Low temperature grouting material based on intelligent anti-freezing microcapsules, and preparation method and use thereof

Abstract

This invention belongs to the field of building materials technology, and discloses a low-temperature grouting material based on intelligent antifreeze microcapsules, its preparation method, and its uses. By mass, the raw materials include: 520-900 parts of cementitious material, 400-550 parts of graded quartz sand, 1-5 parts of flocculant, 5-20 parts of nano-silica, 3-8 parts of water-reducing agent, 0.5-2 parts of defoamer, 15-20 parts of intelligent antifreeze microcapsules, and 120-170 parts of water. The intelligent antifreeze microcapsules include a core material and a shell covering the core material. The core material includes an antifreeze agent and a crack repair agent precursor. This invention can effectively prevent early frost damage, ensure later mechanical properties and durability, and is easy to construct.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a low-temperature grouting material based on intelligent antifreeze microcapsules, its preparation method and uses. This material is suitable for construction in low-temperature or sub-zero temperature environments. Background Technology

[0002] In infrastructure construction, wind power anchoring, road and bridge repair, and winter construction in frigid regions, the application of conventional cement-based grouting materials is severely limited. When the ambient temperature is below 5°C, the cement hydration reaction rate decreases exponentially. When the temperature drops below freezing, the crystallization pressure generated by the freezing of free water within the grout, the expansion stress caused by ice crystal growth, and the resulting water migration severely damage the grout's microstructure, leading to irreversible damage such as indefinitely prolonged setting time, loss of early strength, and significant deterioration of final strength and durability. Existing technologies typically employ measures such as adding chloride or nitrite antifreeze agents, using early-strength cement, or external heating. However, chlorides easily cause steel corrosion, nitrites are toxic, early-strength cement is expensive and its later strength may shrink, and external heating is energy-intensive, complex to construct, and poses safety hazards. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a low-temperature grouting material based on intelligent antifreeze microcapsules, its preparation method, and its applications. This invention can effectively prevent early frost damage, ensure later mechanical properties and durability, and is easy to construct.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A low-temperature grouting material based on intelligent antifreeze microcapsules, comprising, by weight parts: 520-900 parts of cementitious material, 400-550 parts of graded quartz sand, 1-5 parts of flocculant, 5-20 parts of nano silica, 3-8 parts of water-reducing agent, 0.5-2 parts of defoamer, 15-20 parts of intelligent antifreeze microcapsules, and 120-170 parts of water. The intelligent antifreeze microcapsule includes a core material and a shell covering the outside of the core material. The core material includes an antifreeze agent and a crack repair agent precursor.

[0005] Preferably, the cementitious material includes ordinary silicate cement, sulfoaluminate cement, mineral powder, and silica fume, and by mass parts, the low-temperature grouting material based on intelligent antifreeze microcapsules contains: 300-450 parts of ordinary silicate cement, 150-300 parts of sulfoaluminate cement, 50-100 parts of mineral powder, and 20-50 parts of silica fume.

[0006] Preferably, the water-reducing agent is a polycarboxylate superplasticizer.

[0007] Preferably, the preparation method of the intelligent antifreeze microcapsules includes the following steps: Potassium formate, ethylene glycol, and nano-silica sol are mixed evenly to form a homogeneous liquid mixture; The mixture was added to a container of liquid paraffin and then sheared and dispersed to obtain a composite core material suspension. The composite core material suspension was added dropwise to the sodium alginate colloidal solution under continuous stirring. During this process, the sodium alginate colloidal solution was continuously sheared. After the composite core material suspension was completely added, shearing and emulsification continued to form an oil-in-water primary emulsion. The primary emulsion is added dropwise to a composite coagulation bath. After the addition is complete, the mixture is stirred and reacted. After the reaction is complete, solid-liquid separation, washing, and vacuum drying are performed to obtain the intelligent antifreeze microcapsules. The composite coagulation bath is prepared by mixing calcium chloride aqueous solution and chitosan acetic acid solution.

[0008] Preferably, the mass ratio of potassium formate, ethylene glycol, and nano-silica sol is (9.5-10.5):(4.5-5.5):1; The mass ratio of potassium formate to liquid paraffin is 1:(1.5-2.5). The concentration of sodium alginate colloidal solution is 1.8wt%-2.0wt%; The volume ratio of the composite core material suspension to the sodium alginate colloidal solution is 1:(4-6). When preparing the composite coagulation bath, the concentration of calcium chloride aqueous solution is 1.9wt%-2.1wt%, the concentration of chitosan acetic acid solution is 0.9wt%-1.1wt%, and the volume ratio of calcium chloride aqueous solution to chitosan acetic acid solution is 1:(1-1.5). The volume ratio of the primary emulsion to the composite coagulation bath is 1:(3-5).

[0009] Preferably, when the primary emulsion is added dropwise to the composite coagulation bath, the drop height is controlled at 9.5-10.5 cm.

[0010] Preferred method: When potassium formate, ethylene glycol and nano silica sol are mixed evenly to form a uniform liquid mixture, the mixture is stirred at a speed of 500-700 rpm for 14-16 min. When the mixture is added to a container of liquid paraffin and then sheared and dispersed to obtain a composite core material suspension, high-speed shearing dispersion is carried out at a shear rate of 1950-2050 rpm for 30-50 min. The composite core material suspension was added dropwise to the sodium alginate colloidal solution under continuous stirring. During this process, the sodium alginate colloidal solution was continuously sheared. After the composite core material suspension was completely added, shearing and emulsification continued to form an oil-in-water primary emulsion. Then, the composite core material suspension was slowly added dropwise to the sodium alginate colloidal solution at a rate of 5-8 mL / min, while the sodium alginate colloidal solution was continuously sheared at 7500-8500 rpm. After the composite core material suspension was completely added, shearing and emulsification continued for 14-16 min. The primary emulsion is added dropwise to the composite coagulation bath. After the addition is complete, while stirring, the primary emulsion is added dropwise to the composite coagulation bath at a rate of 60-80 drops / min. After the addition is complete, stirring is continued at a rate of 95-105 rpm for 30-45 minutes until the stirring reaction is complete.

[0011] Preferred method: When performing solid-liquid separation, washing, and vacuum drying, solid-liquid separation is carried out by vacuum filtration; during washing, the filtered microspheres are washed multiple times with deionized water until the filtrate is neutral; the vacuum drying temperature is 40-50℃, the vacuum degree is -0.1MPa, and the drying time is 20-30h.

[0012] The present invention also provides a method for preparing low-temperature grouting material based on intelligent antifreeze microcapsules as described above, comprising the following steps: The cementitious material, graded quartz sand, flocculant, nano silica, water-reducing agent, defoamer, and intelligent antifreeze microcapsules are physically dry-mixed to obtain a dry powder mixture. The dry powder mixture is mixed with water until homogeneous to obtain the low-temperature grouting material based on intelligent antifreeze microcapsules.

[0013] The present invention also provides the use of low-temperature grouting material based on intelligent antifreeze microcapsules, which is used for sleeve connection of prefabricated buildings, secondary grouting of equipment foundations or grouting of prestressed ducts during winter construction.

[0014] The present invention has the following beneficial effects: This invention relates to a low-temperature grouting material based on intelligent antifreeze microcapsules. Through a rational formulation of 520-900 parts of cementitious materials, 400-550 parts of graded quartz sand, 1-5 parts of flocculant, 5-20 parts of nano-silica, 3-8 parts of water-reducing agent, 0.5-2 parts of defoamer, and 15-20 parts of intelligent antifreeze microcapsules, a grouting material system adapted to low-temperature environments is formed. Its innovation lies primarily in the application of intelligent antifreeze microcapsules and the synergistic effect of each component. These intelligent antifreeze microcapsules use antifreeze agents and crack repair agent precursors as core materials, with an external encapsulation shell. Unlike traditional grouting materials with a single antifreeze component, this invention not only lowers the freezing point of the liquid phase inside the grout through the antifreeze agent, inhibiting the crystallization pressure and expansion stress generated by the freezing of free water, ensuring normal cement hydration at low temperatures, but also compensates for the damage caused by low temperatures through the crack repair agent precursor. This method effectively addresses the issues of slow setting, lack of early strength, and deterioration of durability in conventional grouting materials at low temperatures by minimizing micro-damage. Simultaneously, 5-20 parts of nano-silica fill grout pores and optimize the microstructure, while 3-8 parts of water-reducing agent, 0.5-2 parts of defoamer, and 1-5 parts of flocculant improve grout dispersibility, reduce air bubbles, and enhance construction fluidity. Working synergistically with cementitious materials and graded quartz sand, it balances low-temperature workability with the mechanical properties and structural stability of the hardened grout. Furthermore, this solution achieves antifreeze functionality through intelligent antifreeze microcapsules, eliminating the need for harmful antifreeze components such as chlorides and nitrites, preventing steel corrosion, posing no toxic risks, and requiring no complex external heating measures. This simplifies construction processes, reduces energy consumption, and broadens the low-temperature construction window, making it suitable for various infrastructure construction needs in frigid regions. Detailed Implementation

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] This invention relates to a low-temperature grouting material based on intelligent antifreeze microcapsules, primarily comprising a dual-cement system cementitious material, graded aggregates, high-efficiency admixtures, and water. The high-efficiency admixtures include intelligent antifreeze microcapsules. Each intelligent antifreeze microcapsule comprises a biopolymer shell and a core material encapsulated within the shell. The biopolymer shell is a composite shell formed by ionic cross-linking of sodium alginate and chitosan. The core material comprises a first-path slow-release component and a second-path stress-release component; the first-path slow-release component is a composite organic antifreeze agent; the second-path stress-release component is a crack repair agent precursor. The cementitious material is primarily composed of ordinary silicate cement and rapid-hardening sulfoaluminate cement, with the addition of mineral powder and silica fume as mineral admixtures.

[0017] Specifically, by weight, the raw materials of the low-temperature grouting material based on intelligent antifreeze microcapsules of this invention include: 520-900 parts of cementitious material, 400-550 parts of graded quartz sand, 1-5 parts of flocculant, 5-20 parts of nano-silica, 3-8 parts of water-reducing agent, 0.5-2 parts of defoamer, 15-20 parts of intelligent antifreeze microcapsules, and 120-170 parts of water. The cementitious material includes ordinary silicate cement, sulfoaluminate cement, mineral powder, and silica fume. By weight, the low-temperature grouting material based on intelligent antifreeze microcapsules contains: 300-450 parts of ordinary silicate cement, 150-300 parts of sulfoaluminate cement, 50-100 parts of mineral powder, and 20-50 parts of silica fume.

[0018] The present invention relates to a method for preparing low-temperature grouting material based on intelligent antifreeze microcapsules, which specifically includes the following steps: Step S1: Weigh the following raw materials by weight: 300-450 parts of ordinary silicate cement, 150-300 parts of sulfoaluminate cement, 400-550 parts of graded quartz sand, 50-100 parts of mineral powder, 20-50 parts of silica fume, 1-5 parts of flocculant, 5-20 parts of nano silica, 3-8 parts of polycarboxylate superplasticizer, 0.5-2 parts of defoamer, and 15-20 parts of intelligent antifreeze microcapsules. Then, physically dry mix these materials to obtain a dry powder mixture.

[0019] Step S2: Mix the dry powder mixture thoroughly with water to obtain the intelligent antifreeze microcapsule low-temperature grouting material.

[0020] The intelligent antifreeze microcapsule low-temperature grouting material described in this invention can be applied to prefabricated building sleeve connections, secondary grouting of equipment foundations, or prestressed duct grouting during winter construction.

[0021] Furthermore, the preparation process of the intelligent antifreeze microcapsules includes the following steps: Step A1: In a dry beaker, accurately weigh potassium formate, ethylene glycol, and nano-silica sol, wherein the mass ratio of potassium formate, ethylene glycol, and nano-silica sol is (9.5-10.5):(4.5-5.5):1. Use a magnetic stirrer to stir at 500-700 rpm for 14-16 minutes at room temperature to ensure thorough mixing and a homogeneous liquid mixture. Then, slowly add this mixture to another beaker containing liquid paraffin, wherein the mass ratio of potassium formate to liquid paraffin is 1:(1.5-2.5). Transfer the mixture to a digital display cantilever stirrer and shear at a shear rate of 2000±50 rpm for 30-50 minutes until a homogeneous, stable, opaque, milky white paste-like oil-phase suspension (i.e., composite core material suspension) is formed. In the composite core material suspension, ethylene glycol and nano-silica sol are fully coated by liquid paraffin under shear force, while potassium formate is partially dissolved in ethylene glycol and partially dispersed in the form of microcrystals.

[0022] Step A2: Weigh sodium alginate powder into a beaker and slowly add it to deionized water preheated to 50±2℃. Dissolve in a constant temperature water bath with continuous magnetic stirring at 300±50 rpm for 1-2 hours until the sodium alginate is completely hydrated, forming a clear, viscous sodium alginate colloidal solution without visible particles. The concentration of the sodium alginate colloidal solution should be 1.8wt%-2.0wt%. After dissolution, cool the sodium alginate colloidal solution to room temperature (e.g., 25±2℃) for later use.

[0023] Step A3: Under continuous stirring, the composite core material suspension is slowly added dropwise to the sodium alginate colloidal solution at a rate of 5-8 mL / min using a constant flow peristaltic pump. During this process, the digital display cantilever stirrer is activated with high-speed shear function, maintaining a speed of 8000±500 rpm to shear and stir the sodium alginate colloidal solution. The oil phase addition is synchronized with the high-speed shear, with a total duration of 15-20 min. The volume ratio of the composite core material suspension to the sodium alginate colloidal solution is 1:(4-6). After the composite core material suspension has been added, continue emulsification under high-speed shear conditions for an additional 14-16 min to form a stable oil-in-water primary emulsion.

[0024] Step A4: Prepare two solutions: Solution A is a 1.9wt%-2.1wt% calcium chloride aqueous solution; Solution B is a 0.9wt%-1.1wt% chitosan-acetic acid solution. Mix Solution A and Solution B at a volume ratio of 1:(1-1.5) and stir at 50-300 rpm for 9-11 min to obtain a composite coagulation bath. Add the prepared primary emulsion to a wide container holding the composite coagulation bath at a rate of 60-80 drops / min using a syringe equipped with a flat needle or a dropping device. The volume ratio of the primary emulsion to the composite coagulation bath is 1:(3-5). Control the dropping height at 10±0.5 cm to reduce droplet deformation during falling. After the dropping is complete, maintain stirring at 100±5 rpm, allowing the droplets to continuously soak and react in the coagulation bath for 30-45 min, obtaining a sodium alginate-chitosan composite shell with a three-dimensional network structure, completely encapsulating the core material.

[0025] Step A5: After solidification, the coagulation bath mixture is vacuum filtered using a Buchner funnel and filter paper to separate the solid microspheres. The filtered microspheres are washed repeatedly with a large amount of deionized water until the washing solution is neutral as determined by pH test paper, to remove residual acetic acid, calcium ions, and unreacted chitosan. The washed, wet microcapsule particles are evenly spread in a petri dish and placed in a vacuum drying oven at 40-50℃ and -0.1MPa vacuum for 20-30 hours until constant weight is achieved, thus obtaining the intelligent antifreeze microcapsules.

[0026] Experiments have determined that the conditions for the shell rupture of the intelligent antifreeze microcapsules obtained by this invention are: the ambient temperature is below -5℃ or the internal crystallization pressure exceeds 0.5MPa.

[0027] The low-temperature grouting material based on intelligent antifreeze microcapsules prepared in this invention has significant intelligent response and multiple protection functions, specifically manifested in the following aspects: First, through its unique "dual-path" release mechanism, it achieves intelligent antifreeze function—at normal low temperatures, the composite organic antifreeze agent inside the capsule (first path) can achieve stable slow release, continuously reducing the freezing point of the grout liquid phase and preventing frost damage; when encountering more severe sub-zero temperatures or stress generated by internal ice crystal growth, the capsule can quickly respond and rupture, releasing a crack repair agent precursor (second path). This precursor reacts in the alkaline environment of cement to form a gel, effectively sealing and repairing existing microcracks, thereby upgrading the single "passive prevention" to an integrated "prevention-repair" active protection system. Second, this design greatly improves the utilization efficiency and precision of functional components, avoiding the problem of traditional admixtures being consumed in large quantities at the initial stage of mixing or failing in the later stage of curing, ensuring continuous effectiveness throughout the entire low-temperature risk period. Third, experimental verification showed that the grout incorporating this microcapsule, under curing conditions at -10℃, exhibited significantly better workability, early strength development, and final mechanical properties than the control sample containing only an equal amount of traditional antifreeze. Furthermore, it showed no strength reduction in the later stages and possessed a denser microstructure. Fourth, this material reduces reliance on complex external heating and stringent insulation measures, broadening the winter construction window. While simplifying the process and saving energy, its use of a natural polymer shell and environmentally friendly core material makes it more environmentally friendly.

[0028] Example 1 This embodiment describes a method for preparing low-temperature grouting material based on intelligent antifreeze microcapsules, which specifically includes the following steps: Step S1: Weigh the following raw materials by weight: 300 parts ordinary silicate cement, 150 parts sulfoaluminate cement, 400 parts graded quartz sand, 50 parts mineral powder, 20 parts silica fume, 1 part flocculant, 5 parts nano silica, 3 parts polycarboxylate superplasticizer, 0.5 parts defoamer, and 15 parts intelligent antifreeze microcapsules. Then, physically dry mix these materials to obtain a dry powder mixture.

[0029] Step S2: Mix the dry powder mixture with 120 parts of water thoroughly to obtain the intelligent antifreeze microcapsule low-temperature grouting material.

[0030] Furthermore, the preparation process of the intelligent antifreeze microcapsules includes the following steps: Step A1: In a dry beaker, accurately weigh potassium formate, ethylene glycol, and nano-silica sol, with a mass ratio of 10:5:1. Stir at 500 rpm for 15 minutes at room temperature using a magnetic stirrer to ensure thorough mixing and a homogeneous liquid mixture. Then, slowly add this mixture to another beaker containing liquid paraffin, with a mass ratio of 1:2 between potassium formate and liquid paraffin. Transfer the mixture to a digital display cantilever stirrer and shear at 2000±50 rpm for 30 minutes until a homogeneous, stable, opaque, milky-white paste-like oil-phase suspension (i.e., composite core material suspension) is formed. In the composite core material suspension, ethylene glycol and nano-silica sol are fully coated by the liquid paraffin under shear force, while potassium formate is partially dissolved in ethylene glycol and partially dispersed in microcrystal form.

[0031] Step A2: Weigh sodium alginate powder into a beaker and slowly add it to deionized water preheated to 50±2℃. Dissolve in a constant temperature water bath with continuous magnetic stirring at 300±50 rpm for 1 hour until the sodium alginate is completely hydrated, forming a clear, viscous sodium alginate colloidal solution with no visible particles. The concentration of the sodium alginate colloidal solution is 1.9 wt%. After dissolution, cool the sodium alginate colloidal solution to 25±2℃ for later use.

[0032] Step A3: Under continuous stirring, the composite core material suspension is slowly added dropwise to the sodium alginate colloidal solution at a rate of 5 mL / min using a constant flow peristaltic pump. During this process, the digital display cantilever stirrer is activated with high-speed shear function, maintaining a speed of 8000±500 rpm to shear and stir the sodium alginate colloidal solution. The oil phase addition is synchronized with the high-speed shear, with a total duration of 15 min. The volume ratio of the composite core material suspension to the sodium alginate colloidal solution is 1:4. After the composite core material suspension has been added, high-speed shear conditions are maintained for an additional 15 min of emulsification to form a stable oil-in-water primary emulsion.

[0033] Step A4: Prepare two solutions: Solution A is a 2.0 wt% calcium chloride aqueous solution; Solution B is a 1.0 wt% chitosan acetic acid solution. Mix Solution A and Solution B at a volume ratio of 1:1 and stir at 150 rpm for 10 min to obtain a composite coagulation bath. Add the prepared primary emulsion to a wide container containing the composite coagulation bath at a rate of 60 drops / min using a syringe equipped with a flat needle or a dropping device. Control the dropping height to 10 cm to reduce droplet deformation during fall. The volume ratio of the primary emulsion to the composite coagulation bath is 1:3. After the addition is complete, maintain stirring at 100 ± 5 rpm, allowing the droplets to continuously soak and react in the coagulation bath for 30 min, obtaining a sodium alginate-chitosan composite shell with a three-dimensional network structure, completely encapsulating the core material.

[0034] Step A5: After solidification, the coagulation bath mixture was vacuum filtered using a Buchner funnel and filter paper to separate the solid microspheres. The filtered microspheres were washed repeatedly with a large amount of deionized water until the washing solution was neutral as determined by pH test paper, to remove residual acetic acid, calcium ions, and unreacted chitosan. The washed, wet microcapsule particles were evenly spread in a petri dish and placed in a vacuum drying oven at 40°C and -0.1 MPa for 24 hours until constant weight was achieved, thus obtaining the intelligent antifreeze microcapsules.

[0035] Example 2 This embodiment describes a method for preparing low-temperature grouting material based on intelligent antifreeze microcapsules, which specifically includes the following steps: Step S1: Weigh the following raw materials by weight: 400 parts of ordinary silicate cement, 250 parts of sulfoaluminate cement, 500 parts of graded quartz sand, 75 parts of mineral powder, 35 parts of silica fume, 3.5 parts of flocculant, 12.5 parts of nano silica, 6 parts of polycarboxylate superplasticizer, 1.5 parts of defoamer, and 18 parts of intelligent antifreeze microcapsules. Then, physically dry mix these materials to obtain a dry powder mixture.

[0036] Step S2: Mix the dry powder mixture with 150 parts of water thoroughly to obtain the intelligent antifreeze microcapsule low-temperature grouting material.

[0037] Furthermore, the preparation process of the intelligent antifreeze microcapsules includes the following steps: Step A1: In a dry beaker, accurately weigh potassium formate, ethylene glycol, and nano-silica sol, with a mass ratio of 9.5:5.5:1. Stir at 600 rpm for 16 minutes at room temperature using a magnetic stirrer to ensure thorough mixing and a homogeneous liquid mixture. Then, slowly add this mixture to another beaker containing liquid paraffin, with a mass ratio of potassium formate to liquid paraffin of 1:1.5. Transfer the mixture to a digital display cantilever stirrer and shear at 2000±50 rpm for 40 minutes until a homogeneous, stable, opaque, milky-white paste-like oil-phase suspension (i.e., the composite core material suspension) is formed. In the composite core material suspension, ethylene glycol and nano-silica sol are fully coated by the liquid paraffin under shear force, while potassium formate is partially dissolved in ethylene glycol and partially dispersed in microcrystal form.

[0038] Step A2: Weigh sodium alginate powder into a beaker and slowly add it to deionized water preheated to 50±2℃. Dissolve in a constant temperature water bath with continuous magnetic stirring at 300±50 rpm for 1.5 hours until the sodium alginate is completely hydrated, forming a clear, viscous sodium alginate colloidal solution with no visible particles. The concentration of the sodium alginate colloidal solution is 1.8 wt%. After dissolution, cool the sodium alginate colloidal solution to 25±2℃ for later use.

[0039] Step A3: Under continuous stirring, the composite core material suspension is slowly added dropwise to the sodium alginate colloidal solution at a rate of 6 mL / min using a constant flow peristaltic pump. During this process, the digital display cantilever stirrer is activated with high-speed shear function, maintaining a speed of 8000±500 rpm to shear and stir the sodium alginate colloidal solution. The oil phase addition is synchronized with the high-speed shear, with a total duration of 18 min. The volume ratio of the composite core material suspension to the sodium alginate colloidal solution is 1:5. After the composite core material suspension has been added, high-speed shear conditions are maintained for an additional 16 min of emulsification to form a stable oil-in-water primary emulsion.

[0040] Step A4: Prepare two solutions: Solution A is a 1.9 wt% calcium chloride aqueous solution; Solution B is a 1.1 wt% chitosan acetic acid solution. Mix Solution A and Solution B at a volume ratio of 1:1.25 and stir at 200 rpm for 10 min to obtain a composite coagulation bath. Add the prepared primary emulsion to a wide container containing the composite coagulation bath at a rate of 70 drops / min using a syringe equipped with a flat needle or a dropping device. The volume ratio of the primary emulsion to the composite coagulation bath is 1:4. Control the dropping height at 10.5 cm to reduce droplet deformation during fall. After the addition is complete, maintain stirring at 100 ± 5 rpm, allowing the droplets to continuously soak and react in the coagulation bath for 35 min, obtaining a sodium alginate-chitosan composite shell with a three-dimensional network structure, completely encapsulating the core material.

[0041] Step A5: After solidification, the coagulation bath mixture is vacuum filtered using a Buchner funnel and filter paper to separate the solid microspheres. The filtered microspheres are washed repeatedly with a large amount of deionized water until the washing solution is neutral as determined by pH test paper, to remove residual acetic acid, calcium ions, and unreacted chitosan. The washed, wet microcapsule particles are evenly spread in a petri dish and placed in a vacuum drying oven at 45°C and -0.1 MPa vacuum for 20 hours until constant weight is achieved, thus obtaining the intelligent antifreeze microcapsules.

[0042] Example 3 This embodiment describes a method for preparing low-temperature grouting material based on intelligent antifreeze microcapsules, which specifically includes the following steps: Step S1: Weigh the following raw materials by weight: 450 parts of ordinary silicate cement, 300 parts of sulfoaluminate cement, 550 parts of graded quartz sand, 100 parts of mineral powder, 50 parts of silica fume, 5 parts of flocculant, 20 parts of nano silica, 8 parts of polycarboxylate superplasticizer, 2 parts of defoamer, and 20 parts of intelligent antifreeze microcapsules. Then, physically dry mix these materials to obtain a dry powder mixture.

[0043] Step S2: Mix the dry powder mixture with 170 parts of water to obtain the intelligent antifreeze microcapsule low-temperature grouting material.

[0044] Furthermore, the preparation process of the intelligent antifreeze microcapsules includes the following steps: Step A1: In a dry beaker, accurately weigh potassium formate, ethylene glycol, and nano-silica sol, with a mass ratio of 10.5:4.5:1. Stir at 700 rpm for 14 minutes at room temperature using a magnetic stirrer to ensure thorough mixing and a homogeneous liquid mixture. Then, slowly add this mixture to another beaker containing liquid paraffin, with a mass ratio of 1:2.5 between potassium formate and liquid paraffin. Transfer the mixture to a digital display cantilever stirrer and shear at 2000±50 rpm for 50 minutes until a homogeneous, stable, opaque, milky-white paste-like oil-phase suspension (i.e., composite core material suspension) is formed. In the composite core material suspension, ethylene glycol and nano-silica sol are fully coated by the liquid paraffin under shear force, while potassium formate is partially dissolved in ethylene glycol and partially dispersed in microcrystal form.

[0045] Step A2: Weigh sodium alginate powder into a beaker and slowly add it to deionized water preheated to 50±2℃. Dissolve in a constant temperature water bath with continuous magnetic stirring at 300±50 rpm for 2 hours until the sodium alginate is completely hydrated, forming a clear, viscous sodium alginate colloidal solution with no visible particles. The concentration of the sodium alginate colloidal solution is 2.0 wt%. After dissolution, cool the sodium alginate colloidal solution to 25±2℃ for later use.

[0046] Step A3: Under continuous stirring, the composite core material suspension is slowly added dropwise to the sodium alginate colloidal solution at a rate of 8 mL / min using a constant flow peristaltic pump. During this process, the digital display cantilever stirrer is activated with high-speed shear function, maintaining a speed of 8000±500 rpm to shear and stir the sodium alginate colloidal solution. The oil phase addition is synchronized with the high-speed shear, with a total duration of 20 min. The volume ratio of the composite core material suspension to the sodium alginate colloidal solution is 1:6. After the composite core material suspension has been added, high-speed shear conditions are maintained for an additional 14 min of emulsification to form a stable oil-in-water primary emulsion.

[0047] Step A4: Prepare two solutions: Solution A is a 2.1 wt% calcium chloride aqueous solution; Solution B is a 0.9 wt% chitosan-acetic acid solution. Mix Solution A and Solution B at a volume ratio of 1:1.5 and stir at 50-300 rpm for 11 minutes to obtain a composite coagulation bath. Add the prepared primary emulsion to a wide container containing the composite coagulation bath at a rate of 80 drops / min using a syringe equipped with a flat needle or a dropping device. The volume ratio of the primary emulsion to the composite coagulation bath is 1:5. Control the dropping height at 9.5 cm to reduce droplet deformation during fall. After the addition is complete, maintain stirring at 100±5 rpm, allowing the droplets to remain immersed in the coagulation bath for 45 minutes to obtain a sodium alginate-chitosan composite shell with a three-dimensional network structure, completely encapsulating the core material.

[0048] Step A5: After solidification, the coagulation bath mixture is vacuum filtered using a Buchner funnel and filter paper to separate the solid microspheres. The filtered microspheres are washed repeatedly with a large amount of deionized water until the washing solution is neutral as determined by pH test paper, to remove residual acetic acid, calcium ions, and unreacted chitosan. The washed, wet microcapsule particles are evenly spread in a petri dish and placed in a vacuum drying oven at 50°C and -0.1 MPa vacuum for 30 hours until constant weight is achieved, thus obtaining the intelligent antifreeze microcapsules.

[0049] Comparative Example 1 Compared with Example 1, Comparative Example 1 uses potassium formate and ethylene glycol instead of smart antifreeze microcapsules, and specifically includes the following steps: Step S1: Weigh the following raw materials by weight: 300 parts ordinary silicate cement, 150 parts sulfoaluminate cement, 400 parts graded quartz sand, 50 parts mineral powder, 20 parts silica fume, 1 part flocculant, 5 parts nano silica, 3 parts polycarboxylate superplasticizer, 0.5 parts defoamer, 10 parts potassium formate, and 5 parts ethylene glycol. Then, physically dry mix these materials to obtain a dry powder mixture.

[0050] Step S2: Mix the dry powder mixture thoroughly with 120 parts of water to obtain Comparative Example 1.

[0051] The dry powders obtained in Examples 1-3 and Comparative Example 1 were mixed to prepare grouting material. Their performance at -10℃ was tested and compared, and the test results are shown in Table 1.

[0052] Table 1

[0053] As shown in Table 1, this application exhibits excellent flowability without bleeding, and its mechanical properties meet the requirements. The initial flowability of the examples is above 320 mm, and after standing at -10℃ for 30 minutes, the flowability remains above 260 mm. Therefore, this invention has excellent performance in winter construction and flowability retention. In contrast, the comparative example without the addition of intelligent antifreeze microcapsules cannot maintain the required flowability for winter construction, which can easily lead to pump blockage or large-scale grouting problems. Directly adding potassium formate and ethylene glycol reduces the internal structure of the grout, resulting in greater strength loss and hindering later maintenance. Meanwhile, the highest 28-day strength of the examples in low-temperature environments can reach over 90 MPa, far exceeding the construction specifications and the comparative example, making it suitable for more challenging construction requirements.

[0054] As can be seen, in this invention, a dual-cement system constitutes the composite cementitious core. Sulfoaluminate cement rapidly hydrates at low temperatures, releasing a large amount of heat to raise the system temperature. Simultaneously, intelligent antifreeze microcapsules are incorporated into the admixtures. These capsules have a biopolymer shell, encapsulating a composite organic antifreeze agent and a crack repair agent precursor, enabling a "dual-path" intelligent response of continuous slow release of antifreeze components at low temperatures and release for repair under freezing stress. The grouting material of this invention maintains good fluidity at sub-zero temperatures, develops strength rapidly, and does not shrink later, exhibiting excellent antifreeze properties and micro-damage self-repair capabilities, making it suitable for various grouting projects in winter.

[0055] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A low-temperature grouting material based on intelligent antifreeze microcapsules, characterized in that, The raw materials, by mass parts, include: 520-900 parts of cementitious material, 400-550 parts of graded quartz sand, 1-5 parts of flocculant, 5-20 parts of nano silica, 3-8 parts of water-reducing agent, 0.5-2 parts of defoamer, 15-20 parts of intelligent antifreeze microcapsules, and 120-170 parts of water. The intelligent antifreeze microcapsule includes a core material and a shell covering the outside of the core material. The core material includes an antifreeze agent and a crack repair agent precursor.

2. The low-temperature grouting material based on intelligent antifreeze microcapsules according to claim 1, characterized in that, The cementitious material includes ordinary silicate cement, sulfoaluminate cement, mineral powder, and silica fume. By mass percentage, the low-temperature grouting material based on intelligent antifreeze microcapsules contains: 300-450 parts of ordinary silicate cement, 150-300 parts of sulfoaluminate cement, 50-100 parts of mineral powder, and 20-50 parts of silica fume.

3. The low-temperature grouting material based on intelligent antifreeze microcapsules according to claim 1, characterized in that, The water-reducing agent used is a polycarboxylate high-efficiency water-reducing agent.

4. The low-temperature grouting material based on intelligent antifreeze microcapsules according to claim 1, characterized in that, The preparation method of the intelligent antifreeze microcapsules includes the following process: Potassium formate, ethylene glycol, and nano-silica sol are mixed evenly to form a homogeneous liquid mixture; The mixture was added to a container of liquid paraffin and then sheared and dispersed to obtain a composite core material suspension. The composite core material suspension was added dropwise to the sodium alginate colloidal solution under continuous stirring. During this process, the sodium alginate colloidal solution was continuously sheared. After the composite core material suspension was completely added, shearing and emulsification continued to form an oil-in-water primary emulsion. The primary emulsion is added dropwise to a composite coagulation bath. After the addition is complete, the mixture is stirred and reacted. After the reaction is complete, solid-liquid separation, washing, and vacuum drying are performed to obtain the intelligent antifreeze microcapsules. The composite coagulation bath is prepared by mixing calcium chloride aqueous solution and chitosan acetic acid solution.

5. A low-temperature grouting material based on intelligent antifreeze microcapsules according to claim 4, characterized in that, The mass ratio of potassium formate, ethylene glycol, and nano-silica sol is (9.5-10.5):(4.5-5.5):1; The mass ratio of potassium formate to liquid paraffin is 1:(1.5-2.5). The concentration of sodium alginate colloidal solution is 1.8wt%-2.0wt%; The volume ratio of the composite core material suspension to the sodium alginate colloidal solution is 1:(4-6). When preparing the composite coagulation bath, the concentration of calcium chloride aqueous solution is 1.9wt%-2.1wt%, the concentration of chitosan acetic acid solution is 0.9wt%-1.1wt%, and the volume ratio of calcium chloride aqueous solution to chitosan acetic acid solution is 1:(1-1.5). The volume ratio of the primary emulsion to the composite coagulation bath is 1:(3-5).

6. A low-temperature grouting material based on intelligent antifreeze microcapsules according to claim 4 or 5, characterized in that, When the primary emulsion is added dropwise to the composite coagulation bath, the drop height is controlled at 9.5-10.5 cm.

7. A low-temperature grouting material based on intelligent antifreeze microcapsules according to claim 4 or 5, characterized in that: When potassium formate, ethylene glycol and nano silica sol are mixed evenly to form a uniform liquid mixture, stir at a speed of 500-700 rpm for 14-16 minutes. When the mixture is added to a container of liquid paraffin and then sheared and dispersed to obtain a composite core material suspension, high-speed shearing dispersion is carried out at a shear rate of 1950-2050 rpm for 30-50 min. The composite core material suspension was added dropwise to the sodium alginate colloidal solution under continuous stirring. During this process, the sodium alginate colloidal solution was continuously sheared. After the composite core material suspension was completely added, shearing and emulsification continued to form an oil-in-water primary emulsion. Then, the composite core material suspension was slowly added dropwise to the sodium alginate colloidal solution at a rate of 5-8 mL / min, while the sodium alginate colloidal solution was continuously sheared at 7500-8500 rpm. After the composite core material suspension was completely added, shearing and emulsification continued for 14-16 min. The primary emulsion is added dropwise to the composite coagulation bath. After the addition is complete, while stirring, the primary emulsion is added dropwise to the composite coagulation bath at a rate of 60-80 drops / min. After the addition is complete, stirring is continued at a rate of 95-105 rpm for 30-45 minutes until the stirring reaction is complete.

8. A low-temperature grouting material based on intelligent antifreeze microcapsules according to claim 4 or 5, characterized in that: During solid-liquid separation, washing, and vacuum drying, solid-liquid separation is performed by vacuum filtration; during washing, the filtered microspheres are washed multiple times with deionized water until the filtrate is neutral; the vacuum drying temperature is 40-50℃, the vacuum degree is -0.1MPa, and the drying time is 20-30h.

9. A method for preparing a low-temperature grouting material based on intelligent antifreeze microcapsules as described in any one of claims 1-8, characterized in that, The process includes the following: The cementitious material, graded quartz sand, flocculant, nano silica, water-reducing agent, defoamer, and intelligent antifreeze microcapsules are physically dry-mixed to obtain a dry powder mixture. The dry powder mixture is mixed with water until homogeneous to obtain the low-temperature grouting material based on intelligent antifreeze microcapsules.

10. The use of a low-temperature grouting material based on intelligent antifreeze microcapsules as described in any one of claims 1-8, characterized in that, The low-temperature grouting material based on intelligent antifreeze microcapsules is used for prefabricated building sleeve connections, secondary grouting of equipment foundations, or grouting of prestressed ducts during winter construction.

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