobic glass microspheres are prepared by the following specific operation: adding the hollow glass microspheres to a sulfuric acid solution, stirring at 40-50°C for 10-20 minutes, filtering, washing, and drying, adding them to an ammonia solution, stirring at 40-50°C for 10-30 minutes, filtering, washing, and drying, adding them to an ethanol aqueous solution, adding a fluorinated silane coupling agent thereto, adjusting the pH value of the system to 3-4, stirring at 70-80°C for 1-2 hours, filtering, and drying.

5. The thermal insulation material for hard rock tunnels in cold regions according to claim 4, characterized in that: The mass ratio of the hollow glass microspheres to the fluorine-containing silane coupling agent is 10-30:1-2.

6. The thermal insulation material for hard rock tunnels in cold regions according to claim 4, characterized in that: The fluorine-containing silane coupling agent is tridecafluorooctyl triethoxysilane or perfluorooctanesulfonylaminopropyl triethoxysilane.

7. The thermal insulation material for hard rock tunnels in cold regions according to claim 1, characterized in that: The quick-setting agent is prepared by the following specific operation: aluminum sulfate, citric acid, aluminum hydroxide, early strength agent, dispersant and water are mixed, stirred at 70-90° C. for 1-2 hours, organic alcohol amine is added and stirred for 1-2 hours, and then cooled to room temperature.

8. The thermal insulation material for hard rock tunnels in cold regions according to claim 7, characterized in that: The mass ratio of aluminum sulfate, citric acid, aluminum hydroxide, early strength agent, dispersant, water and organic alcohol amine is 1-3:0.1-0.5:1-2:1-2:1-2:10-20:1-2; The organic alcoholamine is at least one of ethanolamine, diethanolamine, and triisopropanolamine; The early strength agent is calcium formate and / or sodium nitrate; The dispersant is sodium methylene bisnaphthalene sulfonate.

9. A method for preparing a thermal insulation material for a hard rock tunnel in cold regions according to any one of claims 1 to 8, characterized in that: The steps include: S1. Stir cement, pretreated silica, fly ash, and thermal insulation aggregate for 50-100 seconds to obtain a premix; S2. Add machine-made sand, potassium silicate and water to the premix and mix evenly. Then add water reducer, defoamer and accelerator and stir for 5-15 seconds.

10. A method for applying the thermal insulation material for hard rock tunnels in cold regions according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: pre-wetting the surface to be sprayed, and then spraying the thermal insulation material for hard rock tunnels in cold regions as claimed in any one of claims 1 to 8 onto the surface, with a spraying thickness of 30 to 50 mm.

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