High-performance shotcrete for subsea tunnel and construction application method thereof

Abstract

The application belongs to the technical field of submarine tunnel construction, and discloses a high-performance sprayed concrete for submarine tunnels. The high-performance sprayed concrete comprises independently stored sprayed base concrete and 150-200 parts of an activating agent, wherein the sprayed base concrete comprises 400-500 parts of magnesium oxide, 1-5 parts of a magnesium salt, 1-5 parts of acrylamide, 4-5 parts of a water reducing agent, 1500-1800 parts of a filler and 100-150 parts of water, which are uniformly mixed according to weight parts. The high-performance sprayed concrete maintains large fluidity based on the dispersion of the water reducing agent; the magnesium salt and the activating agent generate struvite-like particles in a weak alkaline environment, provide a crystal nucleus effect for the coagulation and hardening of magnesium oxide on the basis of good corrosion resistance, and the activating agent can also accelerate the hydration and coagulation of magnesium oxide; the acrylamide polymerizes under the action of an initiator, loses fluidity, promotes the coagulation and hardening of magnesium oxide and improves the sprayability. The application also discloses a construction application method of the high-performance sprayed concrete in submarine tunnels.

Description

Technical Field

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

[0002] Shotcrete, as a crucial component of the initial support system for subsea tunnels, comes into direct contact with the rock mass and serves as the first line of defense against external erosion. However, compared to typical urban tunnels and mountain tunnels, subsea tunnels face challenging service environments with high-level ion erosion, high-concentration salt crystallization hazards, and high-pressure water penetration, making them highly susceptible to structural damage, failure, and leakage. Therefore, extending the service life of shotcrete is a vital step towards achieving a century-long service life for subsea tunnels.

[0003] Shotcrete is a concrete structure that uses compressed air or other power sources to propel a mixture of cementitious materials, aggregates, and a quick-setting agent at high speed onto the surface of rock or buildings. Under the action of the quick-setting agent, it hardens rapidly, forming a concrete structure that provides coverage, shielding, and support. It boasts numerous advantages, including high construction efficiency, simple process, and good economic benefits. It can constrain and control the deformation of surrounding rock, maintaining the integrity of the tunnel structure during construction and operation, making it one of the core materials for the safe and rapid construction of submarine tunnels. The special construction process results in a unique submicroscopic structure of shotcrete. Studies show that the porosity of shotcrete under dry spraying is 15%–20%, while under wet spraying it is 8%–12%. These pores provide channels for the transport and erosion of ions in the medium. Simultaneously, with the development of chemical admixture technology, the action of aluminum-phase quick-setting materials produces a large amount of aluminum-phase hydration products, mainly ettringite, after cement hydration. In particular, alkali-free quick-setting agents with aluminum sulfate as the core raw material introduce a large amount of sulfate minerals, making shotcrete highly susceptible to sulfate erosion. Therefore, controlling the microstructure and hydration product types of shotcrete is an important measure to extend its service life.

[0004] Chemical admixtures, especially accelerators, are used to regulate the setting and hardening process of cement and are important components in shotcrete that affect the types of hydration products and the microstructure of cement paste. Alkali-free accelerators achieve setting and hardening by regulating the formation of hydration products such as ettringite and calcium aluminate through sulfate, but this can lead to a deterioration in the sulfate resistance of shotcrete. Therefore, reducing the amount of sulfates such as aluminum sulfate is an important measure to optimize accelerator design and improve the durability of shotcrete. For example, Chinese patent CN107954628A discloses an alkali-free, chloride-free, and sulfate-free liquid accelerator. This liquid accelerator is composed of aluminum dihydrogen phosphate, an organic alcohol amine accelerator, an inorganic fluorine-containing accelerator, an alkali-thickening rheology modifier, an antifreeze agent, and water. By using aluminum dihydrogen phosphate instead of aluminum sulfate, the sulfate content is reduced while ensuring the aluminum phase source, thus improving the sulfate resistance of shotcrete. For example, Chinese patent CN 111253108A discloses a sulfur-free and alkali-free quick-setting agent and its preparation method that are beneficial to the durability of shotcrete. This sulfur-free and alkali-free quick-setting agent contains aluminum nitrate nonahydrate, acidic silica sol, magnesium fluorosilicate, cellulose ether, and water. It uses aluminum nitrate, acidic silica sol, and magnesium fluorosilicate to achieve the setting and hardening of cementitious materials. By replacing aluminum sulfate with aluminum nitrate, the amount of sulfate is reduced, thereby improving the corrosion resistance of shotcrete. However, although the quick-setting system with non-sulfate aluminum phase minerals as the accelerator reduces the sulfate content introduced into shotcrete, its hydration products are still easily corroded substances such as ettringite and calcium aluminate. Moreover, its cement stone microstructure is loose and porous, making it difficult to prevent the entry of corrosive ions. Its durability improvement effect needs to be verified.

[0005] Meanwhile, the dense cement stone structure can hinder the intrusion of harmful media ions, and the hydrated calcium silicate products with a low calcium-to-silica ratio have good corrosion resistance. Mineral admixtures such as fly ash, mineral powder, silica fume, and kaolin can regulate the cement hydration process, increase the density of cement stone, promote the production of low calcium-to-silica hydration products, and reduce the erosion of external harmful ions, which is an important way to improve the durability of shotcrete. For example, Chinese patent CN 116462442A discloses a composite accelerated-setting anti-corrosion material and its preparation method. The composite accelerated-setting anti-corrosion material provided includes the following raw materials in parts by weight: 45-55 parts of mineral admixture, 16-25 parts of anti-corrosion component, 8-12 parts of reinforcing agent, 10-15 parts of accelerated-setting component, and 4-8 parts of expansion agent. It can improve the sulfate resistance of shotcrete, inhibit the corrosion behavior of chloride ions on the shotcrete layer steel bars, enhance the durability of shotcrete, and extend the service life of tunnel structures. For example, Chinese patent CN 113735489A discloses an anti-sulfate corrosion agent, shotcrete, and its preparation method. This anti-sulfate corrosion agent is composed of 30-50 parts mineral admixtures, 10-25 parts silica fume, 5-15 parts calcium powder, 5-10 parts expanding agent, 5-10 parts silica, 0-5 parts graphene oxide, 0-5 parts gypsum, 1-2.5 parts dispersant, 0-0.2 parts defoamer, and 0-1 parts surfactant, with a dosage of 8%-12% of the cement mass. This concrete corrosion agent, through the nucleation effect, micro-filling effect, and pozzolanic effect of different micro- and nano-materials, makes the microstructure of shotcrete denser and the pore size finer, reducing the penetration channels of sulfate media and significantly improving the anti-sulfate corrosion performance of shotcrete. Furthermore, the active ingredients in the cement interact with the active groups on the graphene oxide to form crystal growth points that can compensate for the cracks in the cement matrix under sulfate conditions. However, while high amounts of mineral admixtures improve the durability of shotcrete, they also reduce the amount of alkaline substances in cement and slow down the hydration process and strength development of its cementitious system. This results in poor sprayability and high rebound rate of shotcrete, and the reduction in the amount of alkaline substances also leads to poor reinforcement protection performance.

[0006] Therefore, given the issues of easy erosion of hydration products of traditional shotcrete, numerous microscopic defects in cement stone, poor durability of support structures, and the difficulty in synergistically improving the durability and sprayability of conventional anti-corrosion materials, optimizing the types of hydration products and the microstructure of cement stone in shotcrete to improve its durability, and enhancing its service performance while ensuring good construction performance, is the key to achieving a century-long service life for undersea tunnels. Summary of the Invention

[0007] To address the limitations of existing technologies, such as rapid-setting systems using non-sulfate aluminum phase minerals as accelerators and high amounts of mineral admixtures, which fail to fundamentally improve the service performance of shotcrete while ensuring good construction properties, this invention provides a novel high-performance shotcrete for subsea tunnels. This high-performance shotcrete boasts advantages such as rapid setting and hardening, high support strength, low rebound rate, high corrosion resistance of hydration products, and good durability. It effectively controls the deformation and settlement of the surrounding rock in tunnels and is of great significance for achieving green, low-carbon construction and long-term service of subsea tunnels.

[0008] The present invention specifically adopts the following technical solution: In a first aspect, the present invention provides a high-performance shotcrete for submarine tunnels, comprising separately stored shotcrete and an activator.

[0009] The sprayed plain concrete comprises the following components, which are mixed evenly in parts by weight: 400-500 parts of magnesium oxide; 1-5 parts magnesium salt; Acrylamide 1-5 parts; 4-5 parts water-reducing agent; 1500-1800 parts of filler; 100-150 parts water.

[0010] 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 2300±10kg / m³. 3 .

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

[0012] Optionally, the magnesium oxide is obtained by calcining magnesite at 1150℃~1250℃, wherein the MgO content is 85%~95% and the SiO2 content is 3%~5%; the activity index is 260 s~300 s, and the specific surface area is 450 m². 2 / kg~500 m 2 / kg.

[0013] Optionally, the magnesium salt is selected from any one of magnesium nitrate, magnesium sulfate, magnesium acetate, and magnesium formate, or a mixture of at least two in any proportion.

[0014] Optionally, the water-reducing agent is a polycarboxylate water-reducing agent.

[0015] Optionally, the filler may include sand and gravel.

[0016] 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%.

[0017] Furthermore, the stones are continuously aggregated small stones 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.

[0018] Optionally, the activator is a phosphate suspension containing an initiator.

[0019] 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.

[0020] Optionally, the phosphate is selected from any one of sodium dihydrogen phosphate, aluminum dihydrogen phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, and sodium hydrogen phosphate, or a mixture of at least two in any proportion.

[0021] 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.

[0022] Stabilizers can improve the stability of the supersaturated phosphate suspension, thus ensuring its long-term storage.

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

[0024] The high-performance shotcrete provided by this invention has two main advantages. First, the dispersion effect of the water-reducing agent allows the shotcrete to maintain high fluidity for extended periods, meeting the requirements for long-distance, long-duration shotcreting construction. Second, during shotcreting, magnesium salts and activators react rapidly in the weakly alkaline environment created by magnesium oxide, producing micro-nano struvite particles that provide a nucleation effect for the setting and hardening of magnesium oxide. Simultaneously, the remaining activator accelerates magnesium oxide hydration, leading to rapid setting and hardening under the synergistic effect of the micro-nano struvite particle nucleation effect. The resulting struvite-like cementitious material possesses excellent corrosion resistance, meeting the requirements for support reinforcement and long-term service of submarine tunnels. Furthermore, as magnesium oxide hydrates, the system temperature rises, and acrylamide undergoes free radical polymerization under the action of the initiator in the activator, generating a linear polymer thickener. Its thickening and shrinkage effect reduces the free water content in the corresponding concrete, decreasing the fluidity of the shotcrete. This not only promotes the setting and hardening of the magnesium oxide cementitious material but also improves the sprayability of the shotcrete.

[0025] The high-performance shotcrete provided by this invention can fully leverage the synergistic effect between the activator, magnesium oxide, magnesium salt, and acrylamide, promoting each other's growth. This not only enables the rapid setting and hardening of magnesium oxide shotcrete, meeting the requirements for shotcrete sprayability, but also improves the corrosion resistance of the hydration products of shotcrete, meeting the needs for rapid construction and long-term safe operation of submarine tunnels.

[0026] A second aspect of the present invention provides a method for constructing and applying high-performance shotcrete as described above, comprising the steps of: Preparation of sprayed plain concrete: Mix 400-500 parts of magnesium oxide, 1-5 parts of magnesium salt, 1-5 parts of acrylamide, 4-5 parts of water-reducing agent, 1500-1800 parts of filler, and 100-150 parts of water thoroughly 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.

[0027] All figures above are by weight (parts).

[0028] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The high-performance shotcrete provided by this invention has high fluidity and long holding time. By utilizing the long-term dispersion technology of polycarboxylate superplasticizer and the characteristic that magnesium oxide particles do not undergo hydration reaction under the condition of no activator, the problem of high fluidity and long-term holding time of conventional shotcrete is solved, which meets the needs of long-distance and long-term shotcrete construction in submarine tunnels. There is no segregation or bleeding phenomenon, and its slump after 2 hours is not less than 200 mm and its spread is not less than 500 mm.

[0029] (2) The high-performance shotcrete provided by the present invention has a fast setting and hardening speed and high early strength. Under the action of the activator, magnesium salt promotes the reaction of some of the activator to generate micro-nano struvite particles, providing a nucleation effect for the hydration of magnesium oxide. Under the synergistic effect of the activator and micro-nano struvite particles, magnesium oxide generates struvite-like cementitious substances, which solidify and harden. The system temperature increases with the hydration of magnesium oxide, which promotes the free radical combination of acrylamide under the action of the activator to generate linear thickening polymers, consume free water, and improve the bonding effect with the surrounding rock interface. The three factors work synergistically to achieve rapid solidification and hardening, low spray rebound rate, and good sprayability of the shotcrete. It can solidify and harden within 10 minutes, with a compressive strength of not less than 10.0 MPa at 10 h, not less than 15.0 MPa at 1.0 d, not less than 25.0 MPa at 3 d, not less than 35.0 MPa at 7 d, and not less than 40.0 MPa at 28 d. It has high early strength and no loss of strength in the later stage, meeting the requirements for the reinforcement of the initial support structure. Furthermore, the hydration initiation time depends on the composition and amount of the activator, and the solidification and hardening process can be precisely controlled.

[0030] (3) The high-performance shotcrete provided by the present invention has good corrosion resistance and long service life. The struvite generated by magnesium oxide under the hydration regulation of the activator has a significant corrosion resistance, with a freeze-thaw resistance of D300, a permeability resistance of P10, a sulfate erosion resistance of KS200, and an electrical flux of no more than 1000 C.

[0031] (4) The high-performance shotcrete provided by the present invention, in addition to a small amount of industrial raw materials, mainly uses magnesium oxide as the cementitious material system. Magnesium oxide has a low firing temperature, which is lower than that of traditional silicate cement. It has low carbon emissions, meets the requirements for the preparation of low-carbon cement, and has a low-carbon and environmentally friendly effect. Detailed Implementation

[0032] An embodiment of the present invention provides a high-performance shotcrete for submarine tunnels, comprising separately stored shotcrete and an activator.

[0033] The sprayed plain concrete comprises the uniformly mixed components shown in Table 1 below: Table 1. Composition of sprayed concrete The activator is a phosphate suspension containing an initiator.

[0034] Of the above components: Magnesium oxide is produced by calcining magnesite at a temperature of 1150℃~1250℃, with an MgO content of 85%~95% and a SiO2 content of 3%~5%.

[0035] Furthermore, the activity index of MgO is 260 s~300 s, and the specific surface area is 450 m². 2 / g~500 m 2 / g.

[0036] The magnesium salt is at least one of magnesium nitrate, magnesium sulfate, magnesium acetate, and magnesium formate.

[0037] 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.

[0038] The filler material includes sand and gravel.

[0039] 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.

[0040] The activator is prepared from phosphate, initiator, stabilizer and water.

[0041] 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.

[0042] The preparation method of the activator includes the following steps: S1. Add water and phosphate to a flask in sequence, and stir at 80℃~90℃ 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.

[0043] The phosphate is at least one of sodium dihydrogen phosphate, aluminum dihydrogen phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, and sodium hydrogen phosphate.

[0044] The stabilizer is at least one of magnesium aluminum silicate, diatomaceous earth, attapulgite, sepiolite, and montmorillonite.

[0045] The initiator is at least one of sodium bisulfite, potassium bisulfite, and ammonium bisulfite.

[0046] All reagents (analytical grade) used in the preparation of the activator were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0047] 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 2300±10 kg / m³. 3 .

[0048] To better understand the present invention, the following examples are further illustrative of the invention and are only used to explain the content of the invention, but do not limit the invention. All similar embodiments based on the present invention should be within the scope of protection.

[0049] Example 1 A high-performance shotcrete for submarine tunnels includes separately stored shotcrete and an activator.

[0050] The sprayed plain concrete comprises the following components, which are mixed evenly in parts by weight: 400 parts magnesium oxide; 1.0 part magnesium salt; 4.0 parts water-reducing agent; Acrylamide 1.0 part; 825 portions of sand; 825 portions of pebbles; 100 portions of water.

[0051] The specific surface area of ​​MgO in magnesium oxide is 453 m². 2 / kg.

[0052] The activator has a mass fraction of 150 parts.

[0053] The raw materials for the activator are: 45% sodium dihydrogen phosphate, 0.1% sodium bisulfite, 0.05% sepiolite, and 54.85% water; based on the mass of the activator being 100%.

[0054] 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 80°C for 1.0 h until completely dissolved.

[0055] 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.

[0056] S3. Add 0.1 g of sodium bisulfite to the solution in step S2 and stir until it is completely dispersed and uniform to obtain the activator.

[0057] Example 2 A high-performance shotcrete for submarine tunnels includes separately stored shotcrete and an activator.

[0058] The sprayed plain concrete comprises the following components, which are mixed evenly in parts by weight: 500 parts magnesium oxide; 5.0 parts magnesium salt; 5.0 parts of water-reducing agent; Acrylamide 5.0 parts; 720 portions of sand; 720 portions of pebbles; 150 portions of water; Among them, the specific surface area of ​​MgO in magnesium oxide is 498 m². 2 / kg.

[0059] The activator has a mass fraction of 200 parts.

[0060] The raw materials for the activator are: 40% aluminum dihydrogen phosphate, 20% potassium dihydrogen phosphate, 0.1% sodium bisulfite, 0.2% potassium bisulfite, 0.2% ammonium bisulfite, 0.1% sepiolite, 0.1% magnesium aluminum silicate, 0.1% attapulgite, 0.1% diatomite, 0.1% montmorillonite, and 40.2% water; based on the mass of the activator being 100%.

[0061] The preparation method of the activator includes the following steps: S1. Add 40.2 g of water, 40 g of aluminum dihydrogen phosphate, and 20 g of potassium dihydrogen phosphate to a flask in sequence. Keep the mixture at 90°C and stir for 3.0 h until completely dissolved.

[0062] S2. Under a shear force of 10 m / s, 0.1 g sepiolite, 0.1 g magnesium aluminum silicate, 0.1 g attapulgite, 0.1 g diatomite, 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.

[0063] S3. Add 0.1 g sodium bisulfite, 0.2 g potassium bisulfite, and 0.2 g ammonium bisulfite to the solution in step S2 and stir until completely dispersed and uniform to obtain the activator.

[0064] Example 3 A high-performance shotcrete for submarine tunnels includes separately stored shotcrete and an activator.

[0065] The sprayed plain concrete comprises the following components, which are mixed evenly in parts by weight: 450 parts magnesium oxide; 3.0 parts magnesium salt; 4.5 parts water-reducing agent; Acrylamide 3.0 parts; 782 portions of sand; 782 portions of pebbles; 121 parts water; Among them, the specific surface area of ​​MgO in magnesium oxide is 471 m². 2 / kg.

[0066] The activator has a mass fraction of 160 parts.

[0067] The raw materials for the activator are: 10% sodium dihydrogen phosphate, 10% potassium dihydrogen phosphate, 10% aluminum dihydrogen phosphate, 10% potassium hydrogen phosphate, 10% sodium hydrogen phosphate, 0.1% potassium bisulfite, 0.2% ammonium bisulfite, 0.05% sepiolite, 0.05% diatomite, and 49.6% water; based on the mass of the activator being 100%.

[0068] The preparation method of the activator includes the following steps: S1. In a flask, add 49.6 g of water, 10 g of sodium dihydrogen phosphate, 10 g of potassium dihydrogen phosphate, 10 g of aluminum dihydrogen phosphate, 10 g of potassium hydrogen phosphate, and 10 g of sodium hydrogen phosphate in sequence. Keep the mixture at 86°C and stir for 2.2 h until completely dissolved.

[0069] S2. Under a shear force of 9.2 m / s, 0.05 g sepiolite and 0.05 g diatomaceous earth are 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 0.1 g potassium bisulfite and 0.2 g ammonium bisulfite to the solution in step S2 and stir until completely dispersed and uniform to obtain the activator.

[0071] Example 4 A high-performance shotcrete for submarine 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: 480 parts of magnesium oxide; 4.0 parts magnesium salt; 4.0 parts water-reducing agent; Acrylamide 4.0 parts; 754 portions of sand; 754 portions of pebbles; 124 portions of water; Among them, the specific surface area of ​​MgO in magnesium oxide is 466 m². 2 / kg.

[0073] The activator has a mass fraction of 180 parts.

[0074] The raw materials for the activator are: 20% aluminum dihydrogen phosphate, 20% potassium hydrogen phosphate, 20% sodium hydrogen phosphate, 0.5% ammonium bisulfite, 0.1% sepiolite, 0.1% diatomaceous earth, 0.1% attapulgite, and 39.2% water; based on the mass of the activator being 100%.

[0075] The preparation method of the activator includes the following steps: S1. In a flask, add 39.2 g of water, 20 g of aluminum dihydrogen phosphate, 20 g of potassium hydrogen phosphate, and 20 g of sodium hydrogen phosphate in sequence. Keep the mixture at 87°C and stir for 1.9 h until completely dissolved.

[0076] S2. Under a shear force of 9.6 m / s, 0.1 g sepiolite, 0.1 g diatomite, and 0.1 g attapulgite are added to the solution in step S1, and the solution is slowly cooled to room temperature at a rate of 10℃ / h.

[0077] S3. Add 0.5 g of ammonium bisulfite to the solution in step S2 and stir until it is completely dispersed and uniform to obtain the activator.

[0078] Example 5 A high-performance shotcrete for submarine tunnels includes separately stored shotcrete and an activator.

[0079] The sprayed plain concrete comprises the following components, which are mixed evenly in parts by weight: 460 parts of magnesium oxide; 2.0 parts magnesium salt; 4.5 parts water-reducing agent; Acrylamide 2.0 parts; 760 portions of sand; 760 portions of pebbles; 130 portions of water; The specific surface area of ​​MgO in magnesium oxide is 491 m². 2 / kg.

[0080] The activator has a mass fraction of 175 parts.

[0081] The raw materials for the activator are: 55% potassium hydrogen phosphate, 0.2% ammonium bisulfite, 0.2% potassium bisulfite, 0.1% montmorillonite, 0.1% diatomite, and 44.6% water; based on the mass of the activator being 100%.

[0082] The preparation method of the activator includes the following steps: S1. Add 44.6 g of water and 55 g of potassium hydrogen phosphate to a flask in sequence, and keep it at 84°C with stirring for 2.2 h until completely dissolved.

[0083] S2. Under a shear force of 9.6 m / s, 0.1 g of montmorillonite and 0.1 g of diatomaceous earth are added to the solution in step S1, and the solution is slowly cooled to room temperature at a rate of 10℃ / h.

[0084] S3. Add 0.2 g potassium bisulfite and 0.2 g ammonium bisulfite to the solution in step S2 and stir until completely dispersed and uniform to obtain the activator.

[0085] Example 6 A high-performance shotcrete for submarine tunnels includes separately stored shotcrete and an activator.

[0086] The sprayed plain concrete comprises the following components, which are mixed evenly in parts by weight: 470 parts magnesium oxide; 4.0 parts magnesium salt; 4.5 parts water-reducing agent; Acrylamide 2.0 parts; 758 portions of sand; 758 portions of pebbles; 135 parts water; The specific surface area of ​​MgO in magnesium oxide is 491 m². 2 / kg.

[0087] The activator has a mass fraction of 175 parts.

[0088] The raw materials for the activator are: 15% potassium hydrogen phosphate, 15% sodium hydrogen phosphate, 15% potassium dihydrogen phosphate, 15% sodium dihydrogen phosphate, 0.2% ammonium bisulfite, 0.2% potassium bisulfite, 0.1% montmorillonite, 0.1% diatomaceous earth, 0.1% magnesium aluminum silicate, 0.1% attapulgite, and 39.8% water; based on the mass of the activator being 100%.

[0089] The preparation method of the activator includes the following steps: S1. In a flask, add 39.8 g of water, 15 g of potassium hydrogen phosphate, 15 g of sodium hydrogen phosphate, 15 g of potassium dihydrogen phosphate, and 15 g of sodium dihydrogen phosphate in sequence. Keep the mixture at 82°C and stir for 1.9 h until completely dissolved.

[0090] S2. Under a shear force of 8.7 m / s, 0.1 g montmorillonite, 0.1 g diatomite, 0.1 g magnesium aluminum silicate, and 0.1 g attapulgite are added to the solution in step S1, and the solution is slowly cooled to room temperature at a rate of 10℃ / h.

[0091] S3. Add 0.2 g potassium bisulfite and 0.2 g ammonium bisulfite to the solution in step S2 and stir until completely dispersed and uniform to obtain the activator.

[0092] 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.

[0093] The following Comparative Examples 1 to 6 describe the different types of sprayed concrete.

[0094] 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 magnesium salts are absent in the sprayed plain concrete; thus, a comparative sprayed concrete is provided, as described with reference to Example 3.

[0095] 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 acrylamide is absent in the sprayed concrete; thus, a comparative sprayed concrete is provided, as described with reference to Example 3.

[0096] 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 the absence of an activator; it provides a comparative shotcrete as described in Example 3.

[0097] 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, in the preparation of the activator, the initiator is missing, and the amount of water is increased from 49.6 g to 49.9 g accordingly; thus, a comparative shotcrete is provided, as described with reference to Example 3.

[0098] Comparative Example 5 This comparative example provides a composite coagulation-promoting anticorrosive material prepared with reference to Chinese Patent CN 116462442A.

[0099] The specific preparation process is as follows: The composite coagulating anticorrosive material is composed of: 45 parts mineral admixture, 25 parts anticorrosive component, 12 parts silica fume, 10 parts coagulating component, and 8 parts magnesium oxide.

[0100] The mineral admixture is made by mixing fine powder of calcium carbide slag and modified red mud in a weight ratio of 1:2.5. The preparation method of calcium carbide slag fine powder is as follows: 1) The weighed carbide slag is dried in a drying oven. The specific drying conditions are: drying temperature of 120℃, drying time of 3.5 h, until the carbide slag reaches a constant weight. 2) The dried carbide slag was ball-milled. The specific ball-milling conditions were: a planetary ball mill was used, the ball mill speed was 250 r / min, and the ball milling time was 4 h. 3) The carbide slag after ball milling is screened. The specific screening conditions are: the test sieve mesh number is 200 mesh, the particle size of the carbide slag powder after screening is less than 75 μm, and it has good dispersibility and surface activity.

[0101] The preparation method of modified red mud is as follows: 1) The weighed red mud is dried in a drying oven. The specific drying conditions are: drying temperature of 105℃, drying time of 3 hours, and drying the red mud until constant weight is achieved. 2) The dried red mud was ball-milled. The specific ball-milling conditions were: a planetary ball mill was used, the ball mill speed was 350 r / min, and the ball milling time was 2 h. 3) The ball-milled red mud was sieved. The specific sieve conditions were: the test sieve mesh size was 200 mesh, and the particle size of the sieved red mud powder was less than 75 μm. 4) The sieved red mud is roasted and activated. The specific roasting conditions are: roasting temperature of 600℃ and roasting time of 1 h, in order to stimulate the inherent activity of the red mud.

[0102] The preparation method of mineral admixtures is as follows: According to the set weight ratio, the fine powder of carbide slag and the modified red mud are weighed and mixed in a mixer. The specific mixing conditions are: the mixer speed is 120 r / min, the mixing time is 4 h, and after the mixture is uniform, a modified mineral admixture is obtained.

[0103] The anti-corrosion component is made by mixing ultrafine mica powder, basalt fiber powder and EVA adhesive powder in a weight ratio of 1:1.5:0.8; The coagulating component is made by mixing sodium aluminate, sodium carbonate and limestone powder in a weight ratio of 1:2:2.5; The preparation method of the above-mentioned composite coagulation-promoting anticorrosive material is as follows: according to the set ratio, the modified mineral admixture, anticorrosive component, reinforcing agent, expanding agent and coagulation-promoting component are weighed in sequence, and the mixture is mixed in a mixer. The specific mixing conditions are: the mixer speed is 120 r / min, the mixing time is 8 h, and after the mixture is uniform, a composite coagulation-promoting anticorrosive material is obtained.

[0104] The anti-corrosion material replaces part of the cement or mineral admixtures to prepare shotcrete. It is then mixed with cement, coarse aggregate, fine aggregate, fly ash, silica fume, polycarboxylate high-performance water-reducing agent, aluminum sulfate-based fluorine-free and alkali-free quick-setting agent, and water in a forced mixer to obtain comparative shotcrete. The mixing time is not less than 120 seconds.

[0105] Specifically, the raw material composition of the comparative shotcrete is as follows: 355.5 kg of Conch P·O 42.5 grade cement, 886 kg of 5 mm~10 mm single-grade limestone crushed stone, 886 kg of river sand with a fineness modulus of 2.8, 67.5 kg of grade II fly ash, 27 kg of silica fume, 4.8 kg of polycarboxylate high-performance water-reducing agent, 50 kg of anti-corrosion material, 30 kg of BASF SA type aluminum sulfate-based fluorine-free and alkali-free liquid quick-setting agent, and 200 kg of water.

[0106] Comparative Example 6 The comparative shotcrete provided in this example uses a sulfur-free and alkali-free accelerator prepared as follows: Mix 10 parts aluminum hydroxide and 22 parts water thoroughly, then continuously add 37 parts of 70% nitric acid dropwise, controlling the dropwise addition time to 1.0 h and the temperature to 90℃, stirring for 2.0 h until completely dissolved, controlling the final pH value to 4, add 31 parts water and cool to 30℃ to obtain aluminum nitrate nonahydrate, then add acidic silica sol with pH 7, 3 parts magnesium fluorosilicate and 1 part hydroxypropyl methylcellulose, and stir for 1.0 h to obtain a sulfur-free and alkali-free quick-setting agent that is beneficial to the durability of shotcrete.

[0107] Specifically, the raw material composition of the comparative shotcrete is as follows: 500 kg of P·O 42.5 grade cement, 886 kg of 5 mm~10 mm single-grade limestone crushed stone, 886 kg of river sand with a fineness modulus of 2.8, 5.0 kg of polycarboxylate superplasticizer, 40 kg of sulfur-free and alkali-free quick-setting agent, and 180 kg of water.

[0108] Application examples The application examples of the present invention provide a construction application method for the high-performance shotcrete of the above embodiments, including the following steps: adding magnesium oxide, magnesium salt, acrylamide, water-reducing agent, filler and water in sequence to a forced mixer and mixing to obtain shotcrete; transporting the shotcrete and activator through separate pipelines, mixing them evenly at the nozzle, and spraying them immediately to obtain the high-performance shotcrete for submarine tunnels, for the support and reinforcement of submarine tunnels.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] The comparative shotcrete provided in Comparative Example 5 was applied using the following construction methods to determine its performance: The wet-mix shotcrete method is adopted. According to the designed mix ratio, the weighed cement, silica fume, fly ash, river sand, crushed stone, anti-corrosion materials, polycarboxylate high-performance water-reducing agent and water are added to the forced mixer in sequence. After being mixed evenly, the mixture is loaded into the shotcrete machine. High-pressure air is used to send the concrete to the nozzle to mix with the quick-setting agent, and then the concrete is sprayed onto the surface of the tunnel surrounding rock at high speed.

[0113] In addition, the comparative shotcrete provided in Comparative Example 6 was applied using the following construction application methods to determine its performance: The wet-mix shotcrete method is adopted. According to the designed mix ratio, the weighed cement, river sand, crushed stone, polycarboxylate high-performance water-reducing agent and water are added to the forced mixer in sequence. After being mixed evenly, the mixture is loaded into the shotcrete machine. High-pressure air is used to send the concrete to the nozzle to mix with the quick-setting agent, and then the concrete is sprayed onto the surface of the tunnel surrounding rock at high speed.

[0114] The performance tests of the above high-performance shotcrete are shown in Table 2 below. Among them, the workability test was conducted without the addition of an activator, while the tests of setting time, mechanical strength, spray rebound rate and durability required the addition of an activator.

[0115] Specifically, the performance evaluation of fresh concrete is based on GB50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures"; the mechanical strength evaluation is based on GB50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete"; the durability evaluation is based on GB 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete"; and the specimen molding and rebound rate testing methods are based on JGJ / T 372-2016 "Technical Specification for Application of Shotcrete". Specifically, in the relevant performance tests in Tables 2, 4, and 5 below, the test temperature was 20℃.

[0116] Table 2 Performance tests of high-performance shotcrete in Examples 1-6 As shown in Table 2, in terms of fluidity, the fluidity of the high-performance shotcrete provided in Examples 1 to 6 gradually increases with the increase of the water-cement ratio. Its slump at 1.0 h is ≥210 mm and spread is ≥510 mm; its slump at 2.0 h is ≥205 mm and spread is ≥505 mm. This indicates that the high-performance shotcrete has good initial fluidity and plasticity retention capacity over time, which meets the requirements of long-distance and long-term shotcreting construction of submarine tunnels.

[0117] Regarding setting and hardening, the initial setting time of the high-performance shotcrete provided in Examples 3 to 6 was ≤3.7 min, and the final setting time was ≤8.9 min. With increasing hydration age, the compressive strength of the high-performance shotcrete provided in Examples 1 to 5 gradually increased, showing an inverse correlation with the water-cement ratio; that is, the higher the water-cement ratio, the lower the strength at the same age. Specifically, in the examples, the compressive strength at 10 h was ≥11.8 MPa, at 1.0 d it was ≥15.3 MPa, at 3 d it was ≥26.4 MPa, at 7 d it was ≥32.3 MPa, and at 28 d it was ≥42.7 MPa. The rebound rate was no greater than 8.4%, indicating good workability. The test results of setting time, compressive strength, and shotcrete rebound rate show that the high-performance shotcrete provided in Examples 1 to 6 has the characteristics of fast setting and hardening speed and high early strength.

[0118] Regarding durability, the results of the high-performance shotcrete provided in Examples 1 to 6 on frost resistance and sulfate attack resistance show that the high-performance shotcrete has a frost resistance grade of D250, an impermeability grade of not less than P10, a sulfate attack resistance grade of KS200, and an electrical flux of not more than 1000 C, which indicates that the high-performance shotcrete has excellent service performance.

[0119] The performance of the high-performance shotcrete of Example 3 was tested at 10℃, 20℃, 30℃ and 40℃ respectively. The test results are shown in Table 3 below.

[0120] Table 3 Performance tests of high-performance shotcrete in Example 3 at different temperatures Table 3 shows that within the temperature range of 10℃ to 40℃, as the ambient temperature increases, the fluidity of this high-performance shotcrete decreases, the setting time shortens, the compressive strength before 7 days increases, the frost resistance reaches D250, the impermeability is not less than P10, the sulfate attack resistance meets KS150, and the electrical flux is not greater than 1000 C. Specifically, within the temperature range of 10℃ to 40℃, the minimum 2-hour fluidity of Example 3 is 510 mm, and the longest final setting time is 8.7 min. The shotcrete at 10℃ has the lowest strength before 3 days of curing, with a 10-hour strength of 12.8 MPa, a 1-day strength of 15.7 MPa, and a 3-day strength of 26.9 MPa. That is, temperature does not affect the performance of this high-performance shotcrete, meeting the support and reinforcement requirements of submarine tunnels in environments with high salt erosion, high permeability water pressure, and high salt crystallization.

[0121] 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 4 below.

[0122] Table 4 Performance tests of shotcrete in Examples 3-4 and Comparative Examples 1-4 Table 4 shows that, compared with the examples, the test results of Comparative Example 1 indicate that without magnesium salts, the initial and final setting times of the shotcrete doubled, and the early strength was significantly reduced, especially the 10-hour strength. The decrease in setting time and early strength led to reduced sprayability and increased rebound rate, negatively impacting the overall cost-effectiveness of the shotcrete. The test results of Comparative Examples 2 and 4 show that without acrylamide or initiators, the system could not produce a linear thickening composition, resulting in prolonged setting time and increased rebound rate. Meanwhile, the test results of Comparative Example 3 indicate that, although the absence of an activator did not affect the fluidity of the shotcrete, it significantly increased the setting time and prolonged the final setting time, failing to meet the requirements for rapid support and reinforcement. This demonstrates that magnesium salts, acrylamide, and initiators are key technologies for high-performance shotcrete.

[0123] The above description illustrates that each component in this application is indispensable. The synergistic effect between the activator, magnesium oxide, magnesium salt, and acrylamide promotes each other, resulting in high-performance shotcrete of this invention with excellent comprehensive performance. It not only achieves rapid setting and hardening of magnesium oxide shotcrete, meeting the requirements for shotcrete sprayability, but also improves the corrosion resistance of the hydration products of shotcrete, meeting the needs of rapid construction and long-term safe operation of submarine tunnels. The reaction between magnesium salt and activator creates an acidic environment and generates micro-nano struvite particles, providing a nucleation effect for the setting and hardening of magnesium oxide. Under acidic conditions, the remaining activator accelerates the hydration of magnesium oxide, and the generated struvite cementitious material possesses excellent corrosion resistance. As magnesium oxide hydrates, the system gradually becomes neutral, and the temperature rises. Acrylamide undergoes free radical polymerization under the action of the activator, generating a linear polymer thickener. Its thickening and shrinkage effect reduces free water content, causing a loss of concrete fluidity, promoting the setting and hardening of magnesium oxide cementitious materials, and improving the sprayability of shotcrete. In summary, the high-performance shotcrete of this invention not only achieves rapid setting and hardening of slag powder shotcrete, meeting the requirements for shotcrete sprayability, but also meets the requirements for high durability in the complex erosive environment of submarine tunnels.

[0124] The performance test results of the comparative shotcrete provided in Comparative Examples 5 and 6 are compared with the performance of the high-performance shotcrete provided in Examples 3 and 4 as shown in Table 5 below.

[0125] Table 5 Performance tests of shotcrete in Examples 3-4 and Comparative Examples 5-6 As shown in Table 5, compared with the embodiments, the service performance of the shotcrete prepared by using anti-corrosion admixture for shotcrete in Comparative Example 5 is significantly improved. Its frost resistance can reach D200, impermeability can reach P10, sulfate erosion resistance can reach KS150, and electrical flux is as low as 892 C. However, the shotcrete prepared by this accelerator has poor sprayability and a rebound rate as high as 35.4%. Meanwhile, the shotcrete prepared by using non-sulfate accelerator in Comparative Example 6 has poor frost resistance, impermeability, sulfate erosion resistance, and electrical flux, which is difficult to meet the service requirements of high salt and high humidity environments. This indicates that the shotcrete prepared by using anti-corrosion admixture for shotcrete and non-sulfate accelerator does not meet the service environment requirements of high salt erosion, high permeability water pressure, and high salt crystallization of submarine tunnels, and it is difficult to achieve the green and low-carbon construction requirements of transportation engineering.

[0126] 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 submarine tunnels, characterized in that, It includes separately stored sprayed concrete and an activator; wherein the sprayed concrete comprises the following components, which are mixed uniformly in parts by weight: 400-500 parts of magnesium oxide; 1-5 parts magnesium salt; Acrylamide 1-5 parts; 4-5 parts water-reducing agent; 1500-1800 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 2300±10 kg / m³. 3 ; The activator is present in a mass fraction of 150-200 parts; The activator is a phosphate suspension containing an initiator.

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, aluminum dihydrogen phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, and sodium hydrogen 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 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 1150℃~1250℃, wherein the MgO content is 85%~95% and the SiO2 content is 3%~5%; the activity index is 260 s~300 s and the specific surface area is 450 m². 2 / kg~500 m 2 / kg.

7. The high-performance shotcrete according to any one of claims 1 to 5, characterized in that, The magnesium salt is selected from any one of magnesium nitrate, magnesium sulfate, magnesium acetate, and magnesium formate, 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 material includes sand and gravel; 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.

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: Mix 400-500 parts of magnesium oxide, 1-5 parts of magnesium salt, 1-5 parts of acrylamide, 4-5 parts of water-reducing agent, 1500-1800 parts of filler, and 100-150 parts of water thoroughly to obtain sprayed plain concrete. The sprayed plain concrete and 150-200 parts of activator are transported separately through pipelines, mixed evenly at the nozzle, and sprayed out immediately. All figures above are by weight (parts).

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