Quick-setting special mortar for tunnel repair and preparation method of quick-setting special mortar

Abstract

The invention relates to the technical field of concrete, and particularly discloses quick-setting special mortar for tunnel repair and a preparation method of the quick-setting special mortar. The quick-setting special mortar for tunnel repair is prepared from the following raw materials in parts by weight: 40 to 60 parts of cementing material, 15 to 25 parts of 0.16 to 1.25 mm continuous grading quartz sand, 5 to 10 parts of silica fume, 1 to 5 parts of nano calcium carbonate, 1 to 3 parts of water reducing agent, 1 to 3 parts of reinforced fiber, 2 to 6 parts of styrene-butadiene emulsion and 1 to 3 parts of expanding agent. The preparation method comprises the following steps: mixing and stirring the cementing material, the quartz sand, the silica fume, the nano calcium carbonate, the reinforced fibers, the water reducing agent and the expanding agent to obtain a dry material; adding styrene-butadiene emulsion into the dry material, and stirring to form slurry; and adding water into the slurry according to a water-binder ratio of 0.25-0.30, and stirring to obtain the quick-setting special mortar. The quick-setting special mortar for tunnel repair has the advantages of high strength, high durability and high impermeability.

Description

Technical Field

[0001] The present application relates to the field of concrete technology, and more specifically, to a fast-setting special mortar for tunnel repair and a preparation method thereof. Background Art

[0002] In recent years, my country's infrastructure construction has developed rapidly, and more and more tunnels have been built for roads and railways. As the service time has prolonged, many tunnels have suffered from various defects such as lining cracking, deformation, falling blocks, and leakage, affected by factors such as surrounding rock conditions, geological structure, and environmental climate. These defects have seriously reduced the safety and stability of the tunnel structure and threatened the safety of tunnel driving, and they must be rectified.

[0003] Existing technologies generally select remediation plans based on tunnel geological conditions, operating environment, and disease conditions. For tunnels with relatively minor disease conditions, grouting, surface sealing, and local repair are generally used for remediation, which are low-cost and easy to construct. However, due to technical defects, the repair effect is not ideal and the disease is prone to recurrence. The remediation method of using corrugated plates and mortar to reinforce the diseased tunnel structure as a whole has achieved significant improvement over other methods and significantly improved the effect. However, this construction method has problems such as loose grouting behind the corrugated plates, voids, weak adhesion between the injected sulphoaluminate cement-based grouting material and the original lining, and extremely high cost. Especially in coastal areas, due to high humidity and high salt content in the air, the corrugated plates and their metal fittings such as bolts are prone to rust, leading to other diseases.

[0004] In addition, tunnel diseases are mainly concentrated in the secondary lining. The secondary lining usually uses ordinary C35 or C40 concrete, which has poor bearing capacity, durability and impermeability. Therefore, it is prone to various diseases under the influence of factors such as surrounding rock pressure and groundwater erosion, affecting driving safety. Moreover, due to its low compressive strength, the required bearing capacity can only be achieved by increasing the thickness. Its thickness reaches 30cm-40cm, which makes the tunnel excavation section larger and the cost increased. Especially for tunnels with poor surrounding rock conditions, it causes great construction difficulties. Therefore, a material with high strength, good durability and other excellent properties is needed to replace C35 / C40 concrete as the tunnel secondary lining, reduce the thickness of the secondary lining, and reduce construction and subsequent maintenance costs. Summary of the Invention

[0005] In order to improve the bearing capacity, durability and impermeability of concrete for tunnel repair, the present application provides a fast-setting special mortar for tunnel repair and a preparation method thereof.

[0006] The application provides a fast-setting special mortar for tunnel repair using the following technical solution: A quick-setting special mortar for tunnel repair, whose raw materials, measured by weight, include 40-60 parts of cementitious material, 15-25 parts of 0.16-1.25mm continuously graded quartz sand, 5-10 parts of silica fume, 1-5 parts of nano-calcium carbonate, 1-3 parts of water reducer, 1-3 parts of reinforcing fiber, 2-6 parts of styrene-butadiene emulsion, and 1-3 parts of expansion agent.

[0007] By adopting this technical solution, the synergistic effect of multiple components significantly improves the overall performance of the repair material. 0.16-1.25mm continuously graded quartz sand optimizes particle size, increasing the concrete bulk density, reducing mortar porosity, and improving compressive strength and scour resistance. Silica fume fills the micropores of the cement paste, reducing permeability, and reacts with Ca(OH)2 to form CSH gel, enhancing density. Nano-calcium carbonate acts as hydration nuclei, accelerating the formation of ettringite in sulfoaluminate cement, shortening setting time and improving fiber-matrix interfacial bond strength. Reinforced fibers form a three-dimensional crack-resistant network within the concrete, increasing the mortar's fracture energy and inhibiting crack formation. Styrene-butadiene emulsion forms a flexible film within the mortar, enhancing bond strength, lowering the elastic modulus, and reducing stress concentration. The expansive agent limits concrete shrinkage, offsetting shrinkage stresses and preventing hollowing in the repair layer. This formulation maintains concrete rigidity while improving durability and impermeability, meeting the requirements for rapid repairs and long-term use in tunnel environments.

[0008] Optionally, the cementitious material includes sulphoaluminate cement, silicate cement and mineral powder, and the sulphoaluminate cement, silicate cement and mineral powder are compounded in a mass ratio of (4-5):(1-2):1.

[0009] By adopting the above technical solution, sulphoaluminate cement leads the early hydration to generate needle-shaped ettringite, forming an initial strength skeleton; silicate cement generates CSH gel in the later stage to fill the gaps in the AFt skeleton, and the later strength of concrete is significantly improved; mineral powder reacts with cement hydration product Ca(OH)2 to generate secondary CSH, which reduces the porosity of concrete and consumes free Ca 2 + , suppressing the risk of alkali-aggregate reaction.

[0010] Optionally, the expansion agent includes calcium sulfoaluminate and magnesium oxide, and the calcium sulfoaluminate and magnesium oxide are compounded in a mass ratio of (4-6):3.

[0011] By adopting the above technical solution, calcium sulfoaluminate hydrates to form AFt in the early stage of solidification and curing to compensate for plastic shrinkage; magnesium oxide hydrates to form Mg(OH)2 in the later stage of curing to compensate for drying shrinkage; through the cooperation of the two, the segmented expansion is matched with the cement hydration shrinkage, avoiding excessive expansion in the early stage or insufficient compensation in the later stage of a single expansive agent.

[0012] Optionally, the reinforcing fibers include 40-50% by mass of basalt fibers and 50-60% by mass of polypropylene fibers.

[0013] By adopting the above technical solution, basalt fiber bears the load and inhibits the expansion of macro cracks; polypropylene fiber disperses micro cracks through the "bridging-pullout" mechanism to improve impact resistance.

[0014] Optionally, 3-5 parts of phase change microcapsules are further included, wherein the wall material of the phase change microcapsules is obtained by compounding polyurea and silicon dioxide, and the core material of the phase change microcapsules is paraffin.

[0015] By adopting the above technical solution, paraffin wax, a typical organic phase change material, features high latent heat of phase change and a moderate phase change temperature range. In tunnel environments, diurnal temperature differences or seasonal temperature fluctuations can cause the concrete lining to expand and contract, and accumulated thermal stress can easily lead to cracking. When the ambient temperature rises, paraffin wax melts from a solid state to a liquid state, absorbing and storing heat, suppressing the sudden temperature rise within the mortar. When the temperature drops, paraffin wax solidifies from a liquid state to a solid state, releasing the stored heat and mitigating the sudden temperature drop. This process buffers the rate of temperature change and reduces the magnitude of thermal stress, thereby minimizing shrinkage and expansion cracking caused by temperature gradients. It is particularly suitable for tunnels with large temperature differences, such as those in plateaus, cold regions, or shallow tunnels. Directly adding paraffin wax can easily lead to poor material compatibility and precipitation and migration during long-term service. Microencapsulation, however, encapsulates the paraffin wax within the wall material, preventing direct contact with the mortar matrix and ensuring the long-term stability of the phase change function without affecting the mortar's mechanical properties and workability. Polyurea is a high-performance elastic material with excellent flexibility, chemical resistance, and high bond strength. During the mortar hardening process, the polyurea wall material forms an interfacial transition zone with the cementitious material, strengthening the adhesion between the microcapsules and the mortar matrix and preventing performance failure caused by interfacial debonding. Its elastic properties synergize with the deformation of the mortar matrix to withstand forces, reducing the risk of microcapsules rupturing under load or shrinkage. As a composite component of the wall material, silica enhances its strength, hardness, and high-temperature resistance. Furthermore, silica's hydrophilic surface improves compatibility with cement-based materials, further improving the interfacial bonding between the microcapsules and the mortar.

[0016] Optionally, the preparation method of the phase change microcapsules is: Heat paraffin until it melts, add hexamethylene diisocyanate at a rate of 10-15% of the mass of the paraffin, and stir to form an oil phase liquid; Ultrasonic dispersion of nano-silica in deionized water, with the amount of nano-silica accounting for 5-10% of the total mass of the wall material, adding polyetheramine in a molar ratio of 1:1 to hexamethylene diisocyanate, and adjusting the pH to 8-9 to obtain an aqueous phase liquid; Add the oil phase to the water phase containing 2-3% Tween, stir and emulsify to form an O / W emulsion, then add the water phase to the O / W emulsion and react at 45-50°C for 3-4 hours; After the reaction is completed, the product is separated and freeze-dried in vacuum to obtain phase change microcapsules.

[0017] Optionally, the paraffin wax is obtained by compounding C18-C28 alkanes in a gradient, wherein C18-C20 alkanes account for 30-40%, C22-C24 alkanes account for 40-50%, and C26-C28 alkanes account for 10-20%.

[0018] By employing this technical solution, the phase transition temperature of the gradient-blended paraffin wax ranges from 28°C to 60°C, closely matching the typical temperature range within tunnels. The melting points of different carbon chain alkanes are distributed in a gradient, and the latent heat of phase change is released and absorbed in stages, creating a "multi-stage thermal buffer" effect. This more effectively smooths the rate of temperature change than single paraffin wax, reduces peak thermal stresses, and significantly reduces temperature-induced cracking.

[0019] In a second aspect, the present application provides a method for preparing a fast-setting special mortar for tunnel repair, which adopts the following technical solution: A method for preparing a quick-setting special mortar for tunnel repair comprises the following steps: Mix the cementitious material, quartz sand, silica fume, nano calcium carbonate and reinforcing fiber for 5-8 minutes, then add the water reducer and expansion agent in sequence, and continue stirring for 3-5 minutes to obtain dry material; Add styrene-butadiene emulsion to the dry material and stir at 60-80 rpm for 5-10 minutes to form a uniform slurry; Add water to the slurry with a water-to-binder ratio of 0.25-0.30, and stir at 100-120 rpm for 3-5 minutes to obtain a fast-setting special mortar.

[0020] Optionally, phase change microcapsules are added simultaneously with the addition of the styrene-butadiene emulsion.

[0021] By adopting the above technical solution, the lubricating effect of the emulsion reduces the mechanical damage of the microcapsules.

[0022] In summary, this application has the following beneficial effects: 1. This application utilizes a cementitious material as a strength framework. A combination of sulfoaluminate and Portland cement balances rapid setting with long-term strength. Continuously graded quartz sand optimizes particle packing density, increasing compressive strength. Silica fume fills micropores, improving permeability. Nano-calcium carbonate accelerates hydration and strengthens interfaces. Reinforcement fibers inhibit crack propagation. Styrene-butadiene emulsion enhances bond strength. Expansive agents compensate for shrinkage in stages. This concrete formula achieves high strength while also combining rapid setting, high strength, and impermeability and durability.

[0023] 2. In this application, the cementitious material is preferably a compound of sulphoaluminate cement, silicate cement, and mineral powder. Sulphoaluminate cement is dominant in the early formation of ettringite, silicate cement supplements the later CSH gel, and the mineral powder reduces the chloride ion permeability by 30% through the pozzolanic effect; the expansive agent is a compound of calcium sulphoaluminate and magnesium oxide. Calcium sulphoaluminate expands in the early stage of curing to compensate for plastic shrinkage, and magnesium oxide expands in the later stage to offset drying shrinkage, synergistically controlling and reducing the shrinkage rate of concrete, avoiding cracking and hollowing, and improving volume stability.

[0024] 3. The phase-change microcapsules in this application are preferably coated with a gradient paraffin wax composite material, a polyurea / SiO2 composite wall material. This wall material is highly alkali-resistant, and the paraffin wax gradient design effectively buffers thermal stress. Furthermore, the incorporation of the microcapsules does not affect the compressive strength of the mortar. Their uniform dispersion synergizes with the styrene-butadiene emulsion to form a thermal buffer network, significantly reducing the thermal expansion coefficient and improving the thermal stability and service life of the tunnel patch layer. DETAILED DESCRIPTION

[0025] The present application is further described in detail below with reference to the examples. It is particularly noted that if no specific conditions are specified in the following examples, the reactions are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples can be obtained from common commercial sources.

[0026] Preparation example of phase change microcapsules Preparation Example 1 Preparation example of a phase change microcapsule: Prepare the following ingredients: 50kg paraffin (C22 alkane), 6.5kg hexamethylene diisocyanate (HDI, industrial grade, purity ≥98%), 8.9kg polyetheramine (Jeffamine D-230), 1.2kg nano-silica (particle size 20-30nm), 3kg Tween (Tween-80, HLB=15, chemically pure), 80kg deionized water, 0.2kg triethylamine (TEA, analytical grade), and 0.5kg anhydrous ethanol (industrial grade).

[0027] Heat paraffin to 75°C and stir for 30 minutes until it becomes a homogeneous liquid. Add hexamethylene diisocyanate to the melted paraffin and stir at 70°C for 10 minutes to form a homogeneous oil phase.

[0028] Nano-SiO2 was added to deionized water and ultrasonically dispersed at a power of 300 W for 30 minutes to form a stable suspension. Jeffamine D-230 (molar ratio with HDI 1:1) was added to the suspension and stirred until completely dissolved. Triethylamine (TEA) was added dropwise to adjust the pH of the aqueous phase to 8-9 to obtain an aqueous phase liquid.

[0029] Slowly pour the oil phase into the aqueous phase containing Tween-80, maintaining the temperature at 70°C. High-speed shear emulsification is performed at 12,000 rpm for 15 minutes to form an emulsion with a particle size of 2-5 μm. Add the aqueous phase dropwise to the emulsion at a rate of 0.5 L / min. Maintain the temperature at 45-50°C, stir at 300 rpm, and allow the reaction time to last for 3 hours.

[0030] The temperature was lowered to 25°C, and ethanol was added to terminate unreacted isocyanate groups. The emulsion was centrifuged at 3000 rpm for 5 minutes, the supernatant discarded, and the mixture was washed three times with deionized water. The reaction product was frozen at -40°C for 6 hours to form solid microcapsules. The product was heated from -40°C to 25°C under a vacuum of 10 Pa and dried for 24 hours to obtain a white powder.

[0031] Preparation Example 2 A preparation example of phase change microcapsules: The difference from Preparation Example 1 is that 50 kg paraffin, 5 kg hexamethylene diisocyanate, 6.8 kg polyetheramine, and 0.6 kg nano-silica are used.

[0032] Preparation Example 3 A preparation example of phase change microcapsules: The difference from Preparation Example 1 is that 50 kg paraffin, 7.5 kg hexamethylene diisocyanate, 10.3 kg polyetheramine, and 1.8 kg nano-silica are used.

[0033] Preparation Example 4 A preparation example of phase change microcapsules: The difference from Preparation Example 1 is that paraffin wax is mixed with C18-C20: 35%, C22-C24: 45%, and C26-C28: 20% by mass. Example

[0034] Example 1 A method for preparing a quick-setting special mortar for tunnel repair: Prepare the following ingredients: 520kg cementitious material, selected from sulphoaluminate cement, fast hardening type, in compliance with GB20472-2006, Al2O3 content ≥ 28%; 180kg 0.16-1.25mm continuously graded quartz sand, SiO2 content ≥ 99%, mud content ≤ 0.5%, moisture content ≤ 0.3%; 80kg silica fume, SiO2 content ≥92%, average particle size 0.1-0.3μm, specific surface area ≥15,000m 2 / kg, loss on ignition ≤ 3%; 35kg nano calcium carbonate, particle size 30-80nm, specific surface area ≥25m 2 / g; 20kg polycarboxylic acid water reducer, solid content 40%, water reduction rate ≥30%, pH value 6-8, chloride ion content ≤0.1%; 25kg reinforcing fiber, made of basalt fiber, diameter 13±2μm, length 12mm; 40kg styrene-butadiene emulsion, solid content 48±1%, glass transition temperature (Tg) 5±2°C, pH 8-9, viscosity ≤500mPa·s (25°C); 15kg expansion agent, selected calcium sulfoaluminate, purity ≥90%, particle size 1-10μm.

[0035] Add the cementitious material, quartz sand, silica fume, nano calcium carbonate and reinforcing fiber into a forced mixer and dry mix at 50 rpm for 6 minutes; Add water reducer and expander in sequence and continue stirring at 60 rpm for 4 minutes; Add styrene-butadiene emulsion and stir at 70 rpm for 8 minutes to form a uniform slurry; Deionized water was added, the water-cement ratio of the concrete slurry was controlled at 0.28, and the material was stirred at a high speed of 110 rpm for 4 minutes to obtain a fast-setting special mortar.

[0036] Example 2 A method for preparing a quick-setting special mortar for tunnel repair: The difference from Example 1 is that the raw materials selected are 400 kg of cementitious material, 150 kg of 0.16-1.25 mm continuously graded quartz sand, 50 kg of silica fume, 10 kg of nano-calcium carbonate, 10 kg of water reducer, 10 kg of reinforcing fiber, 20 kg of styrene-butadiene emulsion, and 10 kg of expansion agent.

[0037] Example 3 A method for preparing a quick-setting special mortar for tunnel repair: The difference from Example 1 is that the raw materials selected are 600 kg of cementitious material, 250 kg of 0.16-1.25 mm continuously graded quartz sand, 100 kg of silica fume, 50 kg of nano-calcium carbonate, 30 kg of water reducer, 30 kg of reinforcing fiber, 60 kg of styrene-butadiene emulsion, and 30 kg of expansion agent.

[0038] Example 4 A method for preparing a fast-setting specialty mortar for tunnel repair: This method differs from Example 1 in that the cementitious material comprises sulphoaluminate cement, Portland cement, and mineral powder in a mass ratio of 4.5:1.5:1. The Portland cement is P.O42.5 grade, complying with GB175-2020, and the mineral powder is S95 grade slag powder.

[0039] Example 5 A method for preparing a quick-setting special mortar for tunnel repair: The difference from Example 1 is that the cementitious material is a compound of sulphoaluminate cement, silicate cement and mineral powder in a mass ratio of 3.5:0.5:1.

[0040] Example 6 A method for preparing a quick-setting special mortar for tunnel repair: The difference from Example 1 is that the cementitious material is a compound of sulphoaluminate cement, silicate cement, and mineral powder in a mass ratio of 5.5:2.5:1.

[0041] Example 7 A method for preparing a fast-setting specialty mortar for tunnel repair differs from Example 1 in that the expansive agent is a mixture of calcium sulfoaluminate and magnesium oxide in a mass ratio of 5:3. The magnesium oxide has an active MgO content of ≥85%, a loss on ignition of ≤5%, and a particle size of 5-20 μm.

[0042] Example 8 A method for preparing a fast-setting special mortar for tunnel repair: The method differs from Example 1 in that the reinforcing fibers are 45% basalt fiber and 55% polypropylene fiber, by weight. The polypropylene fiber has a diameter of 48±5 μm, a length of 6 mm, and an elongation at break of ≥15%.

[0043] Example 9 A method for preparing a fast-setting special mortar for tunnel repair: The difference from Example 1 is that 40 kg of phase change microcapsules are added at the same time as the styrene-butadiene emulsion, and the phase change microcapsules are prepared by the method described in Preparation Example 1.

[0044] Example 10 A method for preparing a fast-setting special mortar for tunnel repair: The difference from Example 9 is that 30 kg of phase change microcapsules are added.

[0045] Example 11 A method for preparing a fast-setting special mortar for tunnel repair: the difference from Example 9 is that 50 kg of phase change microcapsules are added.

[0046] Example 12 A method for preparing a fast-setting special mortar for tunnel repair: The difference from Example 9 is that the phase change microcapsules are prepared by the method described in Preparation Example 2.

[0047] Example 13 A method for preparing a fast-setting special mortar for tunnel repair: The difference from Example 9 is that the phase change microcapsules are prepared by the method described in Preparation Example 3.

[0048] Example 14 A method for preparing a fast-setting special mortar for tunnel repair: The difference from Example 9 is that the phase change microcapsules are prepared by the method described in Preparation Example 4.

[0049] Comparative Example Comparative Example 1 A method for preparing a quick-setting special mortar for tunnel repair: the method differs from Example 1 in that no nano-calcium carbonate is added.

[0050] Comparative Example 2 A method for preparing a quick-setting special mortar for tunnel repair: The difference from Example 1 is that the quartz sand used has a particle size of 0.6-0.8 mm.

[0051] Comparative Example 3 A method for preparing a quick-setting special mortar for tunnel repair: the method differs from Example 1 in that no styrene-butadiene emulsion is added.

[0052] Performance testing Test method: Compressive strength: Tested according to GB / T17671-2021, specimen size 40mm×40mm×160mm.

[0053] Chloride ion diffusion coefficient: RCM method (NTBUILD492) is used for 28-day-old specimens.

[0054] Drying shrinkage: According to GB / T50082-2009, the specimen is measured after curing at 25℃ / 60%RH for 28 days.

[0055] Thermal expansion coefficient: DL / T5150-2017, temperature range 20-60℃, heating rate 2℃ / min.

[0056] Impact resistance: Drop hammer method (ASTM D7136), record the energy absorbed when the specimen breaks.

[0057] Table 1 Test data Combining Example 1 and Comparative Example 1 with Table 1, it can be seen that in the comparison between Example 1 and Comparative Example 1, Comparative Example 1 did not add nano calcium carbonate, resulting in the early compressive strength decreasing from 35.2 MPa to 28.4 MPa, and the 28d compressive strength decreasing from 68.5 MPa to 62.7 MPa. This difference stems from the key role of nano calcium carbonate: it acts as a hydration nucleus to accelerate the formation of ettringite in sulphoaluminate cement, shortening the setting time and improving the early strength; at the same time, nanoparticles fill the matrix micropores and enhance the fiber-matrix interface bonding, optimizing the long-term density. In addition, the chloride ion diffusion coefficient decreased from 2.8×10 -12 m 2 / s increased to 3.5×10 -12 m 2 / s, impact resistance from 8.5kJ / m 2 Reduced to 6.8 kJ / m 2 This further demonstrates the ability of nano-calcium carbonate to block permeation pathways and inhibit crack propagation by refining pores and strengthening interfaces. Nano-calcium carbonate is an essential component for balancing rapid setting, high strength, and impermeability.

[0058] Combining Example 1 and Comparative Example 2 with Table 1, it can be seen that Example 1 uses 0.16-1.25mm continuously graded quartz sand, while Comparative Example 2 uses single particle size sand. The results show that the 28d compressive strength of Comparative Example 2 is 11.9% lower than that of Example 1, and the impact resistance is 8.5kJ / m 2 Reduced to 7.1 kJ / m 2 Continuously graded sand optimizes the ratio of coarse, medium, and fine sand to enhance load transfer efficiency and reduce stress concentration. Single-size sand has a loose packing and high porosity, which leads to deterioration of mechanical properties.

[0059] Combining Example 1 and Comparative Example 3 with Table 1, it can be seen that in Comparative Example 3, no styrene-butadiene emulsion was added, and the bonding strength was reduced from 3.2 MPa to 1.9 MPa, and the drying shrinkage was reduced from 280×10 -6 Increased to 345×10 -6 , the chloride ion diffusion coefficient is from 2.8×10 -12 m 2 / s increased to 4.7×10 -12 m 2 During the hardening process, styrene-butadiene emulsion forms a flexible polymer film, which strengthens the bond between the new and old concrete interfaces while also sealing capillaries and buffering shrinkage stress, thereby inhibiting penetration and cracking. The absence of the emulsion increases the risk of interfacial debonding and significantly expands shrinkage stress and penetration pathways.

[0060] Combining Examples 1-3 and Table 1, it can be seen that a comparison of Example 1 (median ratio), Example 2 (lower limit ratio) and Example 3 (upper limit ratio) shows that the comprehensive effect achieved by the ratio of Example 1 of the present application is the best.

[0061] Combining Examples 1 and 4-6 with Table 1, it can be seen that Example 4 exhibits the best 28-day compressive strength and impermeability. Sulphoaluminate cement leads to early ettringite skeleton formation, while Portland cement supplements the later CSH gel. Mineral powder reduces pozzolanicity through the pozzolanic effect. A cementitious material ratio of 4-5:1-2:1 achieves optimal synergy between rapid setting and long-term performance.

[0062] Combining Examples 1 and 7 with Table 1, it can be seen that Example 7, using a composite expansion agent of calcium sulfoaluminate and magnesium oxide, achieved a 34% reduction in drying shrinkage compared to Example 1, and a slight increase in 28-day compressive strength from 68.5 MPa to 69.8 MPa. Calcium sulfoaluminate forms ettringite during the plastic phase, compensating for early shrinkage, while magnesium oxide hydrates to form Mg(OH)2 during the later stages, compensating for drying shrinkage. This staged expansion mechanism precisely matches the shrinkage process, avoiding overexpansion or undercompensation. The composite expansion agent significantly improves volume stability through multi-stage compensation.

[0063] Combining Examples 1 and 8 with Table 1, it can be seen that in Example 8, the reinforcing fiber is changed to 45% basalt fiber + 55% polypropylene fiber, and its impact resistance is increased from 8.5 kJ / m 2 Increased to 9.6kJ / m 2 The bond strength increased slightly from 3.2 MPa to 3.3 MPa. Basalt fiber inhibits macrocrack propagation, while polypropylene fiber disperses microcracks through a "bridging-pullout" mechanism. The two synergistically form a multi-scale crack-resistant network. The fiber blend, 40-50% basalt fiber + 50-60% polypropylene fiber, maximizes crack resistance.

[0064] Combining Examples 1 and 9-14 with Table 1, it can be seen that the addition of phase-change microcapsules significantly reduces the thermal expansion coefficient, while maintaining the 28-day compressive strength. The gradient-compounded paraffin absorbs and releases heat through multi-stage phase transitions, buffering thermal stress. The polyurea / SiO2 composite wall material enhances interfacial stability and prevents paraffin leakage. Phase-change microcapsules significantly improve thermal stability without sacrificing strength.

[0065] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A quick-setting special mortar for tunnel repair, characterized in that: The raw materials include 40-60 parts of cementitious material, 15-25 parts of 0.16-1.25mm continuously graded quartz sand, 5-10 parts of silica fume, 1-5 parts of nano calcium carbonate, 1-3 parts of water reducing agent, 1-3 parts of reinforcing fiber, 2-6 parts of styrene-butadiene emulsion and 1-3 parts of expansion agent by weight.

2. The fast-setting special mortar for tunnel repair according to claim 1, characterized in that: The cementitious material comprises sulphoaluminate cement, silicate cement and mineral powder, and the sulphoaluminate cement, silicate cement and mineral powder are compounded in a mass ratio of (4-5):(1-2):

1.

3. The fast-setting special mortar for tunnel repair according to claim 1, characterized in that: The expansion agent includes calcium sulfoaluminate and magnesium oxide, and the calcium sulfoaluminate and magnesium oxide are compounded in a mass ratio of (4-6):

3.

4. The fast-setting special mortar for tunnel repair according to claim 1, characterized in that: The reinforcing fibers include 40-50% by mass of basalt fibers and 50-60% by mass of polypropylene fibers.

5. The fast-setting special mortar for tunnel repair according to claim 1, characterized in that: It also includes 3-5 parts of phase-change microcapsules, wherein the wall material of the phase-change microcapsules is obtained by compounding polyurea and silicon dioxide, and the core material of the phase-change microcapsules is paraffin.

6. The fast-setting special mortar for tunnel repair according to claim 5, characterized in that: The preparation method of the phase change microcapsules is as follows: Heat paraffin until it melts, add hexamethylene diisocyanate at a rate of 10-15% of the mass of the paraffin, and stir to form an oil phase liquid; Ultrasonic dispersion of nano-silica in deionized water, with the amount of nano-silica accounting for 5-10% of the total mass of the wall material, adding polyetheramine in a molar ratio of 1:1 to hexamethylene diisocyanate, and adjusting the pH to 8-9 to obtain an aqueous phase liquid; Add the oil phase to the water phase containing 2-3% Tween, stir and emulsify to form an O / W emulsion, then add the water phase to the O / W emulsion and react at 45-50°C for 3-4 hours; After the reaction is completed, the product is separated and freeze-dried in vacuum to obtain phase change microcapsules.

7. The fast-setting special mortar for tunnel repair according to claim 5, characterized in that: The paraffin wax is obtained by compounding C18-C28 alkanes in a gradient, wherein C18-C20 alkanes account for 30-40%, C22-C24 alkanes account for 40-50%, and C26-C28 alkanes account for 10-20%.

8. A method for preparing the fast-setting special mortar for tunnel repair according to any one of claims 1 to 7, characterized in that: The following steps are involved: Mixing and stirring the cementitious material, quartz sand, silica fume, nano calcium carbonate, reinforcing fiber, water reducing agent and expansion agent to obtain dry material; Add styrene-butadiene emulsion to the dry material and stir at 60-80 rpm for 5-10 minutes to form a slurry; Add water to the slurry with a water-to-binder ratio of 0.25-0.30, and stir at 100-120 rpm for 3-5 minutes to obtain a fast-setting special mortar.

9. The method for preparing the fast-setting special mortar for tunnel repair according to claim 8, characterized in that: Phase change microcapsules are added simultaneously with the addition of the styrene-butadiene emulsion.

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