A heat-insulating and heat-resistant shotcrete and its preparation method

Abstract

This invention discloses a heat-insulating and heat-resistant shotcrete and its preparation method. This heat-insulating and heat-resistant shotcrete is composed of cement, modified silica mortar, modified heat-insulating ceramsite, fine aggregate, water, admixtures, and accelerators. In this invention, high-strength shale ceramsite with surface modification using hydrogel is introduced as a heat-insulating filler, significantly improving the dispersion and stability of lightweight aggregate in the mortar. It also possesses strong water absorption and slow-release capabilities and surface sealing functions, enabling it to provide pore insulation and internal curing through water storage and release in high-temperature environments. The addition of modified silica mortar, which effectively improves the high-temperature stability and density of the mortar hydration products, comprehensively enhances the homogeneity of the shotcrete mixture, the heat insulation performance of the hardened body, and the strength development and durability under high-temperature conditions. This effectively improves tunnel chamber temperature and extends the service life of the shotcrete under high-temperature conditions. The heat-insulating and heat-resistant shotcrete technology has a clear working mechanism, simple production process, and excellent performance. It is suitable for large-scale production and is of great significance for the high-quality construction of underground projects such as tunnels and mines in high-temperature and high-temperature water inrush environments.

Description

Technical Field

[0001] This invention belongs to the field of concrete materials, specifically relating to the preparation of heat-insulating and heat-resistant shotcrete and its application in underground engineering in high geothermal environments. Background Technology

[0002] How to reduce the construction temperature of the tunnel and improve the heat insulation and high temperature resistance of shotcrete is a technical problem that urgently needs to be solved in the construction of high geothermal tunnels.

[0003] The reduction of thermal conductivity in shotcrete is mainly achieved by extending the internal heat transfer pathways of the concrete and introducing air pores with low thermal conductivity. Conventional techniques include foamed concrete (incorporating foam), fiber-reinforced insulating concrete (incorporating low thermal conductivity fibers), and lightweight aggregate concrete (incorporating porous lightweight aggregates). Among these, foamed concrete has the lowest thermal conductivity, but due to its numerous pores, it has poor strength and weak support, making it only suitable for non-load-bearing components and some infill applications. Fiber-reinforced insulating concrete primarily reduces thermal conductivity by increasing the heat transfer pathways through fiber orientation, making it difficult to control and resulting in weaker insulation performance. Therefore, introducing high-strength lightweight aggregates with porous structures to create lightweight, high-strength, and insulating concrete has become the preferred method for preparing concrete with structural support properties.

[0004] Currently, researchers have conducted studies on heat-insulating shotcrete or heat-insulating cast-in-place concrete for high geothermal tunnel environments. For example, patent CN113045260B discloses a high-strength heat-insulating ceramsite concrete, which improves the heat insulation and overall performance of the concrete by modifying ceramsite with fiber. Patent CN102718443B discloses a double-blended ceramsite shotcrete for tunnel high-temperature rock surfaces, which improves the stability and performance of ceramsite concrete by compounding polypropylene fiber and ceramsite. Patent CN116283145A discloses a high-strength, high-toughness heat-insulating functional shotcrete, which effectively improves its mechanical properties and bond strength and reduces the heat transfer coefficient by 35% by adding special admixtures and steel fibers. Patent CN116903336A discloses a lightweight corn cob shotcrete material, which forms a fiber-type heat-insulating concrete paste by adding modified corn cob aggregate, and forms a hardened concrete body with a large number of small pores, exhibiting good heat insulation and mechanical properties.

[0005] While some progress has been made in the research and development of the aforementioned materials and technologies, several challenges remain. First, the density of lightweight aggregates in insulating concrete is significantly lower than that of the paste, leading to a tendency for them to rise to the surface and resulting in uneven distribution of the mixture and hardened material. This is particularly pronounced in shotcrete, which has a high fluidity and is formed by jet molding. Second, shotcrete exhibits significant rebound during the jet molding process, with aggregates rebounding much more than the paste. This has a substantial impact on insulating shotcrete, which relies heavily on aggregates for its insulating structure. Third, high geothermal conditions can cause long-term water loss and microstructural damage in concrete, leading to decreased strength and even cracking. Therefore, improving the homogeneity of insulating shotcrete, reducing rebound loss, minimizing heat conduction and thermal damage, and developing high-performance, heat-resistant insulating shotcrete are crucial for the advancement of related technologies and the industry. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned problems, provide a heat-insulating and heat-resistant shotcrete, and provide its preparation and application methods.

[0007] The heat-insulating and heat-resistant shotcrete of this invention is prepared from the following components in the following mass ratio: 400-480 parts cement, 50-100 parts modified silica fume slurry, 325-400 parts modified heat-insulating ceramsite, 800-975 parts fine aggregate, 4-5.5 parts admixture, 120-170 parts water, and 25-40 parts quick-setting agent; wherein the modified silica fume slurry is a mixture of silica fume and nano-CSH crystal nuclei; wherein the modified heat-insulating ceramsite is obtained by surface grafting modification of high-strength shale ceramsite using a hydrogel precursor, wherein the thickness of the hydrogel modification layer is 50-70 μm; the hydrogel precursor is prepared by using unsaturated carboxylic acid monomers and unsaturated silane monomers in a solvent. The surface-modified precursor obtained by polymerization has a viscosity of 350~550 mPa·s, wherein the molar ratio of unsaturated carboxylic acid monomers to unsaturated silane monomers is 1:(0.005~0.05), wherein the unsaturated carboxylic acid monomers are at least one of acrylic acid, methacrylic acid, fumaric acid, itaconic acid, and acrylamide, and wherein the unsaturated silane monomers are at least one of γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, vinyltritert-butoxysilane, and vinyltriacetoxysilane.

[0008] The cement used in this heat-insulating and heat-resistant shotcrete is ordinary Portland cement with a strength grade of 42.5; the fine aggregate is river sand or manufactured sand with a fineness modulus of 2.3~3.0. The admixture is a high-performance admixture formulated with polycarboxylate superplasticizer and functional additives, with a water reduction rate of 28%~33%, wherein the functional additive is at least one of a retarder, air-entraining agent, defoamer, and thickener. The accelerator is a fluorine-free and alkali-free accelerator, with an initial setting time of ≤3min, a final setting time of ≤5min, and a mortar strength ≥1MPa after 6 hours.

[0009] The modified silica fume slurry in this heat-insulating and heat-resistant shotcrete is a suspended stable slurry prepared by multi-stage efficient dispersion of silica fume and nano-CSH crystal nuclei in water at a mass ratio of 3:1, with a mass concentration of 50%. The silica fume is dense silica fume with an SiO2 content greater than 90%.

[0010] The high-strength shale ceramsite in this heat-insulating and heat-resistant shotcrete has a particle size of 5-10 mm and a bulk density of 500-700 kg / m³. 3 The cylinder compressive strength is above 6MPa.

[0011] The preparation method of the modified heat-insulating ceramsite in this heat-insulating and heat-resistant shotcrete is as follows:

[0012] (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in a strong alkaline solution for 2-4 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite.

[0013] (2) Add unsaturated carboxylic acid, unsaturated silane, chain transfer agent, initiator and solvent into a reaction vessel and mix evenly. Stir the solution at 60-80℃ for 1-3 hours. After the reaction is completed, add rheology modifier to adjust the liquid viscosity to 350-550 mPa·s to obtain the hydrogel surface modification precursor.

[0014] (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor. After the ceramic particles were fully wetted, they were slowly and steadily removed. After the excess hydrogel precursor on the surface was naturally drained, the ceramic particles were placed in a constant temperature and humidity environment of 50℃ and 90%RH for 24 hours to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles.

[0015] The strong alkaline solution in the preparation method is at least one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and ammonia solution; the chain transfer agent is (3-mercaptopropyl)trimethoxysilane, and the amount used is 0.1%-1% of the monomer amount; the initiator is at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dicumyl peroxide, and di-tert-butyl peroxide, and the amount used is 0.1%-1% of the monomer amount; the solvent is at least one of methanol, ethanol, isopropanol, n-butanol, tert-butanol, tetrahydrofuran, dioxane, dimethylformamide, and dimethyl sulfoxide; the rheology modifier is at least one of xanthan gum, guar gum, styrax, polyethylene glycol 2000, and cellulose ether.

[0016] The preparation method of this heat-insulating and heat-resistant shotcrete includes the following steps: cement, fine aggregate, modified heat-insulating ceramsite, and modified silica fume are added to a mixer and stirred for 30 seconds. Then, water and admixtures are added and stirred for 3 minutes to obtain a concrete mixture. The mixture is then added to a wet spraying equipment and sprayed together with a quick-setting agent to the target area to obtain the heat-insulating and heat-resistant shotcrete.

[0017] This heat-insulating and heat-resistant shotcrete can be used as a heat-insulating support structure in high-temperature tunnels, high-temperature water inrush tunnels, high-geothermal mines, and related underground engineering projects.

[0018] The positive effects of the heat-insulating and heat-resistant shotcrete of the present invention are:

[0019] The heat-insulating and heat-resistant shotcrete prepared in this invention uses high-strength shale ceramsite with hydrogel surface modification as aggregate. Compared with conventional technology, ceramsite with a hydrogel-modified surface layer has the following three advantages: (1) Stronger dispersion performance in the slurry. Due to the polyelectrolyte layer on the surface, its compatibility and affinity with the slurry are better, the viscous resistance to floating in the slurry is increased, and the homogeneity of the mixture is significantly improved; (2) Stronger hydrophilic water absorption capacity. Water absorption can be completed during mixing without pre-wetting process. In addition, the hydrogel layer gives the ceramsite a strong water retention and slow-release capacity, which can play an effective role in slow-release internal curing of water in concrete under high geothermal environment, preventing concrete damage caused by rapid water loss due to high temperature; (3) The surface hydrogel layer can effectively prevent fine particles from entering the pores of the ceramsite, and prevent the increase of thermal conductivity of the hardened body caused by the pores being filled and blocked by particles.

[0020] In addition, modified silica fume slurry is added to the heat-insulating and heat-resistant shotcrete. Compared with powdered silica fume, silica fume slurry dispersed by an efficient dispersion process has significantly improved dispersion performance in the mixture. On the one hand, it improves the workability of the slurry and further prevents the floating process of the heat-insulating filler. On the other hand, due to the addition of CSH crystal nuclei and silica fume compounding, it can induce the production of a large amount of heat-resistant calcium silicate products in the early stage, effectively preventing thermal damage caused by the thermal decomposition of hydration products such as AFt, and improving the performance of concrete throughout its entire lifespan in high geothermal environments.

[0021] As can be seen from the above description, the technology has a clear mechanism of action, a simple production process, and excellent performance, making it suitable for large-scale production. It is of great significance for expanding the application scope of thermally insulated shotcrete structures in high geothermal environments. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to specific embodiments.

[0023] Example 1: A heat-insulating and heat-resistant shotcrete, the preparation process of which is as follows:

[0024] (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in sodium hydroxide solution for 3 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite.

[0025] (2) 360 parts of acrylic acid, 355 parts of acrylamide, 37.2 parts of γ-methacryloxypropyltrimethoxysilane, 5 parts of (3-mercaptopropyl)trimethoxysilane, 3.5 parts of azobisisobutyronitrile and 4000 parts of ethanol were added to a container and mixed evenly. The solution was stirred and reacted at 75°C for 2 hours. After the reaction was completed, cellulose ether was added to adjust the liquid viscosity to 350~550 mPa·s to obtain the hydrogel surface modification precursor a1.

[0026] (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor a1. After the ceramic particles were completely immersed for 30 minutes, they were slowly and steadily removed. After the excess hydrogel precursor on the surface was naturally drained, the ceramic particles were placed in a constant temperature and humidity environment of 50℃ and 90%RH for 24 hours to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles A1.

[0027] Add 450 parts of PO 42.5 grade ordinary Portland cement, 837 parts of river sand fine aggregate, 370 parts of modified heat-insulating ceramsite A1, and 60 parts of modified silica fume to a mixer and mix for 30 seconds. Then add 157 parts of water and 4.5 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 36 parts of alkali-free quick-setting agent to the target area to obtain heat-insulating and heat-resistant shotcrete.

[0028] Example 2: A heat-insulating and heat-resistant shotcrete, the preparation process of which is as follows:

[0029] (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in potassium hydroxide solution for 3 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite.

[0030] (2) 720 parts of acrylic acid, 58 parts of γ-methacryloxypropyltriethoxysilane, 6.2 parts of (3-mercaptopropyl)trimethoxysilane, 5.6 parts of azobisisoheptanenitrile and 4200 parts of tetrahydrofuran were added to a container and mixed evenly. The solution was stirred and reacted at 75°C for 2.5 h. After the reaction was completed, xanthan gum was added to adjust the liquid viscosity to 350~550 mPa·s to obtain hydrogel surface modification precursor a2.

[0031] (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor a2. After the ceramic particles were completely immersed for 30 minutes, they were slowly and steadily removed. After the excess hydrogel precursor on the surface was naturally drained, the ceramic particles were placed in a constant temperature and humidity environment of 50℃ and 90%RH for 24 hours to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles A2.

[0032] Add 420 parts of PO 42.5 grade ordinary Portland cement, 872 parts of river sand fine aggregate, 355 parts of modified heat-insulating ceramsite A2, and 90 parts of modified silica fume to a mixer and mix for 30 seconds. Then add 150 parts of water and 5 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 30 parts of alkali-free quick-setting agent to the target area to obtain heat-insulating and heat-resistant shotcrete.

[0033] Example 3: A heat-insulating and heat-resistant shotcrete, the preparation process of which is as follows:

[0034] (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in sodium hydroxide solution for 2 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite.

[0035] (2) 860 parts of methacrylic acid, 66.6 parts of vinyltrimethoxysilane, 4.6 parts of (3-mercaptopropyl)trimethoxysilane, 3.2 parts of benzoyl peroxide and 4500 parts of isopropanol were added to a container and mixed evenly. The solution was stirred and reacted at 70°C for 3 hours. After the reaction was completed, warm sizing agent was added to adjust the liquid viscosity to 350~550 mPa·s to obtain hydrogel surface modification precursor a3;

[0036] (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor a3. After the ceramic particles were completely immersed for 30 minutes, they were slowly and steadily removed. After the excess hydrogel precursor on the surface was naturally drained, the ceramic particles were placed in a constant temperature and humidity environment of 50℃ and 90%RH for 24 hours to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles A3.

[0037] Add 470 parts of PO 42.5 grade ordinary Portland cement, 850 parts of river sand fine aggregate, 360 parts of modified heat-insulating ceramsite A3, and 50 parts of modified silica fume to a mixer and mix for 30 seconds. Then add 171 parts of water and 5.2 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 30 parts of alkali-free quick-setting agent to the target area to obtain heat-insulating and heat-resistant shotcrete.

[0038] Example 4: A heat-insulating and heat-resistant shotcrete, the preparation process of which is as follows:

[0039] (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in sodium hydroxide solution for 3 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite.

[0040] (2) 430 parts of methacrylic acid, 355 parts of acrylamide, 29 parts of γ-methacryloxypropyltriethoxysilane, 5.7 parts of (3-mercaptopropyl)trimethoxysilane, 2.9 parts of azobisisobutyronitrile and 4000 parts of ethanol were added to a container and mixed evenly. The solution was stirred and reacted at 70°C for 2.5 h. After the reaction was completed, cellulose ether was added to adjust the liquid viscosity to 350~550 mPa·s to obtain hydrogel surface modification precursor a4.

[0041] (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor a4. After the ceramic particles were completely immersed for 30 minutes, they were slowly and steadily removed. After the excess hydrogel precursor on the surface was naturally drained, the ceramic particles were placed in a constant temperature and humidity environment of 50℃ and 90%RH for 24 hours to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles A4.

[0042] Add 440 parts of PO 42.5 grade ordinary Portland cement, 935 parts of river sand fine aggregate, 325 parts of modified heat-insulating ceramsite A4, and 60 parts of modified silica fume slurry to a mixer and mix for 30 seconds. Then add 155 parts of water and 4.3 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 33 parts of alkali-free quick-setting agent to the target area to obtain heat-insulating and heat-resistant shotcrete.

[0043] Example 5: A heat-insulating and heat-resistant shotcrete, the preparation process of which is as follows:

[0044] (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in ammonia water for 2-4 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite.

[0045] (2) 1160 parts of fumaric acid, 66.5 parts of vinyltriethoxysilane, 4.9 parts of (3-mercaptopropyl)trimethoxysilane, 3.1 parts of benzoyl peroxide and 4200 parts of dioxane solvent were added to a reaction vessel and mixed evenly. The solution was stirred and reacted at 75°C for 3 hours. After the reaction was completed, polyethylene glycol 2000 was added to adjust the liquid viscosity to 350~550 mPa·s to obtain hydrogel surface modification precursor a5;

[0046] (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor a5. After the ceramic particles were completely immersed for 30 minutes, they were slowly and steadily removed. After the excess hydrogel precursor on the surface was naturally drained, the ceramic particles were placed in a constant temperature and humidity environment of 50℃ and 90%RH for 24 hours to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles A5.

[0047] Add 460 parts of PO 42.5 grade ordinary Portland cement, 863 parts of river sand fine aggregate, 360 parts of modified heat-insulating ceramsite A5, and 70 parts of modified silica fume to a mixer and mix for 30 seconds. Then add 164 parts of water and 4.5 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 32 parts of alkali-free quick-setting agent to the target area to obtain heat-insulating and heat-resistant shotcrete.

[0048] Example 6: A heat-insulating and heat-resistant shotcrete, the preparation process of which is as follows:

[0049] (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in sodium hydroxide solution for 4 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite.

[0050] (2) 360 parts of acrylic acid, 580 parts of fumaric acid, 25.8 parts of vinyltritert-butoxysilane, 4.3 parts of (3-mercaptopropyl)trimethoxysilane, 3.5 parts of azobisisoheptanenitrile and 5000 parts of methanol were added to a reaction vessel and mixed evenly. The solution was stirred and reacted at 80°C for 2.5 h. After the reaction was completed, cellulose ether was added to adjust the liquid viscosity to 350~550 mPa·s to obtain the hydrogel surface modification precursor a6.

[0051] (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor a6. After the ceramic particles were completely immersed for 30 minutes, they were slowly and steadily removed. After the excess hydrogel precursor on the surface was naturally drained, the ceramic particles were placed in a constant temperature and humidity environment of 50℃ and 90%RH for 24 hours to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles A6.

[0052] Add 460 parts of PO 42.5 grade ordinary Portland cement, 845 parts of river sand fine aggregate, 365 parts of modified heat-insulating ceramsite A6, and 65 parts of modified silica fume to a mixer and mix for 30 seconds. Then add 165 parts of water and 5 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 34 parts of alkali-free quick-setting agent to the target area to obtain heat-insulating and heat-resistant shotcrete.

[0053] Example 7: A heat-insulating and heat-resistant shotcrete, the preparation process of which is as follows:

[0054] (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in potassium hydroxide solution for 3 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite.

[0055] (2) 1300 parts itaconic acid, 29 parts γ-methacryloxypropyltriethoxysilane, 19 parts vinyltriethoxysilane, 6.7 parts (3-mercaptopropyl)trimethoxysilane, 4.7 parts azobisisobutyronitrile and 4100 parts ethanol were added to a reaction vessel and mixed evenly. The solution was stirred at 80°C for 1.5 h. After the reaction was completed, polyethylene glycol 2000 was added to adjust the liquid viscosity to 350~550 mPa·s to obtain hydrogel surface modification precursor a7.

[0056] (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor a7. After the ceramic particles were completely immersed for 30 minutes, they were slowly and steadily removed. After the excess hydrogel precursor on the surface was naturally drained, the ceramic particles were placed in a constant temperature and humidity environment of 50℃ and 90%RH for 24 hours to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles A7.

[0057] Add 435 parts of PO 42.5 grade ordinary Portland cement, 880 parts of river sand fine aggregate, 345 parts of modified heat-insulating ceramsite A7, and 100 parts of modified silica fume to a mixer and mix for 30 seconds. Then add 140 parts of water and 4.8 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 38 parts of alkali-free quick-setting agent to the target area to obtain heat-insulating and heat-resistant shotcrete.

[0058] Example 8: A heat-insulating and heat-resistant shotcrete, the preparation process of which is as follows:

[0059] (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in ammonia water for 4 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite.

[0060] (2) 258 parts of methacrylic acid, 390 parts of itaconic acid, 284 parts of acrylamide, 37.2 parts of γ-methacryloxypropyltrimethoxysilane, 8.2 parts of (3-mercaptopropyl)trimethoxysilane, 5.8 parts of di-tert-butyl peroxide and 4800 parts of dimethyl sulfoxide were added to a reaction vessel and mixed evenly. The solution was stirred and reacted at 75°C for 2.5 h. After the reaction was completed, guar gum was added to adjust the liquid viscosity to 350~550 mPa·s to obtain the hydrogel surface modification precursor a8.

[0061] (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor a8. After the ceramic particles were completely immersed for 30 minutes, they were slowly and steadily removed. After the excess hydrogel precursor on the surface was naturally drained, the ceramic particles were placed in a constant temperature and humidity environment of 50℃ and 90%RH for 24 hours to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles A8.

[0062] Add 470 parts of PO 42.5 grade ordinary Portland cement, 902 parts of river sand fine aggregate, 335 parts of modified heat-insulating ceramsite A8, and 55 parts of modified silica fume to a mixer and mix for 30 seconds. Then add 168 parts of water and 5 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 34 parts of alkali-free quick-setting agent to the target area to obtain heat-insulating and heat-resistant shotcrete.

[0063] Comparative Example 1: Conventional Shotcrete

[0064] Add 470 parts of PO 42.5 grade ordinary Portland cement, 935 parts of river sand fine aggregate, and 818 parts of 5-10mm crushed stone coarse aggregate to a mixer and mix for 30 seconds. Then add 170 parts of water and 4.3 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 33 parts of alkali-free quick-setting agent to the target area to obtain conventional shotcrete.

[0065] Comparative Example 2: Unmodified ceramsite shotcrete

[0066] 470 parts of PO 42.5 grade ordinary Portland cement, 935 parts of river sand fine aggregate, and 325 parts of high-strength shale ceramsite were added to a mixer and mixed for 30 seconds. Then, 186 parts of water and 4.3 parts of admixture were added and mixed for 3 minutes to obtain a concrete mixture. The mixture was then added to a wet spraying equipment and sprayed together with 33 parts of alkali-free quick-setting agent to the target area to obtain unmodified ceramsite shotcrete.

[0067] Comparative Example 3: Unmodified ceramsite silica mortar sprayed concrete

[0068] 440 parts of PO 42.5 grade ordinary Portland cement, 60 parts of silica mortar, 935 parts of river sand fine aggregate, and 325 parts of high-strength shale ceramsite are added to a mixer and mixed for 30 seconds. Then, 155 parts of water and 4.3 parts of admixture are added and mixed for 3 minutes to obtain a concrete mixture. The mixture is then added to a wet spraying equipment and sprayed together with 33 parts of alkali-free quick-setting agent to the target area to obtain unmodified ceramsite silica mortar sprayed concrete.

[0069] Comparative Example 4: Modified ceramsite shotcrete

[0070] Add 470 parts of PO 42.5 grade ordinary Portland cement, 935 parts of river sand fine aggregate, and 325 parts of modified heat-insulating ceramsite A4 to a mixer and mix for 30 seconds. Then add 186 parts of water and 4.3 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 33 parts of alkali-free quick-setting agent to the target area to obtain modified ceramsite shotcrete.

[0071] Comparative Example 5: Uncrosslinked modified ceramsite shotcrete

[0072] (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in potassium hydroxide solution for 3 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite.

[0073] (2) 778 parts of acrylic acid, 6.2 parts of (3-mercaptopropyl)trimethoxysilane, 5.6 parts of azobisisoheptanenitrile and 4200 parts of tetrahydrofuran were added to a container and mixed evenly. The solution was stirred and reacted at 75°C for 2.5 h. After the reaction was completed, xanthan gum was added to adjust the liquid viscosity to 350~550 mPa·s to obtain the surface-modified precursor a9.

[0074] (3) Immerse the surface-activated high-strength shale ceramic particles into the modified precursor a9. After the ceramic particles are completely wetted for 30 minutes, slowly and steadily remove them. After the excess precursor on the surface is naturally drained, place the ceramic particles in a constant temperature and humidity environment of 50℃ and 90%RH for a post-crosslinking reaction for 24 hours to obtain uncrosslinked modified heat insulation ceramic particles A9.

[0075] Add 420 parts of PO 42.5 grade ordinary Portland cement, 872 parts of river sand fine aggregate, 355 parts of non-crosslinked modified thermal insulation ceramsite A9, and 90 parts of modified silica fume to a mixer and mix for 30 seconds. Then add 150 parts of water and 5 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 30 parts of alkali-free quick-setting agent to the target area to obtain non-crosslinked modified ceramsite shotcrete.

[0076] Comparative Example 6: Modified ceramsite shotcrete

[0077] (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in sodium hydroxide solution for 3 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite.

[0078] (2) 360 parts of acrylic acid, 355 parts of acrylamide, 37.2 parts of γ-methacryloxypropyltrimethoxysilane, 5 parts of (3-mercaptopropyl)trimethoxysilane, 3.5 parts of azobisisobutyronitrile and 4000 parts of ethanol were added to a container and mixed evenly. The solution was stirred and reacted at 75°C for 2 hours. After the reaction was completed, the viscosity of the liquid was adjusted to below 100 mPa·s to obtain the hydrogel surface modification precursor a10.

[0079] (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor a10. After the ceramic particles were completely immersed for 30 minutes, they were slowly and steadily removed. After the excess hydrogel precursor on the surface was naturally drained, the ceramic particles were placed in a constant temperature and humidity environment of 50℃ and 90%RH for 24 hours to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles A10.

[0080] Add 450 parts of PO 42.5 grade ordinary Portland cement, 837 parts of river sand fine aggregate, 370 parts of modified heat-insulating ceramsite A10, and 60 parts of modified silica fume slurry to a mixer and mix for 30 seconds. Then add 157 parts of water and 4.5 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 36 parts of alkali-free quick-setting agent to the target area to obtain modified ceramsite shotcrete.

[0081] Comparative Example 7: Modified ceramsite shotcrete

[0082] (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in sodium hydroxide solution for 3 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite.

[0083] (2) 360 parts of acrylic acid, 355 parts of acrylamide, 37.2 parts of γ-methacryloxypropyltrimethoxysilane, 5 parts of (3-mercaptopropyl)trimethoxysilane, 3.5 parts of azobisisobutyronitrile and 4000 parts of ethanol were added to a container and mixed evenly. The solution was stirred and reacted at 75°C for 2 hours. After the reaction was completed, cellulose ether was added to adjust the liquid viscosity to 800~900 mPa·s to obtain the hydrogel surface modification precursor a11.

[0084] (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor a11. After the ceramic particles were completely immersed for 30 minutes, they were slowly and steadily removed. After the excess hydrogel precursor on the surface was naturally drained, the ceramic particles were placed in a constant temperature and humidity environment of 50℃ and 90%RH for 24 hours to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles A11.

[0085] Add 450 parts of PO 42.5 grade ordinary Portland cement, 837 parts of river sand fine aggregate, 370 parts of modified heat-insulating ceramsite A11, and 60 parts of modified silica fume slurry to a mixer and mix for 30 seconds. Then add 157 parts of water and 4.5 parts of admixture and mix for 3 minutes to obtain a concrete mixture. Add the mixture to a wet spraying equipment and spray it together with 36 parts of alkali-free quick-setting agent to the target area to obtain modified ceramsite shotcrete.

[0086] Effect description:

[0087] The heat-insulating and heat-resistant shotcrete prepared in Examples 1-8 of this invention was compared with the comparative shotcrete in Comparative Examples 1-8 in terms of performance.

[0088] The thermal conductivity of concrete was tested using the transient flat plate heat source method according to ISO 22007-2:2015. The segregation degree of the concrete mixture was characterized by the change in unit weight before and after standing. A 30L concrete mixture was prepared, and its outlet unit weight was measured as m1. After standing the mixture in a 30L container for 30 minutes, the top 10L of mixture was taken, stirred evenly, and its unit weight was measured as m2. The segregation degree of the mixture was then calculated as m2 / m1. The compressive strength of the concrete was tested using a universal testing machine according to GB / T 50081-2019. The permeability grade of the concrete was tested using a permeability testing machine according to GB / T 50082-2009.

[0089] The relevant test results are summarized in Table 1:

[0090] Table 1. Performance test results of shotcrete

[0091]

[0092] As can be seen from the data in Table 1, the heat-insulating and heat-resistant shotcrete prepared in the examples exhibits excellent homogeneity of the mixture, heat insulation performance and impermeability of the hardened body, as well as the ability to maintain and develop strength in the later stages under different high rock temperatures. This is of great value for the application of related concrete structures in tunnel initial supports and other support structures in environments with high geothermal or high-temperature water inrush, ensuring the structure's long-term service life under high-temperature conditions and extending its service life.

[0093] A comparison of the performance of Comparative Examples 1-8 with the Examples shows a significant difference in overall performance, particularly in thermal conductivity and strength development under high-temperature conditions. This is mainly due to the synergistic effect of the modified insulating ceramsite's internal curing and the modified silica fume's densifying and reinforcing properties in the Examples, leading to differences in the formation and distribution of hydration products and microporous structures in the concrete. A detailed analysis follows.

[0094] Comparative Example 1 shows conventional shotcrete. It can be seen that due to the use of conventional crushed stone aggregate, its homogeneity is relatively good. However, because the crushed stone aggregate has a solid structure, its thermal insulation performance is poor. Furthermore, due to the poor heat resistance of the hydration products and severe water loss in the matrix under high-temperature conditions, as well as severe interface damage and pore structure deterioration, its strength development is poor under high-temperature curing conditions, resulting in significant later-stage strength loss. Regarding impermeability, due to the addition of a quick-setting agent during molding, the density of the shotcrete is relatively weak, thus its overall impermeability is poor.

[0095] Comparative Examples 2 and 4 show shotcrete made using only unmodified or modified ceramsite. The test results show that, firstly, due to the low density of ceramsite, it has a strong tendency to float during placement, resulting in relatively poor homogeneity. This is especially true for unmodified ceramsite aggregate, which floats even faster in the paste. Secondly, the introduction of porous aggregate reduces the thermal conductivity of the hardened mixture in both types. Modified ceramsite, due to its surface sealing effect, maintains a better pore structure, resulting in a lower thermal conductivity. Regarding high-temperature strength development, the addition of ceramsite aggregate improves later-stage strength development due to its water-absorbing and internal curing properties, but the overall trend still shows a gradual decrease in later-stage strength. Comparatively, ceramsite with a hydrogel surface exhibits better performance due to its stronger water absorption and retention capacity. Finally, the addition of ceramsite alone does not significantly improve impermeability.

[0096] Comparative Example 3 shows shotcrete made with conventional expanded clay aggregate and silica fume slurry. The results indicate that while silica fume slurry improved the slurry viscosity to some extent, it did not completely suppress the floating of expanded clay aggregate, resulting in poor homogeneity. Furthermore, the addition of fine silica fume filled and blocked some of the expanded clay aggregate pores during mixing and subsequent hydration, generating thermally conductive products, thus significantly reducing its thermal insulation performance. However, the addition of silica fume slurry increased the proportion of heat-resistant calcium silicate hydration products during later hydration, improving matrix density. Combined with the internal curing effect of expanded clay aggregate, the hardened body showed relatively good later-stage strength development under high-temperature curing conditions, maintaining a strong trend without significant degradation. Moreover, the addition of silica fume slurry significantly improved the matrix's impermeability.

[0097] Comparative Example 5 is a shotcrete using acrylic modified ceramsite. Due to the lack of unsaturated silane components, the adhesion and cross-linking between the hydrogel and the ceramsite substrate are insufficient, making it difficult to retain water and provide barrier effects. It only has some benefits in preventing the ceramsite from floating and improving homogeneity. In other aspects, it is less different from Comparative Example 3 and significantly different from the examples.

[0098] Comparative Examples 6 and 7 are modified ceramsite prepared using hydrogel modification precursors with lower and higher viscosity, respectively. The main difference between them and the examples is that the thickness of their modified layer is not within the optimal modification thickness range. When the viscosity of the hydrogel modification precursor is low, the thickness of the modified layer is thin, which cannot effectively increase dispersibility, water absorption, and sealing. Therefore, their performance is not significantly different from that of conventional ceramsite. However, when the viscosity of the hydrogel modification precursor is high, the thickness of its modified layer is too thick, which leads to an obvious curve at the interface between the aggregate and the slurry, and the degree of hydration within the hardened body is affected. Therefore, the overall strength is significantly reduced compared to the examples.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments without departing from the technical essence of the present invention shall still fall within the scope of the present invention.

Claims

1. A heat resistant, insulated shotcrete, characterized in that It is prepared from the following components in the following mass ratio: 400-480 parts cement, 50-100 parts modified silica fume slurry, 325-400 parts modified thermal insulation ceramsite, 800-975 parts fine aggregate, 4-5.5 parts admixture, 120-170 parts water, and 25-40 parts quick-setting agent; wherein the modified silica fume slurry is a mixture of silica fume and nano-CSH crystal nuclei; wherein the modified thermal insulation ceramsite is obtained by surface grafting modification of high-strength shale ceramsite using a hydrogel precursor, wherein the thickness of the hydrogel modification layer is 50-70 μm; wherein the hydrogel precursor is a surface-modified material obtained by polymerizing unsaturated carboxylic acid monomers and unsaturated silane monomers in a solvent. The modified precursor has a viscosity of 350~550 mPa·s, wherein the molar ratio of unsaturated carboxylic acid monomers to unsaturated silane monomers is 1:(0.005~0.05), wherein the unsaturated carboxylic acid monomers are at least one of acrylic acid, methacrylic acid, fumaric acid, itaconic acid, and acrylamide, and wherein the unsaturated silane monomers are at least one of γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, vinyltritert-butoxysilane, and vinyltriacetoxysilane.

2. The heat resistant thermal sprayed concrete according to claim 1, wherein The modified silica fume slurry is a suspended stable slurry prepared by multi-stage efficient dispersion of silica fume and nano-CSH crystal nuclei in water at a mass ratio of 3:1, with a mass concentration of 50%; wherein the silica fume is dense silica fume with a SiO2 content greater than 90%.

3. The heat resistant thermal sprayed concrete according to claim 1, wherein The high-strength shale ceramsite has a particle size of 5-10 mm, a bulk density of 500-700 kg / m 3 , and a cylinder compressive strength of 6 MPa or more.

4. The heat resistant thermal sprayed concrete according to claim 1, wherein The preparation method of the modified heat-insulating ceramic particles is as follows: (1) Rinse the high-strength shale ceramsite with tap water to remove surface impurities, dry it and soak it in a strong alkaline solution for 2-4 hours. Then rinse the high-strength shale ceramsite with water until the rinsing water is neutral. Then dry the high-strength shale ceramsite to obtain surface-activated high-strength shale ceramsite. (2) Add unsaturated carboxylic acid, unsaturated silane, chain transfer agent, initiator and solvent into a reaction vessel and mix evenly. Stir the solution at 60-80℃ for 1-3 hours. After the reaction is completed, add rheology modifier to adjust the liquid viscosity to 350-550 mPa·s to obtain the hydrogel surface modification precursor. (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor. After the ceramic particles were completely immersed for 30 minutes, they were slowly and steadily removed. After the excess hydrogel precursor on the surface was naturally drained, the ceramic particles were placed in a constant temperature and humidity environment of 50℃ and 90%RH for 24 hours to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles.

5. The method of claim 4, wherein The strong alkaline solution is at least one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and ammonia solution; the chain transfer agent is (3-mercaptopropyl)trimethoxysilane, used in an amount of 0.1%-1% of the monomer amount; the initiator is at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dicumyl peroxide, and di-tert-butyl peroxide, used in an amount of 0.1%-1% of the monomer amount; the solvent is at least one of methanol, ethanol, isopropanol, n-butanol, tert-butanol, tetrahydrofuran, dioxane, dimethylformamide, and dimethyl sulfoxide; the rheology modifier is at least one of xanthan gum, guar gum, styrax, polyethylene glycol 2000, and cellulose ether.

6. The heat resistant thermal sprayed concrete according to claim 1, wherein The cement is ordinary Portland cement with a strength grade of 42.5; the fine aggregate is river sand or manufactured sand with a fineness modulus of 2.3 to 3.

0.

7. The insulating refractory gunite as claimed in claim 1, wherein The admixture is a high-performance admixture formulated with polycarboxylate superplasticizer and functional additives, with a water reduction rate of 28% to 33%. The functional additive is at least one of retarder, air-entraining agent, defoamer, and thickener.

8. The insulating refractory gunite concrete as claimed in claim 1, wherein The accelerator is a fluorine-free and alkali-free accelerator, with an initial setting time of ≤3min, a final setting time of ≤5min, and a mortar strength of ≥1MPa after 6 hours.

9. A heat resistant thermal sprayed concrete according to claim 1, wherein the method of preparation comprises the steps of: Cement, fine aggregate, modified heat-insulating ceramsite, and modified silica fume are added to the mixer and stirred for 30 seconds. Then, water and admixtures are added and stirred for 3 minutes to obtain a concrete mixture. The mixture is then added to a wet spraying equipment and sprayed together with a quick-setting agent to the target area to obtain heat-insulating and heat-resistant shotcrete.

10. The application of the heat-insulating and heat-resistant shotcrete as described in claim 1 as a heat-insulating support structure in high-temperature tunnels, high-temperature water inrush tunnels, high-geothermal mines and related underground engineering projects.

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