Silicate modified fly ash based low temperature grouting material and preparation method thereof

Abstract

The application discloses a silicate modified fly ash based low-temperature grouting material and a preparation method thereof, and belongs to the technical field of grouting materials. The grouting material is obtained by mixing dry-mixed powder and water, and the dry-mixed powder comprises silicate modified fly ash, a basic cementing component, a low-temperature nucleation component, a water phase regulating component and a rheological adjusting component, wherein the silicate modified fly ash is a core-shell structure particle with a silicate coating layer on the surface. The application further discloses a preparation method of fly ash pretreatment, surface composite modification, temperature control drying film forming, step-by-step dry mixing and on-site water adding slurry forming. The material is suitable for grouting construction under low-temperature conditions.

Description

Technical Field

[0001] This invention belongs to the field of grouting materials technology, specifically a silicate-modified fly ash-based low-temperature grouting material and its preparation method. Background Technology

[0002] Fly ash, as a bulk pozzolanic material, is inexpensive. Adding fly ash to grouting materials can effectively reduce material costs, improve the utilization of solid waste, and enhance the greening of building materials. Furthermore, its morphological and micro-aggregate effects can effectively improve the rheological properties of the grout. However, fly ash exhibits insufficient early activity even at room temperature, and this deficiency is significantly amplified at low temperatures. Low temperatures not only inhibit the gelation reaction and prolong the induction period but also cause free water freezing and hindered ion migration. This makes fly ash easily degenerate from a "functional component" to an "inert diluent component" in low-temperature systems, resulting in delayed early hydration, significantly prolonged setting time, decreased stone formation rate, and insufficient early load-bearing capacity.

[0003] To address the issue of insufficient activity in fly ash systems under low-temperature conditions, existing technologies primarily employ two compensation approaches: First, maintaining reaction conditions through external heat sources, as exemplified by traditional methods described in CN102976699B, such as preheating, hot water mixing, and post-grouting insulation. Second, enhancing early-stage reactions through rapid-hardening cement, readily soluble sodium silicate, antifreeze agents, strong salts, or low-temperature accelerators. For instance, CN102173662A utilizes rapid-hardening cement, double-rapid-hardening cement, readily soluble sodium silicate, early-strength agents, and antifreeze agents to construct low-temperature ultra-early-strength support grouting materials, while CN110218055B achieves rapid setting at low temperatures by preparing the accelerator into a core-shell structure. However, the core of this core-shell structure is the low-temperature accelerator (such as aluminates or carbonates), and the outer shell is a slow-release coating. Its purpose is to control the release rate of the accelerator, rather than altering the location of the reaction. The former type of solution is complex to construct and consumes a lot of energy; while the latter type of solution can improve the low-temperature reaction rate, it is also prone to problems such as indiscriminate acceleration in the liquid phase, narrowing of the construction window, and even increased durability and corrosion risks. Therefore, the existing technology still lacks a fly ash-based grouting material that can automatically start a low-temperature curing mechanism under heating and insulation conditions and transform fly ash from a traditional dilution filler component into a low-temperature functional reactive component. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a silicate-modified fly ash-based low-temperature grouting material and its preparation method. This invention primarily addresses the problems of existing fly ash-blended grouting materials exhibiting hindered activity release, delayed setting, and heavy reliance on external thermal processes at low temperatures.

[0005] According to one aspect of the present invention, a silicate-modified fly ash-based low-temperature grouting material is provided, the low-temperature grouting material being composed of dry-mixed powder and water;

[0006] By mass, the dry-mixed powder comprises the following components: 20-60 parts silicate-modified fly ash, 20-50 parts basic cementitious components, 2-10 parts low-temperature nucleation components, 2-7 parts aqueous phase conditioning components, and 0.2-1.5 parts rheology conditioning components.

[0007] The amount of water added is 40% to 60% of the total mass of the dry-mixed powder;

[0008] Silicate-modified fly ash is a core-shell structured particle, which includes a fly ash core and a silicate coating layer covering the surface of the fly ash core.

[0009] Existing technologies for improving the insufficient low-temperature activity of fly ash-based low-temperature grouting materials typically involve directly adding strong activators, antifreeze agents, or setting accelerators to the mixing water or liquid phase components. This allows the active components to dissolve rapidly in the liquid phase and participate in the reaction. While this approach can improve the reaction rate under low-temperature conditions to some extent, the preferential distribution of the active components throughout the liquid phase system can easily lead to non-selective accelerated reactions in the grout bulk phase. This results in a rapid increase in grout viscosity, shortened working time, and, in severe cases, a decline in grout pumpability and crack propagation capacity. It is difficult to simultaneously achieve both fluidity and controlled setting performance under low-temperature construction conditions.

[0010] This invention differs from the traditional approach of liquid-phase dosing. Instead, it employs a "pre-construction of an active shell at the solid-phase interface" technique. By modifying the silicate surface of fly ash particles, silicate components are pre-fixed onto the surface of the fly ash particles, forming a silicate coating layer that covers the outer surface of the fly ash core. Consequently, the active silicon source, which was originally indiscriminately dispersed in the liquid phase, is pre-positioned and anchored at the solid-phase particle interface. This alters the location and manner of the reaction in the low-temperature grouting system, causing subsequent hydration, nucleation, and gel formation processes to preferentially occur around the surface of the fly ash particles.

[0011] After mixing with water, the silicate coating layer first comes into contact with the aqueous phase, forming a locally rich silica reaction interface on the particle surface. Simultaneously, calcium ions released by the basic cementing components, soluble calcium salts provided by the low-temperature nucleating components, and nanocrystal seeds preferentially accumulate near the silicate coating layer. Since the coating layer is directly located on the surface of the fly ash particles, it can serve as an interfacial nucleation substrate under low-temperature conditions, allowing early hydration products and the gel phase to preferentially grow at the solid-liquid interface of the fly ash particles, rather than precipitating disorderly throughout the liquid phase. Thus, the non-selective accelerated gelation mode of the existing grouting system can be transformed into a controlled coagulation mode that prioritizes the interface, initiates locally, and expands gradually.

[0012] Furthermore, the aqueous phase control component is used to reduce the freezing tendency of free water under low-temperature conditions and maintain the continuity of the liquid phase, while the rheology control component is used to improve the dispersion of modified fly ash and cementitious particles in the slurry and inhibit bleeding and local water loss. Together with the silicate coating layer and the low-temperature nucleation component, these components enable the slurry to maintain good stirability, pumpability, and diffusivity under low-temperature conditions, and provide a stable liquid phase environment for preferential nucleation and gel growth at the solid-liquid interface.

[0013] Therefore, this invention does not simply increase the low-temperature reaction rate by increasing the concentration of activator in the liquid phase, but rather transforms the low-temperature curing process from "indiscriminate reaction of the liquid phase" to "preferential reaction at the solid-liquid interface" by pre-constructing a silicate coating layer on the surface of fly ash particles. This technical approach can balance the construction fluidity and low-temperature setting and hardening ability of the grout under conditions of no heating and no insulation, thereby effectively solving the problems of easy overall thickening, short working time, and insufficient early activity in existing low-temperature grouting materials with fly ash.

[0014] Preferably, the silicate coating layer is formed by in-situ deposition of a silicate modifier on the surface of the fly ash core;

[0015] Silicate modifiers include one or at least two of water glass, sodium metasilicate, potassium metasilicate, lithium silicate, and silica sol.

[0016] Preferably, the basic cementitious component includes at least one of silicate cement, sulfoaluminate cement, and slag powder.

[0017] Preferably, the low-temperature nucleation components include soluble calcium salts and nanocrystal seeds;

[0018] The soluble calcium salt is selected from at least one of calcium formate, calcium nitrate, or calcium nitrite.

[0019] The nano-seeds are selected from nano-CSH seeds or nano-silica, with an average particle size of 10nm to 100nm, and the nano-seeds are dispersed in the dry powder of the grouting material in a dry powder state.

[0020] Nanocrystals possess a high specific surface area and, after being mixed with water, can serve as heterogeneous nucleation sites in the slurry, promoting the precipitation and deposition of early hydration products near the silicate coating layer. Because the nanocrystals are at the nanoscale, their dispersion in the slurry increases the number of interfacial nucleation centers, thereby reducing the initial nucleation process's activation requirements under low-temperature conditions, resulting in a shorter reaction induction period and faster early gel formation.

[0021] Furthermore, upon adding water, soluble calcium salts release Ca2+ during the initial hydration phase. 2+This creates a locally high concentration of calcium ions around the silicate coating layer. This locally high calcium environment is conducive to the reaction of active silicon species on the silicate coating layer with Ca. 2+ The reaction between the particles promotes the formation of CSH-type gels or related hydration products at the particle interface. Compared with systems using only nanocrystals, the introduction of soluble calcium salts further enhances the nucleation and growth rates at the interface.

[0022] Under the synergistic effect of the above components, nanocrystals mainly provide heterogeneous nucleation sites, while soluble calcium salts mainly provide an early calcium-supplying environment. Together, they promote interfacial nucleation and gel network formation on the surface of silicate-modified fly ash particles. Therefore, early reactions under low-temperature conditions are more likely to occur near the silicate coating layer, rather than proceeding disorderly throughout the liquid phase. This characteristic is beneficial for shortening the low-temperature reaction induction period and improving the early strength development level of the grouting material.

[0023] Preferably, the aqueous phase conditioning components include inorganic antifreeze salts and polyols;

[0024] The inorganic antifreeze salt is selected from at least one of sodium formate or sodium nitrate; the polyol is selected from at least one of ethylene glycol, propylene glycol or glycerol.

[0025] Inorganic antifreeze salts dissolve in the liquid phase of the slurry, which can reduce the freezing tendency of free water under low-temperature conditions by lowering the freezing point of the pore solution. The strong interaction between the hydroxyl groups in the polyol molecules and water molecules helps to alter the aggregation state of water molecules in the liquid phase and reduces the likelihood of water molecules forming ordered ice crystals under low-temperature conditions. The combination of these two components improves the stability of the slurry liquid phase under low-temperature conditions and mitigates the adverse effects of ice crystal formation on the continuous liquid phase structure of the slurry.

[0026] Furthermore, the combined action of inorganic antifreeze salts and polyols can, to some extent, reduce the problem of excessively high liquid-phase ionic strength caused by relying solely on high-concentration inorganic salts for antifreeze, thereby mitigating the adverse effects of the high-salt environment on the dispersion state of nanocrystals and their early surface reaction environment. Consequently, the low-temperature nucleation component, silicate coating layer, and basic gelling component can maintain a relatively stable interfacial reaction environment under low-temperature conditions, which is beneficial for the continuous generation and development of the early gel phase near the pregel shell.

[0027] Therefore, the aqueous phase control component is not only used to improve the antifreeze performance of the grout under low temperature conditions, but also helps to maintain the continuity of the liquid phase and the interfacial reaction conditions in the low temperature grouting system, thereby taking into account both the pumpability of the grout and the stable progress of the low temperature setting and hardening process.

[0028] Preferably, the rheology modifiers include water-reducing agents and thickeners;

[0029] The water-reducing agent is a polycarboxylic acid-based water-reducing agent with a main chain and polyether side chain comb-like structure; the thickener is selected from at least one of xanthan gum or modified cellulose ether.

[0030] Polycarboxylate superplasticizers can adsorb onto the surfaces of silicate-modified fly ash, basic cementitious components, and low-temperature nucleating components. Their molecular backbone enhances adsorption stability on particle surfaces, while the polyether side chains provide steric hindrance, thereby improving the dispersion of solid particles in the slurry and reducing the tendency for particle agglomeration. This helps maintain the uniform distribution of nanocrystalline seeds and modified fly ash particles in the slurry and improves the slurry's fluidity and pumpability under low-temperature conditions.

[0031] Xanthan gum or modified cellulose ethers can thicken and retain water in the liquid phase of the slurry, improving the cohesiveness and anti-segregation ability of the slurry system, and to some extent inhibiting free water migration, bleeding, and particle sedimentation. This effect helps maintain the uniformity of solid-liquid distribution within the slurry during low-temperature grouting, thus providing a relatively stable local environment for interfacial nucleation and early gel formation near the silicate coating layer.

[0032] Furthermore, when polycarboxylate superplasticizers are used in combination with thickeners, they can improve the dispersion and flow behavior of the slurry under shear stress, while maintaining the water retention and system stability of the slurry. This helps reduce the risk of disturbance to the interfacial active structure caused by local agglomeration, bleeding, or uneven particle distribution during grouting and transportation, allowing the coated modified fly ash particles and low-temperature nucleation components to be transported more stably to the grouting site and promoting the filling and consolidation of microcracks.

[0033] Preferably, the silicate coating layer is an amorphous silicate pregel layer with a low degree of polymerization;

[0034] Based on dry weight, the silicate modifier that forms the silicate coating layer accounts for 0.5% to 8.0% of the fly ash core weight.

[0035] Compared to highly polymerized or crystalline silicate layers, low-polymerized amorphous pregel layers exhibit greater structural disorder and more active sites on the particle surface. After mixing with water, they are more readily contacted with the liquid phase of the slurry and participate in early interfacial reactions. Therefore, the silicate coating layer not only coats the fly ash core but also serves as a reaction interface on the particle surface at low temperatures. This facilitates the accumulation of active ions released by low-temperature nucleation components and basic cementing components in their vicinity, and promotes the formation of an early gel phase on the coating layer surface.

[0036] Furthermore, the silicate coating exists in a pre-gel state, indicating that it does not form a dense, highly crystalline, inert film on the surface of the fly ash core, but rather maintains strong interfacial reactivity. This characteristic is beneficial for shortening the process from wetting and ion contact to initial gel deposition on the particle surface under low-temperature conditions, and promotes the formation of a continuous gel network at the solid-liquid interface. Compared with fly ash particles without a pre-gel layer, modified fly ash with this type of coating exhibits faster setting initiation and higher early structure building ability in low-temperature slurries.

[0037] Based on dry weight, the silicate modifier forming the silicate coating layer accounts for 0.5% to 8.0% of the fly ash core mass. When the amount of silicate modifier is below the lower limit of this range, the coating degree on the particle surface is insufficient, making it difficult to form a continuous or effectively distributed interfacial reaction layer on the fly ash core surface, which is not conducive to preferential nucleation and early gel deposition on the particle surface under low temperature conditions. When the amount of silicate modifier is above the upper limit of this range, the coating layer on the particle surface is prone to be too thick, which may increase the tendency of particle adhesion and agglomeration, and adversely affect the slurry fluidity, dry-mixed storage stability and subsequent water addition and dispersion process.

[0038] Therefore, controlling the amount of silicate modifier within the range of 0.5% to 8.0% of the fly ash core mass is beneficial to forming a low-polymerization degree amorphous silicate pregel layer with appropriate thickness, uniform distribution and interfacial reaction capability on the particle surface, thereby taking into account the storage stability of dry-mixed powder, the dispersibility of grouting slurry and the ability of interfacial nucleation and early gel formation under low temperature conditions.

[0039] The thickness of the silicate coating layer is 10 nm to 100 nm, preferably 20 nm to 50 nm. The thickness of the coating layer can be obtained by observing the cross-section of fly ash particles and measuring the thickness of the surface silicate layer using a transmission electron microscope.

[0040] The silicate coating has a coating rate of 80% to 95%. The coating rate can be determined by scanning electron microscopy. The specific method is as follows: randomly select 100 fly ash particles, count the percentage of particles with silicate coating on the surface, and calculate the coating rate by weighting by mass.

[0041] Low degree of polymerization refers to the degree of polymerization distribution of silicates, where Q... 1 and Q 2 The sum of structural units accounts for ≥60%, which can be determined by Si solid nuclear magnetic resonance; amorphous means that in the X-ray diffraction pattern, there are diffuse peaks in the range of 2θ=20°~35°, without obvious crystal diffraction peaks (such as characteristic peaks of quartz and cristobalite).

[0042] In another aspect, the present invention provides a method for preparing a silicate-modified fly ash-based low-temperature grouting material, comprising the following steps:

[0043] S1. Pre-treat the fly ash; the pre-treatment includes: drying and dewatering the raw fly ash and screening it to remove impurities, obtaining fly ash with a moisture content of less than 1.0%, followed by grinding and mechanical activation to obtain fly ash with a specific surface area of ​​400 m². 2 / kg~700m 2 / kg of fly ash core;

[0044] Drying and sieving reduce the interference of free water and impurities in the raw fly ash on the coating process; ensure that the subsequent silicate modifier can act more uniformly on the surface of fly ash particles; at the same time, it can reduce the adhesion and agglomeration between particles and improve the stability and repeatability of surface modification.

[0045] Furthermore, the grinding and mechanical activation are carried out (using at least one of ball milling, vibratory milling, stirred milling or planetary milling, preferably to achieve a specific surface area of ​​400-700 m²). 2 / kg or median particle size D50 in the range of 4.0μm to 10.0μm as the endpoint of mechanical activation) to increase the specific surface area of ​​fly ash, thereby increasing the number of active sites on the particle surface and improving the particle size distribution, thus improving the adhesion and coating effect of liquid silicate modifier on the particle surface.

[0046] S2. A liquid silicate modifier is used to perform surface composite modification on the fly ash core, so that the silicate modifier is deposited in situ on the surface of the fly ash core and dried under controlled temperature to form a silicate coating layer, thus obtaining silicate-modified fly ash with a core-shell structure.

[0047] The active silicon source, originally dispersed in the liquid phase, is pre-fixed onto the surface of fly ash particles, transforming the fly ash from ordinary filler particles into functional particles with an interfacial reaction layer. Therefore, during subsequent water addition and mixing, the low-temperature reaction can preferentially initiate near the particle surface, rather than proceeding indiscriminately throughout the liquid phase. Simultaneously, the temperature-controlled drying process gradually transforms the silicate deposition layer on the particle surface from a liquid state into a solid coating layer, maintaining good interfacial continuity and subsequent redispersibility. This results in a core-shell structured powder suitable for both dry-mixed storage and re-participation in interfacial reactions after water addition.

[0048] S3. Silicate-modified fly ash is mixed with basic cementitious components, low-temperature nucleation components, aqueous phase regulating components and rheology regulating components to obtain premixed grouting dry-mix powder.

[0049] S4. Add water to the premixed dry powder obtained in step S3 at a ratio of 40% to 60% of the total mass of the dry powder and stir evenly to obtain low-temperature grouting material.

[0050] Preferably, in step S2, the silicate modifier is applied to the fly ash surface by at least one of impregnation, atomized spraying, or high-speed stirring and coating.

[0051] The temperature for temperature-controlled drying is controlled between 50℃ and 120℃, and the time is 1-4.5 hours.

[0052] Impregnation facilitates full contact between the liquid modifier and the particle surface; atomized spraying improves the uniformity of modifier distribution in the powder and reduces localized over-wetting; high-speed stirring and coating improves particle separation under mechanical dispersion and promotes the spreading of the modifier on the particle surface. Using one or more of these methods can improve the deposition uniformity and coating integrity of silicate modifiers on fly ash particle surfaces, thereby promoting the formation of more uniformly distributed core-shell structured particles.

[0053] By controlling the temperature of the drying process between 50℃ and 120℃, the liquid silicate modifier on the particle surface can be gradually dehydrated and formed into a film, creating a solid silicate coating layer. On the other hand, it can also prevent the coating layer from over-condensing, crystallizing, or becoming too dense due to excessive temperature, which would affect its interfacial reaction capability under subsequent low-temperature conditions.

[0054] Preferably, the specific mixing process of step S3 is as follows: first, the silicate-modified fly ash is dry-mixed with the basic cementing component and the rheology regulating component, and then the low-temperature nucleation component and the aqueous phase regulating component are added and mixed evenly.

[0055] The main purpose of this mixing sequence is to improve the storage stability and component distribution uniformity of the dry-mixed powder. First, the silicate-modified fly ash is pre-mixed with the basic cementing components and rheology modifiers. This facilitates the initial uniform dispersion of core-shell structured particles in the powder system, and the rheology modifiers improve the looseness and anti-agglomeration properties of the powder particles. Subsequently, low-temperature nucleating components and aqueous phase control components are added. This reduces the chance of long-term direct contact between highly active, hygroscopic components and the silicate coating layer, thereby mitigating premature hydration, agglomeration, or surface consolidation caused by localized moisture absorption during storage.

[0056] Low-temperature nucleation components and aqueous phase control components typically contain certain hygroscopic or highly ionicly reactive substances. If these substances are mixed with core-shell particles for an extended period and exposed to ambient moisture during the initial stage, it may induce premature moisture absorption, localized swelling, or even early reactions in the outer coating layer. Adopting a gradient feeding sequence helps to reduce these adverse effects and maintain the structural integrity of the coating layer before construction and its interfacial reactivity after subsequent water addition.

[0057] This stepwise mixing method also improves the uniformity and dispersibility of the final dry-mixed powder, making it easier for different functional components to work simultaneously after being mixed with water. This, in turn, helps to obtain a low-temperature grout with more stable fluidity and a more controllable setting process at the construction site.

[0058] The beneficial effects of this invention are as follows:

[0059] 1. This invention transforms the active silicon source from a freely dispersed state in the liquid phase to a pre-placed active source fixed at the interface of solid particles by pre-constructing a silicate coating layer on the surface of fly ash particles. This allows the early reaction under low-temperature conditions to preferentially unfold around the surface of fly ash particles, which helps to reduce the risk of rapid thickening and decreased pumpability caused by the overall indiscriminate accelerated reaction of the slurry in the liquid phase.

[0060] 2. The low-temperature nucleating component, aqueous phase regulating component and silicate coating layer of this invention work synergistically to maintain a relatively stable interfacial reaction environment under low-temperature conditions, promote interfacial nucleation and early gel formation near the particle surface, thereby shortening the low-temperature reaction induction period and improving the early strength development level of the material.

[0061] 3. This invention uses dry-mixed powder for storage and transportation, and reduces the adverse effects of highly active and hygroscopic components on the stability of the coating layer through temperature-controlled drying film formation and step-by-step mixing processes. This is beneficial to improving the product's storage stability, on-site ease of use, and consistency of the construction process.

[0062] 4. While maintaining the performance of low-temperature grouting construction, this invention improves the resource utilization level of fly ash in grouting materials, reduces the amount of cementitious materials and material costs, and is conducive to obtaining a solidified body with low porosity and dense structure.

[0063] 5. The three-dimensional water-retaining network constructed by the interface-preferred nucleation mechanism provided by the silicate coating layer and the rheology-modifying components is beneficial to improving the stone formation rate under low temperature conditions. In the preferred embodiment, the stone formation rate can reach more than 98% at -5℃, ensuring the full consolidation of deep microcracks.

[0064] 6. This invention utilizes a compound system of "inorganic eutectic non-chloride salt + polyol". This eliminates the introduction of chloride ions at the chemical source, avoiding the potential corrosion risks associated with chloride-based antifreeze agents and improving the engineering durability of the grouting material. Detailed Implementation

[0065] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0066] Example 1:

[0067] Components: Raw fly ash: Class II fly ash of type F conforming to GB / T1596-2017 standard, with an initial moisture content of 1.5% to 2.5% and an initial specific surface area of ​​approximately 320 m². 2 / kg.

[0068] Silicate modifier: Commercially available industrial-grade liquid sodium silicate (water glass) with a modulus (M) precisely calibrated to 2.5 and an initial solid content of 35wt% is selected. To ensure atomization and spreading effect, deionized water is added before use to dilute it to a modified solution with a solid content of 20%.

[0069] Basic cementitious components: Ordinary Portland cement, P·O42.5 grade (specific surface area 360m²), is selected. 2 / kg); sulfoaluminate rapid-hardening cement of grade R-SAC42.5 is selected.

[0070] Low-temperature nucleation components: Calcium formate is selected from industrial-grade ultra-fine dry powder with a purity ≥98%; nano-CSH seed crystals can be commercially available nano-CSH seed crystal powder, or obtained by solution reaction followed by freeze-drying. The average particle size (D50) is measured to be 40 nm by a laser particle size analyzer, and the specific surface area is ≥150 m². 2 / g; the calcium-to-silicon ratio is preferably 0.8 to 2.0.

[0071] Aqueous phase control components: Sodium nitrate is selected as dry powder with a purity of ≥99%; ethylene glycol is selected as the polyol.

[0072] Rheology modifiers: The water-reducing agent is a powdered comb-shaped polycarboxylate high-efficiency water-reducing agent (solid content ≥98%, water reduction rate ≥25%); the thickener is xanthan gum powder with a purity of 200 mesh.

[0073] Process steps:

[0074] This embodiment prepares a total of 100 kg of premixed dry-mixed grouting powder, with each component allocated by mass (totaling 100 parts, i.e., 1 part = 1.0 kg). The specific replication steps are as follows:

[0075] S1. High-energy pretreatment of fly ash:

[0076] Drying and dehydration: Spread 50.0 kg of raw fly ash evenly on a stainless steel tray (thickness < 3 cm), place it in a forced convection drying oven, and dry at a constant temperature of 105℃ for 3 hours. After cooling, the free moisture content was measured by a rapid moisture analyzer and found to be reduced to 0.3%.

[0077] Mechanical activation: The dried fly ash was fed into a horizontal planetary ball mill, with alumina grinding balls graded at a ball-to-material ratio of 3:1. The spindle speed was set to 400 r / min, and grinding was performed continuously for 45 minutes. After discharge, the specific surface area was measured to be increased to 550 m². 2 / kg, D50 is 6.5μm. Pass through a 120-mesh standard sieve, and take 43.27kg of the sieve-passing material as fly ash core for later use.

[0078] S2, fly ash silicate shell modification:

[0079] Precise solution preparation: The amount of silicate modifier in the silicate coating layer is set to 4.0% of the dry weight of the fly ash core. Weigh 4.95 kg of liquid sodium silicate (water glass, modulus 2.5, solid content 35%), which is equivalent to 1.73 kg of pure solid sodium silicate; then add 3.71 kg of deionized water to prepare a low-viscosity modified solution with a total mass of 8.66 kg and a solid content of 20%.

[0080] Fluidized atomization coating: 43.27 kg of fly ash core was fed into a plow-type mixer equipped with high-speed flying blades. The main shaft was started (speed 120 r / min) to fluidize the powder. The pneumatic atomizing nozzles were turned on (puffing air pressure 0.4 MPa), and the above 8.66 kg of atomized liquid was sprayed uniformly onto the powder surface over 10 minutes. After spraying, the high-speed flying blades (2500 r / min) were turned on to continue strong shearing and dispersing for 5 minutes to prevent liquid bridge agglomeration.

[0081] Temperature-controlled drying for film formation: The wet composite powder is spread evenly and transferred into an industrial temperature-controlled oven, where a constant temperature of 80℃ is strictly set, and forced ventilation is used for drying for 2.5 hours. After being removed from the oven and allowed to cool naturally, the pseudo-agglomerates are broken up using a mild deagglomeration machine. 45.0 kg of silicate-modified fly ash with a low degree of polymerization and an amorphous pre-gel layer on the surface is accurately weighed for subsequent compounding.

[0082] S3. Gradient dry mixing for preparing premixed powder:

[0083] Two-stage gradient mixing is performed using a 300L dual-ribbon horizontal dry powder mixer:

[0084] First stage: Add 45.0 kg of modified fly ash obtained from S2, 28.0 kg of silicate cement, 12.0 kg of R-SAC42.5 cement, 0.8 kg of polycarboxylate superplasticizer powder, and 0.2 kg of xanthan gum powder. Mix in a closed mixer at 45 r / min for 8 minutes to pre-coat the core-shell fly ash and cement particles with the hydrophobic polymer.

[0085] Second stage: Pause the machine and add 6.0 kg of calcium formate powder, 2.0 kg of nano-CSH seed crystals, and 4.0 kg of sodium nitrate dry powder. Restart the mixer and, at a speed of 45 r / min, evenly spray 2.0 kg of liquid ethylene glycol onto the powder using a high-pressure micro-mist nozzle over 3 minutes. Utilizing the extremely large specific surface area of ​​the dry powder system and the micropores of xanthan gum, the liquid ethylene glycol is instantly adsorbed and dispersed. Continue mixing for 5 minutes, then discharge the material to obtain 100 kg of premixed dry-mixed grouting powder with excellent flowability and no caking. Pack it in a moisture-proof bag with an inner membrane for later use.

[0086] S4. Pulping without heating under extreme low temperature conditions:

[0087] Environmental calibration: Simulating extreme cold construction in winter, dry-mixed powder, tap water and mortar mixer were all moved into a -5℃ walk-in constant temperature freezer and left to cool completely for 24 hours.

[0088] Precision pulp preparation: In a -5℃ chamber, weigh 10.0 kg of freeze-dried powder and pour it into a mixing tank. Add 4.0 kg of 0-2℃ ice water at a rate of 40% of the powder's mass. Strictly follow the procedure of "slow stirring (140 rpm) for 1 minute → stopping and scraping the tank walls for 15 seconds → rapid stirring (285 rpm) for 2 minutes." Immediately conduct flowability and solidification tests on the resulting pulp.

[0089] Example 2:

[0090] The process equipment and operating procedures are the same as in Example 1, with only the following quantitative parameters adjusted:

[0091] Step S1: Mill spindle speed 300 r / min, grinding time 25 minutes, control specific surface area to 400 m². 2 / kg.

[0092] Step S2: Reduce the dry basis amount of sodium silicate coating to 0.5%; set the temperature control drying temperature to the lower limit red line of 50℃ (to ensure dehydration and film formation, extend the baking time to 4.5 hours).

[0093] Step S3: Prepare 20.0 kg of modified fly ash according to the lower limit of the component ratio.

[0094] Basic cementitious component 50.0 kg

[0095] 2.0 kg of low-temperature nucleation components (e.g., 1.0 kg of calcium formate + 1.0 kg of nano-silica)

[0096] 2.0 kg of aqueous phase control component (e.g., 1.0 kg sodium formate + 1.0 kg ethylene glycol)

[0097] Rheology modifier 0.2kg (polycarboxylate superplasticizer 0.15kg + xanthan gum 0.05kg).

[0098] Example 3:

[0099] The process equipment and operating procedures are the same as in Example 1, with only the following quantitative parameters adjusted:

[0100] Step S1: Extend the ball milling time to 65 minutes, and control the specific surface area to 700 m². 2 / kg.

[0101] Step S2: The dry basis weight of sodium silicate coating is increased to 8.0%; the temperature control drying temperature is set to 120℃ (to prevent burn-out, the baking time is shortened to 1.0 hour).

[0102] Step S3: Prepare the ingredients according to the upper limit of the component (60.0 kg modified fly ash, 22.0 kg R-SAC42.5 cement, 8.0 kg calcium formate + 2.0 kg nano CS-H, 4.0 kg sodium nitrate + 3.0 kg atomized liquid propylene glycol with a purity ≥99%, 1.2 kg polycarboxylate superplasticizer + 0.3 kg xanthan gum). Total: 100.5 kg.

[0103] Step S4: Add cold water at 60% of the total mass of the dry-mixed powder to make a slurry.

[0104] Example 4:

[0105] S1. High-energy pretreatment of fly ash:

[0106] The raw ash was dried at 105℃ until the free moisture content was below 0.3%, then fed into a planetary ball mill for mechanical activation, with the grinding time adjusted to 35 minutes. After discharge, the specific surface area was measured and controlled to be 500 m². 2 / kg, D50 is 5.5μm. After sieving, accurately weigh 38.84kg of fly ash kernels for later use.

[0107] S2, fly ash silicate shell modification (intermediate coating amount 3.0% and intermediate temperature 90℃):

[0108] The amount of silicate modifier in the silicate coating layer is set to 3.0% of the dry weight of the fly ash core. 3.33 kg of liquid sodium silicate (water glass, solid content 35%) is weighed, which is equivalent to 1.16 kg of pure solid sodium silicate; then 2.50 kg of deionized water is added to prepare a modified solution with a total mass of 5.83 kg and a solid content of 20%.

[0109] 38.84 kg of fly ash core was fed into a plow-type mixer equipped with high-speed flying blades and fluidized. The pneumatic atomizing nozzle was activated, and 5.83 kg of the atomized liquid was uniformly sprayed onto the powder surface over 10 minutes. The powder was then transferred to an industrial temperature-controlled oven, where a constant temperature and exhaust drying temperature of 90°C was set for 2.0 hours. After natural cooling and depolymerization, 40.0 kg of silicate-modified fly ash with a low-polymerization amorphous pre-gel layer on its surface was accurately weighed for subsequent compounding.

[0110] S3. Gradient dry mixing to prepare premixed powder (total weight accurately weighed: 81.0 kg):

[0111] Two-stage gradient mixing is performed using a 300L dual-ribbon horizontal dry powder mixer:

[0112] First stage: Add 40.0 kg of modified fly ash obtained from S2; 30.0 kg of basic cementitious components (including accurately weighed 15.0 kg of ordinary Portland cement and 15.0 kg of slag powder conforming to national standard S95); and 1.0 kg of rheology modifier components (including accurately weighed 0.8 kg of polycarboxylate superplasticizer powder and 0.2 kg of modified cellulose ether dry powder). Mix in a closed mixer at 45 r / min for 8 minutes.

[0113] Second stage: Pause the machine and add 6.0 kg of low-temperature nucleation component (containing 4.0 kg of calcium nitrite powder and 2.0 kg of nano-silica dry powder with an average particle size of 50 nm); and 2.0 kg of aqueous phase regulating solid component, i.e., sodium formate dry powder. Restart the mixer and use a high-pressure micro-mist nozzle to spray 2.0 kg of aliphatic polyol containing 3 carbon atoms (i.e., liquid glycerol with a purity ≥99%) onto the powder at a uniform speed over 3 minutes. Continue mixing for 5 minutes and then discharge the material, obtaining a total of 81.0 kg of moisture-proof premixed grouting dry-mixed powder.

[0114] S4. Pulping without heating under extreme low temperature conditions:

[0115] In a -5℃ constant temperature chamber simulating extreme cold construction, accurately weigh 10.0 kg of the thoroughly cooled dry-mixed powder and pour it into a mortar mixing pot. Add 4.5 kg of ice water (0-2℃) at a rate of 45% of the dry powder mass. Prepare the slurry according to the standard procedure of "slow mixing for 1 minute → stopping the machine and scraping the pot wall for 15 seconds → rapid mixing for 2 minutes". Immediately conduct flowability and curing tests on the resulting slurry.

[0116] Comparative Example 1:

[0117] The difference from Example 1 is that step S2 is omitted. In the S3 dry mixing stage, 45.0 kg of unmodified raw ash kernels treated only in S1 are directly added. In the S4 pulping stage, 5.14 kg of liquid water glass (containing 35% solids) of equivalent efficiency in Example 1 is directly dissolved in the mixing liquid phase water, and this high-concentration activating solution is used to stir the dry-mixed powder.

[0118] Comparative Example 2:

[0119] The difference from Example 1 is that 2.0 kg of nano-CSH seed crystals were removed in the second-stage dry mixing in S3. To maintain the same total mass, 2.0 kg of inert quartz micropowder with a particle size of 2 μm was used as an equal substitute.

[0120] Comparative Example 3:

[0121] The difference from Example 1 is that 2.0 kg of liquid ethylene glycol is removed in the second stage dry mixing of S3. The aqueous phase control component is changed to 6.0 kg of pure sodium nitrate powder (artificially creating a pure inorganic high-salt antifreeze environment).

[0122] Comparative Example 4:

[0123] The difference from Example 1 is that 0.2 kg of xanthan gum thickener was removed in the first stage dry mix (S3). Only 0.8 kg of polycarboxylate superplasticizer was retained as the rheology modifier.

[0124] Comparative Example 5:

[0125] The difference from Example 1 is that: only in the temperature-controlled drying film-forming process of S2, the forced exhaust temperature of the oven is incorrectly set to 160°C and baked continuously for 2.5 hours, so that the amorphous silicates coated on the surface of fly ash undergo high-temperature dehydration and crystallization.

[0126] Comparative Example 6:

[0127] The difference from Example 1 is that the two-stage gradient mixing process is removed. Modified fly ash, cement, highly active hygroscopic salts, and ethylene glycol are all added to the mixer at once and mixed vigorously for 15 minutes. Subsequently, the dry powder is placed in an open container in a high-humidity environment of 20°C and 85% relative humidity for 14 days, and then transferred to a -5°C environmental chamber for water addition and slurry preparation tests.

[0128] Test example: Standardized test method for -5℃;

[0129] Pumpable time: The initial flowability after adding water is tested using a truncated cone mold (GB / T50448) for 5 minutes; the flowability is retested every 10 minutes by stirring and turning, and the time taken for the flowability to decay to the unpumpable threshold (<180mm) is recorded as the pumpable time.

[0130] Compressive strength: 40×40×160mm specimens were frozen and cured in a mold at -5℃ for 24 hours to determine the 1-day early strength; under the same conditions, they were frozen and cured for another 3 days to determine the 3-day compressive strength; then they were transferred to a standard curing room at 20℃ for 28 days to determine the later strength.

[0131] Low-temperature stone formation rate: 100 mL of the mixed slurry was injected into a stoppered graduated cylinder, sealed and placed in a -5℃ environment for 24 h, and the percentage of the final solidified volume to the initial total slurry volume was measured.

[0132] Freeze-thaw durability (strength retention rate after 50 freeze-thaw cycles): 28-day standard-cured specimens were subjected to 50 extreme cold freeze-thaw cycles (-15℃ to 5℃) using the slow freezing method, and the compressive strength retention rate before and after the cycles was tested.

[0133] Micro porosity: The total porosity of the core region sample of the 28-day solidified body was determined by a high-performance mercury porosimeter (MIP) after hydration was terminated with anhydrous ethanol. The test results are shown in Table 1.

[0134] Table 1. Performance test results of grouting materials in the examples and comparative examples:

[0135]

[0136] As shown in Table 1, Examples 1-3 all exhibited high initial fluidity, long pumpable time, short initial setting time, and high 1-day compressive strength at -5℃. The 28-day compressive strength remained at a high level, and the microporosity of the consolidated body was low. Compared to Comparative Examples 1-6, without surface shell construction, lack of nanocrystal seeds, lack of polyols, lack of thickeners, excessively high drying temperature, or without gradient mixing processes, the pumpable time was significantly shortened, the initial setting time was prolonged or excessively rapid flow loss occurred, early strength decreased, and porosity increased. This indicates that the silicate-modified fly ash core-shell structure, low-temperature nucleating components, aqueous phase control components, rheology regulating components, and corresponding preparation methods used in this invention have a synergistic effect, enabling the slurry to achieve good workability, early strength, and later densification performance under low-temperature conditions.

[0137] As shown in Table 1, Example 3 was used to verify the upper limit of the parameters. Under the conditions of high fly ash content and high water-to-solid ratio, the decrease in absolute strength in the later stage is a normal phenomenon. However, it still maintains a short initial setting time and a high 1-day strength at -5℃, indicating that the present invention still has good low-temperature early solidification ability under the boundary conditions of high solid waste content.

[0138] Example 2 (e.g., 20 parts modified fly ash, 0.5% coating) and Example 3 (e.g., 60 parts modified fly ash, 8.0% coating) serve as the lower and upper limits of the core proportion boundary, respectively. The newly added Example 4 (e.g., 40 parts modified fly ash, 3.0% coating) precisely covers the intermediate value of the key components and successfully verifies the effectiveness of "slag powder" and "glycerol (a polyol with 2-6 carbon atoms)" as lower-level substitutes. The above examples constitute a tight matrix closed loop, fully demonstrating that within the broad parameter range defined by the claims, the technical solution can stably achieve the inventive objectives of improving early strength, stone formation rate, and freeze-thaw durability, obtaining detailed and irrefutable experimental support.

[0139] To further verify the performance of the present invention under different low-temperature conditions, the dry-mixed powder of Example 1 was tested at 0℃, -5℃, -10℃, and -15℃, respectively. The results are shown in Table 2.

[0140] Table 2 shows the performance of Example 1 at different temperatures;

[0141]

[0142] As shown in Table 2, the present invention maintains good low-temperature construction performance in a wide temperature range from -15℃ to 0℃.

[0143] The embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A silicate-modified fly ash-based low-temperature grouting material, characterized in that: The grouting material is made by mixing dry powder and water; The dry-mixed powder comprises the following components by mass: 20-60 parts silicate-modified fly ash, 20-50 parts basic cementitious components, 2-10 parts low-temperature nucleation components, 2-7 parts aqueous phase conditioning components, and 0.2-1.5 parts rheology conditioning components. The amount of water added is 40% to 60% of the total mass of the dry-mixed powder; The silicate-modified fly ash is a core-shell structured particle, which includes a fly ash core and a silicate coating layer covering the surface of the fly ash core. The silicate coating layer is a low-polymerization amorphous silicate pregel layer; The low-temperature nucleation components include soluble calcium salts and nanocrystal seeds; The aqueous phase conditioning components include inorganic antifreeze salts and polyols; The rheology modifiers include water-reducing agents and thickeners; The silicate modifier forming the silicate coating layer accounts for 0.5% to 8.0% of the mass of the fly ash core, based on dry weight. The silicate modifier includes one or at least two of water glass, sodium metasilicate, potassium metasilicate, lithium silicate, and silica sol. The thickness of the silicate coating layer is 20 nm to 50 nm, and the coating rate is 80% to 95%. The low degree of polymerization refers to the Q in the silicate coating layer. 1 Structural unit and Q 2 The total proportion of structural units shall not be less than 60%; The amorphous shape refers to the silicate coating layer exhibiting diffuse peaks in the X-ray diffraction pattern within the range of 2θ = 20° to 35°, without obvious crystalline diffraction peaks.

2. The silicate-modified fly ash-based low-temperature grouting material according to claim 1, characterized in that: The silicate coating layer is formed by in-situ deposition of a silicate modifier on the surface of the fly ash core.

3. The silicate-modified fly ash-based low-temperature grouting material according to claim 2, characterized in that: The basic cementitious component includes at least one of silicate cement, sulfoaluminate cement, and slag powder.

4. The silicate-modified fly ash-based low-temperature grouting material according to claim 3, characterized in that: The soluble calcium salt is selected from at least one of calcium formate, calcium nitrate, or calcium nitrite; The nanocrystal seeds are selected from nano-CSH seeds or nano-silica, with an average particle size of 10nm to 100nm, and the nanocrystal seeds are dispersed in the dry-mixed powder of the grouting material in a dry powder state.

5. The silicate-modified fly ash-based low-temperature grouting material according to claim 4, characterized in that: The inorganic antifreeze salt is selected from at least one of sodium formate or sodium nitrate; the polyol is selected from at least one of ethylene glycol, propylene glycol or glycerol.

6. The silicate-modified fly ash-based low-temperature grouting material according to claim 5, characterized in that: The water-reducing agent is a polycarboxylic acid-based water-reducing agent with a main chain and polyether side chain comb-like structure; the thickener is selected from at least one of xanthan gum or modified cellulose ether.

7. A method for preparing a silicate-modified fly ash-based low-temperature grouting material, used to prepare the grouting material according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Pre-treat the fly ash; the pre-treatment includes: sequentially drying and dehydrating the raw fly ash and screening to remove impurities, obtaining fly ash with a moisture content of less than 1.0%, and then grinding and mechanically activating the fly ash to obtain a specific surface area of ​​400 m². 2 / kg~700m 2 / kg of the fly ash core; S2. A liquid silicate modifier is used to perform surface composite modification on the fly ash core, so that the silicate modifier is deposited in situ on the surface of the fly ash core, and then dried under controlled temperature to form the silicate coating layer, thereby obtaining the silicate-modified fly ash with a core-shell structure; the silicate modifier is applied to the surface of the fly ash by at least one of impregnation, atomized spraying, or high-speed stirring coating. The temperature for temperature-controlled drying is controlled between 50℃ and 120℃, and the time is controlled between 1 and 4.5 hours. S3. The silicate-modified fly ash is mixed with the basic cementitious component, the low-temperature nucleating component, the aqueous phase regulating component, and the rheology regulating component to obtain a premixed grouting dry-mixed powder. The specific mixing process is as follows: the silicate-modified fly ash is first dry-mixed with the basic cementitious component and the rheology regulating component, and then the low-temperature nucleating component and the aqueous phase regulating component are added and mixed evenly. S4. Add water to the premixed dry powder obtained in step S3 at a ratio of 40% to 60% of the total mass of the dry powder and stir evenly to obtain the low-temperature grouting material.

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