Solid powder composite additive for fluidized soil and preparation method thereof

Abstract

The invention relates to the technical field of backfill materials, in particular to a solid powder composite additive for fluidized soil and a preparation method of the solid powder composite additive. The composite additive is prepared by mixing slow-release powder, a water reducing agent and hydroxypropyl methyl cellulose, the slow-release powder takes a silane-modified zeolite molecular sieve as a carrier and vacuum-loaded dipropylene glycol tert-butyl ether as a reduction inner core; a temperature-sensitive gel shell layer is constructed through in-situ polymerization, and cyclodextrin is grafted on the surface of the microsphere. The method effectively solves the problem of compatibility of the shrinkage reducing agent and the water reducing agent in the high-viscosity fluidized soil, remarkably reduces the surface tension and eliminates early-stage plastic shrinkage cracks while ensuring excellent fluidity of slurry, and is particularly suitable for preparing high-performance fluidized soil from subway shield muck and being used for pipe gallery backfilling engineering.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of backfill materials, and particularly relates to a solid powder composite additive for fluidized soil and a preparation method thereof. BACKGROUND

[0002] With the rapid development of urban rail transit construction, a large amount of waste muck is generated by subway shield construction. Resource utilization of these mucks to prepare fluidized soil for backfilling of fat grooves and pipe gallery filling is an important way to realize green construction and low-carbon emission reduction. However, in actual engineering applications, especially for common high clay content and high liquid limit shield mucks, the preparation and application of fluidized soil face serious technical challenges.

[0003] Such high clay mucks contain a large amount of hydrophilic clay minerals (such as montmorillonite and illite), have a large specific surface area and strong water absorption capacity. In order to meet the requirements of pumping and self-leveling construction, a high water content or a large amount of water reducing agent is often needed. However, in the initial curing stage (plastic stage) of the water-rich slurry after pouring, water will evaporate from the surface at a very fast rate. Due to the small capillary pore size between clay particles, water evaporation will generate a large capillary negative pressure (capillary tension) at the solid-liquid interface. When this shrinkage stress exceeds the extremely weak tensile strength of the plastic state of the slurry, dense cracks will occur on the surface of the soil body, and even penetrating plastic shrinkage cracks will occur. This not only seriously damages the appearance quality of the backfill body, but also greatly reduces the integrity, impermeability and durability of the backfill project due to the water and harmful ion channels provided by the cracks.

[0004] In order to solve the problem of plastic shrinkage cracking, the existing technology usually adopts two means: one is to add polypropylene fiber and other physical anti-cracking materials, but in high clay soil, the fiber is easy to form a ball, which significantly increases the viscosity of the slurry and seriously sacrifices the self-leveling property of the fluidized soil; the other is to add shrinkage reducing agent (such as alcohol ether organic matter) to reduce the surface tension of the pore solution, thereby reducing the capillary negative pressure. However, this chemical path has a fatal compatibility paradox in high clay fluidized soil: as an organic solvent, if the alcohol ether shrinkage reducing agent is directly added, it will quickly change the double electric layer structure of the clay particle surface, compress the diffuse double electric layer, and cause the clay particles to flocculate; at the same time, the organic molecules will compete with the polycarboxylic acid water reducing agent, causing it to fail. As a result, although the surface tension is reduced, the slurry loses its fluidity instantly and cannot be pumped for construction; or in order to maintain the fluidity, excessive water is added, which in turn aggravates segregation and bleeding, resulting in more serious settlement shrinkage.

[0005] Therefore, there is an urgent need to develop an intelligent additive system that can identify the construction cycle of fluidized soil, maintain absolute sealing during the mixing and transportation period to ensure fluidity, and precisely release additives during the hydration and heating period to prevent cracking. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a solid powder composite additive for fluidized soil and its preparation method, so as to provide a solid powder composite additive that can significantly reduce the water evaporation rate and surface tension without reducing fluidity, and eliminate early plastic shrinkage cracking of high-cohesive fluidized soil.

[0007] To achieve the above objectives, the present invention provides a solid powder composite additive for fluidized soil, which is composed of the following raw materials in parts by weight: 90-110 parts of slow-release powder, 18-22 parts of water-reducing agent, and 4-6 parts of hydroxypropyl methylcellulose. The slow-release powder is produced by calcining zeolite molecular sieves at high temperature, modifying and grafting them with 3-methacryloyloxypropylmethyldimethoxysilane, and then vacuum adsorbing dipropylene glycol tert-butyl ether to form a zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether. Subsequently, under the action of potassium persulfate, a polymerization reaction is initiated to grow an amino-rich thermosensitive gel shell layer on the surface of the zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether, forming a core-shell structure zeolite molecular sieve. Finally, the cyclodextrin is rigidly grafted onto the shell network by a nucleophilic substitution reaction between the amino groups in the core-shell structure zeolite molecular sieve shell and mono-(6-O-p-toluenesulfonyl)-β-cyclodextrin.

[0008] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent.

[0009] Preferably, the viscosity of the hydroxypropyl methylcellulose is 100,000 mPa·s (20°C).

[0010] Preferably, the zeolite molecular sieve is a ZSM-5 type molecular sieve with a SiO2 / Al2O3 molar ratio of 40%-50%.

[0011] Preferably, the high-temperature calcination temperature is 550-600℃ and the calcination time is 4-5 hours to thoroughly remove adsorbed water and impurities from the molecular sieve channels.

[0012] Preferably, the weight ratio of the zeolite molecular sieve to 3-methacryloyloxypropylmethyldimethoxysilane is 90-110:6.0-8.0.

[0013] Preferably, the silane modification grafting reaction is carried out in a 95% (v / v) ethanol solution at a reaction temperature of 75-85°C for 6-8 hours.

[0014] Preferably, the vacuum adsorption requires the vacuum degree to be reduced to -0.09 MPa and maintained for 45 minutes. After adsorption, the vacuum needs to be allowed to stand and soak for 2-4 hours before returning to normal pressure, so that dipropylene glycol tert-butyl ether can fill the zeolite channels.

[0015] Preferably, the weight ratio of the zeolite molecular sieve to dipropylene glycol tert-butyl ether is 1:1.

[0016] Preferably, the weight ratio of the zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether, N-isopropylacrylamide, allylamine, N,N'-methylenebisacrylamide, and potassium persulfate is 90-110:11-13:0.9-1.1:0.9-1.1:0.9-1.1.

[0017] Preferably, the polymerization reaction conditions are a nitrogen atmosphere, a reaction temperature of 60-70°C, and a reaction time of 4-6 hours.

[0018] Preferably, the weight ratio of the core-shell structured zeolite molecular sieve to mono-(6-O-p-toluenesulfonyl)-β-cyclodextrin is 90-110:16-20.

[0019] Preferably, the nucleophilic substitution reaction is carried out at a temperature of 45-55°C and for a time of 10-14 hours.

[0020] Furthermore, the present invention also provides a method for preparing a solid powder composite additive for fluidized soil, wherein a slow-release powder, a water-reducing agent, and hydroxypropyl methylcellulose are placed in a high-speed mixer and mixed evenly before being discharged to obtain the target product, the solid powder composite additive for fluidized soil.

[0021] The beneficial effects of this invention are: This invention utilizes hydrophobically modified zeolite as a deep reservoir, combined with a dense polymer shell, to construct a highly efficient physical-chemical dual shielding system. During the mixing and transportation stages of fluidized soil (usually at room temperature), the shrinkage component (dipropylene glycol tert-butyl ether) is firmly locked inside the microcapsules. This invention introduces poly(N-isopropylacrylamide) as a temperature-sensitive switch shell. This shell is highly sensitive to temperature. When the temperature rises to near the critical phase transition temperature due to cement hydration after the grout is poured, the shell network undergoes a rapid volume shrinkage and phase transition, actively opening the release channel and pumping the high concentration of shrinkage-reducing components into the capillary pores. This significantly reduces or even completely eliminates early plastic shrinkage cracks, greatly improving the integrity and durability of the backfill. This invention introduces rigid cyclodextrin macrocyclic molecules into a temperature-sensitive gel network through chemical bonding. Utilizing the special cavity structure and large steric hindrance effect of cyclodextrin, it acts as a molecular plug at the microscale, effectively sealing micro-defects that may exist in the polymer gel network, greatly improving the sealing performance of microcapsules at low temperatures, and preventing permeability loss. Compared to the early strength reduction problem caused by directly adding organic shrinkage-reducing agents, this invention avoids the encapsulation and obstruction of cement particles by organic components during the hydration induction period. In summary, this invention fundamentally solves the technical bottleneck of achieving both high fluidity and low shrinkage in high-clay fluidized soil. It not only significantly improves the integrity and durability of the backfill, but also effectively avoids the obstruction of cement hydration by traditional organic shrinkage reducing agents, eliminates the phenomenon of early strength shrinkage, and achieves comprehensive optimization of the construction performance and mechanical properties of fluidized soil. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Figure 1 This is a schematic diagram of the reaction process in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram showing the changes in water evaporation test data in the embodiments and comparative examples of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0025] This invention provides a method for preparing a solid powder composite additive for fluidized soil, comprising the following steps: (1) After the zeolite molecular sieve is calcined at high temperature, it is subjected to silane modification and grafting reaction with 3-methacryloxypropylmethyldimethoxysilane in a 95% ethanol solution. The trace amount of water in the ethanol promotes the hydrolysis of silane and causes the generated silanol to dehydrate and condense with the hydroxyl groups on the zeolite surface, thereby successfully grafting 3-methacryloxypropylmethyldimethoxysilane onto the zeolite surface. After purification and drying, the product is subjected to vacuum adsorption of dipropylene glycol tert-butyl ether to form a zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether. (2) Zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether, N-isopropylacrylamide, allylamine and N,N'-methylenebisacrylamide were polymerized under nitrogen atmosphere and potassium persulfate to form a zeolite molecular sieve with a core-shell structure. (3) A nucleophilic substitution reaction was carried out between a core-shell structured zeolite molecular sieve and mono-(6-O-p-toluenesulfonyl)-β-cyclodextrin to obtain a sustained-release powder; (4) Mix the slow-release powder, polycarboxylate superplasticizer and hydroxypropyl methylcellulose to form a solid powder composite additive for fluidized soil.

[0026] Regarding step (1): In this invention, the zeolite molecular sieve is of type ZSM-5, and the SiO2 / Al2O3 molar ratio is preferably 40%-50%, specifically 40%, 43%, 45%, 48%, or 50%.

[0027] In this invention, the preferred temperature for high-temperature calcination is 550-600℃, specifically 550℃, 560℃, 570℃, 580℃, or 600℃; the duration of high-temperature calcination is 4-5 hours, specifically 4 hours, 4.5 hours, or 5 hours.

[0028] In this invention, the preferred temperature for the silane modification grafting reaction is 75-85℃, specifically 75℃, 80℃, or 85℃, and the preferred time is 6-8h, specifically 6h, 6.5h, 7h, 7.5h, or 8h.

[0029] Regarding step (2): In this invention, the preferred temperature of the polymerization reaction is 60-70℃, specifically 60℃, 65℃, or 70℃; the preferred reaction time is 4-6h, specifically 4h, 4.5h, 5h, 5.5h, or 6h.

[0030] Regarding step (3): In this invention, the temperature of the nucleophilic substitution reaction is preferably 45-55℃, specifically 45℃, 50℃, or 55℃, and the reaction time is preferably 10-14h, specifically 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13h, 13.5h, or 14h.

[0031] Regarding step (4): In this invention, the weight parts of the slow-release powder, polycarboxylate superplasticizer, and hydroxypropyl methylcellulose are preferably 90-110 parts, 18-22 parts, and 4-6 parts, respectively. Specifically, it can be 90 parts slow-release powder, 18 parts polycarboxylate superplasticizer, and 4 parts hydroxypropyl methylcellulose; 110 parts slow-release powder, 22 parts polycarboxylate superplasticizer, and 6 parts hydroxypropyl methylcellulose; 100 parts slow-release powder, 20 parts polycarboxylate superplasticizer, and 5 parts hydroxypropyl methylcellulose; 95 parts slow-release powder, 19 parts polycarboxylate superplasticizer, and 5 parts hydroxypropyl methylcellulose; or 105 parts slow-release powder, 21 parts polycarboxylate superplasticizer, and 5 parts hydroxypropyl methylcellulose.

[0032] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples: The sources or properties of the raw materials used in the embodiments and comparative examples of this invention are as follows: Zeolite molecular sieve: ZSM-5 type, purchased from Maclean's, catalog number Z875520, SiO2 / Al2O3 ratio 45%; Mono-(6-O-p-toluenesulfonyl)-β-cyclodextrin: purchased from Maclean's, catalog number M830137, 1.591 g / cm³ 3 Polycarboxylate superplasticizer: high-performance superplasticizer dry powder of polycarboxylate ether, with a water reduction rate of 30%; Hydroxypropyl methylcellulose: viscosity of 100,000 mPa·s (20℃).

[0033] Example 1: A method for preparing a solid powder composite additive for fluidized soil, the specific steps of which are as follows: (1) Weigh 90g of zeolite molecular sieve and place it in a muffle furnace and calcine it at 550℃ for 4h. After cooling to room temperature, disperse it in 280mL of 95% ethanol solution and add 6.0g of 3-methacryloyloxypropylmethyldimethoxysilane. Reflux and stir the reaction at 75℃ for 6h. After the reaction is completed, filter the product and wash it three times with ethanol. Dry it in a vacuum drying oven at 60℃ for 12h. Then place the dried product in a vacuum impregnation tank and evacuate it to -0.09MPa for 45min to remove air from the pores. Under vacuum, use a conduit to draw in 90g of dipropylene glycol tert-butyl ether using negative pressure. After standing and impregnating for 2h, restore normal pressure to obtain zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether. (2) 90g of zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether was dispersed in 180mL of deionized water. After being ultrasonically dispersed evenly, 11g of N-isopropylacrylamide, 0.9g of allylamine and 0.9g of N,N'-methylenebisacrylamide were added. After purging with nitrogen for 30min, 0.9g of potassium persulfate was added as a water-soluble initiator. The reaction was carried out at a constant temperature of 60℃ in a water bath and stirred at 300rpm for 4h. The product was separated by centrifugation and washed twice with deionized water to obtain a zeolite molecular sieve with a core-shell structure. (3) 90g of zeolite molecular sieve with core-shell structure was redispersed in 140mL of deionized water and 16g of mono-(6-O-p-toluenesulfonyl)-β-cyclodextrin and 1.8g of anhydrous sodium carbonate were added. The mixture was stirred at 45℃ for 10h. After the reaction was completed, the mixture was filtered and dried in a vacuum drying oven at 40℃ for 24h to obtain the slow-release powder. (4) Weigh 90g of slow-release powder, and place it in a high-speed mixer with 18g of polycarboxylate superplasticizer and 4g of hydroxypropyl methylcellulose. Mix physically at 400rpm for 10min, and discharge to obtain the target product, a solid powder composite additive for fluidized soil.

[0034] Example 2: A method for preparing a solid powder composite additive for fluidized soil, the specific steps of which are as follows: (1) Weigh 100g of zeolite molecular sieve and place it in a muffle furnace and calcine it at 580℃ for 4.5h. After cooling to room temperature, disperse it in 300mL of 95% ethanol solution and add 7.0g of 3-methacryloyloxypropylmethyldimethoxysilane. Reflux and stir the reaction at 80℃ for 7h. After the reaction is completed, filter the product and wash it three times with ethanol. Dry it in a vacuum drying oven at 60℃ for 12h. Then place the dried product in a vacuum impregnation tank and evacuate it to -0.09MPa for 45min to remove air from the pores. Under vacuum, use a conduit to draw in 100g of dipropylene glycol tert-butyl ether using negative pressure. After standing and impregnating for 3h, restore normal pressure to obtain zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether. (2) 100g of zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether was dispersed in 200mL of deionized water. After being ultrasonically dispersed evenly, 12g of N-isopropylacrylamide, 1g of allylamine and 1g of N,N'-methylenebisacrylamide were added. After purging oxygen with nitrogen for 30min, 1g of potassium persulfate was added as a water-soluble initiator. The reaction was carried out at a constant temperature of 65℃ in a water bath and stirred at 350rpm for 5h. The product was separated by centrifugation and washed twice with deionized water to obtain a zeolite molecular sieve with a core-shell structure. (3) 100g of zeolite molecular sieve with core-shell structure was redispersed in 150mL of deionized water and 18g of mono-(6-O-p-toluenesulfonyl)-β-cyclodextrin and 2g of anhydrous sodium carbonate were added. The mixture was stirred at 50℃ for 12h. After the reaction was completed, the mixture was filtered and dried in a vacuum drying oven at 40℃ for 24h to obtain the slow-release powder. (4) Weigh 100g of slow-release powder, and place it in a high-speed mixer with 20g of polycarboxylate superplasticizer and 5g of hydroxypropyl methylcellulose. Mix physically at 500rpm for 13min, and discharge to obtain the target product, solid powder composite additive for fluidized soil.

[0035] Example 3: A method for preparing a solid powder composite additive for fluidized soil, the specific steps of which are as follows: (1) Weigh 110g of zeolite molecular sieve and place it in a muffle furnace and calcine it at 600℃ for 5h. After cooling to room temperature, disperse it in 320mL of 95% ethanol solution and add 8.0g of 3-methacryloyloxypropylmethyldimethoxysilane. Reflux and stir the reaction at 85℃ for 8h. After the reaction is completed, filter the product and wash it three times with ethanol. Dry it in a vacuum drying oven at 60℃ for 12h. Then place the dried product in a vacuum impregnation tank and evacuate it to -0.09MPa for 45min to remove air from the pores. Under vacuum, use a conduit to draw in 110g of dipropylene glycol tert-butyl ether using negative pressure. After standing and impregnating for 4h, restore normal pressure to obtain zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether. (2) 110g of zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether was dispersed in 220mL of deionized water. After being ultrasonically dispersed evenly, 13g of N-isopropylacrylamide, 1.1g of allylamine and 1.1g of N,N'-methylenebisacrylamide were added. After purging with nitrogen for 30min, 1.1g of potassium persulfate was added as a water-soluble initiator. The reaction was carried out at a constant temperature of 70℃ in a water bath and stirred at 400rpm for 6h. The product was separated by centrifugation and washed twice with deionized water to obtain a zeolite molecular sieve with a core-shell structure. (3) 110g of zeolite molecular sieve with core-shell structure was redispersed in 160mL of deionized water and 20g of mono-(6-O-p-toluenesulfonyl)-β-cyclodextrin and 2.2g of anhydrous sodium carbonate were added. The mixture was stirred at 55℃ for 14h. After the reaction was completed, the mixture was filtered and dried in a vacuum drying oven at 40℃ for 24h to obtain the slow-release powder. (4) Weigh 110g of slow-release powder, and place it in a high-speed mixer with 22g of polycarboxylate superplasticizer and 6g of hydroxypropyl methylcellulose. Mix physically at 600rpm for 15min, and discharge to obtain the target product, a solid powder composite additive for fluidized soil.

[0036] Comparative Example 1: The difference from Example 2 is that the modified zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether and the subsequent coating structure are not used. Instead, a direct physical mixing method is used. 100g of untreated zeolite molecular sieve, 100g of dipropylene glycol tert-butyl ether, 12g of poly(N-isopropylacrylamide) powder, 18g of mono-(6-O-p-toluenesulfonyl)-β-cyclodextrin, 20g of polycarboxylate superplasticizer powder and 5g of hydroxypropyl methylcellulose are placed in a high-speed mixer and physically mixed at 500 rpm for 12 minutes. The mixture is then discharged to obtain a solid powder composite additive for fluidized soil.

[0037] Comparative Example 2: The difference from Example 2 is that in step (1), 3-methacryloyloxypropylmethyldimethoxysilane is replaced with vinyltrimethoxysilane, while the other conditions are the same as in Example 2.

[0038] Comparative Example 3: The difference from Example 2 is that the temperature-sensitive shell coating and cyclodextrin grafting processes in steps (2) and (3) are omitted, while the other conditions are the same as in Example 2.

[0039] The difference between Comparative Example 4 and Example 2 is that in step (2), an equal amount of acrylamide was used to replace N-isopropylacrylamide, while the other conditions remained the same as in Example 2.

[0040] The difference between Comparative Example 5 and Example 2 is that the cyclodextrin grafting step (3) is omitted, while the other conditions are the same as those in Example 2.

[0041] The difference between Comparative Example 6 and Example 2 is that no chemical grafting reaction was carried out in step (3), but the cyclodextrin was physically mixed in step (4). The other conditions were the same as those in Example 2.

[0042] Performance testing Preparation before the experiment: Typical high-clay content subway tunnel waste soil (clay content >30%, liquid limit >40%) was selected, vacuum extruded and dried, crushed and sieved at 105℃ for later use. The mix proportion (parts by mass) was: 1000 parts of dry tunnel waste soil powder, 150 parts of PO 42.5 ordinary Portland cement, and 500 parts of water (adjust the water-cement ratio to make the initial fluidity within the range of 200±10mm). On this basis, the additives obtained in Examples 1-3 and Comparative Examples 1-6 were added externally, and the dosage was 2.0% of the mass of cementitious materials (cement). At the same time, a blank group without any additives was set up. Flowability: The flowability of cement mortar was determined according to GB / T 2419-2005 "Method for Determination of Flowability of Cement Mortar". The specific operating steps are as follows: Using a flowability tester (jump table) and a truncated cone mold (upper diameter 70mm, lower diameter 100mm, height 60mm), the weighed shield tunneling slag, cement, and different groups of additives were dry-mixed evenly. A certain amount of water was added, and the mixture was slowly stirred for 120s, then rapidly stirred for 60s in a planetary mixer. After standing for 90s, it was rapidly stirred for another 60s to obtain the test slurry. Initial fluidity determination: The mixed slurry is poured into a truncated cone mold in two layers. The first layer is filled to 2 / 3 of the mold height and tamped 15 times at the edge with a knife. The second layer is filled to the top and above the mold opening, and tamped 10 times in the same way. The mold opening is leveled with a scraper and the mold is lifted vertically upward. Since the fluidized soil has self-leveling properties, no table vibration is required. The mold is left to stand for 30 seconds. The two diameters perpendicular to each other on the bottom surface of the slurry diffusion are measured with calipers, and the average value is recorded as the initial fluidity (mm). Time loss determination: Place the remaining slurry in the mixing pot, cover it with a damp cloth to prevent evaporation, and stir it again for 30 seconds after standing for 60 minutes. Measure the fluidity according to the above steps and calculate the fluidity retention value. Moisture evaporation test: The test was conducted in accordance with GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". The specific operation steps were as follows: The test was conducted in an environmental test chamber with the temperature controlled at 30℃ (simulating the initial stage of hydration heating) and the relative humidity controlled at 50%. The axial flow fan was turned on to keep the wind speed on the sample surface at 4.5m / s. Sample molding: Cylindrical plastic petri dishes were used as containers. Freshly mixed fluidized soil slurry of different groups was put into the petri dishes, vibrated to compact it, and the surface was leveled. The total initial mass of the sample and the mold (m0, where m0 is specified as 500.00g) was recorded. Three parallel samples were set up for each group. The samples were placed in the air duct of the environmental test chamber. From the start of the test, the samples were taken out every 30 minutes and weighed quickly on a balance with an accuracy of 0.01g. The weights were recorded as m1, m2, ... mn. The test lasted for 6 hours. Surface tension temperature-sensitive response test: The test was conducted according to the ring method in GB / T 22237-2008 "Determination of surface tension of surfactants". The specific operation steps are as follows: Prepare fluidized soil slurries of different groups. Take a portion of the slurry and seal it at 20℃ for 30 min. Take another portion of the slurry and heat it in a water bath to 40℃ (simulating the peak temperature of the exothermic hydration reaction) under sealed conditions and keep it at that temperature for 30 min. Centrifuge it at 5000 rpm for 10 min using a high-speed centrifuge. Extract the supernatant as the pore solution to be tested. Use a fully automatic surface tension meter to clean and calibrate the platinum ring with anhydrous ethanol and distilled water to ensure that the surface tension reading of distilled water at 25℃ is 72.0 mN / m. Place the extracted pore solution in a sample cup and keep the test temperature consistent with the extraction temperature. Operate the instrument to immerse the platinum ring below the liquid surface and then slowly pull it up at a constant speed. Record the maximum tensile force value at the moment the liquid film breaks. Early-stage plastic shrinkage cracking performance test of flat plate: The test was conducted according to the flat plate induced cracking method in GB / T 50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete". The specific operation steps are as follows: A steel flat plate mold with a diameter of 600mm×600mm×63mm was used. The mold was equipped with 7 parallel bolts as crack induction generators. The mixed fluidized soil was poured into the mold and the surface was smoothed. The mold was immediately placed in an accelerated drying channel with an ambient temperature of 30℃, relative humidity of 50%, and wind speed of 5m / s. The timer started from the completion of pouring and the mold was continuously blown and observed for 24 hours. After 24 hours, the width and length of all cracks on the surface of the specimen were measured using a crack microscope (accuracy 0.01mm), and two key indicators were calculated: the total area of ​​cracks per unit area. Unconfined compressive strength test: The test was conducted according to JGJ / T 70-2009 "Standard for Test Methods of Basic Performance of Building Mortar". Specific procedures included: filling freshly mixed fluidized soil into a 70.7mm×70.7mm×70.7mm triple cubic steel mold, compacting it, and preparing 6 test blocks per group. The blocks were cured in a standard curing room (temperature 20℃, humidity 95%) for 24 hours with the mold in place, then demolded and continued standard curing until the specified age (7 days and 28 days). After reaching the specified age, the test blocks were removed, the surface moisture was wiped dry, and the compressive strength was tested using a computer-controlled pressure testing machine. The loading speed was controlled at 0.10kN / s until the test block failed. The arithmetic mean of the 6 test blocks was taken as the strength test result for that age. The test results are shown in Table 1.

[0043] Table 1 Performance Test Results

[0044] Data analysis: As can be seen from the data of Examples 1-3 in Table 1, the solid powder composite additive for fluidized soil prepared in this invention exhibits excellent comprehensive application performance in shield tunnel slag backfill materials, and successfully solves the contradiction between maintaining the fluidity of high-viscosity slurry and early plastic crack resistance.

[0045] As can be seen from the data in Example 2 and Comparative Example 1 in Table 1, the hydrophobic zeolite-thermosensitive shell-molecular plug microcapsule system constructed in this invention produces a significant synergistic effect compared to the direct physical mixing of the components. It is speculated that this is because the active component is concealed in the zeolite channels during the low-temperature stirring period through microencapsulation technology, achieving a high fluidity retention value of 210 mm, while the drug effect is released only during the heating period, which not only ensures an extremely low crack area but also avoids the negative impact on early strength.

[0046] As can be seen from the data in Example 2 and Comparative Example 2 in Table 1, the carbon chain structure and chemical activity of the hydrophobic modifier on the zeolite carrier surface have a decisive influence on the loading efficiency and controlled release performance of the microcapsules. It is speculated that because the vinylsilane molecular chain is relatively short, it is difficult to form a sufficiently deep hydrophobic barrier at the zeolite pores, resulting in a reduction in the effective loading of dipropylene glycol tert-butyl ether. As a result, it causes significant leakage during the stirring period at 20°C, and during the high-temperature period of 40°C when release is required, it cannot effectively reduce the tension due to insufficient loading margin, thus failing to achieve the expected crack resistance effect.

[0047] As can be seen from the data in Example 2 and Comparative Example 3 in Table 1, without the protection of a temperature-sensitive polymer shell, the hydrophobically modified zeolite alone cannot achieve intelligent control of the surface tension of the liquid phase. It is speculated that because the shell coating and cyclodextrin grafting were omitted, physical adsorption alone is far from sufficient to resist the displacement effect of water molecules, resulting in the premature loss of the shrinkage component in the early stage of hydration, and the inability to maintain a high concentration of surfactant distribution at the critical time point when water evaporation is most intense.

[0048] As can be seen from the data in Example 2 and Comparative Example 4 in Table 1, the temperature-sensitive phase change characteristics of the shell material are the core switching mechanism for achieving dual optimization of crack resistance and fluidity of fluidized soil. It is speculated that this is due to the use of the low critical dissolution temperature of poly(N-isopropylacrylamide) to achieve a reversible conversion of shell permeability under the drive of temperature field, thus realizing the technical concept of sealing during the stirring period and releasing during the heating period.

[0049] As can be seen from the data in Example 2 and Comparative Example 5 in Table 1, covalently grafted cyclodextrin macromolecules have a significant enhancing effect on the sealing performance and controlled release accuracy of the microcapsule shell. It is speculated that this is because the introduction of cyclodextrin macromolecules with a cavity structure further improves the sealing density at low temperatures, making the release at high temperatures more thorough and concentrated, thereby achieving better surface tension regulation and crack resistance at extremely low dosages.

[0050] As can be seen from the data in Example 2 and Comparative Example 6 in Table 1, the chemical grafting method of cyclodextrin is more critical for constructing an efficient intelligent response system than physical mixing; it is speculated that this is because although free cyclodextrin has a certain thickening or water-retaining effect, it cannot synergistically enhance the structural function of the polymer shell.

[0051] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A solid powder composite additive for fluidized soil, characterized in that, It is composed of the following raw materials in parts by weight: 90-110 parts slow-release powder, 18-22 parts water-reducing agent, and 4-6 parts hydroxypropyl methylcellulose; The slow-release powder is obtained by calcining zeolite molecular sieves at high temperature, modifying and grafting them with 3-methacryloyloxypropylmethyldimethoxysilane, and then vacuum adsorbing dipropylene glycol tert-butyl ether to form a zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether. Subsequently, under the action of potassium persulfate, N-isopropylacrylamide, allylamine, and N,N'-methylenebisacrylamide are polymerized on the surface of the zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether to form a core-shell structure zeolite molecular sieve. Finally, the core-shell structured zeolite molecular sieve is grafted with mono-(6-O-p-toluenesulfonyl)-β-cyclodextrin through a nucleophilic substitution reaction. The weight ratio of the zeolite molecular sieve to 3-methacryloyloxypropylmethyldimethoxysilane is 90-110:6.0-8.0; The weight ratio of the zeolite molecular sieve loaded with dipropylene glycol tert-butyl ether, N-isopropylacrylamide, allylamine, N,N'-methylenebisacrylamide, and potassium persulfate is 90-110:11-13:0.9-1.1:0.9-1.1:0.9-1.1; The weight ratio of the core-shell structured zeolite molecular sieve to mono-(6-O-p-toluenesulfonyl)-β-cyclodextrin is 90-110:16-20.

2. The solid powder composite additive for fluidized soil according to claim 1, characterized in that, The zeolite molecular sieve is a ZSM-5 type molecular sieve with a SiO2 / Al2O3 molar ratio of 40%-50%.

3. The solid powder composite additive for fluidized soil according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate water-reducing agent.

4. The solid powder composite additive for fluidized soil according to claim 1, characterized in that, The viscosity of the hydroxypropyl methylcellulose is 100,000 mPa·s.

5. The solid powder composite additive for fluidized soil according to claim 1, characterized in that, The high-temperature calcination temperature is 550-600℃, and the calcination time is 4-5 hours.

6. The solid powder composite additive for fluidized soil according to claim 1, characterized in that, The silane modification grafting reaction was carried out in a 95% (v / v) ethanol solution at a temperature of 75-85°C for 6-8 hours.

7. The solid powder composite additive for fluidized soil according to claim 1, characterized in that, The vacuum adsorption process requires evacuating the vacuum to -0.09 MPa and maintaining it for 45 minutes. After adsorption, the vacuum needs to be left to stand and soak for 2-4 hours before returning to normal pressure.

8. The solid powder composite additive for fluidized soil according to claim 1, characterized in that, The polymerization reaction conditions are a nitrogen atmosphere, a reaction temperature of 60-70℃, and a reaction time of 4-6 hours.

9. The solid powder composite additive for fluidized soil according to claim 1, characterized in that, The nucleophilic substitution reaction is carried out at a temperature of 45-55℃ for a time of 10-14 hours.

10. A method for preparing a solid powder composite additive for fluidized soil according to any one of claims 1-9, characterized in that, The target product, a solid powder composite additive for fluidized soil, is obtained by mixing the slow-release powder, water-reducing agent, and hydroxypropyl methylcellulose.

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