High-stability foamed concrete powder foaming agent and preparation process

Abstract

This invention discloses a high-stability powder foaming agent for foamed concrete, comprising a foaming component, a foam-stabilizing component, a nano-interface armor component, an active powder carrier component, and a mineralization nucleation promoter, forming a multi-stage core-shell microcapsule morphology. Upon contact with water, it sequentially triggers three foam-stabilizing mechanisms: enhanced viscoelasticity of the polymer hydration network, nanoparticle Pickering interface armor, and in-situ mineralization shell formation. This invention also provides a preparation process for the powder foaming agent, including three stages: high-shear homogenization of the precursor liquid phase, microcapsule spray drying granulation, and high-shear dry mixing and isolation of the bulk active carrier.

Description

Technical Field

[0001] This invention relates to the field of chemical additives for building materials, specifically to a high-stability powder foaming agent for foamed concrete and its preparation process. Background Technology

[0002] Foamed concrete, a novel silicate building material, is a lightweight porous material containing numerous pores formed by introducing pre-made foam into a matrix slurry composed of cement, admixtures, and water, followed by curing. It has significant applications in building energy conservation, backfilling of mined-out areas, and lightweight walls. Its physical and mechanical properties largely depend on its microstructure; the performance of the foaming agent and the foaming process are the core factors determining this structure. Currently, most mainstream physical foaming agents on the market are anionic or nonionic surfactant systems. These foaming systems rely on the single- or double-layer adsorption of organic molecules at the gas-liquid interface to reduce surface tension. When these thermodynamically unstable foams are introduced into a high-density, high-viscosity, strongly alkaline (pH>12.5) cement slurry containing a large number of solid particles, the liquid film undergoes rapid capillary drainage and rupture driven by gravity and Laplace pressure differential. Simultaneously, irreversible Oswald curing occurs under the drive of the gas concentration gradient, leading to the disappearance of numerous small bubbles and the abnormal expansion of large bubbles, forming interconnected, destructive macropores. In addition, the pure organic liquid film lacks sufficient mechanical stiffness, and the bursting of air bubbles leads to a local increase in the water-cement ratio in the pore wall area. The gel generated by hydration becomes loose and porous, resulting in a significant decrease in the compressive strength of foamed concrete in the ultra-lightweight range (such as 400-600 kg / m³).

[0003] To mitigate foam bursting issues, existing technologies typically employ compounded polymeric foam stabilizers. However, these systems almost exclusively exist in the form of liquid aqueous solutions or high-water-content emulsions. Liquid systems contain a large amount of ineffective free water, which not only significantly increases long-distance logistics costs but also makes them highly susceptible to phase separation, polymer degradation, and microbial spoilage at extreme temperatures, resulting in a short shelf life. More importantly, liquid foaming agents cannot be directly premixed into the specialized dry-mixed mortar systems urgently needed for modern prefabricated buildings. Existing powdered chemical foaming systems (such as those incorporating aluminum powder) face technical bottlenecks such as uncontrollable gas release, the flammability and explosiveness of hydrogen, and a high risk of cross-pore collapse. High-performance powdered physical foaming agents face insurmountable barriers in industrial applications. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a high-stability powder foaming agent for foamed concrete and its preparation process, comprising the following components: a foaming component, a foam-stabilizing component, a nano-interface armor component, an active powder carrier component, and a mineralization nucleation promoting agent; wherein the active powder carrier component includes a water-soluble polysaccharide excipient and mesoporous silica fume. The powder foaming agent exhibits a multi-stage core-shell microcapsule morphology in its microstructure. The inner layer is the microcapsule core, with the water-soluble polysaccharide excipient serving as the film-forming wall material. The foaming component, the foam-stabilizing component, and the nano-interface armor component are physically encapsulated within the skeletal network formed by the film-forming wall material after dehydration. The outer layer is a physical isolation layer composed of the mesoporous silica fume and the mineralization nucleation promoting agent, which coats and adsorbs onto the outer surface of the microcapsule core. This unique configuration allows the powdered foaming agent to dissolve in water, resulting in rapid wetting of the external hydrophilic silica particles. The water-soluble polysaccharide excipient skeleton instantly disintegrates, releasing the internal active ingredients. The foaming component rapidly reduces surface tension and attracts air, while the foam-stabilizing component's macromolecules fully swell and expand in the aqueous phase, forming a three-dimensional polymeric hydration network liquid film through intermolecular chain entanglement. This increases the plastic viscosity of the continuous phase and delays capillary drainage. Simultaneously, the nano-interface armor component undergoes irreversible adsorption and self-assembly at the gas-liquid interface due to its specific contact angle, forming a solid particle armor (Pick) with a two-dimensional shear modulus at the macroscopic mechanical level. The ring effect completely negates the Laplace pressure difference through huge spatial steric hindrance, locking the Oswald curing path; after the foam is mixed into the slurry, the mesoporous silica fume and mineralization nucleation promoter enriched on the outer edge of the bubbles are subjected to polarization attack by the strongly alkaline pore liquid during cement hydration, causing the amorphous silica network to depolymerize and release active silicate ions. Using the mineralization nucleation promoter as heterogeneous nucleation points, in-situ mineralization occurs in the micro-regions at the gas-liquid interface to generate a high-density, low-calcium-silicon ratio calcium silicate hydrate (CSH) and acicular ettringite (AFt) inorganic mineralization shell, transforming the flexible liquid film into a hard ceramic mineral microporous shell.

[0005] According to one aspect of the invention, based on the total mass of all components being 100%, the foaming component comprises 3.0% to 10.0% by mass, the foam-stabilizing component comprises 1.0% to 5.0%, the nano-interface armor component comprises 2.0% to 8.0%, the water-soluble polysaccharide excipient comprises 8.0% to 15.0%, the mesoporous silica fume comprises 50.0% to 80.0%, and the mineralization nucleation promoting agent comprises 3.0% to 10.0%. More preferably, the foaming component comprises 5.0% to 8.0% by mass, the foam-stabilizing component comprises 2.0% to 3.5%, the nano-interface armor component comprises 3.0% to 5.0%, the water-soluble polysaccharide excipient comprises 10.0% to 12.0%, the mesoporous silica fume comprises 65.0% to 75.0%, and the mineralization nucleation promoting agent comprises 5.0% to 8.0%. The foaming component is controlled within the above range. If it is below 5.0%, the reduction in the free energy at the gas-liquid interface will be insufficient, resulting in a low basic foaming ratio. If it is above 8.0%, excessive surfactant micelles will compete for adsorption, which will interfere with the interfacial anchoring of the nano-armor. The water-soluble polysaccharide excipient is controlled between 10.0% and 12.0% to provide a perfect microcapsule film-forming coating effect. If the content is too low, it will not be able to completely wrap the polymer network, causing the dry powder to easily absorb moisture and clump. If it is too high, it will slow down the rehydration and dissolution rate. The high proportion of bulk mesoporous silica fume, between 65.0% and 75.0%, can ensure that a sufficiently thick physical isolation barrier is formed when the powder is dry-mixed. At the same time, it meets the material conservation requirements of the massive total surface area of ​​the air bubbles for the coating of the armor layer at the micro-geometric level, ensuring a sufficient supply of silicon source for the subsequent in-situ mineralization.

[0006] Preferably, the foaming component is selected from at least one of sodium α-olefin sulfonate, sodium dodecyl sulfate, and sodium fatty alcohol polyoxyethylene ether sulfate, and must contain sodium α-olefin sulfonate; sodium α-olefin sulfonate has an extremely low Krafft point and excellent water solubility, and its hydrocarbon tail chains are arranged hydrophobically towards the air phase, which can significantly reduce the surface tension of water to an extremely low level under instantaneous shear. The foam stabilizing component is selected from at least one of hydroxypropyl methylcellulose, polyvinyl alcohol, and carboxymethyl starch ether, and must contain low-viscosity hydroxypropyl methylcellulose; preferably, the low-viscosity hydroxypropyl methylcellulose is subjected to glyoxal micro-crosslinking surface treatment before use. This treatment can effectively avoid the problem of polymer powders quickly sticking together on the water surface to form "fish-eye" clumps, ensuring that it swells rapidly and uniformly when preparing the precursor sol, and the non-polar groups and the foaming agent tail chains are intertwined by van der Waals forces, constructing an ultra-elastic composite film resistance network with both rigidity and flexibility.

[0007] More preferably, the nano-interface armor component is selected from at least one of surface-modified hydrophobic amphiphilic nano-silica and nano-alumina; wherein the original particle size of the amphiphilic nano-silica is 15 nm to 30 nm, and its surface is modified by at least one modifier selected from hexadecyltrimethoxysilane and octyltriethoxysilane, so that its gas-liquid-solid three-phase contact angle is close to 90 degrees. By precisely tailoring the contact angle of the nano-silica to close to 90 degrees, it is placed in the highest extreme energy state of thermodynamic desorption free energy. Once it touches the gas-liquid interface, half of it is wedged into the gas phase and half remains in the liquid phase. The adsorption is extremely strong and irreversible, forming a pure rigid solid particle barrier that prevents bubble coalescence.

[0008] Furthermore, the water-soluble polysaccharide excipient is maltodextrin with a DE value of 15 to 20. The DE value (glucose equivalent) is controlled between 15 and 20. If it is below 15, the water solubility and film-forming flexibility drop sharply. If it is above 20, its polyhydroxy structure exhibits extremely strong hygroscopicity, making it prone to sticking to the wall during spray drying. This range can form a dense and non-shrinking spherical skeleton instantly during spraying. The mesoporous silica fume has an amorphous silica mass content of more than 85%, an average primary particle size of 0.1 μm to 0.3 μm, and a microaggregate specific surface area of ​​more than 15 m² / g. The ultra-high specific surface area and rich internal mesoporous structure can generate strong capillary suction force, strongly adsorbing and pulling free microcapsules during the dry mixing stage, and providing an extremely high concentration of soluble silicate oligomer network during the hydration stage.

[0009] Preferably, the mineralization nucleation promoter is selected from at least one of nano-calcium carbonate and calcium formate, and must include nano-calcium carbonate; the original particle size of the nano-calcium carbonate is 40 nm to 80 nm, and it is cubic light precipitated calcium carbonate with a surface activated by stearic acid. The stearic acid activated nano-calcium carbonate can play the role of a high surface energy crystallization nucleus in the micro-region, and its lattice parameters are extremely well matched with the newly formed calcium silicate hydrate. Through the epitaxial growth effect, the thermodynamic precipitation barrier of this micro-region is lowered to the extreme, which promotes the rapid pozzolanic chemical reaction between free calcium ions and activated silicate ions on its surface.

[0010] According to another embodiment of the present invention, the powdered foaming agent is in the form of free-flowing microspheres with an average particle size concentrated between 50 μm and 150 μm, and the residual moisture content of the finished product is less than or equal to 2.5%. This microstructure eliminates electrostatic and capillary adhesion between materials, ensuring the uniformity of dispersion when the material is directly premixed into any special dry-mixed mortar system, and giving it a shelf life of more than two years in extreme climates.

[0011] According to another preferred embodiment of the present invention, the preparation process of the powder foaming agent includes: Step 1, high-shear homogenization of the precursor liquid phase: First, under low temperature conditions, the foaming component and the foam-stabilizing component are added to deionized water and stirred under high shear until completely swollen and dissolved. Then, the temperature is raised, the water-soluble polysaccharide excipient is added and stirred to dissolve. Subsequently, the nano-interface armor component is pre-dispersed in anhydrous ethanol and then added, and ultrasonic cavitation dispersion treatment is performed to obtain Pickering foam-stabilizing precursor colloidal sol. Step 2, microcapsule spray drying granulation: The colloidal sol obtained in Step 1 is pumped into a high-temperature co-current spray drying tower for centrifugal atomization. During the instantaneous explosive evaporation of water, the water-soluble polysaccharide excipient shrinks and concentrates to the surface to form a film, forming microcapsule dry powder that encapsulates the core foaming and foam-stabilizing components.

[0012] More preferably, prior to step one, the low-viscosity hydroxypropyl methylcellulose in the foam-stabilizing component is pretreated with glyoxal micro-crosslinking: HPMC powder is suspended in a high-speed fluidized bed, and a 1.5% to 2.5% glyoxal aqueous solution (0.8% to 1.2% of the dry weight of HPMC) is uniformly sprayed onto the particle surface using an atomizing nozzle. Subsequently, the mixture is fluidized and dried at 45°C to 55°C for 30 minutes, allowing the polyhydroxyl groups on the HPMC particle surface to undergo a hemiacetal crosslinking reaction with the dialdehyde groups of glyoxal, forming an extremely thin micro-crosslinked surface shell. This effectively prevents the "fish-eye" clumping phenomenon caused by rapid surface swelling of the HPMC powder during the aqueous dissolution process in step one, ensuring rapid and uniform swelling of the polymer. It should be noted that the hemiacetal bond formed between glyoxal and the polyhydroxyl groups on the HPMC surface is a thermodynamically reversible weak covalent crosslinking. In a cold water environment, water molecules gradually penetrate the extremely thin cross-linked shell (cross-linking depth is only about 5 μm to 10 μm) through osmosis. The hemiacetal bonds are hydrolyzed and broken with the participation of water, and the HPMC particles release molecular chain segments layer by layer from the outside to the inside. This process avoids the formation of a gel barrier ("fish-eye phenomenon") by rapid swelling of the surface, and ensures that the particles can be completely dissolved within the time scale of the process operation (about 15 to 20 minutes of high-shear stirring). In step one, the foaming component and the foam-stabilizing component treated with glyoxal micro-crosslinking are first added to deionized water at a low temperature of 20°C to 35°C and stirred under high shear until completely swollen and dissolved. This is because HPMC has typical lower critical temperature (LCST) characteristics, and its solubility is highest and its molecular chains are most fully extended in cold water. Therefore, the dissolution of the foaming component and the foam-stabilizing component must be completed within this low temperature range. After the HPMC is fully dissolved, the system is heated to 55°C to 62°C, and the water-soluble polysaccharide excipient is added and stirred to dissolve. The purpose of this heating is to accelerate the dissolution of maltodextrin and reduce the viscosity of the system to facilitate subsequent spray feeding. Fully dissolved HPMC exhibits sufficient kinetic stability in complex systems containing surfactant micelles, and does not undergo macroscopic phase separation within the temperature range of 55°C to 62°C and the operating timescale. However, this temperature must be strictly below the thermal gel transition temperature of HPMC (approximately 65°C to 70°C). If the temperature exceeds 62°C, HPMC will face the risk of dehydration and aggregation of methyl hydrophobic groups and flocculation and precipitation of polymers from the solution, leading to a deterioration in the homogeneity of the system. The nano-interface armor component pre-dispersed in anhydrous ethanol is then added for ultrasonic cavitation dispersion. The mass of deionized water added is 2.5 to 3.5 times the total solid content of the aqueous phase in the formulation, and the mechanical shearing speed is 1500 rpm to 2000 rpm. The 20 kHz ultrasonic cavitation microjets can completely break down the soft aggregates of nanoparticles, forcing them to be monodispersed in polymer micelles.In step two, the inlet air temperature of the spray drying tower is set to 150°C to 170°C, the exhaust outlet temperature is precisely kept constant at 65°C to 75°C, and the centrifugal atomizing disc rotation speed is 15,000 rpm to 18,000 rpm. The exhaust outlet temperature must be strictly controlled within a very narrow safety window of 65°C to 75°C. If this range is exceeded, the internal material temperature of the droplets may approach or even exceed the thermogel transition temperature of hydroxypropyl methylcellulose during the intermediate stage of evaporation when the droplets still contain a lot of moisture. This will cause the chain segments to undergo local dehydration shrinkage and microphase separation in a semi-dry state, affecting the dispersion uniformity of the foaming and foam-stabilizing components inside the microcapsules and reducing the foaming efficiency after reconstitution. If the temperature is below 65°C, the droplets will not evaporate thoroughly, causing the microspheres to collapse and stick to the wall.

[0013] Furthermore, the preparation process also includes step three, high-shear dry mixing and isolation of bulk active carriers: the microcapsule dry powder obtained in step two is collected, cooled to below 40°C, and then fed together with the pre-dried mesoporous silica fume and the mineralization nucleation promoter into a gravity-free biaxial paddle mixer. The main shaft is started to tumble and the flying blades are turned on to perform high-frequency shear mixing at a speed of 2000 rpm to 3000 rpm for 15 to 25 minutes, so that the mesoporous silica fume physically coats and isolates the microcapsule dry powder. After filtration and sieving, the powder foaming agent is obtained. Cooling to below 40°C avoids the polymer softening and adhesion caused by residual heat; the high-frequency shear mixing at 2000 rpm to 3000 rpm uses strong impact and extrusion force to force the extremely fine hydrophilic silica fume particles to form a dense secondary physical isolation layer on the outside, completely cutting off the channels for water molecules to penetrate inward, giving the final product excellent moisture-proof and anti-caking properties.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The foaming agent system of this invention overcomes the thermodynamic instability defects of traditional pure organic foaming agents in harsh cement environments. By constructing a multidimensional liquid film structure of "flexible polymer hydration network + rigid nanoparticle armor," the strong Pickering effect generated by the amphiphilic modified nanoparticles at the gas-liquid interface provides enormous macroscopic steric hindrance, increasing the surface viscosity of the liquid film by several orders of magnitude. This fundamentally inhibits the mechanical rupture of the liquid film and the gas diffusion curing driven by the Laplace pressure difference in high-density cement paste, resulting in a near-zero foam water separation rate and extremely uniform micropore size and a very high closed-cell rate after curing.

[0016] This invention achieves multiphase micro-region chemical activation and in-situ directional mineralization enhancement of bubble-liquid films. The system's abundant active mesoporous silica fume carrier and nano-nucleating seeds are chemically activated in the strongly alkaline environment of early cement hydration, spontaneously epitaxially growing a dense, high-silica-to-calcium-silicate hydrate (CSH) gel shell and ettringite crystal clusters at the most vulnerable pore wall gas-liquid interface. This mineralization mechanism irreversibly solidifies the fragile, flexible organic film into a high-rigidity inorganic ceramic framework, blocking the propagation of stress microcracks, resulting in a doubling of the ultimate compressive strength of ultra-lightweight foamed concrete (e.g., with a dry apparent density of 600 kg / m³).

[0017] This invention's pioneering multi-stage microencapsulation granulation technology overcomes the industrialization barrier of liquid foaming agents' inability to be incorporated into dry powder systems. Utilizing water-soluble polysaccharide excipients as the primary spray film-forming wall material, combined with high-shear secondary physical isolation from bulk mesoporous silica fume, a high-viscosity, multi-component, poorly compatible water-based foaming system is successfully transformed into a free-flowing microsphere dry powder with excellent desiccant resistance. This significantly extends the product's shelf life, reduces logistics costs, and allows for the instantaneous release of active ingredients in cold water. It also possesses excellent compatibility for direct premixing into various specialty dry-mix mortars and 3D printing dry powder materials. Detailed Implementation

[0018] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are for explanation and illustration only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, the reagents, materials, and instruments used in the following embodiments are all commercially available.

[0019] The core technology of the high-stability foamed concrete powder foaming agent of this invention lies in the following: by encapsulating multiple functional components with specific interfacial activity in an active powder carrier in a multi-stage core-shell microcapsule physical configuration, three independent bubble stabilization mechanisms are triggered sequentially upon resolubilization in water. The first mechanism is the viscoelastic enhancement of the continuous liquid film phase by the swollen polymer hydration network. The second mechanism is the irreversible Pickering adsorption armor of amphiphilic nanoparticles at the gas-liquid interface. The third mechanism is the in-situ formation of a volcanic ash mineralization shell under the alkaline environment of cement hydration. These three mechanisms progress sequentially on the time scale and are superimposed layer by layer from the inside out on the spatial scale, together irreversibly transforming the thermodynamically unstable organic bubble liquid film into a rigid inorganic ceramic microporous shell.

[0020] The preparation method of the powder foaming agent of this invention is generally divided into three stages. The first stage is the high-shear homogenization of the precursor liquid phase. First, under the low-temperature water bath conditions of 20°C to 35°C, the foaming component sodium α-olefin sulfonate (AOS) and the auxiliary surfactant are added to deionized water and completely dissolved under mechanical high-shear stirring to form a transparent micelle solution. Subsequently, within the same low-temperature range, the foam-stabilizing component, namely low-viscosity hydroxypropyl methylcellulose (HPMC) treated with glyoxal micro-crosslinking and the auxiliary polymeric foam stabilizer, is added, and stirring continues until the polymeric chain segments are fully swollen and stretched, and the system presents a uniform, transparent, viscous liquid state. Since HPMC has the characteristic of lower critical temperature of dissolution (LCST), its solubility is the highest and its molecular chains are most fully stretched in cold water. Therefore, the dissolution of the foaming component and the foam-stabilizing component must be completed in the low-temperature stage. After HPMC is fully dissolved, the system is slowly heated to 55°C to 62°C. Water-soluble polysaccharide excipient maltodextrin is added and stirred until dissolved. This heating aims to accelerate the dissolution of maltodextrin and reduce the system viscosity to facilitate subsequent spray feeding. The dissolved HPMC exhibits sufficient kinetic stability in complex systems containing surfactant micelles, and no macroscopic phase separation occurs within this temperature range and operating timescale. Finally, while continuously stirring, a nano-interface armor component pre-dispersed in a small amount of anhydrous ethanol is added—namely, surface-hydrophobically modified amphiphilic nano-silica. An ultrasonic probe is immediately activated for cavitation dispersion. The surface contact angle of the nano-interface armor component, after hydrophobic modification, is close to 90 degrees. If directly added to the aqueous phase, it will float and agglomerate due to its strong hydrophobicity. Therefore, it needs to be pre-wetted and dispersed with a small amount of anhydrous ethanol to achieve compatibility transition and ensure effective introduction into the aqueous system. At an ultrasonic frequency of 20 kHz, the transient microjets generated by the collapse of cavitation microbubbles (with instantaneous local temperatures reaching thousands of degrees and pressures reaching hundreds of atmospheres) effectively disperse the soft aggregates of nanoparticles formed by van der Waals forces, forcing them to disperse as primary particles in a continuous aqueous phase containing polymeric micelles, forming a Pickering-stabilized bubble precursor colloidal sol. This sol does not stratify under static conditions, and its absolute Zeta potential is greater than 35 mV, indicating good colloidal stability. Temperature control is crucial at this stage: the foaming and stabilizing components must dissolve within a low-temperature range of 20°C to 35°C to fully utilize the optimal solubility of HPMC at low temperatures; subsequently, the temperature is raised to 55°C to 62°C to dissolve maltodextrin. This temperature range is lower than the thermal gelation temperature of HPMC (approximately 65°C to 70°C), ensuring that the dissolved HPMC molecular chains do not undergo irreversible thermal phase separation (dehydration and aggregation of methyl hydrophobic groups leading to flocculation and precipitation). When the formulation contains sodium fatty alcohol polyoxyethylene ether sulfate (AES), this temperature range also helps to prevent the polyoxyethylene ether segments from becoming turbid due to excessively high temperatures.

[0021] The second stage involves microencapsulation spray drying granulation. The colloidal sol obtained in the first stage is transported at a constant flow rate by a peristaltic pump to the centrifugal atomizing disc of a high-temperature co-current spray drying tower. The atomizing disc rotates at a high speed of 15,000 to 18,000 rpm, shearing and breaking the sol into fine droplets with an average diameter of approximately 20 to 50 μm. In co-current contact with hot air at 150°C to 170°C, the droplets experience explosive evaporation of moisture from their surface at an extremely high rate. During this process, the dissolved maltodextrin (DE value 15 to 20) reaches a supersaturated concentration on the droplet surface due to rapid moisture loss. Its polyhydroxy short-chain starch molecules rapidly form a dense, glassy thin film shell, physically locking and encapsulating the still concentrated foaming components, foam-stabilizing polymer segments, and dispersed nano-armor particles within this shell framework. The exhaust outlet temperature is precisely controlled within an extremely narrow window of 65℃ to 75℃. This temperature determines the actual material temperature of the droplets during the evaporation process. If the exhaust temperature is higher than 75℃, the internal material temperature of the droplets may approach or even exceed the thermogel transition temperature of HPMC during the intermediate stage of evaporation when the droplets still contain a significant amount of moisture. This causes localized dehydration and shrinkage of HPMC segments and microphase separation in a semi-dry state, affecting the uniformity of dispersion of the foaming and stabilizing components within the microcapsules, thereby reducing the foaming efficiency and foam stabilization performance after product reconstitution. If the exhaust temperature is lower than 65℃, insufficient evaporation of moisture within the droplets leads to microsphere collapse and adhesion to the walls, resulting in excessive product moisture content and severe particle deformation. The collected microcapsule powder consists of milky white to slightly yellow spherical particles, with particle sizes mainly distributed in the range of 20μm to 80μm.

[0022] The third stage involves high-shear dry mixing and isolation of the bulk active carrier. Microcapsule powder cooled to below 40°C is fed into a gravity-free biaxial paddle mixer along with mesoporous silica fume pre-dried at 105°C for 2 hours and mineralization nucleation promoters (nano-calcium carbonate and calcium formate). While the main shaft is started at a low speed (approximately 50 to 80 rpm) for large-scale tumbling and convection mixing, the blades are activated at a high speed of 2000 to 3000 rpm for high-frequency shearing. During this process, extremely fine mesoporous silica fume micro-aggregates (primary particle size 0.1 μm to 0.3 μm) are forcibly embedded into the outer surface of the microcapsule spheres under the action of high-speed collision and extrusion force. They are firmly anchored by electrostatic adsorption and capillary cohesion generated by their large specific surface area (greater than 15 m² / g), forming a dense inorganic physical isolation coating layer. Simultaneously, nano-calcium carbonate and calcium formate particles are also uniformly dispersed and embedded in this isolation layer. The process lasts 15 to 25 minutes, followed by filtration through an 80-mesh vibrating sieve to remove a small amount of oversized agglomerates, yielding the final product. The finished powdered foaming agent is in the form of grayish-white, free-flowing microspheres with an average particle size concentrated between 50 μm and 150 μm (the particle size is slightly larger than that of the second-stage microcapsules due to the outer silica fume isolation layer). The residual moisture content is less than or equal to 2.5%, the angle of repose is less than 40°, and it has excellent flowability. It can be directly premixed into various special dry-mixed mortars or 3D printing dry powder material systems in dry powder form.

[0023] When this powdered foaming agent is mixed with cement-based slurry at the construction site, the release of its functional components and the foam-stabilizing mechanism unfold in the following time sequence: First, the outer layer of hydrophilic mesoporous silica fume is rapidly wetted within seconds of contact with the mixing water, and the capillary suction effect quickly guides the water to the surface of the microcapsule core; then, the maltodextrin glassy shell swells and disintegrates upon contact with water, completely releasing the encapsulated foaming component AOS, foam-stabilizing component HPMC, and nano-armor particles into the aqueous phase within approximately 10 to 30 seconds. AOS molecules diffuse and adsorb to the newly formed gas-liquid interface at an extremely fast rate, rapidly reducing the dynamic surface tension of water from approximately 72 mN / m to 28 mN / m to 32 mN / m. Under the mechanical shear energy input of high-speed stirring, a large amount of gas is drawn in, producing a dense and delicate foam system. Within almost the same timescale, the swollen HPMC molecular chains fully extend in the liquid film continuous phase. Their nonpolar methyl and hydroxypropyl side chains undergo van der Waals hydrophobic association with the hydrocarbon tail chains of AOS, forming a three-dimensional hydrated polymer network of intermolecular chain entanglement. This network increases the surface shear viscosity of the liquid film continuous phase by two to three orders of magnitude, effectively delaying the gravity-driven liquid film drainage process. Within a time window of approximately 30 seconds to 2 minutes after the formation of this network, the nano-armor component (i.e., amphiphilic modified nano-silica, with a three-phase contact angle of approximately 85° to 95°) is pushed to the gas-liquid interface and undergoes irreversible Pickering adsorption as the liquid film continues to thin. Because the contact angle is close to 90°, each nanoparticle is embedded in the interface with its equatorial plane, half exposed to the gas phase and half immersed in the liquid phase. In this state, the desorption free energy of a single particle, ΔGdes = πr²γow(1-|cosθ|)², can reach the order of several thousand kBT (where r is the particle radius, γow is the gas-liquid interfacial tension, and θ is the contact angle), far exceeding the thermal fluctuation energy, which means that once adsorption occurs, it is irreversible. The two-dimensional solid particle armor layer formed by the close self-assembly of massive nanoparticles at the interface has a macroscopically measurable two-dimensional elastic modulus (approximately tens to hundreds of mN / m), generating a huge steric hindrance effect. This physically eliminates the thermodynamic driving force of gas transmembrane diffusion (i.e., Oswald curing) driven by the Laplace pressure difference (ΔP = 2γ / R, with higher pressure in small bubbles and lower pressure in large bubbles) between adjacent bubbles. At the same time, it endows the liquid film with extremely high mechanical yield strength to resist the impact of solid particles in cement paste.

[0024] It should be noted that the system of this invention contains both anionic surfactants and hydrophobically modified nanoparticles, which compete for adsorption at the gas-liquid interface. In the initial stage of bubble formation, small molecule surfactants such as AOS, with their diffusion coefficients much higher than those of the nanoparticles, are the first to adsorb onto the nascent gas-liquid interface and reduce surface tension, a necessary condition for efficient gas entrainment. As the liquid film thins, the nanoparticles are transported to the interfacial region under the drive of capillary pressure and convection within the liquid film, and achieve interfacial anchoring by partially replacing the adsorbed surfactant molecules through their covalently grafted hydrophobic alkyl segments. Although surfactant molecules may undergo physical adsorption at the exposed hydrophilic sites of the nanoparticles through van der Waals forces, causing the effective three-phase contact angle of the particles to shift slightly from its intrinsic value (approximately 87°±3°), the covalently Si-O-Si bonded hexadecyl segments (carbon content 3.5% to 5.0%) are not replaced by the physically adsorbed surfactant molecules, and the particles retain sufficient amphiphilicity to maintain the irreversibility of interfacial adsorption. This invention controls the foaming component dosage within a preferred range of 5.0% to 8.0% (corresponding to an effective concentration in the working solution near the critical micelle concentration) precisely to ensure sufficient gas entrainment while minimizing the interference of surfactants on the interfacial behavior of nanoparticles to an acceptable level. Furthermore, in the precursor sol preparation stage (step one), after the nanoparticles are pre-dispersed in anhydrous ethanol, an aqueous phase is added. Ethanol, as an intermediate solvent, forms a transitional solvation layer on the nanoparticle surface, which can buffer the immediate coating effect of surfactant micelles on the nanoparticle surface to a certain extent. Subsequently, during spray drying, water and ethanol are simultaneously evaporated and removed. The foaming component, foam-stabilizing component, and nanoparticles are all encapsulated in a solid state within the maltodextrin framework. At this point, the molecular motion between the components is frozen, and there are no conditions for surfactant migration and adsorption to the particle surface. When the microcapsules are re-dissolved to generate fresh bubbles, each component is simultaneously released onto a large number of newly formed interfaces instantaneously. The surfactants and nanoparticles function dynamically in competition, rather than antagonizing each other under static equilibrium conditions.

[0025] During the initial hydration stage of cement, approximately 5 minutes to several hours after the foam is uniformly incorporated into the cement paste, the third foam-stabilizing mechanism, namely the in-situ mineralization mechanism, is chemically activated. (The text abruptly shifts to a seemingly unrelated topic about tricalcium silicate in cement.) ) and dicalcium silicate ( During hydration, a large amount of [something] is released. This causes the pH of the pore fluid to rapidly rise to 12.5 to 13.5. Under this strongly alkaline environment, the Si-O-Si network structure of amorphous silica in the mesoporous silica fume enriched in the micro-regions at the outer interface of the bubbles is subjected to [a stress / damage]. The nucleophilic attack of ions causes depolymerization and releases a high concentration of active silicate monomers. And its oligomers. These active silicate groups diffuse and migrate towards the interfacial microregions driven by the concentration gradient, and interact with the high concentration of free silicates in the pore fluid. Ions meet. Simultaneously, within approximately 3 to 10 minutes after hydration begins, the pH of the pore liquid rises above 12.5. The mineralization nucleation promoter pre-embedded in the interfacial microregions, namely the stearic acid-activated nano-calcium carbonate, undergoes a rapid saponification reaction in the strongly alkaline pore liquid due to its stearic acid coating layer (coating amount only about 2.0% to 3.0%, at the monolayer level). The removal of the calcite crystals exposes the high surface energy calcite crystal faces, which then act as a crucial heterogeneous nucleation catalyst. The cubic calcite crystal faces of nano-calcium carbonate provide a lattice epitaxial template that is highly compatible with the CSH gel precursor. Through the epitaxial orientation epitaxial effect, the extremely high supersaturation barrier required for homogeneous CSH nucleation is significantly reduced, enabling… With extremely low thermodynamic driving force, active silicate groups can rapidly undergo pozzolanic condensation reaction on the surface of nano-calcium carbonate: (Low calcium-to-silicon ratio CSH gel with a calcium-to-silicon ratio of approximately 0.8 to 1.2). Simultaneously, the dissociation of calcium formate under alkaline conditions in the system provides additional... It supplements and reacts with aluminate and sulfate ions in the pore fluid to form needle-shaped ettringite ( The newly formed CSH gel and ettringite crystal clusters grow densely and intertwine in the micro-regions of the bubble interface, gradually forming a dense inorganic mineralized shell with a thickness of about 0.5 μm to 2 μm. This irreversibly solidifies the originally flexible organic polymer-nanoparticle composite liquid film into a mineral microporous shell with ceramic-level hardness and rigidity, fundamentally eliminating any possibility of foam breakage or merging during the entire cement hardening process.

[0026] The following details the sources, specifications, and necessary pretreatment methods of the key raw materials used in this invention.

[0027] Foaming component sodium α-olefin sulfonate (AOS, The active ingredient content is ≥92%, and the product used is an industrial-grade product (brand name AOS-K) produced by Jiangsu Liwang Daily Chemical Co., Ltd.; the auxiliary foaming component, sodium dodecyl sulfate (SDS), is analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd.; the auxiliary foaming component, sodium fatty alcohol polyoxyethylene ether sulfate (AES), has an active ingredient content of ≥70% and is an industrial-grade product from Shanghai Fine Chemical Co., Ltd.

[0028] The foam stabilizing component, hydroxypropyl methylcellulose (HPMC), is a low-viscosity product (brand name MH4000, 2% aqueous solution viscosity approximately 4000 mPa·s) produced by Shandong Heda Group Co., Ltd. Before use, it needs to undergo glyoxal micro-crosslinking surface treatment: HPMC powder is suspended in a high-speed fluidized bed, and a 2.0% glyoxal aqueous solution (glyoxal dosage is 0.8% to 1.2% of the dry weight of HPMC) is uniformly sprayed onto the surface of the particles using an atomizing nozzle, followed by fluidized drying at 50°C for 30 minutes. This treatment induces a hemiacetal crosslinking reaction between the polyhydroxyl groups on the surface of HPMC particles and the dialdehyde groups of glyoxal, forming an extremely thin micro-crosslinked surface shell (crosslinking depth approximately 5 μm to 10 μm). This shell, in a dry state, inhibits the rapid swelling of the particle surface upon contact with water, preventing the formation of a high-viscosity gel layer (i.e., the "fisheye" phenomenon). This allows the particles to rapidly disperse into single particles in the cold water system of step one and dissolve layer by layer from the inside out, achieving rapid and uniform swelling. This ensures the full extension and uniform spatial distribution of HPMC molecular chains in the precursor sol. The hemiacetal crosslinking is a thermodynamically reversible weak covalent bond, which can be completely hydrolyzed and broken within 15 to 20 minutes under high-shear stirring conditions in cold water, without the need for additional alkali to promote dissolution. It is worth noting that the foaming components, such as sodium α-olefin sulfonate (AOS), provide a weakly alkaline environment (pH 8 to 10) after dissolution. This weakly alkaline environment effectively catalyzes the rapid hydrolysis of hemiacetal bonds on the HPMC surface, thereby achieving efficient and complete swelling of HPMC in cold water within 15 to 20 minutes. The inherent weak alkalinity of each foaming component also functions as a de-crosslinking catalyst, forming an additional synergistic effect with the foam stabilizing components. The auxiliary foam stabilizing component, polyvinyl alcohol (PVA), is a product of Anhui Wanwei High-Tech Materials Co., Ltd. (brand name PVA1788, degree of alcoholysis 87% to 89%, degree of polymerization approximately 1700 to 1800).

[0029] Amphiphilic nano-silica, a component of the nano-interface armor, was prepared by hydrophobic modification of fumed silica as a raw material: Evonik Degussa AEROSIL® 200 hydrophilic fumed silica (native particle size approximately 12 nm, BET specific surface area approximately 200 m² / g) was dispersed in anhydrous toluene, and hexadecyltrimethoxysilane (HDTMS, purchased from Nanjing Shuguang Fine Chemical Co., Ltd.) was added. The amount of silane was 8% to 12% of the mass of the nano-silica. The reaction was carried out under nitrogen protection and refluxed at 110°C for 6 hours. After the reaction was completed, the mixture was filtered, washed three times with anhydrous ethanol to remove unreacted monomers and the byproduct methanol, and then vacuum dried at 80°C for 12 hours. The resulting product was then pulverized through a 200-mesh sieve to obtain the hydrophobically modified amphiphilic nano-silica. The modified product, measured by the Wilhelmy plate method, showed a water contact angle of 87°±3° and a carbon content (elemental analysis) of approximately 3.5% to 5.0%, indicating that the hexadecyl carbon chain was successfully anchored to the nanoparticle surface via covalent Si-O-Si bonds. Its original particle size increased slightly to approximately 15 nm to 30 nm due to minor agglomeration during the modification process. The auxiliary nano-armor component, nano-alumina, was prepared by calcining Sasol Disperal® P2 pseudoboehmite at 400°C for 2 hours. The nanoparticles (average particle size of about 20 nm to 40 nm, BET specific surface area of ​​about 180 m² / g) were hydrophobically modified by hydrolysis and condensation treatment with octyltriethoxysilane in a mixed solvent of ethanol / water (volume ratio 9:1) at room temperature for 4 hours before use, so that the surface was grafted with octylalkyl segments of medium carbon chain length, and the water contact angle was about 75° to 85°.

[0030] The water-soluble polysaccharide excipient, maltodextrin, is a food-grade product from Shandong Xiwang Sugar Industry Co., Ltd., with a DE value (glucose equivalent) of 15 to 20, a moisture content of ≤5.0%, and a solubility (in water at 25℃) greater than 50 g / 100 mL.

[0031] Mesoporous silica fume, using high-quality densified silica fume product (grade SF-96) from Sichuan Xinminhui Mining Co., Ltd. The content is ≥96% (far exceeding the 85% lower limit required by this invention), the average primary particle size is about 0.15 μm, the BET specific surface area is about 20 m² / g to 25 m² / g, and the bulk density is about 550 kg / m³ to 650 kg / m³. Before use, it is pre-dried in a 105℃ forced-air oven for 2 hours to reduce the residual moisture to below 1.0%, preventing the introduction of additional moisture during the dry mixing stage, which would cause the microcapsule shell to dissolve prematurely and fail.

[0032] The mineralization nucleation promoter, nano-calcium carbonate, is a product of Shanxi Lanhua Nanomaterials Co., Ltd. (brand name LH-T). It is a cubic crystal form (calcite phase) light precipitated calcium carbonate with a primary particle size of approximately 40 nm to 80 nm and a BET specific surface area of ​​approximately 25 m² / g to 35 m² / g. It has been pre-activated by the factory with stearic acid (stearic acid coating amount of approximately 2.0% to 3.0%), with an activation degree ≥95%. The auxiliary mineralization promoter, calcium formate, is of industrial purity (content ≥98%) and was purchased from Shandong Huachen New Materials Co., Ltd., with a particle size exceeding 100 mesh.

[0033] The main testing equipment and instruments used in the following examples include: TD-1 foam stability analyzer (for determining foaming ratio and foam water separation rate), high-speed dispersion mixer (planetary mixer equipped with different blades for slurry preparation and foaming), NETZSCH-2020 spray drying tower, WMH-200 zero-gravity biaxial blade mixer, SEM scanning electron microscope (ZEISS Sigma 300, for microscopic morphology observation), X-ray diffractometer (Bruker D8 Advance, for phase analysis of mineralized products), and universal testing machine (MTS Exceed E45.105, for compressive strength testing).

[0034] The following are the standard methods and specific test conditions upon which the performance testing of this invention is based.

[0035] (a) Foaming ratio and foam water separation rate test. The determination was conducted according to Appendix A of JC / T 2199-2013 "Foaming Agents for Foamed Concrete". The powdered foaming agent was dissolved in deionized water at 20℃ at a dosage of 3.0% of the dry powder mass, stirred for 30 seconds to ensure complete dissolution, and then foamed for 3 minutes at 1200 rpm using a high-speed disperser. The foaming ratio (the ratio of the volume after foaming to the volume of the liquid before foaming) was determined using the graduated cylinder method. 1000 mL of foam was placed in a graduated conical graduated cylinder, allowed to stand for 1 hour, and the volume of the liquid separated at the bottom was read. The water separation rate after 1 hour was calculated as (separated liquid volume / original foam liquid phase volume × 100%). Simultaneously, the ratio of the residual height of the foam column after 1 hour to the initial height was recorded, i.e., the foam volume retention rate after 1 hour.

[0036] (b) Preparation and curing of foamed concrete specimens. Refer to the relevant provisions of JG / T 266-2011 "Foamed Concrete". Using P·O 42.5 ordinary Portland cement (Conch brand) as the cementitious material, with a water-cement ratio of 0.50 (referring to the net water-cement ratio, excluding water introduced by silica fume in the foaming agent), the powdered foaming agent was directly added to the dry cement powder for premixing. After adding water, the mixture was stirred at low speed (approximately 140 rpm) for 1 minute with a planetary mixer to ensure uniformity. Then, the mixture was switched to high speed (approximately 285 rpm) for 3 minutes for mechanical foaming. The target dry apparent density was controlled by adjusting the foaming agent dosage. The foamed slurry was poured into a standard 100mm × 100mm × 100mm triple mold, the surface was smoothed, and covered with plastic film. After curing in a standard curing room at 20℃±2℃ and relative humidity ≥95% for 24 hours, the specimens were demolded and continued to be cured according to standard for 28 days.

[0037] (c) 28-day compressive strength test. The compressive strength test method was performed according to GB / T 11969-2020 "Test Methods for Performance of Autoclaved Aerated Concrete". Specimens cured to 28 days were dried to constant weight in an oven at 105℃±5℃, removed, and cooled to room temperature. The ultimate compressive strength was then tested using an MTS universal testing machine at a loading rate of 0.5 kN / s. At least six specimens were tested in each group, and the arithmetic mean was taken after removing the maximum and minimum values.

[0038] (d) Determination of apparent dry density. Refer to JG / T 266-2011. After drying the 28-day-old specimens at 105℃±5℃ to constant weight, measure the geometric dimensions with vernier calipers and weigh the dried mass, and calculate the apparent dry density.

[0039] (e) Closed-cell ratio test. The true volume of the skeleton of the specimen was determined using a Quantachrome Ultrapyc 5000 gas displacement true density analyzer (using helium as the working gas) according to ASTM D6226-2021 standard. The closed-cell ratio (the percentage of closed-cell volume to total pore volume) was then calculated by combining the known geometric appearance volume and dry apparent density.

[0040] (f) Average pore diameter and pore diameter uniformity coefficient. After cutting and polishing the 28-day-old specimens, cross-sectional images (approximately 5 mm × 5 mm per field of view) were acquired using a ZEISS Sigma 300 scanning electron microscope in backscatter mode. The equivalent circular diameter of each pore was statistically analyzed using ImageJ image analysis software. The average pore diameter was calculated as the area-weighted average diameter of all pores. The pore diameter uniformity coefficient was defined as: ,in This represents the aperture corresponding to 60% of the area cumulative frequency. The U value represents the aperture corresponding to the 10% cumulative area frequency. The closer the U value is to 1, the more uniform the aperture distribution.

[0041] Example 1

[0042] The formulation of this embodiment is located near the center of the preferred scope of the claims and represents the optimal implementation of the present invention. Based on a total mass of 100% for the powder foaming agent, the components and their mass percentage content are as follows: foaming component 6.5% (including 5.0% sodium α-olefin sulfonate and 1.5% sodium dodecyl sulfate), foam stabilizing component 3.0% (including 2.5% low-viscosity HPMC treated with glyoxal micro-crosslinking and 0.5% polyvinyl alcohol), nano-interface armor component 4.0% (4.0% amphiphilic nano-silica), water-soluble polysaccharide excipient (maltodextrin, DE value 18) 11.0%, mesoporous silica fume 69.5%, and mineralization nucleation promoter 6.0% (including 4.5% nano-calcium carbonate and 1.5% calcium formate).

[0043] The preparation process is as follows. Step 1: Add approximately 723 g of deionized water (approximately 2.95 times the total solid content of the aqueous phase of the formulation, which is 245.0 g) to a 5 L stainless steel reactor, and turn on the constant temperature water bath to control the temperature at 25℃. First, add 50.0 g of sodium α-olefin sulfonate and 15.0 g of sodium dodecyl sulfate, and stir at 1800 rpm for 10 minutes until completely dissolved; then, at the same temperature, add 25.0 g of HPMC treated with glyoxal micro-crosslinking and 5.0 g of polyvinyl alcohol, and continue stirring for 20 minutes until the polymers are fully swollen and the system is a transparent viscous liquid; then, slowly raise the temperature to 60℃, add 110.0 g of maltodextrin, and stir for 10 minutes until completely dissolved; finally, add 40.0 g of amphiphilic nano-silica pre-dispersed in 50 mL of anhydrous ethanol, and turn on the ultrasonic probe (20 kHz, 600 W power) for cavitation dispersion for 15 minutes. Pickering stable foam precursor colloidal sol was obtained. It was a uniform milky white semi-transparent sol with no obvious precipitation or stratification.

[0044] Step 2: The colloidal sol obtained in Step 1 is pumped into a NETZSCH-2020 spray drying tower at a flow rate of approximately 3.5 L / h using a peristaltic pump. The inlet air temperature is set to 160℃, and the outlet air temperature is precisely controlled at 70℃±2℃ (achieved by adjusting the feed flow rate). The centrifugal atomizing disc rotates at 16000 rpm. The microcapsule dry powder collected from the bottom outlet of the cyclone separator is a milky white, fine spherical particle.

[0045] Step 3: After the microcapsule powder cools to room temperature, take 245.0 g of the microcapsule powder (i.e., the total dry weight of the foaming component, foam stabilizing component, nano-armor component, and maltodextrin mentioned above) and add it together with 695.0 g of pre-dried mesoporous silica fume, 45.0 g of nano-calcium carbonate, and 15.0 g of calcium formate into a WMH-200 zero-gravity twin-shaft paddle mixer. Start the main shaft tumbling and turn on the fly knife to perform high-frequency shearing and mixing at 2500 rpm for 20 minutes. After discharge, pass the mixture through an 80-mesh vibrating sieve to obtain the powdered foaming agent product of this embodiment. The finished product is a grayish-white free-flowing microsphere powder with an average particle size of approximately 85 μm (laser particle size analyzer), a residual moisture content of 1.8% (drying method at 105℃), and an angle of repose of 36°.

[0046] Preparation of foamed concrete: P·O 42.5 cement is used as the cementitious material, with a water-cement ratio of 0.50. The above-mentioned powdered foaming agent is premixed into the cement dry powder at a dosage of 6.0% of the cement mass (i.e., 6.0 g of foaming agent dry powder per 100 g of cement). After adding water, it is stirred and foamed according to the aforementioned standard method and then poured into molds. Standard curing is carried out for 28 days.

[0047] Example 2

[0048] The formulation of this embodiment is located in the lower limit of the broad scope of the claims. Based on the total mass of all components of the powder foaming agent as 100%: foaming component 3.5% (sodium α-olefin sulfonate 3.0%, sodium fatty alcohol polyoxyethylene ether sulfate 0.5%), foam stabilizing component 1.5% (low viscosity HPMC treated with glyoxal micro-crosslinking 1.2%, carboxymethyl starch ether 0.3%), nano-interface armor component 2.5% (amphiphilic nano-silica 2.5%), water-soluble polysaccharide excipient (maltodextrin, DE value 15) 8.5%, mesoporous silica fume 78.0%, and mineralization nucleation promoter 6.0% (nano-calcium carbonate 4.5%, calcium formate 1.5%).

[0049] Preparation process parameters: Step 1: First, add the foaming component and foam-stabilizing component to deionized water at 25℃ and stir under high shear until completely swollen and dissolved. Then, raise the temperature to 58℃ and add maltodextrin while stirring to dissolve. The amount of deionized water added is 3.5 times the total solid content of the aqueous phase. The mechanical shearing speed is 1500 rpm, and ultrasonic cavitation dispersion is performed for 20 minutes. Step 2: The inlet air temperature is 150℃, the exhaust air temperature is 65℃±2℃, and the centrifugal atomizing disc speed is 18000 rpm. Step 3: The flying knife speed is 2000 rpm, and the dry mixing time is 25 minutes. The residual moisture content of the finished product is 2.3%, the average particle size is approximately 110 μm, and the angle of repose is 38°. The preparation conditions for foamed concrete are the same as in Example 1.

[0050] Example 3

[0051] The formulation of this embodiment is located in the upper limit of the broad scope of the claims. Based on the total mass of all components of the powder foaming agent as 100%: foaming component 9.5% (sodium α-olefin sulfonate 7.0%, sodium dodecyl sulfate 2.5%), foam stabilizing component 4.5% (low-viscosity HPMC micro-crosslinked with glyoxal 3.5%, polyvinyl alcohol 1.0%), nano-interface armor component 7.5% (amphiphilic nano-silica 5.5%, surface-modified nano-alumina 2.0%), water-soluble polysaccharide excipient (maltodextrin, DE value 20) 14.0%, mesoporous silica fume 55.0%, and mineralization nucleation promoter 9.5% (nano-calcium carbonate 7.0%, calcium formate 2.5%).

[0052] Preparation process parameters: Step 1: First, add the foaming component and the foam-stabilizing component to deionized water at 25℃ and stir under high shear until completely swollen and dissolved. Then, raise the temperature to 62℃ and add maltodextrin while stirring to dissolve. The amount of deionized water added is 2.5 times the total solid content of the aqueous phase. The mechanical shearing speed is 2000 rpm, and ultrasonic cavitation dispersion is performed for 15 minutes. Step 2: The inlet air temperature is 170℃, the exhaust air temperature is 75℃±2℃, and the centrifugal atomizing disc speed is 15000 rpm. Step 3: The flying knife speed is 3000 rpm, and the dry mixing time is 15 minutes. The residual moisture content of the finished product is 1.5%, the average particle size is about 72 μm, and the angle of repose is 35°. The preparation conditions of the foamed concrete are the same as in Example 1.

[0053] Example 4

[0054] This embodiment aims to investigate the foam-stabilizing effect of the nano-interface armor component at a low dosage. Based on a total mass of 100% for the powdered foaming agent: foaming component 7.0% (sodium α-olefin sulfonate 5.5%, sodium dodecyl sulfate 1.5%), foam-stabilizing component 2.5% (low-viscosity HPMC micro-crosslinked with glyoxal 2.0%, polyvinyl alcohol 0.5%), nano-interface armor component 3.0% (amphiphilic nano-silica 3.0%), water-soluble polysaccharide excipient (maltodextrin, DE value 17) 11.5%, mesoporous silica fume 70.0%, and mineralization nucleation promoter 6.0% (nano-calcium carbonate 5.0%, calcium formate 1.0%).

[0055] Preparation process parameters: Step 1, firstly, add the foaming component and the foam-stabilizing component to deionized water at 25℃ and stir under high shear until completely swollen and dissolved. Then, raise the temperature to 60℃ and add maltodextrin while stirring to dissolve. The remaining process parameters are the same as in Example 1. The finished product has a residual moisture content of 1.9%, an average particle size of approximately 90 μm, and an angle of repose of 37°. The preparation conditions for foamed concrete are the same as in Example 1.

[0056] Example 5

[0057] This embodiment aims to investigate the mineralization enhancement effect of the mineralization nucleation promoter at a higher dosage. Based on the total mass of all components of the powdered foaming agent as 100%, the foaming component is 5.5% (sodium α-olefin sulfonate 4.5%, sodium fatty alcohol polyoxyethylene ether sulfate 1.0%), the foam-stabilizing component is 2.5% (low-viscosity HPMC treated with glyoxal micro-crosslinking 2.0%, carboxymethyl starch ether 0.5%), the nano-interface armor component is 4.5% (amphiphilic nano-silica 3.5%, surface-modified nano-alumina 1.0%), the water-soluble polysaccharide excipient (maltodextrin, DE value 18) is 10.5%, the mesoporous silica fume is 68.0%, and the mineralization nucleation promoter is 9.0% (nano-calcium carbonate 6.5%, calcium formate 2.5%).

[0058] Preparation process parameters: Step 1: First, add the foaming component and foam-stabilizing component to deionized water at 25℃ and stir under high shear until completely swollen and dissolved. Then, raise the temperature to 60℃ and add maltodextrin while stirring to dissolve. The amount of deionized water added is 3.0 times the total solid content of the aqueous phase. The mechanical shearing speed is 1800 rpm, and ultrasonic cavitation dispersion is performed for 18 minutes. Step 2: The inlet air temperature is 165℃, the exhaust air temperature is 72℃±2℃, and the centrifugal atomizing disc speed is 16500 rpm. Step 3: The flying knife speed is 2800 rpm, and the dry mixing time is 18 minutes. The residual moisture content of the finished product is 1.6%, the average particle size is about 80 μm, and the angle of repose is 36°. The preparation conditions of the foamed concrete are the same as in Example 1.

[0059] Example 6

[0060] This embodiment aims to verify the feasibility of a single foaming component system. Based on a total mass of 100% for all components of the powdered foaming agent: foaming component 8.0% (sodium α-olefin sulfonate only 8.0%), foam stabilizing component 3.5% (low-viscosity HPMC micro-crosslinked with glyoxal 3.0%, polyvinyl alcohol 0.5%), nano-interface armor component 5.0% (amphiphilic nano-silica 5.0%), water-soluble polysaccharide excipient (maltodextrin, DE value 16) 12.0%, mesoporous silica fume 65.0%, and mineralization nucleation promoter 6.5% (nano-calcium carbonate 5.0%, calcium formate 1.5%).

[0061] Preparation process parameters: Step 1, firstly, add the foaming component and the foam-stabilizing component to deionized water at 25℃ and stir under high shear until completely swollen and dissolved. Then, raise the temperature to 60℃ and add maltodextrin while stirring to dissolve. The remaining process parameters are the same as in Example 1. The finished product has a residual moisture content of 2.0%, an average particle size of approximately 95 μm, and an angle of repose of 37°. The preparation conditions for foamed concrete are the same as in Example 1.

[0062] Comparative Example 1

[0063] This comparative example aims to verify the necessity of the nano-interface armor component (Pickering effect). The formulation is completely identical to that of Example 1, but the nano-interface armor component (4.0% amphiphilic nano-silica) is completely removed and replaced with an equal mass of mesoporous silica fume. That is: foaming component 6.5%, foam stabilizing component 3.0%, nano-interface armor component 0%, water-soluble polysaccharide excipient 11.0%, mesoporous silica fume 73.5% (original 69.5% + 4.0%), and mineralization nucleation promoter 6.0%. The preparation process and foam concrete preparation conditions are exactly the same as in Example 1.

[0064] Comparative Example 2

[0065] This comparative example aims to verify the necessity of the mineralization nucleation promoting agent. The formulation is completely identical to that of Example 1, but the mineralization nucleation promoting agent (4.5% nano-calcium carbonate and 1.5% calcium formate) is completely removed, and this 6.0% portion is replaced with an equal mass of mesoporous silica fume. That is: foaming component 6.5%, foam stabilizing component 3.0%, nano-interface armor component 4.0%, water-soluble polysaccharide excipient 11.0%, mesoporous silica fume 75.5% (original 69.5% + 6.0%), and mineralization nucleation promoting agent 0%. The preparation process and foam concrete preparation conditions are exactly the same as in Example 1.

[0066] Comparative Example 3

[0067] This comparative example aims to verify the impact of HPMC glyoxal micro-crosslinking treatment on the quality of the preparation process in the foam stabilizing component. The formulation is completely identical to that of Example 1 in terms of chemical composition, but the 2.5% HPMC foam stabilizing component is replaced with conventional low-viscosity HPMC (from the same batch of raw materials, grade MH4000, only the glyoxal spraying crosslinking process is omitted) without glyoxal micro-crosslinking treatment. The dosage of the remaining components, the preparation process parameters, and the foam concrete preparation conditions are exactly the same as in Example 1.

[0068] Comparative Example 4

[0069] This comparative example uses a conventional liquid foaming agent scheme from the existing technology as the overall benchmark. A conventional animal protein-based liquid foaming agent (commercially available "cement foaming-specific protein-type foaming agent", an aqueous solution with a solid content of approximately 6%) was used to prepare foam via a pre-foaming method before being incorporated into the cement paste. Specifically, the protein liquid foaming agent was diluted with water at a ratio of 1:40, and pre-foam was prepared using a foam generator under compressed air pressure of 0.4 MPa, resulting in a foam density of approximately 50 kg / m³. Separately, a pure cement paste (P·O 42.5) with a water-cement ratio of 0.50 was prepared. The pre-foam was mixed into the paste at an appropriate volume ratio to achieve a target dry apparent density similar to that of the example (approximately 600 kg / m³). After thorough mixing, the paste was cast and molded, and the curing conditions were the same as in the example.

[0070] The following is a summary of the performance test results for each embodiment and comparative example.

[0071] A systematic analysis of the above experimental data shows that the foamed concrete prepared in each embodiment of the present invention is significantly better than that in each comparative example in terms of key performance indicators, which fully demonstrates the indispensability of the core technical features of the present invention and their synergistic effect mechanism.

[0072] From the overall performance of Examples 1 to 6, all examples, within the ultra-lightweight range of a target dry apparent density of approximately 600 kg / m³, achieved a 28-day compressive strength of 3.12 MPa to 3.92 MPa, a closed-cell rate of 88.7% to 93.1%, an average pore size controlled between 208 μm and 268 μm, and a pore size uniformity coefficient U-value fluctuating within an extremely narrow range of 1.7 to 2.3. Among them, Examples 1 and 5 performed best. Their common characteristic was that the dosage of the nano-interface armor component and the mineralization nucleation promoter were both within the optimal range. This indicates that the Pickering interface armor effect and the in-situ mineralization shell formation mechanism achieved optimal synergistic matching within this ratio range. The compressive strength of Example 5 was even slightly higher than that of Example 1 (3.92 MPa vs 3.86 MPa), which is related to its higher content of mineralization nucleation aid (9.0% vs 6.0%). More heterogeneous nucleation sites of nano-calcium carbonate and the additional calcium source provided by calcium formate accelerated the mineralization deposition rate of CSH gel at the bubble interface, forming a thicker and denser mineralized shell. This inference is also corroborated by its highest closed-pore ratio (93.1%) and smallest average pore size (208 μm). Example 2 is at the lower limit of the wide formulation range, with lower content of foaming component and nano-armor component, resulting in a correspondingly lower foaming ratio (21.3) and a slightly higher water separation rate (3.5%). However, its overall performance is still far superior to the comparative examples, indicating that even at lower dosages, the synergistic effect of the three foam stabilizing mechanisms is still effective. Example 3 is at the upper limit of the wide range of formulations. Although the foaming component of up to 9.5% brought the highest foaming ratio (32.8), the excessive surfactant micelles competed with the nano-armor particles for adsorption at the interface, resulting in a slight deterioration in the water separation rate (2.1%) and pore size uniformity coefficient (2.1) compared to Example 1. The compressive strength also did not reach the optimal level. This verifies the statement in the specification that the amount of foaming component should not be too high.

[0073] In Comparative Example 1, after completely removing the nano-interface armor component, although the foaming and stabilizing components were intact, the 1-hour water separation rate of the foam increased sharply from 1.2% in Example 1 to 12.6%, the foam volume retention rate plummeted from 97.8% to 78.3%, the closed-cell rate after curing was only 72.5%, the average pore size expanded to 485 μm and the uniformity coefficient deteriorated to 4.6, and the 28-day compressive strength was only 1.95 MPa, a decrease of approximately 49.5% compared to Example 1. These results clearly reveal the core role of the nano-Pickering interface armor in the entire foam stabilization system: without the rigid solid armor layer formed by nanoparticles at the gas-liquid interface, the viscoelastic enhancement provided solely by the polymer hydration network cannot effectively resist the Oswald curing process driven by the Laplace pressure difference. In the highly alkaline and high solids content environment of cement paste, the drainage rate of organic polymer liquid film is accelerated due to the lack of steric barrier. Small bubbles rapidly transport gas to large bubbles under pressure difference, causing irreversible coarsening and merging, and finally leaving a large number of through irregular pores in the solidified body. These pores, as stress concentration sources, greatly weaken the load-bearing capacity of the material.

[0074] Comparative Example 2, which retained the Pickering armor but removed the mineralization nucleation promoter, showed little difference in stability indicators during the foaming stage (water separation rate 1.8%, volume retention rate 96.5%) compared to Example 1. This confirms that the mineralization nucleation promoter contributes only a limited amount to the stability of the foam liquid stage, where the foam stabilization function is mainly undertaken by the polymer network and nano-armor. However, the 28-day compressive strength of the cured specimen was only 2.63 MPa, a decrease of approximately 31.9% compared to Example 1, and the closed-cell rate also decreased to 83.6%. This difference reveals the key contribution of the in-situ mineralization mechanism to the final mechanical properties: although Comparative Example 2 still contained a large amount of mesoporous silica fume (75.5%), in the absence of efficient heterogeneous nucleation sites provided by nano-calcium carbonate, the homogeneous nucleation of the CSH gel required a higher degree of supersaturation to drive it. The nucleation rate was slow and spatially randomized, failing to form a concentrated and dense mineralized shell in the micro-regions of the bubble interface. In the early hardening stage of cement hydration, some bubble walls still rely on the organic polymer-nanoparticle composite membrane for support. Under the stress of hydration exothermic reaction and volume shrinkage, this flexible membrane is prone to microcracks that gradually expand, causing some closed pores to become open pores. The local mechanical weak points of the pore walls become the initiation points of compression failure.

[0075] In Comparative Example 3, after replacing the HPMC in the foam-stabilizing component with a conventional product without glyoxal micro-crosslinking treatment, although the chemical composition of the formulation was completely identical to that of Example 1, the foaming ratio was only 22.4, the water separation rate increased to 4.3% after 1 hour, and the compressive strength after 28 days was only 2.88 MPa, a decrease of approximately 25.4% compared to Example 1. The root cause of this degradation lies in the quality difference in the first stage of the preparation process. During the cold water dissolution process in step one, the conventional HPMC powder without glyoxal micro-crosslinking treatment easily forms a high-viscosity gel barrier layer (i.e., the "fish-eye" phenomenon) on the outer surface of the particles due to hydration expansion, hindering further dissolution of the internal powder. Although macroscopic dissolution can eventually be achieved under high-shear stirring conditions, the process takes significantly longer, and the degree of molecular-level homogenization of HPMC in the system is not as rapid and uniform as that after micro-crosslinking treatment. Differences in the extent of expansion and spatial uniformity of HPMC molecular chain segments in the precursor sol will be transmitted to the internal microstructure of the spray-dried microcapsules: the uneven dispersion of the foam-stabilizing polymer within the microcapsules leads to local fluctuations in the spatial concentration of HPMC molecular chain segments released into the liquid phase after resolution. This results in two consequences: first, insufficient polymer hydration network density in some liquid film regions weakens the viscoelastic enhancement effect and accelerates the drainage rate; second, the inhomogeneity of the polymer network causes localized differences in the density of the nano-armor particles at the interface, weakening the integrity of the Pickering armor. Furthermore, the decreased homogenization of the precursor sol also leads to reduced stability in the spray drying process, a wider microcapsule particle size distribution, and consequently affects the overall foaming efficiency.

[0076] Comparative Example 4 uses an animal protein-based liquid foaming agent, widely used in existing technologies, as the overall benchmark. The results most intuitively demonstrate the technological leap of this invention. Although the foam produced by the protein liquid foaming agent in the air using the pre-foaming method appears dense and delicate, these pure protein organic liquid films, once in contact with cement paste with a high pH value (greater than 12.5) and high solid content (a water-cement ratio of 0.50 corresponds to a paste density of approximately 1900 kg / m³), rapidly collapse under the multiple attacks of alkaline hydrolysis, solid particle collision, gravity drainage, and Laplace pressure differential gas diffusion. The water separation rate is as high as 18.5% after 1 hour, and the volume retention rate is only 62.4%. Microstructural observation of the cured specimens revealed a severe polarization in the internal pores: on the one hand, numerous irregular, interconnected macropores (composed of multiple merged air bubbles) existed on the order of several millimeters; on the other hand, extremely fine residual closed pores were scattered within the cement matrix between the macropores, resulting in a highly uneven overall pore size distribution (U=5.8), with an average pore size as high as 560 μm and a closed-cell rate of only 65.8%. Correspondingly, the 28-day compressive strength was only 1.52 MPa, a mere 39.4% of that in Example 1 of this invention. This significant performance gap powerfully demonstrates, from the opposite perspective, the fundamental advantages of the "flexible polymer network + rigid nanoparticle Pickering armor + in-situ mineralized shell" three-in-one foam-stabilizing system of this invention in harsh cement environments.

[0077] A comprehensive comparison of all the embodiments and comparative examples leads to the conclusion that the three foam-stabilizing mechanisms of the powder foaming agent of this invention—namely, the viscoelastic enhancement of the polymer hydration network, the Pickering interface armor of nanoparticles, and the alkali-activated in-situ mineralization shell—are indispensable. These three mechanisms form a rigorous, hierarchical, progressive protection system across both temporal and spatial scales. The absence or weakening of any one mechanism will lead to a significant degradation in overall performance, rather than a simple linear additive relationship, indicating a significant nonlinear synergistic effect among the three. Furthermore, although the glyoxal micro-crosslinking surface treatment of HPMC in the preparation process is a non-formulation-level process optimization, it plays an irreplaceable role in ensuring the homogenization quality of the precursor sol and the uniformity of the final microcapsule internal microstructure, the effect of which was fully verified by Comparative Example 3. This invention achieves a 28-day compressive strength of 3.12 MPa to 3.92 MPa within the ultralight range of approximately 600 kg / m³ dry apparent density. Compared to the existing protein-based liquid foaming agent system (1.52 MPa), this represents an improvement of 105% to 158%, demonstrating significant, albeit non-obvious, technical effects.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-stability powder foaming agent specifically for foamed concrete, characterized in that, It contains the following components: The powder foaming agent comprises a foaming component, a foam-stabilizing component, a nano-interface armor component, an active powder carrier component, and a mineralization nucleation promoting agent; the active powder carrier component includes a water-soluble polysaccharide excipient and mesoporous silica fume; the powder foaming agent exhibits a multi-level core-shell microcapsule morphology in its microstructure, wherein: The inner layer is a microcapsule core, with the water-soluble polysaccharide excipient as the film-forming wall material. The foaming component, the foam-stabilizing component, and the nano-interface armor component are physically encapsulated inside the skeleton network formed by the film-forming wall material after dehydration. The outer layer is a physical isolation layer, composed of the mesoporous silica fume and the mineralization nucleation promoting agent, which covers and adsorbs onto the outer surface of the microcapsule core. After the powdered foaming agent dissolves in water, the water-soluble polysaccharide excipient disintegrates and releases the effective components. The foaming component and the foam-stabilizing component form a bubble liquid film containing a polymer hydration network. The nano-interface armor component undergoes irreversible adsorption and self-assembly at the gas-liquid interface to form a solid particle armor. The mesoporous silica fume and the mineralization nucleation promoting agent are used to generate an inorganic mineralized shell of calcium silicate hydrate and ettringite in situ at the gas-liquid interface micro-region under the excitation of the strongly alkaline pore liquid during cement hydration.

2. The powder foaming agent according to claim 1, characterized in that, With the total mass of all components being 100%, the mass percentage content of each component is as follows: the foaming component: 3.0% to 10.0%; the foam stabilizing component: 1.0% to 5.0%; the nano-interface armor component: 2.0% to 8.0%; the water-soluble polysaccharide excipient: 8.0% to 15.0%; the mesoporous silica fume: 50.0% to 80.0%; and the mineralization nucleation promoting agent: 3.0% to 10.0%.

3. The powder foaming agent according to claim 2, characterized in that, Based on the total mass of all components being 100%, the mass percentage content of each component is as follows: the foaming component: 5.0% to 8.0%; the foam stabilizing component: 2.0% to 3.5%; the nano-interface armor component: 3.0% to 5.0%; the water-soluble polysaccharide excipient: 10.0% to 12.0%; the mesoporous silica fume: 65.0% to 75.0%; and the mineralization nucleation promoting agent: 5.0% to 8.0%.

4. The powder foaming agent according to any one of claims 1 to 3, characterized in that, The foaming component is selected from at least one of sodium α-olefin sulfonate, sodium dodecyl sulfate, and sodium fatty alcohol polyoxyethylene ether sulfate, and must contain sodium α-olefin sulfonate; the foam stabilizing component is selected from at least one of hydroxypropyl methylcellulose, polyvinyl alcohol, and carboxymethyl starch ether, and must contain low-viscosity hydroxypropyl methylcellulose.

5. The powder foaming agent according to any one of claims 1 to 3, characterized in that, The nano-interface armor component is selected from at least one of amphiphilic nano-silica and nano-alumina with hydrophobic modification of the surface; wherein the original particle size of the amphiphilic nano-silica is 15 nm to 30 nm, and its surface is modified by at least one modifier selected from hexadecyltrimethoxysilane and octyltriethoxysilane so that its gas-liquid-solid three-phase contact angle is close to 90 degrees.

6. The powder foaming agent according to any one of claims 1 to 3, characterized in that, The water-soluble polysaccharide excipient is maltodextrin with a DE value of 15 to 20; the mesoporous silica fume has an amorphous silica content of more than 85%, an average primary particle size of 0.1 μm to 0.3 μm, and a microaggregate specific surface area of ​​more than 15 m² / g.

7. The powder foaming agent according to any one of claims 1 to 3, characterized in that, The mineralization nucleation promoter is selected from at least one of nano-calcium carbonate and calcium formate, and must include nano-calcium carbonate; the original particle size of the nano-calcium carbonate is 40 nm to 80 nm, and it is cubic light precipitated calcium carbonate with surface activated by stearic acid.

8. The powder foaming agent according to claim 1, characterized in that, The powdered foaming agent is in the form of free-flowing microsphere powder with an average particle size between 50 μm and 150 μm, and the residual moisture content of the finished product is less than or equal to 2.5%.

9. The preparation process of the high-stability foamed concrete powder foaming agent according to claim 1, characterized in that, Includes the following steps: Step 1, Precursor liquid phase high shear homogenization: First, under low temperature conditions, the foaming component and the foam stabilizing component are added to deionized water and stirred under high shear until completely swollen and dissolved. Then, the temperature is raised, the water-soluble polysaccharide excipient is added and stirred to dissolve. Subsequently, the nano-interface armor component is pre-dispersed in anhydrous ethanol and then added, and ultrasonic cavitation dispersion is performed to obtain Pickering foam stabilizing precursor colloidal sol. Step 2, microcapsule spray drying granulation: The colloidal sol obtained in Step 1 is pumped into a high-temperature co-current spray drying tower for centrifugal atomization. During the instantaneous burst evaporation of water, the water-soluble polysaccharide excipient shrinks and concentrates to the surface to form a film, forming microcapsule dry powder that encapsulates the foaming component, the foam-stabilizing component and the nano-interface armor component.

10. The preparation process according to claim 9, characterized in that, Prior to step one, the low-viscosity hydroxypropyl methylcellulose in the foam-stabilizing component is pre-treated with glyoxal micro-crosslinking: hydroxypropyl methylcellulose powder is sprayed onto the surface in a fluidized bed with a glyoxal aqueous solution of 1.5% to 2.5% by mass, the amount of glyoxal being 0.8% to 1.2% of the dry weight of hydroxypropyl methylcellulose, followed by fluidized drying at 45°C to 55°C; in step one, the foaming component and the foam-stabilizing component are first added to deionized water at a temperature of 20°C to 35°C and stirred under high shear until completely swollen and dissolved, then the temperature is raised to 55°C to 62°C, the water-soluble polysaccharide excipient is added and stirred to dissolve, and then the nano-interface armor component pre-dispersed in anhydrous ethanol is added for ultrasonic cavitation dispersion; the mass of deionized water added is 2.5 to 3.5 times the total solid content of the aqueous phase of the formulation, the mechanical shearing speed is 1500 rpm to 2000 rpm, and the working frequency of ultrasonic cavitation dispersion is 20 rpm. kHz; In step two, the inlet air temperature of the spray drying tower is set to 150℃ to 170℃, the outlet air temperature is set to 65℃ to 75℃, and the centrifugal atomizing disc rotation speed is set to 15000 rpm to 18000 rpm; The preparation process of the powder foaming agent also includes: Step three, high-shear dry mixing and isolation of bulk active carrier: Collect the microcapsule dry powder obtained in step two, and after cooling to below 40℃, put it into a gravity-free biaxial paddle mixer together with the pre-dried mesoporous silica fume and the mineralization nucleation promoting agent. Start the main shaft to tumble and turn on the flying knife to perform high-frequency shear mixing at a speed of 2000 rpm to 3000 rpm for 15 minutes to 25 minutes, so that the mesoporous silica fume physically covers and isolates the microcapsule dry powder. After filtration and sieving, the powder foaming agent is obtained.

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