High-performance sprayed concrete for high-rock-temperature tunnel and construction application method of high-performance sprayed concrete

Abstract

The invention belongs to the technical field of tunnel engineering, and particularly discloses high-performance sprayed concrete for a high-rock-temperature tunnel. The high-performance sprayed concrete comprises independently stored sprayed plain concrete and 150-200 parts of an activation activator, and the sprayed plain concrete comprises 400-500 parts by weight of magnesium oxide, 1-5 parts by weight of calcium salt, 0.5-1 part by weight of a foaming agent, 0.5-1 part by weight of acrylic acid, 0.5-1 part by weight of acrylamide, 4-5 parts by weight of a water reducing agent, 1300-1650 parts by weight of a filler and 100-150 parts by weight of water which are uniformly mixed. The high-performance sprayed concrete maintains high fluidity based on the dispersion effect of the water reducing agent; calcium salt and phosphate react to generate calcium phosphate particles, the crystal nucleus effect is exerted, setting and hardening of magnesium oxide are promoted, and the temperature resistance is improved; acrylic acid and acrylamide are subjected to free radical polymerization under the action of an initiator, fluidity is lost, setting and hardening of magnesium oxide are promoted, and sprayability is improved; and the foaming agent is decomposed to generate nitrogen to reduce compactness and thermal conductivity, exert heat insulation and resist heat damage. The invention further discloses a construction application method of the device in a high-rock-temperature tunnel.

Description

Technical Field

[0001] This invention belongs to the field of tunnel engineering technology, specifically, it relates to a high-performance shotcrete for high-temperature tunnels and its construction application method in high-temperature tunnels. Background Technology

[0002] As my country's engineering construction extends to higher altitudes, the number of high-temperature tunnel projects is increasing. These tunnels typically operate at temperatures ranging from 40℃ to 100℃, making the high-temperature environment a significant challenge in tunnel construction. Shotcrete, with its advantages of high construction efficiency, simple process, and cost-effectiveness, is a core material for the safety protection and rapid support of tunnel lining structures. However, research and engineering practice have shown that while high temperatures can increase the early strength of concrete, they can negatively impact its later strength development. This is because, in high-temperature environments, conventional silicate cement shotcrete accelerates water evaporation, alters the hydration process, increases porosity, and leads to deterioration in the composition and structure of hydration products, damaging the cement paste microstructure. Simultaneously, an internal temperature gradient is generated, resulting in reduced mechanical strength, temperature cracks, and decreased support effectiveness. Therefore, inhibiting the deterioration of shotcrete performance and preparing shotcrete suitable for high-temperature environments has become a crucial concern for engineering technicians.

[0003] Optimizing the temperature control methods of the lining structure, such as burying cooling water pipes and erecting air insulation layers, can accelerate the dissipation of high-temperature heat inside the surrounding rock, reduce the temperature difference between the surrounding rock and concrete, and between the inner and outer layers of concrete, improve the cement hydration environment temperature, and reduce temperature difference cracks. This is an important measure to avoid thermal damage to high-temperature lining concrete. For example, Chinese patent application CN116877149A discloses a double-gradient lining support structure and construction method for high-temperature tunnels. This technology proposes a gradient lining structure based on a solid insulation layer or an air insulation layer, introducing an insulation layer into the lining structure layer to achieve stable coordination of insulation, support, and overall durability, extend the service life of the support structure, increase heat dissipation in high-temperature tunnels, and reduce the impact of high-temperature thermal damage. For example, Chinese patent application CN 108561162A discloses a support structure and construction method for ultra-high geothermal tunnels. Addressing the support needs of ultra-high geothermal tunnels, it embeds a circumferential serpentine water circulation pipe between the initial and secondary shotcrete layers of the initial support structure, circulating cold water to achieve good heat dissipation, reducing the impact of high temperatures on concrete setting and hardening, and solving the problems of insufficient bond strength between shotcrete and surrounding rock, and temperature cracking between shotcrete and secondary lining concrete. Simultaneously, the serpentine high-strength steel pipe embedded in the initial support structure acts as an upper scaffold, improving the safety and durability of the tunnel lining structure under long-term high temperatures. While incorporating heat insulation and heat dissipation support structures in high-rock-temperature tunnel linings can improve the service environment temperature of the lining concrete and reduce thermal damage in high-rock-temperature environments, its construction process is complex, costly, and difficult to implement on-site. Furthermore, the heat dissipation equipment can affect the stability of the surrounding rock.

[0004] Insulating (blocking) heat materials in concrete lining structures can effectively block or delay the spread of heat, thereby avoiding or reducing thermal damage to the concrete lining, which is an important measure in the construction of high-temperature tunnels. For example, Chinese patent CN 204646252U discloses a support structure for ultra-high-temperature tunnels. This technology involves setting rigid polyurethane insulation material in the circumferential surrounding rock of the tunnel. The excellent insulation effect of rigid polyurethane insulation material can reduce the temperature difference between the inner side of the initial shotcrete and the concrete itself during pouring, reduce the working temperature of the waterproof layer, and reduce the temperature difference of the secondary lining concrete upon placement, thus minimizing the impact of high-temperature surrounding rock on the construction and operation environment inside the tunnel. For example, Chinese patent application CN 112664234A discloses a thermal insulation support structure and construction method for high-temperature highway tunnels. It proposes using rigid polyurethane thermal insulation material sprayed onto the initial support surface to form a thermal insulation layer. This sprayed rigid polyurethane thermal insulation material can solve problems such as poor durability of shotcrete, high operating temperature, and secondary lining cracking caused by harsh high-temperature conditions, providing favorable environmental conditions for the sustainable operation of high-temperature highway tunnels. Another example is Chinese patent application CN 117645450A, which discloses a method to improve the high-temperature performance of shotcrete. This method involves applying a silicone rubber tackifier and thermal insulation agent to a high-temperature rock surface to form a tackifier and thermal insulation layer. This tackifier and thermal insulation layer provides effective adhesion and layered thermal insulation before the shotcrete slurry contacts the rock surface. Simultaneously, fibers are used to bridge the tackifier and thermal insulation layer with the shotcrete slurry. After the shotcrete slurry is sprayed onto the rock surface, the concrete is tightly bonded, effectively solving the problems of traditional shotcrete being unsuitable for high-temperature rock conditions, having poor high-temperature stability, poor adhesion, and high rebound rate. Chinese patent application CN 106988769A discloses a thermal insulation lining structure and its construction method for deep high-temperature tunnels. Addressing the high humidity and heat hazards of deep high-temperature tunnels, it designs a support structure consisting of a grouting insulation ring, a primary lining insulation layer, and a secondary lining insulation layer. Low thermal conductivity materials such as vitrified microspheres, ceramsite, and asbestos are introduced to optimize the support material, ensuring the stability of the tunnel support structure. Multiple insulation measures effectively prevent heat from spreading into the tunnel. While multi-layered insulation can delay heat transfer in a short time, it does not consider the heat dissipation function of the support structure, and its heat release damage effect needs further verification. Furthermore, the adhesion problem between the insulation material and the shotcrete affects subsequent shotcrete construction.

[0005] Controlling the material composition of shotcrete and introducing porous aggregates, such as vitrified microspheres, expanded perlite, and ceramsite, can reduce the thermal conductivity of shotcrete and slow down heat propagation, thereby improving the quality of the lining concrete. This is an important method for constructing high-geothermal tunnels. For example, Chinese patent application CN 117684543A discloses a shotcrete structure and its preparation method suitable for high rock temperature environments. This technology proposes a shotcrete structure design based on a rapid-setting thermal insulation mortar layer of vitrified microspheres, expanded perlite, and ceramsite. This structure can adapt to high rock temperature environments, maintain its strength in the later stages, improve durability and crack resistance, and comprehensively enhance the support performance of shotcrete in high rock temperature environments. For example, Chinese patent application CN117985977A discloses a heat-insulating and heat-resistant shotcrete and its preparation method. It introduces high-strength shale ceramsite with surface modification using hydrogel as a heat-insulating filler, comprehensively improving the homogeneity of the shotcrete mixture and the heat insulation performance of the hardened body. This solves the problems of strength development and durability under high-temperature conditions, effectively improving tunnel chamber temperature and extending the service life of shotcrete under high-temperature conditions. While replacing aggregates with vitrified microspheres, expanded perlite, and ceramsite can increase matrix porosity and reduce thermal conductivity, thus improving the service environment of lining concrete, the significant difference in density between these alternative aggregates and the concrete system means that their uniform distribution directly affects the matrix porosity, making it difficult to coordinate their heat conduction and insulation effects. Furthermore, concrete matrices in contact with high-temperature surrounding rock still face the challenge of thermal damage.

[0006] Furthermore, optimizing the composition of shotcrete materials, improving the hydration environment of cement concrete, increasing the density of the cement paste matrix, and avoiding the generation of harmful cracks have also been applied to the construction of high-temperature tunnel lining concrete. For example, Chinese patent application CN 119390398A discloses a SAP geopolymer shotcrete and its application in the initial lining of high-temperature tunnels. This patent describes the preparation of SAP geopolymer-based shotcrete, which can reduce the thermal conductivity of concrete under high-temperature conditions, improve the heat insulation capacity of shotcrete, and reduce construction and maintenance costs. Simultaneously, it optimizes the hydration environment of cement concrete, reduces the rate of water evaporation under high temperatures, and avoids the strength reduction problem in the initial lining. Another example is Chinese patent application CN117946329A, which discloses a high-thixotropic shotcrete additive suitable for high geothermal conditions and its preparation method. This technology prepares an organic polymer material with water retention and thickening thixotropy through in-situ polymerization, which intertwines with an inorganic thixotropic material. This significantly reduces the rebound rate of shotcrete, improves early strength, and enhances construction performance, making it suitable for shotcrete construction under high-temperature conditions. For example, Chinese patent application CN 117776584A discloses a material for inhibiting thermal damage to concrete in high geothermal environments, its preparation method, and its application. This technology improves the density of cement paste by rationally combining various components such as mineral admixtures, quartz sand, metakaolin, nanomaterials, thickeners, and retarders, ensuring uniform strength development and reducing the rate of water evaporation, thus avoiding structural deterioration under high geothermal temperatures. It also avoids the problems of reduced strength in the later stages of concrete and uneven distribution of early hydration products under high geothermal conditions, improving its durability. Another example is Chinese patent application CN115385597A, which discloses an accelerator for shotcrete in high-heat areas, its preparation, and application method. Addressing the needs of shotcrete in high-heat areas, it develops an accelerator material containing calcium oxide and magnesium oxide expansion components. Through the synergistic reaction between the accelerator components, hydration products have sufficient time and space to effectively precipitate into the pores, reducing the porosity of shotcrete during high-temperature curing and increasing the density of the hardened paste. This effectively improves the problem of mid-to-late-stage strength deterioration in high-temperature shotcrete. Chinese patent application CN 116283145A discloses a high-strength, high-toughness, heat-insulating functional shotcrete for high-temperature hot water tunnels. This technology develops concrete admixtures that can adapt to high-temperature hot water tunnels, minimizing negative effects such as thermal damage from high rock temperatures, thereby ensuring the bearing capacity of the support structure and the safety of the tunnel structure. Reducing the porosity of cement concrete, especially the reduction of harmful pores, and increasing the matrix density helps avoid water loss and shrinkage cracking in shotcrete; however, the existence of temperature differences makes temperature cracking in shotcrete difficult to avoid. Simultaneously, at high temperatures, the water loss and decomposition of silicate hydration products AFt and AFm still occur, making strength degradation difficult to avoid.

[0007] Therefore, in high-temperature rock environments, the hydration process of silicate cement concrete is affected by temperature, leading to accelerated water evaporation, temperature cracks and shrinkage cracks, and the deterioration of hydration products at high temperatures affecting mid-to-late-stage strength. The key to achieving rapid construction and safe operation of high-temperature rock mining projects lies in regulating the setting and hardening process of shotcrete to ensure rapid setting and hardening without the risk of mid-to-late-stage strength degradation while guaranteeing long-distance, long-term transport of shotcrete. Furthermore, optimizing the shotcrete layer structure system, reducing thermal conductivity, and improving the service environment durability of other lining structures are also crucial. Summary of the Invention

[0008] To address the challenges posed by high-temperature tunnel environments, where shotcrete is affected by temperature, leading to accelerated moisture evaporation, shrinkage cracks due to temperature gradients, and degradation of hydration products at high temperatures that hinders mid-to-late-stage strength development, current technologies lack fundamental solutions. This invention provides a high-performance shotcrete for high-temperature tunnel engineering. This high-performance shotcrete boasts advantages such as rapid setting and hardening, high early strength, good heat resistance of hydration products with no mid-to-late-stage strength loss, and low thermal conductivity, avoiding heat damage to other lining structures. While effectively ensuring the stability of the surrounding rock structure in high-temperature tunnels, it also reduces the impact of high rock temperatures on the tunnel lining structure, which is of great significance for achieving green construction and long-term service of tunnels.

[0009] The present invention specifically adopts the following technical solution: In a first aspect, the present invention provides a high-performance shotcrete for high rock temperature tunnels, comprising separately stored shotcrete and an activator.

[0010] Shotcrete comprises the following components, which are mixed evenly in parts by weight: 400-500 parts of magnesium oxide; Calcium salt 1-5 parts; 0.5~1.0 parts of foaming agent; Acrylic acid 0.5~1.0 parts; Acrylamide 0.5~1.0 parts; Water-reducing agent: 4.0~5.0 parts; 1300~1650 parts of filler; 100-150 parts water.

[0011] The activator is present in a mass fraction of 150-200 parts.

[0012] The water-cement ratio of the sprayed plain concrete is 0.25~0.30, the sand ratio is 45%~55%, and the bulk density is 2310±10 kg / m³. 3 .

[0013] Optionally, the magnesium oxide is obtained by calcining magnesite at 800℃~1100℃, wherein the MgO content is 80%~85% and the SiO2 content is 5%~10%; the activity index is 180 s~250 s, and the specific surface area is 500 m². 2 / kg~600 m 2 / kg.

[0014] Optionally, the calcium salt is selected from any one of calcium nitrate, calcium nitrite, and calcium acetate, or a mixture of at least two in any proportion.

[0015] Optionally, the foaming agent is an azo compound.

[0016] Furthermore, the foaming agent is selected from any one of diisopropyl azodicarbonate, azobisisobutyronitrile, azodicarbonamide, and diethyl azodicarbonate, or a mixture of at least two in any proportion.

[0017] Optionally, the water-reducing agent is a polycarboxylate water-reducing agent.

[0018] Optionally, the filler may include sand and gravel.

[0019] Furthermore, the sand is continuously aggregated medium sand with a fineness modulus of 2.3 to 3.2 and a mud content of no more than 3.0%.

[0020] Furthermore, the gravel is continuously aggregated small gravel with a mud content of no more than 3.0%, a mud lump content of no more than 1.0%, and a particle size of 4.75 mm to 9.5 mm.

[0021] Optionally, the activator is a phosphate suspension containing an initiator.

[0022] Furthermore, the activator is prepared using the following method: S1. Dissolve 45-60 parts by weight of phosphate in water to prepare a phosphate aqueous solution; S2. Under shearing conditions of 8 m / s to 10 m / s, 0.05 to 0.5 parts by mass of stabilizer are added to an aqueous phosphate solution to obtain a precursor solution. S3. Add 0.1~0.5 parts by weight of the initiator to the precursor solution until it is completely dispersed to obtain the activator. The total mass of the activating agent is 100 parts by mass.

[0023] Optionally, the phosphate is selected from any one of sodium dihydrogen phosphate, sodium hydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, and potassium phosphate, or a mixture of at least two in any proportion.

[0024] Optionally, the stabilizer is selected from any one of magnesium aluminum silicate, diatomaceous earth, attapulgite, sepiolite, and montmorillonite, or a mixture of at least two in any proportion.

[0025] Stabilizers can improve the stability of the supersaturated phosphate suspension, thus ensuring its long-term storage.

[0026] Optionally, the initiator is selected from any one of benzoyl oxide, sodium bisulfite, potassium bisulfite, and ammonium bisulfite, or a mixture of at least two in any proportion.

[0027] Generally, in step S1, the phosphate aqueous solution can be prepared by stirring at 65℃~75℃ for 1 h~3 h.

[0028] The high-performance shotcrete provided by this invention has two main advantages. First, based on the dispersing effect of the water-reducing agent, the shotcrete can maintain high fluidity for a long time, meeting the requirements of shotcrete construction. Second, during shotcrete construction, acrylic acid and acrylamide first undergo free radical polymerization under the action of the initiator in the activator to generate a linear polymer thickener. Its thickening and shrinkage effect reduces the amount of free water, causing loss of fluidity in the shotcrete, promoting the setting and hardening of the cementitious material, and thus improving the sprayability of the shotcrete. Moreover, the calcium salt and the phosphate in the activator react to generate micro-nano calcium phosphate particles, which can exert a nucleation effect and promote the setting and hardening of magnesium oxide. The phosphate in the activator also hydrates with magnesium oxide to generate struvite-like cementitious substances with good temperature resistance. At the same time, under the high-temperature environment formed by the exothermic hydration, the foaming agent decomposes to generate nitrogen gas. The nitrogen gas forms closed, uniform, and stable small bubbles in the incompletely set and hardened cementitious matrix, reducing the density and thermal conductivity of the shotcrete, which can play a heat insulation role and resist the thermal damage problem of high rock temperature tunnels.

[0029] The high-performance shotcrete provided by this invention can fully leverage the synergistic effects of activators, magnesium oxide, calcium salts, foaming agents, acrylic acid, and acrylamide, promoting each other's growth. This not only enables the rapid setting and hardening of magnesium oxide-based shotcrete, meeting the requirements for shotcrete sprayability, but also reduces the thermal conductivity of the initial support shotcrete, protecting other lining structures from thermal damage and meeting the requirements for long-term safe operation of high-temperature tunnels.

[0030] A second aspect of the present invention provides a method for constructing high-performance shotcrete for high-temperature tunnels as described above, comprising the steps of: Preparation of sprayed plain concrete: 400-500 parts magnesium oxide, 1-5 parts calcium salt, 0.5-1.0 parts foaming agent, 0.5-1.0 parts acrylic acid, 0.5-1.0 parts acrylamide, 4.0-5.0 parts water-reducing agent, 1300-1650 parts filler and 100-150 parts water are thoroughly mixed to obtain sprayed plain concrete; The sprayed plain concrete is transported separately with 150-200 parts of activator through pipelines, mixed evenly at the nozzle, and sprayed out immediately.

[0031] All figures above are by weight (parts).

[0032] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The high-performance shotcrete for high-temperature tunnels provided by this invention has the advantages of good heat resistance and low thermal conductivity. The struvite particles generated by magnesium oxide under the action of phosphate have good heat resistance, no risk of high-temperature decomposition, and no loss of strength in the later stage; at the same time, the closed, uniform and stable small bubbles generated by the decomposition of foaming agent under heat significantly reduce the density and thermal conductivity of the shotcrete, improve the service environment of the subsequent lining, and avoid the harm of heat damage.

[0033] (2) The high-performance shotcrete for high rock temperature tunnels provided by this invention has good workability and strong fluidity retention, meeting the needs of long-term and long-distance transportation in tunnel construction. Magnesium oxide cannot react directly with calcium salts, foaming agents, acrylic acid, and acrylamide. Under the action of water-reducing agents, they can coexist for a long time and have good pumpability. Under the action of activators, magnesium oxide is rapidly hydrated, and calcium salts quickly generate calcium phosphate to play a nucleation role, accelerating the solidification and hardening of magnesium oxide particles. Acrylic acid and acrylamide undergo free radical combination to generate thickening polymers, consume free water, improve the bonding effect with the surrounding rock interface, and promote the solidification and hardening of magnesium oxide. The three work together to achieve a low rebound rate and good sprayability of the shotcrete.

[0034] (3) The high-performance shotcrete for high-temperature tunnels provided by the present invention, wherein the cementitious material system, apart from a small amount of industrial raw materials, is mainly magnesium oxide; magnesium oxide has a low firing temperature, lower than that of traditional silicate cement, and low carbon emissions, which meets the requirements for the preparation of low-carbon cement. That is, the high-performance shotcrete for high-temperature tunnels also has the effect of low carbon and environmental protection. Detailed Implementation

[0035] An embodiment of the present invention provides a high-performance shotcrete for high rock temperature tunnels, which includes separately stored shotcrete and an activator.

[0036] The sprayed plain concrete comprises the uniformly mixed components shown in Table 1 below: Table 1. Composition of sprayed concrete The activator is present in a mass fraction of 150-200 parts.

[0037] The activator is a phosphate suspension containing an initiator.

[0038] Of the above components: Magnesium oxide is produced by calcining magnesite at a temperature of 800℃~1100℃, with an MgO content of 80%~85% and a SiO2 content of 5%~10%.

[0039] Furthermore, the activity index of MgO is 180 s~250 s, and the specific surface area is 500 m². 2 / g~600 m 2 / g.

[0040] The calcium salt is at least one of calcium nitrate, calcium nitrite, and calcium acetate.

[0041] The foaming agent is an azo compound, such as at least one of diisopropyl azodicarbonate, azobisisobutyronitrile, azodicarbonamide, and diethyl azodicarbonate.

[0042] The water-reducing agent is a polycarboxylate water-reducing agent, such as PCA®-I polycarboxylate high-performance water-reducing agent produced by Jiangsu Subote New Material Co., Ltd.

[0043] The filler material includes sand and gravel.

[0044] Furthermore, the sand is continuously aggregated medium sand with a fineness modulus of 2.3 to 3.2 and a mud content of no more than 3.0%; the gravel is continuously aggregated small gravel with a mud content of no more than 3.0%, a mud lump content of no more than 1.0%, and a particle size of 4.75 mm to 9.5 mm.

[0045] The water-cement ratio of this sprayed plain concrete is 0.25~0.30, the sand ratio is 45%~55%, and the bulk density is 2310±10 kg / m³. 3 .

[0046] The activator is prepared from phosphate, initiator, stabilizer and water.

[0047] Specifically, the raw materials of the activator, based on 100 parts by weight, include the following components: 45-60 parts of phosphate, 0.1-0.5 parts of initiator, 0.05-0.5 parts of stabilizer, and the balance being water.

[0048] The preparation method of the activator includes the following steps: S1. Add water and phosphate to a flask in sequence, and stir at 65℃~75℃ for 1.0 h~3.0 h until completely dissolved to obtain an aqueous solution of phosphate. S2. Under shear action of 8 m / s to 10 m / s, the stabilizer is added to the phosphate aqueous solution and the solution is slowly cooled to room temperature at a rate of about 10℃ / h to obtain the precursor solution. S3. Add the initiator to the precursor solution and stir until it is completely and evenly dispersed to obtain the activator.

[0049] The phosphate is at least one of sodium dihydrogen phosphate, sodium hydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, and potassium phosphate.

[0050] The stabilizer is at least one of magnesium aluminum silicate, diatomaceous earth, attapulgite, sepiolite, and montmorillonite.

[0051] The initiator is at least one of benzoyl oxide, sodium bisulfite, potassium bisulfite, and ammonium bisulfite.

[0052] According to the present invention, the following embodiments describe in more detail the high-performance shotcrete used in the high-temperature tunnel, and these embodiments are given by way of illustration so that those skilled in the art can understand the content of the invention and implement it accordingly, but these embodiments do not limit the scope of the invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

[0053] Example 1 A high-performance shotcrete for high-temperature tunnels includes separately stored shotcrete and an activator.

[0054] The sprayed plain concrete comprises the following components, which are mixed evenly in parts by weight: 400 parts magnesium oxide; 1 part calcium salt; 0.5 parts foaming agent; 4.0 parts water-reducing agent; 0.5 parts acrylic acid; Acrylamide 0.5 parts; 820 portions of sand; 820 portions of pebbles; 100 portions of water.

[0055] Among them, the specific surface area of ​​magnesium oxide is 503 m². 2 / kg.

[0056] The foaming agent is diisopropyl azodicarbonate.

[0057] The activator has a mass fraction of 150 parts.

[0058] The raw materials for the activator are: 45% sodium dihydrogen phosphate, 0.1% potassium persulfate, 0.05% sepiolite, and 54.85% water; based on the mass of the activator being 100%.

[0059] The preparation method of the activator includes the following steps: S1. Add 54.85 g of water and 45 g of sodium dihydrogen phosphate to a flask in sequence, and stir at 65°C for 1.0 h until completely dissolved.

[0060] S2. Under a shear force of 8.5 m / s, 0.05 g of sepiolite is added to the solution from step S1, and the solution is slowly cooled to room temperature at a rate of 10℃ / h.

[0061] S3. Add 0.1 g of potassium persulfate to the solution in step S2 and stir until it is completely dispersed and uniform to obtain the activator.

[0062] Example 2 A high-performance shotcrete for high-temperature tunnels includes separately stored shotcrete and an activator.

[0063] The sprayed plain concrete comprises the following components, which are mixed evenly in parts by weight: 500 parts magnesium oxide; Calcium salts 5.0 parts; 1.0 part foaming agent; 5.0 parts of water-reducing agent; 1.0 part acrylic acid; Acrylamide 1.0 part; 720 portions of sand; 720 portions of pebbles; 150 portions of water.

[0064] Among them, the specific surface area of ​​magnesium oxide is 598 m². 2 / kg.

[0065] The foaming agents diisopropyl azodicarbonate and azobisisobutyronitrile are mixed in equal mass.

[0066] The activator has a mass fraction of 200 parts.

[0067] The raw materials for the activator are: 60% potassium dihydrogen phosphate, 0.5% ammonium persulfate, 0.5% magnesium aluminum silicate, and 39% water; based on the mass of the activator being 100%.

[0068] The preparation method of the activator includes the following steps: S1. Add 39 g of water and 60 g of potassium dihydrogen phosphate to a flask in sequence, and keep it at 75°C and stir for 3.0 h until completely dissolved.

[0069] S2. Under a shear force of 9.2 m / s, 0.5 g of magnesium aluminum silicate is added to the solution in step S1, and the solution is slowly cooled to room temperature at a rate of 10℃ / h.

[0070] S3. Add 0.5 g of ammonium persulfate to the solution in step S2 and stir until it is completely dispersed and uniform to obtain the activator.

[0071] Example 3 A high-performance shotcrete for high-temperature tunnels includes separately stored shotcrete and an activator.

[0072] The sprayed plain concrete comprises the following components, which are mixed evenly in parts by weight: 450 parts magnesium oxide; 4.5 parts calcium salt; 0.8 parts foaming agent; 4.5 parts water-reducing agent; 1.0 part acrylic acid; Acrylamide 0.5 parts; 770 portions of sand; 770 portions of pebbles; 125 portions of water.

[0073] Among them, the specific surface area of ​​magnesium oxide is 558 m². 2 / kg.

[0074] The foaming agent is a mixture of diisopropyl azodicarbonate, azobisisobutyronitrile, azodicarbonamide, and diethyl azodicarbonate in equal masses.

[0075] The activator has a mass fraction of 180 parts.

[0076] The raw materials for the activator are: 25% potassium hydrogen phosphate, 25% potassium dihydrogen phosphate, 0.1% benzoyl peroxide, 0.2% sodium persulfate, 0.1% diatomaceous earth, 0.1% magnesium aluminum silicate, and 49.5% water; based on the mass of the activator being 100%.

[0077] The preparation method of the activator includes the following steps: S1. Add 49.5 g of water, 25 g of potassium hydrogen phosphate, and 25 g of potassium dihydrogen phosphate to a flask in sequence, and keep it at 70°C with stirring for 1.5 h until completely dissolved.

[0078] S2. Under a shear force of 9.2 m / s, 0.1 g of diatomaceous earth and 0.1 g of magnesium aluminum silicate are added to the solution in step S1, and the solution is slowly cooled to room temperature at a rate of 10℃ / h.

[0079] S3. Add 0.1 g benzoyl peroxide and 0.2 g sodium persulfate to the solution in step S2 and stir until completely dispersed and uniform to obtain the activator.

[0080] Example 4 A high-performance shotcrete for high-temperature tunnels includes separately stored shotcrete and an activator.

[0081] The sprayed plain concrete comprises the following components, which are mixed evenly in parts by weight: 450 parts magnesium oxide; 3 parts calcium salt; 0.8 parts foaming agent; 4.5 parts water-reducing agent; Acrylic acid 0.6 parts; Acrylamide 0.9 parts; 770 portions of sand; 770 portions of pebbles; 125 portions of water.

[0082] Among them, the specific surface area of ​​magnesium oxide is 558 m². 2 / kg.

[0083] The foaming agent is a mixture of azobisisobutyronitrile, azodicarbonamide, and diethyl azodicarbonate in equal mass.

[0084] The activator has a mass fraction of 180 parts.

[0085] The raw materials for the activator are: 10% sodium dihydrogen phosphate, 10% sodium hydrogen phosphate, 10% sodium phosphate, 10% potassium dihydrogen phosphate, 10% potassium hydrogen phosphate, 10% potassium phosphate, 0.1% benzoyl peroxide, 0.1% potassium persulfate, 0.1% ammonium persulfate, 0.1% sodium persulfate, 0.1% magnesium aluminum silicate, 0.1% attapulgite, 0.1% sepiolite, 0.1% montmorillonite, and 39.2% water; based on the mass of the activator being 100%.

[0086] The preparation method of the activator includes the following steps: S1. In a flask, add 39.2 g of water, 10 g of sodium dihydrogen phosphate, 10 g of sodium hydrogen phosphate, 10 g of sodium phosphate, 10 g of potassium dihydrogen phosphate, 10 g of potassium hydrogen phosphate, and 10 g of potassium phosphate in sequence. Keep the mixture at 75°C and stir for 2.0 h until completely dissolved.

[0087] S2. Under a shear force of 8.6 m / s, 0.1 g magnesium aluminum silicate, 0.1 g attapulgite, 0.1 g sepiolite, and 0.1 g montmorillonite are added to the solution in step S1, and the solution is slowly cooled to room temperature at a rate of 10℃ / h.

[0088] S3. Add 0.1 g benzoyl peroxide, 0.1 g potassium persulfate, 0.1 g ammonium persulfate, and 0.1 g sodium persulfate to the solution in step S2 and stir until completely dispersed and uniform to obtain the activator.

[0089] Example 5 A high-performance shotcrete for high-temperature tunnels includes separately stored shotcrete and an activator.

[0090] The sprayed plain concrete comprises the following components, which are mixed evenly in parts by weight: 480 parts of magnesium oxide; 4 parts calcium salt; 0.6 parts foaming agent; 4.5 parts water-reducing agent; 0.8 parts acrylic acid; Acrylamide 0.5 parts; 760 portions of sand; 760 portions of pebbles; 120 portions of water.

[0091] Among them, the specific surface area of ​​magnesium oxide is 538 m². 2 / kg.

[0092] The foaming agent is a mixture of azo compound, azodicarbonamide, and diethyl azodicarbonate in equal masses.

[0093] The activator has a mass fraction of 180 parts.

[0094] The raw materials for the activator are: 15% sodium dihydrogen phosphate, 15% sodium hydrogen phosphate, 15% potassium dihydrogen phosphate, 15% potassium hydrogen phosphate, 0.2% benzoyl peroxide, 0.2% potassium persulfate, 0.1% attapulgite, 0.1% sepiolite, 0.2% montmorillonite, and 39.2% water; based on the mass of the activator being 100%.

[0095] The preparation method of the activator includes the following steps: S1. In a flask, add 39.2 g of water, 15 g of sodium dihydrogen phosphate, 15 g of sodium hydrogen phosphate, 15 g of potassium dihydrogen phosphate, and 15 g of potassium hydrogen phosphate in sequence. Keep the mixture at 70°C and stir for 2.5 h until completely dissolved.

[0096] S2. Under a shear force of 9.4 m / s, 0.1 g of attapulgite, 0.1 g of sepiolite, and 0.2 g of montmorillonite are added to the solution from step S1, and the solution is slowly cooled to room temperature at a rate of 10℃ / h.

[0097] S3. Add 0.2 g benzoyl peroxide and 0.2 g potassium persulfate to the solution in step S2 and stir until completely dispersed and uniform to obtain the activator.

[0098] It should be noted that in the above embodiments, when the foaming agent is a mixture of multiple materials, they can be mixed in any proportion, not limited to the equal mass mixing mentioned above. This is because the foaming agent is an azo compound, which decomposes to produce nitrogen gas under heating conditions, regardless of its mixing ratio.

[0099] To demonstrate the outstanding performance of the high-performance shotcrete with the specific components and proportions provided by the present invention, shotcrete materials with similar components to the high-performance shotcrete provided in the embodiments of the present invention were prepared by selecting shotcrete materials from the prior art or by adjusting some of the components, as comparative shotcrete materials.

[0100] The following Comparative Examples 1 to 5 describe the different types of sprayed concrete.

[0101] Comparative Example 1 The similarities between this comparative example and Example 3 will not be repeated here; only the differences from Example 3 will be described. The difference between this comparative example and Example 3 is that calcium salts are absent in the sprayed plain concrete; thus, a comparative sprayed concrete is provided, as described with reference to Example 3.

[0102] Comparative Example 2 The similarities between this comparative example and Example 3 will not be repeated here; only the differences from Example 3 will be described. The difference between this comparative example and Example 3 is that the sprayed concrete lacks a foaming agent; thus, a comparative sprayed concrete is provided, as described with reference to Example 3.

[0103] Comparative Example 3 The similarities between this comparative example and Example 3 will not be repeated here; only the differences from Example 3 will be described. The difference between this comparative example and Example 3 is that acrylic acid and acrylamide are absent in the sprayed concrete; thus, a comparative sprayed concrete is provided, as described with reference to Example 3.

[0104] Comparative Example 4 The similarities between this comparative example and Example 3 will not be repeated here; only the differences from Example 3 will be described. The difference between this comparative example and Example 3 is that the activator lacks phosphate; thus, as described with reference to Example 3, it provides a comparative shotcrete.

[0105] Comparative Example 5 This comparative example provides a heat-insulating and heat-resistant shotcrete prepared in accordance with Chinese Patent CN 117985977A.

[0106] The preparation process of modified thermal insulation ceramsite is as follows: (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.

[0107] (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 h. After the reaction was completed, cellulose ether was added to adjust the liquid viscosity to 350 mPa·s~550 mPa·s to obtain hydrogel surface modification precursor a1.

[0108] (3) The surface-activated high-strength shale ceramic particles were immersed in the hydrogel modification precursor a1. After the ceramic particles were completely wetted for 30 min, 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 h to carry out the post-crosslinking reaction to obtain the modified heat-insulating ceramic particles A1.

[0109] Application examples The application example of this invention provides a construction application method for the above-mentioned high-performance shotcrete for high-temperature tunnels, including the following steps: adding magnesium oxide, calcium nitrite, acrylic acid, acrylamide, water-reducing agent, sand, gravel and water sequentially into a forced mixer and mixing to obtain shotcrete; transporting the shotcrete and activator through separate pipelines, mixing them evenly at the nozzle, and immediately spraying them out to obtain the high-performance shotcrete for high-temperature tunnels, which is used to complete the support and reinforcement of high-temperature tunnels.

[0110] Specifically, each component is added to a forced mixer and mixed for about 120 seconds to obtain sprayed plain concrete; the sprayed plain concrete and the activator are mixed evenly at the nozzle under the action of high-speed air pressure of 0.5 MPa to 1.0 MPa.

[0111] Based on the construction application methods provided in the above application examples, various properties of the high-performance shotcrete provided in each embodiment were tested.

[0112] Meanwhile, the performance of the comparative shotcrete provided in Comparative Examples 1 to 4 was tested using the same construction application method as in the above application examples.

[0113] The comparative shotcrete provided in Comparative Example 5 was applied using the following construction methods to determine its performance: Add 450 parts of P·O 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 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 heat-insulating and heat-resistant shotcrete.

[0114] The evaluation of the fresh concrete performance of the embodiments and comparative examples involved in the application examples of this invention refers to GB50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", the evaluation of mechanical performance strength refers to GB50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", the specimen molding and rebound rate test methods refer to JGJ / T 372-2016 "Technical Specification for Application of Shotcrete", and the thermal conductivity test method refers to GB / T 11968-2020 "Autoclaved Aerated Concrete Blocks".

[0115] The fluidity test used plain sprayed concrete, i.e., without the addition of activator, while the other performance indicators were tested with the addition of activator.

[0116] The compressive strength of shotcrete after 28 days was tested using an 80℃ steam curing chamber, and the compressive strength ratio under heat curing was calculated according to Formula 1 below.

[0117] α=T h, 28 d / T 28 d ×100% Formula 1 In Equation 1, α represents the compressive strength ratio after heat curing, expressed in %; T h, 28 d The compressive strength of shotcrete cured at 80℃ for 28 days is given in MPa; T 28 d The compressive strength of shotcrete under standard curing conditions after 28 days is given in MPa.

[0118] Specifically, in the relevant performance tests in Tables 2 to 4 below, the test temperature was 20℃.

[0119] The performance tests of the above high-performance shotcrete are shown in Table 2 below.

[0120] Table 2 Performance test results of high-performance shotcrete for high-temperature tunnels in Examples 1-5 As shown in Table 2, in terms of fluidity, the plain shotcrete for high-temperature tunnels provided in Examples 1 to 5 has good fluidity retention ability. Its slump at 1.0 h is ≥210 mm and spread is ≥505 mm; its slump at 2.0 h is ≥495 mm and spread is ≥505 mm. This indicates that the high-performance shotcrete has good initial fluidity and plasticity retention ability over time, which meets the requirements of long-distance and long-term shotcreting construction in high-temperature tunnels.

[0121] Regarding setting and hardening, the high-performance shotcrete for high-temperature tunnels provided in Examples 1-5 exhibits short setting times, with initial setting times all ≤3.2 min and final setting times all ≤9.1 min. As the hydration age increases, the compressive strength of the high-performance shotcrete for high-temperature tunnels provided in Examples 1-5 gradually increases without any later-stage strength reduction. Specifically, the compressive strength in the examples is ≥11.2 MPa at 10 h, ≥15.6 MPa at 1.0 d, ≥27.3 MPa at 3 d, ≥36.4 MPa at 7 d, and ≥45.1 MPa at 28 d. Furthermore, the rebound rate of the high-performance shotcrete for high-temperature tunnels provided in Examples 1-5 is no greater than 7.1%, demonstrating good construction performance. The test results of setting time, compressive strength, and shotcrete rebound rate indicate that the high-performance shotcrete for high-temperature tunnels provided in Examples 1-5 features rapid setting and hardening speed and high early strength, meeting the requirements for rapid tunnel support construction.

[0122] In terms of compressive strength ratio under heat curing, the high-performance shotcrete for high-temperature tunnels provided in Examples 1 to 5 has a compressive strength ratio under heat curing ≥118%, and the prepared shotcrete does not have the problem of high-temperature strength shrinkage. In terms of thermal insulation performance, the high-performance shotcrete for high-temperature tunnels provided in Examples 1 to 5 has a thermal conductivity ≤0.94, which indicates that the high-performance shotcrete for high-temperature tunnels has thermal insulation performance, which can reduce the service temperature of other lining structures, resist the thermal damage of high-temperature tunnels, and is suitable for the construction needs of high-temperature tunnels.

[0123] The performance test results of the comparative shotcrete provided in Comparative Examples 1 to 4 are compared with the performance of the high-performance shotcrete provided in Examples 3 to 4 in Table 3 below.

[0124] Table 3. Performance test results of shotcrete in Examples 3 and 4 and Comparative Examples 1 to 4 Table 3 shows that, compared with the examples, the test results of Comparative Example 1 indicate that the absence of calcium salts leads to a prolonged setting time, reduced early strength, and increased rebound rate in shotcrete. Meanwhile, the test results of Comparative Example 2 show that the absence of foaming agent does not affect the setting and hardening performance of shotcrete, but it does compromise its density, resulting in a high thermal conductivity and making it susceptible to thermal damage to subsequent lining structures. The test results of Comparative Example 3 show that, without acrylic acid and acrylamide, the setting and hardening time of shotcrete increases, and the rebound rate also increases, indicating that acrylic acid plays an important role in improving setting performance and enhancing the sprayability of concrete.

[0125] Meanwhile, in Comparative Example 4, due to the lack of phosphate in the activator, magnesium oxide could not be hydrated and hardened smoothly. As a result, the concrete was plastic and difficult to harden, making it impossible to evaluate its mechanical strength and construction performance, and thus failing to meet the support and reinforcement requirements for high rock temperature tunnels.

[0126] The above comparative examples demonstrate that the synergistic effect of calcium salts, foaming agents, acrylic acid and acrylamide, and activators is the key technology for ensuring that high-performance shotcrete used in high-temperature tunnels maintains good construction performance and application results.

[0127] As explained above, in the high-performance shotcrete provided by this invention, each component is indispensable. The synergistic interaction between magnesium oxide, foaming agent, acrylic acid and acrylamide, and activator gives the high-performance shotcrete of this invention excellent comprehensive performance. The activator, acting as a catalyst for magnesium oxide activation, reacts first with calcium salts after mixing with the shotcrete. This rapidly generates calcium phosphate, providing conditions for the activation of magnesium oxide particles and further aiding in the activation process. Simultaneously, it provides conditions for the free radical polymerization of acrylic acid and acrylamide, improving the workability of the shotcrete. Furthermore, the foaming agent generates nitrogen gas, ensuring the formation of stable, closed, and uniform bubbles within the shotcrete, reducing its thermal conductivity. In summary, the high-performance shotcrete of this invention not only achieves rapid setting and hardening of magnesium oxide-based shotcrete, meeting the requirements for shotcrete sprayability, but also solves the problem of thermal damage in high-temperature tunnel concrete lining structures.

[0128] The performance test results of the comparative shotcrete provided in Comparative Example 5 are compared with the performance of the high-performance shotcrete provided in Examples 3 and 4 as shown in Table 4 below.

[0129] Table 4 shows the performance test results of the shotcrete provided in Examples 3 and 4 and Comparative Example 5. As shown in Table 4, compared with the embodiments, the shotcrete prepared by Comparative Example 5 using ordinary silicate cement and modified porous aggregates such as ceramsite, although possessing better setting and hardening properties and thermal conductivity, inevitably suffers from thermal damage to high-temperature tunnel concrete. This indicates that shotcrete prepared using conventional silicate cement and ceramsite cannot resist the thermal damage problem of high-temperature tunnels, cannot provide a good service environment for subsequent lining, and cannot guarantee the green and long-life service requirements of transportation engineering.

[0130] The embodiments described above are for illustrative purposes only and do not constitute a specific limitation on the present invention. Any modifications made without departing from the basic concept of the present invention, as well as any obvious modifications derived therefrom, are within the scope of protection of the present invention.

Claims

1. A high-performance shotcrete for high-temperature tunnels, characterized in that, It includes separately stored sprayed concrete and an activator; wherein the sprayed concrete comprises the following components, which are uniformly mixed in parts by weight: 400-500 parts of magnesium oxide; Calcium salt 1-5 parts; 0.5~1.0 parts of foaming agent; Acrylic acid 0.5~1.0 parts; Acrylamide 0.5~1.0 parts; Water-reducing agent: 4.0~5.0 parts; 1300~1650 parts of filler; 100-150 parts water; The water-cement ratio of the sprayed plain concrete is 0.25~0.30, the sand ratio is 45%~55%, and the bulk density is 2310±10 kg / m³. 3 ; The activator is a phosphate suspension containing an initiator; The activator is present in a mass fraction of 150-200 parts.

2. The high-performance shotcrete according to claim 1, characterized in that, The activator was prepared using the following method: S1. Dissolve 45-60 parts by weight of phosphate in water to prepare a phosphate aqueous solution; S2. Under a shear force of 8 m / s to 10 m / s, 0.05 to 0.5 parts by mass of stabilizer are added to the phosphate aqueous solution to obtain a precursor solution; S3. Add 0.1 to 0.5 parts by weight of the initiator to the precursor solution until it is completely dispersed to obtain the activator. The total mass of the activating agent is 100 parts by mass.

3. The high-performance shotcrete according to claim 2, characterized in that, The phosphate is selected from any one of sodium dihydrogen phosphate, sodium hydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, and potassium phosphate, or a mixture of at least two in any proportion.

4. The high-performance shotcrete according to claim 2, characterized in that, The stabilizer is selected from any one of magnesium aluminum silicate, diatomaceous earth, attapulgite, sepiolite, and montmorillonite, or a mixture of at least two in any proportion.

5. The high-performance shotcrete according to claim 2, characterized in that, The initiator is selected from any one of benzoyl oxide, sodium bisulfite, potassium bisulfite, and ammonium bisulfite, or a mixture of at least two in any proportion.

6. The high-performance shotcrete according to any one of claims 1 to 5, characterized in that, The magnesium oxide is obtained by calcining magnesite at 800℃~1100℃, wherein the MgO content is 80%~85% and the SiO2 content is 5%~10%; the activity index is 180 s~250 s, and the specific surface area is 500 m². 2 / kg~600 m 2 / kg.

7. The high-performance shotcrete according to any one of claims 1 to 5, characterized in that, The calcium salt is selected from any one of calcium nitrate, calcium nitrite, and calcium acetate, or a mixture of at least two in any proportion.

8. The high-performance shotcrete according to any one of claims 1 to 5, characterized in that, The water-reducing agent is a polycarboxylate water-reducing agent.

9. The high-performance shotcrete according to any one of claims 1 to 5, characterized in that, The filler includes sand and gravel; the sand is preferably continuously aggregated medium sand with a fineness modulus of 2.3 to 3.2 and a mud content of no more than 3.0%; the gravel is preferably continuously aggregated small gravel with a mud content of no more than 3.0%, a mud lump content of no more than 1.0%, and a particle size of 4.75 mm to 9.5 mm.

10. The construction and application method of high-performance shotcrete as described in any one of claims 1 to 9, characterized in that, Including the following steps: Preparation of sprayed plain concrete: 400-500 parts magnesium oxide, 1-5 parts calcium salt, 0.5-1.0 parts foaming agent, 0.5-1.0 parts acrylic acid, 0.5-1.0 parts acrylamide, 4.0-5.0 parts water-reducing agent, 1300-1650 parts filler and 100-150 parts water are thoroughly mixed to obtain sprayed plain concrete; The sprayed concrete is transported separately with 150-200 parts of activator through pipelines, mixed evenly at the nozzle, and sprayed out immediately. All figures above are by weight (parts).

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